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Title: Animal Life and Intelligence
Author: Morgan, C. Lloyd (Conwy Lloyd)
Language: English
As this book started as an ASCII text book there are no pictures available.
*** Start of this LibraryBlog Digital Book "Animal Life and Intelligence" ***
TRANSCRIBER'S NOTE
In this etext the oe ligature is represented as [oe]. In the table of
Bat arm measurements, the graphic symbols for male and female are
typographical errors which have been corrected, none of which affected
the sense of the text. Inconsistent hyphenation has been retained.
[Illustration: Kentish Plover with Eggs and Young. From the Exhibit in the
British Natural History Museum.]
ANIMAL LIFE AND INTELLIGENCE.
BY
C. LLOYD MORGAN, F.G.S.,
PROFESSOR IN AND DEAN OF UNIVERSITY COLLEGE, BRISTOL;
LECTURER AT THE BRISTOL MEDICAL SCHOOL;
PRESIDENT OF THE BRISTOL NATURALISTS' SOCIETY, ETC.
AUTHOR OF
"ANIMAL BIOLOGY," "THE SPRINGS OF CONDUCT," ETC.
BOSTON, U. S. A.
GINN & COMPANY, PUBLISHERS.
1891.
TO
MY FATHER.
PREFACE.
There are many books in our language which deal with Animal Intelligence
in an anecdotal and conventionally popular manner. There are a few,
notably those by Mr. Romanes and Mr. Mivart, which bring adequate
knowledge and training to bear on a subject of unusual difficulty. In
the following pages I have endeavoured to contribute something
(imperfect, as I know full well, but the result of several years' study
and thought) to our deeper knowledge of those mental processes which we
may fairly infer from the activities of dumb animals.
The consideration of Animal Intelligence, from the scientific and
philosophical standpoint, has been my primary aim. But so inextricably
intertwined is the subject of Intelligence with the subject of Life, the
subject of organic evolution with the subject of mental evolution, so
closely are questions of Heredity and Natural Selection interwoven with
questions of Habit and Instinct, that I have devoted the first part of
this volume to a consideration of Organic Evolution. The great
importance and value of Professor Weismann's recent contributions to
biological science, and their direct bearing on questions of Instinct,
rendered such treatment of my subject, not only advisable, but
necessary. Moreover, it seemed to me, and to those whom I consulted in
the matter, that a general work on Animal Life and Intelligence, if
adequately knit into a connected whole, and based on sound principles of
science and of philosophy, would not be unwelcomed by biological
students, and by that large and increasing class of readers who, though
not professed students, follow with eager interest the development of
the doctrine of Evolution.
Incidentally, but only incidentally, matters concerning man, as compared
with the dumb animals, have been introduced. It is contended that in man
alone, and in no dumb animal, is the rational faculty, as defined in
these pages, developed; and it is contended that among human-folk that
process of natural selection, which is so potent a factor in the lower
reaches of organic life, sinks into comparative insignificance. Man is a
creature of ideas and ideals. For him the moral factor becomes one of
the very highest importance. He conceives an ideal self which he strives
to realize; he conceives an ideal humanity towards which he would raise
his fellow-man. He becomes a conscious participator in the evolution of
man, in the progress of humanity.
But while we must not be blind to the effects of new and higher factors
of progress thus introduced as we rise in the scale of phenomena, we
must at the same time remember that biological laws still hold true,
though moral considerations and the law of duty may profoundly modify
them. The eagle soars aloft apparently in defiance of gravitation; but
the law of gravitation still holds good; and no treatment of the
mechanism of flight which neglected it would be satisfactory. Moral
restraint, a higher standard of comfort, and a perception of the folly
and misery of early and improvident marriage may tend to check the rate
of growth of population: but the "law of increase" still holds good, as
a law of the factors of phenomena; and Malthus did good service to the
cause of science when he insisted on its importance. We may guide or
lighten the incidence of natural selection through competition; we may
in our pity provide an asylum for the unfortunates who are suffering
elimination; but we cannot alter a law which, as that of one of the
factors of organic phenomena, still obtains, notwithstanding the
introduction of other factors.
However profoundly the laws of phenomena may be modified by such
introduction of new and higher factors, the older and lower factors are
still at work beneath the surface. And he who would adequately grasp the
social problems of our time should bring to them a mind prepared by a
study of the laws of organic life: for human beings, rational and moral
though they may be, are still organisms; and man can in no wise alter or
annul those deep-lying facts which nature has throughout the ages been
weaving into the tissue of life.
Some parts of this work are necessarily more technical, and therefore
more abstruse, than others. This is especially the case with Chapters
III., V., and VI.; while, for those unacquainted with philosophical
thought, perhaps the last chapter may present difficulties of a
different order. With these exceptions, the book will not be beyond the
ready comprehension of the general reader of average intelligence.
I have to thank many kind friends for incidental help. Thanks are also
due to Professor Flower, who courteously gave permission that some of
the exhibits in our great national collection in Cromwell Road might be
photographed and reproduced; and to Messrs. Longmans for the use of two
or three illustrations from my text-book of "Animal Biology."
C. LLOYD MORGAN.
UNIVERSITY COLLEGE, BRISTOL,
October, 1890.
CONTENTS.
CHAPTER I.
THE NATURE OF ANIMAL LIFE.
PAGE
The characteristics of animals 2
The relation of animals to food-stuffs 15
The relation of animals to the atmosphere 15
The relation of animals to energy 16
CHAPTER II.
THE PROCESS OF LIFE.
Illustration from respiration 21
Illustration from nutrition 25
The utilization of the materials incorporated 27
The analogy of a gas-engine. Explosive metabolism 30
CHAPTER III.
REPRODUCTION AND DEVELOPMENT.
Reproduction in the protozoa 37
Fission in the metazoa 41
The regeneration of lost parts 41
Reproduction by budding 42
Sexual reproduction 42
Illustration of development 51
Parental sacrifice 56
The law of increase 58
CHAPTER IV.
VARIATION AND NATURAL SELECTION.
The law of persistence 61
The occurrence of variations 63
Application of the law of increase 76
Natural selection 77
Elimination and selection 79
Modes of natural elimination illustrated 80
Protective resemblance and mimicry 82
Selection proper illustrated 93
The effects of natural selection 95
Isolation or segregation 99
Its modes, geographical, preferential and physiological 99
Its effects 108
Utility of specific characters 110
Variations in the intensity of the struggle for existence 112
Convergence of characters 117
Modes of adaptation: Progress 119
Evolution and Revolution 120
CHAPTER V.
HEREDITY AND THE ORIGIN OF VARIATIONS.
Heredity in the protozoa 123
Regeneration of lost parts 124
Sexual reproduction and heredity 129
The problem of hen and egg 130
Reproductive continuity 131
Pangenesis 131
Modified pangenesis 134
Continuity of germ-plasm 138
Cellular continuity with differentiation 142
The inheritance or non-inheritance of acquired characters 146
Origin of variations on the latter view 149
Hypothesis of organic combination 150
The extrusion of the second polar cell 153
The protozoan origin of variations 156
How can the body influence the germ? 159
Is there sufficient evidence that it does? 162
Summary and conclusion 175
CHAPTER VI.
ORGANIC EVOLUTION.
The diversity of animal life 177
The evolution theory 181
Natural selection: not to be used as a magic formula 183
Panmixia and disuse 189
Sexual selection or preferential mating 197
Use and disuse 209
The nature of variations 216
The inheritance of variations 223
The origin of variations 231
Summary and conclusion 241
CHAPTER VII.
THE SENSES OF ANIMALS.
The primary object of sensation 243
Organic sensations and the muscular sense 244
Touch 245
The temperature-sense 249
Taste 250
Smell 257
Hearing 261
Sense of rotation or acceleration 269
Sight 273
Restatement of theory of colour-vision 278
Variation in the limits of colour-vision 281
The four types of "visual" organs 293
Problematical senses 294
Permanent possibilities of sensation 298
CHAPTER VIII.
MENTAL PROCESSES IN MAN.
The physiological aspect 302
The psychological aspect 304
Sensations: their localization, etc. 306
Perceptual construction 312
Conceptual analysis 321
Inferences perceptual and conceptual 328
Intelligence and reason 330
CHAPTER IX.
MENTAL PROCESSES IN ANIMALS: THEIR POWERS OF PERCEPTION
AND INTELLIGENCE.
The two factors in phenomena 331
The basis in organic evolution 336
Perceptual construction in mammalia 338
Can animals analyze their constructs? 347
The generic difference between the minds of man and brute 350
Perceptual construction in other vertebrates 350
"Understanding" of words 354
Perceptual construction in the invertebrates 356
"The psychic life of micro-organisms" 360
The inferences of animals 361
Intelligent not rational 365
Use of words defined 372
Language and analysis 374
CHAPTER X.
THE FEELINGS OF ANIMALS: THEIR APPETENCES AND EMOTIONS.
Pleasure and pain: their organic limits 379
Their directive value 380
An emotion exemplified 382
Sensitiveness and sensibility 385
The expression of the emotions 385
The postponement of action 385
The three orders of emotion 390
The capacities of animals for pleasure and pain 391
Sense-feelings 393
Some emotions of animals 395
The necessity for caution in interpretation 399
The sense of beauty 407
Can animals be moral? 413
Conclusion 414
CHAPTER XI.
ANIMAL ACTIVITIES: HABIT AND INSTINCT.
The nature of animal activities 415
The outer and inner aspect 417
The inherited organization 419
Habitual activities 420
Instinctive activities 422
Innate capacity 426
Blind prevision 429
Consciousness and instinct 432
Mr. Romanes's treatment of instinct 434
Lapsed intelligence and modern views on heredity 435
Three factors in the origin of instinctive activities 447
The emotional basis of instinct 449
The influence of intelligence on instinct 452
The characteristics of intelligent activities 456
The place of volition 459
Perceptual and conceptual volition 460
Consciousness and consentience 461
Classification of activities 462
CHAPTER XII.
MENTAL EVOLUTION.
Is mind evolved from matter? 464
Kinesis and metakinesis 467
Monistic assumptions 470
The nature of ejects 476
The universe as eject 478
Metakinetic environment of mind 481
Conceptual ideas not subject to natural selection 483
Elimination through incongruity 486
Interneural evolution 490
Interpretations of nature 492
Can fetishism have had a natural genesis? 493
The origin of interneural variations 496
Are acquired variations inherited? 497
Summary and conclusion 501
LIST OF ILLUSTRATIONS.
FIG. PAGE
Kentish Plover with Eggs and Young: Frontispiece
1. Spiracles and Air-tubes of Cockroach 3
2. Gills of Mussel 4
3. A Cell greatly magnified 11
4. Am[oe]ba 12
5. Egg-cell and Sperm-cell 13
6. Diagram of Circulation 23
7. Protozoa 38
8. Hydra Virides 43
9. Aurelia: Life-cycle 45
10. Liver-Fluke--Embryonic Stages 47
11. Diagram of Development 51
12. Wing of Bat (Pipistrelle) 64
13. Variations of the Noctule 67
14. Variations of the Long-eared Bat 68
15. Variations of the Pipistrelle 69
16. Variations of the Whiskered Bat 70
17. Variations adjusted to the Standard of the Noctule 73
18. Caterpillar of a Moth on an Oak Spray 85
19. Locust resembling a Leaf 86
20. Mimicry of Bees by Flies 91
21. Egg and Hen 141
22. Stag-Beetles 180
23. Tactile Corpuscules 247
24. Touch-hair of Insect 248
25. Taste-buds of Rabbit 250
26. Antennule of Crayfish 259
27. Diagram of Ear 263
28. Tail of Mysis 266
29. Leg of Grasshopper 266
30. Diagram of Semicircular Canals 270
31. The Human Eye 274
32. Retina of the Eye 274
33. Variation in the Limits of Colour-vision 281
34. Pineal Eye 288
35. Skull of Melanerpeton 288
36. Eyes and Eyelets of Bee 289
37. Eye of Fly 290
38. Diagram of Mosaic Vision 291
39. Direction-retina 295
40. Antennary Structures of Hymenoptera 297
ANIMAL LIFE AND INTELLIGENCE.
CHAPTER I.
THE NATURE OF ANIMAL LIFE.
I once asked a class of school-boys to write down for me in a few words
what they considered the chief characteristics of animals. Here are some
of the answers--
1. Animals move about, eat, and grow.
2. Animals eat, grow, breathe, feel (at least, most of them do), and
sleep.
3. Take a cat, for example. It begins as a kitten; it eats, drinks,
plays about, and grows up into a cat, which does much the same,
only it is more lazy, and stops growing. At last it grows old and
dies. But it may have kittens first.
4. An animal has a head and tail, four legs, and a body. It is a
living creature, and not a vegetable.
5. Animals are living creatures, made of flesh and blood.
Combining these statements, we have the following characteristics of
animals:--
1. Each has a proper and definite form, at present described as "a
head and tail, four legs, and a body."
2. They breathe.
3. They eat and drink.
4. They grow.
5. They also "grow up." The kitten grows up into a cat, which is
somewhat different from the kitten.
6. They move about and sleep.
7. They feel--"at least some of them do."
8. They are made of "flesh and blood."
9. They grow old and die.
10. They reproduce their kind. The cat may have kittens.
11. They are living organisms, but "not vegetables."
Now, let us look carefully at these characteristics, all of which were
contained in the five answers, and were probably familiar in some such
form as this to all the boys, and see if we cannot make them more
general and more accurate.
1. _An animal has a definite form._ My school-boy friend described it as
a head and tail, four legs, and a body. But it is clear that this
description applies only to a very limited number of animals. It will
not apply to the butterfly, with its great wings and six legs; nor to
the lobster, with its eight legs and large pincer-claws; to the limbless
snake and worm, the finned fish, the thousand-legs, the oyster or the
snail, the star-fish or the sea-anemone. The animals to which my young
friend's description applies form, indeed, but a numerically
insignificant proportion of the multitudes which throng the waters and
the air, and not by any means a large proportion of those that walk upon
the surface of the earth. The description applies only to the backboned
vertebrates, and not to nearly all of them.
It is impossible to summarize in a sentence the form-characteristics of
animals. The diversities of form are endless. Perhaps the distinguishing
feature is the prevalence of curved and rounded contours, which are in
striking contrast to the definite crystalline forms of the inorganic
kingdom, characterized as these are by plane surfaces and solid angles.
We may say, however, that all but the very lowliest animals have each
and all a proper and characteristic form of their own, which they have
inherited from their immediate ancestors, and which they hand on to
their descendants. But this form does not remain constant throughout
life. Sometimes the change is slight; in many cases, however, the form
alters very markedly during the successive stages of the life of the
individual, as is seen in the frog, which begins life as a tadpole, and
perhaps even more conspicuously in the butterfly, which passes through a
caterpillar and a chrysalis stage. Still, these changes are always the
same for the same kind of animal. So that we may say, each animal has a
definite form and shape or series of shapes.
2. _Animals breathe._ The essential thing here is that oxygen is taken
in by the organism, and carbonic acid gas is produced by the organism.
No animal can carry on its life-processes unless certain chemical
changes take place in the substance of which it is composed. And for
these chemical changes oxygen is essential. The products of these
changes, the most familiar of which are carbonic acid gas and urea, must
be got rid of by the process of excretion. Respiration and excretion are
therefore essential and characteristic life-processes of all animals.
[Illustration: Fig. 1.--Diagram of spiracles and air-tubes (tracheæ) of
an insect (cockroach).
The skin, etc., of the back has been removed, and the crop (cr.) and
alimentary canal (al.c.) displayed. The air-tubes are represented by
dotted lines. The ten spiracles are numbered to the right of the
figure.]
In us, and in all air-breathing vertebrates, there are special organs
set apart for respiration and excretion of carbonic acid gas. These are
the lungs. A great number of insects also breathe air, but in a
different way. They have no lungs, but they respire by means of a number
of apertures in their sides, and these open into a system of delicate
branching tubes which ramify throughout the body. Many organisms,
however, such as fish and lobsters and molluscs, breathe the air
dissolved in the water in which they live. The special organs developed
for this purpose are the gills. They are freely exposed to the water
from which they abstract the air dissolved therein. When the air
dissolved in the water is used up, they sicken and die. There can be
nothing more cruel than to keep aquatic animals in a tank or aquarium in
which there is no means of supplying fresh oxygen, either by the action
of green vegetation, or by a jet of water carrying down air-bubbles, or
in some other way. And then there are a number of animals which have no
special organs set apart for breathing. In them respiration is carried
on by the general surface of the body. The common earthworm is one of
these; and most microscopic organisms are in the same condition. Still,
even if there be no special organs for breathing, the process of
respiration must be carried on by all animals.
[Illustration: Fig. 2.--Gills of mussel.
o.g., outer gill; i.g., inner gill; mo., mouth; m., muscles for closing
shell; ma., mantle; s., shell; f., foot; h., position of heart; e.s.,
exhalent siphon, whence the water passes out from the gill-chamber;
i.s., inhalent siphon, where the water enters.
The left valve of the shell has been removed, and the mantle cut away
along the dark line.]
3. _They eat and drink._ The living substance of an animal's body is
consumed during the progress of those chemical changes which are
consequent upon respiration; and this substance must, therefore, be made
good by taking in the materials out of which fresh life-stuff can be
formed. This process is called, in popular language, feeding. But the
food taken in is not identical with the life-stuff formed. It has to
undergo a number of chemical changes before it can be built into the
substance of the organism. In us, and in all the higher animals, there
is a complex system of organs set aside for the preparation, digestion,
and absorption of the food. But there are certain lowly organisms which
can take in food at any portion of their surface, and digest it in any
part of their substance. One of these is the am[oe]ba, a minute speck of
jelly-like life-stuff, which lives in water, and tucks in a bit of
food-material just as it comes. And there are certain degenerate
organisms which have taken to a parasitic life, and live within the
bodies of other animals. Many of these can absorb the material prepared
by their host through the general surface of their simple bodies. But
here, again, though there may be no special organs set apart for the
preparation, absorption, and digestion of food, the process of feeding
is essential to the life of all animals. Stop that process for a
sufficient length of time, and they inevitably die.
4. _They grow._ Food, as we have just seen, has to be taken in,
digested, and absorbed, in order that the loss of substance due to the
chemical changes consequent on respiration may be made good. But where
the digestion and absorption are in excess of that requisite for this
purpose, we have the phenomenon of growth.
What are the characteristics of this growth? We cannot, perhaps,
describe it better than by saying (1) that it is organic, that is to
say, a growth of the various organs of the animal in due proportion; (2)
that it takes place, not merely by the addition of new material (for a
crystal grows by the addition of new material, layer upon layer), but by
the incorporation of that new material into the very substance of the
old; and (3) that the material incorporated during growth differs from
the material absorbed from without, which has undergone a preparatory
chemical transformation within the animal during digestion. The growth
of an animal is thus dependent upon the continued absorption of new
material from without, and its transformation into the substance of the
body.
The animal is, in fact, a centre of continual waste and repair, of
nicely balanced constructive and destructive processes. These are the
invariable concomitants of life. Only so long as the constructive
processes outbalance the destructive processes does growth continue.
During the greater part of a healthy man's life, for example, the two
processes, waste and repair, are in equilibrium. In old age, waste
slowly but surely gains the mastery; and at death the balanced process
ceases, decomposition sets in, and the elements of the body are
scattered to the winds or returned to mother earth.
There are generally limits of growth which are not exceeded by any
individuals of each particular kind of animal. But these limits are
somewhat variable among the individuals of each kind. There are big men
and little men, cart-horses and ponies, bloodhounds and lap-dogs. Wild
animals, however, when fully grown, do not vary so much in size. The
period of growth is also variable. Many of the lower backboned animals
probably grow during the whole of life, but those which suckle their
young generally cease growing after a fraction (in us from one-fourth to
one-fifth) of the allotted span of life is past.
5. But animals not only grow--_they also "grow up."_ The kitten grows up
into a cat, which is somewhat different from the kitten. We speak of
this growing up of an animal as its _development_. The proportion of the
various parts and organs progressively alter. The relative lengths of
the arms and legs, and the relative size of the head, are not the same
in the infant as in the man or woman. Or, take a more marked case. In
early spring there is plenty of frog-spawn in the ponds. A number of
blackish specks of the size of mustard seeds are embedded in a
jelly-like mass. They are frogs' eggs. They seem unorganized. But watch
them, and the organization will gradually appear. The egg will be
hatched, and give rise to a little fish-like organism. This will by
degrees grow into a tadpole, with a powerful swimming tail and rounded
head and body, but with no obvious neck between them. Legs will appear.
The tail will shrink in size and be gradually drawn into the body. The
tadpole will have developed into a minute frog.
There are many of the lower animals which go through a not less
wonderful, if not more wonderful, metamorphosis. The butterfly or the
silkworm moth, beginning life as a caterpillar and changing into a
chrysalis, from which the perfect insect emerges, is a familiar
instance. And hosts of the marine invertebrates have larval forms which
have but little resemblance to their adult parents.
Such a series of changes as is undergone by the frog is called
_metamorphosis_, which essentially consists in the temporary development
of certain provisional embryonic organs (such as gills and a powerful
swimming tail) and the appearance of adult organs (such as lungs and
legs) to take their place. In metamorphosis these changes occur during
the free life of the organism. But beneath the eggshell of birds and
within the womb of mammals scarcely less wonderful changes are slowly
but surely effected, though they are hidden from our view. There is no
metamorphosis during the free life of the organism, but there is a
prenatal _transformation_. The little embryo of a bird or mammal has no
gills like the tadpole (though it has for a while gill-slits, pointing
unmistakably to its fishy ancestry), but it has a temporary provisional
breathing organ, called the allantois, pending the full development and
functional use of its lungs.
All the higher animals, in fact--the dog, the chick, the serpent, the
frog, the fish, the lobster, the butterfly, the worm, the star-fish, the
mollusc, it matters not which we select--take their origin from an
apparently unorganized egg. They all, therefore, pass during their
growth from a comparatively simple condition to a comparatively complex
condition by a process of change which is called development. But there
are certain lowly forms, consisting throughout life of little more than
specks of jelly-like life-stuff, in which such development, if it occurs
at all, is not conspicuous.
6. _They move about and sleep._ This is true of our familiar domestic
pets. The dog and the cat, after periods of restless activity, curl
themselves up and sleep. The canary that has all day been hopping about
its cage, or perhaps been allowed the freedom of the dining-room, tucks
its head under its wing and goes to sleep. The cattle in the meadows,
the sheep in the pastures, the horses in the stables, the birds in the
groves, all show alternating periods of activity and repose. But is this
true of all animals? Do all animals "move about and sleep"? The
sedentary oyster does not move about from place to place; the barnacle
and the coral polyp are fixed for the greater part of life; and whether
these animals sleep or not it is very difficult to say. We must make our
statement more comprehensive and more accurate.
If we throw it into the following form, it will be more satisfactory:
Animals exhibit certain activities; and periods of activity alternate
with periods of repose.
I shall have more to say hereafter concerning the activities of animals.
Here I shall only say a few words concerning the alternating periods of
repose. No organism can continue in ceaseless activity unbroken by any
intervening periods of rest. Nor can the organs within an organism,
however continuous their activity may appear, work on indefinitely and
unrestfully. The heart is apparently restless in its activity. But in
every five minutes of the continued action of the great force-pump
(ventricle) of the heart, two only are occupied in the efforts of
contraction and work, while three are devoted to relaxation and repose.
What we call sleep may be regarded as the repose of the higher
brain-centres after the activity of the day's work--a repose in which
the voluntary muscles share.
The necessity for rest and repose will be readily understood. We have
seen that the organism is a centre of waste and repair, of nicely
balanced destructive and reconstructive processes. Now, activity is
accompanied by waste and destruction. But it is clear that these
processes, by which the substance of the body and its organs is used up,
cannot go on for an indefinite period. There must intervene periods of
reconstruction and recuperation. Hence the necessity of rest and repose
alternating with the periods of more or less prolonged activity.
7. _They feel--"at least some of them do."_ The qualification was a wise
one, for in truth, as we shall hereafter see, we know very little about
the feelings of the lower organisms. The one animal of whose feelings I
know anything definite and at first hand, is myself. Of course, I
believe in the feelings of others; but when we come to very lowly
organisms, we really do not know whether they have feelings or not, or,
if they do, to what extent they feel.
Shall we leave this altogether out of account? Or can we throw it into
some form which is more general and less hypothetical? This, at any
rate, we know--that all animals, even the lowest, are sensitive to
touches, sights, or sounds. It is a matter of common observation that
their activities are generally set agoing under the influence of such
suggestions from without. Perhaps it will be objected that there is no
difference between feeling and being sensitive. But I am using the word
"sensitive" in a general sense--in that sense in which the photographer
uses it when he speaks of a sensitive plate, or the chemist when he
speaks of a sensitive test. When I say that animals are sensitive, I
mean that they answer to touches, or sounds, or other impressions (what
are called stimuli) coming from without. They may feel or not; many of
them undoubtedly do. But that is another aspect of the sensitiveness.
Using the term, then, with this meaning, we may say, without
qualification, that all animals are more or less sensitive to external
influences.
8. _They are made of "flesh and blood."_ Here we have allusion to the
materials of which the animal body is composed. It is obviously a loose
and unsatisfactory statement as it stands. An American is said to have
described the difference between vertebrates and insects by saying that
the former are composed of flesh and bone, and the latter of skin and
squash. But even if we amend the statement that animals are made of
"flesh and blood" by the addition of the words, "or of skin and squash,"
we shall hardly have a sufficiently satisfactory statement of the
composition of the animal body.
The essential constituent of animal (as indeed also of vegetable)
tissues is protoplasm. This is a nearly colourless, jelly-like
substance, composed of carbon, hydrogen, nitrogen, and oxygen, with some
sulphur and phosphorus, and often, if not always, some iron; and it is
permeated by water. Protoplasm, together with certain substances, such
as bony and horny matter, which it has the power of producing,
constitutes the entire structure of simple organisms, and is built up
into the organs of the bodies of higher animals. Moreover, in these
organs it is not arranged as a continuous mass of substance, but is
distributed in minute separate fragments, or corpuscles, only visible
under the microscope, called cells. These cells are of very various
shapes--spherical, discoidal, polyhedral, columnar, cubical, flattened,
spindle-shaped, elongated, and stellate.
A great deal of attention has been devoted of late years to the minute
structure of cells, and the great improvements in microscopical powers
and appliances have enabled investigators to ascertain a number of
exceedingly interesting and important facts. The external surface of a
cell is sometimes, but not always in the case of animals, bounded by a
film or membrane. Within this membrane the substance of the cell is made
up of a network of very delicate fibres (the _plasmogen_), enclosing a
more fluid material (the _plasm_); and this network seems to be the
essential living substance. In the midst of the cell is a small round or
oval body, called the nucleus, which is surrounded by a very delicate
membrane. In this nucleus there is also a network of delicate plasmogen
fibres, enclosing a more fluid plasm material. At certain times the
network takes the form of a coiled filament or set of filaments, and
these arrange themselves in the form of rosettes and stars. In the
meshwork of the net or in the coils of the filament there may be one or
more small bodies (nucleoli), which probably have some special
significance in the life of the cell. These cells multiply or give birth
to new cells by dividing into two, and this process is often accompanied
by special changes in the nucleus (which also divides) and by the
arrangement of its network or filaments into the rosettes and stars
before alluded to.
Instead, therefore, of the somewhat vague statement that animals are
made of flesh and blood, we may now say that the living substance of
which animals are composed is a complex material called protoplasm; that
organisms are formed either of single cells or of a number of related
cells, together with certain life-products of these cells; and that each
cell, small as it is, has a definite and wonderful minute structure
revealed by the microscope.
[Illustration: Fig. 3.--A cell, greatly magnified.
c.m., cell-membrane; c.p., cell-protoplasm; n.m., nuclear membrane;
n.p., nuclear protoplasm; n.f., coiled nuclear filament.]
9. _Animals grow old and die._ This is a familiar observation. Apart
from the fact that they are often killed by accident, by the teeth or
claws of an enemy, or by disease, animals, like human beings, in course
of time become less active and less vigorous; the vital forces gradually
fail, and eventually the flame of life, which has for some time been
burning dimmer and dimmer, flickers out and dies. But is this true of
all animals? Can we say that death--as distinct from being killed--is
the natural heritage of every creature that lives?
One of the simplest living creatures is the am[oe]ba. It consists of a
speck of nucleated protoplasm, no larger than a small pin's head. Simple
as it is, all the essential life-processes are duly performed. It is a
centre of waste and repair; it is sensitive and responsive to a
stimulus; respiration and nutrition are effected in a simple and
primitive fashion. It is, moreover, reproductive. First the nucleus and
then the protoplasm of the cell divide, and in place of one am[oe]ba
there are two. And these two are, so far as we can tell, exactly alike.
There is no saying which is mother and which is daughter; and, so far as
we can see at present, there is no reason why either should die. It is
conceivable that am[oe]bæ never die, though they may be killed in
immense numbers. Hence it has been plausibly maintained that the
primitive living cell is by nature deathless; that death is not the
heritage of all living things; that death is indeed an acquisition,
painful indeed to the individual, but, since it leaves the stage free
for the younger and more vigorous individuals, conducive to the general
good.
[Illustration: Fig. 4.--Am[oe]ba.
1. An am[oe]ba, showing the inner and outer substance (endosarc and
ectosarc); a pseudopodium, p.s.; the nucleus, n.; and the contractile
vesicle, c.v. 2. An am[oe]ba dividing into two. 3. The division just
effected.]
In face of this opinion, therefore, we cannot say that all animals grow
old and die; but we may still say that all animals, with the possible
exception of some of the lowest and simplest, exhibit, after a longer or
a shorter time, a waning of the vital energies which sooner or later
ends in death.
10. _Animals reproduce their kind._ We have just seen the nature of
reproduction in the simple unicellular am[oe]ba. The reproduction of the
constituent cells in the complex multicellular organism, during its
natural growth or to make good the inevitable loss consequent on the
wear and tear of life, is of the same character.
When we come to the higher organisms, reproduction is effected by the
separation of special cells called egg-cells, or ova, from a special
organ called the ovary; and these, in a great number of cases, will not
develop into a new organism unless they be fertilized by the union with
them in each case of another cell--the sperm-cell--produced by a
different individual. The separate parents are called male and female,
and reproduction of this kind is said to be sexual.
[Illustration: Fig. 5.--Egg-cell and sperm-cell.
a, ovum or egg; b, spermatozoon or sperm.]
The wonderful thing about this process is the power of the fertilized
ovum, produced by the union of two minute cells from different parents,
to develop into the likeness of these parents. This likeness, however,
though it extends to minute particulars, is not absolute. The offspring
is not exactly like either parent, nor does it present a precise mean
between the characters of the two parents. There is always some amount
of individual variability, the effects of which, as we shall hereafter
see, are of wide importance. We are wont to say that these phenomena,
the transmission of parental characteristics, together with a margin of
difference, are due to heredity with variation. But this merely names
the facts. How the special reproductive cells have acquired the secret
of developing along special lines, and reproducing, with a margin of
variability, the likeness of the organisms which produced them, is a
matter concerning which we can at present only make more or less
plausible guesses.
Scarcely less wonderful is the power which separated bits of certain
organisms, such as the green freshwater hydra of our ponds, possess of
growing up into the complete organism. Cut a hydra into half a dozen
fragments, and each fragment will become a perfect hydra. Reproduction
of this kind is said to be asexual.
We shall have, in later chapters, to discuss more fully some of the
phenomena of reproduction and heredity. For the present, it is
sufficient to say that animals reproduce their kind by the detachment of
a portion of the substance of their own bodies, which portion, in the
case of the higher animals, undergoes a series of successive
developmental changes constituting its life-history, the special nature
of which is determined by inheritance, and the result of which is a new
organism in all essential respects similar to the parent or parents.
11. _Animals are living organisms, and "not vegetables."_ The first part
of this final statement merely sums up the characteristics of living
animals which have gone before. But the latter part introduces us to the
fact that there are other living organisms than those we call animals,
namely, those which belong to the vegetable kingdom.
It might, at first sight, be thought a very easy matter to distinguish
between animals and plants. There is no chance, for example, of
mistaking to which kingdom an oak tree or a lion, a cabbage or a
butterfly, belongs. But when we come down to the simpler organisms,
those whose bodies are constituted by a single cell, the matter is by no
means so easy. There are, indeed, lowly creatures which are hovering on
the boundary-line between the two kingdoms. We need not discuss the
nature of these boundary forms. It is sufficient to state that
unicellular plants are spoken of as _protophyta_, and unicellular
animals as _protozoa_, the whole group of unicellular organisms being
classed together as _protista_. The animals whose bodies are formed of
many cells in which there is a differentiation of structure and a
specialization of function, are called _metazoa_, and the multicellular
plants _metaphyta_. The relations of these groups may be thus
expressed--
Animals. Plants.
/\ /\
--------- ------------- -------------- ------------
Metazoa. Protozoa. Protophyta. Metaphyta.
----------- -------------
\/
Protista.
There are three matters with regard to the life-process of animals and
plants concerning which a few words must be said. These are (1) their
relation to food-stuffs; (2) their relation to the atmosphere; (3) their
relation to energy, or the power of doing work.
With regard to the first matter, that of food-relation, the essential
fact seems to be the dependence of animals on plants. Plants can
manufacture protoplasm out of its constituents if presented to them in
suitable inorganic form scattered through earth and air and water. Hence
the peculiar features of their form, the branching and spreading nature
of those parts which are exposed to the air, and the far-reaching
ramifications of those parts which are implanted in the earth. Hence,
too, the flattened leaves, with their large available surface. Animals
are unable to manufacture protoplasm in this way. They are, sooner or
later, dependent for food on plant-products. It is true that the
carnivora eat animal food, but the animals they eat are directly or
indirectly consumers of vegetable products. Plants are nature's primary
producers of organic material. Animals utilize these products and carry
them to higher developments.
In relation to the atmosphere, animals require a very much larger
quantity of oxygen than do plants. This, during the respiratory process,
combines with carbon so as to form carbonic acid gas; and the atmosphere
would be gradually drained of its oxygen and flooded with carbonic acid
gas were it not that plants, through their green colouring matter
(chlorophyll), under the influence of light, have the power of
decomposing the carbonic acid gas, seizing on the carbon and building it
into their tissues, and setting free the oxygen. Thus are animals and
green plants complementary elements in the scheme of nature.[A] The
animal eats the carbon elaborated by the plant into organic products
(starch and others), and breathes the oxygen which the plant sets free
after it has abstracted the carbon. In the animal's body the carbon and
oxygen recombine; its varied activities are thus kept going; and the
resultant carbonic acid gas is breathed forth, to be again separated by
green, growing plants into carbonaceous food-stuff and vitalizing
oxygen. It must be remembered, however, that vegetable protoplasm, like
animal protoplasm, respires by the absorption of oxygen and the
formation of carbonic acid gas. But in green plants this process is
outbalanced by the characteristic action of the chlorophyll, by which
carbonic acid gas is decomposed.
Lastly, we have to consider the relations of animals and plants to
energy. Energy is defined as the power of doing work, and it is
classified by physicists under two modes--potential energy, or energy of
position; and kinetic energy, or energy of motion. The muscles of my arm
contain a store of potential energy. Suppose I pull up the weight of an
old-fashioned eight-day clock. Some of the potential energy of my arm is
converted into the potential energy of the weight; that is, the raised
weight is now in a position of advantage, and capable of doing work. It
has energy of position, or potential energy. If the chain breaks, down
falls the weight, and exhibits the energy of motion. But, under ordinary
circumstances, this potential energy is utilized in giving a succession
of little pushes to the pendulum to keep up its swing, and in overcoming
the friction of the works. Again, the energy of an electric current may
be utilized in decomposing water, and tearing asunder the oxygen and
hydrogen of which it is composed. The oxygen and hydrogen now have
potential energy, and, if they be allowed to combine, this will manifest
itself as the light and heat of the explosion. These examples will serve
to illustrate the nature of the changes which energy undergoes. These
are of the nature of transferences of energy from one body to another,
and of transformations from one mode or manifestation to another. The
most important point that has been established during this century with
regard to energy is that, throughout all its transferences and
transformations, it can be neither created nor destroyed. But there is
another point of great importance. Transformations of energy take place
more readily in certain directions than in others. And there is always a
tendency for energy to pass from the higher or more readily
transformable to the lower or less readily transformable forms. When,
for example, energy has passed to the low kinetic form of the uniformly
distributed molecular motion of heat, it is exceedingly difficult, or
practically impossible, to transform it into a higher and more available
form.
Now, both animals and plants are centres of the transformation of
energy; and in them energy, notwithstanding that it is being raised to a
high position of potentiality, is constantly tending to be degraded to
lower forms. Hence the necessity of some source from which fresh stores
of available energy may be constantly supplied. Such a source is solar
radiance. This it is which gives the succession of little pushes which
keeps the pendulum of life a-swinging. And it is the green plants which,
through their chlorophyll, are in the best position to utilize the solar
energy. They utilize it in building up, from the necessary constituents
diffused through the atmosphere and the soil, complex forms of organic
material, of which the first visible product seems to be starch; and
these not only contain large stores of potential energy, but are
capable, when combined with oxygen, of containing yet larger stores. The
animal, taking into its body these complex materials, and elaborating
them together with oxygen into yet more complex and more unstable
compounds, then, during its vital activity, makes organized use of the
transformation of the potential energy thus stored into lower forms of
energy. Thus there go on side by side, in both animals and plants, a
building up or synthesis of complex and unstable chemical compounds,
accompanied by a storage of potential energy, and a breaking down or
analysis of these compounds into lower and simpler forms, accompanied by
a setting free of kinetic energy. But in the plant, synthetic changes
and storage of energy are in excess, while in the animal, analytic
changes and the setting free of kinetic energy are more marked. Hence
the variety and volume of animal activities.
The building up of complex organic substances with abundance of stored
energy may be roughly likened to the building up, by the child with his
wooden bricks, of houses and towers and pyramids. The more complex they
become the more unstable they are, until a touch will shatter the
edifice and liberate the stored-up energy of position acquired by the
bricks. Thus, under the influence of solar energy, do plants build up
their bricks of hydrogen, carbon, and oxygen into complex molecular
edifices. Animals take advantage of the structures so elaborated, modify
them, add to them, and build yet more complex molecular edifices. These,
at the touch of the appropriate stimulus, topple over and break
down--not, indeed, into the elemental bricks, but into simpler molecular
forms, and these again in later stages into yet simpler forms, which are
then got rid of or excreted from the body. Meanwhile the destructive
fall of the molecular edifice is accompanied by the liberation of
energy--as heat, maintaining the warmth of the body; as visible or
hidden movements, in locomotion, for example, and the heart-beat; and
sometimes as electrical energy (in electric fishes); as light (in
phosphorescent animals and the glow-worm), or as sound. It is this
abundant liberation of energy, giving rise to many and complex
activities, which is one of the distinguishing features of animals as
compared with plants.
* * * * *
We have now, I trust, extended somewhat and rendered somewhat more exact
our common and familiar knowledge of the nature of animal life. In the
next chapter we will endeavour to extend it still further by a
consideration of the process of life.
NOTES
[A] An interesting problem concerning the atmosphere is suggested by
certain geological facts. In our buried coal-seams and other
carbonaceous deposits a great quantity of carbon, for the most
part abstracted from the atmosphere, has been stored away. Still
greater quantities of carbon are imprisoned in the substance of
our limestones, which contain, when pure, 44 per cent. of this
element. A large quantity of oxygen has also been taken from the
atmosphere to combine with other elements during their oxidation.
The question is--Was the atmosphere, in the geological past, more
richly laden with carbonic acid gas, of which some has entered
into combination with lime to form limestone, while some has been
decomposed by plants, the carbon being buried as coal, and the
oxygen as products of oxidation? Or, has the atmosphere been
furnished with continuous fresh supplies of carbonic acid gas?
CHAPTER II.
THE PROCESS OF LIFE.
In the foregoing chapter, on "The Nature of Animal Life," we have seen
that animals breathe, feed, grow, are sensitive, exhibit various
activities, and reproduce their kind. These may be regarded as primary
life-processes, in virtue of which the animal characterized by them
is a living creature. We have now to consider some of these
life-processes--the sum of which we may term the process of life--a
little more fully and closely.
The substance that exhibits these life-processes is protoplasm, which
exists in minute separate masses termed cells. It seems probable,
however, that these cells, separate as they seem, are in some cases
united to each other by minute protoplasmic filaments. In the higher
animals the cells in different parts of the body take on different forms
and perform different functions. Like cells with like functions are also
aggregated together into tissues. Thus the surfaces of the body,
external and internal, are bounded by or lined with epithelial tissue;
the bones and framework of the body are composed of skeletal tissue;
nervous tissue goes to form the brain and nerves; contractile tissue is
found in the muscles; while the blood and lymph form a peculiar
nutritive tissue. The organs of the body are distinct parts performing
definite functions, such as the heart, stomach, or liver. An organ may
be composed of several tissues. Thus the heart has contractile tissue in
its muscular walls, epithelial tissue lining its cavities, and skeletal
tissue forming its framework. Still, notwithstanding their aggregation
into tissues and organs, it remains true that the body of one of the
higher animals is composed of cells, together with certain
cell-products, horny, calcareous, or other. The simplest animals, called
protozoa, are, however, unicellular, each organism being constituted by
a single cell.
We must notice that, even during periods of apparent inactivity--for
example, during sleep--many life-processes are still in activity, though
the vigour of action may be somewhat reduced. When we are fast asleep,
respiration, the heart-beat,[B] and the onward propulsion of food
through the alimentary canal, are still going on. Even at rest, the
living animal is a _going_ machine. In some cases, however, as during
the hibernating sleep of the dormouse or the bear, the vital activities
fall to the lowest possible ebb. Moreover, in some cases, the
life-processes may be temporarily arrested, but again taken up when the
special conditions giving rise to the temporary arrest are removed.
Frogs, for example, have been frozen, but have resumed their
life-activities when subsequently thawed.
Let us take the function of respiration as a starting-point in further
exemplification of the nature of the life-processes of animals.
The organs of respiration, in ourselves and all the mammalia, are the
lungs, which lie in the thoracic cavity of the chest, the walls of which
are bounded by the ribs and breast-bone, its floor being formed of a
muscular and movable partition, the diaphragm, which separates it from
the stomach and other alimentary viscera in the abdominal region. The
lungs fit closely, on either side of the heart, in this thoracic cavity;
and when the size of this cavity is altered by movements of the ribs and
diaphragm, air is either sucked into or expelled from the lungs through
the windpipe, which communicates with the exterior through the mouth or
nostrils. It is unnecessary to describe the minute structure of the
lungs; suffice it to say that, in the mammal, they contain a vast number
of tubes, all communicating eventually with the windpipe, and
terminating in little expanded sacs or bags. Around these little sacs
courses the blood in a network of minute capillary vessels, the walls of
which are so thin and delicate that the fluid they contain is only
separated from the gas within the sacs by a film of organic tissue.
The blood is a colourless fluid, containing a great number of round red
blood-discs, which, from their minute size and vast numbers, seem to
stain it red. They may be likened to a fleet of little boats, each
capable of being laden with a freight of oxygen gas, while the stream in
which they float is saturated with carbonic acid gas. This latter
escapes into the air-sacs as the fluid courses through the delicate
capillary tubes.
Whither goes the oxygen? Whence comes the carbonic acid gas? The answer
to these questions is found by following the course of the
blood-circulation. The propulsion of the blood throughout the body is
effected by the heart, an organ consisting, in mammals, of two receivers
(auricles) into which blood is poured, and two powerful force-pumps
(ventricles), supplied with blood from the receivers and driving it
through great arteries to various parts of the body. There are valves
between the receivers and the force-pumps and at the commencement of the
great arterial vessels, which ensure the passage of the blood in the
right direction. The two receivers lie side by side; the two force-pumps
form a single muscular mass; and all four are bound up into one organ;
but there is, during adult life, no direct communication between the
right and left receivers or the right and left force-pumps.
Let us now follow the purified stream, with its oxygen-laden
blood-discs, as it leaves the capillary tubes of the lungs. It generally
collects, augmented by blood from other similar vessels, into large
veins, which pour their contents into the left receiver. Thence it
passes on into the left force-pump, by which it is propelled, through a
great arterial vessel and the numerous branches it gives off, to the
head and brain, to the body and limbs, to the abdominal viscera; in
short, to all parts of the body except the lungs. In all the parts thus
supplied, the vessels at length break up into a delicate capillary
network, so that the blood-fluid is separated from the tissue-cells only
by the delicate organic film of the capillary walls. Then the blood
begins to re-collect into larger and larger veins. But a change has
taken place; the blood-discs have delivered up to the tissues their
freight of oxygen; the stream in which they float has been charged with
carbonic acid gas. The veins leading from various parts of the body
converge upon the heart and pour their contents into the right receiver;
thence the blood passes into the right force-pump, by which it is
propelled, by arteries, to the lungs. There the blood-discs are again
laden with oxygen, the stream is again purified of its carbonic acid
gas, and the blood proceeds on its course, to renew the cycle of its
circulation.
[Illustration: Fig. 6.--Diagram of circulation.
L.A., left auricle of the heart; L.V., left ventricle; H., capillary
plexus of the head; B., capillary plexus of the body; A.C., alimentary
canal; Lr., liver; R.A., right auricle of the heart; R.V., right
ventricle; Lu., lungs.]
Now, if we study the process of respiration and that of circulation,
with which it is so closely associated, in other forms of life, we shall
find many differences in detail. In the bird, for example, the mechanism
of respiration is different. There is no diaphragm, and the lungs are
scarcely distensible. There are, however, large air-sacs in the abdomen,
in the thoracic region, in the fork of the merry-thought, and elsewhere.
These are distensible, and to reach them the air has to pass through the
lungs, and as it thus passes through the delicate tubes of the lungs, it
supplies the blood with oxygen and takes away carbonic acid gas. In the
frog there is no diaphragm, and there are no ribs. The lungs are hollow
sacs with honey-combed sides, and they are inflated from the mouth,
which is used as a force-pump for this purpose. In the fish there are no
lungs, respiration being effected by means of gills. In these organs the
blood is separated from the water which passes over them (being gulped
in by the mouth and forced out between the gill-covers) by only a thin
organic film, so that it can take up the oxygen dissolved in the water,
and give up to the water the carbonic acid it contains. In fishes, too,
we have only one receiver and one force-pump, the blood passing through
the gills on its way to the various parts of the body. In the lobster,
again, there are gills, but the mechanism by which the water is drawn
over them is quite different, and the blood passes through them on its
way to the heart, after passing through the various organs of the body,
not on its way from the heart, as in vertebrate fishes. The blood, too,
has no red blood-discs. In the air-breathing insects the mechanism is,
again, altogether different. The air, which obtains access to the body
by spiracles in the sides (see Fig. 1, p. 3), is distributed by delicate
and beautiful tubes to all parts of the organs; so that the oxygen is
supplied to the tissues directly, and not through the intervention of a
blood-stream. In the earthworm, on the other hand, there is a
distributing blood-stream, but there is no mechanism for introducing the
air within the body; while in some of the lowliest forms of life there
is neither any introduction of air within the body nor any distribution
by means of a circulating fluid. Beginning, therefore, with the surface
of the body simply absorbent of oxygen, we have the concentration of the
absorbent parts in special regions, and an increase in the absorbent
surface, either (1) by the pushing out of processes into the surrounding
medium, as in gills; or (2) by the formation of internal cavities,
tubes, or branching passages, as in lungs and the tracheal air-system of
insects.
What, then, is the essential nature of the respiratory process thus so
differently manifested? Clearly the supply of oxygen to the cellular
tissue-elements, and, generally closely associated with this, the
getting rid of carbonic acid gas.
Let us now glance at the life-processes which minister to nutrition,
beginning, as before, with the mode in which these processes are
effected in ourselves.
The alimentary canal is a long tube running through the body from the
mouth to the vent. In the abdominal region it is coiled upon itself, so
that its great length may be conveniently packed away. Opening into this
tube are the ducts of certain glands, which secrete fluids which aid in
the digestion of the food. Into the mouth there open the ducts of the
salivary glands, which secrete the saliva; in the stomach there are a
vast number of minute gastric glands; in the intestine, besides some
minute tubular glands, there are the ducts of the large liver (which
secretes the bile) and the pancreas, or sweetbread. Since, with the
exception of the openings of these ducts, the alimentary canal is a
closed tube, its contents, though lying within the body, are in a sense
outside it, just as the fuel in a tubular boiler, though within the
boiler, is really outside it. The organic problem, therefore, is how to
get the nutritive materials through the walls of the tube and thus into
the body.
At an ordinary meal we are in the habit of consuming a certain amount of
meat, with some fat, together with bread and potatoes, and perhaps some
peas or beans and a little salt. This is followed by, say, milky
rice-pudding, with which we take some sugar; and a cheese course may,
perhaps, be added. The whole is washed down with water more or less
medicated with other fluid materials. Grouping these substances, there
are (1) water and salts, including calcium phosphate in the milk; (2)
meat, peas, milk, and cheese, all of which contain albuminous or allied
materials; (3) bread, potatoes, and rice, which contain starchy matters;
and here we may place the sugar; (4) fat, associated with the meat or
contained in the cream of the milk. Now, of all the materials thus
consumed, only the water, salts, and sugar are capable, in their
unaltered condition, of passing through the lining membrane of the
alimentary canal, and thus of entering the body. The albuminous
materials, the starchy matter, and the fat--that is to say, the main
elements of the food--are, in their raw state, absolutely useless for
nutritive purposes.
The preparation of the food begins in the mouth. The saliva here acts
upon some of the starchy matter, and converts it into a kind of sugar,
which _can_ pass through the lining membrane of the alimentary canal,
and thus enter the body. The fats and albuminous matters here remain
unaltered, though they are torn to pieces by the mastication effected by
the teeth. In the stomach the albuminous constituents of the meat are
attacked by the gastric juice and converted into peptones; and in this
new condition they, too, can soak through the lining membrane of the
alimentary canal, and thus can enter the body. In the stomach all action
on starch is arrested; but in the intestine, through the effect of a
ferment contained in the pancreatic juice, this action is resumed, and
the rest of the starch is converted into absorbable sugar. Another
principle contained in pancreatic juice takes effect on the albuminous
matters, and converts them into absorbable peptones. The pancreatic
juice also acts on the fats, converting them into an emulsion, that is
to say, causing them to break up into exceedingly minute globules, like
the butter globules in milk. It furthermore contains a ferment which
splits up the fats into fatty acids and glycerine; and these fatty
acids, with an alkaline carbonate contained in small quantities in
pancreatic juice, form soluble soaps, which further aid in emulsifying
fats. The bile also aids in emulsifying fats.
The effect, then, of the various digestive fluids upon the food is to
convert the starch, albuminous material, and fat into sugar, peptones,
glycerine, and soap, and thus render them capable of passing through the
lining membrane of the canal into the body.
The materials thus absorbed are either taken up into the blood-stream or
pass into a separate system of vessels called lacteals. All the blood
which comes away from the alimentary canal passes into the liver, and
there undergoes a good deal of elaboration in that great chemical
laboratory of the body. The fluid in the lacteals passes through
lymphatic glands, in which it too undergoes some elaboration before it
passes into the blood-stream by a large vessel or duct.
Thus the blood, which we have seen to be enriched with oxygen in the
lungs, is also enriched with prepared nutritive material through the
processes of digestion and absorption in the alimentary organs and
elaboration in the liver and lymphatic glands.
Here let us again notice that the details of the process of nutrition
vary very much in different forms of life. In some mammals the organs of
digestion are specially fitted to deal with a flesh diet; in others they
are suited for a diet of herbs. In the graminivorous birds the grain is
swallowed whole, and pounded up in the gizzard. The leech swallows
nothing but blood. The earthworm pours out a secretion on the leaves, by
which they are partially digested before they enter the body. Many
parasitic organisms have no digestive canal, the nutritive juices of
their host being absorbed by the general external surface of the body.
But the essential life-process is in all cases the same--the absorption
of nutritive matter to be supplied to the cell or cells of which the
organism is built up.
Thus in the mammal the blood, enriched with oxygen in the lungs, and
enriched also with nutritive fluids, is brought, in the course of its
circulation, into direct or indirect contact with all the myriads of
living cells in the body.
In the first place, the material thus supplied is utilized for and
ministers to the growth of the organs and tissues. This growth is
effected by the multiplication of the constituent cells. The cells
themselves have a very limited power of growth. But, especially in the
early stages of the life of the organism, when well supplied with
nutriment, the cells multiply rapidly, by a process of fission, or the
division of each cell into two daughter cells. The first part of the
cell to divide is the nucleus, the protoplasmic network of which shows,
during the process, curious and interesting arrangements and groupings
of the fibres. When the nucleus has divided, the surrounding protoplasm
is constricted, and separates into two portions, each of which contains
a daughter nucleus.
In addition to the multiplication of cells, there is the formation,
especially during periods of growth, of certain products of cell-life
and cell-activity. Bone, for example, is a more or less permanent
product of the activity of certain specialized cells.
There is, perhaps, no more wonderful instance of rapid and vigorous
growth than the formation of the antlers of deer. These splendid weapons
and adornments are shed and renewed every year. In the spring, when they
are growing, they are covered over with a dark skin provided with short,
fine, close-set hair, and technically termed "the velvet." If you lay
your hand on the growing antler, you will feel that it is hot with the
nutrient blood that is coursing beneath it. It is, too, exceedingly
sensitive and tender. An army of tens of thousands of busy living cells
is at work beneath that velvet surface, building the bony antlers,
preparing for the battles of autumn. Each minute cell knows its work,
and does it for the general good--so perfectly is the body knit into an
organic whole. It takes up from the nutrient blood the special materials
it requires; out of them it elaborates the crude bone-stuff, at first
soft as wax, but ere long to become as hard as stone; and then, having
done its work, having added its special morsel to the fabric of the
antler, it remains embedded and immured, buried beneath the
bone-products of its successors or descendants. No hive of bees is
busier or more replete with active life than the antler of a stag as it
grows beneath the soft, warm velvet. And thus are built up in the course
of a few weeks those splendid "beams," with their "tynes" and "snags,"
which, in the case of the wapiti, even in the confinement of our
Zoological Gardens, may reach a weight of thirty-two pounds, and which,
in the freedom of the Rocky Mountains, may reach such a size that a man
may walk, without stooping, beneath the archway made by setting up upon
their points the shed antlers. When the antler has reached its full
size, a circular ridge makes its appearance at a short distance from the
base. This is the "burr," which divides the antler into a short
"pedicel" next the skull, and the "beam" with its branches above. The
circulation in the blood-vessels of the beam now begins to languish, and
the velvet dies and peels off, leaving the hard, dead, bony substance
exposed. Then is the time for fighting, when the stags challenge each
other to single combat, while the hinds stand timidly by. But when the
period of battle is over, and the wars and loves of the year are past,
the bone beneath the burr begins to be eaten away and absorbed, through
the activity of certain large bone-eating cells, and, the base of
attachment being thus weakened, the beautiful antlers are shed; the
scarred surface skins over and heals, and only the hair-covered pedicel
of the antler is left.[C]
Not only are there these more or less permanent products of
cell-activity which are built up into the framework of the body; there
are other products of a less enduring, but, in the case of some of them,
not less useful character. The secretions, for example, which, as we
have seen, minister in such an important manner to nutrition, are of
this class. The salivary fluids, the gastric juice, the pancreatic
products, and the bile,--all of these are products of cell-life and
cell-activity. And then there are certain products of cell-life which
must be cast out from the body as soon as possible. These are got rid of
in the excretions, of which the carbonic acid gas expelled in the lungs
and the waste-products eliminated through the kidneys are examples. They
are the ultimate organic products of the combustion that takes place in
the muscular, nervous, and other tissues.
The animal organism has sometimes been likened to a steam-engine, in
which the food is the fuel which enters into combustion with the oxygen
taken in through the lungs. It may be worth while to modify and
modernize this analogy--always remembering, however, that it is an
analogy, and that it must not be pushed too far.
In the ordinary steam-engine the fuel is placed in the fire-box, to
which the oxygen of the air gains access; the heat produced by the
combustion converts the water in the boiler into steam, which is made to
act upon the piston, and thus set the machinery in motion. But there is
another kind of engine, now extensively used, which works on a different
principle. In the gas-engine the fuel is gaseous, and it can thus be
introduced in a state of intimate mixture with the oxygen with which it
is to unite in combustion. This is a great advantage. The two can unite
rapidly and explosively. In gunpowder the same end is effected by mixing
the carbon and sulphur with nitre, which contains the oxygen necessary
for their explosive combustion. And this is carried still further in
dynamite and gun-cotton, where the elements necessary for explosive
combustion are not merely mechanically mixed, but are chemically
combined in a highly unstable compound.
But in the gas-engine, not only is the fuel and the oxygen thus
intimately mixed, but the controlled explosions and the resulting
condensation are caused to act directly on the piston, and not through
the intervention of water in a boiler. Whereas, therefore, in the
steam-engine the combustion is to some extent external to the working of
the machine, in the gas-engine it is to a large extent internal and
direct.
Now, instead of likening the organism as a whole to a steam-engine, it
is more satisfactory to liken each cell to a gas-engine. We have seen
that the cell-substance around the nucleus is composed of a network of
protoplasm, the plasmogen, enclosing within its meshes a more fluid
material, the plasm. It is probable that this more fluid material is an
explosive, elaborated through the vital activity of the protoplasmic
network. During the period of repose which intervenes between periods of
activity, the protoplasmic network is busy in construction, taking from
the blood-discs oxygen, and from the blood-fluid carbonaceous and
nitrogenous materials, and knitting these together into relatively
unstable explosive compounds. These explosive compounds are like the
mixed air and gas of the gas-engine. A rested muscle may be likened to a
complex and well-organized battery of gas-engines. On the stimulus
supplied through a nerve-channel a series of co-ordinated explosions
takes place: the gas-engines are set to work; the muscular fibres
contract; the products of the explosions (one of which is carbonic acid
gas) are taken up and hurried away by the blood-stream; and the
protoplasm sets to work to form a fresh supply of explosive material.
Long before the invention of the gas-engine, long before gun-cotton or
dynamite were dreamt of, long before some Chinese or other inventor
first mixed the ingredients of gunpowder, organic nature had utilized
the principle of controlled explosions in the protoplasmic cell.
Certain cells are, however, more delicately explosive than others.
Those, for example, on or near the external surface of the body--those,
that is to say, which constitute the end organs of the special
senses--contain explosive material which may be fired by a touch, a
sound, an odour, the contact with a sapid fluid or a ray of light. The
effects of the explosions in these delicate cells, reinforced in certain
neighbouring nerve-knots (ganglionic cells), are transmitted down the
nerves as along a fired train of gunpowder, and thus reach that
wonderful aggregation of organized and co-ordinated explosive cells, the
brain. Here it is again reinforced and directed (who, at present, can
say how?) along fresh nerve-channels to muscles, or glands, or other
organized groups of explosives. And in the brain, somehow associated
with the explosion of its cells, consciousness and the mind-element
emerges; of which we need only notice here that it belongs to a _wholly
different order of being_ from the physical activities and products with
which we are at present concerned.
No analogies between mechanical contrivances and organic processes can
be pushed very far. To liken the organic cell to a gas-engine is better
than to liken the organism to a steam-engine, because it serves to
indicate the fact that the fuel does not simply combine with the oxygen
in combustion, but that an unstable or explosive combination of "fuel"
and oxygen is first formed; and again, because the effect of this is
direct, and not through the intervention of any substance to which the
combustion merely supplies the necessary heat. But beyond the fact that
a kind of explosive is formed which, like a fulminating compound, can be
fired by a touch, there is no very close analogy to be drawn. Nor must
we press the explosion analogy too far. The essential thing would seem
to be this--which, perhaps, the analogy may have served to lead up
to--that the vital protoplasmic network of the cell has the power of
building up complex and unstable chemical compounds, which are probably
stored in the plasm within the spaces between the threads of the
network; and that these unstable compounds, under the influence of a
stimulus (or, possibly, sometimes spontaneously) break down into simpler
and more stable compounds.[D] In the case of muscle-cells, this latter
change is accompanied by an alteration in length of the fibres and
consequent movements in the organism, the products of the disruptive
change being useless or harmful, and being, therefore, got rid of as
soon as possible. But very frequently the products of explosive activity
are made use of. In the case of bone-cells, one of the products of
disruption is of permanent use to the organism, and constitutes the
solid framework of the skeleton. In the case of the secreting cells of
the salivary and other digestive glands, one of the disruptive products
is of temporary value for the preparation of the food. It is exceedingly
probable that these useful products of disruption, permanent or
temporary, took their origin in waste products for which natural
selection has found a use, and which have been, through natural
selection, rendered more and more efficacious. This, however, is a
question we are not at present in a position to discuss.
In the busy hive of cells which constitutes what we call the animal
body, there is thus ceaseless activity. During periods of apparent rest
the protogen filaments of the cell-net are engaged in constructive work,
building up fresh supplies of complex and unstable materials, which,
during periods of apparent activity, break up into simpler and more
stable substances, some of which are useful to the organism while others
must be got rid of as soon as possible. From another point of view, the
cells during apparent rest are storing up energy which is utilized by
the organism during its periods of activity. The storing up of available
energy may be likened to the winding up of a watch or clock; it is
during apparent rest that the cell is winding itself up; and thus we
have the apparent paradox that the cell is most active and doing most
work when it is at rest. During the repose of an organ, in fact, the
cells are busily working in preparation for the manifestation of
energetic action that is to follow. Just as the brilliant display of
intellectual activity in a great orator is the result of the silent work
of a lifetime, so is the physical manifestation of muscular power the
result of the silent preparatory work of the muscle-cells.[E]
One point to be specially noted is the varied activity of the cells.
While they are all working for the general good of the organism, they
are divided into companies, each with a distinct and definite kind of
work. This is known as the physiological division of labour. It is
accompanied by a morphological differentiation of structure. By the form
of a cell, therefore, we can generally recognize the kind of work it has
to perform. The unstable compounds produced by the various cells must
also be different, though not much is known at present on this subject.
The unstable compound which forms bone and that which forms the salivary
ferment, the unstable matter elaborated by nerve-cells and that built up
by muscle-cells, are in all probability different in their chemical
nature. Whether the formative plasmogen from which these different
substances originate is in all cases the same or in different cases
different, we do not know.
It may, perhaps, seem strange that the products of cellular life should
be reached by the roundabout process of first producing a very complex
substance out of which is then formed a less complex substance, useful
for permanent purposes, as in bone, or temporary purposes, as in the
digestive fluids. It seems a waste of power to build up substances
unnecessarily complex and stored with an unnecessarily abundant supply
of energy. Still, though we do not know that this course is adopted in
all cases, there is no doubt that it is adopted in a great number of
instances. And the reason probably is that by this method the organs are
enabled to act under the influence of stimuli. They are thus like
charged batteries ready to discharge under the influence of the
slightest organic touch. In this way, too, is afforded a means by which
the organ is not dependent only upon the products of the immediate
activity of the protoplasm at the time of action, but can utilize the
store laid up during a considerable preceding period.
Sufficient has now been said to illustrate the nature of the process of
life. The fact that I wish to stand out clearly is that the animal body
is stored with large quantities of available energy resident in highly
complex and unstable chemical compounds, elaborated by the constructive
energy of the formative protoplasm of its constituent cells. These
unstable compounds, eminently explosive according to our analogy, are
built up of materials derived from two different sources--from the
nutritive matter (containing carbon, hydrogen, and nitrogen) absorbed in
the digestive organs, and from oxygen taken up from the air in the
lungs. The cells thus become charged with energy that can be set free on
the application of the appropriate stimulus, which may be likened to the
spark that fires the explosive.
Let us note, in conclusion, that it is through the blood-system,
ramifying to all parts of the body, and the nerve-system, the
ramifications of which are not less perfect, that the larger and higher
organisms are knit together into an organic whole. The former carries to
the cell the raw materials for the elaboration of its explosive
products, and, after the explosions, carries off the waste products
which result therefrom. The nerve-fibres carry the stimuli by which the
explosive is fired, while the central nervous system organizes,
co-ordinates, and controls the explosions, and directs the process of
reconstruction of the explosive compounds.
NOTES
[B] It has before been noticed that the organs themselves have their
periods of rest. The rhythm of rest and repose in the heart is not
that of the activity and sleep of the organism, but that of the
contraction and relaxation of the organ itself.
[C] From a popular article of the author's on "Horns and Antlers," in
_Atalanta_.
[D] It will be well here to introduce the technical terms for these
changes. The general term for chemical actions occurring in the
tissues of a living creature is _metabolism_; where the change is
of such a nature that complex and unstable compounds are built up
and stored for a while, it is called _anabolism_; where complex
unstable compounds break up into less complex and relatively
stable compounds, the term _katabolism_ is applied. We shall speak
of anabolic changes as _constructive_; katabolic, as _disruptive_,
or sometimes, _explosive_.
[E] I do not mean, of course, to imply that there is no reconstruction
during activity, but that it is then distinctly outbalanced by
disruptive changes.
CHAPTER III.
REPRODUCTION AND DEVELOPMENT.
We have now to turn to a fresh aspect of animal life, that of
reproduction; and it will be well to connect this process as closely as
possible with the process of life in general, of which it is a direct
outcome.
It will be remembered that, in the last chapter, it was shown that the
essential feature in the process of life is the absorption by living
protoplasm of oxygen on the one hand and nutritive matter on the other
hand, and the kneading of these together, in subtle metabolism, into
unstable compounds, which we likened to explosives. This is the first,
or constructive, stage of the life-process. Thereupon follows the
second, or disruptive, stage. The unstable compounds break down into
more stable products,--they explode, according to our analogy; and
accompanying the explosions are manifestations of motor activity--of
heat, sometimes of light and electrical phenomena. But in the economy of
nature the products of explosion are often utilized, and in the division
of labour among cells the explosions of some of them are directed
specially to the production of substances which shall be of permanent or
temporary use--for digestion, as in the products of the salivary,
gastric, and intestinal glands; for support, as in bone, cartilage, and
skeletal tissue generally; or as a store of nutriment, in fat or yolk.
The constructive products of protoplasmic activity seem for the most
part to be lodged in the spaces between the network of formative
protoplasm. The disruptive products--those of them, that is to say,
which are of temporary or permanent value to the organism--accumulate
either within the cell, sometimes at one pole, sometimes at the centre,
as in the case of the yolk of eggs, or around the cell, as in the case
of cartilage or bone.
Apart from and either preceding or accompanying these phenomena, is the
growth or increase of the formative protoplasm itself; concerning which
the point to be here observed is that it is not indefinite, but limited.
This was first clearly enunciated by Herbert Spencer, and may be called
Spencer's law. In simplest expression it may thus be stated: _Volume
tends to outrun surface._ Take a cube measuring one inch in the side;
its volume is one cubic inch, its surface six square inches. Eight such
cubes will have a surface of (6 × 8) forty-eight square inches. But let
these eight be built into a larger cube, two inches in the side, and it
will be found that the surface exposed is now only twenty-four square
inches. While the volume has been increased eight times, the surface has
been increased only four times. With increase of size, volume tends to
outrun surface. But in the organic cell the nutritive material and
oxygen are absorbed at the surface, while the explosive changes occur
throughout its mass. Increase of size, therefore, cannot be carried
beyond certain limits, for the relatively diminished surface is unable
to supply the relatively augmented mass with material for elaboration
into unstable compounds. Hence the cell divides to afford the same mass
increased surface. This process of cell-division is called fission, and
in some cases cleavage.
We will now proceed to pass in review the phenomena of reproduction and
development in animals.
[Illustration: Fig. 7.--Protozoa.
A, vorticella extended. B, the same contracted. C, D, monads. E,
am[oe]ba. F, _Param[oe]cium_. G, _Gregarina_. c.f., contractile fibre;
c.v., contractile vesicle; d., disc; end., endoplast; f.v.,
food-vacuole; fl., flagellum; gu., gubernaculum; n., nucleus; p.a.,
potential anus; ps., (in A) peristome, (in E) pseudopodium; vs.,
vestibule.]
Attention has already been drawn to the difference between those lowly
organisms, each of which is composed of a single cell--the protozoa, as
they are termed--and those higher organisms, called metazoa, in which
there are many cells with varied functions. Confining our attention at
first to the former group of unicellular animals, we find considerable
diversities of form and habit, from the relatively large, sluggish,
parasitic _Gregarina_, to the active slipper-animalcule, or
_Param[oe]cium_, or the beautiful, stalked bell-animalcule, or
_Vorticella_; and from the small, slow-moving am[oe]ba to the minute,
intensely active monad. In many cases reproduction is by simple fission,
as in the am[oe]ba, where the nucleus first undergoes division; and then
the whole organism splits into two parts, each with its own nucleus. In
other cases, also numerous, the organism passes into a quiescent state,
and becomes surrounded with a more or less toughened cyst. The nucleus
then disappears, and the contents of the cyst break up into a number of
small bodies or spores. Eventually the cyst bursts, and the spores swarm
forth. In the case of some active protozoa the minute creatures that
swarm forth are more or less like the parent; but in the more sluggish
kinds the minute forms are more active than the parent. Thus in the case
of the gregarina, the minute spore-products are like small am[oe]bæ;
while in other instances the embryos, if so we may call them, have a
whip-like cilium like the monads.
Very frequently, however, there is, in the protozoa, a further process,
which would seem to be intimately associated with fission or the
formation of spores, as the case may be. This is known as conjugation.
Among monads, for example, two individuals may meet together, conjugate,
and completely fuse the one into the other. A triangular cyst results.
After a while, the cyst bursts, and an apparently homogeneous fluid
escapes. The highest powers of the microscope fail to disclose in it any
germ of life; and there, at first sight, would seem to be an end of the
matter. But wait and watch; and there will appear in the field of the
microscope, suddenly and as if by magic, countless minute points, which
prolonged watching shows to be growing. And when they have further
grown, each distinct point is seen to be a monad.
In the slipper-animalcule, conjugation is temporary. But during the
temporary fusion of the two individuals important changes are said to
occur. In these infusorians there is, beside the nucleus, a smaller
body, the paranucleus. This, in the case of conjugating param[oe]cia,
appears to divide into two portions, of which one is mutually exchanged.
Thus when two slipper-animalcules are in conjugation, the paranucleus of
each breaks into two parts, _a_ and _b_, of which _a_ is retained and
_b_ handed over in exchange. The old _a_ and the new _b_ then unite, and
each param[oe]cium goes on its separate way. M. Maupas, who has lately
reinvestigated this matter, considers, as the result of his observations
on another infusorian (_Stylonichia_), that without conjugation these
organisms become exhausted, and multiplication by fission comes to a
standstill. If this be so, conjugation is, in these organisms, necessary
for the continuance of the race. But Richard Hertwig has recently shown
that this is, at any rate, not universally true.
In the bell-animalcule, fission takes place in such a manner as to
divide the bell into two equal portions. Thus there are two bells to one
stalk. But the fate of the two is not the same. One remains attached to
the stalk, and expands into a complete vorticella. The other remains
pear-shaped, and develops round the posterior region of the body a
girdle of powerful vibratile cilia, by the lashing of which the
animalcule tears itself away from the parent stem, and swims off through
the water. After a short active existence, it settles down in a
convenient spot, adhering by its posterior extremity. The hinder girdle
of cilia is lost or absorbed, a stalk is rapidly developed, and the
organism expands into a perfect vorticella.
In some cases, however, the fission is of a different character, with
different results. It may be very unequal, so that a minute,
free-swimming animalcule is disengaged; or minute animalcules may result
by repetition of division. In either case the minute form conjugates
with an ordinary vorticella, its smaller mass being completely merged in
the larger volume of its mate.
There are, of course, many variations in detail in the modes of
protozoan reproduction; but we may say that, omitting such details,
reproduction is either by simple fission or by spore-formation; and that
these processes are in some cases associated with, and perhaps dependent
on, the temporary or permanent union of two individuals in conjugation.
It is essential to notice that the results of fission or of
spore-formation separate, each going on its own way. Hence such
development as we find in the protozoa results from differentiations
within the limits of the single cell. Thus the bell-animalcule has a
well-defined and constant form; a definite arrangement of cilia round
the rim and in the vestibule by which food finds entrance to the body.
The outer layer of the body forms a transparent cuticle, beneath which
is a so-called "myophan" layer, continuous with a contractile thread in
the stalk. Within the substance of the body is a pulsating cavity, or
contractile vesicle, and a nucleus. Such is the nature of the
differentiation which may go on within the protozoan cell.
When we pass to the metazoa, we find that the method of differentiation
is different. These organisms are composed of many cells; and instead of
the parts of the cell differentiating in several directions, the several
cells differentiate each in its own special direction. This is known as
the physiological division of labour. The cells merge their
individuality in the general good of the organism. Each, so to speak,
cultivates some special protoplasmic activity, and neglects everything
else in the attainment of this end. The adult metazoan, therefore,
consists of a number of cells which have diverged in several, sometimes
many, directions.
In some of the lower metazoans, reproduction may be effected by fission.
Thus the fresh-water hydra is said to divide into two parts, each of
which grows up into a perfect hydra. It is very doubtful, however,
whether this takes place normally in natural life. But there is no doubt
that if a hydra be artificially divided into a number of special pieces,
each will grow up into a perfect organism, so long as each piece has
fair samples of the different cells which constitute the body-wall.
Sponges and sea-anemones may also be divided and subdivided, each part
having the power of reproducing the parts that are thus cut away. When a
worm is cut in half by the gardener's spade, the head end grows a new
tail; and it is even stated that a worm not only survived the removal of
the first five rings, including the brain, mouth, and pharynx, but
within fifty-eight days had completely regenerated these parts.
Higher up in the scale of metazoan life, animals have the power of
regenerating lost limbs. The lobster that has lost a claw reproduces a
new one in its stead. A snail will reproduce an amputated "horn," or
tentacle, many times in succession, reproducing in each case the eye,
with its lens and retina. Even a lizard will regenerate a lost tail or a
portion of a leg. In higher forms, regeneration is restricted to the
healing of wounds and the mending of broken bones.
Closely connected with this process of regeneration of lost parts is the
widely prevalent process of reproduction by budding. The cut stump of
the amputated tentacle of the hydra or the snail buds forth a new organ.
But in the hydra, during the summer months, under normal circumstances,
a bud may make its appearance and give rise to a new individual, which
will become detached from the parent, to lead a separate existence. In
other organisms allied to the hydra the buds may remain in attachment,
and a colony will result. This, too, is the result of budding in many of
the sponges. In some worms, too, budding may occur. In the fresh-water
worm (_Chætogaster limnæi_) the animal, as we ordinarily see it, is a
train of individuals, one budded off behind the other--the first fully
developed, those behind it in various stages of development. The
individuals finally separate by transverse division. Another more lowly
worm (_Microstomum lineare_, a Turbellarian) may bud off in similar
fashion a chain of ten or fifteen individuals. In these cases budding is
not far removed from fission.
Now, in the case of reproduction by budding, as in the hydra, a new
individual is produced from some group of cells in the parent organism.
From this it is but a step--a step, however, of the utmost
importance--to the production of a new individual from a single cell
from the tissues of the parental organism. Such a reproductive cell is
called an egg-cell, or ovum. In the great majority of cases, to enable
the ovum to develop into a new individual, it is necessary that the
egg-cell should conjugate or fuse with a minute, active sperm-cell,
generally derived from a different parent. This process of fusion of
germinal cells is called fertilization (see Fig. 5, p. 13).
In sponges, the cells which become ova or sperms lie scattered in the
mid-layer between the ciliated layers which line the cavities and spaces
of the organism. Sometimes the individual sponge produces only ova;
sometimes only sperms; sometimes both, but at different periods. The
cells which become ova increase in size, are passive, and rich in
reserve material elaborated by their protoplasm. The cells which become
sperms divide again and again, and thus produce minute active bodies,
adance with restless motion. These opposite tendencies are repeated and
emphasized throughout the animal kingdom--ova relatively large, passive,
and accumulative of reserve material; sperms minute, active, and the
result of repeated fission. The active sperm, when it unites with the
ovum, imports into it a tendency to fission, or cleavage; but the
resulting cells do not part and scatter--they remain associated
together, and in mutual union give rise to a new sponge.
[Illustration: Fig. 8.--Hydra viridis.
A, hydra half retracted, with a bud and an ovum attached to the shrunken
ovary; B, a small hydra firmly retracted; C, a hydra fully extended. b.,
bud; f., foot; h.s., hypostome; ovm., ovum; ovy., ovary; t., tentacles;
ts., testis.]
In the hydra, generally near the foot or base of attachment, a rounded
swelling often makes its appearance in autumn. Within this swelling one
central cell increases enormously at the expense of the others. It
becomes an ovum. Eventually it bursts through the swelling, but remains
attached for a time. Rarely in the same hydra, more frequently in
another, one or two swellings may be seen higher up, beneath the circle
of tentacles. Within these, instead of the single ovum may be seen a
swarm of sperms, minute and highly active. When these are discharged,
one may fuse with and fertilize an ovum, occasionally in the same, but
more frequently in another individual, with the result that it develops
into a new hydra. Here there are definite organs--an ovary and a
testis--producing the ova or the sperms. But they are indefinite and not
permanent in position.
In higher forms of life the organs which are set apart for the
production of ova or sperms become definite in position and definite in
structure. Occasionally, as in the snail, the same organ produces both
sperms and ova, but then generally in separate parts of its structure.
The two products also ripen at different times. Not infrequently, as in
the earthworm, each individual has both testes and ovaries, and thus
produces both ova and sperms, but from different organs. The ova of one
animal are, however, fertilized by sperms from another. But in the
higher invertebrates and vertebrates there is a sex-differentiation
among the individuals, the adult males being possessed of testes only
and producing sperms, the adult females possessed of ovaries only and
producing ova. There are also, in many cases, accessory structures for
ensuring that the ova shall be fertilized by sperms, while sexual
appetences are developed to further the same end. But however the matter
may thus be complicated, the essential feature is the same--the union of
a sluggish, passive cell, more or less laden with nutritive matter, with
a minute active cell with an hereditary tendency to fission.[F]
It is not, however, necessary in all cases that fertilization of the
ovum should take place. The plant-lice, or _Aphides_ of our rose trees,
may produce generation after generation, and their offspring in turn
reproduce in like manner, without any union or fusion of ovum or sperm.
The same is true of the little water-fleas, or _Daphnids_; while in some
kinds of rotifers fertilization is said never to occur. It is a curious
and interesting fact, which seems now to be established beyond question,
that drone bees are developed from unfertilized ova, the fertilized ova
producing either queens or workers, according to the nature of the food
with which the grubs are supplied. Where, as in the case of aphids and
daphnids, fertilization occasionally takes place, it would seem that
lowered temperature and diminished food-supply are the determining
conditions. Fertilization, therefore, generally takes place in the
autumn; the fertilized ovum living on in a quiescent state during the
winter, and developing with the warmth of the succeeding spring. In the
artificial summer of a greenhouse, reproduction may continue for three
or four years without the occurrence of any fertilization.
[Illustration: Fig. 9.--Aurelia: Life-cycle.
a, embryo; b, _Hydra tuba_; c, _Hydra tuba_, with medusoid segments; d,
medusa separated to lead free existence.]
Mention may here be made of some peculiarly modified modes of
reproduction among the metazoa. The aurelia is a well-known and
tolerably common jelly-fish. These produce ova, which are duly
fertilized by sperms from a different individual. A minute,
free-swimming embryo develops from the ovum, which settles down and
becomes a little polyp-like organism, the _Hydra tuba_. As growth
proceeds, this divides or segments into a number of separable, but at
first connected, parts. As these attain their full development, first
one and then another is detached from the free end, floats off, and
becomes a medusoid aurelia. Thus the fertilized ovum of aurelia
develops, not into one, but into a number of medusæ,[G] passing through
the _Hydra tuba_ condition as an intermediate stage.
Many of the hydroid zoophytes, forming colonies of hydra-like organisms,
give rise in the warm months to medusoid jelly-fish, capable of
producing ova and sperms. Fertilization takes place; and the fertilized
ova develop into little hydras, which produce, by budding, new colonies.
In these new colonies, again, the parts which are to become ovaries or
testes float off, and ripen their products in free-swimming, medusoid
organisms. Such a rhythm between development from ova and development by
budding is spoken of as an alternation of generations.
The fresh-water sponge (_Spongilla_) exhibits an analogous rhythm. The
ova are fertilized by sperms from a different short-lived individual.
They develop into sponges which have no power of producing ova or
sperms. But on the approach of winter in Europe, and of the dry season
in India, a number of cells collect and group themselves into a
so-called gemmule. Round this is formed a sort of crust beset with
spicules, which, in some cases, have the form of two toothed discs
united by an axial shaft. When these gemmules have thus been formed, the
sponge dies; but the gemmules live on in a quiescent state during the
winter or the dry season, and with the advent of spring develop into
sponges, male or female. These have the power of producing sperms or
ova, but no power of producing gemmules. The power of producing ova, and
that of producing gemmules, thus alternates in rhythmic fashion.
[Illustration: Fig. 10.--Liver-fluke: Embryonic stages. (After A. P.
Thomas.)
A. ovum: em., embryo; op., operculum. B. _Limnæus truncatulus_ (natural
size). C. Free embryo: e.s., eye-spot; ex., excretory vessel; g.c.,
germinal cells; h.p., head-papilla. D. Embryo preparing to become a
sporocyst: g.c., germinal cells. E. Sporocyst: g., gastrula; m., morula;
re., redia. F. Redia: b.o., birth-opening; ce., cercaria; col., collar;
di., digestive sac; ph., pharynx; p.pr., posterior processes; re.,
daughter redia. G. Cercaria: cys., cystogenous organ; di., digestive
sac; o.s., oral sucker; p.s., posterior sucker; ph., pharynx.]
But one more example of these modified forms of reproduction can here be
cited (from the author's text-book on "Animal Biology"). The liver-fluke
is a parasitic organism, found in the liver of sheep. Here it reaches
sexual maturity, each individual producing many thousands of eggs, which
pass with the bile into the alimentary canal of the _host_, and are
distributed over the fields with the excreta. Here, in damp places,
pools, and ditches, free and active embryos are hatched out of the eggs.
Each embryo (Fig. 10, C., much enlarged) is covered with cilia, except
at the anterior end, which is provided with a head-papilla (h.p.). When
the embryo comes in contact with any object, it, as a rule, pauses for a
moment, and then darts off again. But if that object be the minute
water-snail, _Limnæus truncatulus_ (Fig. 10, B., natural size), instead
of darting off, the embryo bores its way into the tissues until it
reaches the pulmonary chamber, or more rarely the body-cavity. Here its
activity ceases. It passes into a quiescent state, and is now known as a
_sporocyst_ (Fig. 10, E.). The active embryo has degenerated into a mere
brood-sac, in which the next generation is to be produced. For within
the sporocyst special cells undergo division, and become converted into
embryos of a new type, which are known as _rediæ_ (F.), and which, so
soon as they are sufficiently developed, break through the wall of the
sporocyst. They then increase rapidly in size, and browse on the
digestive gland of the water-snail (known as the _intermediate host_),
to which congenial spot they have in the mean time migrated. The series
of developmental changes is even yet not complete. For within the rediæ
(besides, at times, daughter rediæ) embryos of yet another type are
produced by a process of cell-division. These are known as _cercariæ_
(Fig. 10, G.). Each has a long tail, by means of which it can swim
freely in water. It leaves the intermediate host, and, after leading a
short, active life, becomes encysted on blades of grass. The cyst is
formed by a special larval organ, and is glistening snowy white. Within
the cyst lies the transparent embryonic liver-fluke, which has lost its
tail in the process of encystment.
The last chapter in this life-history is that in which the sheep crops
the blade of grass on which the parasite lies encysted; whereupon the
cyst is dissolved in the stomach of the host, the little liver-fluke
becomes active, passes through the bile-duct into the liver of the
sheep, and there, growing rapidly, reaches sexual maturity, and lays its
thousands of eggs, from each of which a fresh cycle may take its origin.
The sequence of phenomena is characterized by discontinuity of
development. Instead of the embryo growing up continuously into the
adult, with only the atrophy of provisional organs (e.g. the gills and
tail of the tadpole, or embryo frog), it produces germs from which the
adult is developed. Not merely provisional organs, but provisional
organisms, undergo atrophy. In the case of the liver-fluke there are two
such provisional organisms, the embryo sporocyst and the redia.
We may summarize the life-cycle thus--
1. _Ovum_ laid in liver of sheep, passes with bile into intestine,
and thence out with the excreta.
2. _Free ciliated embryo_, in water or on damp earth, passes into
pulmonary cavity of _Limnæus truncatulus_, and develops into
3. _Sporocyst_, in which secondary embryos are developed, known as
4. _Rediæ_, which pass into the digestive glands of _Limnæus_, and
within which, besides daughter rediæ, there are developed tertiary
embryos, or
5. _Cercariæ_, which pass out of the intermediate host and become
6. _Encysted_ on blades of grass, which are eaten by sheep. The cyst
dissolves, and the young flukes pass into the liver of their host,
each developing into
7. A _liver-fluke_, sexual, but hermaphrodite.
Here, again, we notice that one fertilized ovum gives rise to not one,
but a number of liver-flukes.
We must now pass on to consider the growth and development of organisms.
Simple growth results from the multiplication of similar cells. As the
child, for example, grows, the framework of the body and the several
organs increase in size by continuous cell-multiplication. Development
is differential growth; and this may be seen either in the organs or
parts of an organism or in the cells themselves. As the child grows up
into a man, there is a progressive change in his relative proportions.
The head becomes relatively smaller, the hind limbs relatively longer,
and there are changes in the proportional size of other organs.
In the development of the embryo from the ovum, the differentiation is
of a deeper and more fundamental character. Cells at first similar
become progressively dissimilar, and out of a primitively homogeneous
mass of cells is developed a heterogeneous system of different but
mutually related tissues.
This view of development is, however, the outcome of comparatively
modern investigation and perfected microscopical appliances. The older
view was that development in all cases is nothing more than differential
growth, that there is no differentiation of primitively similar into
ultimately different parts. Within the fertilized ovum of the horse or
bird lay, it was supposed, in all perfection of structure, a miniature
racer or chick, the parts all there, but too minute to be visible. All
that was required was that each part should grow in due proportion.
Those who held this view, however, divided into two schools. The one
believed that the miniature organism was contained within the ovum, the
function of the sperm being merely to stimulate its subsequent
developmental growth. The other held that the sperm was the miniature
organism, the ovum merely affording the food-material necessary for its
developmental growth. In either case, this unfolding of the invisible
organic bud was the _evolution_ of the older writers on organic life.
More than this. As Messrs. Geddes and Thomson remind us,[H] "the germ
was more than a marvellous bud-like miniature of the adult. It
necessarily included, in its turn, the next generation, and this the
next--in short, all future generations. Germ within germ, in ever
smaller miniature, after the fashion of an infinite juggler's box, was
the corollary logically appended to this theory of preformation and
unfolding."
Modern embryology has completely negatived any such view as that of
preformation, and as completely established that the evolution is not
the unfolding of a miniature germ, but the growth and differentiation of
primitively similar cell-elements. In different animals, as might be
expected, the manner and course of development are different. We may
here illustrate it by a very generalized and so to speak diagrammatic
description of the development of a primitive vertebrate.
[Illustration: Fig. 11.--Diagram of development. See text. The fine line
across G. indicates the plane of section shown in H.]
The ovum before fertilization is a simple spherical cell, without any
large amount of nutritive material in the form of food-yolk (A.). It
contains a nucleus. Previous to fertilization, however, in many forms of
life, portions of the nucleus, amounting to three parts of its mass, are
got rid of in little "polar cells" budded off from the ovum. The import
of this process we shall have to consider in connection with the subject
of heredity. The sperm is also a nucleated cell; and on its entrance
into the ovum there are for a short time two nuclei--the female nucleus
proper to the ovum, and the male nucleus introduced by the sperm. These
two unite and fuse to form a joint nucleus. Thus the fertilized ovum
starts with a perfect blending of the nuclear elements from two cells
produced by different parents.
Then sets in what is known as the segmentation or cleavage of the ovum.
First the nucleus and then the cell itself divides into two equal halves
(B.), each of these shortly afterwards again dividing into two. We may
call the points of intersection of these two planes of division the
"poles," and the planes "vertical planes." We thus have four cells
produced by two vertical planes (C.). The next plane of division is
equatorial, midway between the poles. By this plane the four cells are
subdivided into eight (D.). Then follow two more vertical planes
intermediate between the first two. By them the eight cells are divided
into sixteen. These are succeeded by two more horizontal planes midway
between the equator and the poles. Thus we get thirty-two cells. So the
process continues until, by fresh vertical and horizontal planes of
division, the ovum is divided into a great number of cells.
But meanwhile a cavity has formed in the midst of the ovum. This makes
its appearance at about the eight-cell stage, the eight cells not quite
meeting in the centre of the ovum. The central cavity so formed is thus
surrounded by a single layer of cells, and it remains as a single layer
throughout the process of segmentation, so that there results a hollow
vesicle composed of a membrane constituted by a single layer of cells
(E.).
The cells on one side of the vesicle are rather larger than the others,
and the next step in the process is the apparent pushing in of this part
of the hollow sphere; just as one might take a hollow squash indiarubber
ball, and push in one side so as to form a hollow, two-layered cup (F.).
The vesicle, then, is converted into a cup, the mouth of which gradually
closes in and becomes smaller, while the cup itself elongates (G.).[I]
Thus a hollow, two-layered, stumpy, worm-like embryo is produced, the
outer layer of which may be ciliated, so that by the lashing of these
cilia it is enabled to swim freely in the water. The inner cavity is the
primitive digestive cavity.
A cross-section through the middle of the embryo at this stage will show
this central cavity surrounded by a two-layered body-wall (H.). A little
later the following changes take place (J. K.): Along a definite line
on the surface of the embryo, marking the region of the back, the outer
layer becomes thickened; the edges of the thickened band so produced
rise up on either side, so as to give rise to a median groove between
them; and then, overarching and closing over the groove, convert it into
a tube. This tube is called the neural tube, because it gives rise to
the central nervous system. In the region of the head it expands; and
from its walls, by the growth and differentiation of the cells, there is
formed--in the region of the head, the brain, and along the back, the
spinal cord. Immediately beneath it there is formed a rod of cells,
derived from the inner layer. This rod, which is called the notochord,
is the primitive axial support of the body. Around it eventually is
formed the vertebral column, the arches of the vertebræ embracing and
protecting the spinal cord.
Meanwhile there has appeared between the two primitive body-layers a
third or middle layer.[J] The cells of which it is composed arise from
the inner layer, or from the lips of the primitive cup when the outer
and inner layer pass the one into the other. This middle layer at first
forms a more or less continuous sheet of cells between the inner and the
outer layers. But ere long it splits into two sheets, of which one
remains adherent to the inner layer and one to the outer layer. The
former becomes the muscular part of the intestinal or digestive tube,
the latter the lining of the body-wall. The space between the two is
known as the body-cavity. Beneath the throat the heart is fashioned out
of this middle layer.
Very frequently--that is to say, in many animals--the opening by which
the primitive digestive tube communicated with the exterior has during
these changes closed up, so that the digestive cavity does not any
longer communicate in any way with the exterior. This is remedied by the
formation of a special depression or pit at the front end for the mouth,
and a similar pit at the hinder end.[K] These pits then open into the
canal, and communications with the exterior are thus established. The
lungs and liver are formed as special outgrowths from the digestive
tube. The ovaries or testes make their appearance _at a very early
period_ as ridges of the middle layer projecting into the body-cavity.
For some time it is impossible to say whether they will produce sperms
or ova; and it is said that in many cases they pass through a stage in
which one portion has the special sperm-producing, and another the
special ovum-producing, structure. But eventually one or other prevails,
and the organs become either ovaries or testes.
Thus from the outer layer of the primitive embryo is produced the outer
skin, together with the hairs, scales, or feathers which it carries;
from it also is produced the nervous system, and the end-organs of the
special senses. From the inner layer is formed the digestive lining of
the alimentary tube and the glands connected therewith; from it also the
primitive axial support of the body. But this primitive support gives
place to the vertebral column formed round the notochord; and this is of
mid-layer origin. Out of the middle layer are fashioned the muscles and
framework of the body; out of it, too, the heart and reproductive
organs. The tissues of many of the organs are cunningly woven out of
cells from all three layers. The lens of the eye, for example, is a
little piece of the outer layer pinched off and rendered transparent.
The retina of that organ is an outgrowth from the brain, which, as we
have seen, was itself developed from the outer layer. But round the
retina and the lens there is woven from the middle layer the tough
capsule of the eye and the circular curtain or iris. The lining cells of
the digestive tube are cells of the inner layer, but the muscular and
elastic coats are of middle-layer origin. The lining cells of the
salivary glands arise from the outer layer where it is pushed in to form
the mouth-pit; but the supporting framework of the glands is derived
from the cells of the middle layer.
Enough has now been said to give some idea of the manner in which the
different tissues and organs of the organism are elaborated by the
gradual differentiation of the initially homogeneous ovum. The cells
into which the fertilized egg segments are at first all alike; then
comes the divergence between those which are pushed in to line the
hollow of the cup, and those which form its outer layer. Thereafter
follows the differentiation of a special band of outer cells to form the
nervous system, and a special rod, derived from the inner cells, to form
the primitive axial support. And when the middle layer has come into
existence, its cells group themselves and differentiate along special
lines to form gristle or bone, blood or muscle.
The description above given is a very generalized and diagrammatic
description. There are various ways in which complexity is introduced
into the developmental process. The store of nutritive material present
in the egg, for example, profoundly modifies the segmentation so that
where, as in the case of birds' eggs, there is a large amount of
food-yolk, not all the ovum, but only a little patch on its surface,
undergoes segmentation. In this little patch the embryo is formed. Break
open an egg upon which a hen has been sitting for five or six days, and
you will see the little embryo chick lying on the surface of the yolk.
The large mass of yolk to which it is attached is simply a store of
food-material from which the growing chick may draw its supplies.
For it is clear that the growing and developing embryo must obtain, in
some way and from some source, the food-stuff for its nutrition. And
this is effected, among different animals, in one of three ways. Either
the embryo becomes at a very early stage a little, active, voracious,
free-swimming larva, obtaining for itself in these early days of life
its own living; as is the case, for example, with the oyster or the
star-fish. Or the egg from which it is developed contains a large store
of food-yolk, on which it can draw without stint; as is the case with
birds. Or else the embryo becomes attached to the maternal organism in
such a way that it can draw on her for all the nutriment which it may
require; as is the case with the higher mammals.
In both these latter cases the food-material is drawn from the maternal
organism, and is the result of parental sacrifice; but in different
ways. In the case of the bird, the protoplasm of the ovum has acquired
the power of storing up the by-products of its vital activity. The ovum
of such an animal seems at first sight a standing contradiction to the
statement, made some pages back, that the cell cannot grow to any great
extent without undergoing division or fission; and this because volume
tends to outrun surface. For the yolk of a bird's egg is a single cell,
and is often of large size. But when we come to examine carefully these
exceptional cases of very large cells--for what we call the yolk of an
egg is, I repeat, composed of a single cell--we find that the formative
protoplasm is arranged as a thin patch on one side of the yolk in the
case of the bird's egg, or as a thin pellicle surrounding the yolk in
the case of that of the lobster or the insect. All the rest is a product
of protoplasmic life stowed away beneath the patch or within the
pellicle. And this stored material is relatively stable and inert, not
undergoing those vital disruptive changes which are characteristic of
living formative protoplasm. The mass of formative protoplasm, even in
the large eggs of birds, is not very great, and is so arranged as to
offer a relatively extensive surface. All the rest, the main mass of the
visible egg-yolk, is the stored product of a specialized activity of the
formative protoplasm. But all this material is of parental origin--is
elaborated from the nutriment absorbed and digested by the mother.
Thus we see, in the higher types of life, parental sacrifice, fosterage,
and protection. For in the case of mammals and many birds, especially
those which are born in a callow, half-fledged condition, even when the
connection of mother and offspring is severed, or the supplies of
food-yolk are exhausted, and the young are born or hatched, there is
still a more or less prolonged period during which the weakly offspring
are nourished by milk, by a secretion from the crop ("pigeon's milk"),
or by food-stuff brought with assiduous care by the parents. There is a
longer or shorter period of fosterage and protection--longer in the case
of man than in that of any of the lower animals--ere the offspring are
fitted to fend for themselves in life's struggle.
And accompanying this parental sacrifice, first in supplying food for
embryonic development, and then in affording fosterage and protection
during the early stages of growth, there is, as might well be supposed,
a reduction in the number of ova produced and of young brought forth or
hatched. Many of the lower organisms lay hundreds of thousands of eggs,
each of which produces a living active embryo. The condor has but two
downy fledglings in a year; the gannet lays annually but a single egg;
while the elephant, in the hundred years of its life, brings forth but
half a dozen young.
We shall have to consider by what means these opposite tendencies (a
tendency to produce enormous numbers of tender, ill-equipped embryos,
and a tendency to produce few well-equipped offspring) have been
emphasized. The point now to be noted is that every organism, even the
slowest breeder that exists, produces more young than are sufficient to
keep up the numbers of the species. If every pair of organisms gave
birth to a similar pair, and if this pair survived to do likewise, the
number of individuals in the species would have no tendency either to
increase or to diminish. But, as a matter of fact, animals actually do
produce from three or four times to hundreds or even thousands of times
as many new individuals as are necessary in this way to keep the numbers
constant. This is the _law of increase_. It may be thus stated: _The
number of individuals in every race or species of animals is tending to
increase._ Practically this is only a tendency. By war, by struggle, by
competition, by the preying of animals upon each other, by the stress of
external circumstances, the numbers are thinned down, so that, though
the births are many, the deaths are many also, and the survivals few. In
the case of those species the numbers of which are remaining constant,
out of the total number born only two survive to procreate their kind.
We may judge, then, of the amount of extermination that goes on among
those animals which produce embryos by the thousand or even the hundred
thousand. The effects of this enormous death-rate on the progress of the
race or species we shall have to consider in the next chapter, when the
question of the differentiation of species is before us.
There is one form of differentiation, however, which we may glance at
before closing this chapter--the differentiation of sex. We are not in a
position to discuss the ultimate causes of sex-differentiation, but we
may here note the proximate causes as they seem to be indicated in
certain cases.
Among honey-bees there are males (drones), fertile females (queens), and
imperfect or infertile females (workers). It has now been shown, beyond
question, that the eggs from which drones develop are not fertilized.
The presence or absence of fertilization in this case determines the
sex. During the nuptial flight, a special reservoir, possessed by the
queen bee, is stored with sperms in sufficient number to last her
egg-laying life. It is in her power either to fertilize the eggs as they
are laid or to withhold fertilization. If the nuptial flight is
prevented, and the reservoir is never stored with sperms, she is
incapable of laying anything but drone eggs. The cells in which drones
are developed are somewhat smaller than those for ordinary workers; but
what may be the nature of the stimulus that prompts the queen to
withhold fertilization we at present do not know. The difference between
the fertile queen and the unfertile worker seems to be entirely a matter
of nutrition. If all the queen-embryos should die, the workers will tear
down the partitions so as to throw three ordinary worker-cells into one;
they will destroy two of the embryos, and will feed the third on highly
nutritious and stimulating diet; with the result that the ovaries and
accessory parts are fully developed, and the grub that would have become
an infertile worker becomes a fertile queen. And one of the most
interesting points about this change, thus wrought by a stimulating
diet, is that not only are the reproductive powers thus stimulated, but
the whole organism is modified. Size, general structure, sense-organs,
habits, instincts, and character are all changed with the development of
the power of laying eggs. The organism is a connected whole, and you
cannot modify one part without deeply influencing all parts. This is the
_law of correlated variation_.
Herr Yung has made some interesting experiments on tadpoles. Under
normal circumstances, the relation of females to males is about 57 to
43. But when the tadpoles were well fed on beef, the proportion of
females to males rose so as to become 78 to 32; and on the highly
nutritious flesh of frogs the proportion became 92 to 8. A highly
nutritious diet and plenty of it caused a very large preponderance of
females.
Mrs. Treat, in America, found that if caterpillars were half-starved
before entering upon the chrysalis state, the proportion of males was
much increased; while, if they were supplied with abundant nutritious
food, the proportion of female insects was thereby largely increased.
The same law is said to hold good for mammals. Favourable vital
conditions are associated with the birth of females; unfavourable, with
that of males. Herr Ploss attempts to show that, among human folk, in
hard times there are more boys born; in good times, more girls.
On the whole, we may say that there is some evidence to show that in
certain cases favourable conditions of temperature, and especially
nutrition, tend to increase the number of females. We have seen that
many animals pass through a stage where the reproductive organs are not
yet differentiated into male and female, while in some there is a
temporary stage where the outer parts of the organ produce ova and the
inner parts sperms. We have also seen that the ova are cells where
storage is in excess; the sperms are cells in which fission is in
excess. Favourable nutritive conditions may, therefore, not
incomprehensibly lead to the formation of well-stored ova; unfavourable
nutritive conditions, on the other hand, to the formation of highly
subdivided sperms. By correlated variation,[L] the ova-bearing or
sperm-bearing individuals then develop into the often widely different
males and females.
NOTES
[F] Professor Geddes and Mr. J. Arthur Thomson, in their interesting
work on "The Evolution of Sex," regard the ovum in especial, and
the female in general, as preponderatingly anabolic (see note, p.
32); while the sperm in especial, and the male in general, are on
their view preponderatingly katabolic. Regarding, as I do, the
food-yolk as a katabolic product, I cannot altogether follow them.
The differentiation seems to me to have taken place along
divergent lines of katabolism. In the ovum, katabolism has given
rise to storage products; in the sperm, to motor activities
associated with a tendency to fission. The contrast is not between
anabolic and katabolic tendencies, but between storage katabolism
and motor katabolism. Nor do I think that "the essentially
katabolic male-cell brings to the ovum a supply of characteristic
waste products, or katastates, which stimulate the latter to
division" (_l.c._, p. 162). I believe that it brings an inherited
tendency to fission, and thus reintroduces into the fertilized
ovum the tendency which, as ovum, it had renounced in favour of
storage katabolism.
[G] On the other hand, three ova of the crustacean _Apus_ are said to
coalesce to form the single ovum from which one embryo develops.
[H] "The Evolution of Sex," p. 84.
[I] In some forms of life the opening of the cup marks the position of
the future mouth: in others, of the future vent. In yet others it
elongates into a slit, occupying the whole length of the embryo;
the middle part of the slit closes up, and the opening at the far
ends mark the position, the one of the future mouth, the other of
the future vent.
[J] In technical language, the outer layer of cells is called the
_epiblast_, the inner layer the _hypoblast_, and the mid-layer
between them the _mesoblast_.
[K] In technical language, the opening by which the primitive digestive
cavity (or _mesenteron_) communicates with the exterior is called
the _blastopore_. When this closes, the new opening for the mouth
is called the _stomod[oe]um_; that for the vent, the
_proctod[oe]um_.
[L] We have seen that when volume tends to outrun surface, fission may
take place, whereby the same volume has increased surface. But in
unfavourable nutritive conditions, the same surface which had
before been sufficient for nutrition may become, under the less
favourable circumstances, insufficient, and fission may again take
place to give a larger absorbent surface. Hence, possibly, the
connection between insufficient nutriment and highly subdivided
sperms.
CHAPTER IV.
VARIATION AND NATURAL SELECTION.
Everything, so far as in it lies, said Benedict Spinoza, tends to
persist in its own being. This is _the law of persistence_. It forms the
basis of Newton's First Law of Motion, which enunciates that, if a body
be at rest, it will remain so unless acted on by some external force;
or, if it be in motion, it will continue to move in the same straight
line and at a uniform velocity unless it is acted on by some external
force. Practically every known body is thus affected by external forces;
but the law of persistence is not thereby disproved. It only states what
would happen under certain exceptional or perhaps impossible
circumstances. To those ignorant of scientific procedure, it seems
unsatisfactory, if not ridiculous, to formulate laws of things, not as
they are, but as they might be. Many well-meaning but not very
well-informed people thus wholly misunderstand and mistake the value of
certain laws of political economy, because in those laws (which are
generalized statements of fact under narrowed and rigid conditions, and
do not pretend to be inculcated as rules of conduct) benevolence,
sentiment, even moral and religious duty, are intentionally excluded.
These laws state that men, under motives arising out of the pursuit of
wealth, will act in such and such a way, unless benevolence, sentiment,
duty, or some other motive, lead them to act otherwise. Such laws, which
hold good, not for phenomena in their entirety, but for certain isolated
groups of facts under narrowed conditions, are called _laws of the
factors_ of phenomena. And since the complexity of phenomena is such
that it is difficult for the human mind to grasp all the interlacing
threads of causation at a single glance, men of science have endeavoured
to isolate their several strands, and, applying the principle of
analysis, without which reasoning is impossible, to separate out the
factors and determine their laws. In this chapter we have to consider
some of the factors of organic progress, and endeavour to determine
their laws.
The law of heredity may be regarded as that of persistence exemplified
in a series of organic generations. When, as in the am[oe]ba and some
other protozoa, reproduction is by simple fission, two quite similar
organisms being thus produced, there would seem to be no reason why
(modifications by surrounding circumstances being disregarded)
hereditary persistence should not continue indefinitely. Where, however,
reproduction is effected by the detachment of a single cell from a
many-celled organism, hereditary persistence[M] will be complete only on
the condition that this reproductive cell is in some way in direct
continuity with the cells of the parent organism or the cell from which
that parent organism itself developed. And where, in the higher animals,
two cells from two somewhat different parents coalesce to give origin to
a new individual, the phenomena of hereditary persistence are still
further complicated by the blending of characters handed on in the ovum
and the sperm; still further complication being, perhaps, produced by
the emergence in the offspring of characters latent in the parent, but
derived from an earlier ancestor. And if characters acquired by the
parents in the course of their individual life be handed on to the
offspring, yet further complication will be thus introduced.
It is no matter for surprise, therefore, that, notwithstanding the law
of hereditary persistence, variations should occur in the offspring of
animals. At the same time, it must be remembered that the occurrence of
variations is not and cannot be the result of mere chance; but that all
such variations are determined by some internal or external influences,
and are thus legitimate and important subjects of biological
investigation. In the next chapter we shall consider at some length the
phenomena of heredity and the origin of variations. Here we will accept
them without further discussion, and consider some of their
consequences. But even here, without discussing their origin, we must
establish the fact that variations do actually occur.
Variations may be of many kinds and in different directions. In colour,
in size, in the relative development of different parts, in complexity,
in habits, and in mental endowments, organisms or their organs may vary.
Observers of mammals, of birds, and of insects are well aware that
colour is a variable characteristic. But these colour-variations are not
readily described and tabulated. In the matter of size the case is
different. In Mr. Wallace's recent work on "Darwinism" a number of
observations on size-variations are collected and tabulated. As this is
a point of great importance, I propose to illustrate it somewhat fully
from some observations I have recently made of the wing-bones of bats.
In carrying out these observations and making the necessary
measurements, I have had the advantage of the kind co-operation of my
friend Mr. Henry Charbonnier, of Clifton, an able and enthusiastic
naturalist.[N]
The nature of the bat's wing will be understood by the aid of the
accompanying figure (Fig. 12). In the fore limb the arm-bone, or
humerus, is followed by an elongated bone composed of the radius and
ulna. At the outer end of the radius is a small, freely projecting
digit, which carries a claw. This answers to the thumb. Then follow four
long, slender bones, which answer to the bones in the palm of our hand.
They are the metacarpals, and are numbered II., III., IV., and V. in the
tabulated figures in which the observations are recorded. The
metacarpals of the second and third digits run tolerably close together,
and form the firm support of the anterior margin of the wing. Those of
the third and fourth make a considerable angle with these and with each
other, and form the stays of the mid part of the wing. Beyond the
metacarpals are the smaller joints or phalanges of the digits, two or
three to each digit. The third digit forms the anterior point or apex of
the wing. The fourth and fifth digits form secondary points behind this.
Between these points the wing is scalloped into bays.
[Illustration: Fig. 12.--"Wing" of bat (Pipistrelle).
Hu., humerus, or arm-bone; Ul., conjoined radius and ulna, a bone in the
forearm; Po., pollex, answering to our thumb; II., III., IV., V.,
second, third, fourth, and fifth digits of the manus, or hand. The
figures are placed near the metacarpals, or palm-bones. These are
followed by the phalanges. Fe., femur or thigh-bone; Ti., tibia, the
chief bone of the shank. The digits of the pes, or foot, are short and
bear claws. Ca., calcar.]
From the point of the fifth or last digit the leathery wing membrane
sweeps back to the ankle. The bones of the hind limb are the femur, or
thigh-bone, and the tibia (with a slender, imperfectly developed
fibula). There are five toes, which bear long claws. From the ankle
there runs backward a long, bony and gristly spur, which serves to
support the membrane which stretches from the ankle to the tip (or near
the tip) of the tail.
Thus the wing of the bat consists of a membrane stretched on the
expanded or spread fingers of the hand, and sweeping from the point of
the little finger to the ankle. Behind the ankle there is a membrane
reaching to the tip of the tail. This forms a sort of net in which some
bats, at any rate, as I have myself observed, can catch insects.
I have selected the wing of the bat to exemplify variation, (1) because
the bones are readily measured even in dried specimens; (2) because they
form the mutually related parts of a single organ; and (3) because they
offer facilities for the comparison of variations, not only among the
individuals of a single species, but also among several distinct
species.
The method employed has been as follows: The several bones have been
carefully measured in millimetres,[O] and all the bones tabulated for
each species. Such tables of figures are here given in a condensed form
for three species of bats.
Bat-Measurements (in Millimetres).
--------------------------------------------------------------------------
|R | P | 2nd | Third | Fourth | Fifth |T |
|a | o |Digit.| Digit. | Digit. | Digit. |i |
|d U | l |------|--------------|--------------|------------|b |
|i l | l | M | M | P | P | M | P | P | M | P | P |i |
|u n | e | e | e | h | h | e | h | h | e | h | h |a |
|s a | x | t | t | a | a | t | a | a | t | a | a |. |
| . | . | a | a | l | l | a | l | l | a | l | l | |
|a | | c | c | a | a | c | a | a | c | a | a | |
|n | | a | a | n | n | a | n | n | a | n | n | |
|d | | r | r | g | g | r | g | g | r | g | g | |
| | | p | p | e | e | p | e | e | p | e | e | |
| | | a | a | | s | a | | s | a | | s | |
| | | l | l | 1 | | l | 1 | | l | 1 | | |
| | | . | . | . | 2,| . | . | 2,| . | . | 2,| |
| | | | | | 3 | | | 3 | | | 3 | |
| | | | | | . | | | . | | | . | |
-------------------------------------------------------------------------
Hairy-armed bat (_Vesperugo leisleri_).
|41 |6.5| 38 |40 |16 |19 | 38 |14 | 7 | 32 | 8 | 7 |16|[Male]
|41 |6 | 38 |40 |16 |19 | 39 |15.5| 7 | 33 | 8 |6.5|16| "
|41 |6 | 39 |40 |16 |18 | 39 |16 | 6.5| 33 | 8 | 7 |16| "
|41.5|5 | 39 |40.5|17 |20 | 39 |16 | 7 | 33 | 8 | 7 |15| "
|40 |6 | 39 |37 |15.5|18 | 37 |14.5| 7 | 32 | 8 |6.5|15|[Fem.]
|41 |5.5| 38.5 |39 |16.5|20 | 39 |15 | 7.5| 33 | 8 |7.5|17| "
|41 |6 | 39 |40 |15.5|20.5| 39 |15.5| 7 | 33 | 8 | 7 |16| "
Horseshoe bat (_Rhinolophus ferri-equinum_).
|51 | 5 | 39 |36 | 19 | 29 | 40 | 11 | 18 | 40 |13 |15 |22|[Male]
|54 | 5 | 40 |36 | 18 | 32 | 40 | 11 | 19 | 40 |14 |16 |28|[Fem.]
|52 | 5 | 39 |36 | 18 | 31 | 39 | 10 | 19 | 40 |13 |14 |23| "
|54 | 5 | 39 |36 | 18 | 32 | 40 | 11 | 17 | 40 |13 |13 |25| "
|46 | 5 | 36 |34 | 16 | 29 | 36 | 10 | 19 | 36 |13 |17 |22| ?
Lesser horseshoe bat (_Rhinolophus hipposideros_).
|34 | 4 | 25 |23 | 12 | 17 | 26 | 6.5| 12 | 26 | 9 |13 |17|[Male]
|37 | 3 | 26 |24 | 13 | 20 | 28 | 8 | 13 | 28 | 9 |14 |17| "
|35 | 3 | 26 |24.5| 13 | 17 | 27 | 7 | 12 | 26 |10 |12 |15| "
-------------------------------------------------------------------------
It would be troublesome to the reader to pick out the meaning from these
figures. I have, therefore, plotted in the measurements for four other
species of bats in tabular form (Figs. 13, 14, 15, 16).
Fig. 13, for example, deals with the common large noctule bat, which may
often be seen flying high up on summer evenings. Now, the mean length of
the radius and ulna in eleven individuals was 51.5 millimetres. Suppose
all the eleven bats had this bone (for the two bones form practically
one piece) of exactly the same length. There would then be no variation.
We may express this supposed uniformity by the straight horizontal line
running across the part of the figure dealing with the radius and ulna.
Practically the eleven bats measured did not have this bone of the same
length; in some of them it was longer, in others it was shorter than the
mean. Let us run through the eleven bats (which are represented by the
numbers at the head of the table) with regard to this bone. The first
fell below the average by a millimetre and a half, the length being
fifty millimetres. This is expressed in the table by placing a dot or
point three quarters of a division below the mean line. Each division on
the table represents two millimetres, or, in other words, the distance
between any two horizontal lines stands for two millimetres measured.
Half a division, therefore, is equivalent to one measured millimetre; a
quarter of a division to half a millimetre. The measurements are all
made to the nearest half-millimetre. The second bat fell short of the
mean by one millimetre. The bone measured 50.5 millimetres. The third
exceeded the mean by a millimetre and a half; the fourth, by three
millimetres and a half. The fifth was a millimetre and a half above the
mean; and the sixth and seventh were both half a millimetre over the
mean. The eighth fell short by half a millimetre; the ninth and tenth by
a millimetre and a half; and the eleventh by two millimetres and a half.
The points have been connected together by lines, so as to give a curve
of variation for this bone.
[Illustration: Fig 13.--The noctule (_Vesperugo noctula_).]
[Illustration: Fig. 14.--The long-eared bat (_Plecotus auritus_).]
[Illustration: Fig. 15.--The pipistrelle (_Vesperugo pipistrellus_).]
[Illustration: Fig. 16.--The whiskered bat (_Vespertilio mystacinus_).]
The other curves in these four tables are drawn in exactly the same way.
The mean length is stated; and the amount by which a bone in any bat
exceeds or falls short of the mean can be seen and readily estimated by
means of the horizontal lines of the table. Any one can reconvert the
tables into figures representing our actual measurements.
Now, it may be said that, since some bats run larger than others, such
variation is only to be expected. That is true. But if the bones of the
wing all varied equally, _all the curves would be similar_. That is
clearly not the case. The second metacarpal is the same length in 5 and
6. But the third metacarpal is two millimetres shorter in 6 than in 5.
In 10 the radius and ulna are _longer_ than in 11; but the second
metacarpal is _shorter_ in 10 than in 11. A simple inspection of the
table as a whole will show that there is a good deal of _independent_
variation among the bones.
The amount of variation is itself variable, and in some cases is not
inconsiderable. In the long-eared bats 4 and 5 in Fig. 14, the phalanges
of the third digit measured 26.5 millimetres in 4, and 34 millimetres in
5--a difference of more than 28 per cent. This is unusually large, and
it is possible that there may have been some slight error in the
measurements.[P] A difference of 10 or 12 per cent. is, however, not
uncommon.
In any case, the observations here tabulated show (1) that variations of
not inconsiderable amount occur among the related bones of the bat's
wing; and (2) that these variations are to a considerable extent
independent of each other.
So far we have compared a series of individuals of the same species of
bat, each table in Figs. 13-16 dealing with a distinct species. Let us
now compare the different species with each other. To effect such a
comparison, we must take some one bone as our standard, and we must
level up our bats for the purposes of tabulation. I have selected the
radius and ulna as the standard. In both the noctule and the greater
horseshoe bats the mean length of this bone is 51.5 millimetres. The
bones of each of the other bats have been multiplied by such a number as
will bring them up to the level of size in these two species. Mr.
Galton, in his investigations on the variations of human stature, had to
take into consideration the fact that men are normally taller than
women. He found, however, that the relation of man to woman, so far as
height is concerned, is represented by the proportion 108 to 100. By
multiplying female measurements by 1.08, they were brought up to the
male standard, and could be used for purposes of comparison. In the same
way, by multiplying in each case by the appropriate number, I have
brought all the species in the table (Fig. 17) up to the standard of the
noctule. When so multiplied, the radius and ulna (selected as the
standard of comparison) has the same length in all the species, and is
hence represented by the horizontal line in the table.
[Illustration: Fig. 17.--Variations adjusted to the standard of the
noctule.]
Compared with this as a standard, the mean length of the second
metacarpal in the seven species is forty-three millimetres; that of the
third metacarpal, forty-four millimetres; and so on. The amount by which
each species exceeds or falls short of the mean is shown on the table,
and the points are joined up as before. Here, again, the table gives the
actual measurements in each case. For example, if the mean length of the
third metacarpal of the greater horseshoe bat be required, it is seen by
the table to fall short of the mean by four horizontal divisions and a
quarter, that is to say, by eight millimetres and a half. The length is
therefore (44 - 8-1/2) 35.5 millimetres.
Now, it will be seen from the table that the variation in the mean
length of the bones in different species is much greater than the
individual variations in the members of the same species. The table also
brings out in an interesting way the variation in the general character
of the wing. The noctule, for example, is especially strong in the
development of the second and third metacarpals, the phalanges of the
third digit being also a little above the average. Reference to the
figure of the bat's wing on p. 64 will show that these excellences give
length to the wing. It fails, however, in the metacarpal and phalanges
of the fifth digit, and in the length of the hind leg as represented by
the tibia. On consulting the figure of the wing, it is seen that these
are the bones which give breadth to the wing. Here the noctule fails.
Its wing is, therefore, long and narrow. It is a swallow among bats.
On the other hand, the horseshoe bats fail conspicuously in the second
and third metacarpals, though they make up somewhat in the corresponding
digits. On the whole, the wing is deficient in length. But the phalanges
of the fourth and fifth digits, and the length of the hind limb
represented by the tibia, give a corresponding increase of breadth. The
wing is, therefore, relatively short and broad. The long-eared bat,
again, has the third metacarpal and its digits somewhat above the mean,
and therefore a somewhat more than average length. But it has the fifth
metacarpal with its digit and also the tibia decidedly above the mean,
and therefore more than average breadth. Without possessing the great
length of the noctule's wing, or the great breadth of that of the
horseshoe, it still has a more than average length and breadth.
The total wing-areas are very variable, the females having generally an
advantage over the males. I do not feel that our measurements are
sufficiently accurate to justify tabulation. Taking, however, the radius
and ulna as the standard for bringing the various species up to the same
level, the greater horseshoe seems to have decidedly the largest
wing-area; the noctule stands next; then come the lesser horseshoe and
the long-eared bat; somewhat lower stands the hairy-armed bat; while the
pipistrelle and the whiskered bat (both small species) stand lowest.[Q]
Sufficient has now been said in illustration of the fact that variations
in the lengths of the bones in the bat's wing do actually occur in the
various individuals of one species; that the variations are independent;
and that the different species and genera have the character of the wing
determined by emphasizing, so to speak, variations in special
directions. I make no apology for having treated the matter at some
length. Those who do not care for details will judiciously exercise
their right of skipping.
As before mentioned, Mr. Wallace has collected and tabulated other
observations on size and length variations. And in addition to such
variations, there are the numerous colour-variations that do not admit
of being so readily tabulated. Mr. Cockerell tells us that among
snail-shells, taking variations of banding alone, he knows of 252
varieties of _Helix nemoralis_ and 128 of _H. hortensis_.[R]
That variations do occur under nature is thus unquestionable. And it is
clear that all variations necessarily fall under one of three
categories. Either they are of advantage to the organism in which they
occur; or they are disadvantageous; or they are neutral, neither
advantageous nor disadvantageous to the animal in its course through
life.
We must next revert to the fact to which attention was drawn in the last
chapter, that every species is tending, through natural generation, to
increase in numbers. Even in the case of the slow-breeding elephant, the
numbers tend to increase threefold in each generation; for a single pair
of elephants give birth to three pairs of young. In many animals the
tendency is to increase ten, twenty, or thirtyfold in every generation;
while among fishes, amphibians, and great numbers of the lower
organisms, the tendency is to multiply by a hundredfold, a thousandfold,
or even in some cases ten thousandfold. But, as before noticed, this is
only a tendency. The law of increase is a law of one factor in life's
phenomena, the reproductive factor. In any area, the conditions of which
are not undergoing change, the numbers of the species which constitute
its fauna remain tolerably constant. They are not actually increasing in
geometrical progression. There is literally no room for such increase.
The large birth-rate of the constituent species is accompanied by a
proportionate death-rate, or else the tendency is kept in check by the
prevention of certain individuals from mating and bearing young.[S]
Now, the high death-rate is, to a large extent among the lower organisms
and in a less degree among higher animals, the result of indiscriminate
destruction. When the ant-bear swallows a tongue-load of ants, when the
Greenland whale engulfs some hundreds of thousands of fry at a gulp,
when the bear or the badger destroys whole nests of bees,--in such cases
there is wholesale and indiscriminate destruction. Those which are thus
destroyed are nowise either better or worse than those which escape. At
the edge of a coral reef minute, active, free-swimming coral embryos are
set free in immense numbers. Presently they settle down for life. Some
settle on a muddy bottom, others in too great a depth of water. These
are destroyed. The few which take up a favourable position survive. But
they are no better than their less fortunate neighbours. The destruction
is indiscriminate. So, too, among fishes and the many marine forms which
produce a great number of fertilized eggs giving rise to embryos that
are from an early period free-swimming and self-supporting. Such embryos
are decimated by a destruction which is quite indiscriminate. And again,
to take but one more example, the liver-fluke, whose life-history was
sketched in the last chapter, produces its tens or hundreds of thousands
of ova. But the chances are enormously against their completing their
life-cycle. If the conditions of temperature and moisture are not
favourable, the embryo is not hatched or soon dies; even if it emerges,
no further development takes place unless it chances to come in contact
with a particular and not very common kind of water-snail. When it
emerges from the intermediate host and settles on a blade of grass, it
must still await the chance of that blade being eaten by a sheep or
goat. It is said that the chances are eight millions to one against it,
and for the most part its preservation is due to no special excellence
of its own. The destruction is to a large extent, though not entirely,
indiscriminate.
Even making all due allowance, however, for this indiscriminate
destruction--which is to a large extent avoided by those higher
creatures which foster their young--there remain more individuals than
suffice to keep up the normal numbers of the species. Among these there
arises a struggle for existence, and hence what Darwin named _natural
selection_.
"How will the struggle for existence"--I quote, with some omissions, the
words of Darwin--"act in regard to variation? Can the principle of
selection, which is so potent in the hands of man, apply under nature? I
think that we shall see that it can act most efficiently. Let the
endless number of slight variations and individual differences be borne
in mind; as well as the strength of the hereditary tendency. Let it also
be borne in mind how infinitely complex and close-fitting are the mutual
relations of all organic beings to each other and to their physical
conditions of life; and consequently what infinitely varied diversities
of structure might be of use to each being under changing conditions of
life. Can it, then, be thought improbable, seeing that variations useful
to man have undoubtedly occurred, that other variations, useful in some
way to each being in the great and complex battle of life, should occur
in the course of many successive generations? If such do occur, can we
doubt (remembering that many more individuals are born than can possibly
survive) that individuals having any advantage, however slight, over
others, would have the best chance of surviving and of procreating their
kind? On the other hand, we may feel sure that any variation in the
least degree injurious would be rigidly destroyed. This preservation of
favourable individual differences and variations, and the destruction of
those which are injurious, I have called Natural Selection, or the
Survival of the Fittest. Variations neither useful nor injurious would
not be affected by natural selection, and would be left either a
fluctuating element, or would ultimately become fixed, owing to the
nature of the organism and the nature of the conditions."[T]
"The principle of selection," says Darwin, elsewhere, "may conveniently
be divided into three kinds. _Methodical selection_ is that which guides
a man who systematically endeavours to modify a breed according to some
predetermined standard. _Unconscious selection_ is that which follows
from men naturally preserving the most valued and destroying the less
valued individuals, without any thought of altering the breed. Lastly,
we have _Natural selection_, which implies that the individuals which
are best fitted for the complex and in the course of ages changing
conditions to which they are exposed, generally survive and procreate
their kind."[U]
I venture to think that there is a more logical division than this. A
man who is dealing with animals or plants under domestication may
proceed by one of two well-contrasted methods. He may either select the
most satisfactory individuals or he may reject the most unsatisfactory.
We may term the former process _selection_, the latter _elimination_.
Suppose that a gardener is dealing with a bed of geraniums. He may
either pick out first the best, then the second best, then the third,
and so on, until he has selected as many as he wishes to preserve. Or,
on the other hand, he may weed out first the worst, then in succession
other unsatisfactory stocks, until, by eliminating the failures, he has
a residue of sufficiently satisfactory flowers. Now, I think it is clear
that, even if the ultimate result is the same (if, that is to say, he
selects the twenty best, or eliminates all but the twenty best), the
method of procedure is in the two cases different. Selection is applied
at one end of the scale, elimination at the other. There is a difference
in method in picking out the wheat-grains (like a sparrow) and
scattering the chaff by the wind.
Under nature both methods are operative, but in very different degrees.
Although the insect may select the brightest flowers, or the hen-bird
the gaudiest or most tuneful mate, the survival of the fittest under
nature is in the main the net result of the slow and gradual process of
the elimination of the unfit.[V] The best-adapted are not, save in
exceptional cases, selected; but the ill-adapted are weeded out and
eliminated. And this distinction seems to me of sufficient importance to
justify my suggestion that _natural selection_ be subdivided under two
heads--_natural elimination_, of widespread occurrence throughout the
animal world; and _selection proper_, involving the element of
individual or special choice.
The term "natural elimination" for the major factor serves definitely to
connect the natural process with that struggle for existence out of
which it arises. The struggle for existence is indeed the reaction of
the organic world called forth by the action of natural elimination.
Organisms are tending to increase in geometrical ratio. There is not
room or subsistence for the many born. The tendency is therefore held in
check by elimination, involving the struggle for existence. And the
factors of elimination are three: first, elimination through the action
of surrounding physical or climatic conditions, under which head we may
take such forms of disease as are not due to living agency; secondly,
elimination by enemies, including parasites and zymotic diseases; and
thirdly, elimination by competition. It will be convenient to give some
illustrative examples of each of these.
Elimination through the action of surrounding physical conditions, taken
generally, deals with the very groundwork or basis of animal life. There
are certain elementary mechanical conditions which must be fulfilled by
every organism however situated. Any animal which fails to fulfil these
conditions will be speedily eliminated. There are also local conditions
which must be adequately met. Certain tropical animals, if transferred
to temperate or sub-Arctic regions, are unable to meet the requirements
of the new climatic conditions, and rapidly or gradually die. Fishes
which live under the great pressure of the deep sea are killed by the
expansion of the gases in their tissues when they are brought to the
surface. Many fresh-water animals are killed if the lake in which they
live be invaded by the waters of the sea. If the water in which corals
live be too muddy, too cold, or too fresh--near the mouth of a great
river on the Australian coast, for example--they will die off. During
the changes of climate which preceded and followed the oncoming of the
glacial epoch, there must have been much elimination of this order. Even
under less abnormal conditions, the principle is operative. Darwin tells
us that in the winter of 1854-5 four-fifths of the birds in his grounds
perished from the severity of the weather, and we cannot but suppose
that those who were thus eliminated were less able than others to cope
with or stand the effects of the inclement climatic conditions. My
colleague, Mr. G. Munro Smith, informs me that, in cultivating microbes,
certain forms, such as _Bacillus violaceus_ and _Micrococcus
prodigiosus_, remain in the field during cold weather when other less
hardy microbes have perished. The insects of Madeira may fairly be
regarded as affording another instance. The ground-loving forms allied
to insects of normally slow and heavy flight have in Madeira become
wingless or lost all power of flight. Those which attempted to fly have
been swept out to sea by the winds, and have thus perished; those which
varied in the direction of diminished powers of flight have survived
this eliminating process. On the other hand, among flower-frequenting
forms and those whose habits of life necessitate flight, the Madeira
insects have stronger wings than their mainland allies. Here, since
flight could not be abandoned without a complete change of life-habit,
since all must fly, those with weaker powers on the wing have been
eliminated, leaving those with stronger flight to survive and procreate
their kind.[W] In Kerguelen Island Mr. Eaton has found that all the
insects are incapable of flight, and most of them in a more or less
wingless condition.[X] Mr. Wallace regards the reduction in the size of
the wing in the Isle of Man variety of the small tortoiseshell butterfly
as due to the gradual elimination of larger-winged individuals.[Y] These
are cases of elimination through the direct action of surrounding
physical conditions. Even among civilized human folk, this form of
elimination is still occasionally operative--in military campaigns, for
example (where the mortality from hardships is often as great as the
mortality from shot or steel), in Arctic expeditions, and in arduous
travels. But in early times and among savages it must be a more
important factor.
Elimination by enemies needs somewhat fuller exemplification. Battle
within battle must, throughout nature, as Darwin says, be continually
recurring with varying success. The stronger devour the weaker, and wage
war with each other over the prey. In the battle among co-ordinates the
weaker are eliminated, the stronger prevail. When the weaker are preyed
upon by the stronger and a fair fight is out of the question, the slow
and heavy succumb, the agile and swift escape; stupidity means
elimination, cunning, survival; to be conspicuous, unless it be for some
nasty or deleterious quality, is inevitably to court death: the
sober-hued stand at an advantage. In these cases, if there be true
selection at work, it is the selection of certain individuals, the
plumpest and most toothsome to wit, for destruction, not for survival.
This mode of elimination has been a factor in the development of
protective resemblance and so-called mimicry, and we may conveniently
illustrate it by reference to these qualities. If the hue of a creature
varies in the direction of resemblance to the normal surroundings, it
will render the animal less conspicuous, and therefore less liable to be
eliminated by enemies. This is well seen in the larvæ or caterpillars of
many of our butterflies and moths. It is not easy to distinguish the
caterpillar of the clouded yellow, so closely does its colour assimilate
to the clover leaves on which it feeds, nor that of the Lulworth skipper
on blades of grass. I would beg every visitor to the Natural History
Museum at South Kensington to look through the drawers containing our
British butterflies and moths and their larvæ, in the further room on
the basement, behind the inspiring statue of Charles Darwin. Half an
hour's inspection will serve to bring home the fact of protective
resemblance better than many words.
It may, however, be remarked that not all the caterpillars exhibit
protective resemblance; and it may be asked--How have some of these
conspicuous larvæ, that of the magpie moth, for example, escaped
elimination? What is sauce for the Lulworth goose should be sauce for
the magpie gander. How is it that these gaudy and variable caterpillars,
cream-coloured with orange and black markings, have escaped speedy
destruction? Because they are so nasty. No bird, or lizard, or frog, or
spider would touch them. They can therefore afford to be
bright-coloured. Nay, their very gaudiness is an advantage, and saves
them from being the subject of unpleasant experiments in the matter.
Other caterpillars, like the palmer-worms, are protected by barbed hairs
that are intensely irritating. They, too, can afford to be conspicuous.
But a sweet and edible caterpillar, if conspicuous, is eaten, and thus
by the elimination of the conspicuous the numerous dull green or brown
larvæ have survived.
A walk through the Bird Gallery in the National collection will afford
examples of protective resemblance among birds. Look, for example, at
the Kentish plover with its eggs and young--faithfully reproduced in our
frontispiece--and the way in which the creature is thus protected in
early stages of its life will be evident. The stone-curlew, the
ptarmigan, and other birds illustrate the same fact, which is also seen
with equal clearness in many mammals, the hare being a familiar example.
Many oceanic organisms are protected through general resemblance. Some,
like certain medusæ, are transparent. The pellucid or transparent sole
of the Pacific (_Achirus pellucidus_), a little fish about three inches
long, is so transparent that sand and seaweed can be seen distinctly
through its tissues. The salpa is transparent save for the intestine and
digestive gland, which are brown, and look like shreds of seaweed. Other
forms, like the physalia, are cærulean blue. The exposed parts of
flat-fish are brown and sandy coloured or speckled like the sea-bottom;
and in some the sand-grains seem to adhere to the skin. So, too, with
other fish. "Looking _down_ on the dark back of a fish," says Mr. A. R.
Wallace, "it is almost invisible, while to an enemy looking _up_ from
below, the light under surface would be equally invisible against the
light of clouds and sky." Even some of the most brilliant and gaudiest
fish, such as the coral-fish (_Chætodon, Platyglossus_, and others), are
brightly coloured in accordance with the beautiful tints of the
coral-reefs which form their habitat; the bright-green tints of some
tropical forest birds being of like import. No conception of the range
of protective resemblance can be formed when the creatures are seen or
figured isolated from their surroundings. The zebra is a sufficiently
conspicuous animal in a menagerie or a museum; and yet Mr. Galton
assures us that, in the bright starlight of an African night, you may
hear one breathing close by you, and be positively unable to see the
animal. A black animal would be visible; a white animal would be
visible; but the zebra's black and white so blend in the dusk as to
render him inconspicuous.
To cite but one more example, this time from the invertebrates.
Professor Herdman found in a rock-pool on the west coast of Scotland "a
peculiarly coloured specimen of the common sea-slug (_Doris
tuberculata_). It was lying on a mass of volcanic rock of a dull-green
colour, partially covered with rounded spreading patches of a purplish
pink nullipore, and having numerous whitish yellow _Spirorbis_ shells
scattered over it--the general effect being a mottled surface of dull
green and pink peppered over with little cream-coloured spots. The upper
surface of the Doris was of precisely the same colours arranged in the
same way.... We picked up the Doris, and remarked the brightness and the
unusual character of its markings, and then replaced it upon the rock,
when it once more became inconspicuous."[Z]
Then, too, there are some animals with variable protective
resemblance--the resemblance changing with a changing environment. This
is especially seen in some Northern forms, like the Arctic hare and fox,
which change their colour according to the season of the year, being
brown in summer, white and snowy in winter. The chamæleon varies in
colour according to the hue of its surroundings through the expansion
and contraction of certain pigment-cells; while frogs and cuttle-fish
have similar but less striking powers. Mr. E. B. Poulton's[AA] striking
and beautiful experiments show that the colours of caterpillars and
chrysalids reared from the same brood will vary according to the colour
of their surroundings.
[Illustration: Fig. 18.--Caterpillar of a moth (_Ennomos tiliaria_) on
an oak-spray. (From an exhibit in the British Natural History Museum.)]
If this process of protective resemblance be carried far, the general
resemblance in hue may pass into special resemblance to particular
objects. The stick-insect and the leaf-insect are familiar
illustrations, though no one who has not seen them in nature can realize
the extent of the resemblance. Most of us have, at any rate, seen the
stick-caterpillars, or loopers (Fig. 18), though, perhaps, few have
noticed how wonderful is the protective resemblance to a twig when the
larva is still and motionless, for the very reason that the resemblance
is so marked that the organism at that time escapes, not only casual
observation, but even careful search. Fig. 19 gives a representation of
a locust with special protective resemblance to a leaf--not a perfect
leaf, but a leaf with fungoid blotches. This insect and the
stick-caterpillar may be seen in the insect exhibits on the basement at
South Kensington, having been figured from them by the kind permission
of Professor Flower.
[Illustration: Fig. 19.--A locust (_Cycloptera speculata_) which closely
resembles a leaf. (From an exhibit in the British Natural History
Museum.)]
Perhaps one of the most striking instances of special protective
resemblance is that of the Malayan leaf-butterfly (_Kallima paralecta_).
So completely, when the wings are closed, does this insect resemble a
leaf that it requires a sharp eye to distinguish it. These butterflies
have, moreover, the habit of alighting very suddenly. As a recent
observer (Mr. S. B. T. Skertchly) remarks, they "fly rapidly along, as
if late for an appointment, suddenly pitch, close their wings, and
become leaves. It is generally done so rapidly that the insect seems to
vanish."[AB] Instances might be multiplied indefinitely. Mr. Guppy thus
describes a species of crab in the Solomon Islands: "The light purple
colour of its carapace corresponds with the hue of the coral at the base
of the branches, where it lives; whilst the light red colour of the big
claws, as they are held up in their usual attitude, similarly imitates
the colour of the branches. To make the guise more complete, both
carapace and claws possess rude hexagonal markings which correspond
exactly in size and appearance with the polyp-cells of the coral."[AC]
When the special protective resemblance is not to an inanimate object,
but to another organism, it is termed mimicry. It arises in the
following way:--
Many forms, especially among the invertebrates, escape elimination by
enemies through the development of offensive weapons (stings of wasps
and bees), a bitter taste (the Heliconidæ among butterflies), or a hard
external covering (the weevils among beetles). The animals which prey
upon these forms learn to avoid these dangerous, nasty, or indigestible
creatures; and the avoidance is often instinctive. It thus becomes an
advantage to other forms, not thus protected, to resemble the animals
that have these characteristics. Such resemblance is termed mimicry,
concerning which it must be remembered that the mimicry is unconscious,
and is reached by the elimination of those forms which do not possess
this resemblance. Thus the _Leptalis_, a perfectly sweet insect, closely
resembles the _Methona_, a butterfly producing an ill-smelling yellow
fluid. The quite harmless _Clytus arietis_, a beetle, resembles, not
only in general appearance, but in its fussy walk, a wasp. The
soft-skinned _Doliops_, a longicorn, resembles the strongly encased
_Pachyrhyncus orbifex_, a weevil. The not uncommon fly _Eristalis tenax_
(Fig. 20), is not unlike a bee, and buzzes in an unpleasantly suggestive
manner.[AD]
Mimicry is not confined to the invertebrates. A harmless snake, the
eiger-eter of Dutch colonists at the Cape, subsists mainly or entirely
on eggs. The mouth is almost or quite toothless; but in the throat
hard-tipped spines project into the gullet from the vertebræ of the
column in this region. Here the egg is broken, and there is no fear of
losing the contents. Now, there is one species of this snake that
closely resembles the berg-adder. The head has naturally the elongated
form characteristic of the harmless snakes. But when irritated, this
egg-eater flattens it out till it has the usual viperine shape of the
"club" on a playing-card. It coils as if for a spring, erects its head
with every appearance of anger, hisses, and darts forward as if to
strike its fangs into its foe, in every way imitating an enraged
berg-adder. The snake is, however, quite harmless and inoffensive.[AE]
Here we have mimicry both in form and habit. Another case of imperfect
but no doubt effectual mimicry is given by Mr. W. Larden, in some notes
from South America.[AF] Speaking of the rhea, or South American ostrich,
he says, "One day I came across an old cock in a nest that it had made
in the dry weeds and grass. Its wings and feathers were loosely
arranged, and looked not unlike a heap of dried grass; at any rate, the
bird did not attract my attention until I was close on him. The long
neck was stretched out close along the ground, the crest feathers were
flattened, and an appalling hiss greeted my approach. It was a
pardonable mistake if for a moment I thought I had come across a huge
snake, and sprang back hastily under this impression."
Protective resemblance and mimicry have been considered at some length
because, on the hypothesis of natural selection, they admirably
illustrate the results which may be reached through long-continued
elimination by enemies.
Sufficient has now been said to show that this form of elimination is an
important factor. We are not at present considering the question how
variations arise, or why they should take any particular direction. But
granting the fact that variations may and do occur in all parts of the
organism, it is clear that, in a group of organisms surrounded by
enemies, those individuals which varied in the direction of swiftness,
cunning, inconspicuousness,[AG] or resemblance to protected forms,
would, other things being equal, stand a better chance of escaping
elimination.
Elimination by competition is, as Darwin well points out, keenest
between members of the same group and among individuals of the same
species, or between different groups or different species which have, so
to speak, similar aims in life. While enemies of various kinds are
preying upon weaker animals, and thus causing elimination among them,
they are also competing one with another for the prey. While the slower
and stupider organisms are succumbing to their captors, and thus leaving
more active and cunning animals in possession of the field, the slower
and stupider captors, failing to catch their cunning and active prey,
are being eliminated by competition. While protective resemblance aids
the prey to escape elimination by enemies, a correlative resemblance,
called by Mr. Poulton aggressive resemblance, in the captors aids them
in stealing upon their prey, and so gives advantage in competition. Thus
the hunting spider closely resembles the flies upon which he pounces,
even rubbing his head with his fore legs after their innocent fashion.
As in the case of protective resemblance, so, too, in its aggressive
correlative, the resemblance may be general or special, or may reach the
climax of mimicry. And since the same organism is not only a would-be
captor, but sometimes an unwilling prey, the same resemblance may serve
to protect it from its enemies and to enable it to steal upon its prey.
The mantis, for example, gains doubly by its resemblance to the
vegetation among which it lives. Certain spiders, described by Mr. H. O.
Forbes, in Java, closely resemble birds'-droppings. This may serve to
protect them from elimination by birds; but it also enables them to
capture without difficulty unwary butterflies, which are often attracted
by such excreta. A parasitic fly (_Volucella bombylans_) closely
resembles (Fig. 20) a bumble-bee (_Bombus muscorum_), and is thus
enabled to enter the nest of the bee without molestation. Its larvæ feed
upon the larvæ of the bee. The cuckoo bee _Psithyrus rupestris_, an idle
quean, who collects no pollen, and has no pollen-baskets, steals into
the nest of the bumble-bee _Bombus lapidarius_, and lays her eggs there.
The resemblance between the two is very great, and it not only enables
the mother bee to enter unmolested, but the young bees, when they are
hatched, to escape. Another bee (_Nomada solidaginis_), which plays the
cuckoo on _Halictus cylindricus_, does not resemble this bee, but is
wasp-like, and thus escapes molestation, not because it escapes notice,
but because it looks more dangerous than it really is.[AH]
Many are the arts by which, in keen competition, organisms steal a march
upon their congeners--not, be it remembered, through any conscious
adaptation, but through natural selection by elimination. Mr. Poulton
describes an Asiatic lizard (_Phrynocephalus mystaceus_) in which the
"general surface resembles the sand on which it is found, while the fold
of their skin at each angle of the mouth is of a red colour, and is
produced into a flower-like shape exactly resembling a little red flower
which grows in the sand. Insects, attracted by what they believe to be
flowers, approach the mouth of the lizard, and are, of course,
captured."[AI] The fishing frog, or angler-fish, is possessed of
filaments which allure small fry, who think them worms, into the
neighbourhood of the great mouth in which they are speedily engulfed;
and certain deep-sea forms discovered during the _Challenger_ expedition
have the lure illumined by phosphorescent light.
[Illustration: Fig. 20.--Mimicry of bees by flies.
a, b, _Bombus muscorum_; c, d, _Volucella bombylans_; e, _Eristalis
tenax_; f, _Apis mellifica_. The underwings of the hive bee (f) were
invisible in the photograph from which the figure was drawn. (From an
exhibit in the British Natural History Museum.)]
We need say no more in illustration of the resemblances which have
enabled certain organisms to escape elimination by competition. Once
more, be it understood that we are not at present considering _how_ any
of these resemblances have been brought about; we are merely indicating
that, given certain resemblances, advantageous either for captor or
prey, those organisms which possess them not will have to suffer
elimination--elimination by enemies, or else elimination by competition.
The interaction between these two kinds of elimination is of great
importance. Hunters and hunted are both, so to speak, playing the game
of life to the best of their ability. Those who fail on either side are
weeded out; and elimination is carried so far that those who are only as
good as their ancestors are placed at a disadvantage as compared with
their improving congeners. The standard of efficiency is thus improving
on each side; and every improvement on the one side entails a
corresponding advance on the other. Nor is there only thus a competition
for subsistence, and arising thereout a gradual sharpening of all the
bodily and mental powers which could aid in seeking or obtaining food;
there is also in some cases a competition for mates, reaching
occasionally the climax of elimination by battle. There is, indeed,
competition for everything which can be an object of appetence to the
brute intelligence; and, owing to the geometrical tendency in
multiplication--the law of increase--the competition is keen and
unceasing.
Such, then, in brief, are the three main modes of elimination:
elimination by physical and climatic conditions; elimination by enemies;
elimination by competition. Observe that it is a differentiating
process. Unlike the indiscriminate destruction before alluded to, the
incidence of which is on all alike, good, bad, and indifferent, it
separates the well-adapted from the ill-adapted, dooming the latter to
death, and allowing the former to survive and procreate their kind. The
destruction is not indiscriminate, but differential.
Let us now turn to cases of selection, properly so called, where Nature
is in some way working at the other end of the scale; where her method
is not the elimination of the unfit, but the selection of the fit. Such
a case may be found on Darwin's principles in brightly coloured flowers
and fruits. "Flowers," he says, "rank amongst the most beautiful
productions of nature; but they have been rendered conspicuous in
contrast with the green leaves, and, in consequence, at the same time
beautiful, so that they may be easily observed by insects. I have come
to this conclusion from finding it an invariable rule that, when a
flower is fertilized by the wind, it never has a gaily coloured corolla.
Several plants habitually produce two kinds of flowers--one kind open
and coloured, so as to attract insects; the other closed, not coloured,
destitute of nectar, and never visited by insects. Hence we may conclude
that, if insects had not been developed on the face of the earth, our
plants would not have been decked with beautiful flowers, but would have
produced only such poor flowers as we see on our fir, oak, nut, and ash
trees, on grasses, spinach, docks, and nettles, which are all fertilized
through the agency of the wind. A similar line of argument holds good
with fruits; that a ripe strawberry or cherry is as pleasing to the eye
as to the palate; that the gaily coloured fruit of the spindle-wood
tree, and the scarlet berries of the holly, are beautiful objects,--will
be admitted by every one. But this beauty serves merely as a guide to
birds and beasts, in order that the fruit may be devoured and manured
seeds disseminated: I infer that this is the case from having as yet
found no exception to the rule that seeds are always thus disseminated
when embedded within a fruit of any kind (that is, within a fleshy or
pulpy envelope), if it be coloured of any brilliant tint, or rendered
conspicuous by being white or black."[AJ]
Here we have a case of the converse of elimination--a case of genuine
selection under nature. But even here the process of elimination also
comes into play, for the visitations of flowers by insects involve
cross-fertilization. The flowers of two distinct individuals of the same
species of plants in this manner fertilize each other; and the act of
crossing, as Darwin firmly believed, though it is doubted by some
observers nowadays, gives rise to vigorous seedlings, which consequently
would have the best chance of flourishing and surviving--would best
resist elimination by competition. So that we here have the double
process at work; the fairest flowers being selected by insects, and
those plants which failed to produce such flowers being eliminated as
the relatively unfit.
If we turn to the phenomena of what Darwin termed sexual selection, we
find both selection and elimination brought into play. By the law of
battle, the weaker and less courageous males are eliminated so far as
the continuation of their kind is concerned. By the individual choice of
the females (on Darwin's view, by no means universally accepted), the
finer, bolder, handsomer, and more tuneful wooers are selected.
Let us again hear the voice of Darwin himself. "Most male birds," he
says, "are highly pugnacious during the breeding season, and some
possess weapons especially adapted for fighting with their rivals. But
the most pugnacious and the best-armed males rarely or never depend for
success solely on their power to drive away or kill their rivals, but
have special means for charming the female. With some it is the power of
song, or of emitting strange cries, or of producing instrumental music;
and the males in consequence differ from the females in their vocal
organs or in the structure of certain feathers. From the curiously
diversified means for producing various sounds, we gain a high idea of
the importance of this means of courtship. Many birds endeavour to charm
the females by love-dances or antics, performed on the ground or in the
air, and sometimes at prepared places. But ornaments of many kinds, the
most brilliant tints, combs and wattles, beautiful plumes, elongated
feathers, top-knots, and so forth, are by far the commonest means. In
some cases, mere novelty appears to have acted as a charm. The ornaments
of the males must be highly important to them, for they have been
acquired in not a few cases at the cost of increased danger from
enemies, and even at some loss of power in fighting with their
rivals[AK].... What, then, are we to conclude from these facts and
considerations? Does the male parade his charms with so much pomp and
rivalry for no purpose? Are we not justified in believing that the
female exerts a choice, and that she receives the addresses of the male
who pleases her most?"[AL]
Here again, then, we have the combined action of elimination
and selection. And now we may note that selection involves
intelligence--involves the play of appetence and choice. Hence it is
that, when we come to consider the evolution of human-folk, the
principle of elimination is so profoundly modified by the principle of
selection. Not only are the weaker eliminated by the inexorable pressure
of competition, but we select the more fortunate individuals and heap
upon them our favours. This enables us also to soften the rigour of the
blinder law; to let the full stress of competitive elimination fall upon
the worthless, the idle, the profligate, and the vicious; but to lighten
its incidence on the deserving but unfortunate.
Both selection and elimination occurring under nature, but elimination
having by far the wider scope, we may now inquire what will be their
effect as regards the three modes of variation--advantageous,
disadvantageous, and neutral. It must be remembered that these modes are
relative and dependent upon circumstances, so that variations, neutral
under certain conditions, may become relatively disadvantageous under
other conditions. Selection clearly leads to the preservation of
advantageous variations alone, and these variations are advantageous in
so far as they meet the taste of the selecting organism. For selection
depends upon individual choice; and uniformity of selection is entirely
dependent upon uniformity in the standard of taste. If, as Darwin
contends, the splendid plumage and tuneful notes of male birds are the
result of a selection of mates by the hens, there must be a remarkable
uniformity of taste among the hens of each particular species, since
there is a uniformity of coloration among the cock-birds. It may be said
that in all their mental endowments there is greater uniformity among
animals than among men; and it is true that individuation has not been
carried so far in them as in human-folk. Still, careful observers of
animals see in them many signs of individual character; and this
uniformity in the standard of taste in each species of birds seems to
many naturalists a real difficulty in the way of the acceptance of
sexual selection. We shall, however, return to this point. For the
present it is clear that selection chooses out advantageous variations,
that the advantage is determined by the taste of the selector, and that
uniform selection implies uniformity of taste.
Turning to elimination, it is clear that it begins by weeding out, first
the more disadvantageous, then the less disadvantageous variations. It
leaves both the advantageous and the neutral in possession of the field.
I imagine that many, perhaps most, of the variations tabulated by Mr.
Wallace and other observers belong to the neutral category. Their
fluctuating character seems to indicate that this is so. In any case,
they are variations which have so far escaped elimination. And I think
they are of great and insufficiently recognized importance. They permit,
through interbreeding, of endless experiments in the combination of
variations, some of which cannot fail to give favourable results.
It is just possible that it may be asked--If in natural elimination
there is nothing more than the weeding out of the unfit and the
suppression of disadvantageous variations, where is the possibility of
advance? The standard may thus be maintained, but where is the
possibility of progress? Such an objection would, however, imply
forgetfulness of the fact that all the favourable variations remain to
leaven the residual lump. Given a mean, with plus and minus variations:
if in any generations the minus variations are got rid of, the mixture
of the mean with the plus variations will give a new mean nearer the
plus or advantageous end of the scale than the old mean. By how much the
favourable variations tend to raise the mean standard, by so much will
the race tend to advance. But in this process I see no reason why the
neutral variations should be eliminated, except in so far as, in the
keen struggle for existence, they become relatively unfavourable.
It is clear, however, that the intercrossing and interbreeding which
occurs between average individuals on the one hand, and those possessing
favourable variations on the other, while it tends gradually to raise
the mean standard, tends also at the same time to reduce the
advantageous variations towards the mean. It must tend to check advance
by leaps and bounds, and to justify the adage, _Natura nil facit per
saltum_. At the same time, it will probably have a greater tendency to
reduce to a mean level neutral variations indefinite in direction than
advantageous variations definite in direction. Still, it is a most
important factor, and one not to be neglected. It tends to uniformity in
the species, and checks individualism. It may act as a salutary brake on
what we may figuratively term hasty and ill-advised attempts at
progress. And at the same time, it favours repeated new experiments in
the combination of variations, occasionally, we may suppose, with happy
results.
But it does more than this. It tends to check, and, if the offspring
always possessed the blended character of both parents, would be
absolutely fatal to, divergence of character within the interbreeding
members of a species. And yet no fact is more striking than this
divergence of character. It is seen in the diversified products of human
selection; for example, among pigeons. It is seen in the freedom of
nature. Mr. Wallace gives many examples. "Among our native species," he
says, "we see it well marked in the different species of titmice,
pipits, and chats. The great titmouse, by its larger size and stronger
bill, is adapted to feed on larger insects, and is even said sometimes
to kill small and weak birds. The smaller and weaker coal-titmouse has
adopted a more vegetarian diet, eating seeds as well as insects, and
feeding on the ground as well as among trees. The delicate little blue
titmouse, with its very small bill, feeds on the minutest insects and
grubs, which it extracts from crevices of bark and from the buds of
fruit trees. The marsh-titmouse, again, has received its name from the
low and marshy localities it frequents; while the crested titmouse is a
Northern bird, frequenting especially pine forests, on the seeds of
which trees it partially feeds. Then, again, our three common
pipits--the tree-pipit, the meadow-pipit, and the rock-pipit, or
sea-lark--have each occupied a distinct place in nature, to which they
have become specially adapted, as indicated by the different form and
size of the hind toe and claw in each species. So the stone-chat, the
whin-chat, and the wheat-ear are all slightly divergent forms of one
type, with modifications in the shape of the wing, feet, and bill
adapting them to slightly different modes of life."[AM] There is
scarcely a genus that does not afford examples of divergent species. The
question then naturally occurs--How have these divergent forms escaped
the swamping effects of intercrossing?
That perfectly free intercrossing, between any or all of the individuals
of a given group of animals, is, so long as the characters of the
parents are blended in the offspring, fatal to divergence of character,
is undeniable. Through the elimination of less favourable variations,
the swiftness, strength, and cunning of a race may be gradually
improved. But no form of elimination can possibly differentiate the
group into swift, strong, and cunning varieties, distinct from each
other, so long as all three varieties freely interbreed, and the
characters of the parents blend in the offspring. Elimination may and
does give rise to progress in any given group as a group; it does not
and cannot give rise to differentiation and divergence, so long as
interbreeding with consequent interblending of characters be freely
permitted. Whence it inevitably follows, as a matter of simple logic,
that where divergence has occurred, intercrossing and interblending must
in some way have been lessened or prevented.
Thus a new factor is introduced, that of _isolation_, or _segregation_.
And there is no questioning the fact that it is of great importance.[AN]
Its importance can, indeed, only be denied by denying the swamping
effects of intercrossing, and such denial implies the tacit assumption
that interbreeding and interblending are held in check by some form of
segregation. The isolation explicitly denied is implicitly assumed.
There are several ways in which isolation, or segregation, may be
effected. Isolation by geographical barriers is the most obvious. A
stretch of water, a mountain ridge, a strip of desert land, may
completely, or to a large extent, prevent any intercrossing between
members of a species on either side of the barrier. The animals which
inhabit the several islands of the Galapagos Archipelago are closely
allied, but each island has its particular species or well-marked
varieties. Intercrossing between the several varieties on the different
islands is prevented, and divergence is thus rendered possible and
proceeds unchecked. It is said that in the Zuyder Zee a new variety of
herrings, the fry of which are very small compared with open-sea
herrings, is being developed. And the salmon introduced into Tasmania
seem to be developing a fresh variety with spots on the dorsal fin and a
tinge of yellow on the adipose fin. In the wooded valleys of the
Sandwich Islands there are allied but distinct species of land-shells.
The valleys that are nearest each other furnish the most nearly related
forms, and the degree of divergence is roughly measured by the number of
miles by which they are separated. Here there is little or no
intercrossing between the slow-moving molluscs in adjoining valleys;
none at all between those at any distance apart.
But even if there are no well-marked physical barriers, the members of a
species on a continent or large island tend to fall into local groups,
between which, unless the animal be of a widely ranging habit, there
will be little intercrossing. Hence local varieties are apt to occur,
and varieties show the first beginnings of that divergence which, if
carried further and more deeply ingrained, results in the
differentiation of species. Geographically, therefore, we may have
either complete isolation or local segregation, and in both cases the
possibility of divergence.
Another mode of segregation arises also out of geographical conditions.
If variations of habits occur (and structure is closely correlated with
habit) such that certain individuals take to the mountains, others to
the plains or valleys; or that certain individuals take to the forests,
others to the open country; the probabilities are that the forest forms
will interbreed frequently with each other, but seldom with those in the
open, and so with the other varieties. The conditions of forest life or
mountain life being thus similar throughout a large area, and life being
through elimination slowly but surely adapted to its environment, there
might thus arise two distinct varieties scattered throughout the length
and breadth of the area, the one inhabiting the mountains, the other the
forests. In illustration of this mode of segregation, we may take the
case of two species of rats which have recently been found by Mr. C. M.
Woodford on one of the Solomon Islands. These two quite distinct species
are regarded by Mr. Oldfield Thomas as slightly modified descendants of
one parent species, the modifications resulting from the fact that of
this original species some individuals have adopted a terrestrial,
others an arboreal life, and their respective descendants have been
modified accordingly. Thus _Mus rex_ lives in trees, has broad
foot-pads, and a long rasp-like, probably semi-prehensile, tail; while
_Mus imperator_ lives on the ground, has smaller pads, and a short,
smooth tail. The segregation of these two species has probably been
effected by the difference of their mode of life, and each has been
adapted to its special environment through the elimination of those
individuals which were not in harmony with the condition of their life.
It is probable that this mode of segregation has been an important one.
And it is clear that in many cases competition would be a co-operating
factor in this process, weaker organisms being forced into otherwise
uncongenial habitats through the stress of competitive elimination, the
weaker forms not perishing, but being eliminated from more favoured
areas.
Protective coloration may also be a means of segregation. A species of
insects having no protective resemblance might vary in two
directions--in the direction of green tints, assimilating their hue to
that of vegetation; and in the direction of sandy or dull earthy
colours, assimilating them to the colour of the soil. In the one variety
elimination would weed out all but the green forms, and these would be
left to intercross. In the other variety, green forms would be
eliminated, dull-brown forms being left to interbreed. Stragglers from
one group into the other would stand a chance of elimination before
interbreeding was effected.[AO]
In the case of birds whose freedom of flight gives them a wide range,
sometimes almost a world-wide range, it would seem at first sight that
their facilities for interbreeding and intercrossing are so great that
divergence is well-nigh impossible. And yet the examples of divergence I
cited from Mr. Wallace were taken from birds, and it is well known that
divergence is particularly well shown in this class. But when the habits
of birds are studied attentively, it is found that, wide as is their
range, their breeding area is often markedly restricted. The sanderling
and knot range freely during the winter throughout the Northern
hemisphere; but their breeding area is restricted to the north polar
region. The interbreeding within this area keeps the species one and
homogeneous, notwithstanding its wide range, and, at the same time,
prevents intercrossing with allied species with different
breeding-grounds.
Another most important mode of segregation among animals arises out of
habitual or instinctive preferences. Where varieties are formed there is
a tendency for like to breed with like. In the Falkland Islands the
differently coloured herds of cattle, all descended from the same stock,
keep separate, and interbreed with each other, but not with individuals
outside their own colour-caste. If two flocks of merino sheep and heath
sheep be mixed together, they do not interbreed. In the Forest of Dean
and in the New Forest, the dark and pale coloured herds of fallow deer
have never been known to intermingle.[AP] Here we have a case of
selective _segregation through preferential mating_, and may find
therein the basis of sexual selection in its higher ranges as advocated
by Darwin.
The question of sexual selection will, however, be briefly considered in
the chapter on "Organic Evolution." At present what we have to notice is
that, through preferential mating, segregation is effected. The forms
that interbreed have a distinguishing colour. From this it is but a step
to the possession, not merely of a distinguishing colour, but of
distinguishing colour-markings. Hence, through preferential mating, may
arise those special markings which so frequently distinguish allied
species. They not only enable _us_ to recognize species as distinct, but
enable the species which possess them to recognize the members of their
own kind. Mr. Wallace calls these diacritical marks _recognition-marks_,
and gives many illustrative examples.[AQ] They are especially noticeable
in gregarious animals and in birds which congregate in flocks or which
migrate together. Mr. Wallace considers that they "have in all
probability been acquired in the process of differentiation for the
purpose of checking the intercrossing of allied forms;" for "one of the
first needs of a new species would be to keep separate from its nearest
allies, and this could be more readily done by some easily seen external
mark of difference." This language seems, however, to savour of
teleology (that pitfall of the evolutionist). The cart is placed before
the horse. The recognition-marks were, I believe, not produced to
prevent intercrossing, but intercrossing has been prevented because of
preferential mating between individuals possessing special
recognition-marks. To miss this point is to miss an important
segregation-factor. Undoubtedly, other tendencies co-operate in
maintaining the standard of the recognition-marks. Stragglers who failed
in the matter of recognition would get separated from their fellows, and
stand a greater chance of elimination by enemies; young who failed in
this respect would be in like condemnation. Still, I cannot doubt that
the foundations of recognition-marks were laid in preferential mating,
and that in this we have an important factor in segregation.
We may here note, in passing, as also arising out of preference, how the
selection of flowers by insects may lead to segregation; for insects
seem often to have habitual or instinctive colour-preferences. Flowers
of similar colour would be thus cross-fertilized, but would not
intercross with those of different colour, whence colour-varieties might
arise. It is important to note that in these cases there is a
psychological factor in evolution.
We have so far assumed that intercrossing of parents and interblending
of their characters in the offspring always go together. This, we must
now notice, is not always the fact. If a blue-eyed Saxon marry a
dark-eyed Italian, the children will have blue eyes _or_ dark eyes, not
eyes of an intermediate tint. The characters do not interblend. The
_ancon_, or otter-sheep, a breed with a long body and short, bandy legs,
appeared in Massachusetts as a chance sport in a single lamb. The
offspring of this ram were either ancons or ordinary sheep. The ancon
characters did not blend. Hence for a time a definite breed was
maintained. We may call this mode of isolation _isolation by exclusive
inheritance_.
A further mode of isolation or segregation, for which Mr. Romanes[AR]
claims a foremost, indeed, the foremost, place, is _physiological
isolation_ as due to differential fertility. One among the many
variations to which organisms are subject is a variation in fertility,
which may reach the climax of absolute sterility. But it is clear that a
sterile variation carries with it its own death-warrant, since the
sterile individual leaves no descendants to inherit its peculiarity.
Relative infertility, too, unless it chances to be correlated with some
unusual excellence, would be no advantage, would be transmitted to few
descendants, and would tend to be extinguished. The same is not true,
however, of differential fertility. "It is by no means rare," said
Darwin,[AS] "to find certain males and females which will not breed
together, though both are known to be perfectly fertile with other males
and females." Mr. Romanes assumes, as a starting-point, the converse of
this, namely, that certain males and females will breed together, though
they are infertile with all other members of the species.
Suppose, then, a variety to arise which is perfectly fertile within the
limits of the varietal form, but imperfectly fertile or infertile with
the parent species. Such a variety would have to run the risks of those
ill effects which, as Darwin showed,[AT] are attendant upon close
interbreeding. But Mr. Wallace points out[AU] that these ill effects may
not be so marked under nature as they are under domestication. Suppose,
then, that it escapes these ill effects. In this case, Mr. Romanes
urges, it would neither be swamped by intercrossing nor die out on
account of sterility. But although it could not be swamped by
intercrossing, still, if it arose sporadically, here a case, there a
case, and so on, the chances would be enormously against the
perpetuation of the variety, unless some co-operating mode of
segregation aided in bringing together the varying individuals. If, for
example, there were a segregation of these variants in a particular
habitat--all the variants meeting in some definite locality for breeding
purposes; or if there were a further segregation through mutual
preferences; or if, again, there were a further segregation in time the
variety might obtain a firm footing. But without these co-operating
factors it is clear that if one male and one female in a hundred
individuals varied in this particular way, the chances would be at least
forty-nine to one against their happening to mate together.
It is interesting to note that almost the only particular example given
by Mr. Romanes in illustration of his theory is one that involves the
co-operation of one of these further segregation-factors. Suppose, he
says, the variation in the reproductive system is such that the season
of flowering or of pairing becomes either advanced or retarded. This
particular variation being inherited, the variety breeding, let us say,
in May, the parent species in July, there would arise two races, each
perfectly fertile within its own limits, but incapable of crossing with
the other. Thus is constituted "a barrier to intercrossing quite as
effectual as a thousand miles of ocean." Yes! a time-barrier instead of
a space-barrier. The illustration is faulty, inasmuch as it introduces a
mode of segregation other than that in question. I think it very
improbable that differential fertility alone, without the co-operation
of other segregation-factors, would give rise to separate varieties
capable of maintaining themselves as distinct species.
That distinct species are generally mutually infertile, or more
frequently still, that their male offspring are sterile, is, however, an
undoubted fact. But there are, exceptions. Fertile hybrids between the
sheep and the goat seem to be well authenticated. Of rats Darwin says
that "in some parts of London, especially near the docks, where fresh
rats are frequently imported, an endless variety of intermediate forms
may be found between the brown, black, and snake rat, which are all
three usually ranked as distinct species."[AV] Fertile hybrids have been
produced between the green-tinted Japanese and the long-tailed Chinese
pheasants. Mr. Thomas Moore, of Fareham, in Hants, has been particularly
successful in producing a hybrid breed between the golden pheasant
(_Thaumalia picta_), whose habitat is Southern and South-eastern China,
and the Amherst pheasant (_Thaumalia amherstiæ_), which is found in the
mountains of Yunnan and Thibet. In answer to my inquiries, Mr. Moore
kindly informs me that he "has bred the half-bred gold and Amherst
pheasant, crossed them again with gold, and recrossed them with
half-bred Amherst, and kept on crossing until only a strain of the gold
pheasant remained. The result is that the birds so produced are far
handsomer than either breed, since the feathers composing their tiplets
as well as those under the chin are of so beautiful a colour that they
beggar description. They all breed most freely, and are much more
vigorous than the pure gold or Amherst, and their tails reach a length
of over three feet. They are also exceedingly prolific. Out of a batch
of forty-two eggs, forty chickens were hatched out, of which
thirty-seven were reared to perfection."
Still, though there are exceptions, the general infertility of allied
species when crossed is a fact in strong contrast with the marked
fertility of varieties under domestication; concerning which, however,
it should be noted that our domesticated animals have been selected to a
very large extent on account of the freedom with which they breed in
confinement, and that domestication has probably a tendency to increase
fertility. The question, therefore, arises--Is the infertility between
species, and the general sterility of their male offspring, a secondary
effect of their segregation? or is their segregation the direct effect
of their differential fertility? The former is the general opinion; the
latter is held by Mr. Romanes. He contends that sterility is the primary
distinction of species, other specific characters being secondary, and
regards it as a pure assumption to say that the secondary differences
between species have been historically prior to the primary difference.
I do not propose to discuss this question. While it seems to me in the
highest degree improbable that differential fertility, apart from other
co-operating factors, has been or could be a practical mode of
segregation, it has probably been a not unimportant factor in
association with other modes of segregation or isolation. Suppose, for
example, two divergent local varieties were to arise in adjacent areas,
and were subsequently (by stress of competition or by geographical
changes) driven together into a single area: we are justified in
believing, from the analogy of the Falkland Island cattle, the Forest of
Dean deer, and other similar observed habits, that preferential
breeding, kind with kind, would tend to keep them apart. But, setting
this on one side, let us say they interbreed. If, then, their unions are
fertile, the isolation will be annulled by intercrossing--the two
varieties will form one mean or average variety. But if the unions be
infertile, the isolation will be preserved, and the two varieties will
continue separate. Suppose now, and the supposition is by no means an
improbable one, that this has taken place again and again in the
evolution of species: then it is clear that those varietal forms which
had continued to be fertile together would be swamped by intercrossing;
while those varietal forms which had become infertile would remain
isolated. Hence, in the long run, isolated forms occupying a common area
would be infertile. Or suppose, once more, that, instead of the unions
between the two varietal forms being infertile, they are fertile, but
give rise to sterile (mule) or degenerate offspring, as is said to be
the case in the unions of Japanese and Ainos: then it is clear that the
sterile or degenerate offspring of such unions would be eliminated, and
intercrossing, even though it occurred, would be inoperative while
breeding within the limits of the variety continued unchecked.
Sufficient has now been said concerning the modes of isolation and
segregation, geographical, preferential, and physiological. We must now
consider their effects. Where the isolated varieties are under different
conditions of life, there will be, through the elimination of the
ill-adapted in each case, differential adoption to these different
conditions. But suppose the conditions are similar: can there be
divergence in this case? The supposition is a highly hypothetical one,
because it postulates that all the conditions, climatal, environmental,
and competitive, are alike, which would seldom, if ever, be likely to
occur. Let us, however, make the supposition. Let us suppose that an
island is divided into two equal halves by the submersion of a stretch
of lowland running across it. Then the only possible causes of
divergence would lie in the organisms themselves[AW] thus divided into
two equal groups. We have seen that variations may be advantageous,
disadvantageous, or neutral. The neutral form a fluctuating, unfixed,
indefinite body. But they afford the material with which nature may
make, through intercrossing, endless experiments in new combinations,
some of which may be profitable. Such profitable variations would escape
elimination, and, if not bred out by intercrossing, would be preserved.
In any case, the variety would tend to advance through elimination as
previously indicated. But in the two equal groups we are supposing to
have become geographically isolated, the chances are many to one against
the same successful experiments in combination occurring in each of the
two groups. Hence it follows that the progress or advance in the two
groups, though analogous, would not be identical, and divergence would
thus be possible under practically similar conditions of life.
In his observations on the terrestrial molluscs of the Sandwich Islands,
Mr. Gulick notes that different forms are found in districts which
present essentially the same environment, and that there is no greater
divergence when the climatic conditions are dissimilar than there is
when those conditions are similar. As before noticed, the degree of
divergence is, roughly speaking, directly as the distance the varietal
forms are apart. Again, Darwin notes that the climate and environment in
the several islands of the Galapagos group are much the same, though
each island has a somewhat divergent fauna and flora. These facts lend
countenance to the view that divergence can and does occur under similar
conditions of life, if there be isolation. They seem, also, so far as
they go, to negative the view that the species is moulded directly by
the external conditions. For, if this factor were powerful, it would
override the effects of experimental combination of characters when the
conditions were similar, and would give rise to well-marked varietal
forms when the conditions were diverse.
If we admit preferential breeding as a segregation-factor (and arising
out of it sexual selection, in a modified form, as a determining one in
the evolution of the plumage of male birds), it is evident that the
standard of recognition-marks can only be maintained by a uniformity of
preference or taste. Still, the uniformity is not likely to be absolute.
In this matter, as in others, variations will occur, and after the lapse
of a thousand generations, in which elimination has been steadily at
work, it is hardly probable that the recognition standard would remain
absolutely unchanged. For, though there may not be any direct
elimination in this particular respect, there might well be
colour-eliminations in other (e.g. protective) respects, and the mental
nature would not remain quite unchanged. Moreover, we know that
secondary sexual characters are remarkably subject to variation, as may
be well seen in the case of ruffs (_Machetes pugnax_) in the British
Natural History Museum. In the case of our two islands with isolated
faunas, therefore, if they formed separate breeding-areas for birds, the
chances would be many to one against the change in the standard of
recognition-marks being identical in each area. Hence might arise those
minute but definite specific distinctions which are so noteworthy in
this class of the animal kingdom. Instance the Old and New World species
of teal, the Eastern and Western species of curlew and whimbrel, and
other cases numerous.[AX] This, in fact, is probably in many cases the
true explanation of the occurrence of representative species, slight
specific variations of the same form as it is traced across a continent
or through an archipelago of islands.
The question has been raised, and of late a good deal discussed, whether
specific characters, those traits by which species are distinguishable,
are always of use to the species which possess them. Here it is
essential to define what is meant by utility. Characters may be of use
in enabling the possessor to resist elimination; or, like the colours of
flowers, they may be of use in attracting insects, and thus furthering
selection; or, like recognition-marks, they may be of use in effecting
segregation. This last form of utility is apt to be overlooked or lost
sight of. In speaking of humming-birds, the Duke of Argyll says that "a
crest of topaz is no better in the struggle for existence than a crest
of sapphire. A frill ending in spangles of the emerald is no better in
the battle of life than a frill ending in spangles of the ruby." But if
these characters be recognition-marks, they may be of use in
segregation. They are a factor in isolation. But it may be further
asked--What is the use of the segregation? Wherein lies the utility of
the divergence into two forms? This question, however, involves a
complete change of view-point. The question before us is whether
specific characters are of use to the species which possesses them. To
this question it is sufficient to answer that they are useful in
effecting or preserving segregation, without which the species, _as a
distinct species_, would cease to exist. We are not at present concerned
with the question whether divergence in itself is useful or
advantageous. If it be pressed, we must reply that, although divergence
is undoubtedly of immense advantage to life in general, enabling, as
Darwin said, its varying and divergent forms to become adapted to many
and highly diversified places in the economy of nature, still in many
individual cases it is neither possible nor in any respect necessary to
our conception of evolution to assign any grounds of utility or
advantage for the divergence itself.
In any case, we are dealing at present with the utility of specific
characters to the species which possess them; and under the head of
utility we are including usefulness in effecting or maintaining
segregation. Now, we have already seen that variations may be either
advantageous (useful), or neutral (useless), or disadvantageous (worse
than useless). The latter class we may here disregard; elimination will
more or less speedily dispose of them. With regard to neutral (useless)
variations, we must also note that they may be correlated with
variations of the other two classes. If correlated with disadvantageous
variations, they will be eliminated along with them; if correlated with
advantageous variations, they will escape elimination (or will be
selected) together with them. There remain neutral, or useless,
variations, not correlated with either of the other two classes. Are
these in any cases distinctive of species?
It is characteristic of specific distinctions that they are relatively
constant. Elimination, selection, or preferential breeding gives them
relative fixity. On the other hand, it is characteristic of neutral
variations that they are inconstant. There is nothing to give them
fixity. It is, of course, conceivable that all the migrants to a new
area were possessed of a useless neutral character, which those in the
mother area did not possess; or that such a useless character was in
them preponderant, and by intercrossing formed a less fluctuating,
useless character than their progenitors exhibited. Still, the extensive
occurrence of such neutral, or useless, characteristics would be in the
highest degree improbable. Our ignorance often prevents us from saying
in what particular way a character is useful. We must neither, on the
one hand, demand proof that this, that, or the other specific character
is useful, nor, on the other hand, demand negative evidence (obviously
impossible to produce) that it is without utilitarian significance; but
we may fairly request those who believe in the wide occurrence of
useless specific characters to tell us by what means these useless
characters have acquired their relative constancy and fixity. A
suggestion on this head will be found in the next chapter.
We must now pass on to consider briefly a most important factor in the
struggle for existence. Hitherto we have regarded this struggle as
uniform in intensity; we must now regard it as variable, with
alternations of good times and hard times, and indicate the causes to
which such variations are due.
With variations of climate, such as we know to occur from year to year,
or from decade to decade, there are variations in the productiveness of
the soil; and when we remember how closely interwoven are the web and
woof of life, we shall see that the increased or diminished
productiveness of any area will affect for good or ill all the life
which that area supports. The introduction of new forms of life into an
area, or their preponderance at certain periods owing to climatic or
other conditions particularly favourable to them as opposed to other
forms, may alter the whole balance of life in the district. We are often
unable to assign any reason for the sudden increase or diminution of the
numbers of a species; we can only presume that it is the result of some
favourable or unfavourable change of conditions. Thus Mr. Alexander
Becker[AY] has recently drawn attention to the fact that whereas for
several years various species of grasshoppers appeared in great numbers
in South-east Russia, there came then one year of sudden death for most
of them. They were sitting motionless on the grasses and dying. He gives
similar cases of butterflies for a while numerous, and then rare, and
states that a squirrel common near Sarepta suddenly disappeared in the
course of one summer, probably, he adds, succumbing to some contagious
disease. Such is the nice balance of life, that the partial
disappearance of a single form may produce remarkable and
little-expected effects. Darwin amusingly showed how the clover crops
might be beneficially affected by the introduction of a family of old
maids into a parish. The clover is fertilized by humble-bees, the bees
are preyed upon by mice; the relations between cats and mice, and
between old maids and cats, are well known and familiar: more old maids,
more cats; more cats, less mice; less mice, more humble-bees; more
humble-bees, better fertilization. A little thing may modify the balance
of life, and increase or diminish the struggle for existence, and the
rigour of the process of elimination.
But when we take a more extended view of the matter, and include secular
changes of climate, the possible range of variation in the struggle for
existence is seen to be enormously increased. It is well known to those
who have followed the progress of geology, that in early Kainozoic times
a mild climate extended to within the Arctic circle, while during the
glacial epoch much of the north temperate zone was fast locked in ice,
and the climate of the northern hemisphere was profoundly modified. The
animals in the north temperate zone were driven southwards.[AZ] Not only
was there much elimination from the severe climatic conditions, but the
migrants were driven southwards into areas already well stocked with
life, and the competition for means of subsistence in these areas must
have been rendered extremely severe. Elimination was at a maximum. Then
followed the withdrawal of glacial conditions. The increasing geniality
of the climate allowed an expansion of life within a given area, and the
withdrawal of snow and ice further and further north set free new areas
into which this expanding life could migrate and find subsistence. The
hard times of the glacial period were succeeded by good times of
returning warmth and an expanding area; and if, as some geologists
believe, there was an inter-glacial period (or more than one such
period) in the midst of the Great Ice Age, then hard times and good
times alternated during the glacial epoch.
Expansion and contraction of life-areas have also been effected again
and again in the course of geological history by elevations and
subsidences of the land. At the beginning of Mesozoic times much of
Europe was dry land. In Triassic and Rhætic times there were lakes in
England and in Germany, and a warm Mediterranean Sea to the south.
Subsidence of the European area brought with it a lessened land-area and
an increased sea-area: bad times and increased competition for land
animals; good times and a widening life-area for marine forms of life.
This continued, with minor variations, till its culmination in the
Cretaceous period. Then came the converse process: the land-areas
increased, the sea was driven back. A good time had come for terrestrial
life; the marine inhabitants of estuaries and inland seas felt the
pressure of increased competition in a lessening area. And so there
emerged the continental Europe of the beginning of the Kainozoic era.
And it is scarcely necessary to remind those who are in any degree
conversant with geology that during tertiary times there have been
alternate expansions and contractions of life-areas, marine and
terrestrial, the former bringing good times, the latter hard times and a
heightened struggle for existence.
Now, what would be the result of this alternation of good times and hard
times? During good times varieties, which would be otherwise unable to
hold their own, might arise and have time to establish themselves. In an
expanding area migration would take place, local segregation in the
colonial areas would be rendered possible, differential elimination in
the different migration-areas would produce divergence. There would be
diminished elimination of neutral variations, thus affording
opportunities for experimental combinations. In general, good times
would favour variation and divergence.
Intermediate between good times and hard times would come, in logical
order, the times in which there is neither an expansion nor a
contraction of the life-area. One may suppose that these are times of
relatively little change. There is neither the divergence rendered
possible by the expansion of life-area, nor the heightened elimination
enforced by the contraction of life-area.[BA] Elimination is steadily in
progress, for the law of increase must still hold good. Divergence is
still taking place, for the law of variation still obtains. But neither
is at its maximum. These are the good old-fashioned times of slow and
steady conservative progress. They are, perhaps, well exemplified by the
fauna of the Carboniferous period, and it is not at all improbable that
we are ourselves living in such a quiet, conservative period.
On the other hand, hard times would mean increased elimination. During
the exhibitions at South Kensington there were good times for rats. But
when the show was over, there followed times that were cruelly hard. The
keenest competition for the scanty food arose, and the poor animals were
forced to prey upon each other. "Their cravings for food," we read in
_Nature_, "culminated in a fierce onslaught on one another, which was
evidenced by the piteous cries of those being devoured. The method of
seizing their victims was to suddenly make a raid upon one weaker or
smaller than themselves, and, after overpowering it by numbers, to tear
it in pieces." Elimination by competition, passing in this way into
elimination by battle, would, during hard times, be increased. None but
the best organized and best adapted could hope to escape. There would be
no room for neutral variations, which, in the keenness of the struggle,
would be relatively disadvantageous. Slightly divergent varieties,
before kept apart through local segregation, would be brought into
competition. The weakest would in some cases be eliminated. In other
cases, the best-adapted individuals of each variety might survive. If
their experiments in intercrossing, should such occur, gave rise to
fertile offspring, more vigorous and better adapted than either
parent-race, these would survive, and the parent-forms would be
eliminated. But if such experiments in intercrossing gave rise to
infertile, weakly offspring, these would be eliminated. Thus sterility
between species would become fixed. Wherever, during the preceding good
times, divergence had taken place in two different directions of
adaptation, and some intermediate forms, fairly good in both directions,
had been able to escape elimination, the chances are that these
intermediates would be in hard times eliminated, and the divergent forms
left in possession of the field. Wherever, during good times, a species
had acquired or retained a habit of flexibility, that habit would stand
it in good stead in the midst of the changes wrought by hard times; but
when it had, on the other hand, acquired rigidity (like the proverbially
"inflexible goose"), it would be at a disadvantage in the stress of a
heightened elimination.
The alternation of good times and hard times may be illustrated by an
example taken from human life. The introduction of ostrich-farming in
South Africa brought good times to farmers. Whereupon there followed
divergence in two directions. Some devoted increased profits to
improvements upon their farms, to irrigation works which could not
before be afforded, and so forth. For others increased income meant
increased expenditure and an easier, if not more luxurious, mode of
life. Then came hard times. Others, in Africa and elsewhere, learnt the
secret of ostrich-farming. Competition brought down profits, and
elimination set in--of which variety need hardly be stated.
I believe that the alternation of good times and hard times, during
secular changes of climate and alternate expansions and contractions of
life-areas through geological upheavals and depression of the land, has
been a factor of the very greatest importance in the evolution of varied
and divergent forms of life, and in the elimination of intermediate
forms between adaptive variations. It now only remains in this chapter
to say a few words concerning convergence, adaptation, and progress.
Convergence, which is the converse of divergence, is brought about
through the adaptation of different forms of life to similar conditions
of existence. The somewhat similar form of the body and fin-like limbs
of fishes, of ancient reptiles (the ichthyosaurus and its allies), of
whales, seals, and manatees, is a case in point. Both birds, bats, and
pterodactyls have keeled breastbones for the attachment of the large
muscles for flight. A whole series of analogous adaptations, as the
result of analogous modes of life, are found in the placental mammals of
Europe and Asia, on the one hand, and the marsupial forms of Australia
on the other hand. The flying squirrel answers to the flying phalanger,
the fox to the vulpine phalanger, the bear to the koala, the badger to
the pouched badger, the rabbit to the bandicoot, the wolverine to the
Tasmanian devil, the weasel to the pouched weasel, the rats and mice to
the kangaroo rats and mice, and so on. A familiar example of convergence
is to be seen in our swallows and martins, on the one hand, and the
swifts on the other. Notwithstanding their superficial similarity in
external form and habits, they are now generally regarded as belonging
to distinct orders of birds.
These are examples of convergence.[BB] Animals of diverse descent and
ancestry have, through similarity of surrounding conditions or of habits
of life, become, in certain respects, assimilated. But some zoologists
go further than this. They maintain that the same genus or species may,
through adaptation to similar circumstances, be derived from dissimilar
ancestors. Some palæontologists, for example, believe that the horse has
been independently evolved along parallel lines in Europe and in
America. Professor Cope considers that in the one continent
_Protohippus_, and in the other _Hipparion_, was the immediate ancestor
of _Equus_. The probabilities are, however, so strongly against such a
view, that it cannot be accepted until substantiated by stronger
evidence than is yet forthcoming.
A special and particular form of convergence, at any rate in certain
obvious, if superficial, characters, has already been noticed in our
brief consideration of mimicry. In the first place, among a number of
closely related species of inedible butterflies, the tendency to
divergence is checked, so far as external markings and coloration are
concerned, that all may continue to profit by the resemblance, and that
the numbers tasted by young birds in gaining their experience (for the
avoidance seems to be at most incompletely instinctive) may be divided
amongst all the species, thus lessening the loss to each. Secondly,
there may be a convergence of certain genera of distantly related
inedible groups (e.g. among the Heliconidæ and the Danaidæ), which gain
by being apparently one species, since the loss from young birds is
shared between them. And lastly, there is the true mimicry of quite
distinct families of butterflies, not themselves inedible, but
sheltering themselves under the guise and sharing the bad reputation of
the mimicked forms. Such forms of convergence are in special adaptation
to a very special environment.
We must remember that in all cases adaptation is a matter of life and
environment. And these, we may now note, may be related in one or more
of three ways. In the first place, there is the adaptation of life to an
unchanging environment; for example, the adaptation of all forms of life
to the fixed and unchanging properties of inorganic matter. If we liken
life to a statue and the environment to a mould in which it is cast, we
have in this case a rigid mould and a plastic statue. Secondly, the
adaptation may be mutual, as, for example, when the structures of
insects and flowers are fitted each to the other, or when the speed of
hunters and hunted is steadily increased through the elimination of the
slow in either group. Here the mould and statue are both somewhat
plastic, and yield to each other's influence. Thirdly, the environment
may be moulded to life. This, again, is only relative, since life never
wholly loses its plasticity. The bird that builds a nest, the beaver
that constructs a dam, the insect that gives rise to a gall,--these, so
far, mould the environment to the needs of their existence. Man in
especial has the power, through his developed intelligence, of
manufacturing his own environment. Here the statue is relatively rigid,
and the mould plastic.
Progress may be defined as continuous adaptation. In modern phrase, this
is called evolution. The continuity makes the difference between
evolution and revolution. Both are natural. Both occur in the organic,
the social, and the intellectual sphere. Evolution is the orderly
progress of the organism or group of organisms, by which it becomes more
and more in harmony with surrounding conditions. If the conditions
become more and more complex, the organism will progress in complexity;
but if the conditions be more and more simple, progress (if such it may
still be called) will be towards simplicity of structure, unnecessary
complexity being eliminated, or, in any case, disappearing. Hence, in
parasites and some forms of life which live under simple conditions, we
have the phenomena of degeneration, or a passage from a more complex to
a more simple condition.
Revolution in organic life is the destruction of one organism or group
of organisms, and the replacement in its stead of a wholly different
organism or group of organisms. During hard times there may be much
revolution, or replacement of one set of organic forms by another set of
organic forms. It was by revolution that the dominant reptiles of the
Mesozoic epoch were replaced by the dominant mammals of Kainozoic times.
It was by revolution that pterodactyls were supplanted by birds.
Revolution has exterminated many a group in geological ages. On the
other hand, it was by evolution that the little-specialized Eocene
ungulates gave rise to the horse, the camel, and the deer; by divergent
evolution that the bears and dogs were derived from common ancestors.
Palæontology testifies both to evolution and revolution.[BC] That
history does the same, I need not stay to exemplify. The same laws also
apply to systems of thought. Darwinism has revolutionized our
conceptions of nature. Darwin placed upon a satisfactory basis a new
order of interpretation of the organic world. By it other
interpretations have been supplanted. And now this new conception is
undergoing evolution, not without some divergence.
In this chapter we have seen how evolution is possible under natural
conditions. If the law of increase be true, if more are born than can
survive to procreate their kind, natural selection is a logical
necessity. We must not blame our forefathers for not seeing this. Until
geology had extended our conception of time, no such conclusions could
be drawn. If organisms have existed but six or seven thousand years, and
if in the last thousand years little or no change in organic life has
occurred, the supposition that they could have originated by any such
process as natural selection is manifestly absurd. Lyell was the
necessary precursor of Darwin. Given, then, increase and elimination
throughout geological time, natural selection is a logical necessity. No
one who adequately grasps the facts can now deny it. It is an
unquestionable factor in organic evolution. Whether it is the sole
factor, is quite another matter, and one we will consider in the chapter
on "Organic Evolution."
NOTES
[M] Samuel Butler in England, and Ewald Hering in Prague, have
ingeniously likened this hereditary persistence to "organic
memory." What are ordinarily called memory, habit, instinct, and
embryonic reconstruction, are all referable to the memory of
organic matter. The analogy, if used with due caution, is a
helpful one, what we call memory being the psychical aspect (under
certain special organic and neural conditions) of what under the
physical aspect we call persistence.
[N] I have also to thank Mr. Edward Wilson for kindly giving me the
measurements of three or four bats in the Bristol Museum.
[O] A millimetre is about 1/25 of an inch, or more exactly .03937 inch.
[P] In nearly all cases the measurements were checked by comparing the
two wings. In one or two instances there were differences of as
much as two or three millimetres between the bones of the two
sides of the body, but in most cases they exactly corresponded.
[Q] We are anxious to extend our observations and to compare series of
bats from different localities. If any of my readers should feel
disposed to help us, by sending specimens (_with the locality duly
indicated_) to Mr. H. Charbonnier, 7, The Triangle South, Clifton,
Bristol, we shall be grateful.
[R] _Nature_, vol. xli. p. 393. The variation in molluscs is often
considerable. In one of the bays in the basement hall of the
Natural History Museum is a series showing the variation in size,
form, and sculpturing of _Paludomus loricatus_, which is found in
the streams of Ceylon. These varieties have in former times been
named as ten distinct species!
[S] More observations and fuller knowledge on this latter point and on
the relative numbers of the sexes in different species are much to
be desired. It is clear that the number of offspring mainly
depends upon the number of females. But if it be true that good
times and favourable conditions lead to an increased production of
females, while hard times and unfavourable conditions lead to a
relative increase of males, then it is evident that good times
will lead to a more rapid increase and hard times to a less rapid
increase of the species. Suppose, for example, in a particular
district food and other conditions were especially favourable for
frogs. Among the well-nourished tadpoles there would be a
preponderance of females. In the next generation the many females
would produce abundant offspring (for one male may fertilize the
ova laid by several females). There would be a greater number of
tadpoles to compete for the same amount of nutriment. They would
be less nourished. There would be less females; and in the
succeeding generation a diminished number of tadpoles. Thus to
some extent a balance between the number of tadpoles and the
amount of available nutrition would be maintained. These
conclusions are, perhaps, too theoretical to be of much value,
while the tendency here indicated would be but one factor among
many.
[T] "Origin of Species," pp. 62, 63.
[U] "Animals and Plants under Domestication," vol. ii. p. 177.
[V] I may here draw attention to the fact that the bats whose wing-bone
measurements were given above are those which have so far survived
and escaped such elimination as is now in progress.
[W] "Origin of Species," p. 109.
[X] "Darwinism," p. 106.
[Y] Ibid. p. 106.
[Z] Proceedings Liverpool Biological Society, 1889.
[AA] Since this chapter was written, Mr. Poulton has published his
interesting and valuable work on "The Colours of Animals," from
which I have contrived to insert one or two additional examples.
[AB] _Ann. and Mag. Nat. Hist._, September, 1889, p. 209, quoted by
Poulton, "Colours of Animals," p. 55.
[AC] Nature, vol. xxxv. p. 77.
[AD] Many other instances might be added. The hornet clear-wing moth
(_Sphecia apiformis_) mimics the hornet or wasp; the
narrow-bordered bee-hawk moth (_Sesia bombyliformis_) mimics a
bumble-bee. These insects may be seen in the lepidoptera drawers
in the Natural History Museum. But perhaps the most wonderful
instance of insect-mimicry is that observed by Mr. W. L. Sclater,
and given by Mr. E. B. Poulton, in his "Colours of Animals" (p.
252), where a (probably) homopterous insect mimics a leaf-cutting
ant, _together with its leafy burden_--a membranous expansion in
the mimic closely resembling the piece of leaf carried by the
particular kind of ant he resembles.
[AE] The late Mr. H. W. Oakley first drew my attention to this snake.
Since then Mr. Hammond Tooke has described the facts in _Nature_,
vol. xxxiv. p. 547.
[AF] _Nature_, vol. xlii. p. 115.
[AG] Since the above was written and sent to press, there has been
added, at the Natural History Museum, in the basement hall, a case
illustrating the adaptation of external colouring to the
conditions of life. All the animals, birds, etc., there grouped
were collected in the Egyptian desert, whence also the rocks,
stones, and sand on which they are placed were brought. Though
somewhat crowded, they exemplify protective resemblance very well.
[AH] I have to thank Mr. H. A. Francis for drawing my attention to
this, and showing me the insects in his cabinet.
[AI] "Colours of Animals," p. 73.
[AJ] "Origin of Species," p. 161.
[AK] "Descent of Man," summary of chap. xvi. pt. ii.
[AL] Ibid. chap. xiv.
[AM] "Darwinism," p. 108.
[AN] Its importance in artificial selection was emphasized by Darwin:
"The prevention of free crossing, and the intentional matching of
individual animals, are the corner-stones of the breeder's art"
("Animals and Plants under Domestication," ii. 62).
[AO] From the absence of interblending in some cases (to be considered
shortly), both brown _and_ green forms may be produced; and under
certain circumstances, even a power of becoming either brown _or_
green in the presence of appropriate stimuli.
[AP] Wallace, "Darwinism," p. 172, where other examples are cited.
[AQ] Ibid. pp. 217, _et seq._
[AR] _Journal of the Linnæan Society_, vol. xix. No. 115: "Zoology."
[AS] "Animals and Plants under Domestication," p. 145.
[AT] Ibid. chap. xvii.
[AU] "Darwinism," p. 326.
[AV] "Animals and Plants under Domestication," vol. ii. p. 65. For
Darwin's general conclusions on hybridism, see vol. ii. p. 162 of
the same work.
[AW] "In every case there are two factors, namely, the nature of the
organism and the nature of the conditions. The former seems to be
much the more important; for nearly similar variations sometimes
arise under, as far as we can judge dissimilar conditions; and, on
the other hand, dissimilar variations arise under conditions which
appear to be nearly uniform" ("Origin of Species," p. 6).
[AX] See "Evolution without Natural Selection," by Charles Dixon. This
author's facts are valuable; his theories are ill digested.
[AY] _Nature_, vol. xlii. p. 136.
[AZ] We may here note, in passing, the fact that the changes of
life-forms in a succession of beds points in nine cases out of ten
rather to substitution through migration than to transmutation.
Still, there are notable cases of transmutation, as in the
fresh-water _Planorbes_ of Steinhem, in Wittenberg (described,
after Hilgendorf, by O. Schmidt, "The Doctrine of Descent," p.
96).
[BA] I would ask historians whether there have not been, in English
history, good times of free and beneficial divergence exemplified
in diverse intellectual activity, hard times of rigorous
elimination, and intermediate times of placid, somewhat humdrum
conservatism.
[BB] Two more technical examples may be noticed in a note. (1)
Professor Haeckel has recently (_Challenger_ Reports, vol.
xxviii.) shown that the Siphonophora include two groups, closely
resembling each other, but of different ancestry: (_a_) The
Disconanthæ, traceable to trachomedusoid ancestors; (_b_) the
Siphonanthæ, traceable to anthomedusoid ancestors like Sarsia. (2)
M. Paul Pelseneer has been led to the conclusion that the pteropod
molluscs also include two groups resembling each other, but of
different ancestry: (_a_) The Thecosomes, traceable to tornatellid
ancestors; (_b_) the Gymnosomes, traceable to aphysiid ancestors.
In each case, the ancestral sea-slug has been modified for a
free-swimming life.
[BC] For evidence in copious abundance, see Nicholson's "Manual of
Palæontology," new edition, vol. i.: "Vertebrata," by R. Lydekker.
CHAPTER V.
HEREDITY AND THE ORIGIN OF VARIATIONS.
The law of heredity, I have said above, may be regarded as that of
persistence exemplified in a series of organic generations. Variation
results--it is clear that it must result--from some kind of
differentiating influence. Such statements as these, however, though
they are true enough, do not help us much in understanding either
heredity or variation.
Let us first notice that normal cases of reproduction exemplify both
phenomena--heredity with variation; hereditary similarity to the parents
in all essential respects, individual variations in minor points. This
is seen in man. Brothers and sisters may present family resemblances
among each other and to their parents, but each has individual traits of
feature and of character. Only in particular cases of so-called
"identical twins" are the variations so slight as not to be readily
perceptible by even a casual observer.
Now, when we seek an explanation of these well-known facts, we may be
tempted to find it in the supposition that the character of the parents
does not remain constant, that the character influences the offspring,
and that therefore the children born at successive periods will differ
from each other, while twins born in the same hour will naturally
resemble each other. As Darwin himself says,[BD] "The greater
dissimilarity of the successive children of the same family in
comparison with twins, which often resemble each other in external
appearance, mental disposition, and constitution, in so extraordinary a
manner, apparently proves that the state of the parents at the exact
period of conception, or the nature of the subsequent embryonic
development, has a direct and powerful influence on the character of the
offspring." But a little consideration will show that, though this
might, in the absence of a better explanation, account for variation in
character, it could not account for variation in form and feature,
unless we regard these as in some way determined by the character.
Moreover, as we shall see presently, it is open to question whether
acquired modifications of structure or character in the parent can in
any way influence the offspring. Again, in the litter of puppies born of
the same bitch by the same dog there are individual variations, often as
well marked as those in successive births.
The facts, then, to be accounted for are--first, the close hereditary
resemblance in all essential points of offspring to parent; and,
secondly, the individual differences in minor points among the offspring
produced simultaneously or successively by the same parents. These are
the facts as they occur in the higher animals. It will be well to lead
up to our consideration of them by a preliminary survey of the facts as
they are exemplified by some of the lower organisms.
In the simpler protozoa, where fission occurs, and where the organism is
composed of a single cell, where also there is a single nucleus which
apparently undergoes division into two equal and similar parts, it is
easy to understand that the two organisms thus resulting from the
halving of a single organism partake completely of its nature. If the
fission of an am[oe]ba is such as to divide it into two similar parts,
there is no reason why these two similar parts should not be in all
respects alike, and should not, by the assimilation of new material,
acquire the size and all the characteristics of the parent form. In the
higher and more differentiated protozoa, the case is not quite so
simple; for the two halves are not each like the whole parent, but have
to be remodelled into a similar organism. But if we suppose, as we seem
to have every right to suppose, that it is the nucleus that controls the
formative processes in the cell, there is not much difficulty in
understanding how, when the nucleus divides into two similar portions,
each directs, so to speak, the similar refashioning of its own separated
protoplasmic territory.
From the protozoa we may pass to such a comparatively simple metazoon as
the hydra. Here the organism is composed, not of a single cell, but of a
number of cells. These cells are, moreover, not all alike, but have
undergone differentiation with physiological division of labour. There
is an inner layer of large nutritive cells, and an outer layer of
protective cells, some of which are conical with fine processes
proceeding from the point of the cone; others are smaller, and fill in
the interstices between the apices of the cones, while others have
developed into thread-cells, each with a fine stinging filament. Between
the two layers there is a thin supporting lamella. The essential point
we have here to notice is that there are two distinct layers with cells
of different form and function.
Now, it has again and again been experimentally proved that if a hydra
be divided into a number of fragments, each will grow up into a complete
and perfect hydra. All that is essential is that, in the separated
fragment, there shall be samples of the cells of both layers. Under
these conditions, the separated cells of the outer layer regenerate a
complete external wall, and the separated cells of the inner layer
similarly regenerate a complete internal lining. From these facts, it
would appear that such a small adequately sampled fragment has the
power, when isolated, of assimilating nutriment and growing by the
multiplication of the constituent cells, and that the growth takes such
lines that the original form of the hydra is reproduced.
Here we may note, by way of analogy, what takes place in the case of
inorganic crystals. If a fragment of an alum crystal be suspended in a
strong solution of alum, the crystal will be recompleted by the growth
of new parts along the broken edges. We say that this is effected under
the influence of molecular polarity. Similarly, we may say that the
fragment of the hydra rebuilds the complete form under the influence of
an hereditary morphological tendency residing in the nuclei of the
several cells. The case, though still comparatively simple, is more
complex than that of the higher protozoa. There the divided nucleus in
two separated cells directs each of these in hereditary lines of
morphological growth. Here not only do the cells and their nuclei
divide, but they are animated by a common morphological principle, and
in their multiplication _combine_ to form an organism possessing the
ancestral symmetry. If, however, we call this an hereditary
morphological tendency or a principle of symmetry; or, with the older
physiologists, a _nisus formativus_; or, with Darwin, "the co-ordinating
power of the organization" (all of these expressions being somewhat
unsatisfactory);--we must remember that these terms merely imply a play
of molecular forces analogous to that which causes the broken crystal of
alum to become recompleted in suitable solution. The inherent molecular
processes in the nuclei[BE] in the one case enable the cells to
regenerate the hydra; the inherent molecular stresses in the crystalline
fragment in the other case lead to the reproduction of the complete
crystal. In either case there is no true explanation, but merely a
restatement of the facts under a convenient name or phrase.
The power of regeneration of lost parts, which is thus seen in the
hydra, is also seen, in a less degree so far as amount is concerned, but
in a higher degree so far as complexity goes, in animals far above the
hydra in the scale of life. The lobster that has lost a claw, the snail
whose tentacle has been removed, the newt which has been docked of a
portion of its tail or a limb, are able more or less completely to
regenerate these lost parts. And the regeneration may involve complex
structures. With the tentacle of the snail the eye may be removed, and
this, not once only, but a dozen times. After such mutilation, no part
of the eye remains, though the stump of its nerve is, of course, left;
still the perfect organ is reconstructed again and again, as often as
the tentacle is removed. The cells at the cut end of the nerve-stump
divide and multiply, as do also those of the surrounding tissues, and
the growing nerve terminates in an optic cup, as it did previously under
the influences of normal development before the mutilation. Here we have
phenomena analogous to, and in some respects more complex than, those
which are seen in the regenerative process in hydra. It is well known,
however, that, in the case of higher animals, in birds and mammals, this
power of regenerating lost parts does not exist. When a bone is broken,
osseous union of the broken pieces may indeed take place; and in
flesh-wounds, the gash is filled in and heals over, not without
permanent signs of its existence, as may often be seen in the faces of
German students. But beyond this there is normally no regeneration. The
soldier who has lost an arm in battle cannot return home and in quiet
seclusion reproduce a new limb. That which seems to be among lower
animals a well-established law of organic growth does not here obtain.
This is probably due to the fact that the higher histological
differentiation of the tissues in the more highly developed forms of
life is a bar to regeneration. In their devotion to special and minute
details of physiological work, the cells have, so to speak, forgotten
their more generalized reproductive faculties. In any case, however the
fact is to be explained, the higher organisms have in many cases almost
completely lost the power of regenerating lost parts. But this loss of
the regenerative power in the more highly differentiated animals does
not alter or invalidate the law of organic growth we are considering.
The law may be thus stated: _Whenever, after mutilation, free growth of
the mutilated surface occurs, that growth is directed in such lines as
to reproduce the lost part and restore the symmetrical integrity of the
organism._ This is a matter of heredity. And we may regard the
hereditary reconstructive power as residing either (1) in those cells at
or adjoining the mutilated surface which are concerned in the regrowth
of the lost part; or (2) in the general mass of cells of the mutilated
organism.
There are difficulties in either view. Professor Sollas, supporting the
former, says,[BF] "This power [in the snail] of growing afresh so
complex and specialized an organ as an eye is certainly, at first sight,
not a little astonishing, but it appears to be capable of a very simple
explanation. The cells terminating the cut stump of the tentacle are the
ancestors of those which are removed; a fresh series of descendants are
derived from them, similarly related to the ancestral cells as their
predecessors which they replace; the first generation of descendants
become in turn ancestors to a second generation, similarly related to
them as were the second tier of extirpated cells; and this process of
descent being repeated, the completed organ will at length be rebuilt."
This explanation is, however, misleading in its simplicity. The cells
terminating the cut stump are not the direct ancestors of those which
are removed, except in the same sense as gorillas are ancestors of men.
They are rather collateral descendants of common ancestors. I think that
Professor Sollas would probably agree that, though the lens and "retina"
are of epiblastic (outer layer) origin, their relationship with the
epiblastic cells at the cut stump is a somewhat distant one. In the
reproduction of the lens the cell-heredity is not direct, but markedly
indirect. And it is somewhat difficult to understand by what means the
ordinary epiblastic cells of the cut stump, which have had no part in
the special and peculiar work of lens-production, should be enabled to
produce cell-offspring, some of which, and those in a special relation
to other deeper-lying cells, possess this peculiar power.
On the other hand, if we turn to the view that the reproduction is
effected, not by the cells of the cut surface alone, but by the general
mass of cells in the mutilated organism, we have to face the difficulty
of understanding how the influence of cells other than those partaking
in the regrowth can be brought to bear on these so as to direct their
lines of development. If we say that the organism is pervaded by a
principle of symmetry such that both growth and regrowth, whenever they
take place, are constrained to follow the lines of ancestral symmetry,
we are really doing little more than restating the facts without
affording any real organic explanation. That which we want to know is in
what organic way this symmetrical growth is effected--how the hereditary
tendency is transmitted through the nuclear network which is concerned
in cell-division. I do not think that we are at present in a position to
give a satisfactory answer to this question.
Let us now return to the hydra, the artificial fission of which has
suggested these considerations. Multiplication in this way is probably
abnormal. Under suitable conditions, however, if well fed, the hydra
normally multiplies by budding. At some spot, generally not far from the
"foot," or base of attachment, a little swelling occurs, and the growth
of the cells in this region takes such lines that a new hydra is formed.
This is at first in direct connection with the parent stem, the two
having a common internal cavity; but eventually it separates and lives a
free existence as a distinct organism (see Fig. 9, p. 45).
Now, here we may notice, as an implication from these facts, that the
size of the organism is limited. When the normal limits of size are
reached, any further assimilation of nutriment ministers, not to the
further growth of the organism, but to the formation of a new outgrowth,
or bud. What determines that the outgrowth, or bud, should originate in
this or that group of cells, we do not know. But, like the isolated
fragment in the hydra subdivided by fission, the little group in which
budding commences contains a fair sample of the various kinds of cells
which constitute the hydra. And here, too, we see that their growth and
development follow definite lines of hereditary symmetry.
But there is a third method of multiplication in hydra: this is the
sexual mode of reproduction, and occurs generally in the autumn. On the
body-wall of certain individuals, near the tentacles, conical swellings
appear. Within these swellings are great numbers of minute sperms, with
small oval heads and active, thread-like tails. They appear to originate
from the interstitial cells of the outer layer (see p. 124). Nearer the
foot, or base of attachment, and generally, but not quite always, in
separate individuals, there are other larger swellings, different in
appearance, of which there is generally only one in the same individual
at the same time. Each contains a single ovum, or egg-cell, surrounded
by a capsule. It, too, and the cells which surround it would appear to
be developed from the interstitial cells. It grows rapidly at the
expense of the surrounding tissue, but when mature, it bursts through
the enveloping capsule, and is freely exposed. A sperm-cell, which
seems, in some cases at least, to be produced by the same individual,
now unites with it; the egg-cell then begins to undergo division,
becomes detached, falls to the bottom, and develops into a young hydra.
Here, then, we have that sexual mode of reproduction which occurs in all
the higher animals. It is, however, in some respects peculiar in hydra.
In the first place, the ovum is nearly always in other animals (but
occasionally not in hydra) fertilized by the sperm from a separate and
distinct individual. In the second place, the germinal cells are
generally produced, not from the outer layer, but from the middle layer,
which appears between the two primitive layers. In some allies of hydra,
however, they take their origin in the inner layer; and it has been
suggested that, even in hydra, the true germinal cells may migrate from
the inner to the outer layer. But of this there does not seem to be at
present sufficient evidence. In any case, however, the essential fact to
bear in mind is that a new individual is produced by the union of a
single cell produced by one organism and of another cell produced in
most cases (but not always in the hydra) from a different individual. In
the higher forms of animal life, the organisms are either female
(egg-producing) or male (sperm-producing). But there are many
hermaphrodite forms which produce both eggs and sperms, as in the common
snail and earthworm. Even in these cases, however, there are generally
special arrangements by which it is ensured that the sperm from one
individual should fertilize the ovum produced by another individual.
* * * * *
What, we must next inquire, is the relation in the higher forms of
life--for we may now leave the special consideration of hydra--of the
ovum or sperm to the organism which produces it? This is but one mode of
putting a very old question--Does the hen produce the egg, or does the
egg produce the hen? Of course, in a sense, both are true; for the hen
produces an egg which, if duly fertilized, will develop into a new hen.
But the question has of late been asked in a new sense; and many eminent
naturalists reply, without hesitation--The egg produces the hen, but
under no circumstances does the hen produce the egg. What, then, it may
be asked, does produce the egg? To this it is replied--The egg was
produced by a previous egg. At first sight, this may seem a mere
quibble; for it may be said that, of course, if an egg produces a hen
which contains other eggs, these eggs may be said to be produced by the
first. But it is really more than a quibble, and we must do our best
clearly to grasp what is meant.
We have seen that, in development, the fertilized egg-cell undergoes
division into two cells, each of which again divides into two, and so
on, again and again, until from one there arises a multitude of cells.
Nor is this all. The multitude are organized into a whole. The
constituent cells have different forms and structures, and perform
diverse functions. Some are skeletal, such as bone and connective
tissue; some are protective, such as those which give rise to feathers
or scales; some form nerves or nerve-centres; some, muscles; some give
rise to glandular tissue; and lastly, some form the essential elements
in reproduction. If, now, we express the development of tissues and the
sequence of organisms in the following scheme, the continuity of the
reproductive cells will be apparent:--
Reproductive | Skeletal and protective cells
cell o< Nerve and muscle cells
| Glandular and nutritive cells | Skeletal, etc.
| Reproductive cells -------- o< Nerve, etc.
| Glandular, etc. | s.
| Reproductive -- o< n.
| gl.
| r.-etc
It is clear that there is a continuity of reproductive cells, which does
not obtain with regard to nerve, gland, or skeleton. If, then, we class
together as body-cells those tissue-elements which constitute what we
ordinarily call the body, i.e. the head, trunk, limbs--all, in fact,
except the reproductive cells, our scheme becomes--
Reproductive | Body
cell o< | Body
| Reproductive cells o< | b.
| Reproductive cells o<
| r.
From this, again, it is clear that the body does not produce the egg, or
reproductive cell, but that the reproductive cell does produce the body.
Of course, it should be noted that we are here using the term "body" as
distinguished from, and not as including, the reproductive cells. But
this is convenient, in that it emphasizes the fact that the muscular,
nervous, skeletal, and glandular cells take (on this view) no part
whatever in producing those reproductive cells which are concerned in
the continuance of the species.
Such, in brief, is the view that the egg produces the hen. We will
return to it presently when we have glanced at the alternative view that
the hen produces the egg.
On this view, the reproductive elements are not merely cells, the result
of normal cell-division, which have been set aside for the continuance
of the species. They are, so to speak, the concentrated extract of the
body, and contain minute or infinitesimal elements derived from all the
different tissues of the organism which produces them. Darwin[BG]
suggested that all the cells of the various tissues produce minute
particles called gemmules, which circulate freely throughout the body,
but eventually find a home in the reproductive cells. Just as the
organism produces an ovum from which an organism like itself develops,
so do the cells of the organism produce gemmules, which find their way
to the ovum and become the germs of similar cells in the developing
embryo. "The child, strictly speaking," says Darwin, "does not grow into
a man, but includes germs which slowly and successively become developed
and form the man." "Each animal may be compared with a bed of soil full
of seeds, some of which soon germinate, some lie dormant for a period,
whilst others perish." Or, to vary the analogy, "an organic being is a
microcosm--a little universe formed of a host of self-propagating
organisms." This is Darwin's provisional hypothesis of pangenesis, which
has recently been accepted in a modified form by Professor W. K. Brooks
in America, to some extent by De Vries on the Continent, by Professor
Herdman of Liverpool, and by other biologists. The ovum on this view is
to be regarded as a composite germ containing the germs of the cellular
constituents of the future organism. The scheme representing this view
will stand thus--
Reproductive | Skeletal and protective cells | | sk. & pr. | | s.
cell o< Nerve and muscle cells >o< ne. & mu. >o< n.
| Glandular and nutritive cells | | gl. & nu. | | gl.
It is clear that, on this hypothesis, we may frame an apparently simple
and, on first sight, satisfactory theory of heredity. Since all the
body-cells produce gemmules, which collect in or give rise to the
reproductive cells, and since each gemmule is the germ of a similar
cell, what can be more natural than that the ovum, thus composed of
representative cell-germs, should develop into an organism resembling
the parent organism? Modifications of structure acquired during the life
of the organism would thus be transmitted from parent to offspring; for
the modified cells of the parent would give rise to modified gemmules,
which would thus hand on the modification. The inheritance of ancestral
traits from grandparent or great-grandparent might be accounted for by
supposing that some of the gemmules remained latent to develop in the
second or third generation. The regeneration of lost parts receives also
a ready explanation. If a part be removed by amputation, regrowth is
possible because there are disseminated throughout the body gemmules
derived from each part and from every organ. A stock of nascent cells or
of partially developed gemmules may even be retained for this special
purpose, either locally or throughout the body, ready to combine with
the gemmules derived from the cells which come next in due succession.
Similarly, in budding, the buds may contain nascent cells or gemmules in
a somewhat advanced stage of development, thus obviating the necessity
of going through all the early stages in the genesis of tissues. The
gemmules derived from each part being, moreover, thoroughly dispersed
through the system, a little fragment of such an organism as hydra may
contain sufficient to rebuild the complete organism; or, if it contains
an insufficient number, we may assume that the gemmules, in their
undeveloped state, are capable of multiplying indefinitely by
self-division. Finally, variations might arise from the superabundance
of certain gemmules and the deficiency of others, and from the varying
potency of the gemmules contained in the sperm and ovum. Where the
maternal and paternal gemmules are of equal potency, the cell resulting
from their union will be a true mean between them; where one or other is
prepotent, the resulting cell will tend in a corresponding direction.
And since the parental cells are subject to modification, transmitted
through the gemmules to the reproductive elements, it is clear that
there is abundant room and opportunity for varietal combinations.
It is claimed, as one of the chief advantages of some form of pangenetic
hypothesis, that it, and it alone, enables us to explain the inheritance
of characters or modifications of structure acquired by use (or lost by
disuse) during the life of the organism, or imprinted on the tissues by
environmental stresses. The evidence for the transmission of such
acquired characters we shall have to consider hereafter. We may here
notice, however, that at first sight the hypothesis seems to prove too
little or too much. For while modifications of tissues, the effects of
use and disuse, are said to be inherited, the total removal of tissues
by amputation, even if repeated generation after generation, as in the
docking of the tails of dogs and horses, formerly so common, does not
have the effect of producing offspring similarly modified. Professor
Weismann has recently amputated the tails of white mice so soon as they
were born, for a number of generations, but there is no curtailment of
this organ in the mice born of parents who had not only themselves
suffered in this way, but whose parents, grandparents, and
great-grandparents were all rendered tailless. The pangenetic answer to
this objection is that gemmules multiply and are transmitted during long
series of generations. We have only to suppose that the gemmules of
distantly ancestral tails have been passing through the mutilated mice
in a dormant condition, awaiting an opportunity to develop, and the
constant reappearance of tails is seen to be no real anomaly. In this
case the gemmules of the parental and grandparental tail are simply
absent. But if the muscles of the parental tail were modified through
unwonted use, the modified cells would give rise to modified gemmules,
which would unite in generation with ancestral gemmules, and to a
greater or less degree modify them. The difference is between the mere
absence of gemmules and the presence of modified gemmules. And the fact
that it takes some generations for the effects of use or disuse to
become marked is (pangenetically) due to the fact that it takes some
time for the modified gemmules to accumulate and be transmitted in
sufficient numbers to affect seriously the numerous ancestral gemmules.
The direction in which Professor W. K. Brooks has recently sought to
modify Darwin's pangenetic hypothesis may here be briefly indicated. He
holds that it is under unwonted and abnormal conditions that the cells
are stimulated to produce gemmules, and that the sperm is the special
centre of their accumulation. Hence it is the paternal influence which
makes for variation, the maternal tendency being conservative. The
reproductive cell is not merely or chiefly a microcosm of gemmules. It
is a cell produced by ordinary cell-division from other reproductive
cells. The ovum remains comparatively unaffected by changes in the body;
but it receives from the sperm, with which it unites, gemmules from such
tissues in the male as were undergoing special modification. The hen
does not produce the egg; but the cock does produce the sperm; and the
union of the two hits the happy mean between the conservatism of the one
view and the progressive possibilities of the other.
Mr. Francis Galton, in 1876,[BH] suggested a modification of Darwin's
hypothesis, which included, as does that of Professor Brooks, the idea
of germinal continuity which had been suggested by Professor (now Sir
Richard) Owen, in 1849. He calls the collection of gemmules in the
fertilized ovum the "stirp." Of the gemmules which constitute the stirp
only a certain number, and they the most dominant, develop into the
body-cells of the embryo. The rest are retained unaltered to form the
germinal cells and keep up a continuous tradition. Mr. Galton's place in
the history of theories of heredity can scarcely be placed too high.
Only one further modification of pangenesis can here be mentioned,
namely, that proposed in 1883 by Professor Herdman, of Liverpool. He
suggested "that the body of the individual is formed, not by the
development of gemmules alone and independently into cells, but by the
gemmules in the cells causing, by their affinities and repulsions, these
cells so to divide as to give rise to new cells, tissues, and organs."
Such are Darwin's provisional hypothesis of pangenesis, and some more
recent modifications thereof. Bold and ingenious as was Darwin's
speculation, supported as it at first sight seems to be by organic
analogies, it finds to-day but few adherents. With all our increased
modern microscopical appliances, no one has ever seen the production of
gemmules. Although it appears sufficiently logical to say that, just as
a large organism produces a small ovum, so does each small cell produce
an exceedingly minute gemmule; when closely investigated, the analogy is
not altogether satisfactory. It is denied, as we have seen, by many
biologists that the organism does produce the ovum. Multiplication is
normally by definite, visible cell-division. Nuclear fission can be
followed in all its phases. But where is the nuclear fission in the
formation of gemmules? It is true that the conjugation of monads is
followed by the pouring forth of a fluid which must be crowded with
germs from which new monads arise, and that these germs are so minute as
to be invisible, even under high powers of the microscope. It might be
suggested, then, that in every tissue some typical cell or cells might
thus break up into a multitude of invisible gemmules. But there is at
present no evidence that they do so. And even if this were the case, it
would not bear out Darwin's view, that every cell is constantly throwing
off numerous gemmules. It is known, however, or at least generally
believed, that there is a constant replacement of tissues during the
life of the organism. It is said, for example, that in the course of
seven years the whole cellular substance of the human body is entirely
renewed. The fact is, I think, open to question. Granting it, however,
it might be suggested that the effete cells, ere they vanish, give rise
to minute gemmules, which find their way to the ova. But it must be
remembered that the new tissue-cells in the supposed successional
renewal of the organs are the descendants of the old tissue-cells; that
these are, therefore, already reproducing their kind directly; and that
the formation of gemmules would thus be a special superadded provision
for a future generation. Still, there is no reason why cells should not
have this double mode of reproduction, if any definite evidence of its
existence could be brought forward. Without such definite evidence, we
may well hesitate before we accept it even provisionally.
The existence of gemmules, then, is unproven, and their supposed mode of
origin not in altogether satisfactory accordance with organic analogies.
Furthermore, the whole machinery of the scheme of heredity is
complicated and hyper-hypothetical. It is difficult to read Darwin's
account of reversion, the inheritance of functionally acquired
characters, and the non-inheritance of mutilation, or to follow his
skilful manipulation of the invisible army of gemmules, without being
tempted to exclaim--What cannot be explained, if this be explanation?
and to ask whether an honest confession of ignorance, of which we are
all so terribly afraid, be not, after all, a more satisfactory position.
That the hen produces the egg, that "gemmules are collected from all
parts of the system to constitute the sexual elements, and that their
development in the next generation forms a new being," is further
rendered improbable by direct observation upon the mode of origin of the
germinal cells, ova, or sperms.
It will be remembered that the view that the egg produces the hen, while
the hen does not produce the egg, suggested the question--What, then,
does produce the egg? to which the answer was--The egg is the product of
a previous egg. On this view, then, the germinal cells, ova, or sperms
are the direct and unmodified descendants of an ovum and sperm which
have entered into fertile union. Now, in certain cases, notably in the
fly _Chironomus_, studied by Professor Balbiani, but also in a less
degree in some other invertebrate forms, it is possible to trace the
continuity of the germinal cells with the fertilized ovum from which
they are derived. In _Chironomus_, for example, "at a very early stage
in the embryo, the future reproductive cells are distinguishable and
separable from the body-forming cells. The latter develop in manifold
variety, into skin and nerve, muscle and blood, gut and gland; they
differentiate, and lose almost all protoplasmic likeness to the mother
ovum. But the reproductive cells are set apart; they take no share in
the differentiation, but remain virtually unchanged, and continue
unaltered the protoplasmic tradition of the original ovum."[BI] In such
a case, then, observation flatly negatives the view that the germinal
cells are "constituted" by gemmules collected from the body-cells,
though, of course (on a modified pangenetic hypothesis), they might be
the recipients of such gemmules.
It is only in a minority of cases, however, that the direct continuity
of germinal cells _as such_ is actually demonstrable. In the higher
vertebrates, for instance, the future reproductive cells can first be
recognized only after differentiation of some of the body-cells and the
tissues they constitute is relatively advanced. While in cases of
alternation of generations, "an entire asexual generation, or more than
one, may intervene between one ovum and another." In all such cases the
continuity of the chain of recognizably germinal cells cannot be
actually demonstrated.
The impracticability of actually demonstrating a continuity of germinal
cells in the majority of cases has induced Professor Weismann to abandon
the view that there is a continuity of germinal cells, and to substitute
for it the view that there is a continuity of germ-plasm (_keimplasma_).
"A continuity of germ-_cells_," he says,[BJ] "does not now take place,
except in very rare instances; but this fact does not prevent us from
adopting a theory of the continuity of the germ-_plasm_, in favour of
which much weighty evidence can be brought forward." It might, however,
be suggested that, although a continuity of germ-cells cannot be
_demonstrated_, such continuity may, nevertheless, obtain, the future
germinal cells remaining undifferentiated, while the cells around them
are undergoing differentiation. The comparatively slight differentiation
of the body-cells in hydroids renders such a view by no means
improbable. But Professor Weismann does not regard such an idea as
admissible, at all events, in certain cases. "It is quite impossible,"
he says,[BK] "to maintain that the germ-cells of hydroids, or of the
higher plants, exist from the time of embryonic development, as
undifferentiated cells, which cannot be distinguished from others, and
which are only differentiated at a later period." The number of
daughter-cells in a colony of hydroid zoophytes is so great that "all
the cells of the embryo must for a long time act as body-cells, and
nothing else." Moreover, actual observation (e.g. in _Coryne_) convinces
Dr. Weismann that ordinary body-cells are converted into reproductive
cells. After describing the parts of the body-wall in which a sexual bud
arises as in no way different from surrounding areas, he says, "Rapid
growth, then, takes place at a single spot, and some of the young cells
thus produced _are transformed into germ-cells_ which did not previously
exist as separate cells."[BL]
This transformation of body-cells or their daughter-cells into
germ-cells seems therefore, if it be admitted, to negative the
continuity of germ-cells as such. But this fact, says Weismann, does not
prevent us from adopting a theory of the continuity of germ-plasm. "As a
result of my investigations on hydroids," he says,[BM] "I concluded that
the germ-plasm is present in a very finely divided and therefore
invisible state in certain body-cells, from the very beginning of
embryonic development, and that it is then transmitted, through
innumerable cell-generations, to those remote individuals of the colony
in which the sexual products are formed."
This germ-plasm resides in the nucleus of the cell; and it would seem
that by a little skilful manipulation it can be made to account for
anything that has ever been observed or is ever likely to be observed.
It is one of those convenient invisibles that will do anything you
desire. The regrowth of a limb shows that the cells contained some of
the original germ-plasm. A little sampled fragment of hydra has it in
abundance. It lurks in the body-wall of the budding polyp. It is ever
ready at call. It conveniently accounts for atavism, or reversion;
for[BN] "the germ-plasm of very remote ancestors can occasionally make
itself felt. Even a very minute trace of a specific germ-plasm possesses
the definite tendency to build up a certain organism, and will develop
this tendency as soon as the nutrition is, for some reason, favoured
above that of the other kinds of germ-plasm present in the nucleus."
In place, then, of the direct continuity of germ-cells as distinct from
body-cells, we have here the direct continuity of germ-plasm as opposed
to body-plasm. The germ-plasm can give rise to body-plasm to any extent;
the body-plasm can never give rise to germ-plasm. If it seems to do so,
this is only because the nuclei of the body-cells contain some
germ-plasm in an invisible form. The body-plasm dies; but the life of
the germ-plasm is, under appropriate conditions, indefinitely
continuous.
So far as heredity is concerned, it matters not whether there be a
continuity of germ-cells or of germ-plasma. In either case, the
essential feature is that body-cells as such cannot give rise to the
germ--that the hen cannot produce the egg. On either view, characters
acquired by the body cannot be transmitted to the offspring through the
ova or sperms. The annexed diagram illustrates how, on the view that the
hen produces the egg, dints hammered into the body by the environment
will be handed on; while, on the view that the hen does not produce the
egg, the dints of the environment are not transmitted to the offspring.
On the hypothesis of continuity, heredity is due to the fact that two
similar things under similar conditions will give similar products. The
ovum from which the mother is developed, and the ovum from which the
daughter is developed, are simply two fragments separated at different
times from the same continuous germ-plasm.[BO] Both develop under
similar circumstances, and their products cannot, therefore, fail to be
similar. How variation is possible under these conditions we shall have
to consider presently.
[Illustration: Fig. 21.--Egg and hen.
I. "The egg produces the hen." II. "The hen produces the egg." In I. the
dints produced by the environment are not inherited; in II. they are.
The letters indicate successive individuals. The small round circles
indicate the eggs.]
Now, although I value highly Professor Weismann's luminous researches,
and read with interest his ingenious speculations, I cannot but regard
his doctrine of the continuity of germ-plasm as a distinctly retrograde
step. His germ-plasm is an unknowable, invisible, hypothetical entity.
Material though it be, it is of no more practical value than a
mysterious and mythical germinal principle. By a little skilful
manipulation, it may be made to account for anything and everything. The
fundamental assumption that whereas germ-plasm can give rise to
body-plasm to any extent, body-plasm can under no circumstances give
rise to germ-plasm, introduces an unnecessary mystery. Biological
science should set its face against such mysteries. The fiction of two
protoplasms, distinct and yet commingled, is, in my opinion, little
calculated to advance our knowledge and comprehension of organic
processes. For myself, I prefer to take my stand on protoplasmic unity
and cellular continuity.
The hypothesis of cellular continuity is one that the researches of
embryologists tend more and more to justify. The fertilized ovum divides
and subdivides, and, by a continuance of such processes of subdivision,
gives rise to all the cells of which the adult organism is composed. It
is true that in some cases, as in that of peripatus, as interpreted by
Mr. Adam Sedgwick, the cells of the embryo run together or remain
continuous as a diffused protoplasmic mass with several or many nuclei.
But this seemingly occurs only in early stages as a step towards the
separation of distinct cells. And even if the process should be proved
of far wider occurrence, it would not disprove the essential doctrine of
cellular continuity. The nucleus is the essence of the cell. And the
doctrine of cellular continuity emphasizes the fact that the nuclei of
all the cells of the body are derived by a process of divisional growth
from the first segmentation-nucleus which results from the union of the
nuclei of the ovum and the sperm. In this sense, then, however late the
germinal cells appear as such, they are in direct continuity with the
germinal cell from which they, in common with all the cells of the
organism, derive their origin. In this sense there is a true continuity
of germ-cells.
Now, it has again and again been pointed out that the simple cell of
which an am[oe]ba is composed is able to perform, in simple fashion, the
various protoplasmic functions. It absorbs and assimilates food; it is
contractile and responds to stimulation; it respires and exhibits
metabolic processes; it undergoes fission and is reproductive. The
metazoa are cell-aggregates; and in them the cells exemplify a
physiological division of labour. They differentiate, and give rise to
muscle and nerve, gut and gland, blood and connective or skeletal
tissue, ova and sperms. Are these germinal cells mysteriously different
from all the other cells which have undergone differentiation? No. _They
are the cells which have been differentiated and set apart for the
special work of reproduction, as others have been differentiated and set
apart for other protoplasmic functions._
Cell-reproduction is, however, in the metazoa of two kinds. There is the
direct reproduction of differentiated cells, by which muscle-cells,
nerve-cells, or others reproduce their kind in the growth of tissues or
organs; and there is the developmental reproduction, by which the
germinal cells under appropriate conditions reproduce an organism
similar to the parent. The former is in the direct line of descent from
the simple reproduction of am[oe]ba. The latter is something peculiarly
metazoan, and is, if one may be allowed the expression, specialized in
its generality.
That the metazoa are derived from the protozoa is generally believed.
How they were developed is to a large extent a matter of speculation.
But, however originating, their evolution involved the production, from
cells of one kind, of cells of two or more kinds, co-operating in the
same organism. Whenever and however this occurred, the new phase of
developmental reproduction must have had its origin. And if in
cell-division there is any continuity of protoplasmic power, the faculty
of producing diverse co-operating cells would be transmitted. On any
view of the origin of the metazoa, this diverse or developmental
reproduction is a new protoplasmic faculty; on any view, it must have
been transmitted, for otherwise the metazoa would have ceased to exist.
This new faculty of developmental reproduction, then, with the inception
of the metazoa, takes its place among other protoplasmic faculties, and,
with the progress of differentiation and the division of labour, will
become the special business of certain cells. On this view, the
specialization of the reproductive faculty and of germinal cells takes
its place in line with other cell-differentiations with division of
labour; and the difficulties of comprehending and following the process
of differentiation in this matter are similar to those which attend
physiological division of labour in general.
It is probable that, in the lower metazoa, in which differentiation has
not become excessively stereotyped, the power of developmental
reproduction is retained by a great number of cells, even while it is
being specialized in certain cells. Hence the ability to produce lost
parts and the reproduction of hydra by fission. But, on the other hand,
the special differentiation of a tissue on particular lines has always a
tendency to disqualify the cells from performing other protoplasmic
faculties, and that of developmental reproduction among the number. I do
not know of any definite, well-observed cases on record in the animal
kingdom of ova or sperms being derived from cells which are highly
differentiated in any other respect. In the vertebrata, the mesoblastic,
or mid-layer, cells, from which the germinal epithelium arises, have
certainly not been previously differentiated in any other line. And in
the case of the hydroid zoophytes, quoted by Professor Weismann, the
cells which give rise to the germinal products have never been so highly
differentiated as to lose the protoplasmic faculty of developmental
reproduction.
Some such view of developmental reproduction, based upon cellular
continuity and the division of labour, seems to me more in accord with
the general teachings of modern biology than a hypothetical and
arbitrary distinction between a supposed germ-plasm and a supposed
body-plasm.
To which category, then, does this hypothesis belong? Does it support
the view that the hen produces the egg or that the egg produces the hen?
Undoubtedly the latter. It is based on cellular continuity, and is
summarized by the scheme on p. 131. It adequately accounts for
hereditary continuity, for there is a continuity of the germinal cells,
the bearers of heredity. But how, it may be asked, on this view, or on
any continuity hypothesis, are the origin of variations and their
transmission to be accounted for? To this question we have next to turn.
But before doing so, it will be well to recapitulate and summarize the
positions we have so far considered.
We saw at the outset that the facts we have to account for are those of
heredity with variation. To lead up to the facts of sexual heredity, we
considered fission, the regeneration of lost parts, and budding in the
lower animals. We saw that, if a hydra be divided, each portion
reproduces appropriately the absent parts. But we found it difficult to
say whether this power resides, in such cases, in the cells along the
plane of section or in the general mass of cells which constitute the
regenerating portion.
Having led up to the sexual mode of reproduction, we inquired whether
the egg produces the hen or the hen produces the egg. We saw that there
is a marked difference between a _direct continuity_ of reproductive
cells, giving rise to body-cells as by-products, and an _indirect
continuity_ of reproductive cells, these cells giving rise to the hen,
and then the hen to fresh reproductive cells, which, on this view, are
to be regarded as concentrated essence of hen.
Darwin's hypothesis of pangenesis as exemplifying the latter view was
considered at some length, and the modifications suggested by Professor
Brooks, Mr. Galton, and Professor Herdman were indicated. The
hypothesis, so far as it is regarded as a theory of the main facts of
heredity, was rejected.
It was then pointed out that only in a few cases has a direct continuity
of germinal cells _as such_ been actually demonstrated. Whence Professor
Weismann has been led to elaborate his doctrine of the continuity of
germ-plasm. This germ-plasm can give rise to, but cannot originate from,
body-plasm. It may lurk in body-cells, which may, by its subsequent
development, be transformed into germ-cells. But any external influences
which may affect these body-cells produce no change on the germ-plasm
which they may contain. We regarded this hypothesis as a retrograde
step, much as we admire the genius of its propounder, and considered
that the fiction of two protoplasms, distinct and yet commingled, is
little calculated to advance our comprehension of organic processes.
In the known and observed phenomena of cellular continuity and
cell-differentiation, we found a sufficiently satisfactory hypothesis of
heredity. The reproductive cells are the outcome of normal
cell-division, and have been differentiated and set apart for the
special work of developmental reproduction, as others have been
differentiated and set apart for other protoplasmic functions. Such a
view adequately accounts for hereditary continuity, for there is a
continuity of the germinal cells, the bearers of heredity. But how, we
repeat, on this view or any other hypothesis of direct continuity, are
the origin of variations and their transmission to be accounted for?
* * * * *
Every individual organism reacts more or less markedly under the stress
of environing conditions. The reaction may take the form of passive
resistance, or it may be exemplified in the performance of specially
directed motor-activities. The power to react in these ways is inborn;
but the degree to which the power is exercised depends upon the
conditions of existence, and during the life of the individual the power
may be increased or diminished according to whether the conditions of
life have led to its exercise or not. The effects of training and
exercise on the performance of muscular feats and in the employment of
mental faculties are too well known to need special exemplification. By
manual labour the skin of the hand is thickened; and by long-continued
handling of a rifle a bony growth caused by the weapon in drilling, the
so-called _exercierknochen_ of the Germans, is developed. Now, it is
clear that if these acquired structures or faculties are transmitted
from parent to offspring, we have here a most important source and
origin of variations--a source from which spring variations just in the
particular direction in which they are wanted. The question is--Are they
transmitted? and if so, how?
Let us begin with the protozoa. Dr. Dallinger made some interesting
experiments on monads. They extended over seven years, and were directed
towards ascertaining whether these minute organisms could be gradually
acclimatized to a temperature higher than that which is normal to them.
Commencing at 60° Fahr., the first four months were occupied in raising
the temperature 10° without altering the life-history. When the
temperature of 73° was reached, an adverse influence appeared to be
exerted on the vitality and productiveness of the organism. The
temperature being left constant for two months, they regained their full
vigour, and by gradual stages of increase 78° was reached in five months
more. Again, a long pause was necessary, and during the period of
adaptation a marked development of vacuoles, or internal watery spaces,
was noticed, on the disappearance of which it was possible to raise the
temperature higher. Thus by a series of advances, with periods of rest
between, a temperature of 158° Fahr. was reached. It was estimated that
the research extended over half a million generations. Here, then, these
monads became gradually acclimatized to a temperature more than double
that to which their ancestors had been accustomed to--a temperature
which brought rapid death to their unmodified relatives.
Now, in such observations it is impossible to exclude elimination. It is
probable that there were numbers of monads which were unable to
accommodate themselves to the changed conditions, and were therefore
eliminated. But in any case, the fact remains that the survivors had, in
half a million generations, acquired a power of existing at a
temperature to which no individual in its single life could become
acclimatized. Here, then, we have the hereditary transmission of a
faculty. But the organisms experimented on were protozoa. In them there
is no distinction between germ-cell and body-cell. Multiplication is by
fission. And if the cell which undergoes fission has been modified, the
two separate cell-organisms which result from that fission will retain
the special modification. In such cases the transmission of acquired
characters is readily comprehensible. We have an hereditary summation of
effects.
With the metazoa the case is different. In the higher forms the germinal
cells are internal and sheltered from environing influences by the
protecting body-wall. It is the body-cells that react to environmental
stresses; it is muscle and nerve in which faculty is strengthened by use
and exercise, or allowed to dwindle through neglect. The germ-cells are
shielded from external influences. They lead a sheltered and protected
life within the body-cavity. It is no part of their business to take
part in either passive resistance or responsive activity. During the
individual life, then, the body may be modified, may acquire new tissue,
may by exercise develop enhanced faculties. But can the body so modified
affect the germ-cells which it carries within it?
Biologists are divided on this question. Some say that the body cannot
affect the germ; others believe that it can and does do so.
It might seem an easy matter to settle one way or another. But, in
truth, it is by no means so easy. Suppose that a man by strenuous
exercise brings certain muscles to a high degree of strength or
co-ordination. His son takes early to athletics, and perhaps excels his
parent. Is this a case of transmitted fibre and faculty? It may be. But
how came it that the father took to athletics, and was enabled to
develop so lithe and powerful a frame? It must have been "in him," as we
say. In other words, it must have been a product of the germ-cells from
which he was developed. And since his son was developed, in part at
least, from a germ-cell continuous with these, what more natural than
that he too should have an inherent athletic habit? Every faculty that
is developed in any individual is potential in the germ-stuff from which
he springs; the tendency to develop any particular faculty is there too;
and both faculty and tendency to exercise it are handed on by the
continuity of germ-protoplasm or germ-cells. Logically, there is no
escape from the argument if put as follows: The body and all its
faculties (I use the term "faculties" in the broadest possible sense)
are the product of the germ; the acquisition of new characters or the
strengthening of old faculties by the body is therefore a germinal
product; there is continuity of the germs of parent and child; hence the
acquisition by the child of characters acquired by the parent is the
result of germinal or cellular continuity. It is not the acquired
character which influences the germ, but the germ which develops what
appears to be an acquired character. Finally, if an acquired character,
so called, is better developed in the child than in the parent, what is
this but an example of variation? And if, in a series of generations,
the acquired character continuously increases in strength, this must be
due to the continued selection of favourable variations. It is clear
that the organism that best uses its organs has, other things equal, the
best chance of survival. It will therefore hand on to its offspring
germinal matter with an inherent tendency to make vigorous use of its
faculties.
Those who argue thus deny that the body-cells can in any way affect the
germ-cells. To account for any continuous increase in faculty, they
invoke variation and the selection of favourable varieties. What, then,
we may now ask, is, on their view, the mode of origin of variations?
In sexual reproduction, with the union of ovum and sperm, we seem to
have a fertile source of variation. The parents are not precisely alike,
and their individual differences are, _ex hypothesi_, germinal products.
In the union of ovum and sperm, therefore, we see the union of somewhat
dissimilar germs. And in sexual reproduction we have a constantly
varying series of experiments in germinal combinations, some of which,
we may fairly suppose, will be successful in giving rise to new or
favourable variations. This view, however, would seem to involve an
hypothesis which may be true, but which, in any case, should be
indicated. For it is clear that if new or favourable variations arise in
this way, the germinal union cannot be a mere mixture, but an organic
combination.
An analogy will serve to indicate the distinction implied in these
phrases. It is well known that if oxygen and hydrogen be mixed together,
at a temperature over 100°C., there will result a gaseous substance with
characters intermediate between those of the two several gases which are
thus commingled. But if they are made to combine, there will result a
gas, water-vapour, with quite new properties and characters. In like
manner, if, in sexual union, there is a mere mixture, a mere commingling
of hereditary characters, it is quite impossible that new characters
should result, or any intensification of existing characters be produced
beyond the mean of those of ovum and sperm. If, for example, it be true,
as breeders believe, that when an organ is strongly developed in both
parents it is likely to be even more strongly developed in the
offspring, and that weakly parts tend to become still weaker, this
cannot be the result of germinal mixture. Let us suppose, for the sake
of illustration, that a pair of organisms have each an available store
of forty units of growth-force, and that these are distributed among
five sets of organs, _a_ to _e_, as in the first two columns. Then the
offspring will show the organs as arranged in the third column.[BP]
Parents. Offspring.
----/\----
| |
_a_ 10 10 10
_b_ 8 10 9
_c_ 9 5 7
_d_ 7 9 8
_e_ 6 6 6
-- -- --
40 40 40
There is no increase in the set of organs _a_, which are strongly
developed in both parents; and no decrease in the set of organs e, which
are weakly developed in both parents. By sexual admixture alone there
can be no increase or decrease beyond the mean of the two parental
forms. If, then, the union of sperm and ovum be the source of new or
more favourable variations other than or stronger than those of either
parent, this must be due to the fact that the hereditary tendencies not
merely commingle, but under favourable conditions combine, in some way
different indeed from, but perhaps analogous to, that exemplified in
chemical combination.
Such organic combination, as opposed to mere commixture, is altogether
hypothetical, but it may be worth while to glance at some of its
implications. If it be analogous to chemical combination, the products
would be of a definite nature; in other words, the variations would be
in definite directions. Selection and elimination would not have to deal
with variations in any and all directions, but would have presented to
them variations specially directed along certain lines determined by the
laws of organic combination. As Professor Huxley has said, "It is quite
conceivable that every species tends to produce varieties of a limited
number and kind, and that the effect of natural selection is to favour
the development of some of these, while it opposes the development of
others along their predetermined line of modification." Mr. Gulick[BQ]
and others have been led to believe in a tendency to divergent evolution
residing in organic life-forms. Such a tendency might be due to special
modes of organic combination giving rise to particular lines of
divergence. Again, we have seen that some naturalists believe that
specific characters are not always of utilitarian significance. But, as
was before pointed out, on the hypothesis of all-round variation, there
is nothing to give these non-useful specific characters fixity and
stability, nothing to prevent their being swamped by intercrossing. If,
however, on the hypothesis of combination, we have definite organic
compounds, instead of, or as well as, mere hereditary mixtures; if, in
other words, variations take definite lines determined by the laws of
organic combination (as the nature and properties of chemical compounds
are determined by the laws of chemical combination), then this
difficulty disappears. There is no reason why a neutral divergence--one
neither useful nor deleterious--should be selected or eliminated. And if
its direction is predetermined, there is no reason why it should not
persist, though, of course, it will not be kept at a high standard by
elimination. It has again and again been pointed out as a difficulty in
the path of natural selection that, in their first inception, certain
characters or structures cannot yet be of sufficient utility to give the
possessor much advantage in the struggle for existence. If, however,
these be definite products of organic combination, this difficulty also
disappears. So long as they are not harmful, they will not be
eliminated, and by fortunate combinations will progress slowly until
natural selection gets a hold on them and pushes them forward,
developing to the full the inherent tendency. Finally, we must notice
that, on this hypothesis, our conception of panmixia, or intercrossing,
would have to be modified. As generally held, this doctrine is based
upon hereditary mixture, not organic combination. It is a doctrine of
means and averages. There is a good deal of evidence that intercrossing
does not, at least in all cases, produce mean or average results. And
according to the hypothesis of organic combination, it need not always
do so. According to this hypothesis, then, divergent modifications might
arise and be perpetuated without the necessity of isolation. Sterility
might result from the fact that divergence had been carried so far that
organic combination was no longer possible; reversion, due to
intercrossing, from the fact that combinations long rendered impossible
by the isolation of the necessary factors in distinct varieties, are
again rendered possible when these varieties interbreed.
On this hypothesis of organic combination, to which we shall recur in
the chapter on "Organic Evolution," the varied forms of animal life are
the outcome of definite organic products with definite organic
structure, analogous to the definite chemical compounds with definite
crystalline and molecular structure; and the analogy between the
regeneration of hydra and the reconstruction of a crystal is carried on
a step further. I do not say that I am myself at present prepared to
adopt the hypothesis, at least in this crude form; but it is, perhaps,
worth a passing consideration. Its connection with Mr. Herbert Spencer's
doctrine of physiological units is obvious. The analogy there is with
crystallization; here it is with chemical combination.
We must now return to the point which gave rise to this digression, and
repeat that mere hereditary commixture in the union of ovum and sperm
cannot give rise to new characters or raise existing structures (1)
where there is free intercrossing beyond the mean of the species, and
(2) where there is rigorous elimination beyond the existing maximum of
the species. Variations beyond this existing maximum must be due to some
other cause.
Professor Weismann has suggested, as a cause of variation, the extrusion
of the polar cells from the ovum. It has before been mentioned that,
generally previous to fertilization, the ripe ovum buds off two minute
polar bodies. The nucleus of the ovum divides, and one half is extruded
in the first polar cell; the nucleus then (except in parthenogenetic[BR]
forms, where there is no union of ovum and sperm) again divides, and a
second polar cell is extruded. In accordance with his special view of
the absolute distinction between the body-plasm and the germ-plasm, the
first polar cell is formed to carry off the body-plasm of the
ovum-nucleus. For the ovum, besides being a germ-bearer, is a
specialized cell, and its special form is determined by the body-plasm
it contains. This is got rid of in the first polar cell, and nothing but
germ-plasm remains. Now, if nothing further took place, all the ova of
this same individual containing similar germ-plasm would be identical,
and similarly with all the sperms from the same parent. The union of
these similar ova from one parent with similar sperms from another
should therefore give rise to similar offspring. But the offspring are
not all similar; they vary. Professor Weismann here makes use of the
second polar cell.[BS] "A reduction of the germ-plasm," he says, "is
brought about by its formation, a reduction not only in quantity, but
above all, in the complexity of its constitution. By means of the second
nuclear division, the excessive accumulation of different kinds of
hereditary tendencies or germ-plasms is prevented. With the nucleus of
the second polar body, as many different kinds of plasm are removed from
the egg as will be afterwards introduced by the sperm-nucleus." "If,
therefore, every egg expels half the number of its ancestral germ-plasms
during maturation, the germ-cells of the same mother cannot contain the
same hereditary tendencies, unless we make the supposition that
corresponding ancestral germ-plasms chance to be retained by all eggs--a
supposition that cannot be sustained."
The two polar cells are therefore, on this view, of totally different
character; and the nuclear division in each case of a special kind and
_sui generis_. I do not think that the evidence afforded by observation
lends much support to this view. But with that we are not here specially
concerned. We have to consider how this reduction of the number of
ancestral germ-plasms can further the kind of variation required. Now,
it is difficult to see, and Professor Weismann does not explain, how the
getting rid of certain ancestral tendencies can give rise to new
characters or the enhancement of old characters. One can understand how
this "reducing division," as Dr. Weismann calls it, can reduce the level
of now one and now another character. But how it can raise the level
beyond that attained by either parent is not obvious. It is perhaps
possible, though Professor Weismann does not, I think, suggest it, that,
by a kind of compensation,[BT] the reduction of certain characters may
lead to the enhancement of others. Let us revert to the illustration on
p. 150, where each individual has an available store of forty units of
growth-force; and let us express by the minus sign the units lost in the
parents by the extrusion of the polar cell and an analogous process
which may occur in the genesis of the sperm. Then the units of
growth-force which may thus be lost by a "reducing division" in _b_,
_c_, and _e_ may be, in the offspring, applied to the further growth of
_a_; thus--
Parents. Offspring.
-------/\------
| |
_a_ 10 10 14
_b_ 8-1 10-3 7
_c_ 9-1 5-1 6
_d_ 7 9 8
_e_ 6-2 6 5
Here the reduction of the characters _b_, _c_, and _e_ has led to the
enhancement of _a_, which thus stands at a higher level than in either
parent.
On such an hypothesis we may, perhaps, explain the fact to which
breeders of stock testify--that the organ strongly developed in both
parents (_a_) is yet more strongly developed in some of their offspring,
and that weakly parts (_e_) tend to become still weaker. I know not
whether this way of putting the matter would commend itself to Professor
Weismann or his followers; but some such additional hypothesis of
transference of growth-force from one set of organs to another set of
organs seems necessary to complete his hypothesis.
Professor Weismann's view, then, assumes (1) that the cell-division
which gives rise to the ova in the ovary is so absolutely equal and
similar that all ova have precisely the same characters; (2) that the
first polar cell leaves the germinal matter unaffected, merely getting
rid of formative body-plasm; (3) that the nuclear division giving rise
to the second polar cell is unequal and dissimilar, effecting the
differential reduction of ancestral germ-plasms. Concerning all of which
one can only say that it may be so, but that there is not much evidence
that it is so. And, without strong confirmatory evidence, it is
questionable whether we are justified in assuming these three quite
different modes of nuclear division.
There remains one more question for consideration, on the hypothesis
that the germ-cells cannot in any special way be affected by the
body-cells. In considering the union of ovum and sperm as a source of
variation, we have taken for granted the existence of variations. We
have been dealing with the mixture or combination of already existing
variations. How were variations started in the first instance?
We have already seen that in the protozoa parent and offspring are
still, in a certain sense, one and the same thing; the child is a part,
and usually half, of the parent. If, therefore, the individuals of a
unicellular species are acted upon by any of the various external
influences, it is inevitable that hereditary individual differences will
arise in them; and, as a matter of fact, it is indisputable that changes
are thus produced in these organisms, and that the resulting characters
are transmitted. Hereditary variability cannot, however, arise in the
metazoa, in which the germ-plasm and the body-plasm are differentiated
and kept distinct. It can only arise in the lowest unicellular
organisms. But when once individual difference had been attained by
these, it necessarily passed over into the higher organisms when they
first appeared. Sexual reproduction coming into existence at the same
time, the hereditary differences were increased and multiplied, and
arranged in ever-changing combinations. Such is Professor Weismann's
solution of the difficulty, told, for the most part, in his own words.
I do not know that Professor Weismann has anywhere distinctly stated
what he conceives to be the relation of body-plasm and germ-plasm in the
protozoa. Are the two as yet undifferentiated? This can hardly be so,
seeing the fundamental distinction he draws between them. Is it the
germ-plasm or the body-plasm that is influenced by external stresses? If
the former, does it transfer its influence to the body-plasm during the
life of the individual? If the latter, then the body-plasm must either
directly influence the germ-plasm in unicellular organisms (it would
seem that, according to Professor Weismann, it cannot do so in the
metazoa), or the changed body-plasm, which shares in the fission of the
protozoon, must participate in that so-called immortality which is often
said to be the special prerogative of germinal matter.
These, however, are matters for Professor Weismann and his followers to
settle. I regard the sharp distinction between body-plasm and germ-plasm
as an interesting biological myth. For me, it is sufficient that the
protoplasm of the protozoon is modified, and the modification handed on
in fission. And it is clear that Professor Weismann is correct in saying
that the commixture or combination of characters takes its origin among
the protozoa. If the unicellular individuals are differently modified,
however slightly, then, whenever conjugation occurs between two such
individuals, there will be a commingling or combination of the different
characters. The transmissible influence of the environment, however,
ceases when the metazoon status is reached, and special cells are set
apart for reproductive purposes--ceases, that is to say, in so far as
the influence on the body is concerned. There may, of course, be still
some direct[BU] influence on the germinal cells themselves. Except for
this further influence, the metazoon starts with the stock of variations
acquired by that particular group of protozoa--whatever it may be--from
which it originated. All future variations in even the highest metazoa
arise from these.
Now, it is obvious that no mere commingling and rearrangement of
protozoan characters could conceivably give rise to the indefinitely
more complex metazoan characters. But if there be a combination and
recombination of these elements in ever-varying groups, the
possibilities are no longer limited. Let us suppose that three simple
protozoan characters were acquired. The mere commixture of these three
could not give much scope for further variation. It would be like mixing
carbon, oxygen, and hydrogen in varying proportions. But let them in
some way combine, and you have, perhaps, such varied possibilities as
are open to chemical combinations of oxygen, hydrogen, and carbon, whose
name is legion, but whose character is determined by the laws of
chemical combination.
Summing up now the origin of variations, apart from those which are
merely individual, on the hypothesis that particular modifications of
the body-cells cannot be transmitted to the germ-cells, we have--
1. In protozoa, the direct influence of the environment and the induced
development of faculty.
2. In metazoa--
(_a_) Some direct and merely general influence of the environment on the
germ, including under the term "environment" the nutrition, etc.,
furnished by the body.
(_b_) The combination and recombination of elementary protoplasmic
faculties (specific molecular groupings) acquired by the protozoa.
(_c_) Influences on the germ, the nature of which is at present unknown.
* * * * *
We may now pass on to consider the position of those who give an
affirmative answer to the question--Can the body affect the germ? Two
things are here required. First, definite evidence of the fact that the
body does so affect the germ; i.e. that acquired characters are
inherited. Secondly, some answer to the question--How are the body-cells
able to transmit their modifications to the germ-cells? We will take the
latter first, assuming the former point to be admitted.
Let us clearly understand the question. An individual, in the course of
its life, has some part of the epidermis, or skin, thickened by
mechanical stresses, or some group of muscles strengthened by use, or
the activity of certain brain-cells quickened by exercise: how are the
special modifications of these cells, here, there, or elsewhere in the
body, communicated to the germ, so that its products are similarly
modified in the offspring? The following are some of the hypotheses
which have been suggested:--
(_a_) Darwin's pangenesis.
(_b_) Haeckel's perigenesis; Spencer's physiological units.
(_c_) The conversion of germ-plasm into body-plasm, and its return to
the condition of germ-plasm (Nägeli).
(_d_) The unity of the organism.
(_a_) Concerning pangenesis, nothing need be added to what has already
been said. Although, as we have seen, it has been adopted with
modifications by Professor Brooks; although Mr. Francis Galton, a
thinker of rare ability and a pioneer in these matters, while contending
for continuity, admitted a little dose of pangenesis; although De Vries
has recently renewed the attempt to combine continuity and a modified
pangenesis;--this hypothesis does not now meet with any wide acceptance.
(_b_) With the pamphlet in which Professor Haeckel brought forward his
hypothesis termed the perigenesis of the plastidule, I cannot claim
first-hand acquaintance. According to Professor Ray Lankester, who gave
some account of it in _Nature_,[BV] protoplasm is regarded by Haeckel as
consisting of certain organic molecules called plastidules. These
plastidules are possessed of special undulatory movements, or
vibrations. They are liable to have their undulations affected by every
external force, and, once modified, the movement does not return to its
pristine condition. By assimilation, they continually increase to a
certain size and then divide, and thus perpetuate in the undulatory
movement of successive generations the impressions or resultants due to
the action of external agencies on the individual plastidules. On this
view, then, the form and structure of the organism are due to the
special mode of vibration of the constituent plastidules. This vibration
is affected by external forces. The modified vibration is transmitted to
the plastidules by the germ, which, therefore, produce a similarly
modified organism. As Mr. J. A. Thomson says, "In metaphorical language,
the molecules remember or persist in the rhythmic dance which they have
learned."
Darwin's hypothesis was frankly and simply organic--the gemmules are
little germs. This of Professor Haeckel tries to go deeper, and to
explain organic phenomena in terms of molecular motion. Mr. Herbert
Spencer long ago suggested that, just as molecules are built up, through
polarity, into crystals, so physiological units are built up, under the
laws of organic growth, into definite and special organic forms. Both
views involve special units. With Mr. Herbert Spencer, their "polarity"
is the main feature; with Professor Haeckel, their "undulatory
movements." According to Mr. Spencer, "if the structure of an organism
is modified by modified function, it will impress some corresponding
modification on the structures and polarities of its units."[BW]
According to Professor Haeckel, the vibrations of the plastidules are
permanently affected by external forces. In either case, an explanation
is sought in terms of molecular science, or rather, perhaps, on
molecular analogies. So far good. Such "explanation," if hypothetical,
may be suggestive. It may well be that the possibilities of fruitful
advance will be found on these lines.
But though, as general theories, these suggestions may be valuable, they
do not help us much in the comprehension of our special point. To talk
vaguely about "undulatory movements" or "polarities" does not enable us
to comprehend with any definiteness how this particular modification of
these particular nerve-cells is so conveyed to the germ that it shall
produce an organism with analogous nerve-cells modified in this
particular way.
(_c_) The hypothesis that the germ-plasm may be converted into
body-plasm, which, on its return again to the condition of germ-plasm,
may retain some of the modifications it received as body-plasm, seems to
be negatived, so far as most animals are concerned, by the facts of
embryology and development. The distinction of germ-plasm and body-plasm
I hold to be mythical. And there is no evidence that cells specially
differentiated along certain lines can become undifferentiated again,
and then contribute to the formation of ova or sperms. From the
view-point of cell-differentiation, which seems to me the most tenable
position, there does not seem any evidence for, or any probability of,
the occurrence of any roundabout mode of development of the germinal
cells which could enable them to pick up acquired characters _en route_.
(_d_) We come now to the contention that the organism, being one and
continuous, if any member suffers, the germ suffers with it. The organs
of the body are not isolated or insulated; the blood is a common medium;
the nerves ramify everywhere; the various parts are mutually dependent:
may we not, therefore, legitimately suppose that long-continued
modification of structure or faculty would soak through the organism so
completely as eventually to modify the germ? The possibility may fairly
be admitted. But how is the influence of the body brought to bear on the
germ? The common medium of the blood, protoplasmic continuity, the
influence of the products of chemical or organic change,--these are well
enough as vague suggestions. But how do they produce their effects? Once
more, how is this increased power in that biceps muscle of the oarsman
able to impress itself upon the sperms or the ova? No definite answer
can be given.
We are obliged to confess, then, that no definite and satisfactory
answer can be given to the question--How can the body affect the germ so
that this or that particular modification of body-cells may be
transmitted to the offspring? We may make plausible guesses, or we may
say--I know not how the transmission is effected; but there is the
indubitable fact.
This leads us to the evidence of the fact.
It must be remembered that no one questions the modifiability of the
individual. That the epidermis of the oarsman's hand is thickened and
hardened; that muscles increase by exercise; that the capacity for
thinking may be developed by steady application;--these facts nobody
doubts. That well-fed fish grow to a larger size than their ill-fed
brethren; that if the larger shin-bone (the tibia) of a dog be removed,
the smaller shin-bone (the fibula) soon acquires a size equal to or
greater than that of the normal tibia; that if the humerus, or arm-bone,
be shifted through accident, a new or false joint will be formed, while
the old cavity in which the head of the bone normally works, fills up
and disappears; that canaries fed on cayenne pepper have the colour of
the plumage deepened, and bullfinches fed on hemp-seed become black;
that the common green Amazonian parrot, if fed with the fat of siluroid
fishes, becomes beautifully variegated with red and yellow; that climate
affects the hairiness of mammals;--these and many other reactions of the
individual organism in response to environing conditions, will be
admitted by every one.[BX] That constitutional characters of germinal
origin are inherited is also universally admitted. The difficulty is to
produce convincing evidence that what is acquired is really inherited,
and what is inherited has been really acquired.
Attempts have been made to furnish such evidence by showing that certain
mutilations have been inherited. I question whether many of these cases
will withstand rigid criticism. Nor do I think that mutilations are
likely to afford the right sort of evidence one way or the other. We
must look to less abnormal influences. What we require is evidence in
favour of or against the supposition that _modifications_ of the
body-cells are transmitted to the germ-cells. Now, these modifications
must clearly be of such a nature as to be receivable by the cells
without in any way destroying their integrity. The destruction or
removal of cells is something very different from this. If it were
proved that mutilations are inherited, this would not necessarily show
that normal cell-modifications are transmissible. And if the evidence in
favour of inherited mutilations breaks down, as I believe it does, this
does not show that more normal modifications such as those with which we
are familiar, as occurring in the course of individual life, are not
capable of transmission. I repeat, we must not look to mutilations for
evidence for or against the supposition that acquired characters are
inherited. We must look to less abnormal influences.
These readily divide themselves into two classes. The first includes the
direct effects on the organism of the environment--effects, for example,
wrought by changes of climate, alteration of the medium in which the
organism lives, and so forth. The second comprises the effects of use
and disuse--the changes in the organism wrought by the exercise of
function.
Taking the former first, we have the remarkable case of _Saturnia_,
which was communicated to Darwin by Moritz Wagner. Mr. Mivart thus
summarizes it: "A number of pupæ were brought, in 1870, to Switzerland
from Texas of a species of _Saturnia_, widely different from European
species. In May, 1871, the moths developed out of the cocoons (which had
spent the winter in Switzerland), and resembled entirely the Texan
species. Their young were fed on leaves of _Juglans regia_ (the Texan
form feeding on _Juglans nigra_), and they changed into moths so
different, not only in colour, but also in form, from their parents,
that they were reckoned by entomologists as a distinct species."[BY]
Professor Mivart also reminds us that English oysters transported to the
Mediterranean are recorded by M. Costa to have become rapidly like the
true Mediterranean oyster, altering their manner of growth, and forming
prominent diverging rays; that setters bred at Delhi from carefully
paired parents had young with nostrils more contracted, noses more
pointed, size inferior, and limbs more slender than well-bred setters
ought to have; and that cats at Mombas, on the coast of Africa, have
short, stiff hair instead of fur, while a cat from Algoa Bay, when left
only eight weeks at Mombas, underwent a complete metamorphosis--having
parted with its sandy-coloured fur. Very remarkable is the case of the
brine-shrimp _Artemia_, as observed and described by Schmankewitsch. One
species of this crustacean, _Artemia salina_, lives in brackish water,
while _A. milhausenii_ inhabits water which is much saltier. They have
always been regarded as distinct species, differing in the form of the
tail-lobes and the character of the spines they bear. And yet, by
gradually altering the saltness of the water, either of them was
transformed into the other in the course of a few generations. So long
as the altered conditions remained the same, the change of form was
maintained.
Many naturalists believe that climate has a direct and determining
effect on colour, and contend or imply that it is hereditary. Mr. J. A.
Allen correlates a decrease in the intensity of colour with a decrease
in the humidity of the climate. Mr. Charles Dixon, in his "Evolution
without Natural Selection," says, "The marsh-tit (_Parus palustris_) and
its various forms supply us with similar facts [illustrative of the
effects of climate on the colours of birds]. In warm, pluvial regions we
find the brown intensified; in dry, sandy districts it is lighter;
whilst in Arctic regions it is of variable degrees of paleness, until,
in the rigorous climate of Kamschatka, it is almost white." Mr. Dixon
does not think that these changes are the result of natural selection.
"Depend upon it," he says, with some assurance,[BZ] in considering a
different case, "it is the white of the ptarmigan (modified by climatic
influence) that has sent the bird to the snowy wastes and bare
mountain-tops, and rigorously keeps it there; not the bird that has
assumed, by a long process of natural selection, a white dress to
conceal itself in such localities." Professor Eimer[CA] contends that in
the Nile valley the perfectly gradual transition in the colour of the
inhabitants from brownish-yellow to black in passing from the Delta to
the Soudan is particularly conclusive for the direct influence of
climate, for the reason that various races of originally various colours
dwell there.
Mr. A. R. Wallace says[CB] of the island of Celebes "that it gives to a
large number of species and varieties (of Papilionidæ) which inhabit it,
(1) an increase of size, and (2) a peculiar modification in the form of
the wings, which stamp upon the most dissimilar insects a mark
distinctive of their common birthplace." But this similarity may
largely, or at least in part, be due to mimicry. Most interesting and
valuable are the results of Mr. E. B. Poulton's experiments on
caterpillars and chrysalids.[CC] They show that there is a definite
colour-relation between the caterpillar (e.g. the eyed hawk-moth,
_Smerinthus ocellatus_) and its food-plant, adjustable within the limits
of a single life; that the predominant colour of the food-plant is
itself the stimulus which calls up a corresponding larval colour; that
there is also a direct colour-relation between the chrysalids of the
small tortoiseshell butterfly (_Vanessa urticæ_) and the surrounding
objects, the pupæ being dark grey, light grey, or golden, according to
the nature and colour of the surroundings; and that the larvæ of the
emperor moth (_Saturnia carpini_) spin dark cocoons in dark
surroundings, but white ones in lighter surroundings. These are but
samples of the interesting results Mr. Poulton has obtained.
What shall we say of such cases? Some of them seem to indicate the very
remarkable and interesting fact that changes of salinity of the medium,
or changes of food, or the more general influence of a special climate,
may modify organisms in _particular_ and little-related ways. The larvæ
of a Texan _Saturnia_ fed on a new food-plant develop into imagos so
modified as to appear new species. Changes of salinity of the water
modify one species of _Artemia_ into another. If these be adaptations,
the nature of the adaptation is not obvious. If the new character
produced in this way be of utilitarian value, where the utility comes in
is not clear. The facts need further confirmation and extension, which
may lead to very valuable results. Mr. Poulton's observations,
on the other hand, give us evidence of direct adaptation to
colour-surroundings. But the effects are, in the main, restricted to the
individual. What is hereditary is the power to assume one of two or
three tints, that one being determined by the surrounding colour. His
experiments neither justify a denial nor involve an assertion of the
transmissibility of environmental influence. Secondly, some of the cases
above cited seem to show clearly that, under changed conditions of life,
the changes which have been wrought in one generation may _reappear_ in
the next. But are they inherited? Is there sufficient evidence to show
conclusively that the body-cells have been modified, and have handed on
the modification to the germ? Can we exclude the direct action of the
more or less saline water, or the products of the unwonted food on the
germinal cells? Can we be sure that there is really a summation of
results--that each generation is not affected _de novo_ in a similar
manner? No one questions that the individual is modifiable, and that
such modification is most readily effected in the early and plastic
stages of life. If each plastic embryo is moulded in turn by similar
influence, how can we conclusively prove hereditary summation? Take a
case that has been quoted in support of hereditary modification.
Greyhounds transported from England to the uplands of Mexico are unable
to course, owing to the rarity of the atmosphere. Their pups are,
however, able to run down the fleetest hares without difficulty. Now,
this may be due to the fact that the dogs acquire a certain amount of
accommodation to a rare atmosphere, and hand on their acquired power to
their offspring, which carry it on towards perfection. But it may also
be due to the fact that the pups, subject from the moment of birth to
the conditions of a rarified atmosphere, are developed in accordance
with these conditions.
Or take another case that has been brought forward. English dogs are
known in hot climates, like that of India, to degenerate in a few
generations. Let us suppose that these degenerate dogs are removed back
to England, and that their pups, born in English air and in our
temperate climate, are still degenerate: would not this, it may be
asked, show that the influence of climate on the body is inherited? I do
not think that such a case would be convincing. For the climate might
well influence the germ through the body. The body being unhealthy and
degenerate, the germ-cells must, one may suppose, suffer too. The
degenerate pup born in England might well owe its degeneracy to effects
wrought upon the germinal cells. In other words, such a case would
indicate some _general_ influence of the environment (including the
environing body) on the germ. It does not convince us that _particular_
modifications of body-cells as such are transmitted under normal and
healthy conditions.
On the whole, it seems to me that the evidence we at present possess on
this head is not convincing or conclusive in favour of the effects on
the body alone being transmitted to offspring. If cases can be brought
forward in which there can be no direct influence on the germ, in which
elimination is practically excluded, and in which there is a _gradual
and increasing_ accommodation of successive generations of organisms to
changed conditions _which remain constant_, then such transmission will
be rendered probable. I do not know that there are observations of this
kind of sufficient accuracy to warrant our accepting this conclusion as
_definitely proved_.
Attention may here be drawn to a peculiar and remarkable mode of
influence. If a pure-bred mare have foals by an ill-bred sire, they will
be ill-bred. This we can readily understand. But if she subsequently
have a foal by a perfectly well-bred sire, that foal, too, may in some
cases be tainted by the blemish of the previous sire. So, too, with
dogs. If a pure-bred bitch once produce a mongrel litter, no matter how
carefully she be subsequently matched, she will have a tendency to give
birth to pups with a mongrel taint. This subsequent influence of a
previous sire is a puzzling fact. It may be that some of the male
germ-nuclei are absorbed, and influence the germ-cells of the ovary. But
this seems an improbable solution of the problem. It is more likely,
perhaps, that in the close relation of mother and f[oe]tus during
gestation, each influences the other (how it is difficult to say). On
this view the bitch retains the influence of the mongrel puppies--is
herself, in fact, partially mongrelized--and therefore mongrelizes
subsequent litters. It would not be safe, however, to base any
far-reaching conclusions on so peculiar a case, the explanation of which
is so difficult. At all events, it is impossible to exclude the
possibility of direct action on the germ, though the _particular_ nature
of the results of such influence are noteworthy.
We may pass now to the evidence that has been adduced in favour of a
cumulative effect in the exercise of function, or of the inheritance of
the results of use or disuse. Here, again, it must be remembered that no
one questions the effects of use and disuse in the individual. What we
seek is convincing evidence that such effects are inherited.
Physiologically, the effects of use or disuse are, in the main, effects
on the relative nutrition, and hence on the differential growth of
organs. When an organ is well exercised, there is increased nutrition
and increased growth of tissue, muscular, nervous, glandular, or other.
When an organ is, so to speak, neglected, there is diminished
blood-supply, diminished growth, and diminished functional power. The
development of a complex activity would necessitate a complex adjustment
of size and efficiency of parts, involving a nice balance of
differential growth dependent on delicately regulated nutrition. What is
the evidence that adjusted nutrition can be inherited?
With regard to man, there is some evidence which bears upon this
subject. Mr. Arbuthnot Lane, in his valuable papers in the _Journal of
Anatomy and Physiology_, has shown that certain occupations, such as
shoemaking, coal-heaving, etc., produce recognizable effects upon the
skeleton, the muscular system, and other parts of the organization. And
he believes[CD] that such effects are inherited, being very much more
marked in the third generation than they were in the first. Sir William
Turner informed Professor Herdman that, in his opinion, the peculiar
habits of a tribe, such as tree-climbing among the Australians, or those
natives of the interior of New Guinea whose houses are built in the
upper branches of lofty trees, not only affect each generation
individually, but have an intensified action through the influence of
heredity.[CE]
Mr. Francis Galton's results mainly deal with human faculty; and though
faculty has undoubtedly an organic basis, I do not propose to consider
the evidence afforded by instinct, intelligence, or intellectual
faculties in this chapter. Mention should, however, be made of the
interesting results of his study of twins. Twins are either of the same
sex, in which case they are remarkably alike, or of different sexes, in
which case they are apt to differ even more widely than is usual with
brothers and sisters. The former are believed to be developed from one
ovum which has divided into two halves, each of which has given rise to
a distinct individual; the latter from two different ova. Mr. Galton
collected a large mass of statistics concerning twins of both classes.
The result of this analysis seems to be that, in the case of "identical
twins," the resemblances are not superficial, but extremely intimate;
that they are not apt to be modified to any large extent by the
circumstances of life; that where marked diversity sets in it is due to
some form of illness; and, on the whole, that innate tendencies
outmaster acquired modifications. "Nature is far stronger than nurture
within the limited range that I have been careful to assign to the
latter." On the other hand, speaking of dissimilar twins, Mr. Galton
says, "I have not a single case in which my correspondents speak of
originally dissimilar characters having become assimilated through
identity of nurture." "The impression that all this evidence leaves on
the mind is one of some wonder whether nurture can do anything at all,
beyond giving instruction and professional training." "There is no
escape from the conclusion that nature prevails enormously over nurture
where the differences of nurture do not exceed what is commonly to be
found among persons of the same rank of society and in the same
country."[CF]
Combining the results of Messrs. Lane and Galton, we may say that it
requires persistent and long-continued influence to modify the
individual, and change, even by a little, the structure inherited or
given by nature; but that if this structure is thus modified, there may
be a tendency for such modification to increase by hereditary summation
of effects. We require, however, further and fuller observations to
render the evidence of such hereditary summation to any extent
convincing.
Turning now from the evidence afforded by man[CG] to that afforded by
animals, we may consider first that presented by domesticated breeds.
They might be expected to afford exceptionally good examples. Their
modifiability and the readiness with which they interbreed are two of
the determining causes of their selection for domestication. They have,
moreover, been placed under new conditions of life, and they undoubtedly
exhibit changes of structure, many of which Darwin[CH] regarded as
attributable to the effects of use and disuse. In domestic ducks, the
relative weight and strength of the wing-bones have been diminished,
while conversely the weight and strength of the leg-bones have been
increased. The bones of the shoulder-girdle have been decreased in
weight and "the prominence of the crest of the sternum, relatively to
its length, is also much reduced in all the domestic breeds. These
changes," says Darwin, "have evidently been caused by the lessened use
of the wings." The shoulder-girdle and breast-bone of domestic fowls
have been similarly reduced. After a careful consideration of numerous
facts concerning the brains of rabbits, Darwin concluded that this "most
important and complicated organ in the whole organization is subject to
the law of decrease in size from disuse." And Sir J. Crichton Browne has
recently shown that, in the wild duck, the brain is nearly twice as
heavy in proportion to the body as it is in the comparatively imbecile
domestic duck. In pigs, the nature of the food supplied during many
generations has apparently affected the length of the intestines; for,
according to Cuvier, their length to that of the body in the wild boar
is as 9 to 1, in the common domestic boar as 13.5 to 1, and in the Siam
breed as 16 to 1. With regard to horses, Darwin tells us that
"veterinarians are unanimous that horses are affected with spavins,
splints, ring-bones, etc., from being shod and from travelling on hard
roads, and they are almost unanimous that a tendency to these
malformations is transmitted."
These are samples of the effects of domestication. It has been
suggested, however, that, quite apart from any diminution from disuse,
the reduction of size in parts or organs may be the result of the
absence or cessation of selection. If an organ be subject to selection,
the mean size in adult creatures will be that of the selected
individuals; but if selection ceases, it will be the mean of those born.
Let us suppose that nine individuals are born, and that the size of some
organ varies in these from 1, the most efficient, to 9, the least
efficient. The birth-mean will therefore be, as shown on the left-hand
side of the following table, at the level of number 5, four being more
efficient, and four less efficient. But if, of these nine, six be
eliminated, then the mean of the survivals will be as shown on the
right-hand side of the table:--
1
2--Survival-mean.
3
4 }
Birth-mean--5 }
6 } Eliminated individuals.
7 }
8 }
9 }
The result, then, of the cessation of selection will be to reduce the
survival-mean to the birth-mean, and that without any necessary effect
of disuse. But unless this be accompanied by a tendency to diminution
due to economy of growth or some other cause, this cannot produce any
well-marked or considerable amount of reduction. I very much question,
for example, whether the cessation of selection, even with the
co-operation of the principle of economy of growth, will adequately
account for the reduction to nearly one-half its original proportion of
the brain of the duck. The subject will be more fully discussed,
however, in the next chapter.
There is probably but little tendency for disused parts to be reduced in
size through artificial selection. An imbecile duck does not probably
taste nicer than one with bigger brains. On the other hand, the increase
of size in organs may presumably, in certain cases, be increased by
selection. Pigs, for example, have been selected according to their
fattening capacity. Those with longer intestines, and therefore
increased absorbent surface, may well have an advantage in this respect.
Hence, in selecting pigs for fattening, breeders may have been
unconsciously selecting those with the longest intestines. Of course, on
this view, the longer intestine must be there to be selected, and the
increased length must be due to variation. But this may be all-round
variation (cause unknown), not variation in one direction, the result of
increased function.
Another point that has to be taken into consideration is the amount of
_individual_ increment or decrement, owing to individual use or disuse,
apart from any possible summation of results.
Seeing, then, that it is difficult to estimate the amount of purely
individual increment or decrement, and that it is difficult, if not
impossible, to exclude the disturbing effects of cessation of selection
with economy of growth on the one hand, reducing the size of organs, and
artificial selection on the other hand, increasing the size or
efficiency of parts, it is clear that such cases cannot afford
convincing evidence that the observed variations are the directly
inherited results of use and disuse. Indeed, I am not aware of any
experiments or direct observations on animals which are individually
conclusive in favour of the hereditary summation of functionally
produced modifications.
It may, however, be said--Although no absolutely convincing experiments
or observations are forthcoming (for, from the nature of the case, it is
almost impossible logically to prove that this interpretation of the
facts is alone possible), still there are cases which are much more
readily explained on the hypothesis that the effects of use and disuse
are inherited, than on any other hypothesis. But, so far as Professor
Weismann and his followers are concerned, such an argument is wholly
beside the question. They are ready to admit that inherited
modifications of the body, if they could be proved, would render the
explanation of many results of evolution much easier. It would, no
doubt, they say, be easier to account for the shifting of the eye of a
flat-fish from one side of the head to the other on the supposition that
individual efforts were inherited, until, by an hereditary summation of
effort, the eye at last came round. The question is--Are we justified in
accepting the easier explanation if it be based on a mere assumption, at
present unproved, the _modus operandi_ of which is inexplicable?
Let us consider very briefly these two points--first, the "mere
assumption;" secondly, "the inexplicable _modus operandi_." Is there any
reason why we should not assume the inheritance of effects of use or
disuse as a working hypothesis, if it is not in opposition to any known
biological law, and if it does enable us to explain certain observed
phenomena? I see no such reason. We do not know enough about the causes
of variation to be rigidly bound by the law of parcimony. I am not aware
of any biological law that would render the acceptance of this view as a
provisional hypothesis unjustifiable.
But how, it is asked, can we accept it if its _modus operandi_ is
inexplicable? I question the validity of this argument. I fear our
knowledge of organic nature is not at present so full and exact as to
justify us in excluding an hypothesis because we are not able to give an
adequate answer to the question--How are these effects produced? Of
course, if it can be shown that no _modus operandi_ is possible, there
is an end of the matter. But who shall dare thus to limit the
possibilities of organic nature? And, if possible, then that natural
selection in which the neo-Darwinians place their sole trust would
certainly develop so advantageous a mode of influence. It is clear that
a species sensitive to every shock of the environment on the organism
would be unstable, and hence at a disadvantage. But, on the other hand,
the ability to answer by adaptation to long-continued and persistent
environmental influence or to oft-repeated and consistent performance of
function would be so distinct an advantage to the species which
possessed it, that, if it lay within the possibilities of organic
nature, natural selection, always, as we are told, on the look out for
every possible advantage, would assuredly seize upon it and develop it.
Those who believe in the absolute sway of natural selection have not at
present given any adequate answer to the question--How are particular
variations (e.g. the twisted skull of flat-fish) produced? They say that
constitutional variations, which are alone inheritable, are due to
variations in the germs. When asked how these variations are produced,
they are forced to reply--We cannot say. But when it is suggested that
they may be in some unknown way transmitted to the germ from the body,
they are up in arms, and exclaim--You have no right to believe that, or
ask us to believe it, unless you can tell us plainly how the effect is
produced. Unable themselves to give the _modus operandi_ of the origin
of particular variations, they demand the exact _modus operandi_ from
those who suggest that variations may arise through this mode of
influence of the body on the germ.
We shall have to consider this question from a more general standpoint
in the next chapter on "Organic Evolution." We may now very briefly
summarize some of the results we have reached in this chapter.
The ova and sperms are specially differentiated cells which have, in the
division of labour, retained and emphasized the function of
developmental reproduction.
There is a continuity of such cells. The cells which become ova or
sperms have never become differentiated into anything else.
Hereditary similarity is due to the fact that parents and offspring are
derived eventually from the same germinal cells.
Variation in the existing world is partly due to sexual union. But if
there be mere admixture, new characters cannot arise in this way, nor
can old characters be strengthened beyond the existing maximum.
Some mode of organic combination (analogous to chemical combination)
might afford an explanation of the occurrence of new variations and the
increase of existing characters.
In the protozoa there may be a summation of the effects of the
environment in succeeding generations.
There is no convincing evidence that in the metazoa special
modifications of the body so influence the germ as to become hereditary.
But there is no reason why such influence should not be assumed as a
provisional hypothesis.
NOTES
[BD] "Animals and Plants under Domestication," vol ii. p. 239.
[BE] Or in certain "physiological units" (Herbert Spencer), or
"plastidules" (Haeckel), which may be regarded as organic
molecules exhibiting their special properties under vital
conditions.
[BF] _Nature_, vol. xxxix. p. 486.
[BG] Darwin, "Animals and Plants under Domestication," 2nd edit., vol.
ii. chap. xxvii., from which the following description and
quotations are taken.
[BH] For an excellent account of the genesis and growth of the modern
views of heredity, see Mr. J. Arthur Thomson's paper on "The
History and Theory of Heredity:" Proceedings of the Royal Society
of Edinburgh, 1889.
[BI] Geddes and Thomson, "The Evolution of Sex," p. 92.
[BJ] Weismann, "Essays on Heredity," English translation, p. 173.
[BK] Weismann, "Essays on Heredity," p. 205.
[BL] A few pages earlier (p. 200) in the same essay, Professor Weismann
says, "A sudden transformation of the nucleo-plasm of a somatic
cell into that of a germ-cell would be almost as incredible as the
transformation of a mammal into an am[oe]ba." This at first sight
does not seem quite consistent with the subsequent sentence which
I have quoted in the text; for here, at any rate, the daughters of
"mammals" are said to be converted into "am[oe]bæ." But this is no
doubt because the am[oe]bæ (germ-plasms) are _contained in_ the
mammals (body-cells). (See the quotations that follow in the
text.)
[BM] Weismann, "Essays on Heredity," p. 207.
[BN] Weismann, "Essays on Heredity," p. 179.
[BO] It will, of course, be understood that a minute fragment of
germ-plasm is capable of almost unlimited growth by assimilation
of nutritive material, its properties remaining unchanged during
such growth.
[BP] Latency is here neglected. Mr. Francis Galton has shown,
statistically, that the offspring, among human folk, inherit 1/4
from each parent, 1/16 from each grandparent, and the remaining
1/4 from more remote ancestors. In domesticated animals, reversion
to characters of distant ancestors sometimes occurs. This,
however, does not invalidate the argument in the text, which is
that sexual admixture tends towards the mean of the race
(ancestors included), and cannot be credited with new and
unusually favourable variations. The prepotency of one parent is
also here neglected.
[BQ] See his valuable paper on "Divergent Evolution," Lin. Soc. Zool.,
No. cxx.
[BR] One parthenogenetic form--the drone--has been shown by Blochmann
to extrude a second polar cell. This observation is in serious
opposition to Dr. Weismann's theory.
[BS] Weismann, "Essays on Heredity," pp. 355, 378.
[BT] The law of compensation of growth or balancement was suggested at
nearly the same time by Goethe and Geoffrey Saint-Hilaire. The
application in the text has not, so far as I know, been before
suggested.
[BU] Darwin spoke of changed conditions acting "directly on the
organization or indirectly through the reproductive system." Now,
since Professor Weismann has taught us to reconsider these
questions, we speak of such conditions as acting directly on the
germ or indirectly through the body. The germ is no longer
subordinate to the body, but the body to the germ.
[BV] July 15, 1876. Since reprinted in "The Advancement of Science," p.
273.
[BW] Herbert Spencer, "Principles of Biology," vol. i. p. 256.
[BX] Mr. J. A. Thomson has published a most valuable "Synthetic Summary
of the Influence of the Environment upon the Organism"
(Proceedings Royal Physiological Society, Edinburgh: vol. ix. pt.
3, 1888). The case of the Amazonian parrots was communicated to
Darwin by Mr. Wallace ("Animals and Plants under Domestication,"
vol. ii. p. 269).
[BY] St. George Mivart, "On Truth," p. 378.
[BZ] _Op. cit._, p. 47. I venture to say, "with some assurance,"
because Charles Darwin, who had also considered this matter,
writes, "Who will pretend to decide how far the thick fur of
Arctic animals, or their white colour, is due to the direct action
of a severe climate, and how far to the preservation of the
best-protected individuals during a long succession of
generations?" ("Animals and Plants under Domestication," p. 415).
[CA] "Organic Evolution," English translation, p. 88.
[CB] "Contributions to Natural Selection," p. 197.
[CC] Since this was written, Mr. Poulton has described his results in
an interesting volume on "The Colours of Animals" (_q.v._).
[CD] See _Journal of Anatomy and Physiology_, vol. xxii. p. 215.
[CE] See Professor Herdman's Inaugural Address, Liverpool Biological
Society, 1888.
[CF] Francis Galton, "Inquiries into Human Faculty," p. 216.
[CG] That the epidermis is thicker on the palms of the hands and the
soles of the feet in the infant long before birth, may be
attributable to the inherited effects of use or pressure. It can
hardly be held that the thickening of the skin in these parts is
of elimination value.
[CH] The instances cited are from "Animals and Plants under
Domestication."
CHAPTER VI.
ORGANIC EVOLUTION.
It is difficult to realize the wealth, the variety, the diversity, of
"animal life." Even if we endeavour to pass in review all that we have
seen in woodland and meadow, in pond or pool, in the air, on the earth,
in the waters, in temperate or tropical regions; even when we try to
remember the results of all anatomical and microscopic investigation
displaying new wonders and new diversities hidden from ordinary and
unaided vision; even when we call to mind the multifarious contents,
recent and fossil, of all the natural history museums we have ever
visited, and throw in such mental pictures as we have formed of all the
diverse adaptations we have read about or heard described;--even so we
cannot but be conscious that not one-tenth, not one-hundredth, part of
the diversity and variety of animal life has passed before our mental
vision even in sample. It is said that our greatest living poet once,
when a young man, left his companions to gaze into the waters of a
clear, still pool. "What an imagination God has!" he said, as he
rejoined his friends. Fit observation for the poet, whose sensitive
nature must be keenly alive to the varied endowments which Nature has
lavishly showered upon her animate children.
Certain it is that words, mere words, can never present, though they may
aid in recalling, an adequate picture of either the wealth or the beauty
of animal life. Fortunately for those who visit London (and who nowadays
does not?), we have, in our national collection in South Kensington, the
means of getting some insight into the wealth of life. And much is being
done there to aid the imagination and to facilitate study for those who
are not professed students. Many of the birds are now to be seen set in
their natural surroundings, with their life-history illustrated. Our
frontispiece is taken from one of these cases. And this admirable system
will, no doubt, so far as space permits, be extended; and, perhaps,
dramatic incidents may be introduced, like those (notably in the life of
heron and hawk) which form so marked a feature in the little museum at
Exeter. Anything which leads us to understand the life of animals, and
to go forth and study it for ourselves, has an educational value.
In our National Museum, again, much is being wisely done to illustrate
the diversity and variety of structure and the principles that underlie
them. Observe, as you enter the central hall, the case containing
stuffed specimens of ruffs (_Machetes pugnax_). Among the young autumn
birds there is not much difference between males and females, the male
being distinguished chiefly by its somewhat larger size. Nor do the old
birds, male and female, differ much during the winter months. But in
pairing-time, May and June, the females are somewhat richer in colour;
while the males not only don the ruff to which the bird owes its popular
name, but develop striking colour-tints. Among different individuals it
will be seen that the colour-variation is tolerably wide; but the same
individual keeps strictly, we are told, in successive seasons, to the
same summer dress. Note, next, in a bay to the right, the great variety
of form, ornamentation, and colouring among the molluscan shells there
exhibited. Observe that the rich colours are often hidden during life by
the dull epidermis. Half an hour's attentive study of these varied
molluscan forms will give a better idea of the beauty and diversity of
these life-products than pages of mere description.
Pass on, too, to note, in a further bay to the right, the extraordinary
modifications of the antenna, or feeler, in insects. There is the long,
whip-like form in the locust; the clubbed whip in the ant-lion and the
butterfly; the feathered form in certain moths and flies; the hooked
form characteristic of the sphinx-moths; the many-leaf form in the
lamellicorn beetles, like the cockchafer; and the feathered plate of
other beetles. Equally wonderful are the diverse developments of the
mouth-organs of insects, the spiral tube of the butterfly or moth, the
strong jaws of the great beetles, the lancets of the gnat, the
sucking-disc of the fly,--all of them special modifications of the same
set of structures. Then, in the same bay, note some of the striking
differences between the males and females of certain insects. In some
there is an extraordinary difference in size (e.g. the locust
_Xiphocera_, and the moth _Attacus_); in others, like the stag-beetle,
it is the size of the jaws that distinguishes the males; in others,
again, the most notable differences are in the length, development, or
complexity of the antennæ, or feelers; in some beetles the males have
great horns on the head or thorax; while in many butterflies it is in
richness of colour that the difference chiefly lies--the brilliant green
of the _Ornithoptera_ there exhibited contrasting strongly with the
sober brown of his larger mate.
The fact that the special characteristics of the male, which we have
seen to be variable in the ruff, are also variable among insects, is
well exemplified in the case of the stag-beetle, in some males of which
the mandibles are far larger than in others. This is shown in Fig. 22,
which is copied from the series displayed in the British Museum, by the
kind permission of Professor Flower.
[Illustration: Fig. 22.--Variations in the size of, and especially in
the head and mandibles of, the male stag-beetle (_Lucanus cervus_).
(From an exhibit in the British Natural History Museum.)]
Crossing the hall to where the vertebrate structures are displayed, the
development of hair, of feathers, of teeth, the modifications of the
skull and of legs, wings, and fins are being exemplified. Note here and
elsewhere the special adaptations of structure, of which we may select
two examples. The first is that seen in the _Balistes_, or trigger-fish.
The anterior dorsal fin is reduced to three spines, of which that which
lies in front is a specially modified weapon of defence, while that
which follows it is the so-called trigger. These two are so hinged to
the underlying interspinous bones and so related to each other that,
when once the defensive spine in front is erected, it cannot be forced
down until the trigger is lowered. The second example of special
adaptation is well displayed in specimens of the mud-tortoise _Trionyx_.
Between the last vertebra of the neck and the first fixed vertebra of
the dorsal series is a beautiful hinge-joint, enabling the neck to be
bent back, S-fashion, when the creature withdraws its head within the
carapace. These are only one or two particular instances of what any one
who will visit the National Museum may see for himself admirably
displayed and illustrated.
No one can, one would suppose, pass through the galleries in Cromwell
Road and remain quite insensible to the beauties of animal life. Beauty
of form and beauty of colour are conspicuously combined in many species
of birds and insects. And much of this colour-beauty and splendid
iridescence is known to be due to minute scales, to thin films of air or
fluid, and to microscopically fine lines developed upon scales or
feathers. But there is one phase of beauty which cannot be exhibited in
the museum--the beauty that comes of life as opposed to death. For this
we must go out into the free air of nature, where the animals not only
have lived, but are still instinct with the glow of life, and where the
silence of the museum galleries is replaced by the song of birds and the
hum of insect-wings.
How have this wealth, this diversity, this beauty, this manifold
activity, which we summarize under the term "animal life," been
produced?
If we answer this question in a word--the word "evolution"[CI]--we must
remember that this word merely expresses our belief in a general fact;
and we must not forget that many questions remain behind, all centering
round that little question, to which an adequate answer is so difficult
to give, the question--How? Reduced to its simplest expression, the
doctrine of evolution merely states that the animal world as it exists
to-day is naturally developed out of the animal world as it existed
yesterday, and will in turn develop into the animal world as it shall
exist to-morrow. This is the central belief of the evolutionist. No
matter what moment in the past history of life you select, the life at
that moment was in the act of insensibly passing from the previous
towards a future condition. Then at once arises the question--Does life
remain the same yesterday, to-day, and to-morrow? A thousand indubitable
facts at once make answer--No! Underlying the law of continuity there is
a law of change. Life to-day is not what it was yesterday, nor will it
be to-morrow the same as to-day. What, then, is the nature of this
change? If it be replied that the change must be either for the better
or the worse, we shall have to answer the further question--Better or
worse in what respects?
Let us narrow our view from the contemplation of life as a whole to the
more particular consideration of an organism as one of its constituent
units. The individual life of that organism depends on (some would say
consists in) its ceaseless adaptation to surrounding circumstances. The
circumstances remaining the same, or only varying within constant
limits, the adaptation may be _more_ or _less_ perfect. A change in the
direction of more perfect adaptation will be a change for the better, a
tendency to less perfect adaptation will be a change for the worse.
But the relation of an organism to its circumstances or environment is
itself subject to change. The environment itself may alter, or the
organism may be brought into relation with a new environment. We have to
consider not only the changes in an organism in the direction of more or
less perfect adaptation to its environment, but also changes in the
environment. These changes are in the direction of increased simplicity
or of increased complexity. So that we may say that the modification of
life is in the direction of more or of less complete adaptation to
simpler or to more complex conditions. Where the adaptation advances to
more complex conditions, we speak of elaboration; where it retrogrades
to less complex conditions, we speak of degeneration; but both fall
under the head of evolution in its more general sense. Viewed as a
whole, there can be little doubt that the general tendency of evolution
is towards more complete adaptation to more diverse and complex
environment. And this tendency is accompanied by a general increase of
differentiation and of integration; of differentiation whereby the
constituent elements of life, whether cells, tissues, organs, organisms,
or groups of organisms, become progressively more specialized and more
different from one another; of integration whereby these elements become
progressively more interdependent one on the other. We may conveniently
sum up the tendency towards more perfect adaptation to more complex
circumstances in the word _progress_; the tendency to differentiation in
the word _individuality_; and the tendency to integration in the word
_association_.
Nobody now doubts the propositions thus briefly summarized, and it is
therefore unnecessary to bring forward evidence in their favour.
We may pass, then, to the question--How? Evolution being continuity,
associated with change, tending in certain directions, and accompanied
by certain processes, how has it been effected? What are its methods?
_Natural Selection._
Natural selection claims a foremost place. We have already devoted a
chapter to its consideration. Animals vary; more are born than can
survive to procreate their kind; hence a struggle for existence, in
which the weaker and less adapted are eliminated, the stronger and
better adapted surviving to continue the race.
It is scarcely possible to over-estimate what Darwin's labour and genius
have done for the study of animal life. Through Darwin's informing
spirit, biology has become a science. But now we must be on our guard.
So long as natural selection was winning its way to acceptance, every
application of the theory had to be made with caution, and was subjected
to keen, if sometimes ignorant, criticism. Now there is, perhaps, some
danger lest it should suffer the Nemesis of triumphant creeds, and be
used blindly as a magic formula.
First, we should be careful not to use the phrase, "of advantage to the
species," vaguely and indefinitely, but should in all cases endeavour
clearly to indicate wherein lies the particular advantage, and how its
possession enables the organism to escape elimination; next, we must
remember that the advantage must be immediate and present, prospective
advantage being, of course, inoperative; then we must endeavour to show
that the advantage is really sufficient to decide the question of
elimination or non-elimination; lastly, we must distinguish between
indiscriminate and differential destruction, between mere numerical
reduction by death or otherwise and selective elimination.
(1) In illustration of the first point, we may select a passage from the
writings of even so great a biologist as Professor Weismann. As is well
known, Professor Weismann believes that senility and death are no part
of the natural heritage of animal life, but have been introduced among
the metazoa on utilitarian grounds. In his earlier papers, he attributed
the introduction of death, and the tissue-degeneration that precedes it,
to the direct action of natural selection.[CJ] More lately, he
attributes it to the cessation of selection.[CK] Concerning this later
view, we shall have somewhat to say presently; we may now consider the
former as an example of too indefinite a use of such phrases as "of
advantage to the species." "Worn-out individuals," says Professor
Weismann, "are not only valueless to the species, but they are even
harmful, for they take the places of those which are sound. Hence, by
the operation of natural selection, the life of our hypothetically
immortal individual would be shortened by the amount which was useless
to the species. It would be reduced to a length which would afford the
most favourable conditions of existence of as large a number as possible
of vigorous individuals at the same time." This may be so, but, as it
stands, the _modus operandi_ is not given, and is not obvious. We start
with a hypothetically immortal metazoon. Barring accidents, it will go
on existing indefinitely. But you cannot bar accidents for an indefinite
time; hence, the longer the individual lives, the more defective and
crippled it becomes. There is neither natural decay nor natural death
here. The organism is gradually crippled through accident and injury.
But the crippled individuals are harmful to the species, because they
take the places of those which are sound. Therefore, says Professor
Weismann, natural decay and death step in to take them off before they
have time to become cripples. Now, the point I wish to notice is that
there is no definite statement how or why natural decrepitude should
thus be introduced. We must remember that it is not until a late stage
in evolution that, through the association of its members, groups of
organisms compete with other groups. In the earlier stages, when we must
suppose decrepitude and death to arise on Professor Weismann's
hypothesis, the law of the struggle for existence is--each for himself
against all. The question, therefore, is--What advantage _to the
individual_ is there in natural decay and death to enable it, through
the possession of these attributes, to escape elimination? Surely none
as such. At the same time, it is quite conceivable that natural decay
and death may be the penalty the individual has to pay for increased
strength and vitality in the early stages of life. This, probably, was
Professor Weismann's meaning. But, if so, it would surely have been
better to state the matter in such a way as to lay the chief stress on
the really important feature, and to say that, through natural
selection, those individuals have survived which exhibited predominant
strength and vitality for a shortened period, even at the expense of
natural decay and death. The increased life-power, not the seeds of
decay and death, was that which natural selection picked out for
survival, or rather that which elimination allowed to survive.
In such ways--a short life with heightened activity being of advantage
to some forms, a more prolonged existence at a lower level of vitality
being essential to others--natural selection may have determined in some
degree the relative longevity of different organisms. That it caused the
introduction of senility as a preparation for death is a less tenable
hypothesis.
And here we may note, in passing, that in using the phrase, "of
advantage to the race or species," we must steadily bear in mind the
fact that it is with _individuals_ that the process of elimination
deals. In the individual it is that every modification must make good
its claim to existence and transmission. Where the principle of
association for mutual benefit obtains, as in the case of social
insects, it is still the individual that must resist elimination.
Self-sacrifice, whether conscious or unconscious, must not be carried so
far as to lead to the elimination of the self-sacrificing individual,
for in this event it cannot but defeat its own ends. Within these
limits, self-sacrifice is of advantage, as in the case of parental
self-sacrifice, in that it enables certain other individuals to escape
elimination. We should endeavour, then, not to use the phrase, "of
advantage to the species," vaguely and indefinitely, but to indicate in
what particular ways certain individuals are to be so advantaged as to
escape the Nemesis of elimination.
(2) The second point that I mentioned above scarcely needs
exemplification. That the advantage which enables an organism to escape
elimination must be present and existent, not merely prospective, is
obvious. Still, the mistake is sometimes made. I have heard it stated
that feathers were evolved for the sake of flight. But clearly, unless
the wing sprang into existence already sufficiently developed for
flight, this would be impossible. The same is true of the first stages
of many structures which could not be of service for the purpose and use
to which they were subsequently turned. Not impossibly, the earliest
"wings" were for diving, and flight was, so to speak, an after-thought.
Undoubtedly, structures which have been fostered under the wing of one
form of advantage have been subsequently applied to new purposes, and
fostered through new modes of adaptation. Teeth, for example, are
probably modified scales, such as are found in the thorn-back skate. But
the early development of these scales could have had no reference to
their future application to purposes subservient to alimentation.
Again, such and such a structure is sometimes spoken of as a "prevision
against emergencies." In his interesting and valuable work on "The
Colours of Animals," for example, Mr. E. B. Poulton says, "Dimorphism
[in the larvæ of butterflies and moths] is also valuable in another way:
the widening range of a species may carry it into countries in which one
of its forms may be especially well concealed, while in other countries
the other form may be more protected. Thus a dimorphic form is more
fully provided against emergencies than one with only a single form."
And after giving, as an example, the fact that the convolvulus hawk-moth
has a browner and a greener form of caterpillar, of which the browner is
more prevalent under European conditions, and the greener under those
which obtain in the Canary Islands, Mr. Poulton adds, "This result
appears to have been brought about by the ordinary operation of natural
selection, leading to the extermination of the less-protected variety."
Now, I do not mean for one moment to imply that so careful and able a
naturalist as Mr. Poulton believes that any character has been evolved
through natural selection in prevision for future emergencies. But I do
think that his statement is open to this criticism.
(3) It is sometimes said, in bold metaphor, that natural selection is
constantly on the watch to select any modification, however slight,
which is of advantage to the species. And it is true that elimination is
ceaselessly operative. But it is equally certain that the advantage must
be of sufficient value to decide the question whether its possessor
should be eliminated or should escape elimination. If it does not reach
this value, Natural Selection, watch she never so carefully, can make no
use of it. Elimination need not, however, be to the death; exclusion
from any share in continuing the species is sufficient. To breed or not
to breed, that is the question. Any advantage affecting this essential
life-function will at once catch the eye of a vigilant natural
selection. But it must be of sufficient magnitude for the machinery of
natural selection to deal with. That machinery is the elimination of a
certain proportion of the individuals which are born. Which shall be
eliminated, and which shall survive, depends entirely on the way in
which the individuals themselves come out in life's competitive
examination. The manner in which that examination is conducted is often
rude and coarse, too rough-and-ready to weigh minute and infinitesimal
advantages.
What must be the value of a favourable or advantageous modification to
decide the question of elimination, to make it an _available advantage_,
must remain a matter of conjecture. It will vary with the nature and the
pressure of the eliminative process. And perhaps it is scarcely too much
to say that, at present, we have not observational grounds on which to
base a reliable estimate in a single instance. We must not let our
conviction of its truth and justice blind us to the fact that natural
selection is a logical inference rather than a matter of direct
observation. A hundred are born, and two survive; the ninety-eight are
eliminated in the struggle for existence; we may therefore infer that
the two escaped elimination in virtue of their possession of certain
advantageous characters. There is no flaw in the logic that has thus
convinced the world that natural selection is a factor in evolution. But
by what percentage of elimination-marks the second of the two successful
candidates beats the senior on the list of failures we do not know. We
can only see that, on the hypothesis of natural selection, it must have
been sufficiently appreciable to determine success or failure.
(4) And then, to come to our fourth point, we must remember that, apart
from the differentiating process of elimination, there is much
fortuitous destruction. A hundred are born, and but two survive. But of
the ninety-eight which die, and fail to procreate, how many are
eliminated, how many are fortuitously destroyed, we do not find it easy
to say. And indiscriminate destruction gets rid of good, bad, and
indifferent alike. It is a mistake to say that of the hundred born the
two survivors are necessarily the very best of the lot. It is quite
possible that indiscriminate destruction got rid of ninety of all sorts,
and left only ten subject to the action of a true elimination. "In the
majority of birds," says Professor Weismann, "the egg, as soon as it is
laid, becomes exposed to the attacks of enemies; martens and weasels,
cats and owls, buzzards and crows, are all on the look out for it. At a
later period, the same enemies destroy numbers of the helpless young,
and in winter many succumb in the struggle against cold and hunger, or
to the numerous dangers which attend migration over land and
sea--dangers which decimate the young birds." There is here, first, a
certain amount of fortuitous destruction; secondly, some selection
applied to the eggs; thirdly, a selection among the very young
nestlings; and, fourthly, a selection among the young migratory birds.
What may be the proportion of elimination to destruction at each stage
it is difficult to say. Among the eggs and fry of fishes fortuitous
destruction probably very far outbalances the truly differentiating
process.
_Panmixia and Disuse._
We may now pass on to consider shortly some of the phenomena of
degeneration, and the dwindling or disappearance of structures which are
no longer of use.
Many zoologists believe, or until lately have believed, that disuse is
itself a factor in the process. Just as the well-exercised muscle is
strengthened, so is the neglected muscle rendered weak and flabby. Until
recently it was generally held that the effects of such use or disuse
are inherited. But now Professor Weismann has taught us, if not to doubt
ourselves, at least to admit that doubt is permissible. On the older
view, the gradual dwindling of unused parts was readily comprehensible.
But now, if Professor Weismann is right, we must seek another
explanation of the facts; and, in any case, we may be led to recognize
other factors (than that of disuse alone) in the process.
Professor Weismann regards panmixia, or free intercrossing, when the
preserving influence of natural selection is suspended, as the efficient
cause of a reduction or deterioration in the organ concerned. And Mr.
Romanes had, in England, drawn attention to the fact that the "cessation
of natural selection" would lead to some dwindling of the organ
concerned, since it was no longer kept up to standard. In illustration
of his panmixia, Professor Weismann says, "A goose or duck must possess
strong powers of flight in the natural state, but such powers are no
longer necessary for obtaining food when it is brought into the
poultry-yard, so that a rigid selection of individuals with
well-developed wings at once ceases among its descendants. Hence, in the
course of generations, a deterioration of the organs of flight must
necessarily ensue, and the other members and organs of the bird will be
sensibly affected."[CL] And, again, "As at each stage of retrogressive
transformation individual fluctuations always occur, a continued decline
from the original degree of development will inevitably, although very
slowly, take place, until the last remnant finally disappears."[CM] Now,
I think it can be shown that panmixia, or the cessation of selection,
alone cannot affect much reduction. It can only affect a reduction from
the "survival-mean" to the "birth-mean." This was referred to in the
chapter on "Heredity and the Origin of Variations," but may be again
indicated. Suppose the number of births among wild ducks be represented
by the number nine, of which six are eliminated through imperfections in
the organs of flight. Let us place the nine in order of merit in this
respect, as is done in the table on p. 172. The average wing-power of
the nine will be found in No. 5, there being four ducks with superior
wing-power (1-4), and four with inferior wing-power (6-9). The
birth-mean will therefore be at the level of No. 5, as indicated to the
left of the table. But if six ducks with the poorest wings be
eliminated, only three survive. The average wing-power will now be found
in No. 2, one duck being superior and one inferior to it in this
respect. It is clear that this survival-mean is at a level of higher
excellence than the birth-mean. Now, when the ducks are placed in a
poultry-yard, selection in the matter of flight ceases, and, since all
nine ducks survive, the survival-mean drops to the birth-mean. We may
variously estimate this retrogression; but it cannot be a large
percentage--I should suppose, in the case under consideration, one or
two per cent. at most. But Professor Weismann says, "A _continued_
decline from the original degree of development must inevitably take
place." It is not evident why such decline should continue. If
variations continue in the same proportion as before, the birth-mean
will be preserved, since there are as many positive or favourable
variations above the mean as there are negative or unfavourable
variations below the mean. A continuous decline must result from a
preponderance of negative over positive variations, and for this some
other principle, such as atavism, or reversion to ancestral characters,
must be called in. But in the case of so long-established and stable an
organ as that of flight, fixed and rendered constant through so many
generations, it is hardly probable that reversion would be an important
factor. Mr. Galton has calculated that among human-folk the offspring
inherits one-fourth from each parent, one-sixteenth from each
grandparent, leaving one-fourth to be contributed by more remote
ancestors. There is no doubt, however, that among domesticated animals
reversion occurs to characters which have been lost for many
generations. But we should probably have to go a very long way back in
the ancestry of wild ducks for any marked diminution in wing-power. It
must be remembered that, in the case of the artificial selection of
domesticated animals, man has been working against and not with the
stream of ancestral tendency. Reversion in their case is towards a
standard which was long maintained and had become normal before man's
interference. Reversion in domesticated ducks should therefore be
towards the greater wing-power of their normal ancestry before
domestication, not in the direction of lessened wing-power and
diminished wing-structure. The whole question of reversion is full of
interest, and needs further investigation.
In the dwindling of disused structures, Mr. Romanes has suggested
"failure of heredity" as an efficient cause. I find it difficult,
however, to distinguish this failure of heredity from the effects of
disuse. To what other cause is the failure of heredity due? If natural
selection has intervened to hasten this failure, this can only be
because the failure is advantageous, since it permits the growth-force
to be applied more advantageously elsewhere. And this involves a
different principle. Even so it is difficult to exclude the possibility
(to put it no stronger) that the diversion of growth-force from a less
useful to a more useful organ is in part due to the use of the one and
the disuse of the other. But of disuse Mr. Romanes says, "There is the
gravest possible doubt lying against the supposition that any really
inherited decrease is due to the inherited effects of disuse." We may
fairly ask Mr. Romanes, therefore, to explain to what cause the failure
of heredity is due. In any case, Professor Weismann and his school are
not likely to accept this failure of heredity as an efficient factor in
the process. Nor is Professor Weismann likely to fall back upon any
innate tendency to degeneration. Unless, therefore, some cause be shown
why the negative variations should be prepotent over the positive
variations, we must, I think, allow that unaided panmixia cannot affect
any great amount of reduction.
In this connection we may notice Professor Weismann's newer view of the
introduction of bodily mortality. He says, "The problem is very easily
solved if we seek assistance from the principle of panmixia. As soon as
natural selection ceases to operate upon any character, structural or
functional, it begins to disappear. As soon, therefore, as the
immortality of somatic [body-] cells became useless, they would begin to
lose this attribute."[CN] Even granting that panmixia could continuously
reduce the size of ducks' wings, it is not easy to see how it could get
rid of immortality. The essence of the idea of panmixia is that, when
the natural selection which has raised an organ to a high functional
level, and sustains it there, ceases or is suspended, the organ drops
back from its high level. But on Professor Weismann's hypothesis,
immortality has neither been produced nor is it sustained by natural
selection. How, therefore, the cessation of selection can cause the
disappearance of immortality--a character with which natural selection
has had nothing whatever to do--Professor Weismann does not explain. He
seems to be using "panmixia" in the same vague way that, in his previous
explanation, he used "natural selection."
If panmixia alone cannot, to any very large extent, reduce an organ no
longer sustained by natural selection, to what efficient cause are we to
look? Mr. Romanes has drawn attention to the reversal of selection as
distinguished from its mere cessation. When an organ is being improved
or sustained by selection, elimination weeds out all those which have
the organ in an ill-developed form. Under a reversal of selection,
elimination will weed out all those which possess the organ well
developed. In burrowing animals, the eyes may have been reduced in size,
or even buried beneath the skin, through a reversal of selection. The
tuco-tuco (_Ctenomys_), a burrowing rodent of South America, is
frequently blind. One which Darwin kept alive was in this condition, the
immediate cause being inflammation of the nictitating membrane. "As
frequent inflammation of the eyes," says Darwin, "must be injurious to
any animal, and as eyes are certainly not necessary to animals having
subterranean habits, a reduction in their size, with the adhesion of the
eyelids and growth of fur over them, might in such cases be an
advantage; and, if so, natural selection would aid the effect of
disuse."[CO] Granting that the inflammation of the eyes is a sufficient
disadvantage to lead to elimination, such cases may be assigned to the
effects of a reversal of selection.
Perhaps the best instances of the reversal of selection are to be found
in the insects of wind-swept islands, in which, as we have already seen
(p. 81), the power of flight has been gradually reduced or even done
away with. Such instances are, however, exceptional. And one can hardly
suppose that such reversal of selection can be very far-reaching in its
effects, at least, through any direct disadvantage from the presence of
the organ. One can hardly suppose that the presence of an eye in a
cave-dwelling fish[CP] could be of such direct disadvantage as to lead
to the elimination of those members which still possess this structure.
But may it not be of indirect disadvantage? May not this structure be
absorbing nutriment which would be more advantageously utilized
elsewhere? This is Darwin's principle of economy. Granting its
occurrence, is it effective? We may put the matter in this way: The
crustacea which have been swept into a dark cave may be divided into
three classes so far as fortuitous variations of eyes and antennæ are
concerned. First, those which preserve eyes and antennæ in the original
absolute and relative proportion and value; secondly, those in which,
while the eyes remain the same, the antennæ are longer and more
sensitive; thirdly, those in which, while the antennæ are longer and
more sensitive, the eyes are reduced in size and elaboration. According
to the principle of economy, the third class have sufficient advantage
over the first and second to enable them to survive and escape the
elimination which removes those with fully developed eyes. It may be so.
We cannot estimate the available advantage with sufficient accuracy to
deny it. But we may fairly suppose that, in general, it is only where
the useless organ in question is of relatively large size, and where
nutriment is deficient, that economy of growth is an important factor.
We may here note the case of the hermit crab as one which exemplifies
degeneration through the reversal of natural selection. This animal, as
is well known, adopts an empty whelk-shell or other gasteropod shell as
its own. The hinder part of the body which is thus thrust into the shell
loses its protective armour, and is quite soft. Professor Weismann seems
to regard this loss of the hardened cuticle as due entirely to panmixia.
If what has been urged above has weight, this explanation cannot be
correct. No amount of promiscuous interbreeding of crabs could reduce
the cuticle to a level indefinitely below that of any of the
interbreeding individuals. But it is clear that an armour-sheathed
"tail" would be exceedingly ill adapted to thrusting into a whelk-shell.
Hence there would, by natural selection, be an adaptation to new needs,
involving not the higher development of cuticle, but the reverse. So far
as the cuticle is concerned, it is a case of reversed selection. Whether
this reversal alone will adequately account for the facts is another
matter.
Mr. Herbert Spencer has made a number of observations and measurements
of the jaws of pet dogs, which lead him to conclude that there has been
a reduction in size and muscular power due to disuse. The creatures
being fed on sops, have no need to use to any large extent the
jaw-muscles. In this case, he argues, the principle of economy is not
likely to be operative, since the pampered pet habitually overeats, and
has therefore abundant nutriment and to spare to keep up the jaws. It is
possible, however, that artificial selection has here been a factor.
There may have been a competition among the old ladies who keep such
pets to secure the dear little dog that never bites, while the nasty
little wretch that does occasionally use his jaws for illegitimate
purposes may have been speedily eliminated. Pet dogs are, moreover, a
pampered, degenerate, and for the most part unhealthy race, often
deteriorated by continued in-breeding, so that we must not build too
much on Mr. Spencer's observations, interesting as they undoubtedly are.
There is one feature about the reduction of organs which must not be
lost sight of. They are very apt to persist for a long time as remnants
or vestiges. The pineal gland is the vestigial remnant of a structure
connected with the primitive, median, or pineal eye. The whalebone
whales and the duck-bill platypus have teeth which never cut the gum and
are of no functional value. With regard to these, it may be asked--If
disuse leads to the reduction of unused structures, how comes it that it
has not altogether swept away these quite valueless structures? In
considering this point, we must notice the unfortunate and misleading
way in which disuse is spoken of as if it were a positive determinant,
instead of the mere absence of free and full and healthy exercise. Few
will question the fact that in the individual, if an organ is to be kept
up to its full standard of perfection, it must be healthily and
moderately exercised; and that, if not so exercised, it will not only
cease to increase in size, but will tend to degenerate. The healthy,
functionally valuable tissue passes into the condition of degenerate,
comparatively useless tissue. Now, those who hold that the inheritance
of functional modifications is still a tenable hypothesis, carry on into
the history of the race that which they find to hold good in the history
of the individual. They believe that, in the race, the continued
functional activity of an organ is necessary for the maintenance of the
integrity and perfection of its structure, and that, if not so
exercised, the organ will inevitably tend to dwindle to embryonic
proportions and to degenerate. The healthy, functionally valuable tissue
passes at last into the condition of degenerate, comparatively useless
tissue. The force of heredity will long lead to the production in the
embryo of the structure which, in the ancestral days of healthy
exercise, was to be of service to the organism. At this stage of life
the conditions have not changed. The degeneration sets in at that period
when the ancestral use is persistently denied. There is no reason why
"disuse" should in all cases remove all remnants of a structure; but if
the presence of the degenerate tissue is a source of danger to the
organism which possesses it, that organism will be eliminated, and those
(1) which possess it in an inert, harmless form, or (2) in which it is
absent, will survive. Thus natural selection (which will fall under Mr.
Romanes's reversed selection) will step in--will in some cases reduce
the organ to a harmless and degenerate rudiment, and in others remove
the last vestiges of the organ.
On the whole, even taking into consideration the effects of panmixia, of
reversed selection, and of the principle of economy, the reduction of
organs is difficult to explain, unless we call into play "disuse" as a
co-operating factor.
_Sexual Selection, or Preferential Mating._
It is well known that, in addition to and apart from the primary sexual
differences in animals, there are certain secondary characters by which
the males, or occasionally the females, are conspicuous. The antlers of
stags, the tail of the peacock, the splendid plumes of the male bird of
paradise, the horns or pouches of lizards, the brilliant frilled crest
of the newt, the gay colours of male sticklebacks, the metallic hues of
male butterflies, and the large horns or antennæ of other
insects,--these and many other examples which will at once occur to the
reader are illustrations of the fact.
As a contribution towards the explanation of this order of phenomena,
Darwin brought forward his hypothesis of sexual selection, of which
there are two modes. In the first place, the males struggle together for
their mates; in this struggle the weakest are eliminated; those
possessed of the most efficient weapons of offence and defence escape
elimination. In the second place, the females are represented as
exercising individual choice, and selecting (in the true sense of the
word) those mates whose bright colours, clear voices, or general
strength and vigour render them most pleasing and attractive. For this
mode I shall employ the term "preferential mating." Combining these two
in his summary, Darwin says, "It has been shown that the largest number
of vigorous offspring will be reared from the pairing of the strongest
and best-formed males, victorious in contests over other males, with the
most vigorous and best-nourished females, which are the first to breed
in the spring. If such females select the more attractive and, at the
same time, vigorous males, they will rear a larger number of offspring
than the retarded females, which must pair with the less vigorous and
less attractive males. So it will be if the more vigorous males select
the more attractive and, at the same time, healthy and vigorous females;
and this will especially hold good if the male defends the female, and
aids in providing food for the young. The advantage thus gained by the
more vigorous pairs in rearing a larger number of offspring has
apparently sufficed to render sexual selection efficient."[CQ]
With regard to the first of the two modes, little need be said. There
can be no question that there are both elimination by battle and
elimination by competition in the struggle for mates. It is well known
that the emperor moth discovers his mate by his keen sense of smell
residing probably in the large, branching antennæ. There can be little
doubt that, if an individual is deficient in this sense, or
misinterprets the direction in which the virgin female lies, he will be
unsuccessful in the competition for mates; he will be eliminated from
procreation. And it is a familiar observation of the poultry-yard that
the law of battle soon determines which among the cock birds shall
procreate their kind. The law of battle for mates is, indeed, an
established fact among many animals, especially those which are
polygamous, and the elimination of the unfit in this respect is a
logical necessity.
It is when we come to the second of the two modes, that which involves
selection proper, that we find differences of opinion among naturalists.
Darwin, as we have seen, suggested that those secondary sexual
characters which can be of no value in aiding their possessor to escape
elimination by combat result from the preferential choice of the female,
the female herself remaining comparatively unaffected. But Mr. Wallace
made an exceedingly valuable suggestion with regard to these
comparatively dull colours of the female. He pointed out that
conspicuousness (unless, as we have seen, accompanied by some protective
character, such as a sting or a bitter taste) increased the risk of
elimination by enemies. Now, the males, since they are generally the
stronger, more active, and more pugnacious, could better afford to run
this risk than their mates. They could to some extent take care of
themselves. Moreover, when impregnation was once effected, the male's
business in procreation was over. Not so the female; she had to bear the
young or to lay the eggs, often to foster or nourish her offspring. Not
only were her risks greater, but they extended over a far longer period
of time. Hence, according to Mr. Wallace, the dull tints of the females,
as compared with those of the males, are due to natural selection
eliminating the conspicuous females in far greater proportion than the
gaudy males.
There is clearly no reason why this view should not be combined with
Darwin's; preferential mating being one factor, natural elimination
being another factor; both being operative at the same time, and each
contributing to that marked differentiation of male and female which we
find to prevail in certain classes of the animal kingdom.
But Mr. Wallace will not accept this compromise. He rejects preferential
mating altogether, or, in any case, denies that through its agency
secondary sexual characters have been developed. He admits, of course,
the striking and beautiful nature of some of these characters; he admits
that the male in courtship takes elaborate pains to display all his
finery before his would-be mate; he admits that the "female birds may be
charmed or excited by the fine display of plumage by the males;" but he
concludes that "there is no proof whatever that slight differences in
that display have any effect in determining their choice of a
partner."[CR]
How, then, does Mr. Wallace himself suppose that these secondary sexual
characters have arisen? His answer is that "ornament is the natural
outcome and direct product of superabundant health and vigour," and is
"due to the general laws of growth and development."[CS] At which one
rubs one's eyes and looks to the title-page to see that Mr. Wallace's
name is really there, and not that of Professor Mivart or the Duke of
Argyll. For, if the plumage of the argus pheasant and the bird of
paradise is due to the general laws of growth and development, why not
the whole animal? If Darwin's sexual selection is to be thus superseded,
why not Messrs. Darwin and Wallace's natural selection?
Must we not confess that Mr. Wallace, for whose genius I have the
profoundest admiration, has here allowed himself to confound together
the question of origin and the question of guidance or direction?
Natural selection by elimination and sexual selection through
preferential mating are, supposing them to be _veræ causæ_, guiding or
selecting agencies. Given the variations, however caused, these agencies
will deal with them, eliminating some, selecting others, with the
ultimate result that those specially fitted for their place in nature
will survive. Neither the one nor the other deals with the origin of
variations. That is a wholly different matter, and constitutes the
leading biological problem of our day. Mr. Wallace's suggestion is one
which concerns the origin of variations, and as such is worthy of
careful consideration. It does not touch the question of their guidance
into certain channels or the maintenance of specific standards.
Concerning this Mr. Wallace is silent or confesses ignorance. "Why, in
allied species," he says, "the development of accessory plumes has taken
different forms, we are unable to say, except that it may be due to that
individual variability which has served as the starting-point for so
much of what seems to us strange in form or fantastic in colour, both in
the animal and vegetable world."[CT] It is clear, however, that
"individual variability" cannot be regarded as a _vera causa_ of the
maintenance of a specific standard--a standard maintained _in spite of_
variability.
The only directive agency (apart from that of natural selection) to
which Mr. Wallace can point is that suggested by Mr. Alfred Tylor, in an
interesting, if somewhat fanciful, posthumous work on "Coloration in
Animals and Plants," "namely, that diversified coloration follows the
chief lines of structure, and changes at points, such as the joints,
where function changes." But even if we admit that coloration-bands or
spots originate at such points or along such lines--and the
physiological rationale is not altogether obvious--even if we admit that
in butterflies the spots and bands usually have reference to the form of
the wing and the arrangement of the nervures, and that in highly
coloured birds the crown of the head, the throat, the ear-coverts, and
the eyes have usually distinct tints, still it can hardly be maintained
that this affords us any adequate explanation of the _specific_
colour-tints of the humming-birds, or the pheasants, or the Papilionidæ
among butterflies. If, as Mr. Wallace argues, the immense tufts of
golden plumage in the bird of paradise owe their origin to the fact that
they are attached just above the point where the arteries and nerves for
the supply of the pectoral muscles leave the interior of the body, are
there no other birds in which similar arteries and nerves are found in a
similar position? Why have these no similar tufts? And why, in the birds
of paradise themselves, does it require four years (for it takes so long
for the feathers of the male to come to maturity) ere these nervous and
arterial influences take effect upon the plumage? Finally, one would
inquire how the colour is determined and held constant in each species.
The difficulty of the Tylor-Wallace view, even as a matter of origin, is
especially great in those numerous cases in which the colour is
determined by delicate lines, thin plates, or thin films of air or
fluid.[CU]
Under natural selection, as we have seen, the development of colour is
fostered under certain conditions. The colour is either protective,
rendering the organism inconspicuous amid its normal surroundings, or it
is of warning value, advertising the organism as inedible or dangerous,
or, in the form of recognition-marks, it is of service in enabling the
members of a species to recognize each other. Now, in the case of both
warning colour and recognition-marks, their efficacy depends upon the
perceptual powers of animals. Unless there be a rapidly acquired and
close association of the quality we call nastiness with the quality we
call gaudiness (though, for the animal, there is no such _isolation_ of
these qualities as is implied in our words [CV]), such that the sight of
the gaudy insect suggests that it will be unpleasant to eat, the
gaudiness will be of no avail. And if there is any truth in the doctrine
of mimicry, the association is particular. It is not merely that bright
colours are suggestive of a nasty taste. The insect-eating birds
associate nastiness especially with certain markings and
coloration--"the tawny _Danais_, the barred _Heliconias_, the blue-black
_Euplæas_, and the fibrous _Acræas_;" and this is proved by the fact
that sweet insects mimicking these particular forms are thereby
protected.
So, too, with recognition-marks. If the bird or the mammal have not
sufficient perceptive powers to distinguish between the often not very
different recognition-marks, of what service can they be?
Recognition-marks and mimicry seem, therefore, to show that in the
former case many animals, and in the latter the insect-eating birds,
mammals, lizards, and other animals concerned, have considerable powers
of perception and association.
Among other associations are those which are at the base of what I have
termed preferential mating. We must remember how deeply ingrained in the
animal nature is the mating instinct. _We_ may find it difficult to
distinguish closely allied species. But the individuals of that species
are led to mate together by an impelling instinct that is so well known
as to elicit no surprise. Instinct though it be, however, the mating
individuals must recognize each other in some way. The impulse that
draws them together must act through perceptual agency. It is not
surprising, therefore, to find, when we come to the higher animals,
that, built upon this basis, there are well-marked mating preferences.
And this, as we have before pointed out, following Wallace, is an
efficient factor in segregation. Let us, however, hear Mr. Wallace
himself in the matter.
There is, he says,[CW] "a very powerful cause of isolation in the mental
nature--the likes and dislikes--of animals; and to this is probably due
the fact of the rarity of hybrids in a state of nature. The differently
coloured herds of cattle in the Falkland Islands, each of which keeps
separate, have been already mentioned. Similar facts occur, however,
among our domestic animals, and are well known to breeders. Professor
Low, one of the greatest authorities on our domesticated animals, says,
'The female of the dog, when not under restraint, makes selection of her
mate, the mastiff selecting the mastiff, the terrier the terrier, and so
on.' And again, 'The merino sheep and the heath sheep of Scotland, if
two flocks are mixed together, each will breed with its own variety.'
Mr. Darwin has collected many facts illustrating this point.[CX] One of
the chief pigeon-fanciers in England informed him that, if free to
choose, each breed would prefer pairing with its own kind. Among the
wild horses in Paraguay those of the same colour and size associate
together; while in Circassia there are three races of horses which have
received special names, and which, when living a free life, almost
always refuse to mingle and cross, and will even attack one another. In
one of the Faröe Islands, not more than half a mile in diameter, the
half-wild native black sheep do not readily mix with imported white
sheep. In the Forest of Dean and in the New Forest the dark and pale
coloured herds of fallow deer have never been known to mingle; and even
the curious ancon sheep, of quite modern origin, have been observed to
keep together, separating themselves from the rest of the flock when put
into enclosures with other sheep. The same rule applies to birds, for
Darwin was informed by the Rev. W. D. Fox that his flocks of white and
Chinese geese kept distinct. This constant preference of animals for
their like, even in the case of slightly different varieties of the same
species, is evidently a fact of great importance in considering the
origin of species by natural selection, since it shows us that, so soon
as a slight differentiation of form or colour has been effected,
isolation will at once arise by the selective association of the animals
themselves."
Mr. Wallace thus allows, nay, he lays no little stress on, preferential
mating, and his name is associated with the hypothesis of
recognition-marks. But he denies that preferential mating, acting on
recognition-marks, has had any effect in furthering a differentiation of
form or colour. He admits that so soon as a slight differentiation of
form or colour has been effected, segregation will arise by the
selective association of the animals themselves; but he does not admit
that such selective association can carry the differentiation further.
Now, it is clear that mating preferences must be either fixed or
variable. If fixed, how can differentiation occur in the same flock or
herd? And how can selective association be a means of isolation? Or,
granting that differentiation has occurred, if the mating preferences
are then stereotyped, all further differentiation, so far as colour and
form are concerned, will be rendered impossible; for divergent
modifications, not meeting the stereotyped standard of taste, will for
that reason fail to be perpetuated. We must admit, then, that these
mating preferences are subject to variation. And now we come to the
central question with regard to sexual selection by means of
preferential mating. What guides the variation along special lines
leading to heightened beauty? This, I take it, is the heart and centre
of Mr. Wallace's criticism of Darwin's hypothesis. Sexual selection of
preferential mating involves a standard of taste; that standard has
advanced from what we consider a lower to what we consider a higher
æsthetic level, not along one line, but along many lines. What has
guided it along these lines?
Not as in any sense affording a direct answer to this question, but for
illustrative purposes, we may here draw attention to what seems to be a
somewhat parallel case, namely, the development of flowers through
insect agency. In his "Origin of Species," Darwin contended that flowers
had been rendered conspicuous and beautiful in order to attract insects,
adding, "Hence we may conclude that, if insects had not been developed
on the earth, our plants would not have been decked with beautiful
flowers, but would have produced only such poor flowers as we see on our
fir, oak, nut, and ash trees, on grasses, docks, and nettles, which are
all fertilized through the agency of the wind." "The argument in favour
of this view," says Mr. Wallace,[CY] who quotes this passage, "is now
much stronger than when Mr. Darwin wrote;" and he cites with approval
the following passage from Mr. Grant Allen's "Colour-Sense:" "While man
has only tilled a few level plains, a few great river-valleys, a few
peninsular mountain slopes, leaving the vast mass of earth untouched by
his hand, the insect has spread himself over every land in a thousand
shapes, and has made the whole flowering creation subservient to his
daily wants. His buttercup, his dandelion, and his meadowsweet grow
thick in every English field. His thyme clothes the hillside; his
heather purples the bleak grey moorland. High up among the Alpine
heights his gentian spreads its lakes of blue; amid the snows of the
Himalayas his rhododendrons gleam with crimson light. Even the wayside
pond yields him the white crowfoot and the arrowhead, while the broad
expanses of Brazilian streams are beautified by his gorgeous
water-lilies. The insect has thus turned the whole surface of the earth
into a boundless flower-garden, which supplies him from year to year
with pollen or honey, and itself in turn gains perpetuation by the baits
that it offers to his allurement."[CZ]
Mr. Grant Allen is perfectly correct in stating that the insect has
produced all this beauty. It is the result of insect choice, a genuine
case of selection as contrasted with elimination. And when we ask in
this case, as we asked in the case of the beautiful colours and forms of
animals, what has guided their evolution along lines which lead to such
rare beauty, we are given by Mr. Wallace himself the answer, "The
preferential choice of insects." If these insects have been able to
produce through preferential selection all this wealth of floral beauty
(not, indeed, for the sake of the beauty, but incidentally in the
practical business of their life), there would seem to be no _a priori_
reason why the same class and birds and mammals should not have been
able to produce, through preferential selection, all the wealth of
animal beauty.
It should be noted that the answer to the question is in each case a
manifestly incomplete one. For if we say that these forms of beauty,
floral and animal, have been selected through animal preferences, there
still remains behind the question--How and why have the preferences
taken these _æsthetic_ lines? To which I do not see my way to a
satisfactory answer, though some suggestions in the matter will be made
in a future chapter.[DA] At present all we can say is this--to be
conspicuous was advantageous, since it furthered the mating of flowers
and animals. To be diversely conspicuous was also advantageous. As Mr.
Wallace says, "It is probably to assist the insects in keeping to one
flower at a time, which is of vital importance to the perpetuation of
the species, that the flowers which bloom intermingled at the same
season are usually very distinct, both in form and colour."[DB] But
conspicuousness is not beauty. And the question still remains--From what
source comes this tendency to beauty?
Leaving this question on one side, we may state the argument in favour
of sexual selection in the following form: The generally admitted
doctrine of mimicry involves the belief that birds and other
insect-eating animals have delicate and particular perceptual powers.
The generally received doctrine of the origin of flowers involves the
belief that their diverse forms and markings result from the selective
choice of insects. There are a number of colour and form peculiarities
in animals that cannot be explained by natural selection through
elimination. There is some evidence in favour of preferential mating or
selective association. It is, therefore, permissible to hold, as a
provisional hypothesis, that just as the diverse forms of flowers result
from the preferential choice of insects, so do the diverse secondary
sexual characters of animals result, in part at least, from the
preferential choice of animals through selective mating.
If this be admitted, then the elaborate display of their finery by male
birds, which Mr. Wallace does admit, may fairly be held to have a value
which he does not admit. For if preferential mating is _à priori_
probable, such display may be regarded as the outcome of this mode of
selection. At the same time, it may be freely admitted that more
observations are required. In a recent paper, "On Sexual Selection in
Spiders of the Family _Attidæ_,"[DC] by George W. and Elizabeth G.
Peckham, a full, not to say elaborate, description is given of the
courtship, as they regard it, of spiders. The "love-dances" and the
display of special adornments are described in detail. And the
observers, as the result, be it remembered, of long and patient
investigation and systematic study, come to the conclusion that female
spiders exercise selective choice in their mates. And courtship must be
a serious matter for spiders, for if they fail to please, they run a
very serious risk of being eaten by the object of their attentions. Some
years ago I watched, on the Cape Flats, near Capetown, the courtship of
a large spider (I do not know the species). In this case the antics were
strange, and, to me, amusing; but they seemed to have no effect on the
female spider, who merely watched him. Once or twice she darted forward
towards him, but he, not liking, perhaps, the gleam in her eyes,
retreated hastily. Eventually she seemed to chase him off the field.
We must remember how difficult it is to obtain really satisfactory
evidence of mating preferences in animals. In most cases we must watch
the animals undisturbed, and very rarely can we have an opportunity of
determining whether one particular female selects her mate out of her
various suitors. We watch the courtship in this, that, or the other
case. In some we see that it is successful; in others that it is
unsuccessful. How can we be sure that in the one case it was through
fully attaining, in the other through failing to reach, the standard of
taste? And yet it is evidence of this sort that Mr. Wallace demands.
After noting the rejection by the hen of male birds which had lost their
ornamental plumage, he says, "Such cases do not support the idea that
males with the tail-feathers a trifle longer, or the colours a trifle
brighter, are generally preferred, and that those which are only a
little inferior are as generally rejected,--and this is what is
absolutely needed to establish the theory of the development of these
plumes by means of the choice of the female."[DD] If Mr. Wallace
requires direct observational evidence of this kind, I do not suppose he
is likely to get any large body of it. But one might fairly ask him what
body of direct observational evidence he has of natural selection. The
fact is that direct observational evidence is, from the nature of the
processes involved, almost impossible to produce in either case. Natural
selection is an explanation of organic phenomena reached by a process of
logical inference and justified by its results. It is not claimed for
the hypothesis of selective mating that it has a higher order of
validity.
_Use and Disuse._
As we have already seen, biologists are divided into two schools, one of
which maintains that the effects of use and disuse[DE] have been a
potent factor in organic evolution; the other, that the effects of use
and disuse are restricted to the individual. My own opinion is that we
have not a sufficient body of carefully sifted evidence to enable us to
dogmatize on the subject, one way or the other. But, the position of
strict equilibrium being an exceedingly difficult and some would have us
believe an undesirable attitude of mind, I may add that I lean to the
view that use and disuse, if persistent and long-continued, take effect,
not only on the individual, but also on the species.
It is scarcely necessary to give examples of the kind of change which,
according to the Lamarckian school, are wrought by use and disuse. Any
organ persistently used will have a tendency, on this view, to become in
successive generations more and more adapted to its functional work. To
give but one example. It is well known that certain hoofed creatures are
divisible into two groups--first, those which, like the horse, have in
each limb one large and strong digit armed with a solid hoof; and,
secondly, those which, like the ox, have in each limb two large digits,
so that the hoof is cloven or split. It is also well known that the
ancestral forms from which both horse-group and ox-group are derived
were possessed of five digits to each limb. Professor Cope regards the
differentiation of these two groups as the result of the different modes
of use necessitated by different modes of life. "The mechanical effect,"
he says, "of walking in the mud is to spread the toes equally on
opposite sides of the middle line. This would encourage the equal
development of the digits on each side of the middle line, as in the
cloven-footed types. In progression on hard ground the longest toe (the
third) will receive the greatest amount of shock from contact with the
earth."[DF] Hence the solid-hoofed types. Here, then, the middle digit
in the horse-group, or two digits in the ox-group, having the main
burden to bear, increase through persistent use, while the other digits
dwindle through disuse.[DG]
On the other hand, one who holds the opposite view will say--I do not
believe that use and disuse have had anything whatever to do with the
matter. Fortuitous variations in these digits have taken place. The
conditions have determined which variations should be preserved. In the
horse, variations in the direction of increase of functional value of
the mid digit, and variations in the simultaneous decrease of the
functional value of the lateral digits, have been of advantage, and have
therefore survived the eliminating process of natural selection.
Now, since it is quite clear, in this and numberless similar cases, that
we can explain the facts either way, it is obviously not worth while to
spend much time or ingenuity in devising such explanations. They are not
likely to convince any one worth convincing. What we need is (1) crucial
cases which can only be explained one way or the other; or (2) direct
observation or experiment leading to the establishment of one hypothesis
or the other (or both).
1. Crucial cases are very difficult to find. We cannot exclude the
element of use or disuse, for on both hypotheses it is essential. The
difference is that one school says the organ is developed in the species
_by_ use; the other school says it is developed _for_ use. What we must
seek is, therefore, the necessary exclusion of natural selection; and
that is not easy to prove, in any case, to a Darwinian. If it can be
shown that there exist structures which are of use, but not of vital
importance (that is to say, which have not what I called above the
_available advantage_ necessary to determine the question of elimination
or not-elimination), then we are perhaps able to exclude the influence
of natural selection. I think, if anywhere, such cases are to be found
in faculties and instincts;[DH] and as such they must be considered in a
later chapter. I will, however, here cite one case in illustration of my
meaning.
We have seen that certain insects are possessed of warning colours,
which advertise their nastiness to the taste. Birds avoid these bright
but unpleasant insects, and though there is some individual learning,
there seems to be an instinctive avoidance of these unsavoury morsels.
There is hesitation before tasting; and one or two trials are sufficient
to establish the association of gaudiness and nastiness. Moreover, Mr.
Poulton and others have shown that, under the stress of keen hunger,
these gaudy insects may be eaten, and apparently leave no ill effects.
Birds certainly instinctively avoid bees and wasps; and yet the sting of
these insects can seldom be fatal. It is, therefore, improbable that
nastiness or even the power of stinging can have been an eliminating
agency. In the development of the instinctive avoidance, natural
selection through elimination seems to be excluded, and the inheritance
of individual experience is thus rendered probable. As before pointed
out, it is not enough to say that a nasty taste or a sting in the gullet
is disadvantageous; it must be shown that the disadvantage has an
eliminating value. From my experiments (feeding frogs on nasty
caterpillars, and causing bees to sting chickens), I doubt the
eliminating value in this case. Hence elimination by natural selection
seems, I repeat, to be excluded, and the inheritance of individual
experience rendered probable.
Mr. Herbert Spencer has contended that, in certain modifications,
natural selection is excluded on the grounds of the extreme complexity
of the changes, and adduces the case of the Irish "elk" with its huge
antlers, and the giraffe with its specially modified structure. He
points out that in either case the conspicuous modification--the
gigantic antlers or the long neck--involves a multitude of changes
affecting many and sometimes distant parts of the body. Not only have
the enormous antlers involved changes in the skull, the bones of the
neck, the muscles, blood-vessels, and nerves of this region, but changes
also in the fore limbs; while the long neck of the giraffe has brought
with it a complete change of gait, the co-ordinated movements of the
hind limbs sharing in the general modification. Mr. Spencer, therefore,
argues that it is difficult to believe that these multitudinous
co-ordinated modifications are the result of fortuitous variations
seized upon by natural selection. For natural selection would have to
wait for the fortunate coincidence of a great number of distinct parts,
all happening to vary just in the particular way required. That natural
selection should seize upon the favourable modification of a particular
part is comprehensible enough; that two organs should coincidently vary
in favourable directions we can understand; that half a dozen parts
should, in a few individuals among the thousands born, by a happy
coincidence, vary each independently in the right way is conceivable;
but that the whole organization should be remodelled by fortunately
coincident and fortuitously favourable variations is not readily
comprehensible. It may be answered--Notwithstanding all this, we know
that such happy coincidences have occurred, for there is the resulting
giraffe. The question, however, is not whether these modifications have
occurred or not, but whether they are due to fortuitous variation alone,
or have been guided by functional use. The argument seems to me to have
weight.[DI]
Still, we should remember that among neuter ants--for example, in the
Sauba ant of South America (_Oecodoma cephalotes_)--there are certain
so-called soldiers with relatively enormous heads and mandibles. The
possession of these parts so inordinately developed must necessitate
many correlated changes. But these cannot be due to inherited use, since
such soldiers are sterile.
Furthermore, according to Professor Weismann, natural selection is
really working, not on the organism at large, but on the germ-plasm
which produces it; and it is conceivable that the variation of one or
more of the few cells in early embryonic life may introduce a great
number of variations in the numerous derivative cells. In explanation of
my meaning, I will quote a paragraph from a paper of Mr. E. B. Poulton's
on "Theories of Heredity."[DJ] "It appears," he says, "that, in some
animals, the great groups of cells are determined by the first division
[of the ovum in the process of cleavage[DK]]; in others, the right and
left sides, or front and hind ends of the body; while the cells giving
rise to the chief groups on each side would then be separated at some
later division. This is not theory, but fact; for Roux has recently
shown that, if one of the products of the first division of the egg of a
frog be destroyed with a hot needle, development is not necessarily
arrested, but, when it proceeds, leads to the formation of an embryo
from which either the right or the left side is absent. When the first
division takes place in another direction, either the hind or the front
half was absent from the embryo which was afterwards produced. After the
next division, when four cells were present, destruction of one produced
an embryo in which one-fourth was absent." Now, it is conceivable that a
single modification or variation of the primitive germ might give rise
to many correlated modifications or variations of the numerous cells
into which it develops; just as an apparently trivial incident in
childhood or youth may modify the whole course of a man's subsequent
life. It is difficult, indeed, to see how this could be effected; to
understand what could be the nature of a modification of the germ which
could lead simultaneously to many favourable variations of bones,
muscles, blood-vessels, and nerves in different parts of the body. This,
however, is a question of the origin of variations; and it is, at any
rate, conceivable that, just as by the extirpation with a hot needle of
one cell of the cleaved frog's ovum all the anterior part of the body
should be absent in development, so by the appropriate modification of
this one cell, or the germinal matter which produced it, all the
anterior part of the body should be appropriately modified.
These considerations, perhaps, somewhat weaken the force of Mr.
Spencer's argument, which is not quite so strong now as it was when the
"Principles of Biology" was published.
(2) We may pass now to the evidence afforded by direct observation and
experiment. There is little enough of it. The best results are, perhaps,
those which have been incidentally reached in the poultry-yard and on
the farm in the breeding of domesticated animals. We have seen that,
under these circumstances, certain parts or organs have very markedly
diminished in size and efficiency; others have as markedly increased. Of
the former, or decrease in size and efficiency, the imbecile ducks with
greatly diminished brains have been already mentioned. Mr. Herbert
Spencer draws attention[DL] to the diminished efficiency in ear-muscles,
giving rise to the drooping ears of many domesticated animals. "Cats in
China, horses in parts of Russia, sheep in Italy and elsewhere, the
guinea-pig formerly in Germany, goats and cattle in India, rabbits,
pigs, and dogs in all long-civilized countries, have dependent
ears."[DM] Since many of these animals are habitually well fed, the
principle of economy of growth seems excluded. Indeed, the ears are
often unusually large; it is only their motor muscles that have dwindled
either relatively or absolutely. If what has been urged above be valid,
panmixia cannot have been operative; since panmixia _per se_ only brings
about regression to mediocrity. If the effects in these two cases,
ducks' brains and dogs' ears, be not due to disuse, we know not at
present to what they are due. In the correlative case of increase by
use, we find it exceedingly difficult to exclude the disturbing effects
of artificial selection. The large and distended udders of cows, the
enhanced egg-laying powers of hens, the fleetness or strength of
different breeds of horses,--all of these have been subjects of
long-continued, assiduous, and careful selection. One cannot be sure
whether use has co-operated or not.
Sufficient has now, I think, been said to show the difficulty of
deciding this question, the need of further observation and discussion,
and the necessity for a receptive rather than a dogmatic attitude; and
sufficient, also, to indicate my reasons for leaning to the view that
use and disuse, long-continued and persistent, may be a factor in
organic evolution.
_The Nature of Variations._
The diversity of the variations which are possible, and which actually
occur in animal life, is so great that it is not easy to sum up in a
short space the nature of variations. Without attempting anything like
an exhaustive classification, we may divide variations into three
classes.
1. _Superficial variations_ in colour, form, etc., not necessarily in
any way correlated with
2. _Organic variations_ in the size, complexity, and efficiency of the
organs of the body;
3. _Reproductive and developmental variations._
Any of these variations, if sufficient in amount and value to determine
the question of elimination or not-elimination, selection or
not-selection, may be seized upon by natural selection.
Our domesticated animals exemplify very fully the superficial variations
which, through man's selection, have in many cases been segregated and
to some extent stereotyped. It is unnecessary to do more than allude to
the variations in form and coloration of dogs, cattle, fowls, and
pigeons. These variations are not _necessarily_ in any way correlated
with any deeper organic variations. They are, however, in many cases so
correlated. For example, the form of the pouter pigeon is correlated
with the increased size of the crop, the length of the beak carries with
it a modification of the tongue, the widely expanded tail of the fantail
carries with it an increase in the size and number of the caudal
vertebræ. And here we might take the whole series of secondary sexual
characters. These and their like may be said to be direct correlations.
But there are also correlations which are seemingly indirect, their
connection being apparently remote. That in pigeons the size of the feet
should vary with the size of the beak; that the length of the wing and
tail feathers should be correlated; that the nakedness of the young
should vary with the future colour of the plumage; that white dogs
should be subject to distemper, and white fowls to the "gapes;" that
white cats with blue eyes should be nearly always deaf;--in these cases
the correlation is indirect. But from the existence of correlation,
whether direct or indirect, it follows that variations seldom come
singly. The organism is so completely a unity that the variation of one
part, even in superficial matters, affects directly or indirectly other
parts.
In the freedom of nature such superficial variations are not so obvious.
But among the invertebrates they are not inconsiderable. The case of
land-snails, already quoted, may again be cited. Taking variations in
banding alone, Mr. Cockerell knows of 252 varieties of _Helix nemoralis_
and 128 of _H. hortensis_. Still, among the wild relatives of our
domestic breeds of animals and birds the superficial variations are
decidedly less marked. And this is partly due to the fact that they are
in a state of far more stable equilibrium than our domestic products,
and partly to the constant elimination of all variants which are thereby
placed at a serious or vital disadvantage. White rats, mice, or small
birds, in temperate regions, would soon be seized upon by hawks and
other enemies. If the eggs and young of the Kentish plover, shown in our
frontispiece, were white or yellowish, like the eggs and young of our
fowls, they would soon be snapped up. The varied protective
resemblances, general and special, have been brought about by the
superficial variations of organisms, and the elimination of those which,
from non-variation or wrong variation, remained conspicuous. We need
only further notice one thing here, namely, that, in the case of special
resemblance to an inorganic object or to another organism, the
variations of the several parts must be very closely, and sometimes
completely, correlated. The correlations, however, need not, perhaps,
have been simultaneous--the resemblance having been gradually perfected
by the filling in of additional touches, first one here, then another
there, and so on.
Concerning "organic variations," little need be said. It is clear that
an organ or limb may vary in size, such variation carrying with it a
correlative variation in power; or it may vary in complexity--the teeth
of the horse tribe, for example, having increased in complexity, while
their limbs have been rendered less complex; or it may vary in
efficiency through the more perfect correlation and co-ordination of its
parts.
The evidence of such variations from actual observation is far less in
amount than that of superficial variations. And this is not to be
wondered at, since in many cases it can only be obtained by careful
anatomical investigation. Nevertheless, anatomists, both human and
comparative, are agreed that such variations do occur. And no one can
examine such a collection as that of the Royal College of Surgeons
without acknowledging the fact.
Thirdly, "reproductive and developmental variations" are of very great
importance. The following are among the more important modifications
which may occur in the animal kingdom.
1. Variations in the mode of reproduction, sexual or asexual.
2. Variations in the mode of fertilization.
3. Variations in the number of fertilized ova produced.
4. Variations in the amount of food-yolk and in the way in which it is
supplied.
5. Variations in the time occupied in development.
6. Variations in the time at which reproduction commences.
7. Variations in the duration and amount of parental protection and
fosterage.
8. Variations in the period at which secondary sexual characters and the
maximum efficiency of the several organs is reached.
It is impossible here to discuss these modes of variation _seriatim_. I
shall therefore content myself with but a few remarks on the importance
of protection and fosterage. It is not too much to say that, without
fosterage and protection, the higher forms of evolution would be
impossible. If you are to have a highly evolved form, you must allow
time for its evolution from the egg; and that development may go on
without let or hindrance, you must supply the organism with food and
lighten the labour of self-defence. Most of the higher organisms are
slow in coming to maturity, passing through stages when they are
helpless and, if left to themselves, would inevitably fall a prey to
enemies.
In those animals in which the system of fosterage and protection has not
been developed a great number of fertilized ova are produced, only a few
of which come to maturity. It might be suggested that this is surely an
advantage, since the greater the number produced the greater the chances
of favourable variations taking place. But it has before been pointed
out that these great numbers are decimated, and more than decimated, not
by elimination, but by indiscriminate destruction; embryos, good, bad,
and indifferent, being alike gobbled up by those who had learnt the
secret of fostering their young. The alternative has been between
producing great numbers[DN] of embryos which soon fend for themselves,
and a few young who are adequately provided for during development. And
the latter have proved the winners in life's race. If we compare two
flat-fishes belonging to very different groups, the contrast here
indicated will be readily seen. The skate is a member of the shark
tribe, flattened symmetrically from above downwards. It lays, perhaps,
eighty to a hundred eggs. Each of these is large, and has a rich supply
of nutritive food-yolk. Each is also protected by a horny case with
pointed corners--the so-called sea-purse of seaside visitors. These are
committed by the skate to the deep, and are not further cared for. But
the abundant supply of food-yolk gives the little skate which emerges a
good start in life. On the other hand, the turbot, one of the bony
fishes, flattened from side to side with an asymmetrical head, lays
several millions of eggs, which float freely in the open sea. These are
minute and glassy, and not more than one-thirtieth of an inch in
diameter. When the fishes are hatched, they are not more than about
one-fifth of an inch in length. The slender stock of food-yolk is soon
used up, and henceforth the little turbot (at present more like a
stump-nosed eel than a turbot) has to get its own living. Hundreds of
thousands of them are eaten by other fishes.
Or, if we compare such different vertebrates as a frog, a sparrow, and a
mouse, we find that the frog produces a considerable number of
fertilized ova, though few in comparison with the turbot, each provided
with a small store of food-yolk. The tiny tadpoles very soon have to
obtain their own food and run all the risks of destruction. Few survive.
The sparrow lays a few eggs; but each is supplied with a large store of
food-yolk, sufficient to meet its developmental needs until, under the
fostering influence of maternal warmth, it is hatched. Even on emerging
from the eggs, the callow fledglings enjoy for a while parental
protection and fosterage, and, when sent forth into the world, are very
fairly equipped for life's struggle. The mouse produces minute eggs with
little or no food-yolk; but they undergo development within the womb of
the mother, and are supplied with nutrient fluids elaborated within the
maternal organism. Even when born, they are cherished for a while and
supplied with food-milk by the mother.
The higher stages of this process involve a mental element, and are
developed under the auspices of intelligence or instinct. But the lower
stages, the supply of food-yolk and intra-uterine protection, are purely
organic. A hen cannot by instinctive or intelligent forethought increase
the amount of food-yolk stored up in the ovum, any more than the lily,
which, by an analogous process, stores up in its bulb during one year
material for the best part of next year's growth, can increase this
store by a mental process.
It cannot therefore be questioned that variations in the amount of
capital with which an embryo is provided in generation would very
materially affect its chances of escaping elimination by physical
circumstances, by enemies, and by competition.
Nor can it be questioned that variations in the time occupied in
reaching maturity would, other things equal, not a little affect the
chances of success of an organism in the competition of life. Hence we
have the phenomena of what may be termed acceleration and retardation in
development. These terms have, however, been used by American
zoologists, notably Professors Hyatt and Cope, in a somewhat different
and wider sense; for they include not merely time-changes, but also the
loss of old characters or the acquisition of new characters. "It is
evident," says Professor Cope, "that the animal which adds something to
its structure which its parents did not possess has grown more than
they; while that which does not attain to all the characteristics of its
ancestors has grown less than they." "If the embryonic form be the
parent, the advanced descendant is produced by an increased rate of
growth, which phenomenon is called 'acceleration'; but if the embryonic
type be the offspring, then its failure to attain the condition of the
parent is due to the supervention of a slower rate of growth; to this
phenomenon the term 'retardation' is applied." "I believe that this is
the simplest mode of stating and explaining the law of variation: that
some forms acquire something which their parents did not possess; and
that those which acquire something additional have to pass through more
numerous stages than their ancestors; and those which lose something
pass through fewer stages than their ancestors; and these processes are
expressed by the terms 'acceleration' and 'retardation.'"[DO]
It is clear, however, that we have here something more than acceleration
and retardation of development in the ordinary sense of these words. It
would be, therefore, more convenient to use the term "acceleration" for
the condensation of _the same series_ of developmental changes into a
shorter period of time; "retardation" for the lengthening of the period
in which _the same series_ of changes are effected; and "arrested
development" for those cases in which the young are born in an immature
or embryonic condition. Whether there is any distinct tendency, worthy
of formulation as a law, for organisms to acquire, as a result of
protracted embryonic development, definite characteristics which their
ancestors did not possess, I think very questionable. If so, this will
fall under the head of the origin of variations.
That acceleration, in the sense in which I have used the term, does
occur as a variation is well known. "With our highly improved breeds of
all kinds," says Darwin,[DP] "the periods of maturity and reproduction
have advanced with respect to the age of the animal; and in
correspondence with this, the teeth are now developed earlier than
formerly, so that, to the surprise of agriculturalists, the ancient
rules for judging of the age of an animal by the state of its teeth are
no longer trustworthy." "Disease is apt to come on earlier in the child
than in the parent; the exceptions in the other direction being very
much rarer."[DQ] Professor Weismann contends that the time of
reproduction has been accelerated through natural selection, since the
shorter the time before reproduction, the less the number of possible
accidents. We may, perhaps, see in the curious cases of reproduction
during an otherwise immature condition, extreme instances of
acceleration. The axolotl habitually reproduces in the gilled, or
immature condition. Some species of insects reproduce before they
complete their metamorphoses. And the females of certain beetles
(_Phengodini_) are described by Professor Riley as larviform.[DR]
Precocity is variation in the direction of acceleration, and that
condensed development which is familiar in the embryos of so many of the
higher animals may be regarded as the result of variations constantly
tending in the same direction. That there are fewer examples of
retardation is probably due to the fact that nature has constantly
favoured those that can do the same work equally well in a shorter time
than their neighbours. But there can be no doubt that, accompanying that
fosterage and protection which is of such marked import in the higher
animals, there is also much retardation. And as bearing upon the
supposed law of variation as formulated by Messrs. Hyatt and Cope, it
should be noted that this retardation or _decreased_ rate of growth
leads to the production of the more advanced descendant.
_The Inheritance of Variations._
Given the occurrence of variations in certain individuals of a species,
we have the alternative logical possibilities of their being inherited
or their not being inherited. The latter alternative seems at first
sight to be in contradiction to the law of persistence. Sir Henry
Holland, seeing this, remarked that the real subject of surprise is, not
that a character should be inherited, but that any should ever fail to
be inherited.[DS] Intercrossing may diminish a character, and sooner or
later practically obliterate it: annihilate it at once and in the first
generation it cannot. This logical view, however, ceases to be binding
if we admit, with Professor Weismann, that variations may be produced in
the body without in any way affecting the germ. It is also vitally
affected if we believe that the hen does not produce the egg, though she
may, perhaps, modify the eggs inside her; for the modification of the
hen (i.e. the variety in question) may not be of the right nature or of
sufficient strength to impress itself upon the germinal matter of the
egg. We may at once admit, then, that acquired variations need not be
inherited.
Passing to innate variations--variations, that is to say, which are the
outcome of normal development from the fertilized ovum--must they be
inherited, at any rate, in some degree? It seems to me that they must,
on the hypothesis that sexual generation involves simply the blending or
commingling of the characters handed on in the ovum or the sperm. The
only cases where this would _apparently_ fail to hold good would be
where the ovum and the sperm handed on exactly opposite tendencies--a
variation in excess contributed by the male precisely counterbalancing a
variation in the opposite direction contributed by the female parent.
Even here the tendency is inherited, though it is counterbalanced. On
the hypothesis of "organic combination" before alluded to (p. 150),
variations might, however, in the union of ovum and sperm, be not only
neutralized, but augmented. If the variation be, so to speak, a definite
organic compound resulting from a fortunate combination of characters in
ovum and sperm, it might either fail altogether, or be repeated in an
enfeebled form, or augmented in the offspring, according as the new
conditions of combination were unfavourable or favourable.
Whether innate variations ever actually fail to be inherited, even in an
enfeebled form, it is very difficult to say; for if this, that, or the
other variation fail to be thus inherited, it is difficult to exclude
the possibility of its being an acquired variation not truly innate.
Certainly variations seem sometimes to appear in one generation, and not
to be inherited at all. And, as we have seen, Mr. Romanes appeals to a
gradual failure of heredity, apart from intercrossing, to explain the
diminution of disused organs.
That a variation strongly developed in both parents is apt to be
augmented in the offspring is commonly believed by breeders. Darwin was
assured that to get a good jonquil-coloured canary it does not answer to
pair two jonquils, as the colour then comes out too strong, or is even
brown. Moreover,[DT] "if two crested canaries are paired, the young
birds rarely inherit this character; for in crested birds a narrow space
of bare skin is left on the back of the head, where the feathers are
upturned to form the crest, and, when both parents are thus
characterized, the bareness becomes excessive, and the crest itself
fails to be developed."
On the whole, it would seem that variations may either be neutralized or
augmented in inheritance; but the determining causes are not well
understood.
Another fact to be noticed with regard to the inheritance of variations
is that some characters blend in the offspring, while others apparently
fail to do so. Mr. Francis Galton,[DU] speaking of human characters,
gives the colour of the skin as an instance of the former, that of the
eyes as an example of the latter. If a negro marries a white woman, the
offspring are mulattoes. But the children of a light-eyed father and a
dark-eyed mother are either light-eyed or dark-eyed. Their eyes do not
present a blended tint. Among animals the colour of the hair or feathers
is often a mean or blended tint; but not always. Darwin gives the case
of the pairing of grey and white mice, the offspring of which are not
whitish-grey, but piebald. If you cross a white and a black game bird,
the offspring are either black or white, neither grey nor piebald. Sir
R. Heron crossed white, black, brown, and fawn-coloured Angora rabbits,
and never once got these colours mingled in the same animal, but often
all four colours in the same litter. He also crossed "solid-hoofed" and
ordinary pigs. The offspring did not possess all four hoofs in an
intermediate condition; but two feet were furnished with properly
divided and two with united hoofs.[DV] Professor Eimer[DW] has noticed
that, in the crossing of striped and unstriped varieties of the garden
snail, _Helix hortensis_, the offspring are either striped or unstriped,
not in an intermediate or faintly striped condition.
These facts are of no little importance. They tend to minimize, for some
characters at least, the effects of intercrossing. The variations which
present this trait may be likened to stable organic compounds, which may
be inherited or not inherited, but which cannot be watered down by
admixture and intercrossing. It is well known[DX] that, in 1791, a
ram-lamb was born in Massachusetts, with short, crooked legs and a long
back, like a turn-spit dog. From this one lamb[DY] the _otter_, or
_ancon_, breed was raised. When sheep of this breed were crossed with
other breeds, the lambs, with rare exceptions, perfectly resembled one
parent or the other. Of twin lambs, even, one has been found to resemble
one parent, and the second the other. All that the breeder has to do is
to eliminate those which do not possess the required character. And very
rarely do the lambs of ancon parents fail to be true-bred.
Now, it can scarcely fail that such sports occur in nature. And if they
are stable compounds, they will not be readily swamped by intercrossing.
It only requires some further isolation to convert the sporting
individuals into a distinct and separate variety. Now, Darwin tells us
that the ancons have been observed to keep together, separating
themselves from the rest of the flock when put into enclosures with
other sheep. Here, then, we have preferential mating as the further
isolating factor. I feel disposed, therefore, to agree with Mr. Galton
when he says,[DZ] "The theory of natural selection might dispense with a
restriction for which it is difficult to see either the need or the
justification, namely, that the course of evolution always proceeds by
steps that are severally minute, and that become effective only through
accumulation. That the steps _may_ be small, and that they _must_ be
small, are very different views; it is only to the latter that I object,
and only when the indefinite word 'small' is used in the sense of
'barely discernible,' or as small as compared with such large sports as
are known to have been the origins of new races."
Connected, perhaps, with the phenomena we have just been considering is
that of _prepotency_.[EA] It is found that, when two individuals of the
same race or of different races are crossed, one has a preponderant
influence in determining the character of the offspring. Thus the famous
bull Favourite is believed to have had a prepotent influence on the
short-horn race; and the improved short-horns possess great power in
impressing their likeness on other breeds. The phenomena are in some
respects curiously variable. In fowls, silkiness of feathers seems to be
at once bred out by intercrossing between silk-fowl and any other breed.
But in the silky variety of the fan-tail pigeon this character seems
prepotent; for, when the variety is crossed with any other small-sized
race, the silkiness is invariably transmitted. One may fairly suppose
that prepotent characters have unusual stability; but to what causes
this stability is due we are at present ignorant.
Lastly, we have to consider the phenomenon of _latency_. This is the
lying hid of characters and their subsequent emergence. We may
distinguish three forms of latency.
1. Where characters lie hid till a certain period of life, and then
normally emerge.
2. Where the characters normally lie hid throughout life, but are, under
certain circumstances, abnormally developed.
3. Where the characters lie hid throughout life, but appear in the
offspring or (sometimes distant) descendants.
Latency is often closely connected with correlated variations. Secondary
sexual characters, for example, are correlated with the functional
maturity or activity of the reproductive organs. They therefore lie hid
until these organs are mature and ready for activity. When they are
restricted to the male, they normally remain latent throughout the life
of the female, but reappear in her male offspring. Under abnormal
conditions, such as the removal of the essentially male organs, the
secondary sexual characters correlated with them do not appear, or
appear in a lessened and modified form. The males may even, under such
circumstances, acquire female characters. Thus capons take to sitting,
and will bring up young chickens. Conversely, females which have lost
their ovaries through disease or from other causes sometimes acquire
secondary sexual characters proper to the male. Characters thus normally
latent abnormally emerge. Mr. Bland Sutton[EB] gives a case of a hen
golden pheasant which "presented the resplendent dress of the cock, but
her plumage was not quite so brilliant; she had no spurs, and the iris
was not encircled by the ring of white so conspicuous in the male." Her
ovary was no larger than a split pea.
A curious instance of latent characters correlated with sex is seen in
hive bees. The worker bee differs from the female in the rudimentary
condition of the sexual organs, in size and form, and in the higher
development of the sense-organs. But it is well known that, if a very
young worker grub be fed on "royal jelly," she will develop into a
perfect queen. Not only are the sexual organs stimulated to increased
growth and functional activity, but the correlated size and condition of
the sense-organs are likewise acquired. The characters of queen and
worker are latent in the grub. According to the nature of the food it
receives, the one set of characters or the other emerges. Professor
Yung's tadpoles and Mrs. Treat's butterflies (_ante_, p. 59) afford
similar instances.
We come now to those cases of latency in which this obvious correlation
does not occur. They afford examples of reversion to more or less remote
ancestral characters. In some cases the cause of such reversion--such
unexpected emergence of characters, which have remained latent through
several, perhaps many, generations--is quite unknown. In others, at any
rate among domesticated animals, the determining condition of such
reversion is the crossing of distinct breeds.
Darwin gives[EC] an instance of reversion, on the authority of Mr. R.
Walker. He bought a black bull, the son of a black cow with white legs,
white belly, and part of the tail white; and in 1870 a calf, the
gr-gr-gr-gr-grandchild of this cow, was born, coloured in the same very
peculiar manner, all the intermediate offspring having been black. In
man partial reversions are not infrequent. An additional pair of lumbar
ribs is sometimes developed, and in such cases the fan-shaped tendons
which are normally connected with the transverse processes of the
vertebræ are replaced by functional levator muscles. Since it is
probable that the ancestor of man had more than the twelve pairs of ribs
that are normally present in the human species, we may, perhaps, fairly
regard the supernumerary rib as a reversion. But it may be a new sport
on old lines.
The occasional occurrence in Scotland of red grouse with a large amount
of white in the winter plumage, especially on the under parts, is justly
regarded by Mr. Wallace[ED] as a good example of reversion or latency in
wild birds. There can be little doubt that, as he suggests, the Scotch
red grouse is derived from a form which, like the wide-ranging willow
grouse, has white winter plumage. During the glacial epoch this would be
an advantage. "But when the cold passed away, and our islands became
permanently separated from the mainland, with a mild and equable
climate, and very little snow in winter, the change to white at that
season became hurtful, rendering the birds more conspicuous, instead of
serving as a means of concealment." The red grouse has lost its white
winter dress; but occasional reversions point to the ancestral habit.
That crossing tends to produce reversion is a fact familiar to breeders
and fanciers, and one which is emphasized by Darwin. When pigeons are
crossed, there is a strong tendency to revert to the slatey-blue tint
and black bars of the ancestral rock-pigeon. There is always a tendency
in sheep to revert to a black colour, and this tendency is emphasized
when different breeds are crossed. The crossing of the several equine
species (horse, ass, etc.) "tends in a marked manner to cause stripes to
appear on various parts of the body, especially on the legs," and this
_may be_ a reversion to the condition of a striped and zebra-like
ancestor. Professor Jaeger described a good case with pigs. "He crossed
the Japanese, or masked breed, with the common German breed, and the
offspring were intermediate in character. He then recrossed one of these
mongrels with a pure Japanese, and in the litter thus produced one of
the young resembled in all its characters a wild pig; it had a long
snout and upright ears, and was striped on the back. It should be borne
in mind that the young of the Japanese breed are not striped, and that
they have a short muzzle and ears remarkably dependent."[EE] Darwin
crossed a black Spanish cock with a white silk hen. One of the offspring
almost exactly resembled the _Gallus bankiva_, the remote ancestor of
the parents.
Such cases would seem to show that in our domestic breeds ancestral
traits lie latent. The crossing of distinct varieties may either
neutralize the variations artificially selected, and thus allow the
ancestral characters which have been masked by them to reappear; or they
may allow the elements of the ancestral traits, long held apart in
separate breeds by domestication, to recombine with the consequent
emergence of the normal characters of the wild species. But, in truth,
any attempted explanations of the facts are little better than
guess-work. There are the facts. And the importance of crossing as a
determining condition in domesticated animals should make us cautious in
applying reversion, as it occurs in such cases, to wild species which
live under more stable conditions where crossing is of rare occurrence.
_The Origin of Variations._
The subject of the origin of variations is a difficult one, one
concerning which comparatively little is known, and one on which I am
not able to throw much light.
Taking a simple animal cell as our starting-point, we have already seen
that it performs, in primitive fashion, certain elementary and essential
protoplasmic activities, and gives rise to certain products of
cell-life. In the metazoa, which are co-ordinated aggregates of animal
cells, together with some of their products, there is seen a division of
labour and a differentiation of structure among the cells. We see, then,
that variation among these related cells has led to differences in size,
in form, in transparency, and in function; while the cell-products have
been differentiated into those which are of lifelong value, such as
bone, cartilage, connective tissue, horn, chitin, etc., together with a
variety of colouring matters; those which are of temporary value, such
as the digestive secretions, fat, etc.; and those which are valueless or
noxious, such as carbonic acid gas and urea, which are excreted as soon
as possible. Here are already a number of important and fundamental
variations to be accounted for.
Let us notice that, wide as the variations are, they are to a large
extent hedged in by physical, chemical, and organic limitations. We have
already seen that the size of cells is to a large extent limited,
because during growth mass tends to outrun surface; and because, while
disruptive changes occur throughout the mass, nutriment and oxygen must
be absorbed by the surface. This is a physical limitation. Since the
products of cell-life and cell-activity are chemical products, it is
clear that they can only be produced under the fixed limitations of
chemical combination; and though in organic products these limitations
are not so rigid as among inorganic substances, still that there are
limitations no chemist is likely to question. The organic limitations
are to the varied, but not very numerous, modes of protoplasmic
activity.
Probably, even at the threshold of metazoan life, such variations did
not affect only individual cells, but rather groups of cells. In
other words, the differentiation was at once and primarily a
tissue-differentiation. What do we know, however, about the primitive
tissue-differentiation of the earliest metazoa? Hardly anything. We may
fairly suppose that the first marked difference to appear was that
between the outside and the inside. In the formation of an embryo this
is the first differentiation we notice. From the beginning of
segmentation or, in any case, very early, the outer-layer cells become
marked off from the inner-layer cells. The next step was, perhaps, the
formation of the mid-layer between the outer and inner. But how further
differentiations were effected we really do not know, though we may
guess a little. This, perhaps, we may fairly surmise--that fresh
differentiations presupposed previous differentiations, and formed the
basis of yet further differentiations. Thus calcified cartilage
presupposes cartilage, and leads up to the formation of true bone. In
all this, however, we are very much in the dark. We can watch, always
with fresh wonder, the genesis of tissues in the development of the
embryo; but we do not at present know much of the mode of their
primitive genesis in the early days of organic evolution: how can we,
then, pretend to understand their origins?
If we speculate at all on the matter, we are led to the view that the
variations must be primarily due to the differential incidence of
mechanical stresses and physical or chemical influences. It may be
admitted that this is little more than saying that they are due to some
physical cause. Still, this at least may be taken as certain for what it
is worth--that the primitive tissue-differentiations are due to physical
or chemical influences, direct or indirect, on the protoplasm of the
cell. Here is one mode of the origin of variations.
I do not wish to reopen the question whether these variations originate
in the germ or in the body. I content myself with indicating the
difference, from this standpoint, between the two views. Take, for
example, the end-organs of the special senses, which respond explosively
to physical influences in ways we shall have to consider more fully in
the next chapter. If we hold that variations originating in the body may
be transmitted through the germ to the offspring, then we may say that
these variations are the direct result of the incidence of the physical
or molecular vibrations on the protoplasm. But if we believe, with
Professor Weismann, that all variations originate in the germ, then the
variations in the end-organs of the special senses, fitting them to be
the recipients of special modes of influence, result from physical
effects upon the germ of purely fortuitous origin, that is to say,
wholly unrelated to the end in view. The rods and cones of the retina
are due to purely chance variations, impressed by some chemical or
physical causes completely unknown on the germinal protoplasmic
substance. Those individuals which did not have these chance variations
have been eliminated. It matters not that the rods and cones are
believed to have reached their present excellence through many
intermediate steps from much simpler beginnings. The fact remains that
the origin of all these step-like variations was fortuitous, and not in
any way the direct outcome of the physical influences which their
products, the rods and cones, have become fitted to receive. I am not at
present prepared to accept this theory of the germinal origin of all
tissue-variations.
Whether use and disuse are to be regarded as sources of origin of
variations is, again, a matter in which there is wide difference of
opinion. But if we admit that any variations can take their origin in
the body (as distinguished from the germ), then there is no _à priori_
reason for rejecting use and disuse as factors. As such, we are, I
think, justified, in the present state of our knowledge, in reckoning
them, at all events, provisionally.
It is clear, however, that they are a proximate, not an ultimate, source
of origin. I mean that the structures must be there before they can be
either strengthened or weakened by use or disuse. They are at most a
source of positive or negative variations of existing structures. They
cannot be a direct source of origin of superficial variations. Gain or
loss of colour; form-variations not correlated with organic
variations;--these cannot be directly due to use or disuse. It is in the
nervous and muscular systems and the glandular organs that use and
disuse are mainly operative. When, however, organs are brought into
relation, or fail to be brought into relation, to their appropriate
stimuli, we speak of this, too, as use and disuse. We say, for example,
that persistent disuse may impair the essential tissues of the recipient
end-organs of the special senses, implying that these tissues require to
be brought into continued relation to the appropriate stimuli in order
that their efficiency be maintained. So, too, we say that the epidermis
is thickened by use, meaning that it is brought into relation with
certain mechanical stresses. Through correlation, too, the effects of
use and disuse may be widespread. Thus increase in the size of a group
of muscles may be correlated with increase in the size of the bones to
which they are in relation. In fact, so knit together and co-ordinated
is the organism into a unity, it is probable that hardly any variation
could take place through use or disuse without modifying to some extent
the whole organic being.
Once more, let it be clearly remembered that a large and important
school of zoologists reject altogether use or disuse as a factor in
variation. They believe that those germs are selected through natural
selection in which there is an increased tendency to use or disuse of
certain organs. In this, however, we are all agreed. The real question
is what is the source of origin of this tendency. On the view of
germinal origin, we are forced back on unknown physical or chemical
influences in no wise related in origin (though, of course, related in
result) with the use or disuse to which they give rise.
So far the main distinction between the two biological schools seems to
be that the one, placing the origin of variation in the body-tissues,
regards the variations as evoked in direct reaction to physical or
chemical influences; while the other, placing the origin of variation in
the germ, regards the variations as of fortuitous origin.
I do not use the phrase, "of fortuitous origin," as in any sense
discrediting the theory. I am not attempting the cheap artifice of
damning a view that does not happen to be my own with a phrase or a
nickname. And I therefore hasten to point out what variations I do
believe to have had a fortuitous origin. The phrase is often
misunderstood, and they will serve to explain its meaning.
If the reader will kindly refer to the tables of variations in the bats'
wings (Figs. 14-17), he will see that there are a great number of bones
which vary in length and vary independently. And if he will also refer
to Fig. 18, in which seven species of bats are compared, he will see
that the differences arise from the increased length of one set of bones
in one species and another set of bones in another species. Now, let us
suppose that the long, swallow-like wing of the noctule, a high flyer
with rapid wing-strokes, that catches insects in full flight, and the
broad wings of the horse-shoe, a low flyer, flapping slowly, and, at any
rate, sometimes catching insects on the ground, and covering them with
its wings as with a net; let us suppose, I say, that to each species its
special form of wing is an advantage. Among thousands of independent
variations in the lengths of the bones there would be occasional
combinations of variations, giving either increased length or increased
breadth to the wing. In the noctule, the former would tend to be
selected; in the horse-shoe, the latter. Thus the wing of the noctule
would be lengthened, and that of the horse-shoe broadened, through the
selection of fortuitous combinations of variations which chanced to be
favourable. Now, each individual bone-variation is, we believe, due to
some special cause; but the fortunate combination is fortuitous, due to
what we term "mere chance."
Darwin believed that chance, in this sense, played a very important part
in the origin of those favourable variations for which, as he said,
natural selection is constantly and unceasingly on the watch. And there
can be little question that Darwin was right.
We must now consider very briefly some of the proximate causes of
variations. In most of these cases we cannot hope to unravel the nexus
of causation. When a plexus of environing circumstances acts upon a
highly organized living animal, the most we can do in the present state
of knowledge is to note--we cannot hope to explain--the effects
produced.
All readers of Darwin's works know well how insistent he was that the
nature of the organism is more important than the nature of the
environing conditions. "The organization or constitution of the being
which is acted on," he says,[EF] "is generally a much more important
element than the nature of the changed conditions in determining the
nature of the variation." And, again,[EG] "We are thus driven to
conclude that in most cases the conditions of life play a subordinate
part in causing any particular modification; like that which a spark
plays when a mass of combustible matter bursts into flame--the nature of
the flame depending on the combustible matter, and not on the spark."
Recent investigations have certainly not lessened the force of Darwin's
contention. From which there follows the corollary that the vital
condition of the organism is a fact of importance. Darwin was led to
believe that among domesticated animals and plants good nutritive
conditions were favourable to variation. "Of all the causes which induce
variability," he says,[EH] "excess of food, whether or not changed in
nature, is probably the most powerful." Darwin also held that the male
is more variable than the female--a view that has been especially
emphasized by Professor W. K. Brooks. Mr. Wallace, as we have already
seen, regards the secondary sexual characters of male birds as the
direct outcome of superabundant health and vigour. "There is," he
says,[EI] "in the adult male a surplus of strength, vitality, and
growth-power which is able to expend itself in this way without injury."
And Messrs. Geddes and Thomson contend[EJ] that "brilliancy of colour,
exuberance of hair and feathers, activity of scent-glands, and even the
development of weapons, are in origin and development outcrops of a male
as opposed to a female constitution."
There is, I think, much truth in these several views thus brought into
apposition. Vigour and vitality, predominant activity and the consequent
disruptive changes, with their abundant by-products utilized in
luxuriant outgrowths and brilliant colours, are probably important
sources of variation. They afford the material for natural selection and
sexual selection to deal with. These guide the variations in specific
directions. For I am not prepared to press the theory of organic
combination so far as to believe that this alone has served to give
definiteness to the specific distinctions between secondary sexual
characters, though it may have been to some extent a co-operating
factor. This, however, is a question apart from that of origin.
Superabundant vigour may well, I think, have been a source of _origin_,
not only of secondary sexual characters, but of many other forms of
variation.
And while these forms of variation may be the special prerogative of the
male, we may perhaps see, in superabundant female vigour, a not less
important source of developmental and embryonic variations in the
offspring. The characteristic selfishness of the male applies his
surplus vitality to the adornment of his own person; the characteristic
self-sacrifice of the mother applies her surplus vitality to the good of
her child. Here we may have the source and origin of those variations in
the direction of fosterage and protection which we have seen to have
such important and far-reaching consequences in the development of
organic life. The storage of yolk in the ovum, the incubation of heavily
yolked eggs, the self-sacrificing development in the womb, the
elaboration of a supply of food-milk,--all these and other forms of
fosterage may well have been the outcome of superabundant female vigour,
the advantages of which are thus conferred upon the offspring.
We may now proceed to note, always remembering the paramount importance
of the organism, some of the effects produced by changes in the
environment.
The most striking and noteworthy feature about the effects of changes of
climate and moisture, changes of salinity of the water in aquatic
organisms, and changes of food-stuff, is that, when they produce any
effect at all, they give rise to _definite_ variations. Only one or two
examples of each can here be cited. Mr. Merrifield,[EK] experimenting
with moths (_Selenia illunaria_ and _S. illustraria_), finds that the
variations of temperature to which the pupa, and apparently also the
larva, are subjected tend to produce "very striking differences in the
moths." On the whole, cold "has a tendency, operating possibly by
retardation, to produce or develop a darker hue in the perfect insect;
if so, it may, perhaps, throw some light on the mechanism so often
remarked in north-country examples of widely distributed moths." Mr.
Cockerell[EL] regards moisture as the determining condition of a certain
phase of melanism, especially among Lepidoptera. The same author states
that the snail "_Helix nemoralis_ was introduced from Europe into
Lexington, Virginia, a few years ago. Under the new conditions it varied
more than I have ever known it to do elsewhere, and up to the present
date (1890) 125 varieties have been discovered there. Of these, no less
than 67 are new, and unknown in Europe, the native country of the
species." The effects of the salinity of the water on the brine-shrimp
_Artemia_ have already been mentioned. One species with certain
characteristics was transformed into another species with other
characteristics by gradually altering the saltness of the water. So,
too, in the matter of food, the effects of feeding the caterpillars of a
Texan species of _Saturnia_ on a new food-plant were so marked that the
moths which emerged were reckoned by entomologists as a new species.
The point, I repeat, to be especially noted about these cases and others
which might be cited,[EM] is that the variation produced is a definite
variation. Very probably it is generally, or perhaps always, produced in
the embryonic or larval period of life. In some cases the variation
seems to be transmissible, though definite and satisfactory proofs of
this are certainly wanting. Still, we may say that if the changed
conditions be maintained, the resulting variation will also be
maintained. Under these conditions, at least, the variation is a stable
one. It is probable that, apart from preferential mating, the varieties
thus produced will tend to breed together rather than to be crossed with
the parent form or varieties living under different conditions. In this
way varieties may sometimes arise by definite and perhaps considerable
leaps under the influence of changed conditions. We must not run the
adage, _Natura nil facit per saltum_, too hard, nor interpret _saltum_
in too narrow a sense.
It is true, and we may repeat the statement of the fact for the sake of
emphasis, that we do not know how or why this or that particular
variation should result from this or that change of climate,
environment, or food-stuff; nor do we know why certain variations (such
as that which produced the ancon breed of sheep) should be stable, while
other variations are peculiarly unstable. But in this we are not worse
off than we are in the study of inorganic nature. We do not know why
calcite should crystallize in any particular one of its numerous
varieties of crystalline form; we do not know why some of these are more
stable than others. We may be able to point to some of the conditions,
but we cannot be said to understand why arragonite should be produced
under some circumstances, calcite under others; or why the same
constituents should assume the form of augite in some rocks, and
hornblende in other rocks. We are hedged in by ignorance; and perhaps
one of our chief dangers, becoming with some people a besetting sin, is
that of pretending to know more than we are at present in a position to
know. Our very analogies by which we endeavour to make clear our meaning
may often seem to imply an unwarrantable assumption of knowledge.
In the last chapter I used the term "organic combination," and drew a
chemical analogy. I wished to indicate the particularity and the
stability of certain variations, and the possibility of new departures
through new combinations of variations, the new departure not being
necessarily anything like a mean between the combining variations.[EN] I
trust that this will not be misunderstood as a new chemico-physical
theory of organic forms. I have some fear lest I should be represented
as maintaining that a giraffe or a peacock is a definite organic
compound, with its proper organic form, in exactly the same way as a
rhombohedron of calcite or a rhombic dodecahedron of garnet is a
definite chemical compound, with its proper crystalline form. All that
the analogy is intended to convey is that variations seem, under certain
circumstances, to be definite and stable, and may possibly combine
rather than commingle.
_Summary and Conclusion._
It only remains to bring this chapter to a close with a few words of
summary and conclusion.
The diversity of animal life must first be grasped. We believe that this
diversity is the result of a process or processes of evolution.
Evolution is the term applied to continuity of development. It involves
adaptation; and adaptation to an unchanging environment may become more
and more perfect. But the environment to which organisms are adapted
also changes. Where the change is in the direction of complexity, we
have elaboration; where it is in the direction of simplicity, we have
degeneration. Of these elaboration is the more important. It involves
both a tendency to differentiation giving rise to individuality, and a
tendency to integration giving rise to association. Continued
elaboration is progress; and this is opposed to degeneration.
The factors of evolution fall under two heads--origin and guidance. The
origin of variations lies in mechanical stresses, and chemical or
physical influences. Whether these act on the body (and are transmitted
by inheritance) or only on the germ, is a question which divides
biologists into two schools. In the latter case all variations are
fortuitous; in the former the development of tissue-variations has been
in direct response to the physical or chemical influences. There are,
however, in any case fortuitous combinations of variations.
Whether use and disuse are factors of origin is also a debatable point.
Those who believe that physical influences on the body are transmissible
believe also that the effects of use and disuse are transmissible.
The vital vigour of the organism is a determining condition of
importance. The vital vigour of males has favoured the origin of
secondary sexual characters; that of females, the fostering and
protection of young, and therefore the development in them of vital
vigour.
The almost universally admitted factor in guidance is natural selection.
But we must be careful not to use it as a mere formula.
Whether sexual selection is also a factor is still a matter of opinion.
Without it the specific character and constancy of secondary sexual
features are at present unexplained. If inherited use and disuse are
admitted as factors in origin, they must also be admitted as important
factors in guidance.
Questions of origin and guidance should, so far as is possible, be kept
distinct. These terms, however, apply to the origin and guidance of
variations. In the origin of species guidance is a factor, no doubt a
most important factor. The title of Darwin's great work was, therefore,
perfectly legitimate. And those who say that natural selection plays no
part in the origin of species are, therefore, undoubtedly in error.
NOTES
[CI] It is beyond the scope of this book to give the _evidences_ of
evolution. Such evidence from embryology, from distribution, and
from palæontology, is now abundant. For palæontological evidence,
see Nicholson's "Manual of Palæontology," 3rd edit., especially
the second volume on "Vertebrates," by R. Lydekker.
[CJ] Weismann, "Essays on Heredity," p. 24.
[CK] Ibid. p. 140.
[CL] Weismann, "Essays on Heredity," p. 90.
[CM] Ibid. p. 292. See also a discussion in _Nature_, in which Mr.
Romanes and Professor Ray Lankester took part, beginning vol. xli.
p. 437.
[CN] Weismann, "Essay on Heredity," p. 140.
[CO] "Origin of Species," p. 110.
[CP] With regard to blind cave-fish, Professor Ray Lankester has
suggested that some selection has been effected. Those animals
whose sight-sensitiveness enabled them to detect a glimmer of
light would escape to the exterior, leaving those with
congenitally weak sight to remain and procreate in the darkness of
the cave.
[CQ] Darwin, "Descent of Man," pt. ii. chap. viii.
[CR] "Darwinism," chap. x.
[CS] "Darwinism," p. 295. Messrs. Geddes and Thomson, "The Evolution of
Sex," p. 28, also contend that "combative energy and sexual beauty
rise _pari passu_ with male katabolism."
[CT] "Darwinism," p. 293.
[CU] Mr. Poulton, who takes a similar line of argument in his "Colours
of Animals," lays special stress upon the production of _white_
(see p. 326).
[CV] See Chapter VIII.
[CW] "Darwinism," p. 172.
[CX] See "Animals and Plants under Domestication," vol. ii. p. 80.
[CY] "Darwinism," p. 332.
[CZ] "The Colour-Sense," by Grant Allen, p. 95.
[DA] That on "The Emotions of Animals" (X.).
[DB] "Darwinism," p. 318.
[DC] Natural History Society of Wisconsin, vol. i. (1889).
[DD] "Darwinism," p. 286.
[DE] On the negative character of disuse, see p. 196.
[DF] Cope, "Origin of the Fittest," p. 374.
[DG] It would appear, from certain passages of his "Darwinism," that
Mr. A. R. Wallace (e.g. p. 139, note) holds or held similar views.
"The genera _Ateles_ and _Colobus_," he says, "are two of the most
purely arboreal types of monkeys, and it is not difficult to
conceive that the constant use of the elongated fingers for
climbing from tree to tree, and catching on to branches while
making great leaps, might require all the nervous energy and
muscular growth to be directed to the fingers, the small thumb
remaining useless." I should also have quoted Mr. Wallace's
account of the twisting round of the eyes of flat-fishes--where he
says that the constant repetition of the effort of twisting the
eye towards the upper side of the head, when the bony structure is
still soft and flexible, causes the eye gradually to move round
the head till it comes to the upper side--had he not subsequently
disclaimed this explanation (see _Nature_, vol. xl. p. 619). It is
possible that Mr. Wallace, notwithstanding the words "constant
use" in the passage I have quoted, merely intends to imply that
the elongated fingers are of advantage in climbing, and are thus
subject to natural selection, the thumb diminishing through
economy of growth.
[DH] I find, on rereading one of his articles, that I have here
unwittingly adopted one of Mr. Romance's arguments (see _Nature_,
vol. xxxvi. p. 406). The instance Mr. Romanes cites is the curious
habit of dogs turning round before they lie down.
[DI] Mr. Darwin, while contending that the modifications need not all
have been simultaneous, says, "Although natural selection would
thus tend to give the male elk its present structure, yet it is
probable that the inherited effects of use, and of the mutual
action of part on part, have been equally or more important"
("Animals and Plants under Domestication," vol. ii. p. 328).
[DJ] _Midland Naturalist_, November, 1889.
[DK] See _ante_, p. 52.
[DL] _Nature_, vol. xli. p. 511.
[DM] "Animals and Plants under Domestication," vol. ii. p. 291.
[DN] In the third chapter we saw that in such cases not only are there
an enormous number of ova produced, but that (e.g. in aurelia and
the liver-fluke) each ovum produces, through the intervention of
asexual multiplication, many individuals.
[DO] Cope, "Origin of the Fittest," pp. 226, 125, and 297.
[DP] "Animals and Plants under Domestication," vol. ii. p. 313.
[DQ] Ibid. p. 56.
[DR] _Nature_, vol. xxxvi. p. 592.
[DS] Quoted from "Medical Notes and Reflections," 1855, p. 267, by
Darwin, "Animals and Plants under Domestication," vol. i. p. 446.
[DT] Darwin, "Animals and Plants under Domestication," vol. i. p. 465.
[DU] "Natural Inheritance," p. 12.
[DV] Darwin, "Animals and Plants under Domestication," vol. ii. p. 70.
[DW] "Organic Evolution," Mr. Cunningham's translation, p. 76.
[DX] Darwin, "Animals and Plants under Domestication," vol. i. p. 104.
[DY] Similarly, from a chance sport of a one-eared rabbit, Anderson
formed a breed which steadily produced one-eared rabbits ("Animals
and Plants under Domestication," vol. i. p. 456). This is an
example of asymmetrical variation. Variations are generally, but
not always, symmetrical. Superficial colour-variations are
sometimes asymmetrical. Gasteropod molluscs are nearly always
asymmetrically developed. Among insects, _Anisognathus_ affords an
example of the asymmetrical development of the mandible. Our
right-handedness is a mark of asymmetry.
[DZ] "Natural Inheritance," p. 32.
[EA] See "Animals and Plants under Domestication," vol. ii. p. 40, from
which illustrations are taken.
[EB] "Evolution and Disease," p. 169.
[EC] "Animals and Plants under Domestication," vol. ii. p. 8.
[ED] "Darwinism," p. 107.
[EE] Darwin, "Animals and Plants under Domestication," vol. ii. pp. 17,
18.
[EF] "Animals and Plants under Domestication," vol. ii. p. 201.
[EG] Ibid. p. 282. The phenomena of the seasonal dimorphism of
butterflies and moths show that changes of temperature (and
perhaps moisture, etc.) determine very striking differences in
these insects.
[EH] "Animals and Plants under Domestication," vol. ii. p. 244.
[EI] "Darwinism," p. 293.
[EJ] "Evolution of Sex," p. 22.
[EK] "Incidental Observations in Pedigree Moth-breeding," F.
Merrifield. Transactions Entomological Society, 1889, pt. i. p.
79, _et seq._
[EL] _Nature_, vol. xli. p. 393.
[EM] See Professor Meldola's edition of Professor Weismann's "Studies
in the Theory of Descent," and Mr. Cunningham's translation of
Professor Eimer's "Organic Evolution."
[EN] See Darwin, "Animals and Plants under Domestication," vol. ii. p.
252.
CHAPTER VII.
THE SENSES OF ANIMALS.
It is part of the essential nature of an animal to be receptive and
responsive. The forces of nature rain their influence upon it; and it
reacts to their influence in certain special ways. Other organisms
surround it, compete with it, contend with it, strive to prey upon it,
and occasionally lend it their aid. It has to adjust itself to this
complex environment.
There are two kinds of organic response--one more or less permanent, the
other temporary and transient. We have already seen something of the
former, by which the tissues (the epidermis of the oarsman's hand, and
the muscles of his arm) respond to the call made upon them. The response
is here gradual, and the effects on the organism more or less enduring.
This, however, is not the kind of response with which we have now to
deal. What we have now to consider is that rapid response, transient,
but of the utmost importance, by means of which the organism directly
answers to certain changes in the environment by the performance of
certain activities. The parts specially set aside and adapted to receive
special modes of influence of the environment are the sense-organs. We
human folk get so much pleasure from and through the employment of our
sense-organs, that it is important to remember that the primary object
of the process of reception of the influences from without was not the
æsthetic one of ministering to the enjoyment of life by the recipient
organism, but the essentially practical one of enabling that organism to
respond to these influences. In other words, the _raison d'être_ of the
sense-organs is to set agoing suitable activities--activities in due
response to the special stimuli.
In this chapter we shall consider the modes in which the special
sense-organs are fitted to receive the influences of the environment,
deferring to a future chapter the consideration of the resulting
activities. For the present we take these activities for granted,
observing them only in so far as they give us a clue to the
sense-reaction by which they are originated. In this chapter, too, we
shall deal, for the most part, with the physiological aspects of
sensation. In all other organisms than ourselves, that is to say, than
each one of us individually for himself, the psychological
accompaniments of the physiological reactions of the sense-organs are
matters of inference. Still, so closely and intimately associated are
the physiological and the psychological aspects, that the exclusion of
all reference to the latter would be impracticable, or, if practicable,
unadvisable. What is practicable and advisable is to remember that, even
if the two are mentioned in a breath, the physiological and the
psychological belong to distinct orders of being.
In addition to the time-honoured "five senses," there are certain
_organic sensations_, so called, which take their origin within the
body. These are, for the most part, somewhat vague and indefinite. They
do not arise immediately and in direct response to changes in the
environment, but indicate conditions of the internal organs. Such are
hunger, thirst, nausea, fatigue, and various forms of discomfort.
Although they are of vital importance to the organism, prompting it to
perform certain actions or to desist from others, they need not detain
us here.
More definite than these, but still of internal origin, is the _muscular
sense_. This, too, is of continual service to every active animal. By it
information is given as to the energy of contraction of the muscles, and
of the amount of movement effected--not to mention the rapidity and
duration of the muscular effort. By it the position, or changes of
position, of the motor-organs are indicated. It is obvious, therefore,
that the sensations obtained in this way, some of which are exceedingly
delicate, are an important guide to the organism in the putting forth of
its activities. It is through the muscular sense that we maintain an
upright position. It is through an educated and refined muscular sense
that the juggler and the acrobat can perform their often surprising
feats. Concerning the physiology of the muscular sense, we have at
present no very definite knowledge. Some have held that we judge of
muscular movements by the amount of effort required to initiate them;
but it is much more probable that there are special sensory nerves,
whose terminations are either in the muscles themselves or in the
membranes which surround them.
* * * * *
We come now to the special senses. Of these we will take first the
_sense of touch_. Through this sense we are made aware of bodies solid
or liquid (or perhaps gaseous) which are actually in contact with the
skin or its infoldings at the mouth, nostrils, etc. There are
considerable differences in the sensitiveness of the skin in different
parts of its surface; some parts, like the filmy membrane which covers
the eye, being very sensitive, while others, like the horny skin that
covers the heel of a man who is accustomed to much walking, are
relatively callous. Different from this is the delicacy of the sense of
touch. This delicacy is really the power of discrimination, and
therefore involves some mental activity. But it is also dependent upon
the distribution of the recipient end-organs of the nerve. The highest
pitch of delicacy is reached in the tip of the tongue, which is about
sixty times as delicate as the skin of the back. The power of
discrimination is tested in the following way: The points of a pair of
compasses are blunted, and with them the skin is lightly touched. When
the points are close together, the sensation is of one object; when they
are more divergent, each point is felt as distinct from the other. On
the thigh and in the middle of the back, two distinct points of contact
are not felt unless the compass-tips are about 2-1/3 inches (67.7
millimetres) apart. When the divergence is 2 inches, they are felt as
one. With the tip of the tongue, however, we can distinguish the two
separate points when they are only 1/25 of an inch (1.1 millimetre)
apart. For the finger-tip the distance is about 1/12 of an inch (2
millimetres); for the tip of the nose, about 1/4 of an inch (6.8
millimetres); for the forehead, a little less than an inch (22.6
millimetres); and so on. Shut your eyes, and allow a friend to draw the
compass with the points about 1/2 an inch apart, from the forehead to
the tip of your nose, or (setting the points about 1/4 of an inch apart)
from the ball of your thumb to the finger-tip. The increasing delicacy
and power of discrimination is readily felt, and it is difficult to
believe that the compasses are not being slowly opened.
It is beyond the purpose of this chapter to describe minutely the nature
and structure of the nerve-ends in the sense-organs. This is a matter of
minute anatomy, or histology. A full description of them as they occur
in man will be found in any standard text-book of physiology; while Sir
John Lubbock's "Senses of Animals" gives much information concerning,
and many illustrations of, the minute structure of the sense-organs in
the invertebrates. Here I can only touch very briefly on some of the
more important points.
One of the larger nerves of the body (e.g. the sciatic nerve), consists
of a bundle of nerve-threads collected from a considerable area; some of
these (motor threads) end in muscles, others (sensory threads) in the
skin or its neighbourhood. Each nerve-thread has a central axis-fibre,
which is surrounded by a fatty, insulating medullary sheath, and this by
a delicate primitive sheath. In some parts of the skin the sensory
nerve-threads lose their medullary sheath, and end in very fine branches
between the cells of the tissue. In other cases the cells near their
termination are specially modified to form tactile cells, or tactile
corpuscles, in contact with or surrounding the axis-fibre or its
expansion (Fig. 23).
[Illustration: Fig. 23.--Tactile corpuscles.
1. In the beak of a goose. 2. In the finger of a man. 3. In the
mesentery of a cat.]
Hairs are delicate organs of touch, though, of course, this is not their
only function. They act as little levers embedded in the skin.
Turning now to the vertebrate animals other than man, we find in them a
sense of touch closely analogous to our own. As in us, so in them, the
specially mobile parts are eminently sensitive and delicate; for
instance, the lips in many animals, such as the horse, and the
finger-like organ at the end of the elephant's trunk. In some of them
special hairs are largely developed as organs of touch, as in the
whiskers of the cat and the long hairs on the rabbit's lip. With the aid
of these the rabbit finds its way in the darkness of its burrow; and it
is said that, deprived of these organs, the poor animal blunders about,
and is unable to steer its course in the dark.
The wing of the bat is very sensitive to touch; and it is supposed that
it is through this sense that the bat is able to direct its course in
the darkness of caves. Miss Caroline Bolton thus describes an
experimental trial of this power of the bat at which she was herself
present. A room, about twenty feet by sixteen, was arranged with strings
crossing each other in all directions so as to form a network with about
sixteen inches space between the strands. To each string was attached a
bell in such a way that the slightest touch would make it ring. One
corner of the room was left free for those who were present at the
experiment. A bat, measuring about one foot from the tip of one wing to
that of the other, was let loose in the room when it was quite dark,
"and it was distinctly heard flying about all over the room, but never
once did it touch a string or stop flying. It several times came quite
near to the spectators, so that they could feel the vibration of the air
in their faces. The experiment was continued for half an hour. Then,
when the door was opened and light let in, the bat stopped flying, and
settled down in the darkest corner." Now, here it may be said that,
although the room was dark to human spectators, there may have been
light enough for a bat to see his way. The cruel experiments of
Spalanzani, however, who put out the eyes of bats and obtained a similar
result, seem to show that the animal is guided by some sense other than
that of sight.
[Illustration: Fig. 24.--Touch-Hair of insect.
t.h., touch-hair; cu., cuticle; h.y., hypodermis; g., ganglion-cell
connected with nerve passing into the cavity of the touch-hair (after
Miall). The ganglion is often surrounded by several--eight or
less--accessory cells, which are not figured here.]
The crustaceans and many insects are covered with a dense armour, and it
might be supposed that in them there could be no sense of touch. But
this sense is by no means absent. Seated on the tough integument are
delicate little hairs, to the base of which a nerve-fibril passes
through a perforation in the integument. These are specially numerous in
the antennæ of insects.
In yet lower organisms we know in some cases the manner in which they
are sensitive to touch; but in a great number of cases, although
observation shows that they are thus sensitive, we know nothing definite
as to how the surface is specially fitted to receive the stimuli. Even
the primitive am[oe]ba, however, is sensitive in the sense spoken of on
p. 8; that is to say, it reacts under the influence of a stimulus.
* * * * *
Closely associated with the sense of touch is the _temperature-sense_.
Goldschneider and others have shown that on the skin of the human hand,
for example, there are special points that are sensitive to heat and
cold. Some of these little specialized areas are sensitive to cold;
others are sensitive to heat; and neither of these seem to be sensitive
to pressure. It therefore seems probable that special nerve-fibrils are
set apart for the temperature-sense; but of the manner in which these
fibrils terminate little or nothing is known.
Let us note that this temperature-sense, unlike the sense of touch, may
make us aware of distant bodies. It is, then, what we may term a
_telæsthetic_ sense in contradistinction to a contact-sense. It is
stimulated by a molecular throb; the throbbing body may be in contact,
but it may be as distant as the sun, in which case the molecular
pulsations are brought to us on waves of æther. Whether these waves act
directly on the nerve end-organs, or indirectly on them through the
warming of the skin-surface in which they terminate, we cannot say for
certain. But if the hand be held before a heated stove and be sheltered
from the heat by a screen, the removal of the screen, even for the
fraction of a second, gives rise to a strong stimulation of the
temperature-sense, though the skin-surface be not appreciably raised in
temperature. Hence it is probable that the end-organs are stimulated
directly, and not indirectly.
Concerning the temperature-sense in the lower animals, nothing definite
is known. But it is impossible to see our familiar pets basking in the
sunshine, or a butterfly sunning itself on a bright summer's day,
without feeling confident that the temperature-sense is a channel of
keen enjoyment. As before mentioned, however, this is not to be regarded
as the primary end in sensation. The primary end is not life-enjoyment,
but life-preservation. And we must regard the temperature-sense as
developed in the first instance to enable the organism to escape from
the ill effects of deleterious heat or cold, and to seek those
temperature-conditions which are most helpful to the continued and
healthful fulfilment of the process of life.
* * * * *
The _sense of taste_ is called into play by certain soluble substances,
or liquids, which must come in contact with the specialized
nerve-endings. Under normal circumstances, the sense of taste is closely
associated with that of smell, the result of the combination of the two
special senses being a _flavour_. The _bouquet_ of a choice wine, the
flavour of a peach, involve both senses; quinine involves taste alone;
and garlic and vanilla are nearly, if not quite, tasteless,--what we
call their taste is in reality their action on the organ of smell.
It is difficult to classify tastes. Sweet, bitter, salt, alkaline, sour,
acid, astringent, acrid,--these are the prominent and characteristic
varieties.
[Illustration: Fig. 25.--Taste-buds of rabbit.
i., section across part of the pleated patch (enlarged); ii., taste-buds
further enlarged.]
This sense is generally localized in or near the mouth; in us mainly in
the tongue. One manner, but not the only manner, in which the nerves in
this region terminate is in the minute flask-shaped taste-buds, which
have near one end, where they reach the surface, a funnel-shaped
opening, the taste-pore. They are made up of elongated cells, some of
which near the centre are spindle-shaped, and are called taste-cells.
They are found chiefly round the large circumvallate papillæ; but in the
rabbit and some other animals they are collected in the folds of a
little ridged or pleated patch--the _papilla foliata_--on each side of
the tongue near the cheek-teeth.
It is probable that the stimulation of the end-organs of taste is
effected by the special mode of molecular vibration due to the chemical
nature of the sapid substance. Mr. J. B. Haycroft, in a paper read
before the Royal Society of Edinburgh,[EO] suggests that "a group of
salts of similar chemical properties have their molecules in a similar
vibrating condition, giving rise to similar colours and similar tastes."
"Thus the chlorides and sulphates of a series of similar
elements--called a group of elements by Mendeljeff--have similar
tastes."
The delicacy of the sense of taste in man has been the subject of
investigation by Messrs. E. H. S. Bailey and E. L. Nichols.[EP] They
give the following table:--
I. Quinine--
Male observers detected 1 part in 390,000 parts of water.
Female " " 1 " 456,000 " "
II. Cane-sugar--
Male observers " 1 " 199 " "
Female " " 1 " 204 " "
III. Sulphuric acid--
Male observers " 1 " 2,080 " "
Female " " 1 " 3,280 " "
IV. Bicarbonate of sodium--
Male observers " 1 " 98 " "
Female " " 1 " 126 " "
V. Common salt--
Male observers " 1 " 2,240 " "
Female " " 1 " 1,980 " "
The above figures represent means or averages of a great number of
individuals. There was very considerable variation for some tastes. In
the case of the bitter of quinine, the maximum delicacy was the
detection of 1 part in 5,120,000 parts of water; the minimum 1 part in
456,000 parts of water. Except in the case of salt, the sense was more
delicate in women than in men. It is not stated whether the men tested
were smokers.
It does not seem necessary to say anything concerning the sense of taste
in the lower mammalia.
In birds and reptiles the sense of taste does not appear to be highly
developed. Parrots are, perhaps, better off in this respect than the
majority of their class; and the ducks have special organs on the edges
of the beak, which seem to minister to this sense. A python at the
Zoological Gardens, partially blind owing to a change of skin, is said
to have struck at an animal, but to have only succeeded in capturing its
blanket. This, however, it constricted, and proceeded to swallow with
abundant satisfaction.
It may here be mentioned that the scales and skin of many fishes are
provided with sense-organs which very closely resemble the taste-buds of
higher animals. They occur in the head and along the "lateral line"
which runs down the side of the fish, and may be readily seen, for
example, in the cod. Mr. Bateson's[EQ] careful observations at Plymouth
gave, however, no indication of the possession of an olfactory or
gustatory function, and their place in the sensory economy of the fish
remains problematical. In or near the mouth similar end-organs are found
to be somewhat variously developed in different fishes--on the palate
and lips, on the gill-bars, more rarely on the tongue, and on the
barbels of the rockling and the pout. How far any or all of these have a
gustatory function remains to be proved.
Anglers and fishermen, however, from their everyday experience, and
naturalists from special observations, do not doubt that fishes have a
sense of taste. Professor Herdman's recent experiments on feeding fishes
with nudibranchs[ER] (naked molluscs) seem to show, for example, that
the fishes concerned, including shannies, flat-fish, cod, rockling, and
others, have a sense of taste leading them to reject these molluscs as
nasty. They show, too, that some of the nudibranchs (_Doris_, _Ancula_,
_Eolis_) are protected by warning coloration.
Our knowledge of the sense of taste among the lower (invertebrate)
animals is imperfect, and is largely based rather on observation of
their habits than on the evidence of anatomical structure. Here, again,
comes in the difficulty of distinguishing between taste and smell. But
even if the caterpillars which refuse to eat all but one or two special
herbs, or the races of bloodsuckers which seem to have individual and
special tastes, are guided in part by an olfactory sense, there is much
evidence which seems to admit of no alternative explanation. Moisten,
for example, the antennæ of a cockroach with a solution of Epsom salts
or quinine, and watch him suck it off; or repeat F. Will's experiments
on bees, tempting them with sugar, and then perfidiously substituting
pounded alum. The way in which these little insects splutter and spit
suggests that, whatever may be the psychological effect, the
physiological effect is analogous to that produced in us by an
exceedingly nasty taste. Here smell would seem to be excluded. Forel,
moreover, mixed strychnine with honey, and offered it to his ants. The
smell of the honey attracted them, but when they began to feed, the
effect of the taste was at once evident.
The organs of taste in insects are probably certain minute pits, in each
of which is a delicate taste-hair, which, in some cases, is perforated
at the free end. They occur in the maxillæ and tongue in ants and bees,
and on the proboscis of the fly.
In many of the invertebrates, the crayfish and the earthworm, for
example--to take two instances from very different groups--observation
seems to show that a sense of taste is developed, for they have marked
and decided food-preferences. Nevertheless, the existence of special
organs for this purpose has not been definitely proved.
The sense of taste no doubt ministers to the enjoyment of life. But,
presumably, it has been developed in subservience to the process of
nutrition. Primarily, taste was not an end in itself, but was to guide
the organism in its selection of food that could be assimilated. Nice
and nasty were at first, and still are to a large extent, synonymous
with good-for-eating and not-good-for-eating. With unwonted substances,
however, its testimony may be false. Sugar of lead is sweet, but fatal.
Brought to a new country, cattle often eat, apparently with relish,
poisonous plants. Still, under normal circumstances, the testimony of
taste is reliable.
* * * * *
The _sense of smell_ is, to a large extent, telæsthetic. It is true that
the stimulation of the end-organs is effected by actual contact with the
odoriferous vapour. But since this vapour may be given off from an
odoriferous body at some distance from the organism, such as a flower or
a decomposing carcase, it is clear that the sense gives information of
the existence of such bodies before they themselves come in contact with
us. Primitively, we may suppose that it was developed in connection with
that sense of taste with which, as we have seen, it is so closely
associated. In this respect smell is a kind of anticipatory taste. But
it has now other ends, apart from those which are purely æsthetic. In us
it may serve as a warning of a pestilential atmosphere; in many
organisms, such as the deer, it gives warning of the presence of
enemies; in many again, and some insects among the number, it is the
guiding sense in the search for mates.
The organ of smell in ourselves and in all the mammalia is the delicate
membrane that covers the turbinal bones in the nose. It contains cells
with a largish nucleus, around which the protoplasm is mainly collected.
A filament passes from this to the surface, and ends in a fine hair or
cilium (or a group of hairs or cilia in birds and amphibia); a second
filament runs downwards into the deeper parts of the tissue, and may
pass into a nerve-fibril.
In us and air-breathing creatures, the substance which excites the
sensation of smell must be either gaseous or in a very fine state of
division; but in water-breathers the substance exciting this
sensation--or, in any case, one of anticipatory taste--may be in
solution. The sensitiveness of the olfactory membrane is very
remarkable. A grain of musk will scent a room for years, and yet have
not sensibly lost in weight. Drs. Emil Fischer and Penzoldt found that
our olfactory nerves are capable of detecting the 1/4,600,000 part of a
milligramme of chlorophenol, and the 1/460,000,000 part of a
milligramme, or about one thirty-thousand-millionth of a grain, of
mercaptan. It may be that to such substances our olfactory sensibility
is especially delicate.
Not much is known concerning the manner in which the end-organs of smell
are stimulated. As in the case of taste, it is probably a matter of
molecular vibration; and Professor William Ramsay has suggested that the
end-organs are stimulated by vibrations of a lower order than those
which give rise to sensations of light and heat. He has also drawn
attention to the fact that to produce a sensation of smell, the
substance must have a molecular weight at least fifteen times that of
hydrogen.
It is well known that the sense of smell is in some of the mammalia
exceedingly acute. The dog can track his master through a crowded
thoroughfare. The interesting experiments of Mr. Romanes[ES] show that,
under ordinary conditions of civilized life, the smell of boot-leather
is a factor, and the dog tracks his master's boots. In one case, the
boots were soaked in oil of aniseed, but this to us powerful scent did
not overcome the normal odour of the master's boots. Mr. W. J. Russell,
in a subsequent number of the same periodical, describes how his pug
could find a small piece of biscuit by scent, and this odour of biscuit
was not overmastered by a strong smell of eau-de-Cologne. Deer-stalkers
know well how keen is the sense of smell in the antlered ruminants.
We must not, however, be too ready to conclude, from these observations,
that the olfactory membrane is absolutely more sensitive in such animals
than it is in man. It may well be that, though they are so keen to
detect certain scents, they are dull to those which affect us
powerfully. It is quite possible that the odour of aniseed or
eau-de-Cologne is--possibly from the fact that their end-organs are not
attuned to these special molecular vibrations--out of their range of
smell. Their special interests in life have led to the cultivation of
extreme sensibility to special tones of olfactory sensation. Under
unusual circumstances, man may cultivate unwonted modes of utilizing the
sense of smell. A boy, James Mitchell, who was born blind, deaf, and
dumb, and who was mainly dependent on the sense of smell for keeping up
some connection with the external world, observed the presence of a
stranger in the room, and formed his opinion of people from their
characteristic smell. On the whole, therefore, we may, perhaps, conclude
that the variations in sensitiveness are mainly relative to the needs of
life.
In birds the sense of smell is but little developed, notwithstanding all
that most interesting naturalist, Charles Waterton, wrote on the
subject. Vultures seem unable to discover the presence of food which is
hidden from their sight. Probably reptiles share with them this dulness
of the sense of smell.
It has already been remarked that, in the case of aquatic animals, there
is probably little distinction between taste and smell. It would be
well, perhaps, to restrict the word "smell" to the stimuli produced by
vapours or air-borne particles, and to use the phrase "telæsthetic
taste," or simply "taste," for those cases where the effects are
produced through the medium of solution. In this case, however, the
point to be specially noticed is that taste in aquatic animals becomes a
telæsthetic sense, informing the organism of the presence of more or
less distant food. Thus, if you stir with your finger the water in which
leeches are living, they will soon flock to the spot, showing that the
telæsthetic sense is associated with an appreciation of direction. If a
stick be used to stir the water, they do not take any notice of it. Mr.
W. Bateson[ET] has shown that there are many fishes, among which are the
dog-fish, skate, conger eel, rockling, loach, sole, and sterlet, which
habitually seek their food by scent (telæsthetic taste), aided to some
extent by touch, and but little, if at all, by sight. "None of these
fishes ever starts in quest of food when it is first put into the tank,
but waits for an interval, doubtless until the scent has been diffused
through the water. Having perceived the scent of food, they swim vaguely
about, and appear to seek it by examining the whole area pervaded by the
scent, having seemingly no sense of the direction whence it proceeds." I
venture to think that further observation and experiment may show that
such a sense of direction does in some cases exist. Some years ago I was
fishing in Simon's Bay, at the Cape, with a long casting-line. The sea
was unusually calm, and the water clear as crystal. Beneath me was a
clear patch of granite, two or three yards across, surrounded by tangled
seaweed. Evening was coming on, and I was just going to put up my tackle
when I saw a long dark fish slowly sail into the open space and take up
his position at one side. My line was out, baited, I think, with a piece
of cuttle-fish, and I tried to draw it into the clear space, but only
succeeded in bringing it to within a foot or so of the side furthest
from the fish. There it got hitched in the weed; but the fish being
still undisturbed, I awaited further developments. After two or three
minutes the fish slowly turned, crossed the pool, and remained
motionless for a few moments; then he proceeded straight to the bait;
and in a few minutes I had landed a dog-fish between four and five feet
long. I did not then know that the dog-fish sought its food mainly or
solely by scent (taste); but in any case I do not think in this instance
he could have seen the bait, hidden as it was amid the seaweed.
Although I am aware, and have already mentioned, that Mr. Bateson's
observations do not support the view that the sense-organs of the
lateral line minister to this telæsthetic sense, still I think that
further observations and experiments may show that these sense-organs
are "olfactory," and that the lateral development may be in relation to
the appreciation of the direction in which the food lies. It is,
however, a difficult matter to determine, and the few experiments I have
made are so far inconclusive.
Much has been written concerning the sense of smell in insects. That
they possess such a sense few will be disposed to doubt. The classical
observations of Huber show that bees are affected by the smell of honey,
and that the penetrating odour of fresh bee-poison will throw a whole
hive into a state of commotion. He was of opinion that the impunity with
which his assistant, Francis Burnens, performed his various operations
on bees was due to the gentleness of his motions, and the habit of
repressing his respiration, it being the odour transmitted by the breath
to which the bees objected. Sir John Lubbock formed a little bridge of
paper, and suspended over it a camel's-hair brush containing scent, and
then put an ant at one end. She ran forward, but stopped dead short when
she came to the scented brush. Dr. McCook introduced a pellet of
blotting-paper saturated with eau-de-Cologne into the neighbourhood of
some pavement-ants, who were engaged in a free fight. The effect was
instantaneous; in a very few seconds the warriors had unclasped
mandibles, relaxed their hold of their enemies' legs, antennæ, or
bodies.
The correct localization of the sense of smell has been a matter of
difficulty. Kirby and Spence localized it at the extremity of the
"nose," between it and the upper lip. That the nose, they naïvely
remark, corresponds with the so-named part in mammalia, both from its
situation and often from its form, must be evident to every one who
looks at an insect. Lehman, Cuvier, and others, misled by the fact that
the organ of smell is in us localized at the entrance of the air-track,
supposed that at or near the spiracles of insects were the organs of
smell. Modern research tends more and more clearly to localize the sense
of smell, as first suggested by Réaumur, in the feelers or antennæ, and
in some cases also in the palps. If the antennæ of a cockroach be
extirpated or coated with paraffin, he no longer rushes to food, and
takes little notice of, and will sometimes even walk over,
blotting-paper moistened with turpentine or benzoline, which a normal
insect cannot approach without agitation. There can be little doubt that
it is by means of its large branching antennæ that the male emperor moth
(_Saturnia carpini_) is able to find its mate.[EU] If a collector take a
virgin female into a locality frequented by these moths, he will soon be
surrounded by twenty or thirty males; but if the moth be not a virgin,
he will at most see one or two males. The sense of smell is thus
delicate enough to distinguish the fertilized from the unfertilized
female, and has associated with it a sense of direction by which the
insect is guided to the right spot. Carrion flies whose antennæ have
been removed fail to discover putrid flesh; and E. Hasse has observed
that male humble-bees whose antennæ have been removed cannot discover
the females. The sensory elements are lodged in pits or cones, which may
be filled with liquid, peculiar sensory rods or hairs being associated
with the nerve-endings. Of these pits the queen-bee has, according to
Mr. Cheshire, 1600, the worker 2400, and the drone nearly 19,000, on
each antennæ. On the antennæ of the male cockchafer, Hauser estimates
the number to be 39,000.
In the aquatic crayfish there are, besides the long antennæ, smaller
antennules, each of which has two filaments, an inner and an outer. On
the under surface of most of the joints of the outer filament there are
two bunches of minute, curiously flattened organs, which were regarded
by Leydig, their discoverer, as olfactory. Observation, too, seems to
confirm the view that the sense of smell (or telæsthetic taste) is
located in the antennule. I tried on a crayfish the following
experiment: When it was at rest at the bottom of its tank, I allowed a
current of pure water (the water in which it lived) to flow from a
pipette over its antennæ and antennules. The antennæ moved slowly, but
the antennules remained motionless. I then took some water in which a
cod's head had been boiled, and allowed some of this to stream over the
antennæ and antennules. The former moved slightly as before, but the
antennules were thrown into a rapid up-and-down jerky vibration, and
shortly afterwards the crayfish began moving about the bottom of its
tank. If only one antennule be thus stimulated, or stimulated to a
higher degree than the other, the crayfish seems generally (but not
always) to turn to that side in search of food. Mr. Bateson[EV] has
shown to how large an extent shrimps and prawns seek their food by
smell, and states that a prawn, though blind, will often find his way
back to his proper place, and stay in it.
In the snail the anterior pair of "horns," or tentacles, are said to be
olfactory. Near the end of each is a large ganglion, or nerve-knot, from
which fibres pass to the surface, in which there are said to be
developed sensory knobs. Snails, however, from which these tentacles
have been removed are apparently still possessed of a sense of smell.
Certain lobed processes round the mouth have been regarded as the seat
of olfactory sensation, but this is doubtful. In the foot of the snail,
the part on which it glides, there is a hollow gland, and in this there
are special cells, each of which gives off a delicate rod, enlarging at
the free end into a ciliated knob. These are regarded as sensory and, it
may be, olfactory. In shell-fish like the mussel, in which the water is
sucked in by an inhalent tube or siphon, and ejected through an exhalent
siphon above it (see Fig. 2, p. 4), there is at the entrance of the
incoming current a thin layer of elongated cells which are described as
olfactory, and are in association with a special ganglion. Olfactory
depressions have been described in some worms. But in a great number of
the lower invertebrates very little or nothing is known concerning a
sense of smell.
* * * * *
_Hearing_ is a telæsthetic sense. Through it we become aware of certain
vibratory states of more or less distant objects. The vibrations of
these bodies are transferred to the air or other medium surrounding the
body, and are transmitted through the air or other medium to the ear.
The sound-waves traverse the air at a rate of 337 metres (1106 feet) in
a second; but they travel about four times as fast in water. If the
vibration is periodic or regular, the sound is called a tone;
non-periodic or irregular sounds are noises. The pitch of a tone is
determined by the number of vibrations in a second. The lowest or
gravest tone most of us can hear is that where there are about 30
vibrations in a second; twice this number give us a tone of an octave
higher; twice this again, another octave; and so on. In musical
composition, tones from about 40 to about 4000 vibrations per second are
employed. This is a range of somewhat over six octaves. But many of us
are capable of hearing sounds over a range of about ten octaves, that is
to say, from 30 to 30,000 vibrations per second. The upper limit of
hearing is, however, very variable. Some people are deaf to tones of
more than 15,000 or 20,000 vibrations per second.[EW] Others may hear
shrill tones of 40,000, or even in rare cases 50,000. I could as a boy
hear the shrill squeak of a bat; now I am quite deaf to it. A friend of
mine in South Africa was unable to hear the piping of the frogs in the
pond, which was to me so loud as almost to drown the tones of his voice.
Apart from the pitch of a note is its quality. The same note struck on
different instruments or sung by different persons has a different ring.
This is determined by the number and intensity of overtones, or
partials, which are associated with the fundamental tone. Suppose the
deep fundamental tone of 33 vibrations be sounded; with it there may be
associated overtones, eight or nine in number, all of which are simple
multiples (twice, thrice, four times, and so on) of the fundamental 33.
The effects of these on the organ of hearing fuse or combine with the
predominant effect of the fundamental tone. In harmonious chords, also,
two or more fundamental tones, with their accompaniment of partials,
blend in sensation so completely that it requires a keen musical ear and
some training to analyze them into their component elements.
The delicacy of discrimination of tones is greatest in the mid-region of
hearing; and there is much individual variation in accuracy of ear. I
have made experiments on many individuals to test their powers in this
respect. I found some who were unable, in the mid-region of hearing, to
state which was the higher of two notes sounded on a violin, the tones
of which were separated by a major third, and in one case by a fifth.
With notes on the piano the discrimination was more delicate,
and yet more delicate when the notes were sung. In such cases
tone-discrimination is deficient; and between these and the musician,
who is stated to be able to distinguish tones separated by only 1/64 of
a tone, there are many intermediate stages.
It is beyond my purpose to describe, in more than a very general way,
the nature of the auditory apparatus of man. The vibrations of the air
are received by the drum-membrane, which lies in the auditory passage.
From this it is transmitted, by a chain of small bones, to the inner
auditory apparatus. This consists of two small membranous sacs, with one
of which three membranous looped tubes, the semicircular canals, are
connected; with the other is connected a spiral tube, the cochlear
canal. These membranous sacs and canals are filled with fluid, and are
surrounded by the fluid which fills the bony cavity in which they lie.
This bony cavity has two little windows, one oval and the other round,
across each of which a membrane is stretched. The oval membrane is in
connection with the chain of auditory bones; and when this is made to
vibrate in and out, the membrane of the round window vibrates out and
in. Thus the fluid around and within the membranous sacs and canals is
set in vibration. And the parts are so arranged that the vibrations, in
passing from the oval to the round membrane, must run up one side and
down the other side of the cochlear canal. As they run down they set in
vibration a delicate membrane which is supported on beautiful arched
rods (the organs of Corti). And this membrane contains a number of
special hair-cells, so called because they bear minute hair-like
structures. These are the special end-organs of hearing. It has been
suggested that the fibres of the membrane on the arched rods, which are
of different lengths and may be stretched with differing degrees of
tension, respond to vibrations of different pitch. Thus the hair-cells
on that particular part of the membrane would be stimulated, and the
note might be appreciated in its true position in the scale.
We must now pass on to consider the sense of hearing in animals. That
the mammalia have this sense well developed is a matter of familiar
observation, and in some of them, such as the horse and the deer, it is
exceedingly acute. The form and movements of the external ear also
enable many of the mammalia to collect and attend to sounds from special
directions. The mammalia possess also the power of tone-discrimination,
as is shown by the fact that our domesticated animals recognize
different modulations of the human voice, and that wild creatures
distinguish tones or noises of different quality. A Newfoundland dog,
possessed by a friend of mine, always howled when the tenor D was struck
on the piano, or sung. And Théophile Gautier reports that one of his
cats could not endure the note G, and always put a reproving and
silencing paw on the mouth of any one who sang it.
In birds the sense of hearing is not only very sensitive, but the power
of discrimination is exceedingly delicate. No one who has watched a
thrush listening for worms can doubt that her ear is highly sensitive.
The astonishing accuracy with which many birds imitate, not only the
song of other birds, but such unwonted sounds as the clink of glasses or
the ring of quoits, shows that the delicacy in discrimination has
reached a high level of development. In birds, however, the cochlear
canal has not the same development that it has in mammals, and there are
no arched rods--no organs of Corti.
Nothing special is to be noted concerning the sense of hearing in the
reptiles, amphibia, and fishes. In all (with the exception of the lowly
lancelet) the auditory organ is developed. We shall, however, presently
see reason to question whether the possession of an "auditory organ,"
with well-developed semicircular canals, necessarily indicates the power
of hearing. And Mr. Bateson's recent experiments at Plymouth[EX] seem to
indicate that fishes are not so sensitive in this respect as anglers[EY]
are wont to believe. "The sound made by pebbles rattling inside an
opaque glass tube does not attract or alarm pollack; neither are they
affected by the sharp sound made by letting a hanging stone tap against
an opaque glass plate standing vertically in the water." Carp at Potsdam
are, indeed, said to come to be fed at the sound of a bell. But Mr.
Bateson well remarks that this "can scarcely be taken to prove that the
sound of the bell was heard by them, unless it be clearly proven that
the person about to feed them was hidden from their sight." There is
clearly room for further observation and experiment in this matter.
Turning to the invertebrata, we find, even in creatures as low down in
the scale of life as jelly-fish, around the margin of the umbrella in
certain medusa, simple auditory organs. In some cases they are pits
containing otoliths (minute calcareous or other bodies, which are
supposed to be set a-dance by the sound-vibrations); in others there is
a closed sac with one or more otoliths; in others, again, they are
modified tentacles, partially or completely enclosed in a hood. All
these are generally regarded as auditory, there being specially modified
cells of the nature of hair-cells. We shall see, however, that another
interpretation of organs containing otoliths is at any rate possible.
For the present, we will follow the usual interpretation, and regard
them as auditory.
Vesicular organs containing otoliths are found near the cerebral ganglia
in some of the worms and their relations. But the common earthworm,
though it appears to be sensitive to sound, does not appear to have any
such organs.
Molluscan shell-fish are generally provided with auditory organs. In the
fresh-water mussel it is found in the muscular foot. It can be more
readily seen in the _Cyclas_, if the transparent foot of this small
mollusc be examined under the microscope. It is a small sac containing
an otolith. Mr. Bateson found that the mollusc _Anomia_ "can be made to
shut its shell by smearing the finger on the glass of the tank so as to
make a creaking sound. The animals shut themselves thus when the object
on which they were fixed was hung in the water by a thread." In the
snail and its allies the auditory sac is found in close connection with
the nerve-collar that surrounds the gullet. In the cuttle-fishes it is
found embedded in the cartilage of the head.
[Illustration: Fig. 26.--Antennule of crayfish.
i.j., inner joint; o.j., outer joint; ol., olfactory setæ; ol'., the
same, enlarged; au.op., auditory opening in the basal division, which
has been cut open to show au.s., the auditory sac; au.n., auditory nerve
branching to the two ridges beset with auditory hairs; au.h., auditory
hair, enlarged. (After Howes.)]
[Illustration: Fig. 27.--Diagram of ear.
t.m., tympanic membrane, to which is attached a chain of small bones
stretching across the cavity of the drum, the innermost of which, st.,
fits into the "oval window." The vibrations are transmitted up one side
and down the other side of the cochlear canal, c.c., and thus reach the
"round window," f.r.; s.c. is one of the semicircular canals, the other
two are omitted; e.t. is the Eustachian tube connecting the cavity of
the drum with the mouth-cavity.]
In the lobster or crayfish the auditory organs are found at the base of
the smaller feelers or antennules. They are little sacs formed by an
infolding of the external integument (see Fig. 26, p. 259). Beautifully
feathered auditory hairs project into the sac along specialized ridges,
and the sac in many cases contains grains of sand which play the part of
otoliths. Hensen seems to have proved that shrimps collect the grains of
sand and place them in the auditory sac for this purpose. The curious
shrimp-like _Mysis_ has two beautiful auditory sacs in its tail. These
are provided with auditory hairs. Hensen watched these under the
microscope while a musical scale was sounded, and found that the special
hairs responded each to a certain note. When this particular note was
sounded the hair was thrown into such violent vibration as to become
invisible, but by other notes it was unaffected.
[Illustration: Fig. 28.--Tail of _Mysis_.
au., auditory organ.]
[Illustration: Fig. 29.--Leg of grasshopper.
ty., tympanic membrane.]
Passing now to insects, we may first note that grasshoppers and crickets
have an auditory organ on the front leg. These are provided with
tympanic membranes, and the breathing-tubes, or tracheæ, are so arranged
that the pressure of the air is equalized on the two sides of the
membrane--just as in us and other vertebrates the same end is effected
by a tube which runs from the interior of the drum of the ear to the
mouth-cavity (see Fig. 27). In the organ within the leg there is a group
of cells, followed by a row of similar cells which diminish regularly in
size from above downwards. Each is in connection with a nerve-fibril,
and contains a delicate auditory rod. It has been suggested that the
diminution in size of the cells may have reference to the appreciation
of different notes, but nothing definite is known on the matter. Ants,
too, have an auditory organ, as shown by Sir John Lubbock, in the tibia
of the front leg. But in locusts it is situated on the first segment of
the abdomen. In flies there are a number of vesicles, generally regarded
as auditory (but by some as olfactory), at the base of the rudimentary
hind wings--the so-called halteres, or balancers.
Observation seems to point to the fact that in most insects the sense of
hearing is lodged in the feelers, or antennæ. Kirby made the following
observation on a little moth: "I made," he says, "a quiet, not loud, but
distinct noise; the antenna nearest to me immediately moved towards me.
I repeated the noise at least a dozen times, and it was followed every
time by the same motion of that organ, till at length the insect, being
alarmed, became more agitated and violent in its motions." Hicks wrote,
in 1859, "Whoever has observed a tranquilly proceeding capricorn beetle
which is suddenly surprised by a loud sound, will have seen how
immovably outward it spreads its antennæ, and holds them porrect, as it
were, with great attention, as long as it listens." The same observer
described certain highly specialized organs in the antennæ of the
hymenoptera (ants, bees, and wasps), which he thus describes: "They
consist," he says, "of a small pit leading into a delicate tube, which,
bending towards the base, dilates into an elongated sac having its end
inverted." Of these remarkable organs, Sir John Lubbock says there are
about twelve in the terminal segment, and he has suggested that they may
serve as microscopic stethoscopes.
Mayer, experimenting with the feathered antenna of the male mosquito,
found that some of the hairs were thrown into vigorous vibration when a
note with 512 vibrations per second was sounded. And Sir John Lubbock,
who quotes this observation, adds,[EZ] "It is interesting that the hum
of the female gnat corresponds nearly to this note, and would
consequently set the hairs in vibration." The same writer continues,
"Moreover, those auditory hairs are most affected which are at right
angles to the direction from which the sound comes. Hence, from the
position of the antennæ and the hairs, a sound would act most intensely
if it is directly in front of the head. Suppose, then, a male gnat hears
the hum of a female at some distance. Perhaps the sound affects one
antenna more than the other. He turns his head until the two antennæ are
equally affected, and is thus able to direct his flight straight towards
the female."
It is difficult to determine the range of hearing in the lower
organisms. But it is quite possible, nay, very probable, that the
superior limit of auditory sensation is much more extended in insects
than it is in man. We know that many insects, such as the cicadas, the
crickets and grasshoppers, many beetles, the death's-head moth, the
death-watch, and others, make, in one way or another, sounds audible to
us. But there may be many insect-sounds--we may not call them
voices--which, though beyond our limits of hearing, are nevertheless
audible to insects. At the other end of the scale, on the other hand,
slow pulsations may be appreciated--for example, by aquatic
creatures--by means of what we term the auditory organs, in a way that
is not analogous to the sensation of sound in us. It may be noted that
auditory organs are dotted about the body somewhat promiscuously in the
various invertebrates. We have seen that auditory organs, or what are
generally believed to be such, are found in the foot of bivalves, in the
antennules of lobsters, in the fore legs of crickets and ants, in the
abdomen of locusts, in the balancers of flies, and in the tail of
_Mysis_. But when we come to consider the matter, there is no reason why
the organ of hearing should be in any special part of the body. The
waves of sound rain in upon the organism from all sides. There is no
great advantage in having the organs of hearing in the line of
progression, as with sight, where the rays come in right lines; nor in
having them in close association with the mouth, as in the case of the
organ of smell.
Closely connected with the organ of hearing in vertebrates is the organ
of another and but recently recognized sense. In briefly describing the
auditory apparatus in man, mention was made of three curved membranous
loops, the so-called semicircular canals. A few more words must now be
said about them and the membranous sac with which they are connected.
The sac lies in a somewhat irregular cavity in a bone at the side of the
head, in the walls of which are five openings leading into curved
tunnels in the bone in which lie the membranous loops. The planes in
which the three semicircular canals lie are nearly at right angles to
each other, and they are called respectively the horizontal, the
superior, and the posterior. The two latter unite at one end before they
reach the sac; hence there are five, and not six, openings into the
cavity. At one end of each semicircular canal is a swelling, or ampulla,
in each of which is a ridge, or crest, abundantly supplied with
hair-cells. And in a little recess in the sac there is, occupying its
floor, its front wall, and part of its outer wall, a patch of hair-cells
covered by a gelatinous material with numerous small crystalline
otoliths. The only other point that calls for notice is that the
membranous sac does not fit closely in the bony cavity in which it lies,
while the diameter of the membranous semicircular canals is considerably
less than that of their bony tunnels, except at the ampullæ, or
swellings, where they fit pretty closely. Both the bony cavity and the
membranous labyrinth (as it is called) are filled with fluid.
From its close connection with the organ of hearing, this apparatus was
for long regarded as in some way auditory in its function, and it was
surmised that it enabled us to perceive the direction from which the
sound came. But how it could do so was not clear. In 1820 M. Flourens
made the observation that the injury or division of a membranous canal
gave rise in the patient to rotatory movements of the animal round an
axis at right angles to the plane of the divided canal; and he,
therefore, suggested that the canals might be concerned in the
co-ordination of movement. They are now regarded as the organs of a
sense of rotation or acceleration.
That we have such a sense of rotation has been proved
experimentally.[FA] Let a man, blindfolded, sit on a smooth-running
turn-table. When it begins to rotate he feels that he is being moved
round, but if the rotation be continued at the same rate, this feeling
quickly dies away. If the rotation be increased, he again feels as if he
were being moved round, but this again soon dies away. Further increase
gives a fresh sensation, which in turn subsides, and the man may then be
spinning round rapidly, and be perfectly unconscious of the fact. He is
only aware that he has been gently turned round a little two or three
times. Now let the speed of rotation be slackened. He has a sensation of
being gently turned round a little in the opposite direction. Each time
the speed is lessened he has this sense of being turned the reverse way.
From these experiments we see that what we are conscious of is change of
rate of rotation, or, in technical language, acceleration, positive or
negative.
[Illustration: Fig. 30.--Diagram of semicircular canals.
A. bony labyrinth of human ear (after Sömmering). c, c., the cochlea;
s.c., superior semicircular canal; p.c., posterior semicircular canal;
h.c., horizontal semicircular canal; a, a, a, their swellings, or
ampullæ; f.o., f.r., fenestra ovalis and rotunda (oval and round
windows) in the vestibule.
B. Diagram of semicircular canal to illustrate effect of rotation. The
large arrows indicate the direction of the rotation. The small arrow to
the left indicates the resulting flow of the inner fluid into the
ampulla; that to the right, the flow of the outer fluid into the
vestibule.]
From Professor Crum Brown's paper in_ Nature_ I transcribe, with some
verbal modifications, his account of how the semicircular canals enable
us to feel these changes of motion. Let us consider the action of one
canal. If the head be rotated about a line at right angles to the plane
of the canal, with the ampulla leading, there will be a tendency for the
fluid within the sac to flow into the ampulla, and for the fluid around
the semicircular canal to flow into the cavity in which the sac lies.
These movements will conspire to stretch the membranous ampulla, and
thus to stimulate the hair-cells. This stretching will not take place in
that canal if the rotation be in the reverse direction. But on the
opposite side of the head is another canal in the same plane, but turned
the other way. In the reversed rotation the ampulla in this canal will
lead, and its hair-cells will be stimulated. Thus by means of the two
canals on either side of the head in the same plane, rotation in either
direction can be appreciated. And since there are two other pairs of
semicircular canals in two other planes, rotation in any direction will
be recognized by means of one or more of the six canals.
It is thus by means of the semicircular canals that we can appreciate
acceleration of rotatory motion.[FB] But we can also appreciate
acceleration of movements of translation--forwards or backwards, up or
down. And Professor Mach has suggested that it is through the
stimulation of the hair-cells in the patch in the sac itself (the
so-called _macula acustica_) that we are able to appreciate these
changes. The otoliths, held loosely and lightly in position by the
gelatinous substance in which they are embedded, may, through their
inertia, aid in the stimulation of the sense-hairs.
And this naturally suggests the question whether those sense-organs in
the invertebrates which contain otoliths may not be regarded with more
probability as organs for the appreciation of changes of motion than as
auditory organs. This for some years has been my own belief. I have
always felt a difficulty in understanding how the otoliths are set
a-dance by auditory vibrations. But their inertia would materially aid
in the appreciation of changes of motion. In some forms the otoliths are
held in suspension in a gelatinous material. In others--the molluscs,
for example--the otolith (which is generally single) is retained in a
free position by ciliary action. In aquatic creatures an organ for the
appreciation of changes of motion might be of more service than an
auditory organ. And if one be permitted to speculate, one may surmise
that the sense of hearing may be a refinement of the sense through which
changes of motion are appreciated. First would come a sense of movements
of the organism in the medium through the stimulation of the sense-hairs
by the relative motion of the otolith; then these sense-hairs, with
increased delicacy, might appreciate shocks in the medium; and,
eventually, those more delicate shocks which we know as auditory waves.
In this way we might account for the fact that in the vertebrates the
same organ, through different parts of its structure, appreciates both
change of motion and auditory vibrations. And thus the organs in the
invertebrata which are generally regarded as auditory, and for which has
been suggested the function of reacting to changes of motion, may, in
truth, subserve both purposes--may be organs in which the
differentiation I have hinted at is taking place.
* * * * *
_Sight_, like hearing, is a telæsthetic sense. Through it we become
aware of certain vibratory states of more or less distant objects. The
medium by means of which these vibrations are transmitted is not, as in
the case of hearing, the air, but the æther which pervades all space.
The rate of transmission is about 186,000 miles in a second. That which
answers in vision to pitch in hearing is colour. The lowest, or gravest,
light-tone to which we are sensitive is deep red, where the number of
vibrations per second is about 370 billions (370,000,000,000,000). The
highest, or most acute, light-tone is violet, with about 833 billion
vibrations in a second. If white light be passed through a prism, the
rays are classified according to their vibration-periods, and are spread
out in a spectrum, or band of rainbow colours. But different individuals
vary, as we shall presently see, in their sensibility to the lowest and
the highest vibrations. Some people are, moreover, relatively or
absolutely insensible to certain colours, generally either red or green.
Such persons are said to be colour-blind. When the rainbow colours are
combined in due proportion, or when pairs or sets of them are combined
in certain ways, white light is produced.
We saw that in the case of sound-waves, when the number of vibrations in
a second is doubled, the sound is raised in pitch by an octave. Using
this term in an analogous way for colour-tones, we may say the range in
average vision is about one octave--that is, from about 400 billion to
about 800 billion vibrations in a second. But, though these are the
limits in human vision, we know of the existence of many octaves of
radiant energy physically in continuity with the light-vibrations.
Photography has made us acquainted with ultra-violet vibrations up to
about 1600 billions per second--an octave above the violet. And
Professor Langley's observations with the bolometer indicate the
existence of waves with as low a vibration-period as one billion per
second, and even here, in all probability, the limit has not been
reached. To the vibrations more rapid than those that are concerned in
the sensation of violet, the human organism is apparently in no manner
sensitive. But to infra-red vibrations down to about thirty billions per
second the nerves of the skin respond through the temperature-sense. We
shall have to return to these limits of sensation at the close of this
chapter.
[Illustration: Fig. 31.--The human eye. Horizontal section, to show
general structure.]
[Illustration: Fig. 32.--Retina of the eye. Enlarged section of minute
fragment.
b., back of retina next the outer coat; l.r.c., layer of rods and cones;
i.l., intermediate layers; l.g.c., layer of ganglion-cells; l.n.f.,
layer of nerve-fibres; f., front of retina, the surface turned towards
the pupil.]
The human eye is a nearly spherical organ, capable of tolerably free
movements of rotation in its socket. What we may call the outer case,
which is white and opaque elsewhere, is quite transparent in front.
Through this transparent window may be seen the coloured iris, in the
centre of which is a circular aperture, the pupil. The size of the pupil
changes with the amount of light--it dilates or contracts, according as
the light is less or more intense. Just behind it, and still in the
front part of the eye, is the transparent lens, the convexity of the
anterior surface of which can be altered in the accommodation of the
organ for near or far vision. The space between the lens and iris and
the corneal window of the eye is filled with a watery fluid. Behind the
lens there is a transparent, semi-fluid, jelly-like material, filling
the rest of the chamber of the eye. At the back of the eye is spread out
the sensitive membrane--the retina. The structure of this membrane is
very complicated, and cannot be described here. It is, however,
indicated in Fig. 32. For our present purpose it is sufficient to note
that here are the end-organs of the optic nerve; that these consist of a
number of delicate rods and cones; and that these rods and cones do not
face in the direction from which the light comes, but face towards the
back of the eyeball, where a pigmented substance is developed. The rays
of light are thus focussed through the retina on to this pigmented
substance; the ends of the rods and cones are stimulated; and the
stimulation is handed on, augmented in certain intermediate ganglia, to
the delicate transparent nerve-fibres in the front of the retina. These
collect to a certain spot, where they pass through the retina to form
the optic nerve. Where they pass through the retina there can, of
course, be no rods and cones. And in this spot there is no power of
vision. It is the blind spot. The reality of its existence can easily be
proved. Make a dot on a piece of writing-paper, and about three inches
to the left of it place a threepenny or sixpenny bit. Close the right
eye, and look with the left eye at the dot. The sixpenny bit will also
be seen, but not distinctly. Keep the eye fixed on the dot, and move the
head slowly away from the paper. At a distance of about ten inches the
coin will completely disappear from view. Its image then falls on the
blind spot.
The organ of vision, then, in us consists of an essential sensory
membrane, the retina, with its delicate rods and cones; and an accessory
apparatus for focussing an inverted image on to the sensitive surface of
the retina. The surface is not, however, equally sensitive, or, in any
case, does not give an equal power of discrimination, throughout its
whole extent. This is seen in the experiment above described. When we
look at the dot we see the coin, but not distinctly. The area of clear
and distinct vision is, in fact, very small, constituting the yellow
spot about 1/12 of an inch (2 millimetres) long, and 1/30 of an inch (.8
millimetre) broad. And even within this small area there is a still more
restricted area of most acute sensibility only 1/120 of an inch (.2
millimetre) in diameter. Nevertheless, within this minute area there are
some two thousand cones, the rods being here absent. In carefully
examining an object we allow this area of acute vision to range over it.
Hence the extreme value of that delicate mobility which the eye
possesses--a mobility that is accompanied by muscular sensations of
great nicety.
We saw that the sense of touch in the tongue is sufficiently delicate to
enable us to recognize, as two, points of contact separated by 1/25 of
an inch (1.1 millimetre). What, in similar terms, is the delicacy of
sight? At what distance apart, on the most delicate part of the retina,
can two points of stimulation be recognized as distinct from each other?
If the points of stimulation be not less than 1/6000 of an inch (.004
millimetre) apart, they can be distinguished as two. Below this they
fuse into one. The diameter of the end of a single cone in the yellow
spot is also about 1/6000 of an inch (.0045 millimetre).
With regard to the mode in which the stimulation of the retinal elements
is effected, we have no complete knowledge. Certain observations of Boll
and Kühne, however, show that when an animal is killed in the dark the
retina has a peculiar purple colour which is at once destroyed if the
retina be exposed to light. If a rabbit be killed at the moment when the
image, say, of a window, is formed on the retina, and the membrane at
once plunged in a solution of alum, the image may be fixed, and an
"optogram" of the window may be seen on the retina. The discharge of the
colour of the retinal purple may be regarded as the sign of a chemical
change effected by the impact of the light-vibrations. But in the yellow
spot there seems to be no visual purple. It is, indeed, developed only
in the rods, not in the cones. Here, probably, chemical or metabolic
changes occur without the obvious sign of the bleaching of retinal
purple. In the dusk-loving owl the retinal purple is well developed, but
in the bat it is said to be absent.
We saw that in the case of hearing the auditory organ is fitted to
respond to air-borne vibrations varying from about thirty to thirty
thousand per second. And though the details of the process are at
present not well understood, it is believed that certain parts of the
recipient surface are fitted to respond to low tones, other parts to
intermediate tones, and yet others to high tones. Thus the reception is
serial. If there be two pianos near each other, accurately in tune, any
note struck on one will set the corresponding note vibrating in the
other.[FC] The auditory organ may be likened to this second piano.
Special parts respond to special tones.
Now, in the case of vision, the conditions are different. The reception
cannot be serial. As I range my eye over a flower-bed, I bring the area
of distinct vision on to a number of different colours, and these are
seen to be distinct, though they are received on the same part of the
retinal surface. It might, perhaps, be suggested that special cones were
set apart for each shade of colour. But there are only some two thousand
cones in the central area of most acute vision, and Lyons
silk-manufacturers prepare pattern cards containing as many shades of
coloured silks. So that there would be only one cone to each colour. And
Herschel thought that the workers on the mosaics of the Vatican could
distinguish at least thirty thousand different shades of colour! There
are also many phenomena of colour-blending which show that
colour-reception cannot in any sense be serial.
How, then, are we to account for our wide range of colour-sensation?
Just as the blending by the artist on his palette of a limited number of
pigments gives him the wide range of colour seen on his canvas, so the
blending of a few colour-tones may give us the many shades we are able
to distinguish. The smallest number of fundamental colour-tones which
will fairly well account for the phenomena of colour-vision, is three.
And these three are red, green, and blue or violet. These are the three
so-called primary colours. All others are produced from these elements
by blending.
To explain our ability to appreciate differences of colour, then, it is
supposed, on the hypothesis of Young and Von Helmholtz, that three kinds
of nerve-fibres exist in the retina, the stimulation of which gives
respectively, red, green, and violet in consciousness. Professor
McKendrick, interpreting Von Helmholtz, gives[FD] the following
scheme:--
"1. Red excites strongly the fibres sensitive to red, and feebly the
other two.
"2. Yellow excites moderately the fibres sensitive to red and green,
feebly the violet.
"3. Green excites strongly the fibres sensitive to green, feebly the
other two.
"4. Blue excites moderately the fibres sensitive to green and violet,
feebly the red.
"5. Violet excites strongly the fibres sensitive to violet, feebly the
other two.
"6. When the excitation is nearly equal for the three kinds of fibres,
the sensation is white."
This theory cannot be regarded as more than a provisional hypothesis.
Still, by its means we can explain many colour-phenomena. It is well
known, for example, that if we gaze steadily at a red object, and then
look aside at a grey surface, an after-image of the object will be seen
of a blue colour. According to the theory, the red fibres have been
tired and cannot so readily answer to stimulation. Over this part of the
retina, therefore, the effect of grey light is to stimulate normally the
fibres sensitive to green and violet, but only slightly those sensitive
to red, owing to their tired condition. The result will be, as we see
from the above scheme (4), the sensation of blue. Colour-blind people,
on this view, are those in whom one set of the fibres, generally the red
or the green, are lacking or ill developed.
We may, perhaps, with advantage restate this theory in terms of chemical
change, or metabolism. On this view three kinds of "explosives" are
developed in the retinal cones; for it is seemingly the cones, rather
than the rods, which are concerned in colour-vision. All three explosive
substances are unstable; but one, which we may call R., is especially
unstable for the longer waves of the spectrum; another, G., for the
waves of mid-period; a third, V., for those of smallest wave-length.
Suppose that R. only were developed. If, then, we were to look at a band
of light spread out in spectrum wave-lengths, we should see a band[FE]
of monochromatic _r_. light. Its centre would be bright, and here would
be the maximum instability of R. On either side it would fade away. The
lateral edges of the spectrum would be the limits of the instability of
R. If G. only were developed, we should see only a band of monochromatic
_g._ light. Its centre would not coincide with that for R., but would
lie in a region of smaller wave-length. Here would be the maximum
instability for G. On either side the green would fade away. Its lateral
edges would mark the limits of the instability of G. But though their
centres would not coincide, the R. band and the G. band would to a large
extent overlap. Similarly with the band for V. It, too, would have its
centre of maximum instability and its lateral edges of lessening
instability. Its centre would lie in a region of yet smaller wave-length
than that for G. And the _v._ band would overlap the green and the red.
Normally, all three bands are developed, and their blended overlapping
gives the colours of the rainbow. For this reason the monochromatic
bands _r._, _g._, and _v._ are unknown to us in experience. All the
colour-tints we know are blended tints. What we call full-red light
causes strong disruptive change in R., but decomposes slightly G., and
probably also, but in much less degree, V.
Whether R., G., and V. are all three present in each cone, or whether
they are each developed in separate cones, we do not know for certain.
Nor are we certain that there are separate nerve-fibres for the
transmission of stimuli due to R., G., and V.
When we look steadily at a red object we cause the disruption of R.; and
since it takes some time for the reformation and reconstitution of this
explosive substance, on turning the eye to a grey surface, G. and V. are
alone, or in preponderating proportions, caused to undergo disruption.
Hence the phenomena of complementary after-images. It is not merely a
matter of the tiring of certain nerve-fibres, but a using-up of the
explosive material in certain of the cones.
What is called _colour-blindness_ is probably due to one of several
abnormal conditions. It is _possible_ that in some cases R., G., or V.
may be entirely absent. More frequently they are in abnormal
proportions. They probably vary in their sensitiveness, and not
improbably in the wave-period to which they show the maximum response.
To test the variation, if any, in the limits of instability for R. and
V., or in any case in the limits of colour-vision at the red end and at
the violet end of the spectrum, in apparently normal individuals, my
friend and colleague, Mr. A. P. Chattock, made, at my suggestion, a
number of observations on some of the students of the University
College, Bristol, to whom my best thanks are due for their kind
willingness to be submitted to experiment. The instrument used[FF] was a
single-prism spectro-goniometer.
In the accompanying diagram (Fig. 33) the results of some of these
observations are graphically shown. The middle part of the spectrum,
between the wave-lengths 420 and 740 millionths of a millimetre, is
omitted, only the red end and the violet end being shown. The
observations on thirty-four individuals, seventeen men and seventeen
women, all under thirty years of age, are given for both eyes. The
left-hand vertical line of each pair stands for the right eye in each
case. To the left of the table are placed the wave-lengths in millionths
of a millimetre.
[Illustration: Fig. 33.--Variation in the limits of colour-vision.]
Take, for example, the first pair of vertical lines. The individual
whose colour-range they represent could detect red light in the spectrum
up to 800 millionths of a millimetre wave-length for the right eye, and
up to 811 for the left; and could detect violet light down to 403 and
404. Beyond these limits all was dark. But the last individual in the
series, while his range in the violet was about the same, could only
detect red light up to 743 and 750 millionths of a millimetre. His
spectrum was so much shorter.
It is seen that there is more variation at the red end than at the
violet end of the spectrum, and this notwithstanding that the violet
rays are more spread out by the prism than the red rays. It is seen that
the two eyes are often markedly different. This is not due to inaccuracy
of observation, for certain individuals in which this occurred were
tested several times with similar results. It is seen that the
variations at the red end and the violet end are often independent, and
that the absolute length of the visible spectrum differs in different
individuals.
The following table presents these observations and a few others in
another light:--
Table of Maxima and Minima in Wave-lengths, expressed In
Millionths of a Millimetre.
-------------------------------------------------------------------------
| Violet | Red |
|----------------------+----------------------| No. of
|Highest| Mean | Lowest|Highest| Mean |Lowest|Individuals
|-------+------+-------+-------+-------+------+-----------
Women under 30 | 410.0 |402.75| 394.0 | 811 | 772.85| 743 | 17
Men " " | 413.0 |405.0 | 399.0 | 811 | 772.8 | 743 | 17
Women over 30 | 410.5 |406.65| 401.5 | 792 | 767.8 | 743 | 7
Men " " | 407.0 |404.5 | 402.5 | 787 | 773.7 | 758 | 3
---------------------------------------+---------------------------------
N { right eye | 406 | 687
{ left eye | 407 | 717
-------------------------------------------------------------------------
The individual N showed signs of colour-blindness, and is therefore not
included in the table, but entered separately. He was unable to
recognize the C line of the hydrogen spectrum (wave-length 656), which
was brilliantly obvious to the normal eye.
These observations[FG] need further confirmation and extension. We
intend to continue the investigation each session. They are, however,
sufficient to show that in some individuals R. undergoes disruptive
change on the impact of light-waves which have no noticeable effect on
the retina of other individuals.
It is impossible here to do more than just touch the fringe of the
difficult subject of colour-vision. And the only further fact that can
here be noticed is that trichromatic colour-vision is apparently in us
limited to the yellow-spot and its immediate neighbourhood. Around this
is an area which is said to be bichromatic--all of us being, for this
area, more or less green-blind. In the peripheral area around this,
colour is indistinguishable, and we are only sensitive to light and
shade. So far as the structure of the retina is concerned, we may notice
in this connection that in the central region of most complete
trichromatic vision there are cones only; around the yellow spot each
cone is surrounded by a circle of rods; and further out into the
peripheral region by two, three, or more circles of rods.
Concerning the sense of sight in the lower mammals little need be said.
In many cases the acuteness of vision is remarkable. Mr. Romanes's
experiments on Sally, the bald-headed chimpanzee at Regent's Park, led
him to conclude that she was colour-blind, but I question whether the
experiments described quite justify this conclusion. Sir John Lubbock
was unable to teach his intelligent dog Van to distinguish between
coloured cards; but the failure was as complete when the cards were
marked respectively with one, two, or three dark bands. We are not
justified, therefore, in ascribing the failure to colour-blindness. The
real failure, probably, was in each case to make the animal understand
what was wanted. Bulls are, at any rate, credited with strong
colour-antipathies, and insect-eating mammals are probably not defective
in the colour-sense.
It is said that nocturnal animals, such as mice, bats, and hedgehogs,
have no retinal cones; and if the cones are associated with
colour-vision, they may not improbably be unable to distinguish colours.
Some moles are blind (e.g. the Cape golden mole). But the common
European mole, though the eyes are exceedingly minute (1/25 of an inch
in diameter), has the organ fairly developed, and is even said not to be
very short-sighted. It is protected by long hairs when the animal is
burrowing, and is only used when it comes to the surface of the ground.
It is probably in birds that vision reaches its maximum of acuteness. A
tame jackdaw will show signs of uneasiness when seemingly nothing is
visible in the sky. Presently, far up, a mere speck in the blue, a hawk
will come within the range of far-sighted human vision. Steadily watch
the speck as the hawk soars past, until it ceases to be visible; the
jackdaw will still keep casting his eye anxiously upward for some little
time. He may be only watching for the possible reappearance of the hawk.
But just as he saw it before man could see it, so probably he still
watches it after, to man's sight, it has become invisible. So, too, for
nearer minute objects, the swift, as it wheels through the summer air,
presumably sees the minute insects which constitute its food. And every
one must have noticed how domestic fowls will pick out from among the
sand-grains almost infinitesimal crumbs.
It is probable that the area of acute vision is much more widely
diffused over the retina of birds than it is with us. In any case, the
cones are more uniformly and more abundantly distributed over the
general retinal surface.
An exceedingly interesting and important peculiarity in the retina of
birds, which they share with some reptiles and fishes, is the
development, in the cones, of coloured globules. "The retinæ of many
birds, especially of the finch, the pigeon, and the domestic fowl, have
been carefully examined by Dr. Waelchli, who finds that near the centre
green is the predominant colour of the cones, while among the green
cones red and orange ones are somewhat sparingly interspersed, and are
nearly always arranged alternately--a red cone between two orange ones,
and _vice versâ_. In a surrounding portion, called by Dr. Waelchli the
red zone, the red and orange cones are arranged in chains, and are
larger and more numerous than near the yellow spot; the green ones are
of smaller size, and fill up the interspaces. Near the periphery the
cones are scattered, the three colours about equally numerous and of
equal size, while a few colourless cones are also seen. Dr. Waelchli
examined the optical properties of the coloured cones by means of the
micro-spectroscope, and found, as the colours would lead us to suppose,
that they transmitted only the corresponding portions of the spectrum;
and it would almost seem, excepting for the few colourless cones at the
peripheral part of the retina, that the birds examined must have been
unable to see blue, the whole of which would be absorbed by their
colour-globules."[FH]
These facts are of exceeding interest. They seem to show that for these
birds the retinal explosives are not the same as for us. They are R.,
O., and G. Moreover, the colour-globules will have the effect of
excluding the phenomena of overlapping. For each kind of cone the
spectrum must be limited to the narrow spectral band transmissible
through the associated colour-globule. If these facts be so, it is not
too much to say that the colour-vision of birds must be so utterly
different from that of human beings, that, being human beings, we are
and must remain unable to conceive its nature. The factors being
different, and the blending of the factors by overlap being, by
specially developed structures, lessened or excluded, the whole set of
resulting phenomena must be different from ours. And this is a fact of
the utmost importance when we consider the phenomena of sexual selection
among birds, and those theories of coloration in insects which involve a
colour-sense in birds.
Concerning the sense of sight in reptiles and in amphibians, little need
here be said. At near distances some of them undoubtedly have great
accuracy of vision. This is, perhaps, best seen in the chamæleon. In
this curious animal the eyes are conical, and each moves freely,
independently of the other. The eyelids encase the organ, except for a
minute opening, looking like a small ink-spot at the blunted apex of the
cone. The animal catches the insects on which it feeds by darting on to
them its long elastic tongue and slinging them back into the mouth,
glued to its sticky tip. Its aim is unerring, but it never strikes until
both eyes come to rest on the prey, and great accuracy of vision must
accompany the great accuracy of aim. Frogs and toads capture their prey
in a somewhat similar way; and a great number of reptiles and amphibians
are absolutely dependent for their subsistence on the acuteness and
accuracy of their vision, which is, however, on the whole, markedly
inferior to that of birds.
In fishes, from their aquatic habit, the lens and dioptric apparatus are
specially modified, in accordance with the denser medium in which they
live; and one curious fish, the Surinam sprat, is stated to have the
upper part of the lens suited for aerial, and the lower part for aquatic
vision.
Mr. Bateson[FI] has made some interesting observations on the sense of
sight in fishes. He finds that in the great majority of fishes the shape
and size of the pupil do not alter materially in accordance with the
intensity of the light. The chief exceptions are among the Elasmobranchs
(dog-fishes and skates). In the torpedo the lower limb of the iris rises
so as almost to close the pupil, leaving a horizontal slit at the upper
part of the eye. In the rough dog-fish, the angel-fish, and the
nurse-hound, the pupil closes by day, forming merely an oblique slit. In
the skate a fern-like process descends from the upper limb of the iris.
The contraction in these cases does not seem to take place rapidly as in
land vertebrates, but slowly and gradually.
Among diurnal fishes belonging to the group of the bony fishes
(Teleosteans), the turbot, the brill, and the weever have a semicircular
flap from the upper edge of the iris, which partially covers the pupil
by day, but is almost wholly retracted at night.
None of the fishes observed by Mr. Bateson appears to distinguish food
(worms) at a greater horizontal distance than about four feet, and for
most of them the vertical limit seemed to be about three feet; but the
plaice at the bottom of the tank perceived worms when at the surface of
the water, being about five feet above them. Most of them exhibited
little power of seeing an object below them. But though the distance of
clear vision seems to be so short for small objects in the water, many
of these fish (plaice, mullet, bream) notice a man on the other side of
the room, distant about fifteen feet from the window of the tank. The
sight of some fishes, such as the wrasses (_Labridæ_), is admirably
adapted for vision at very close quarters. "I have often seen," says Mr.
Bateson, "a large wrasse search the sand for shrimps, turning sideways,
and looking with either eye independently, like a chamæleon. Its vision
is so good that it can see a shrimp with certainty when the whole body
is buried in grey sand excepting the antennæ and antenna-plates. It
should be borne in mind that, if the sand be fine, a shrimp will bury
itself absolutely, digging with its swimmerets, kicking the sand
forwards with its chelæ, finally raking the sand over its back, and
gently levelling it with its antennæ; but if the least bit be exposed,
the wrasses will find it in spite of its protective coloration."
* * * * *
[Illustration: Fig. 34.--Pineal eye.
Modified eye-scale of a small lizard, _Varanus benekalensis_. (After
Baldwin Spencer.)]
Although it is probably not functional in any existing form, mention
must here be made of the median or pineal eye. On the head of the common
slow-worm, or blind-worm, there is a dark patch surrounding a brighter
spot. This is the remnant of a median eye. It has been found in varying
states of degeneration in many reptiles (Fig. 34), and in a yet more
vestigial form in some fishes and amphibia. It is connected with a
curious structure, associated with the brain of all vertebrates, and
called the pineal gland. Descartes thought that this was the seat of the
soul; but modern investigation shows it to be a structure which has
resulted from the degeneration of that part of the brain which was
connected with the median eye. There is some reason to suppose that, in
ancient life-forms, like the Ichthyosaurus, and Plesiosaurus, and the
Labyrinthodont amphibians, it was large and functional. In any case,
there is a large hole in the skull (Fig. 35) through which the nervous
connection with the brain may have been established. The structure of
the eye is not similar to that of the lateral eye, but more like that of
some of the invertebrates.
To these invertebrates we must now turn.
[Illustration: Fig. 35.--Skull of _Melanerpeton_.
A Labyrinthodont amphibian from the Permian of Bohemia (after Fritsch).
× 4. Pa., the parietal foramen.]
* * * * *
Insects have eyes of two kinds. If we examine with a lens the head of a
bee, we shall see, on either side, the large compound or facetted eye;
but in addition to these there is on the forehead or vertex a triangle
of three small, bright, simple eyes, or ocelli. These ocelli, or
eyelets, differ, in different insects, as to the details of their
structure; but in general they consist of a lens produced by the
thickening of the integumentary layer which is at the same time rendered
transparent. Behind this lies the so-called vitreous body, composed of
transparent cells, and then follows the retina, in which there are a
number of rods, the recipient ends of which are turned towards the rays
of light, and not away from them as in the vertebrate. Spiders have from
six to eight ocelli, arranged in a pattern on the top of the head.
Facetted eyes are not found in them.
[Illustration: Fig. 36.--Eyes and eyelets of bee.
A. Drone. B. Worker.]
These facetted eyes, which are found in both insects and crustacea, have
apparently a more complex structure than the ocelli. Externally--in the
bee, for example--the surface is seen to be divided up into a great
number of hexagonal areas, each of which is called a facet, and forms
(in some insects, but not in all) a little lens. Of these the queen bee
has on each side nearly five thousand; the worker some six thousand; and
the drone upwards of twelve thousand; while a dragon-fly (_Æschna_) is
stated to have twenty thousand. Beneath each facet (in transverse
section, Fig. 37) is a crystalline cone, its base applied to the lens,
its apex embraced by a group of elongated cells, in the midst of which
is a nerve-rod which is stated to be in direct connection with the
fibres of the optic nerve. Dark pigment is developed around the
crystalline cones. And retinal purple is said to be present in the cells
which underlie it.
With regard to these facetted eyes there has been much discussion. The
question is--Is each facetted organ an eye, or is it an aggregate of
eyes? To this question the older naturalists answered confidently--An
aggregate. A simple experiment seems to warrant this conclusion. If the
facetted surface be cleared of its internal structures (the crystalline
cones, etc.) and placed under the microscope, each lens may, at a
suitable distance of the object-glass, be made to give a separate image
of such an object as a candle reflected in the mirror of the microscope.
If each lens thus gives an image, is not each the focussing apparatus of
a single eye? But a somewhat more difficult experiment points in another
direction. If the facetted cornea be removed _with the crystalline cones
still attached_ (Grenacher was able to do it with a moth's eye), and
placed under the microscope, when the instrument is focussed at the
point of the cone (where the nerve-rod comes), a spot of light, and not
an image, is seen. No image can be seen unless the microscope be
focussed for the centre of the cone; and here there are no structures
capable of receiving it and transmitting corresponding waves of change
to the "brain."
[Illustration: Fig. 37.--Eye of fly.
Transverse section through head. (After Hickson.)]
But what, it may be asked, can be the purpose of an eye-structure which
gives, not an image, but merely a spot of light? The answer to this
question can only be found when it is remembered that there are
thousands of these facets and cones giving thousands of spots of light.
The somewhat divergent cones and facets of the insect's eye (Fig. 37)
embrace, as a whole, an extended field of vision; each has its special
point in that field; and each conveys to the nerve-rod which lies
beneath it a stimulation in accordance with the brightness, or
intensity, or quality of that special point of the field to which it is
directed. The external field of vision is thus reproduced in miniature
mosaic at the points of the crystalline cones--thus there is produced by
the juxtaposition of contiguous points a stippled image. And it must be
remembered that, even in human vision, the stimulation is not that of a
continuum, but is stippled with the fine stippling of the ends of the
rods and cones. In insect-vision the stippling is far coarser, and the
image is produced on different principles.
[Illustration: Fig. 38.--Diagram of mosaic vision.]
In the vertebrate the image is produced by a lens; in the insect's eye,
by the elongated cones. How this is effected will be readily seen with
the aid of the diagram. At _a b_ are a number of transparent rods,
separated by pigmented material absorbent of light. They represent the
crystalline cones. At _c d_ is an arrow placed in front of them; at _e
f_ is a screen placed behind them. Rays of light start in all directions
from any point, _c_, of the arrow; but of these only that which passes
straight down one of the transparent rods reaches the screen. Those
which pass obliquely into other rods are absorbed by the pigmented
material. Similarly with rays starting from any other point of the
arrow. Only those which, in each case, pass straight down one of the
rods reach the screen. Thus there is produced a reduced stippled image,
_c' d'_, of the arrow.
There has been a good deal of discussion as to the relative functions of
the ocelli and the facetted eyes of insects. The view generally held is
that the ocelli are specially useful in dark places and for near vision;
while the facetted eyes are for more distant sight and for the
ascertainment of space-relations. How the two sets of impressions are
correlated and co-ordinated in insect-consciousness, who can say?[FJ]
The interesting observations of Sir John Lubbock seem to show that
insects can distinguish between different colours. "Amongst other
experiments," he says,[FK] "I brought a bee to some honey which I placed
on a slip of glass laid on blue paper, and about three feet off I placed
a similar drop of honey on orange paper. With a drop of honey before her
a bee takes two or three minutes to fill herself, then flies away,
stores up the honey, and returns for more. My hives were about two
hundred yards from the window, and the bees were absent about three
minutes or even less. After the bee had returned twice, I transposed the
papers; but she returned to the honey on the blue paper. I allowed her
to continue this for some time, and then again transposed the papers.
She returned to the old spot, and was just going to alight, when she
observed the change of colour, pulled herself up, and without a moment's
hesitation darted off to the blue. No one who saw her at that moment
could have the slightest doubt about her perceiving the difference
between the two colours."
Passing now to the crustacea, we find in them eyes of the same type as
in insects; but in the higher crustacea ocelli are absent. In the crabs
and lobsters the eyes are seated on little movable pedestals; in the
former the crystalline cones are very long, in the latter they are
short. There can be little doubt that vision is by no means wanting in
acuteness in an animal which, like the lobster, can dart into a small
hole in the rocks with unerring aim from a considerable distance. The
experiments of Sir John Lubbock have shown that the little water-flea
(_Daphnia_) can distinguish differences of colour, yellows and greens
being preferred to blues or reds.
Among the molluscs there are great differences in the power of sight.
Most bivalves, like the mussel, are blind. Interesting stages in the
development of the eye may be seen in such forms as the limpet,
_Trochus_ and _Murex_. The limpet has simply an optic pit, the _Trochus_
a pit nearly closed at the orifice and filled with a vitreous mass, and
the _Murex_ a spherical organ completely closed in with a definite lens.
The snail has a well-developed eye on the hinder and longer horn or
tentacle. But it does not seem to be aware of the presence of an object
until it is brought within a quarter of an inch or less of the tentacle.
In all probability the eye does little more than enable the snail to
distinguish between light and dark. And the same may be said of the eye
of many of the molluscs. In some, however, the cuttle-fishes and their
allies, the eye is so highly developed that it has been compared with
that of the vertebrate. There is an iris with a contractile pupil. And
the ganglion with which it is connected forms a large part of the
so-called brain. The powers of accurate vision in these higher forms are
probably considerable.
It is interesting to note that whereas in the cuttle-fishes and most
molluscs, the rods of the retina are turned towards the light, in
_Pecten_, _Onchidium_ (a kind of slug), and some others, they are, as in
vertebrates, turned from the light. In _Pecten_ the nerve to supply the
retina bends round its edge at one side. But in _Onchidium_ it pierces
the retina as in vertebrates.
In worms, eyes are sometimes present, sometimes absent. In star-fishes
and their allies they often occur. In medusæ (jelly-fish) they are
sometimes found on the margin of the umbrella. Even in lowly organisms,
like the infusoria, eye-spots not unfrequently occur. We must remember,
however, that, in these lower forms of life, the organs spoken of as
eyes or eye-spots merely enable the possessor to distinguish light from
darkness.
Even when eyes or eye-spots are not developed, the organism seems to be
in some cases sensitive to light--using the word "sensitive," once more,
in its merely physical acceptation. The earthworm, for example, though
it has no eyes, is distinctly sensitive to light; and the same has been
shown to be the case with other eyeless organisms. Graber holds that his
experiments demonstrate that the eyeless earthworm can distinguish
between different colours--in other words, is differentially sensitive
to light-waves of different vibration-period--preferring red to blue or
green, and green to blue. And the same observer has shown that animals
provided with eyes--the newt, for example--can distinguish between light
and darkness by the general surface of the skin. M. Dubois, by a number
of experiments on the blind _Proteus_ of the grottoes of Carniola, has
shown that the sensitiveness of its skin to light is about half that of
its rudimentary eyes; and, further, that this sensibility varies with
the colour of the light employed, being greatest for yellow light.[FL]
We have not been able to do more than make a rapid survey of the sense
of sight as it seems to be developed in the invertebrates and lower
animals. The visual organs differ, not only in structure, but in
principle. We may, I think, distinguish four types.
1. Organs for the mere appreciation of light or darkness (shadow),
exemplified by pigment-spots, with or without concentrating apparatus.
2. Organs for the appreciation of the direction of light or shadow, with
or without a lens. The simple retinal eyes of gasteropods, and perhaps
in some cases the ocelli of insects, probably belong to this class.
3. True eyes, or organs in which a retinal image is formed, through the
instrumentality of a lens, as in vertebrates and cephalopods.
4. The facetted eyes of insects, in which a stippled image is formed, on
the principle of mosaic vision.
Unfortunately, all these are called indiscriminately eyes, or organs of
vision. An infusorian or a snail is said to see. But the terms "eye,"
"vision," "sight," imply that final excellence to which only the higher
animals, each on its own line, have attained.
This final excellence probably has its basis and earliest inception in
the fact that the functional activity of protoplasm is heightened in the
presence of ætherial vibrations. If, then, we imagine, as a
starting-point, a primitive transparent organism with a general
susceptibility to the influence of light-vibrations, the formation
within its tissues of pigment-granules absorbent of light will render
the spots where they occur specially sensitive to the ætherial
vibrations. Special refraction-globules would also act as minute lenses,
focussing the light, and thus concentrating it upon certain spots.
[Illustration: Fig. 39.--Direction-retina.
Simple retina for distinguishing the direction of the source of light or
of shadow.]
In many of the lower animals we find such organs, belonging to our first
category, and constituting either eye-spots of pigmented material or
simple lenses covering a pigmented area. If we call these eyes, we must
remember that in all probability they have no power of what we call
vision--only a power of distinguishing light from dark. Where, however,
there exists beneath the lens a so-called retina, that is, a layer of
rod-like endings of a nerve, it might, at first sight, be thought that
there, at any rate, we have true vision. But in all probability, in a
great number of cases the retinal rods are simply for the purpose of
rendering the organism sensitive, not only to the presence of light, but
to its direction. Light straight ahead (_a_) stimulates the middle rods;
from one side (_b_, _c_) it is focussed on the rods of the opposite side
of the retina; and similarly for intermediate positions. The presence of
a retinal layer is thus no infallible sign of a power of vision as apart
from mere sensibility to light. Indeed, in a great number of cases, from
the convexity and position of the lens, the formation of an image is
impossible. Only when it can be shown that a more or less definite image
can be focussed on the retina, or can be formed on the principle of
mosaic vision, can we justly surmise that a power of true vision is
present. I doubt whether this can be shown to be unquestionably the case
in any forms but the higher arthropods, the cuttle-fishes and their
allies, and the vertebrates.
There is one more point for consideration before we leave the sense of
sight--Are the limits of vision the same in the lower forms of life as
they are in man? or, to put the question in a more satisfactory
form--Are the limits of sensibility to light-vibrations the same in them
as in us? M. Paul Bert concluded that they are. But Sir John Lubbock
has, I think, conclusively shown that they are not. For the full
evidence the reader is referred to his "Senses of Animals."[FM] His
experiments on ants, with which those of M. Forel are in complete
accordance, satisfied him that these little animals are sensitive to the
ultra-violet rays which lie beyond the range of our vision. Other
experiments with fresh-water fleas (_Daphnia_) showed that they have
colour-preferences, green and yellow being the favourite colours.
The daphnias were placed in a shallow wooden trough, divided by movable
partitions of glass into divisions. Over this was thrown a spectrum of
rainbow colours. The partitions were removed, and the daphnias allowed
to collect in the differently illuminated parts of the trough. The
partitions were then inserted, and the number of crustaceans in each
division counted. The following numbers resulted from five such
experiments:--
Dark. Violet. Blue. Green. Yellow. Red.
0 3 18 170 36 23
Special experiments seem to show that their limits of vision at the red
end of the spectrum coincide approximately with ours; but at the violet
end their spectrum is longer than ours. Sir John covered up the visible
spectrum, so as to render it dark, and gave the daphnias the option of
collecting in this dark space or in the ultra-violet. To human eyes both
were alike dark. But not so to the daphnian eye; for while only 14
collected in the covered part, 286 were found in the ultra-violet. The
width of the violet visible to man was two inches. Sir John divided the
ultra-violet into three spaces of two inches each. Of the 286 daphnias,
261 were in the space nearest the violet, 25 in the next space, and none
in the furthest of the three spaces. From which it would seem that,
though these little creatures are sensitive to light of higher
vibration-period than that which affects the human eye, their limits do
not very far exceed ours. We have seen that human beings differ not a
little in their limits of violet-susceptibility. We may presume that Sir
John Lubbock and those who assisted him in these experiments were normal
in this respect. But it is possible that some individuals could have
perceived a faint purple where there was darkness to them, and that the
majority of the 261 daphnias were collected in the region just beyond
the partition between ultra-violet and darkened violet. Still, there is
no cause for doubting the general conclusion that daphnias are sensible
to ultra-violet rays beyond the limits of human vision.
* * * * *
[Illustration: Fig. 40.--Antennary structures of hymenoptera. (After
Lubbock.)
a., cuticle; b., hypodermis; c., ordinary hair; d., tactile hair; e.,
cone; f., depressed hair lying over g. cup with rudimentary hair at the
base; h., simple cup; i., champagne-cork-like organ of Forel; k.,
flask-like organ; l., papilla, with a rudimentary hair at the apex.]
Sir John Lubbock has an interesting chapter on problematical organs of
sense. In the antennæ of ants and bees there are modified hairs and pits
in the integument (at least eight different types, according to Sir John
Lubbock), the sensory nature of which is undoubted. But what the sensory
nature in each case may be is more or less problematical. Many worms
have sense-hairs or bristles of the use of which we are ignorant. Some
organs described as tactile or olfactory in the lower invertebrates are
so described on a somewhat slender basis of evidence. The sense-value of
the bright marginal beads of sea-anemones is unknown. Even in animals as
high in the scale of life as fishes, there is a complete set of
sense-organs--the muciparous canals, in the head and along the lateral
line down the side, the function of which we can only guess. By some
they are regarded as olfactory; by others, as fitted to respond to
vibrations or shocks of greater wave-length than the auditory organ can
appreciate; by others, as of importance for the equilibration or
balancing of the fish.
It will thus be seen that, apart from the possibility of unknown
receptive organs as completely hidden from anatomical and microscopic
scrutiny as the end-organs of our temperature-sense, there are in the
lower animals organs which may be fitted to receive modes of influence
to which we human folk are not attuned.
And what are the physical possibilities? We have seen that, through the
telæsthetic senses--hearing, vision, and the temperature-sense--we are
made aware of the vibrations of distant bodies, the effects of which are
borne to us on waves of air or of æther. The limits of hearing with us
are between thirty and about forty thousand (or perhaps, in very rare
cases, fifty thousand) vibrations per second. But these are by no means
the limits of vibrations of the same class. By experiments with
sensitive flames,[FN] Lord Rayleigh has detected vibrations of fifty-six
thousand per second; and Mr. W. F. Barrett has shown that a sensitive
flame two feet long is sensitive to vibrations beyond the limit of his
own hearing and that of several of his friends who were present at the
experiment. We have some reason to suppose that vibrations too rapid to
be audible by man are audible by insects, but not much is known with
regard to the exact limits.
The following table shows what is known concerning the æther-vibrations.
The figures are those given by Professor Langley:--
Wave-lengths Number of
in thousandths vibrations
Quality of radiations. of a per second Effects on man.
millimetre. in billions.
Limit of photography,
artificial source 0.185 160 none known
Limit of photography,
solar source 0.295 none known
Limit of violet to normal eyes 0.36 833 }
Limit of red to normal eyes 0.81 370 } vision.
Probable inferior limit of
temperature-sensations 9.25[FO] 30 temperature-sense
Longest waves hitherto
recognised with bolometer 30.0 1 none known
From this table it will be seen that, apart from the possible extension
of sight beyond human limits, there are possibilities of another sense
for the ultra-violet actinic vibrations as different from sight as is
the infra-red temperature-sense. Moreover, the temperature-sense for us
has no scale; there is nothing corresponding to pitch in sound or colour
in sight. It may not be so with lower organisms. Insects, for example,
may be sensitive to tones of heat. The bee may enjoy a symphony of solar
radiance. I am not saying that it is so; I am merely suggesting
possibilities which we have not sufficient knowledge to authoritatively
deny. We have no right to impose the limits of human sensation on the
entire organic world. Insects may have "permanent possibilities of
sensation" denied to us.
Even within our limits there may be, as we have already seen, great and
inconceivable differences. We saw that our own colour-sensations are
probably due to the blending and overlapping in different proportions of
three primitive monochromatic bands, but that in all probability in
birds the bands are different, and overlapping is largely prevented.
Their colour-phenomena must be inconceivably different from ours. And
what shall we say of the colour-vision of invertebrates? Are we
justified in supposing that for them, as for us, R., G., and V. are the
unstable explosives, and that they are present in the same proportions
as with us? If not, their colour-world cannot be the same as ours. Of
the same order it probably is. And all that we can hope to do is to
show, as has been shown, that colours which differently affect us affect
them also differently.
* * * * *
In conclusion, we may return to the point from which we set out. The
organism is fitted to respond to certain influences of the external
world. The organs for the reception of these influences are the
sense-organs. When they are stimulated waves of change are transmitted
inwards to the great nerve-centres; they are there co-ordinated, and
issue thence to muscles or glands. Thus the organism is fitted to
respond to the influences from without. The activities of organisms are
in response to stimulation.
We have seen that the cells of the organic tissues are like little
packets of explosives, and that the changes which occur in the organism
may be likened to their explosion and the setting free of the energy
stored up in them. The end-organs of the special senses may be regarded
as charged with explosives of extreme sensitiveness. Some are fired by a
touch; the molecular vibrations of sapid or odorous particles explode
others; yet others are fired by the coarser vibrations of sound; others,
once more, by the energy of the ætherial waves. The visual purple is a
highly unstable chemical compound of this kind; expose it for a moment
to light, and it topples over to a new molecular arrangement, the colour
being at the same time discharged. If the retina has been removed from
the body, this is all that happens. But if (in the frog) it be replaced
on the choroid layer from which it has been stripped, the visual purple
is reformed. The explosive is thus reconstructed and the sensibility is
restored. Thus, as fast as the explosives are fired off by
sense-stimuli, so fast in normal life are they reconstituted and the
sensibility restored. Meanwhile the explosion at the end-organs has
fired the train of explosives in the nerve, and created molecular
explosive disturbances in the brain. Thence the explosive waves pass
down other nerves to muscles or glands, and, giving rise therein to
further explosions, take effect in the activities of the organism.
We shall have to consider these activities hereafter. We must now turn
to the psychical or mental accompaniments of the explosive disturbances
in the brain or other aggregated mass of nerve-cells.
NOTES
[EO] See abstract in _Nature_, vol. xxxiv. p. 515.
[EP] See _Nature_, vol. xxxvii. p. 557.
[EQ] "Sense-Organs and Perception of Fishes:" Journal of Marine
Biological Association, New Series, vol. i. No. 3, p. 225.
[ER] _Nature_, vol. xlii. p. 201.
[ES] _Nature_, vol. xxxvi. p. 273.
[ET] Journal of Marine Biological Association, New Series, vol. i. No.
3, p. 235.
[EU] Mr. S. Klein mentions a similar fact in connection with _Bombyx
quercus_ (_Nature_, vol. xxxv. p. 282).
[EV] Journal of Marine Biological Association, New Series, vol. i. No.
2, p. 211.
[EW] A friend of mine informs me that his limit is about 17,500 per
second, 20,000 being quite inaudible.
[EX] Journal of Marine Biological Association, New Series, vol. i. No.
3, p. 251.
[EY] Of course, anglers will say that what may be true for pollack and
other coarse and vulgar sea-fish does not apply to King Salmon or
Prince Trout.
[EZ] "Senses of Animals," p. 117.
[FA] See a very interesting and lucid paper by Professor Crum Brown,
whose name is intimately connected with this subject, in _Nature_,
vol. xl. p. 449.
[FB] It is interesting to note that in the blind-fish (_Amblyopsis
spelæus_) the semicircular canals are, according to Wyman,
unusually large.
[FC] The dampers must, of course, be lifted by depressing the loud
pedal.
[FD] "Special Physiology," p. 636.
[FE] A band and not a line, because R. is unstable to the impact of a
considerable range of light-vibrations.
[FF] Mr. Chattock has kindly supplied me with the following note:--
"Readings at the violet end were taken at the extremity of the
lavender rays, at the point where the faint band of lavender light
seemed to end off about half-way across the field of view (the
cross-wires being invisible).
"At the red end the cross-wires were always visible, and were in
each case set to the point where the top horizontal edge of the
spectrum lost its definition.
"Other things equal, the 'red' readings should be more reliable than
the violet, therefore, from the greater definiteness of the point
observed, and the means of observing it. But against this has to
be set off the fact that the extreme violet rays were spread out
by the prism used more than eight times as much as the red rays.
"In any case, the wide differences observed in the 'red' readings
are much greater than could have been due to misunderstanding or
careless observation--as shown by setting the instrument to
maximum and minimum readings, and noting the very obvious
difference between them apparent to a normal eye. The same
conclusion is rather borne out by the closer (average) agreement
between the two eyes of the same individual than between those of
different persons.
"The source of light was the central portion of an ordinary Argand
burner."
[FG] The variations above indicated throw light on a fact to which Lord
Rayleigh has directed attention. The yellow of the spectrum may be
matched by a blending of spectral red and spectral green; but the
proportions in which these spectral colours must be mixed differ
for different individuals. The complementary colours for different
individuals are also not precisely the same.
[FH] "Colour-Vision and Colour-Blindness," R. Brudenell Carter
(_Nature_, vol. xlii. p. 56).
[FI] Journal of Marine Biological Association, New Series, vol. i. Nos.
2 and 3. His experiments with regard to the colour-sense in fishes
gave, for the most part, negative results.
[FJ] We must remember how largely the antennæ are used when an insect
is finding its way about. Watch, for example, a wasp as it climbs
over your plate. If the antennæ be removed, it seems to stumble
about blindly. The antennæ seem almost to take the place of eyes
at close quarters.
[FK] "Senses of Animals," p. 194.
[FL] See _Nature_, vol. xli. p. 407.
[FM] Chap. x. p. 202.
[FN] The observations are not yet published, and I have to thank Lord
Rayleigh for his courtesy in allowing me to make use of this fact.
[FO] Professor Langley finds that the maximum effect with a radiating
source
at 170° C. is at about 5.0 thousandths of a millimetre wave-length.
" 100° C. " " 7.5 " " "
" 0° C. " " 11.0 " " "
We are sensitive to radiations from a body at 100° C. But when the
temperature falls below the normal temperature of the body we are
not sensitive to heat-vibrations, but to loss of heat from the
surface exposed. The limit of sensibility to heat-vibrations,
therefore, probably lies between 7.5 and 11 thousandths of a
millimetre. I have taken about 9.25 as the limit.
CHAPTER VIII.
MENTAL PROCESSES IN MAN.
I have already drawn attention to the fact that the primary end and
object of the reception of the influences (_stimuli_) of the external
world, or environment, is to enable the organism to answer or respond to
these special modes of influence, or stimuli. In other words, their
purpose is to set agoing certain activities. Now, in the unicellular
organism, where both the reception and the response are effected by one
and the same cell, the activities are for the most part simple, though
even among these protozoa there are some which show no little complexity
of response. Where, however, the organism is composed of a number of
cells, in which a differentiation of structure and a specialization of
function have been effected, certain cells are set apart as
_recipients_, while other cells are set apart to respond
(_respondents_). There is thus the necessity of a channel of
communication between the two. Hence yet other cells (_transmitters_),
arranged end to end, form a line of connection and communication between
the group of receiving cells and the group of responding cells, and
constitute what we term a _nerve_. That which is transmitted may still
be called a stimulus, each cell being stimulated in turn by its
neighbour. Thus a stimulus must be first received and then transmitted.
But little observation is required to convince us of the fact that, in
the higher creatures, a very simple stimulus may give rise to a very
complex response. A light pin-prick will cause a vigorous leap in a
healthy frog--a leap that involves a most intricate, accurate, and
complex co-ordination of muscular activities. And anatomical
investigation shows us that in such creatures there is always, in the
course of the channel of communication or transmission, a group of
closely connected cells, which play the part of co-ordinants. In the
vertebrate animals these co-ordinants are collected in the brain and
spinal cord. In the insects, crustaceans, and worms they are arranged in
a knotted chain running close to the under surface of the body. To this
central nervous system, as it is called, nerves (afferent nerves) run
inwards from the recipient organs. From it nerves (efferent nerves) run
outwards to the organs of response. And in it the transmitted stimuli,
brought in by the afferent nerves, are modified, through intervention of
the co-ordinants, into stimuli carried out by the efferent nerves. A
simple stimulus may create a great commotion among the co-ordinants of
the central nervous system, and give rise to many and complex stimuli
going out to the muscles and other organs of response. How this is
effected is one of the many wonders of the animal mechanism. We believe
that the connection and co-ordinations have gradually been established
during a long process of development and evolution, reaching back far
into the past. How, we can at present scarcely guess.
We must picture to ourselves, then, in the animal organism, a multitude
of nerve-fibres running inwards from all the end-organs of the special
senses, from the muscles, and from the internal organs, and all
converging on the central nervous system. And we must picture to
ourselves a multitude of nerve-fibres passing outwards from the central
system, and diverging to supply the muscles, glands, and other organs
which are to respond to the stimulation from without. We must picture
the fibres coming from or going to related parts or organs collecting
together to form nerves and nerve-trunks, which are, however, only
bundles of isolated nerve-fibres. And, lastly, we must picture the
central nerve-system itself co-ordinating and organizing the stimuli
brought into it by afferent nerves, from the organs of special sense,
and handing over the resultants by efferent nerves to the organs of
special activities. So far we have purely physiological effects, many of
which occur with surprising accuracy and precision when an organism is
in a state of unconsciousness. Place your finger in the palm of a
sleeping child, and the fingers will close over it without the child
awaking to consciousness. If, in a frog, the brain of which has been
extirpated, the side be touched with a drop of acid, the leg of that
side will be drawn up, and the foot will be used to wipe away the acid.
And if that leg be held and prevented from reaching the side, the other
leg will be brought round so as to try and bring the foot within reach
of the irritated spot. The actions are, however, in all probability,
purely physiological, and are performed in complete absence of
consciousness.
* * * * *
When we turn from the physiological to the psychological aspect of the
question, we enter a new world, the world of consciousness, wherein the
impressions received by the recipient organs (no longer regarded as mere
stimuli, but as the elements of consciousness) are co-ordinated and
organized, and are built up into those sensations and perceptions
through which the objects of the external world take origin and shape.
It is with this process that we have now to deal; and we will deal with
it first in man.
The first fact to notice is that, apart from sense-stimuli received and
exciting consciousness, we have also the revival of past impressions.
This revival is the germ of memory. What exactly is the physical basis
of memory, how the effects of stimuli in consciousness come to be
registered, we do not know. It is clearly a matter that falls under the
general law of persistence; but in what organic manner we are largely
ignorant. Still, there can be no question of the fact that, quite apart
from impressions due to immediate influences of the environment _now_
acting on our recipient organs, we have also revivals of bygone
influences of the environment--shadows or after-images of previous modes
of influence. Without this process of registration and revival, stimuli
could never give rise to sensations and perceptions such as we know
them. Without it experience would be impossible.
We may say, then, that impressions (resulting from stimuli) and their
revival in memory are the bricks of the house of knowledge; and these
are built up through experience into what we call the world of things
around us. There may be and is a certain amount of mortar, supplied by
the builder, in addition to the elementary bricks. But without the
bricks no house of knowledge could be built. Let us now examine the
bricks and the building.
From what we have already learnt in the chapter on "The Senses of
Animals," it is clear that the impressions and their revivals in memory
have differences in quality. Here, on the very threshold of the subject,
we must pause. They have differences of quality. But in consciousness
these differences must be distinguished. And this involves their
recognition and discrimination, presupposing, therefore, a corresponding
faculty, however simple, on the part of the recipient. Without cognition
and recognition (twin sisters, born in the same hour) we can never get
beyond mere impressions; which may, indeed, be differentiated
physically, as different stimuli due to diverse action of the
environment, but are psychically undifferentiated. This recognition and
discrimination is thus the primary activity of the recipient mind. Here
is already some of the mortar supplied by the builder. Memory is
absolutely essential to the process. The sense-impression of external
origin gives rise to an impression of similarity or dissimilarity, which
is part of the internal reaction to the external stimulus. Thus
impressions are raised to the level of _sensations_. A sensation is an
impression that has been discriminated from others, and recognized as
being of such and such a nature. The impressions of the sense-organs as
we know them are thus not mere impressions, but impressions raised to
the level of sensations, in so far as they are recognized and
discriminated.
Let us now glance at some of the differences in quality recognized in
sensation. First, we have the broadly distinguished groups of touches
and pressures, temperature-sensations, tastes, smells, sounds, sights,
muscular sensations, and organic sensations from internal parts of the
body. And then, within each of these groups, there are the more or less
delicate and distinct shades of quality, well exemplified in vision by
the different colour-sensations, in hearing by notes of different pitch,
and in smell by the varieties of scents and odours. Many of those
sensations, moreover, which are apparently simple, are in reality
compound. There are differences of quality in the note A as sounded on a
violin, a piano, and a flute; and these differences are due to different
admixtures of overtones, which fuse with the fundamental tone and alter
its timbre. So, too, with vision. The sensation given by a white disc is
a compound sensation, due to waves of different period, which separately
would give sensations of colour. Sensations, then, differ in quality.
They also differ in quantity or intensity. This needs little
illustration. As evening falls, the sight-sensations derived from the
surrounding objects grow more and more feeble. They may remain the same
in quality, but the quantity or intensity gradually diminishes. So, too,
in music, the pianos and fortes give us differences in intensity of
sound-sensations.
Sensations also differ in duration. The stimulation may be either
prolonged or instantaneous. Two or more sensations may, moreover, be
simultaneous or successive. Just as they may be either similar or
different in quality and in intensity, so they may be either
simultaneous or successive in time. Simultaneous sensations are best
exemplified in vision and through touch; successive sensations are given
most clearly by the sense of hearing, through which we recognize a
sequence of sounds.
And then, again, sensations not only differ in time, but they seem also
to differ in place. A sensation of touch may be referred to different
parts of the body--the hand, the foot, or the forehead. But here we open
up an important question--Where do we feel a sensation, such as, for
example, that of pressure on the skin? Common sense answers, without
hesitation, that we feel it at the particular part of the body which is
affected by the external stimulus. I feel the pen with which I write
with my finger-tips. And common sense is perfectly right from its own
point of view. But it is a well-known fact that a person whose leg has
been amputated experiences at times tickling and uneasiness in the
absent member. This is due to irritation of the nerve-ends in the stump
of the limb. But the sensations are referred outwards to the normal
source of origin of impressions, the effects of which were carried
inwards by the nerve affected. We shall have to consider hereafter the
nature of the relation between physiological and psychological
processes--the connection of mind and body. Assuming for the present
that psychical processes have a physical basis in physiological
processes, the fact given above and others of like implication seem to
show that the sensation has for its physiological basis some
nerve-change in the central nervous system--in us, no doubt, in the
brain. Of course, it must be remembered that the sensation, as felt, is
a mental fact (using the word "mental" in its broadest sense, as
belonging to the psychical as opposed to the physiological series). But
it would seem that the physiological accompaniment of this mental fact
is some nerve-change in the brain. This nerve-change is caused by a
stimulus having its origin in the end-organ of the afferent nerve, and
we naturally refer the impression outwards to the place of its source of
origin under ordinary and normal conditions. In other words, we
_localize_ it. That is what common sense means when it says that we feel
pressure at the finger-tips.
To account for this process of localization, it is supposed that every
sensation, apart from its special quality as a touch, a taste, or a
smell, has a more or less defined spatial quality, or local sign,
dependent upon the part of the body to which the stimulus is applied.
These local signs have, doubtless, in the long run, been established by
experience--if under this term we may include a more or less unconscious
process, the outcome of evolution. But they are so rapidly established
in the individual, that we are forced to conclude that we inherit very
highly developed aptitudes for localization.
The refinement of localization is very different in the different
senses. In smell and taste there seems no more than a general
localization in the organ affected--the nose or the mouth. In hearing
there is not much more, unless we regard the discrimination of pitch as
a mode of localization. In touch (and temperature) the refinement is
much higher, but it varies with the part of the body affected.
If the back be touched by two points less than two inches and a third
apart, the sensation will be that of a single point; the finger-tips,
however, can distinguish two points separated by less than one-tenth of
an inch; and the tip of the tongue is still more refined in its power of
discrimination, distinguishing as two, points separated by less than the
twenty-fifth part of an inch. So that the tongue is about sixty times as
refined in its discrimination as the skin of the back. Moreover, the
delicacy of localization may be cultivated, so that in some cases the
refinement may, by practice, be doubled.
When we come to sight, the refinement of localization reaches its
maximum, the local signs in the retina showing the highest stage of
differentiation, the distance on the retina between two points
distinguishable by local signs being, according to Helmholtz, not much
more than 1/6000 of an inch (.0044 millimetre), which nearly corresponds
with the space between two cones in the yellow spot.
We must remember that the presentations of sense are in all cases given
in a stippled form, that is, by the stimulation of a number of separate
and distinct points. In vision the stippling is very fine, owing to the
minute size and close setting of the retinal cones. In the case of
hearing, the stippling, if we may so extend the use of this term, is
also very fine, as is shown by the fact that musicians can, according to
Weber, distinguish notes separated in the scale of sounds by only
one-sixtieth part of a musical tone. In touch the stippling is
comparatively coarse. But in all cases there is a stippling; and yet
from these stippled sensations the mind in all cases elaborates a
continuum. The visual image is continuous, notwithstanding the retinal
stippling and the existence of the blind spot. When we lay our hands on
a smooth table we fill in the interstices between the sensational
points, and feel the surface as continuous. In all cases out of the
stippled sense-stimuli we form a continuum.
The next thing that we have to note is that it is not so much the
sensation itself, as that which gives origin to it, that we habitually
refer outwards to the recipient end of the afferent fibre. In referring
a sensation of touch to a certain part of the skin, it is of something
touching us that we seem to be immediately conscious. We refer the
stimulus to an object in the external world, which we localize, and
which we believe to have given rise to the sensation.
This, however, is more clearly seen in the case of vision. When we look
through the window and see an object such as a house before us, we do
not habitually localize the sensation in a certain part of the retina,
but we refer the object to a particular position more or less distant in
the world around us. This projection of the object outwards in a right
line from the eyes is really a marvellous process, though the wonder of
it is lost in its familiarity. It is the outcome of the experience of
hundreds of generations. And the experience is not gained through vision
alone, but through this in combination with other senses and activities.
We see an object, but we have to go to it before we can touch it. It is
not in contact with us, but distant from us. Its outness and distance is
a matter of what is termed the geometry of the senses; and this geometry
has been elaborated through many generations of organized beings, from
data given by sight, touch, and the muscular sense. It is true that I
can now estimate the distance of the house without going to it; but my
eyes go to it, and I can feel them go. The panes of my window are
separated by iron bars. As I look from them to the distant house and
back to them again, I can feel my eyes going from one to the other. The
lens of the eye is adjusted for near or far distance by the action of a
ciliary muscle, through which its anterior surface can be flattened,
returning again by its own elasticity to the more convex form when the
muscle ceases to act. Each eye, moreover, is moved in its orbit by six
eye-muscles, and in normal vision the two eyes act as one organ. For
near distances they converge; for far distances there is less
convergence. Through the muscular sense, which is here extraordinarily
delicate, we can feel the amount of accommodation and convergence; and
thus we can feel the eyes going to or coming from a near and a distant
object. Of course, we are aided in judging or estimating distances by
the apparent size of the object when the real size is known, by the
clearness of its outlines in a slightly hazy atmosphere, and so forth.
But apart from such judgments, it would probably be impossible to
perceive that an object is near or distant in the absence of muscles of
accommodation and convergence affording the data of the muscular sense.
Not only the distance of two objects from the eye, but their distance
apart, can be measured by the aid of the muscular sense as we move the
eyes from one to the other. And in us this is so delicate that,
according to Weber, a distinct muscular sensation is attached to a
displacement of a sensitive point of the yellow spot through less than
1/6000 of an inch.
Now, if it be true that the consciousness aroused by objects around us,
through sensation, is an accompaniment of certain physiological changes
in the brain, it is clear that the localization of their points of
origin in special parts of the skin, and the outward projection of the
objects exciting vision, is an act of the mind quite distinct from the
mere passive response in consciousness which we call an impression, and
more complex than that mental activity which, through discrimination and
recognition, converts the bare impression into a sensation. It is, in
fact, part of that mental process which is called _perception_.[FP]
Sensation has nothing to do with the objects around us as such; it is by
perception that we are aware of their existence. Let us now follow the
process of perception a little further, always remembering that it
involves certain activities of the mind.
These activities are too often ignored. We often speak of the senses as
the avenues of knowledge, and John Bunyan, likening the soul to a
citadel, spoke of the five gateways of knowledge, Eye-gate, Ear-gate,
Mouth-gate, Smell-gate, and Feel-gate. Hence arises a vague notion that
through the eye-gate, for example, a sort of picture of the external
object somehow enters the mind. And this idea is no doubt fostered by
the fact that an inverted image of the object is formed on the retina,
though how the inverted image is turned right way up again in passing
into the mind bothers some people not a little.[FQ]
A much closer analogy is this: Something stands without and knocks at
the doorway of sense, and from the nature of the knocks we learn
somewhat concerning that which knocks. In other words, at the
bidding of certain stimuli from without we construct that mental
product which we call the object of sense. It is of these mental
constructions--"_constructs_"[FR] I will call them for convenience--that
I have now to speak.
In a fruiterer's shop on the opposite side of a street I see an orange.
That is to say, certain cones of the retina of my eye are stimulated by
light-waves of a yellow quality, and at the bidding of these stimuli I
construct the object which I call an orange. That object is distant,
roundish, yellow, resisting and yet somewhat soft, with a peculiar
smell, and possessed of a taste of its own. Now, it is obvious that I
cannot see all these qualities of the orange, as we call them. I
construct the object on reception of certain light-waves which are
focussed on the retina of my eye. If I go to the orange, however, I can
test the correctness of my construct by the senses of touch, smell, and
taste. But what led me to construct an object with these qualities?
Experience has taught me that these qualities are grouped together in
special ways in an orange. I constructed that particular object through
what is termed the principle of association. I have learnt that these
qualities are grouped together in certain relations to each other, and
when I actually receive sight-stimuli of a certain quality, grouped in
certain ways, they immediately call up the memories of the associated
qualities. That which is actually received is a mere suggestion, the
rest is suggested in memory through association. The object might be
suggested through other senses. I come into a dining-room after dessert,
and the object is suggested through smell. Or my little son says, "Open
your mouth and shut your eyes, and see what the fairies will send you;"
and an orange is suggested by taste. In all these cases the object is
constructed at the bidding of certain sensations, which suggest to my
mind the associated qualities. The object is a _construct_.
And here let us notice that we ascribe the form, the resistance, the
taste, the smell, to the object. We do not say or think,
"Sight-sensations inform me that there is something which I call an
orange, and which is capable of exciting in me sensations of touch,
taste, and smell;" but we say, "There is an orange, which _has_ such and
such a taste, smell, and feel." In other words, we refer these
sensations, related in certain ways, outwards to the object, and name
them qualities of the object that we see. But remember, that we do not
necessarily or normally say or think anything about it. We just
inevitably construct the object, what we build in to the construct
depending upon association through experience.
At this stage, perhaps, Common Sense steps in, and, shaking his head,
says, with characteristic bluntness, "Nonsense; you'll never persuade me
that the things I see and feel around me are nothing but fictions of my
own mind. I don't construct them, as you call it; there they are for me
to see and feel and taste if I will." Now, Common Sense is a sturdy,
hard-headed individual, with whom I desire to keep on friendly terms.
And I therefore hasten to explain that I most fully agree with every
word that he says. The orange that I see before me is not a mere fiction
of my mind. I can, if I will, take it up, feel it, smell it, and taste
it. If it will satisfy Common Sense, I will say that it is the idea of
the orange that I construct. Only I think that Common Sense, who has a
horror of roundabout and indirect statements, will not like my saying,
"I am receiving certain visual sensations related in certain ways, which
lead me to construct an idea of an orange." He will prefer my saying
simply, "I see an orange." Since what he wants me to call our ideas of
things answer point for point to the things as they actually exist for
us human-folk, it is not only more satisfactory but more correct to
merge the two in one, and speak directly and simply of the object. The
object is a thing I construct. That it is real may be proved by
submitting it to the test of all the senses that I have.
And what do I mean by "real"? I mean that what it is for me it is also
for you and any other normally constituted human being. This is, in
truth, the only common-sense criterion of objective reality. Some people
are colour-blind, and tell us that a rose is not red, but green. We
reply that it is really red, but that, through a defect of sight, they
cannot distinguish its redness. Here we take the normal human being as a
standard for objective reality. For him the rose is red. And this is the
only practical criterion that we have. This, however, does not satisfy
some people, who think that the objects around them have the same
reality, independent of man, that they have for us human-folk.
Annihilate, they say, every human being--nay, all life--and the objects
will remain as they are, and retain the same reality. Yes, the same
reality; which means that if just one fortunate fellow escaped
annihilation, he would find them all just as they were. And this nobody
doubts. Nevertheless, it is (to me, at least) inconceivable that things
independently of us are what they appear to us. Think of what we learnt
about the sensations. They all arose in stimulations of the end-organs
of special sense. Thence the explosive waves of change passed inwards to
the brain, and somewhere therein gave rise to mental products. These
mental products, the accompaniments of nerve-changes, can in no sense be
like the outside something which gave rise to them. They are symbols of
that outside something. And it is these symbols that we build up into
objects. Hence I said that it is not only more satisfactory and
convenient, but more correct, to speak directly of the object as
constructed, and not our idea of the object. The mental product _is_ the
object for us, not only for me, but for you and all normal human beings,
since the object is the same for all of us. And hence, also, I said that
the analogy of gateways, through which pictures of objects gain access
to the mind, was false and misleading, and that a truer analogy is that
something stands without and knocks at the doorway of sense, and that
from the nature of the knocks we learn somewhat concerning that which
knocks. The person inside can never open the door to see what manner of
thing it is which knocks. But he can build up a most cunning symbolism
of knocks which shall suffice for all practical purposes. In other
words, the object-world, symbolic though it is, which you and I and the
rest of us construct at the bidding of something without us (the
existence of which I assume), is amply sufficient for all our practical
needs, and constitutes the only practical reality for human-folk.
I am well aware that there are many people who cannot bring themselves
to believe in, or even to listen without impatience to, the view that
the world we see around us is a world of phenomena. It is absurd, they
say, to tell us that yonder tulip, as an object, is in any sense
dependent on our perception of it. There it is, and there it would have
been had man never been created. Can one conceive that the new species
of fossil, which was only yesterday disentombed from the strata in which
it has lain buried for long ages, is dependent on man's observation for
its qualities as an object? To say that it was "constructed" by the
lucky geologist who was fortunate enough first to set eyes on it is
sheer nonsense. Its shelly substance protected a bivalve mollusc
millions of years before man appeared upon the earth. When we see the
orange in the fruiterer's shop, the sight of it merely reminds us of its
other qualities--its taste, its smell, its weight, and the rest, which
are essentially its own, and no endowments of ours--nowise bestowed upon
it by us.
I have no hope of convincing, and not much desire to convince, one who
thus objects. I would merely ask him how and when he stepped outside his
own consciousness to ascertain that these things are so. Does he believe
that consciousness is an accompaniment of certain nervous processes in
the grey cortex of the brain? If so, let him tell us how these conscious
accompaniments resemble (not merely symbolize, but _resemble_) tulips
and oranges and fossil molluscs. If not, let him propound his new theory
of consciousness.
Let it not be supposed that I am denying the existence, and the richly
diversified existence, of the external world. We are fully justified, I
think, in believing that, corresponding to the diversity of mental
symbolism, there is a rich diversity of external existence. But its
nature I hold that we can never know. The objects that we see are the
joint products of two factors--the external existence and the percipient
mind. We cannot eliminate the latter factor so as to see what the
external factor is like without it. Those who, like Professor
Mivart,[FS] say that we can eliminate the percipient factor, and that
the external world without it is just the same as it is with it, are
content to reduce the human mind, in the matter of perception, to the
level of a piece of looking-glass.
There are some people who seek to get behind phenomena by an appeal to
evolution. It will not do nowadays, they say, to make the human mind a
starting-point in these considerations; for the human mind is the
product of evolution, and throughout that evolution has been step by
step moulded to the external world. The external world has, therefore,
the prior existence, and to it our perceptions have to conform. All this
is quite true; but it is beside the point. Mind has, throughout the
process of evolution, been moulded to the external world; our
perceptions do conform to outside existences. But they conform, not in
exact resemblance, but in mental symbolism. They do not copy, but they
correspond to, external existences. It is just because, throughout the
long ages of evolution, mind has lived and worked in this symbolic world
that common sense is unable to shake off the conviction that this is the
only possible world, and exists as such independently of mental
processes. The world of phenomena _is_ the world in which we, as
conscious beings, live and move. No one denies it. But it is none the
less a symbolic world; none the less a world which mind has constructed
in the sense that it is an inalienable factor in its being.
Each of us, when we perceive an object, repeats and summarizes the
constructive process which it has been the end of mental evolution to
compass. Hence it is that, at the bidding of a simple impression,
percepts or constructs take origin and shape in the mind. In taking
possession of this faculty in the early years of life, we are entering
upon a rich ancestral heritage. But if what I have been urging has
truth, what we call objects are human constructs, and cannot by any
manipulation be converted into anything else.
I will now take another and more complex case of construction, which
will bring out some other facts about what I have termed "constructs." I
hear in the street a piercing howl, which suggests a dog in pain. Rising
from my seat and going to the window, I see a white terrier with a black
patch over the left eye limping down the road on three legs. Now, what
was the nature of the construct framed at the bidding of the piercing
howl? A dog in pain. But what dog? The nature of the howl suggested a
small dog; but there was nothing further to particularize him. The
construct was, therefore, exceedingly vague and ill defined, and was not
rendered definite and particular till I went to the window, and saw that
it was a white terrier with a black patch over the eye. The howl,
moreover, suggested certain activities of the dog. The construct was not
merely a passive, inanimate object, like the orange, but an object
capable of performing, and actually performing, certain actions. Here,
again, we can only say that it is through experience that special
activities are associated with certain objects. Just as the construct
orange is capable of exciting sensations of taste, so the construct dog
is capable of doing certain things and performing certain actions, that
is, of affecting us in certain further ways.
But, further, the howl suggested a dog in pain. No amount of sensations
entering into any manner of relations could give me that element of the
construct. I can neither see, touch, taste, smell, nor hear pain in
another being. Pain is entirely subjective and known only to the
sufferer. But I have been a sufferer. I have experienced pain and
pleasure. And just as my experiences, individual and ancestral, lead me
to project into inanimate objects certain qualities, the products of my
sensations, so do my experiences, individual and ancestral, lead me to
project into certain animals feelings analogous to those I have myself
experienced. This is sometimes described as an inference. But if we call
this an inference, then we must, I think, call the taste, smell, and
feel of the orange I see before me inferences. In both cases the
inference, if we so call it, enters at once into the immediate
construct.
And when I went to the window and saw the dog limping down the street, I
saw also a small boy, with arm drawn back, in the act of throwing a
stone. In other words, I saw the objects in the scene before me standing
in certain relations to each other. I concluded that the boy had thrown
a stone at the dog and was about to throw another. In other words, I saw
the scene before me as part of a sequence of events.
One more example I will give to bring out another and important feature
in the mental process. Strolling before breakfast in early spring in my
friend's garden, there is borne to me on the morning air a whiff of
violet fragrance. Not only does this lead me to construct violets, but
it reminds me of a scene in my childhood with which the scent of these
flowers was closely associated. Not only is the object constructed, but
a scene with which their fragrant odour has been associated is
_reconstructed_ in memory. The violets are immediate constructs or
presentations of sense; the remembered scene is a _reconstruct_ or
representation in memory. So, too, when I heard a piercing howl in the
street, the dog I constructed was a vague presentation of sense; but the
street in which I instinctively placed him was a reconstruct or
representation in memory. The difference between a construct or
presentation of sense, and a reconstruct or representation in memory, is
that the former is directly suggested through the immediate action of
some quality or activity of the object, while the latter is indirectly
suggested through some intermediate agency.
Before proceeding further, let us review the conclusions we have thus
far reached. Through the action of certain surroundings on our sensitive
organization, we receive certain impressions, and among these
impressions and others revived in memory we recognize certain
similarities or differences in quality, in intensity, in order of
sequence, and in source of origin. The sensations which thus originate
are mental facts in no sense resembling their causes, but representing
them in mental symbolism. The consciousness of similarity or difference
is no part of the impression, but a further mental fact arising out of
the impression, and with it giving origin to sensation. It deals with
the relation of impressions among each other and to the recipient. It
involves recognition and discrimination. Its basis is laid in memory.
The sensations are instantly localized, referred to objects, and
projected outwards, mainly through the instrumentality of the muscular
sense. The mental symbolism is thus built into the objects around us,
and constructs are formed. But into the tissue of these constructs are
woven, not only the sensations immediately received, but much that is
only suggested through association as the outcome of past experience,
individual and ancestral. The constructs and their associated
reconstructs are thus endowed with qualities which have practical
reality, since they are not for me only, but for you and for mankind.
They are, therefore, in a sense independent of _me_, but nowise
independent of _man_.[FT]
Some of the constructs are endowed with activities, and some with
feelings akin to our own. Finally, in the field of vision which we
construct or reconstruct, the objects are seen to stand in relationship
to each other, and the scene as a whole is perceived to be part of an
orderly sequence of events.
We have already got a long way beyond the impressions with which we
started; and yet, if I may trust my own experience, such construction as
I have described is direct and immediate. A child of four or five would
not only construct as much, but might not improbably go a long way
further, and say, "Naughty boy to throw a stone at poor doggie!" It is,
I say, direct and immediate, and it implies a wonderful amount of mental
activity. Some people seem to imagine that in the simpler forms of
perception, as when I see an orange on the table, the mind is as passive
as the sensitive plate in a photographer's camera. This surely is not
so. It is a false and shallow psychology which teaches it. Just as a
light pin-prick may set agoing complex physical activities in the frog,
so may comparatively simple visual sensations give rise to complex
mental activities in construction and reconstruction. It is to emphasize
this mental activity that I have persistently used the terms "construct"
and "construction." And I wish to emphasize it still further by saying
that without the active and constructive mind no such process of
construction or reconstruction is possible or (I speak for myself)
conceivable. We might just as well suppose that the frog could leap away
on stimulation of a pin-prick in the absence of its complex bodily
organization, as that sensation could give rise to construction and
reconstruction in the absence of a highly organized mind.
We have seen that when a howl suggested the construct dog, that
construct was vague and undefined; but when I went to the window and saw
the terrier, the construct became particularized and defined. This seems
to me the normal order of development: first the vague, general, and
indefinite; then the particular, special, and defined. That which is
immediately suggested at the bidding of sensations received is always
more or less general; it only becomes specialized on further examination
physical or mental--first a dog or an orange; then this dog or this
orange. The more unfamiliar the object, the more vague and indefinite
the construct. The more familiar the object, and the further our
examination of it is carried, the more particular and defined the
construct. I would, therefore, mark two stages in the process of
construction: first, the formation of constructs by immediate
association, more or less vague, indefinite, and ill defined; and,
secondly, the definition of constructs by examination, by which they are
rendered more definite, particular, and special, and supplemented by
intelligent inferences.
I need not stay here to point out the immense importance of this process
of defining and particularizing constructs, or the length to which it
may be carried; nor need I pause to indicate how, through memory and
association, representative or reconstructive elements crowd in to link
or weave the constructs into more or less vivid and brilliant scenes.
But I have next to notice that out of this intelligent examination
arises a new, distinct mental process, _the analysis of constructs_.
This process involves the paying of special attention to certain
qualities of objects, to the intentional exclusion of other qualities.
When I cease to examine an orange as a construct, and pay attention to
its colour or its taste to the exclusion of other properties, with the
purpose of comparing this colour or taste with other colours and tastes,
I am making a step in analysis. So, too, when I consider the form of an
orange for the purpose of comparing it with the form of the earth, I am
making a step in analysis. And, again, when I consider the howl of the
dog with the object of comparing it with other sounds, I am making a
step in analysis. We may call the process by which we select a certain
quality, and consider it by itself to the neglect of other qualities,
_isolation_, and the products of the process we may term _isolates_.[FU]
This process could not be initiated till a large body of constructive
and reconstructive experience had been gained. But once initiated, there
is no end to the process. We pick to pieces all the phenomena of nature,
all the qualities and relationships of objects, the activities and
functions of animals, the mental phenomena of which we are conscious in
ourselves. We isolate the qualities, relationships, feelings; and we
name the isolates we obtain. Hence arises all our science, all our
higher thought. In the terms which we apply to our isolates consists the
richness of our language.
We _name_ the isolates; that is, we apply to each an arbitrary symbol to
stand for the isolated quality or relation. All words (except the
obviously onomatopoetic, such as "bow-wow," "cuckoo," etc.) are
arbitrary symbols associated with objects, or qualities, or relations,
or other phenomena. And abstract names of isolates are, so to speak, the
pegs on which we hang the qualities we have separated by analysis and
isolation, while class-names are pegs upon which we can hang a group of
similars reached by the process of isolation; for all classing and
grouping of objects, or qualities, or relations involves, so far as the
process is a conscious one, the principle of analysis. In classing
objects, we group them in reference to certain characters which they
have in common, disregarding certain other characters in which they
differ. We group together, for example, sights, or sounds, or smells,
and distinguish them from each other and from tastes and touches. And
then we go further, and class all these together as sensations having
certain characteristics in common whereby they are distinguished from
perceptions of relation and so forth.
Perhaps it may be objected that classification comes much earlier in the
mental process than I am now putting it. It may be said that the
recognition of a sensation as a touch, or a smell, or a sound involves a
classification of sensations in these categories, and that the simple
perception of an orange involves the placing of the object in this class
of bodies. And, undoubtedly, we have here the germs of the process.
Sensation and perception give us the materials for classification; the
perception of similarity and difference gives us the _sine quâ non_ of
the process. Nevertheless, although there may be an earlier unconscious
grouping of phenomena, it is only when the mind is specially directed to
these materials, with the object of grouping them according to their
similarities, that we can speak of classification proper--conscious and
intentional classification, as opposed to unconscious grouping. And this
involves the intentional selection of the points of similarity, and
discarding or neglecting the points of difference. It involves the
process of analysis or isolation. There is a vast difference between the
perceptual recognition of objects as similar, and conceptual
classification on grounds of similarity. Just as the recognition of a
sensation as now and not then, or here and not there, or as due to
something outside us, gives us the germs from which, on ultimate
analysis, our ideas of time, space, and causation are reached; so does
the recognition of these sensations as of this kind and not that give us
the germ from which, on analysis, the process of classification may
arise. True, conscious, scientific classification is late in
development.
And here let us notice that the conclusions we have reached in this
chapter are the outcome of analysis and classification. The sensations
with which we started are isolates. In considering their quality,
intensity, sequence, we were isolating and classifying these special
modes of their existence. Localization and outward projection involved
isolation. We simply see the orange before us. To understand and explain
how we come to see it as we do see it involves a somewhat subtle
analysis. We perceive it to be yellow, round, resistant; and then,
isolating these qualities, we reach conceptions of yellowness,
roundness, and resistance, quite apart from oranges. Throughout our
description the terms we used were very largely terms denoting
classified isolates.
Lastly, having enormously increased our knowledge by this process of
isolation, we proceed to build in the knowledge thus gained to the
structure of our constructs. This is the third and last stage in
construction. The first stage is the formation of indefinite constructs
by immediate association; the second is the definition of constructs by
examination; and the third is the completion of constructs by synthesis.
And the further this process of analysis and isolation is carried, the
more we are, so to speak, floated off from the immediate objects of
sense into the higher regions of abstract thought. Furthermore, by
recombining our isolates in new modes and under new relations, we reach
the splendid results of constructive imagination.
In the brief description which I have now given of our mental processes,
I have for the most part avoided certain terms which are current in the
science of psychology. It will be well here to say a few words
concerning these words and their use. The process of _sensation_ is
sometimes defined as the mere reception of a sense-stimulus. But it is
more convenient, and more in accordance with common usage, to call the
simple result of a stimulus an impression, and to apply the term
"sensation" to the discrimination and recognition of the impressions as
of such and such a quality. Sensation, then, is the reception and
discrimination of impressions which result from certain modes of
influence (stimuli) brought to bear on our organization. Viewed in this
way, therefore, even sensation involves a distinct reaction of the mind;
it implies the first stage of mental activity. But when the sensations
are given objective significance, when they suggest the existence of an
object-world without us, they enter the field of _perception_. Here the
discriminated sense-impression is, to use the words of Mr. Sully,
"supplemented by an accompaniment or escort of revived sensations, the
whole aggregate of actual and revived sensations being solidified or
integrated into the form of a _percept_; that is, an apparently
immediate apprehension or cognition of an object now present in a
particular locality or region of space."[FV] Throughout the whole
process of the formation of constructs by immediate association, and
their definition by examination, we were dealing with perception and
percepts. But when we reach the stage when particular qualities were
isolated, then we enter the field of _conception_. The isolates are
_concepts_. Class-names, reached through processes involving isolation,
stand for concepts. And completed constructions, involving synthesis of
the results of analysis, contain conceptual elements. The word
"concept," however, is used in different senses by different authors.
Mr. Sully says,[FW] for example, "A concept, otherwise called a general
notion, or a general idea, is the representation in our minds answering
to a general name, such as 'soldier,' 'man,' 'animal.'... Thus the
concept 'soldier' is connected in my mind with the representations of
various individual soldiers known to me. When I use the word 'soldier,'
... what is in my mind is a kind of composite image formed by the fusion
or coalescence of many images of single objects, in which individual
differences are blurred, and only the common features stand out
distinctly.... This may be called a typical or generic image." But
Noiré, quoted by Professor Max Müller,[FX] taking another illustration,
says, "All trees hitherto seen by me leave in my imagination a mixed
image, a kind of ideal presentation of a tree. Quite different from this
is my concept, which is never an image." I follow Noiré; and I hold that
the image, in so far as it is an image, whether simple or composite,[FY]
is a percept; but that, in so far as there enter into the idea of the
soldier or the tree elements which have been isolated by analysis, just
in so far does the word "soldier" or "tree" stand for a concept. How far
a word stands for a percept, and how far there enter conceptual
elements, depends to a large extent on the level of intelligence of the
hearer. The moment educated and intellectual folk begin to think about
their words, or the objects for which they stand, conceptual elements
are sure to crowd in.
There is one more feature of these mental processes in man, and that by
no means the least important, that remains for brief consideration. I
began by saying that the primary end and object of the reception of the
influences of the external world, or environment, is to enable the
organism to answer to them in activity. We saw that the sight of an
orange suggests, through association, its taste; and that the validity
of the association could be verified by going to the orange and tasting
it. We saw, too, that when I heard a dog howl in the street, and, going
to the window, saw a small boy with a stone in his hand, I concluded
that he was going to throw it at the dog. What I wish now to elicit is
that out of perceptions through association there arise certain
expectations, and that the activities of organisms are moulded in
accordance with these expectations.
It is clear that these expectations or anticipations belong partly to
the presentative or constructive order, and partly to the reconstructive
or representative order. They are in some cases directly suggested by
the presentations of sense; they are also built up out of
representations which have become associated with the constructs in
memory and through experience. But what we have here especially to
notice about them is that, in the latter case, they involve more or less
distinctly the element which we, in the language of our developed
thought, call causation. There is a sequence of events, and the
perception of certain of these gives rise, through association and
experience, to an expectation of certain succeeding phenomena.
Expectations are, therefore, the outcome of the linked nature of
phenomena. And when we come eventually to think about the phenomena, and
how they are linked together into a chain (successional) or web
(coexistent), we reach the conception of causation as the connecting
thread. In early stages of the mental process, such a conception does
not emerge. Nevertheless, the phenomena are perceived as linked or
woven. And the mental process by which we pass from any perceived event
or existence to other preceding, concomitant, or subsequent events or
existences linked or woven with it in the chain or web of phenomena, we
call _inference_.[FZ] When, for example, I find a footprint in the sand,
I infer that a man has passed that way; and when the clouds are heaped
up heavy and black, I infer that a storm is about to burst upon us.
Concerning inference, of which I shall have more to say in the next
chapter, I have now to note that it is of two kinds: first, perceptual
inference, or inference from direct experience; secondly, conceptual
inference, or inference based on experience, but reached through the
exercise of the reasoning faculties. The latter involves the process of
analysis or isolation; the former does not. There is a marked difference
between the two. Perceptual inferences are the outcome of practical
experience, but do not go beyond such practical experience. Conceptual
inferences are also based on experience, but they predict occurrences
never before experienced. Perceptual inferences, again, deal with
matters practically; but conceptual thought explains them.
The expectation of a storm when the thunder-clouds are heavy is a case
of perceptual inference. It is the outcome of a long-established
association, and is not reached by a process of reasoning involving an
analysis of the phenomena. But if, though the sky is clear, a west wind
and a rapidly falling barometer lead me to predict rain, the inference
is conceptual, and gained by me or for me by a process of reasoning; for
the barometer was the outcome of the analysis of phenomena. In the mind
of the rough sailor-lad, however, the fall of the mercury and the
succeeding storm may be connected by mere perceptual inference, the
phenomena being simply associated together. If, however, there is any
attempt at explanation, correct or incorrect, there is so far a
conceptual element. In a little fishing-village on our south coast, a
benevolent lady presented the fishermen with a Fitzroy barometer. I
happened shortly after to remark to one of the men that the summer had
been unusually stormy. "Yes, sir," he said, "it has. But then, you see,
the weather hasn't no chance against that new glass." Here there was an
attempted explanation of the phenomena. The falling glass was conceived
as somehow causing bad weather.
It is hard to draw the line between perceptual and conceptual
inferences, or rather to say, in this or that case, to which class the
inference belongs, because man, through language, lives in a conceptual
atmosphere. Moreover, the same result may, in different cases, be
reached by perceptual or by conceptual inference. A child who had seen a
great number of ascending balloons might, on seeing a balloon, expect it
to ascend by a perceptual inference; but a man, knowing that the balloon
was full of a gas lighter than air, might expect it to ascend through
the exercise of conceptual inference. And just as in adult civilized
life our constructs have more and more conceptual elements built into
them, so do our inferences become more and more reasoned. It is probable
that in an adult Englishman every inference has a larger or smaller dose
of the conceptual element.
With the development of language we state our inferences in the form of
propositions, and call them judgments. "Every proposition," says Mr.
Sully,[GA] "is made up of two principal parts: (1) the subject, or the
name of that about which something is asserted; (2) the predicate, or
the name of that which is asserted. Thus, when we affirm, 'This knife is
blunt,' we affirm or predicate the fact of being blunt of a certain
subject, namely, 'this knife.' Similarly, when we say, 'Air corrodes,'
we assert or predicate the power of corroding of the subject 'air.'" The
proposition always involves conceptual elements; for the predicate of a
proposition is always an abstract idea or general notion.
Propositions so formed may then become links in a chain of reasoning.
"To reason is," says Mr. Sully,[GB] "to pass from a certain judgment or
certain judgments to a new one." And so passing on from judgment to
judgment, we may ascend to the higher levels of abstract thought.
According to Mr. Sully's definition, therefore, we start from a judgment
or judgments in the process of reasoning. The formation of a judgment
(conceptual inference) is, however, the first step in a continuous
process; and I propose, under this term, "reason,"[GC] to include this
first step also. The formation of a conceptual inference I regard as the
first stage of reason. Any mental process involving conceptual inference
I shall call _rational_.
In contradistinction to this, I shall use the term "intelligence" for
the processes by which perceptual inferences are reached. An intelligent
act is an act performed as the outcome of merely perceptual inference. A
rational act is the outcome of an inference which contains a conceptual
element.
NOTES
[FP] I use this term in a broad sense, as the process involved in the
formation of what I shall term _constructs_.
[FQ] And I may add it is not an easy matter to explain to those who
have not considered such questions. It is a matter of the
correlation of the testimony of the sense-organs. A boy stands
before me. I go to him and touch him, and pass my hands downwards
from head to foot. Then I stand a little way off and look at him.
His image on my retina is inverted. But as I run my eye over him I
direct my eye downwards to his feet and upwards to his head. I am
not conscious that the stimuli are running _upwards_ along the
retinal image. Thus my eye-muscles and my other muscular and
tactile sensations seem to tell me that he is one way upwards. The
image on my retina tells me, though I am not conscious of the
fact, that he is the other way upwards. But he cannot be both! The
testimony of one sense has to give way. One standard or the other
has to be adopted. Practically that of touch and the muscular
sensations is unconsciously selected, and sight-sensations are
habitually interpreted in terms of this standard. So long as the
two are sufficiently accurately correlated, the practical
requirements of the case are met. And it is well known that it is
not difficult, with a little practice, to establish a new
correlation. This is indeed done every day by the microscopist,
for whom the images are all reversed by his instrument. He very
soon learns, however, that to move the object, as seen, to the
left, he must push it to the right. A new correlation is rapidly
and correctly established.
[FR] I use this term because the word "percept" is used in different
senses by different writers, e.g. by Mr. Mivart and Mr. Romanes.
[FS] "Let the perception be considered to be made up of x + y; x being
the ego, or self, and y the object. The mind has the power of
supplying its own - x, and so we get (through the imagination of
the mind and the object) x + y - x, or y pure and simple" (Mivart,
"On Truth," p. 135). Mr. Mivart devotes a whole section of this
work to the defence of ordinary common-sense realism. The above
assertion seems to contain the essence of his teaching in the
matter.
[FT] If it be said that the object does exist independently of man,
though not in the phenomenal guise under which we know it, I would
reply--Not so; for it is to the existence _under this phenomenal
guise_ that we apply the word "object." In philosophical language,
the existence, stripped of its phenomenal aspect, is called the
_Ding an sich_. Its essential character is its independence of
man; and hence its unknowability.
[FU] I avoid, for the present, the use of the terms "abstraction" and
"abstract idea" because they are employed in different senses by
different authors.
[FV] "Outlines of Psychology," p. 153.
[FW] Ibid. p. 339.
[FX] "Science of Thought," p. 453.
[FY] For compound or generic ideas "not consciously fixed and signed by
means of an abstract name," Mr. Romanes ("Mental Evolution in
Man," p. 36) has suggested the term "recept." In the photographic
psychology which he adopts, the percept is an individual and
particular photograph, the recept a generalized or composite
photograph. "The word 'recept,'" he says, "is seen to be
appropriate to the class of ideas in question, because, in
receiving such ideas, the mind is passive." This, it will be
observed, is in opposition to the teaching of this chapter, in
which the activity of the mind in perception has been insisted on.
Mr. Romanes's recepts answer in part to what I have termed
_constructs_, which, as we have seen, are, as a rule, from the
first general rather than particular, and in part to concepts
reached through analysis. Mr. Romanes, for example, speaks of
ideas of principles (e.g. the principle of the screw) and ideas of
qualities (e.g. good-for-eating and not-good-for-eating) as
recepts (p. 60). On the other hand, Mr. Mivart ("The Origin of
Human Reason," p. 59; see also his work "On Truth") terms such
generic affections "sensuous universals." It may be well to append
Mr. Romanes's and Mr. Mivart's tabular statements.
_Mr. Romanes._
{ General, abstract, or notional = Concepts.
IDEAS { Complex, compound, or mixed = Recepts, or generic ideas.
{ Simple, particular, or concrete = Memories of percepts.
_Mr. Mivart._
{ General or true universals = Concepts.
IDEAS { Particular or individual = Percepts.
{ Groups of actual experiences }
SENSITIVE { combined with sensuous } = Sensuous universals,
COGNITIVE { reminiscences } or recepts.
AFFECTIONS { Groups of simply juxtaposed } = Sense-perceptions,
{ actual experiences } or sencepts.
In Mr. Mivart's terminology, the representations of the lower group
are "mental images" or "phantasmata." The term "consciousness" is by
him restricted to the higher region of ideas, the term
"consentience" being applied to the faculty by which cognitive
affections are felt, unified, and grouped without consciousness.
_There is a difference in kind_, according to Mr. Mivart, between
"consentience" and "consciousness;" and the former could therefore
never develop into the latter, nor the latter be evolved from the
former. For this reason (because of the philosophy it is intended
to carry with it) I shall not employ the word "consentience,"
which would otherwise be a useful term.
[FZ] We do not speak of the filling in the complement of a percept (the
construction of the object at the bidding of a simple impression)
as a matter of conscious inference. I do not consciously _infer_
that yonder moss-rose is scented. Scent is an integral part of the
construct. From the appearance of the rose, I may, however, infer
that a rose-chafer has disturbed its petals. The complement of the
percept, if inferred at all, is unconsciously inferred.
[GA] "Outlines of Psychology," p. 392.
[GB] "Outlines of Psychology," p. 414.
[GC] Mr. Romanes adopts a different use of the terms "reason" and
"rational," to which allusion will be made in the next chapter.
CHAPTER IX.
MENTAL PROCESSES IN ANIMALS: THEIR POWERS OF PERCEPTION AND INTELLIGENCE.
Two things I have been especially anxious to bring out prominently in
the foregoing chapter: first, that the world we see around us is a joint
product of two factors--the outward existence, on the one hand, and our
active mind on the other; and secondly, that our mental processes and
products fall under two categories--on the one hand, perception, giving
rise to percepts, perceptual inferences, and intelligence, and on the
other, conception (involving the analysis of phenomena), giving rise to
concepts, conceptual inferences, and reason.
Now, I am anxious that the former--to take that first--should be laid
hold of and really grasped as an indubitable fact. It is implied in the
word "phenomena," that is to say, appearances. We can only know the
world as it appears to us; and the world is for us what it appears.
There is nothing here in conflict with common sense; the practical
reality of phenomena is altered no whit. Suppose philosophy tries to get
behind phenomena, so as to get a peep at the world beyond. Suppose
Carlyle tells us that "All visible things are emblems; what thou seest
is not there on its own account; strictly taken, is not there [as such]
at all; matter exists only spiritually, and to represent some idea and
_body_ it forth." Has he altered the reality of the phenomena
themselves? Not in the smallest degree. Suppose the materialist gives us
his analysis of phenomena. Are not the phenomena he analyzes still the
same, still equally real? No matter how far he analyzes phenomena,
behind phenomena he cannot get. The materialist resolves all phenomena
into matter in motion or into energy, and says that these are the only
real existences. But they are no more real (they are a good deal less
real to most of us) than the phenomena with which he started. How can
the results of analysis be more real than that which is analyzed?
Moreover, the matter and energy are still phenomena, and involve, as
such, the percipient mind. Do what you will, you cannot get rid of the
mental factor in phenomena.
It is possible that my use of the word "construct," my saying that the
object is a thing which each of us constructs at the suggestion of
certain sense-stimuli, may lead some to suppose that the process is in
some sense an arbitrary one. This, however, would be a misconception.
The process under normal conditions is just as inevitable as is, under
normal conditions, the fall of a stone to the ground. The law of
construction for human-folk is as much a law of nature as the law of
gravitation. Both laws are condensed statements of the facts of the
case. There is nothing arbitrary, lawless, or unnatural in the one or
the other; the phrase merely emphasizes the essential presence of the
mental factor.
If this principle be once thoroughly grasped, it will be seen how
shallow and misleading is the view that the world is just reflected in
consciousness unchanged as in a mirror, or faithfully photographed as on
a sensitive plate. This is to reduce the human mind, which is surely no
whit _less_ complex than the human body, to the condition of a mere
passive recipient instead of a vital and active agent in the
construction of man's world.
The next point we have to consider is why we believe, as you and I
practically do believe, that the world of phenomena exists as such, not
merely for you and for me, but for man. Is it not because we believe in
the practical unity of mankind? Is it not because we believe that,
greatly as the conceptual and intellectual superstructure may differ in
different individuals, the perceptual basis and foundation are
practically identical? The senses and sense-organs give, in all normal
individuals, sense-data, which differ only within comparatively narrow
limits; and though the intellectual and moral world of the Bushman and
the North Australian may differ profoundly from those of Shakespeare and
Pascal, the perceptual world is, we have every reason to suppose, within
these narrow limits, the same. This we may fairly believe; but even so
there must be, nay, we know that there are, very great differences in
the interpretation of the perceptual world. The individual cannot divest
himself of the intellectual and conceptual part of his nature. We, for
whom phenomena are more or less conditioned by science, find it
difficult to think ourselves into the position of the savage, whose
perceptual world is conditioned by crude superstition. The elements of
his perceptual world are the same as ours, but the light of knowledge in
which we view them is, for him, very dim. When we try to realize his
world we find it exceedingly difficult.
And when we come to the lower animals--even those nearest us in the
scale of life--the difficulties are enormously increased. The sense-data
are probably much the same, but they are combined in different
proportions. Olfactory sensation must, one would suppose, be built into
the constructs of the dog and the deer to an extent which we cannot at
all realize. And then, as Mr. P. G. Hamerton has well said, we have to
take into account the immensity of the ignorance of animals. That
ignorance, in combination with perfect perceptual clearness (ignorance
and mental clearness are quite compatible) and with inconceivably strong
instincts, produces a creature whose mental states we can never
accurately understand.
I am tempted here to give the instance Mr. Hamerton quotes[GD] in
illustration of the ignorance of animals.
"The following account of the behaviour of a cow," he says, "gives a
glimpse of the real nature of the animal. These long-tailed cows, say
Messrs. Huc and Gabet, are so restive and difficult to milk, that to
keep them at all quiet the herdsman has to give them a calf to lick
meanwhile. But for this device, not a single drop of milk can be
obtained from them. One day a Llama herdsman, who lived in the same
house as ourselves, came with a long dismal face to announce that his
cow had calved during the night, and that, unfortunately, the calf was
dying. It died in the course of the day. The Llama forthwith skinned the
poor beast and stuffed it with hay. This proceeding surprised us at
first, for the Llama had by no means the air of a man likely to give
himself the luxury of a cabinet of natural history. When the operation
was completed, we found that the hay-calf had neither feet nor head;
whereupon it occurred to us that, after all, it was perhaps a pillow
that the Llama contemplated. We were in error, but the error was not
dissipated till the next morning, when our herdsman went to milk his
cow. Seeing him issue forth, the pail in one hand and the hay-calf under
the other arm, the fancy occurred to us to follow him. His first
proceeding was to put the hay-calf down before the cow. He then turned
to milk the cow herself. The mamma at first opened enormous eyes at her
beloved infant; by degrees she stooped her head towards it, then smelt
at it, sneezed three or four times, and at last proceeded to lick it
with the most delightful tenderness. This spectacle grated against our
sensibilities; it seemed to us that he who first invented this parody
upon one of the most touching incidents in nature must have been a man
without a heart. A somewhat burlesque circumstance occurred one day to
modify the indignation with which this treachery inspired us. By dint of
caressing and licking her little calf, the tender parent one fine
morning unripped it. The hay issued from within, and the cow,
manifesting not the slightest surprise nor agitation, proceeded
tranquilly to devour the unexpected provender."
Are we surprised at the want of surprise on the part of the cow? Why
should we be? What knows she of anatomy or of physiology? If she could
think at all about the matter, she would, no doubt, have expected her
calf to be composed of condensed milk. But failing that, why not hay?
She had presumably some little experience of _putting_ hay inside. Why
not _find_ hay inside; and, finding hay, why not enjoy the good
provender thus provided? But clearly we must not expect the brutes to
possess knowledge to which they cannot attain about matters which in no
wise concern their daily life.
"In our estimates of the characters of animals," continues Mr. Hamerton,
in his comments on this anecdote, "we always commit one of two
mistakes--either we conclude that the beasts have great knowledge
because they are so clever, or else we fancy that they must be stupid
because they are so ignorant." "The main difficulty in conceiving the
mental states of animals," says the same observer, "is that the moment
we think of them as _human_, we are lost." Yes, but the pity of it is
that we cannot think of them in any other terms than those of human
consciousness. The only world of constructs that we know is the world
constructed by man.
"To Newton and to Newton's dog, Diamond," said Carlyle, "what a
different pair of universes! while the painting in the optical retina of
both was most likely the same." Different, indeed; if we can be
permitted, without extravagance, to speak of the universe as existing at
all for Diamond, or allowed, except in hyperbole, to set side by side a
conception of ultimate generality, like the universe, the summation of
all conceptions, and "the painting in the optical retina." Carlyle's
meaning is, however, clear enough. Given two different minds and the
same facts, how different are the products! In the construct formed on
sight of the simplest object, we give far more than we receive; and what
we give is a special resultant of inheritance and individual
acquisition. No two of us give quite the same in amount or in quality.
It is not too much to say that for no two human beings is the world we
live in quite the same. And if this be so of human-folk, how different
must be the world of man from the world of the dog--the world of Newton
from the world of Diamond!
And we must remember that it is not merely that the same world is
differently mirrored in different minds, but that they are two different
worlds. If there is any truth in what I have urged in the last chapter,
we _construct_ the world that we see. The sensations are, as we have
seen, mental facts, in no sense resembling their causes, but
representing them in mental symbolism. Percepts are the elaborated
products of this mental symbolism. The question, then, is not--How does
the world mirror itself in the mind of the dog? but rather--How far does
the symbolic world of the dog resemble the symbolic world of man? How
far is his symbolism the same as ours? Only by fully grasping the fact
that the external world of objects does not exist independently of us
(though something exists which we thus symbolize), shall we realize the
greatness of the difficulty which stands in the path of the student of
animal psychology. So long as we are content to accept John Bunyan's
crude analogy of the gateways of sense, the difficulty is comparatively
small. There is the outside world self-existent and independent; a
knowledge of it comes into the mind through the five gateways of
sense--a picture of it through the eye-gate, and so on. The dog has also
five similar gateways. The world for him is, therefore, much the same as
for us. But this is not a true analogy. The world we see around us is a
joint product of an external existence, the independent nature of which
we can never know, and the human mind. It is something we construct in
mental symbolism. How far does the dog construct a similar world? The
answer to this question must, as it seems to me, be largely speculative.
And what help have we towards answering it? That afforded by the theory
of organic evolution. If we accept that theory, and accept also the view
that mental or psychical products are the inseparable concomitants of
certain organic or physiological processes, then we have a basis from
which to start. That basis I adopt.
Unfortunately, we have at present but little particular knowledge of the
correlation of psychical and physiological processes. We cannot, by the
dissection of a brain, draw much in the way of valid and detailed
inference as to the nature of the psychical processes which accompany
its physiological action. Fortunately, however, on the other hand, there
are certain physical manifestations which do aid us, and that not a
little, in drawing inferences from the physical to the mental. For
organisms exhibit certain activities, and from these activities we can
infer to some extent the character of the mental processes by which they
are prompted. We are wont, in observing the actions of our fellow-men,
to draw conclusions (often, alas! erroneous) as to the mental processes
which accompany them. We are ourselves active, and we are immediately
conscious of the modes of consciousness which accompany our actions.
Thus the activities of organisms give us some clue to their mental
processes, and it is through observation of their physical activities
that we gain nearly all that is of particular value concerning the
mental activities of animals. These activities we shall have to consider
more fully in a future chapter. In the present chapter we shall consider
them only so far as they give us information concerning the perceptual
world (or worlds) of animals, and the nature of the inferences which we
may suppose animals to draw from the phenomena which fall within their
observation.
I think that, from the fundamental identity of life-stuff, or
protoplasm, in all forms of animal life, and from the observed
similarity of nerves and nerve-cells when nervous tissue has been
developed, and again from the essential resemblance of life-processes in
all animal organisms, we are justified in believing that mental or
conscious processes, when they emerge, are essentially similar in kind.
Exactly when they do emerge in the ascending branches of the great tree
of animal life it is exceedingly difficult, if not quite impossible, to
determine. And it is, I fancy, quite impossible for us so to divest
ourselves of the complexity of human consciousness as to imagine what
the simplicity of the emergent consciousness in very lowly organisms is
like. But I think that we may fairly believe that some dim form of
discrimination is the germ from which the spreading tree of mind shall
develop.[GE]
I assume, then, that, granting the theory of evolution, the early stages
of the process of construction--discrimination, localization, and
outward projection--are the same in kind throughout the whole range of
animal life, wherever we are justified in surmising that psychical
processes occur, and the power of registration and revival in memory has
been established. As will be gathered, however, from what I have already
said, I hold that the nature of the constructs produced is and must be
for us human-folk, since we are human-folk, to a large extent a matter
of speculation. Remembering this, then, endeavouring never to lose sight
of it for a moment, let us consider what we may fairly surmise
concerning the constructs and the process of construction in animals.
* * * * *
There can be no question that the animals nearest us in the scale of
life--the higher mammalia--form constructs analogous to, if not closely
resembling, ours. I do not think the resemblance can be in any sense
close, seeing to how large an extent our constructs are literally our
_handi_-work. For though in many animals the tongue and lips are
delicate organs of touch--not to mention the trunk of the elephant--and
though in the monkeys and many rodents the hands are used for grasping,
still we have no reason to suppose that in any other mammal the
geometrical sense of touch plays so determining a part in the formation
of constructs as in man. On the other hand, in the dog and the deer, for
example, not only must the marvellously acute sense of smell have a far
higher suggestive value, but smells and odours must, one would suppose,
be built into the constructs in a far larger proportion. But although
their constructs may not closely resemble ours, the constructs of
animals may, I believe, be fairly regarded as closely analogous to our
own. And as with us, so with them, a comparatively simple and meagre
suggestion may give rise, through association in experience, to the
construction of a complex object. And again, as with us, so with them,
the suggested construct may be very vague and indefinite.
A dog, for example, is lying asleep upon the mat, and hears an
unfamiliar step in the porch without. There can be no question that this
suggests the construct man. But from the very nature of the case, this
must be vague and indefinite. So, too, when a chamois, bounding across
the snow-fields, stops suddenly when he scents the distant footprints of
the mountaineer, the construct that he forms cannot be in any way
particularized--no more particularized than is to me the sheep that I
hear bleating in the meadow behind yonder wall.
And no one is likely to question the fact that animals habitually
proceed from this first stage--the formation of constructs by immediate
association--to the second stage of construction--the defining of
constructs by examination. In many of the deer tribe, notably the
prong-horn of America, this tendency is so strongly developed that they
may be lured to their destruction by setting up a strange and unfamiliar
object which, as we put it, may excite their curiosity. A strange noise
or appearance will make a dog uneasy until he has by examination
satisfied himself of the nature of that which produces it. Of this an
instance fell under my observation a few days ago. My cat was asleep on
a chair, and my little son was blowing a toy horn. The cat, without
moving, mewed uneasily. I told my boy to continue blowing. The cat grew
more uneasy, and at last got up, stretched herself, and turned towards
the source of discomfort. She stood looking at my boy for a minute as he
blew. Then curling herself up, she went to sleep again, and no amount of
blowing disturbed her further. Similarly, Mr. Romanes's dog was cowed at
the sound of apples being shot on to the floor of a loft above the
stable; but when he was taken to the place, and saw what gave rise to
the sound, he ceased to be disquieted by it. Every one must have seen
animals defining their constructs by examination. A monkey will spend
hours in the examination of an old bottle or a bit of looking-glass. At
the Zoological Gardens connected with the National Museum at Washington,
a monkey was observed with a female opossum on his knee. He had
discovered the slit-like opening of the marsupial pouch, and took out
first one and then another of the young, looked them over carefully, and
replaced them without injury.[GF]
There may possibly be some difference of opinion as to whether animals
are able to infuse into their constructs of other animals the element of
feeling. One would, perhaps, fain believe that the beasts of prey were
wholly unaware of the pain they inflict on other organisms. But I
question whether any close observer of animals could hold this view.
Even if it were supposed that when two dogs fight they are blind to the
pain they are inflicting on each other, their mock-fighting seems to
imply a consciousness of the pain they might inflict, but avoid
inflicting. And many of us have presumably had experiences analogous to
the following: A favourite terrier of mine was once brought home to me
so severely gashed in the abdominal region that I felt it necessary to
sew up the wound. In his pain the poor dog turned round and seized my
hand, but he checked himself before the teeth had closed upon me
tightly, and piteously licked my hand. For myself, I cannot doubt that
animals project into each other the shadows of the feelings of which
they are themselves conscious.
The fact that dogs may be deceived by pictures[GG] shows that they may
be led through the sense of sight to form false constructs, that is to
say, constructs which examination shows to be false. Through my friend
and colleague, Mr. A. P. Chattock, I am able to give a case in point. I
quote from a letter received by Mr. Chattock: "Your father asks me to
tell you about our old spaniel Dash and the picture. I remember it well,
though it must be somewhere, about half a century ago. We had just
unpacked and placed on the old square pianoforte, which then stood at
the end of the dining-room, the well-known print of Landseer's 'A
Distinguished Member of the Humane Society.' When Dash came into the
room and caught sight of it, he rushed forward, and jumped on the chair
which stood near, and then on the pianoforte in a moment, and then
turned away with an expression, as it seemed to us, of supreme disgust."
I think we may say, then, that the higher animals are able to proceed a
long way in the formation and definition of highly complex constructs
analogous to, but probably differing somewhat from, those which we form
ourselves. These constructs, moreover, through association with
reconstructs or representations, link themselves in trains, so that a
sensation or group of sensations may suggest a series of reconstructs or
a series of remembered phenomena. We here approach the question of
inferences, of which more anon. But in this connection passing reference
may be made to the phenomena of dreaming. Dogs and some other animals
undoubtedly seem to dream.
The nature of dreaming may, perhaps, be best illustrated by a rough
analogy. Professor Clifford likened the human consciousness to a rope
made up of a great number of occasionally interlacing strands. Let us
picture such a rope floating in water. Much of it is submerged; only the
upper part is visible at the surface. This upper part is like the series
of mental phenomena of which we are distinctly conscious. Below this lie
other series in the half-submerged state of subconsciousness. Deeper
still lie unconscious physiological processes capable of emerging into
the shadow of subconsciousness or the light of distinct consciousness.
Now picture this rope gradually slipping round as it floats, so that now
one part, now another, sees the light. This is analogous to the musing
state, when we allow our thoughts to wander unchecked by any effort of
attention. Attention is the faculty by which we steady the rope, so that
one particular strand is kept continuously uppermost. The inattentive
mind is one in which the rope keeps slipping round and refuses to be
steadied in this manner; and in unquiet sleep, when the faculty of
attention is dormant, the strands come quite irregularly and haphazard
to the surface, and we have the phantasmagoria of dreams.
In the dog or the ape the rope is presumably incomparably simpler. But
that it is of the nature of a rope we may, perhaps, not improbably
surmise. Interest and the attention it commands steady the rope. Animals
differ widely in their power of attention, as every one knows who has
endeavoured to educate his pets. Darwin tells us that those who buy
monkeys from the Zoological Gardens, to teach them to perform, will give
a higher price if they are allowed a short time in which to select those
in which the power of attention is most developed. And when animals
dream, their consciousness-rope is slipping round unsteadily. That they
do apparently dream is, so far, evidence of their possessing linked
chains of memories.
In speaking of the faculty of attention in animals, it may be well to
note that attention is of two kinds--perceptual or direct, and
conceptual or indirect. In perceptual attention its motive is directly
suggested by the object which stimulates this concentration of the
faculties; a menacing dog, for example, stimulates my perceptual
attention. In conceptual attention the motive is ulterior and indirect.
The concentrated attention which a man devotes to the acquisition of
Sanscrit does not arise directly out of the symbols over which he pores;
it is of intellectual origin.
In the normal life of animals the attention is of the perceptual order;
it is a direct stimulation of the faculties through a perceptual
presentation of sense or representation in memory which gives rise to an
appetence or aversion. The importance of such a faculty is obvious. As
M. Ribot well says, it is no less than a condition of life. The
carnivorous animal that had not its attention roused on sight of prey
would stand but a poor chance of survival; the prey that had not its
attention roused by the approach of its natural enemy would stand but a
poor chance of escape. The emperor moth that had not its attention
roused by the scent of the virgin female would stand but a poor chance
of propagating its species.
We are not, however, at present in a position further to discuss this
matter. For there is a factor in the process which we shall have to
consider more fully hereafter--the emotional factor. The hungry lion is
in a very different position, so far as attention is concerned, from the
satiated animal. The force and volume of the attention depends not
merely, or even mainly, upon the intensity of the stimulus, but on the
emotional state of the recipient organism.
Endeavour to divert the attention of any animal which is intent upon
some action connected with the main business of its life--nutrition,
self-defence, or the propagation of the species--the force of attention
will at once be obvious.
In the training of animals (and young children) artificial associations,
pleasurable or painful, have to be established in connection with
certain actions. Abnormal appetences and aversions have to be introduced
into the mental constitution. In this process much depends on the
plasticity of the constitution. In the absence of such plasticity it is
impossible to establish new associations.
We have seen that words are arbitrary[GH] symbols, which we associate
with objects, or qualities, or actions. Can animals, we may ask, form
such arbitrary associations? There can be little question that they can.
Many of the higher animals understand perfectly some of _our_ words. The
word "cat" or "rats" will suggest a construct to the dog on which he may
take very vigorous action. How far they are able to communicate with
each other is a somewhat doubtful matter. But the signs by which such
communication is effected are probably far less arbitrary. And, in any
case, the communication would seem to refer only to the here and the
now. A dog may be able to suggest to his companion the fact that he has
descried a worriable cat; but can a dog tell his neighbour of the
delightful worry he enjoyed the day before yesterday?
I imagine that what a dog can suggest to his neighbour is what we
symbolize by the simple expression "Come." But I am fully aware that
other observers will interpret the facts in a different way. Here is an
anecdote that is communicated to me by Mr. Robert Hall Warren, of
Bristol. "My grandfather," he says, "a merchant of this city, or, as
Thomas Poole, of Stowey, would have preferred calling him, 'a
tradesman,' had two dogs, one a small one and another larger, who, being
fierce, rejoiced in the appropriate name of Boxer. On one of his
business journeys into Cornwall he took the smaller dog with him, and
for some reason left it at an inn in Devonshire, promising to call for
him on his return from Cornwall. When he did so, the landlord apologized
for the absence of the dog, and said that, some time after my
grandfather left, the little dog fought with the landlord's dog, and
came off much the worse for the fight. He then disappeared, and some
time afterwards returned with another and larger dog, who set upon his
enemy, and, I think, killed him. Then the two dogs walked off, and were
no more seen. From the description given, my grandfather had no doubt
that the larger dog was Boxer, and, on returning home, found that the
little dog had come back, and that both dogs had gone away, and, after a
time, had returned home, where he found them." Now, some will say that
the little dog told Boxer all about it; but I am inclined to believe
that the facts may be explained by the communication "Come."
Dogs can also communicate their wishes to us. The action of begging in
dogs is a mode of communication with us. Mr. Romanes tells of a dog that
was found opposite a rabbit-hutch begging for rabbits. When I was at the
Diocesan College near Capetown, a retriever, Scamp, used to come in and
sit with the lecturers at supper. He despised bread, but used to get an
occasional bone, which he was not, however, allowed to eat in the hall.
He took it to the door, and stood there till it was opened for him. On
one occasion he heard without the excited barking of the other dogs. He
trotted round the hall, picked up a piece of bread which one of the boys
had dropped, and stood with it in his mouth at the door. When it was
opened, he dropped the bread, and raced off into the darkness to join in
the fun. In a similar way, but with less marked intelligence, I have
seen a dog begging before a door which he wished opened. My cat has been
taught to touch the handle of the door with his paw when he wishes to
leave the room. Mr. Arthur Lee, of Bristol, tells me that a favourite
cat has a habit of knocking for admittance by raising the door-mat and
letting it fall. This is an action similar to those communicated by
several observers to _Nature_, where cats have learnt either to knock
for admittance or to ring the bell--an action which, as my friend, Mr.
J. Clifton Ward, informed me, was also performed by a dog of his. I
think, therefore, that it is unquestionable that the higher animals are
able to associate arbitrary signs with certain objects and actions, and
to build these signs into the constructs that they form. Sir John
Lubbock has tried some experiments with his intelligent black poodle
Van, with the object of ascertaining how far the dog could be taught to
communicate his wishes by means of printed cards. "I took," he says,[GI]
"two pieces of cardboard, about ten inches by three, and on one of them
printed in large letters the word 'FOOD,' leaving the other blank. I
then placed the two cards over two saucers, and in the one under the
'Food' card put a little bread-and-milk, which Van, after having his
attention called to the card, was allowed to eat. This was repeated over
and over again till he had had enough. In about ten days he began to
distinguish between the two cards. I then put them on the floor, and
made him bring them to me, which he did readily enough. When he brought
the plain card, I simply threw it back; while, when he brought the
'Food' card, I gave him a piece of bread, and in about a month he had
pretty well learned to realize the difference. I then had some other
cards printed with the words 'Out,' 'Tea,' 'Bone,' 'Water,' and a
certain number also with words to which I did not intend him to attach
any significance, such as 'Nought,' 'Plain,' 'Ball,' etc. Van soon
learned that bringing a card was a request, and soon learned to
distinguish between the plain and printed cards; it took him longer to
realize the difference between words, but he gradually got to recognize
several, such as 'Food,' 'Out,' 'Bone,' 'Tea,' etc. If he was asked
whether he would like to go out for a walk, he would joyfully fish up
the 'Out' card, choosing it from several others, and bring it to me or
run with it in evident triumph to the door.
"A definite numerical statement always seems to me clearer and more
satisfactory than a mere general assertion. I will, therefore, give the
actual particulars of certain days. Twelve cards were put on the floor,
one marked 'Food' and one 'Tea.' The others had more or less similar
words. I may again add that every time a card was brought, another
similarly marked was put in its place. Van was not pressed to bring
cards, but simply left to do as he pleased.[GJ]
"Day 1. Van brought 'Food' 4 times, 'Tea' 2 times.
" 2. " " 6 "
" 3. " " 8 " " 2 "
" 4. " " 7 " " 3 "
" 5. " " 6 " " 4 "
" 6. " " 6 " " 3 " 'Nought' once.
" 7. " " 8 " " 2 "
" 8. " " 5 " " 3 "
" 9. " " 4 " " 2 "
" 10. " " 10 " " 4 " 'Door' once.
" 11. " " 10 " " 3 "
" 12. " " 6 " " 3 "
-- --
80 31
"Thus, out of 113 times, he brought 'Food' 80 times, 'Tea' 31 times, and
[one out of] the other 10 cards only twice. Moreover, the last time he
was wrong he brought a card--namely, 'Door'--in which three letters out
of four were the same as in 'Food.'"
These experiments and observations are of great interest. But, of
course, no stress whatever must be laid on the fact that _words_ chanced
to be printed on the cards instead of any other arrangements of lines. I
draw attention to this because I have heard Sir John Lubbock's
interesting experiments quoted, in conversation, as evidence that the
dog understands the meaning of words, not only spoken, but written! What
they show is that Van is able, under human guidance, to associate
certain arbitrary symbols with certain objects of appetence; and,
desiring the object, will bring its symbol. It would have been better, I
think, because less misleading to the general public, had Sir John
Lubbock selected other arbitrary symbols than the printed words we
employ. Then no one could have run away with the foolish notion that the
dog _understands_ the meaning of these words. No doubt if they had been
written in Greek or Hebrew, some people would have been interested, but
not surprised, to learn that a dog can be taught to understand with
perfect ease these languages!
The next question is--Have the higher animals the power of analyzing
their constructs and forming isolates or abstract ideas of qualities
apart from the constructs of which these qualities are elements? Can we
say, with Mr. Romanes,[GK] "All the higher animals have general ideas of
'good-for-eating' and 'not-good-for-eating,' _quite apart from any
particular objects of which either of these qualities happens to be
characteristic_"? Or with Leroy,[GL] that a fox "will see snares when
there are none; his imagination, distorted by fear, will produce
deceptive shapes, to which he will attach _an abstract notion of
danger_"?
Now, this is a most difficult question to answer. But it seems to me
that, if we take the term "abstract idea" in the sense in which I have
used the word "isolate," we must answer it firmly, but not dogmatically
(this is the last subject in the world on which to dogmatize), in the
negative. Fully admitting, nay, contending, that this is a matter in
which it is exceedingly difficult to obtain anything like satisfactory
evidence, I fail to see that we have any grounds for the assertion that
the higher animals have abstract ideas of "good-for-eating" or
"not-good-for-eating," quite apart from any particular objects of which
either of these qualities happens to be characteristic.[GM]
The particular example is well chosen, since the idea of food is a
dominant one in the mind of the brute. There can be no question that the
quality of eatability is built in by the dog into a great number of his
constructs. But I question whether this quality can be isolated by the
dog, and can exist in his mind divorced from the eatables which suggest
it. If it can, then the dog is capable of forming a concept as I have
defined the term. I can quite understand that a hungry dog, prowling
around for food, has, suggested by his hunger, vague representations in
memory of things good to eat, in which the element of eatability is
predominant and comparatively distinct, while the rest is vague and
indistinct. And that this is a concept in Mr. Sully's use of the term, I
admit. But it appears to me that there is a very great difference
between a perceptual construct with eatability predominant and the rest
vague, and a conceptual isolate or abstract idea of eatability quite
apart from any object or objects of which this quality is
characteristic. And to mark the difference, I venture to call the
prominent quality a _predominant_ as opposed to the _isolate_ when the
quality is floated off from the object. _No doubt it is out of this
perceptual prominence of one characteristic and vagueness of its
accompaniments that conceptual isolation of this one characteristic has
grown, as I believe, through the naming of predominants._ But I should
draw the line between the one and the other somewhere distinctly above
the level of intelligence that is attained by any dumb animal. I am not
prepared either to affirm or deny that this line should be drawn exactly
between brute intelligence and human intelligence and reason, though I
strongly incline to the view that it should. I am not sure that every
savage and yokel is capable of isolation, that he raises the predominant
to the level of the isolate, or abstract idea. I am not sure that these
simple folk submit the phenomena of nature around them, and of their own
mental states to analysis. But they have in language the instrument
which can enable them to do so, even if individually some of them have
not the faculty for using language for this purpose. That is, however, a
different question. But I do not at present see satisfactory evidence of
the fact that animals form isolates, and I think that the probability is
that they are unable to do so. I am, therefore, prepared to say, with
John Locke, that this abstraction "is an excellency which the faculties
of brutes do by no means attain to."
I am anxious, however, not to exaggerate my divergence, more apparent, I
believe, than real, from so able a student of animal psychology as Mr.
Romanes. Let me, therefore, repeat that it is the power of analysis--the
power of isolating qualities of objects, the power of forming "abstract
ideas quite apart from the particular objects of which the particular
qualities happen to be characteristic," as I understand these
words--that I am unable to attribute to the brute. Animals can and do, I
think, form predominants; they have not the power of isolation.
Furthermore, it seems to me that this capacity of analysis, isolation,
and abstraction constitutes in the possessor a new mental departure,
which we may describe as constituting, not merely a specific, but a
generic difference from lower mental activities. I am not prepared,
however, to say that there is a difference in kind between the mind of
man and the mind of the dog. This would imply a difference in origin or
a difference in the essential nature of its being. There is a great and
marked difference in kind between the material processes which we call
physiological and the mental processes we call psychical. They belong to
wholly different orders of being. I see no reason for believing that
mental processes in man differ thus in kind from mental processes in
animals. But I do think that we have, in the introduction of the
analytic faculty, so definite and marked a new departure that we should
emphasize it by saying that the faculty of perception, in its various
specific grades, differs generically from the faculty of conception. And
believing, as I do, that conception is beyond the power of my favourite
and clever dog, I am forced to believe that his mind differs generically
from my own.
* * * * *
Passing now to the other vertebrates, the probabilities are that their
perceptual processes are essentially similar to those of the higher
animals; but, in so far as these creatures differ more and more widely
from ourselves, we may, perhaps, fairly infer that their constructs are
more and more different from ours. Still, the thrush that listens
attentively on the lawn and hops around a particular spot must have a
vague construct of the worm he hopes to have a more particular
acquaintance with ere long. The cobra that I watched on the basal slopes
of Table Mountain, and that raised his head and expanded his hood when I
pitched a pebble on to the granite slope over which he was gliding, must
have had a vague percept suggested thereby. The trout that leaps at your
fly so soon as it touches the water must have a vague percept of an
eatable insect which suggests his action. The carp[GN] that come to the
sound of a bell must have, suggested by that sound, vague percepts of
edible crumbs. And no one who has watched as a lad the fish swimming
curiously round his bait can doubt that they are by examination defining
their percepts, and drawing unsatisfactory inferences of a perceptual
nature.
And here let us notice that the whole set of phenomena which have been
described in previous chapters under the heads of recognition-marks, of
warning coloration, and of mimicry, involve close and accurate powers of
perception. Recognition-marks are developed for the special purpose of
enabling the organisms concerned rapidly and accurately to form
particular perceptual constructs. Of what use would warning coloration
be if it did not serve to suggest to the percipient the disagreeable
qualities with which it is associated? The very essence of the principle
of mimicry is that misleading associations are suggested. Here a false
construct, untrue to fact, that is to say, one that verification would
prove to be false, is formed; just as a well-executed imitation orange,
in china or in soap, may lead a child to form a false construct, one
that is proved to be incorrect so soon as the suggestions of sight are
submitted to verification by touch, smell, and taste.
No one who has carefully watched the habits of birds can have failed to
notice how they submit a doubtful object to examination. Probably the
avoidance of insects protected by warning colours is not perfectly
instinctive. I have seen young birds, after some apparent hesitation,
peck once or twice doubtfully at such insects. A young baboon with whom
I experimented at the Cape seemed to have an undefined aversion to
certain caterpillars, which he could not be induced to taste, though he
smelt at them. Scorpions he darted at, twisted off the sting, and ate
with greedy relish.
If nudibranchs and other marine invertebrates be protectively coloured,
there must be corresponding perceptual powers in the fishes that are
thus led to avoid them; for there seems to be definite avoidance, and
not merely indifference. This, however, might be made the subject of
further experiment, not only with fishes, but with other animals. I
tried some chickens with currant-moth caterpillars, to each of which I
tied with thread a large looper. Some of them would have nothing to do
with the unwonted combination. But one persistently pecked at the
looper, and tried to detach it from its fellow-prisoner. Though, on the
whole, there was some tendency for aversion to the currant-moth
caterpillar to overmaster the appetence for the looper, I was not
altogether satisfied with the result of the experiment. But I think that
if the protectively coloured larva had been regarded with mere
indifference (i.e. neither aversion nor appetence), the appetence for
the loopers should have made the chickens seize them at once.
To return to fishes. It is probably difficult or impossible for us to
imagine what their constructs are like; but that they, too, proceed to
define them by examination seems to be a legitimate inference from some
of their actions. Mr. Bateson says, "The rockling searches [for food] by
setting its filamentous pelvic fins at right angles to the body, and
then swimming about, feeling with them. If the fins touch a piece of
fish or other soft body, the rockling turns its head round and snaps it
up with great quickness. It will even turn round and examine uneatable
substances, as glass, etc., which come in contact with its fins, and
which presumably seem to it to require explanation."[GO] And, speaking
of the sole, the same observer says,[GP] "In searching for food the sole
creeps about on the bottom by means of the fringe of fin-rays with which
its body is edged, and, thus slowly moving, it raises its head upwards
and sideways, and gently pats the ground at intervals, feeling the
objects in its path with the peculiar viliform papillæ which cover the
lower (left) side of its head and face. In this way it will examine the
whole surface of the floor of the tank, stopping and going back to
investigate pieces of stick, string, or other objects which it feels
below its cheek."
If we admit the fact that carp come to be fed at the sound of a bell, we
have evidence that some fishes can associate an arbitrary sound with the
advent of things good to eat. But it is, perhaps, better at present to
regard the fact as one requiring verification.
That some birds can associate arbitrary signs with their percepts will
be admitted by all who have watched their habits. And from its peculiar
and almost unique power of articulation, the parrot shows us that not
only may the words suggest a construct, but that the sight of the
construct may suggest the word that it has heard associated with the
object by man. Mr. Romanes gives evidence which satisfies him that a
parrot which had associated the word "bow-wow" with a particular dog,
uttered this sound when another dog entered the room. The word was here
suggested at sight, not of the same object, but of an object which the
bird recognized as similar. A somewhat similar case is furnished by one
of my own correspondents (Miss Mabel Westlake). "We left London," she
says, "in December, 1888, and brought our grey parrot with us; but left
behind with a friend our favourite cat, a dark tortoiseshell with a
white breast, the forehead clearly marked with a division down the
middle to the tip of the nose. This led to our calling her 'Demi.' For a
week or two after our arrival in Bristol, a black-and-white cat
belonging to the people formerly living here frequented the house. The
parrot seemed delighted to see this cat, which was larger than our old
cat, and called it Dem, as she had been accustomed to do in London. From
that time until the commencement of January (1890), which was over a
year, the parrot had not seen a cat that we are aware of, nor had we
heard her call it for a long time. About six weeks ago, as I was coming
along Kingsdown Parade, a large black kitten followed me home. We took
it in and fed it. The next day it came into the room where the parrot
was, and she immediately said 'Puss! puss! puss! Hullo, dear!' and
during the day called it by the same name, 'Dem! Dem! Dem!' that she had
called our cat in London."
We may here notice that, in most of the tricks which animals are taught
to perform, the action is suggested by a form of words (or the tone and
manner in which they are uttered). Mr. John G. Naish, J.P., of
Ilfracombe,[GQ] has taught his cockatoo the following trick (I quote Mr.
Naish's own words): "I give him a shilling, which he puts into the slit
of a money-box. This is 'enlisting.' After that, I say to him, 'Will you
die for the queen, like a loyal soldier?' Then he lies on his back, with
his paws together, for as long as I hold up my finger. 'Now live for
your master!' He takes hold of my finger and resumes his erect posture.
Last year I took him into the street near my house, and collected on our
'Hospital Saturday.' He worked for more than an hour before he became
impatient. And then he would do no more, but flung the coins over his
head or at the giver in the funniest way. He went to sleep for a long
time after that performance; and when he awoke and I took him, he
covered my face with kisses, as if he was glad to find his bad dream was
over." The weariness and failure to perform the trick when tired, and
the long sleep which succeeded, are interesting points. What I wish
especially to notice is, however, that the actions are suggested by
certain forms of words; but that there is no evidence that the form of
words is in any sense understood. When the onlooker sees a bird lie on
its back when asked if it will die for the queen, and get up again when
told to live for its master, he is apt to think that, since _he_
understands the form of words, the bird must understand them too. But I
am convinced that Mr. Naish's intelligent cockatoo could have been
taught with equal ease to lie down at the command "Abracadabra," and to
stand up again at "Hocus pocus." Tricks taught to animals involve the
performing animal and the human onlooker. The form of words introduced
is _for the sake of the latter_, not for the sake of the former.
So much has been written concerning the intelligence of the parrot, and
so much has been said concerning its imitative power of speech, that I
must say somewhat on this head. I have received from Miss Mildred
Sturge, of Clifton, an interesting account of an African West Coast
parrot which was possessed by Miss Tregelles, of Falmouth. This parrot
used the phrases it had learnt appropriately in time and place. "At
dinner, when he saw the vegetable-dishes, he generally said, 'Polly
wants potato;' at tea he would say, 'Polly wants cake,' or 'Polly's
sop,' or 'Polly's toast.' Our grandmother's house was not far from the
station, and almost before people could hear it, Polly would announce,
'Grandmamma, the train is coming,' and presently the train would quietly
go by. Besides repeating much poetry, Polly made new editions by putting
lines together from different authors; but the remarkable thing was that
he always got the right rhyme. One of his favourite mixtures was, 'Sing
a song of sixpence' and 'I love little pussy.' One day my mother
overheard--
"'Four and twenty blackbirds,
When they die,
Go to that world above,
Baked in a pie.'"
Now, we must not underrate nor overrate the evidence afforded by
parrot-talk. The rhyme-association is interesting; but since we cannot
suppose that the poetry is more to the parrot than a linked series of
sounds, there does not seem much evidence of intelligence here, though
the evidence of memory is important. The correct association of words
and phrases with appropriate objects and actions is of great interest.
But the fact that they are words and phrases does not give them a higher
value than that of imitative actions in the dog or other animal. What
parrot-talk does give us evidence of is (1) remarkable powers of memory;
(2) an almost unique power of articulation; (3) a great faculty of
imitation; (4) and some intelligence in the association of certain
linked sounds which we call phrases with certain objects or actions. The
teaching of phrases to the parrot is certainly not more remarkable than
the teaching of clever tricks to many birds. But the fact that
word-sounds are articulated throws a glamour over these special tricks,
and leads some people to speak of the parrot's using language, instead
of saying that the parrot can imitate some of the sounds made by man,
and can associate these sounds with certain objects.
* * * * *
Coming now to the invertebrates, much has been written concerning the
psychology and intelligence of ants and bees. What shall we say
concerning their constructs? For reasons already given, I think we may
suppose that they are analogous to ours; but it can scarcely be that
they in any way closely resemble ours. Their sense-organs are
constructed on a different plan from ours; they have probably senses of
which we are wholly ignorant. Is it conceivable, by any one who has
grasped the principle of construction, that with these differently
organized senses and these other senses than ours, the world they
construct can much resemble the world we construct? Remember how largely
our perceptual world is the product of our geometrical senses--of our
delicate and accurate sense of touch, and of our binocular vision, with
its delicate and accurate muscular adjustments. Remember how largely
these muscular adjustments enter into our perceptual world as
constructed in vision. And then remember, on the other hand, that the
bee is encased in a hard skin (the chitinous exoskeleton), and that its
tactile sensations are mainly excited by means of touch-hairs seated
thereon. Remember its compound eye with mosaic vision, coarser by far
than our retinal vision, and its ocelli of problematical value, and the
complete absence of muscular adjustment in either the one or the other.
Can we conceive that, with organs so different, anything like a similar
perceptual world can be elaborated in the insect mind? I for one cannot.
Admitting, therefore, that their perceptions may be fairly surmised to
be analogous, that their world is the result of construction, I do not
see how we can for one moment suppose that the perceptual world they
construct can in any accurate sense be said to resemble ours. For all
that, the processes of discrimination, localization, outward projection;
the formation of vague constructs, their definition through experience,
and the association of reconstructs or representations;--all these
processes are presumably similar in kind to those of which we have
evidence in ourselves.
In considering such organisms as ants and bees, however, we must be
careful to avoid the error of supposing that, because they happen to
have no backbones, they are necessarily low in the scale of life and
intelligence. The tree of life has many branches, and, according to the
theory of evolution, these divergent branches have been growing up side
by side. There is no reason whatever why the bee and the ant, in their
branch of life, should not have attained as high a development of
structure and intelligence as the elephant or the dog in their branch of
life. I do not say that they have. As it is difficult to compare their
structure, in complexity and efficiency, with that of vertebrates, so is
it difficult to compare their intelligence. The mere matter of size may
have necessitated the condensation of intelligence into instinct in a
far higher degree than was required in the big-brained mammals. Still,
their intelligence, though of a different order and on a different
plane, may well be as high. And Darwin has said that the so-called brain
of the ant may perhaps be regarded as the most wonderful piece of matter
in the world.
That ants have some power of communication seems to be proved by the
interesting experiments of Sir John Lubbock. He found that they could
carry information to the nest of the presence of larvæ, and that the
greater the number of larvæ to be fetched, the greater the number of
ants brought out to fetch them in a given time. On one occasion Sir John
Lubbock put an ant to some larvæ. "She examined them carefully, and went
home without taking one. At this time no other ants were out of the
nest. In less than a minute she came out again with eight friends, and
the little group made straight for the heap of larvæ. When they had gone
two-thirds of the way, I imprisoned the marked ant; the others hesitated
a few minutes, and then, with curious quickness, returned home." This is
only one observation out of many; and it shows (1) that since the marked
ant took no larva home, she must have given information which led the
others to come out--unless we can suppose that the smell of the larvæ
she had examined still hung about her; and (2) that the communication
was not detailed, and probably was no more than "Come," for, when the
leader of the party was removed, the rest knew not[GR] where to go--very
possibly knew not why they had been summoned.
Passing now to creatures of lower organization, it is exceedingly
difficult so to divest ourselves of our own special mental garments as
to imagine what their simple and rudimentary constructs are like.
Perhaps we may fairly surmise that, as visual, olfactory and auditory
organs develop, and differentiate from a common basis of more simple
sensation, the process of outward projection has its rudimentary
inception. The earthworm, which finds its way to favourite food-stuffs
buried in the earth in which it lives, would seem to possess the power
of outward projection in a dim and possibly not very definite form.
Through their marginal bodies--simple auditory or visual organs--the
medusæ may have a rudimentary form of this capacity. In any case, they
seem to have the power of localization. Mr. Romanes says,[GS] "A medusa
being an umbrella-shaped animal, in which the whole of the surface of
the handle and the whole of the concave surface of the umbrella is
sensitive to all kinds of stimulation, if any point in the last-named
surface is gently touched with a camel-hair brush or other soft (or
hard) object, the handle or manubrium is (in the case of many species)
immediately moved over to that point, in order to examine or brush away
the foreign body." And the same author thus describes[GT] the process of
discrimination in the sea-anemone: "I have observed that if a
sea-anemone is placed in an aquarium tank, and allowed to fasten upon
one side of the tank near the surface of the water, and if a jet of
sea-water is made to play continuously and forcibly upon the anemone
from above, the result, of course, is that the animal becomes surrounded
by a turmoil of water and air-bubbles. Yet, after a short time, it
becomes so accustomed to this turmoil that it will expand its tentacles
in search of food, just as it does when placed in calm water. If now one
of the expanded tentacles is gently touched with a solid body, all the
others close around that body in just the same way as they would were
they expanded in calm water. That is to say, the tentacles are able to
discriminate between the stimulus which is supplied by the turmoil of
the water, and that which is supplied by their contact with the solid
body, and they respond to the latter stimulus notwithstanding that it is
of incomparably less intensity than the former."
Here, in discrimination, we reach the lowest stage of mental activity.
It is exceedingly difficult, however, to determine how far such simple
responses to stimuli are merely organic, and how far there enters a
psychological element.
I ought not, perhaps, to pass over in perfect silence the subject of
protozoan psychology. M. Binet has published a little book on "The
Psychic Life of Micro-Organisms," in the preface of which he says, "We
could, if it were necessary, take every single one of the psychical
faculties which M. Romanes reserves for animals more or less advanced on
the zoological scale, and show that the _greater part_ of these
faculties belonged equally to micro-organisms." He says that "there is
not a single infusory that cannot be frightened, and that does not
manifest its fear by a rapid flight through the liquid of the
preparation," and he speaks of infusoria fleeing "in all directions like
a flock of frightened sheep." He attributes memory to _Folliculina_, and
instinct "of great precision" to _Difflugia_. He regards some of these
animalculæ as "endowed with memory and volition," and he describes the
following stages:--
"1. The perception of the external object.
"2. The choice made between a number of objects.
"3. The perception of their position in space.
"4. Movements calculated either to approach the body and seize it or to
flee from it."
But when we have got thus far, we are brought up by the following
sentence: "We are not in a position to determine whether these various
acts are accompanied by consciousness, or whether they follow as simple
physiological processes." Since, therefore, the fear, memory, instinct,
perception, and choice, spoken of by M. Binet, may be merely
physiological processes (though, of course, they _may be_ accompanied by
some dim unimaginable form of consciousness), it seems scarcely
necessary to say more about them here.
* * * * *
I have now said all that is necessary, and all that I think justified by
the modest scope of this work, concerning the process of construction in
animals, and the nature of the constructs we may presume that they form.
The process I hold to be similar in kind throughout the animal kingdom
wherever we may presume that it occurs at all. But the products of the
process seem to me to be presumably widely different. If we steadily
bear in mind the fact that the world of man is a joint product of an
external existence and the human mind, and then ask whether it is
conceivable that the joint products of this external existence and the
dog-mind, the bird-mind, the fish-mind, the bee-mind, or the worm-mind
are exactly or even closely similar, we must, it seems to me, answer the
question with an emphatic negative.
* * * * *
We will now consider the nature of the inferences of animals. It will be
remembered that a distinction was drawn between perceptual inferences
and inferences involving a conceptual element. As I use the words,
perceptual inferences are a matter, at most, of intelligence; but
conceptual inferences involve the higher faculty of reason.
It will be necessary here to say somewhat more than I have already said
concerning inference. When I see an orange, that object is mentally
constructed at the bidding of certain sight-sensations. All that is
actually received is the stimulus of the retinal elements; the rest is
suggested and supplied by the activity of the mind. It is sometimes said
that this complementary part of the perception is inferred. So, too,
when I hear a howl in the street which suggests the construct dog, it
may be said that I infer the presence of the dog. And again, when the
dog is perceived to be in pain, it may be said that this is an
inference. Now, although the use of the word "inference" to denote the
complementary part of a percept seems a little contrary to
ordinary usage, still there are some advantages in so--with due
qualification--employing it. But since, as it seems to me, the
characteristic of the inference, if so we style it, in the formation of
constructs by immediate association is its unconscious nature (i.e.
unconscious as a process) we may perhaps best meet the case by speaking
of these as unconscious inferences. When the inference is not immediate
and unconscious, but involves a more individual conscious act of the
mind in the perceptual sphere, we may speak of it as intelligent; and
when the inference can only be reached by analysis and the use of
concepts, we may call it rational.
Defining, therefore, "inference" as the passing of the mind from
something immediately given to something not given but suggested through
association and experience, we have thus three stages of inference: (1)
unconscious inference on immediate construction (perceptual); (2)
intelligent inference, dealing with constructs and reconstructs
(perceptual); and (3) rational inference, implying analysis and
isolation (conceptual).
Concerning unconscious inferences in animals, I need add nothing to that
which I have already said concerning the process of construction. It is
concerning the intelligent inferences[GU] of animals that I have now to
speak.
I do not propose here to bring forward a number of new observations on
the highly intelligent actions which animals are capable of performing.
Mr. Romanes has given us a most valuable collection of anecdotes on the
subject in his volume on "Animal Intelligence." It is more to my purpose
to discuss some of the more remarkable of these, and endeavour to get at
the back of them, so as to estimate what are the mental processes
involved. In doing so, the principle I adopt is to assume that the
inferences are perceptual, unless there seem to be well-observed facts
which necessitate the analysis of the phenomena, the formation of
isolates, and therefore the employment of reason (_as I have above
defined it_). In doing this, I shall _seem_ to differ very widely from
Mr. Romanes and other interpreters of animal habits and intelligence.
But I believe that the divergence is less wide than it seems. I believe
that it is largely, but I fear not entirely, a question of the terms we
employ.
Why, then, rediscuss the question under these new terms? Because I
believe that such rediscussion may place the matter in a fresh and,
perhaps, clearer light. The question of the relation of animal
intelligence to human reason is one upon which there is a good deal of
disagreement, and one that has been discussed and rediscussed. I seek to
put it in a somewhat new light. I have endeavoured to define carefully
and accurately the terms I use, and the sense in which I use them. I
have coined for my own purposes unfamiliar terms such as "construct,"
"isolate," and "predominant," that I might thereby be enabled to avoid
the use of terms which, from the different senses in which they are
employed by different writers, have become invested with a certain
ambiguity. I trust, therefore, that even those with whom I seem most to
disagree will allow that my aim has not been mere disputation, but
scientific accuracy and precision in a difficult subject where these
qualities are of essential importance.
I take first some observations communicated by Mr. H. L. Jenkins to Mr.
Romanes, since, though they raise a point which we have already shortly
considered, they form a transition from unconscious to perceptual
inferences. Speaking of the intelligence of the elephant, Mr. Jenkins
says,[GV] "What I particularly wish to observe is that there are good
grounds for supposing that elephants possess abstract ideas; for
instance, I think it is impossible to doubt that they acquire, through
their own experience, notions of hardness and weight." He then details
observations which show that elephants at first hand up things of all
kinds to their mahouts with considerable force, but that after a time
the soft articles are handed up rapidly and forcibly as before, but that
hard and heavy things are handed up gently. "I have purposely," he says,
"given elephants things to lift which they could never have seen before,
and they were all handled in such a manner as to convince me that they
recognized such qualities as hardness, sharpness, and weight."
Now, the question I wish here to ask is--Do the observations of Mr.
Jenkins, the nature of which I have indicated, afford good or sufficient
reasons for supposing that these animals possess abstract ideas? And I
reply--That depends upon what is meant by abstract ideas. If it is
implied that the abstract ideas are _isolates_; that is, qualities
considered quite apart from the objects of which they are
characteristic, I think not. But if Mr. Jenkins means that elephants, in
a practical way, "recognize such qualities as hardness, sharpness, and
weight" as _predominant_ elements in the constructs they form, I am
quite ready to agree with him. I much question, however, whether there
is any conscious inference in the matter. The elephant sees a new
object, and unconsciously and instinctively builds the element hardness
or weight into the construct that he forms. And he shows his great
intelligence by dealing in an appropriate manner with the object thus
recognized. But I do not think any reasoning is required; that is to
say, any process involving an analysis of the phenomena with subsequent
synthesis, any introduction of the conceptual element.
Let us consider next an observation which shows a very high degree of
perceptual intelligence on the part of the dog. Several observers have
described dogs, which had occasion to swim across a stream, entering the
water at such a point as to allow for the force of the current. And both
Dr. Rae and Mr. Fothergill communicated to Mr. Romanes instances[GW] of
the dog's observing whether the tide was ebbing or flowing, and acting
accordingly. Now, I believe that the dog performs this action through
intelligence, and that man explains it by reason. The dog has presumably
had frequent experience of the effect of the stream in carrying him with
it. He has been carried beyond the landing-place, and had bother with
the mud; but when he has entered the stream higher up, he has nearly, if
not quite, reached the landing-stage. His keen perceptions come to his
aid, and he adjusts his action nicely to effect his purpose.
On the bank sits a young student watching him. He sees in the dog's
action a problem, which he runs over rapidly in his mind. Velocity of
stream, two miles an hour. Width, one-eighth of a mile. Dog takes ten
minutes to swim one-eighth of a mile. Distance flowed by the stream in
ten minutes, one-third of a mile. Clever dog that! He allows just about
the right distance. A little short, though! Has rather a struggle at the
end.
The dog intelligently performs the feat; the lad reasons it out.
I do not know whether I am making my point sufficiently clear. A wanton
boy is constantly throwing stones at birds and all sorts of objects. He
does not know much about the force of gravitation or the nature of the
curve his stone marks out; but he allows pretty accurately for the fall
of the stone during its passage through the air. He acquires a catapult;
and, being an intelligent lad, he perceives that he must aim a little
above the object he wishes to hit. This is a perceptual inference.
Reason may subsequently step in and explain the matter, or very
possibly, being human, sparks of reason fly around his intelligent
action.
Am I using the word "reason" in an unnatural and forced sense? I think
not. My use is in accord with the normal use of the word by educated
people. Two men are working in the employ of a mechanical engineer.
Listen to their employer as he describes them. "A most intelligent
fellow is A; he does everything by rule of thumb; but he's wonderfully
quick at perceiving the bearing of a new bit of work; he sees the right
thing to do, though he cannot tell you why it should be done. Now, B is
a very different man; he is slow, but he reasons everything out. A knows
the right thing to do; and B can tell you why it must be done. A has the
keenest intelligence, but B the clearest reasoning faculty. If I have
occasion to question them about any mechanical contrivance, A says, 'Let
me see it work;' but B says, 'Let me think it out.'"
In other words, A, the intelligent man, deals with phenomena as wholes,
and his perceptual inferences are rapid and exact; while B, the
reasoner, analyzes the phenomena, and draws conceptual inferences about
them.
Let us take next Dr. Rae's[GX] most interesting description of the
cunning of Arctic foxes. These clever animals, he tells us, soon learn
to avoid the ordinary steel and wooden traps. The Hudson Bay trappers,
therefore, set gun-traps. The bait is laid on the snow, and connected
with the trigger of the gun by a string fifteen or twenty feet long,
five or six inches of slack being left to allow for contraction from
moisture. The fox, on taking up the bait, discharges the gun and is
shot. But, after one or more foxes have been shot, the cunning beasts
often adopt one of two devices. Either they gnaw through the string, and
then take the bait; or they tunnel in the snow at right angles to the
line of fire, and pull the bait _downwards_, thus discharging the gun,
but remaining uninjured. This is regarded by Dr. Rae as a wonderful
instance of "abstract reasoning."
Here, again, it is the "abstract reasoning" that I question. Do the
clever foxes resemble the intelligent workman A, or the abstract
reasoner B? I believe that their actions are the result of perceptual
inferences. They adopt their cunning devices _after one or more foxes
have been shot_. Their keen perceptions (let me repeat that the
perceptions of wild animals are extraordinarily keen) lead them to see
that this food, quiet as it seems, has to be taken with caution.
With regard to the devices adopted, I think we need further information.
Do Arctic foxes tunnel in the snow for any other purposes? What is the
proportion of those who adopt this device to those who gnaw through the
string? Have careful and reliable observers watched the foxes? or are
their actions, as described by Dr. Rae, inferences, on the part of the
trappers, from the state of matters they found when they came round to
examine their traps? Without fuller information on these points, it is
undesirable to discuss the case further. Even if we had full details,
however, we should be as little able to get at the process of perceptual
inference in the case of the fox as we are in the case of the
intelligent workman, who sees the right thing to do, but cannot tell you
how he reached the conclusion.
No one can watch the actions of a clever dog without seeing how
practical he is. He is carrying your stick in his mouth, and comes to a
stile. A young puppy will go blundering with the stick against the
stile, and, perhaps, go back home, or get through the bars and leave the
stick behind. But practical experience has taught the clever dog better.
He lays down the stick, takes it by one end, and draws it backwards
through the opening at one side of the stile. A friend tells me of a dog
which was carrying a basket of eggs. He came to a stile which he was
accustomed to leap, poked his head through the stile, deposited the
basket, ran back a few yards, took the stile at a bound, picked up the
basket, and continued on his course. "Intelligent fellow!" I exclaim.
"Yes," says my friend, "he _knew the eggs would break_ if he attempted
to leap with the basket!" This is just the little gratuitous,
unwarrantable, human touch which is so often filled in, no doubt in
perfect good faith, by the narrators of anecdotes. Against such
interpolations we must be always on our guard. It is so difficult not to
introduce a little dose of reason.
Mr. Romanes obtained from the Zoological Gardens at Regent's Park a very
intelligent capuchin monkey, on which his sister made a series of most
interesting and valuable observations. This monkey on one occasion got
hold of a hearth-brush, and soon found the way to unscrew the handle.
After long trial, he succeeded in screwing it in again, and throughout
his efforts always turned the handle the right way for screwing. Having
once succeeded, he unscrewed it and screwed it in again several times in
succession, each time with greater ease. A month afterwards he unscrewed
the knob of the fender and the bell-handle beside the mantelpiece.
Commenting on these actions, Mr. Romanes speaks[GY] of "the keen
satisfaction which this monkey displayed when he had succeeded in making
any little discovery, such as that of the mechanical principle of the
screw."
I once watched, near the little village of Ceres, in South Africa, a
dung-beetle trundling his dung-ball over an uneven surface of sand. The
ball chanced to roll into a sand hollow, from which the beetle in vain
attempted to push it out. The sides were, however, too steep. Leaving
the ball, he butted down the sand at one side of the hollow, so as to
produce an inclined plane of much less angle, up which he then without
difficulty pushed his unsavoury sphere.
Now, it seems to me that, if we say, with Mr. Romanes, that the brown
capuchin discovered the _principle of the screw_, we must also say that
the dung-beetle that I observed in South Africa was acquainted with the
_principle of the inclined plane_. Such an expression, I contend,
involves an unsatisfactory misuse of terms. A mechanical principle is a
concept,[GZ] and as such, in my opinion, beyond the reach of the
brute--monkey or beetle. That of which the monkey is capable is the
perceptual recognition of the fact that certain actions performed in
certain ways produce certain results. Why they do so he neither knows
nor cares to know. What the brown capuchin discovered was not the
principle of the screw, but that the action of screwing produced the
results he desired--a very different matter. My friend, Mr. S. H.
Swayne, tells me that the elephant at the Clifton Zoo, having taking a
tennis-racket from a boy who had been plaguing him, broke it by leaning
it against a step and deliberately stepping on it in the middle, where
it was unsupported. A most intelligent action. And it would have been a
capital piece of exercise for the lad's reasoning power, had he been
required to analyze the matter, to show why the elephant's action had
the desired effect, and set forth the principle involved. I do not think
the elephant himself possesses the faculty requisite for such a piece of
reasoning. He is content with the practical success of his actions;
principles are beyond him.
I will now give two instances of intelligence in vertebrates which
exemplify phases of inference somewhat different from those which we
have so far considered. Mr. Watson, in his "Reasoning Power of
Animals,"[HA] tells of an elephant which was suffering from eye-trouble,
and nearly blind. A Dr. Webb operated on one eye, the animal being made
to lie down for the purpose. The pain was intense, and the great beast
uttered a terrific roar. But the effect was satisfactory, for the sight
was partially restored. On the following day the elephant lay down of
himself, and submitted quietly to a similar operation on the other eye.
No doubt the elephant's action here was, in part, the result of its
wonderful docility and training. But there was also probably the
inference that, since Dr. Webb had already given him relief, he would do
so again. The anticipation of relief outmastered the anticipation of
immediate discomfort or pain. I do not think, however, that any one is
likely to contend that any rational analysis of the phenomena is
necessarily involved in the elephant's behaviour.
The other instance I will quote was communicated by Mr. George Bidie to
_Nature_.[HB] He there gives an account of a favourite cat which, during
his absence, was much plagued by two boys. About a week before his
return the cat had kittens, which she hid from her tormentors behind the
book-shelves in the library. But when he returned she took them one by
one from this retreat, and carried them to the corner of his
dressing-room where previous litters had been deposited and nursed. Here
abnormal circumstances and the reign of anarchy and persecution forced
her to adopt a hiding-place where she might bring forth her young; but
the return of normal conditions, sovereignty, and order led her to take
up her old quarters under the protection of her master. Now, look at the
description I have given in explanation of her conduct. See how it
bristles with conceptual terms: "abnormal," with its correlative
"normal;" "anarchy and persecution," "protection" and "order." All this,
I believe, is mine, and not the cat's. For her there was a practical
perception, in the one case of plaguing boys, in the other case of
protecting master; and her action was the direct outcome of these
perceptions through the employment of her intelligence.
Some stress has been laid on the occasional use of tools by animals. Mr.
Peal[HC] observed a young elephant select a bamboo stake, and utilize it
for detaching a huge elephant-leech which had fixed itself beneath the
animal's fore leg near the body. "Leech-scrapers are," he says, "used by
every elephant daily." He also saw an elephant select and trim a shoot
from the jungle, and use it as a switch for flapping off flies. How far,
we may ask, do such actions imply "a conscious knowledge of the relation
between the means employed and the ends attained"?[HD] That, again,
depends upon how much or how little is implied in this phrase.
A boy picks up a stone and throws it at a bird; he comes home and
unlocks the garden-gate with a key; he enters his room, and removes the
large "Liddell and Scott" which he uses as a convenient object to keep
the lid of his play-box shut; he opens the box, and cuts himself a slice
of cake with his pocket-knife. Then he goes to his tutor, who is
teaching him about means and ends, and their relation to each other. He
is told that the throwing of the stone was the means by which the death
of the bird, or the end, was to be accomplished; that the use of the
knife was the means by which the end in view, the severance of a piece
of cake, was to be effected, and so on. He is led to see that the
employment of a great many different things, differing in all sorts of
ways--stones, keys, lexicons, and knives--may be classified together as
means; and that a great many various effects, the death of a bird or the
cutting a bit of cake, may be regarded as ends. He is told that when he
thinks of the means and the ends together, as means and end, he will be
thinking of their relationship. And it is explained to him that means
and ends and their relationships are concepts, and involve the exercise
of his reasoning powers.
Weary and sick to death of concepts and relationships and reason, at
length he escapes to the garden. Picking up a light stick, he sweeps off
the heads of some peculiarly aggravating poppies, and determines to
think no more of means and ends, continuing to use the stick meanwhile
as a most appropriate means to the end of decapitating the poppies. By
all which I mean to imply that there is a great difference between
selecting and using a tool for an appropriate purpose, and possessing a
conscious knowledge of the relation between the means employed and the
ends attained. I do not think that any conception of means, or end, or
relationship is possible to the brute. But I believe that the elephant
can perceive that this stick will serve to remove that leech. And if
this is what Mr. Romanes means by its possessing a conscious knowledge
of the relation between the means employed and the ends attained, then I
am, so far, at one with him in the interpretation of the facts, though I
disagree with his mode of expressing them.
I do not propose to consider particular instances of intelligent
inferences as displayed by the invertebrates. Bees in the manipulation
of their comb, ants in the economy of their nest, spiders in the
construction of their web and the use they make of their silken ropes,
show powers of intelligent adaptation which cannot fail to excite our
wonder and admiration. But apart from the fact that insect psychology is
more largely conjectural than that of the more intelligent mammals, a
consideration of these actions would only lead me to reiterate the
opinion above frequently expressed. In a word, I regard the bees in
their cells, the ants in their nests, the spiders in their webs, as
workers of keen perceptions and a high order of practical intelligence.
But I do not, as at present advised, believe that they reason upon the
phenomena they deal with so cleverly. Intelligent they are; but not
rational.
Once more, let me repeat that the sense in which I use the words
"rational" and "reason" must be clearly understood and steadily borne in
mind. Mr. Romanes uses them in a different sense. "Reason," he says,[HE]
"is the faculty which is concerned in the intentional adaptation of
means to ends. It therefore implies the conscious knowledge of the
relation between means employed and ends attained, and may be exercised
in adaptation to circumstances novel alike to the experience of the
individual and to that of the species. In other words, it implies the
power of perceiving analogies or ratios, and is in this sense equivalent
to the term 'ratiocination,' or the faculty of deducing inferences from
a perceived equivalency of relations. This latter is the only sense of
the word that is strictly legitimate."
It is not my intention to criticize this use of the term "reason."
Whether animals are capable of a conscious knowledge of the relation
between means employed and ends attained, depends, as we have already
seen, upon how much is implied by the word "knowledge"--whether the
knowledge is perceptual or conceptual. My only care is to indicate what
seem to me the advantages of the usage (legitimate or illegitimate) I
adopt.
I repeat, then, that the introduction of the process of analysis appears
to me to constitute a new departure in psychological evolution; that the
process differs generically from the process of perceptual construction
on which it is grafted. And I hold that, this being so, we should mark
the departure in every way that we can. I mark it by a restriction of
the word "intelligence" to the inferences formed in the field of
perception; and the use of the word "reason" when conceptual analysis
supervenes. Whether I am justified in so doing, whether my usage is
legitimate or not, I must leave others to decide. But, adopting this
usage, I see no grounds for believing that the conduct of animals,
wonderfully intelligent as it is, is, in any instances known to me,
rational.
I say that the introduction of the process of analysis appears to me to
constitute a new departure. This, however, must not be construed to
involve any breach of continuity.
I do not believe that there is or has been any such breach of
continuity. Take a somewhat analogous case. I regard the introduction of
aerial respiration in animal life as a new departure. Organisms which
had hitherto been water-breathers became air-breathers. But I do not
imagine that there was any breach of continuity in respiration. The
tadpole begins life as a water-breather only; the frog into which he
develops is an air-breather; but there is no breach of continuity
between the one state and the other. So, too, the little child dwells in
the perceptual sphere; the man into whom he develops is capable of
conceptual thought; but there is no breach of continuity in the mental
life of the child. It is true that, with all our talk on the subject, we
cannot say exactly when in this continuous mental life the new departure
is made. But this is no proof whatever that there is no new departure.
In a sigmoidal curve there is a new departure where the convex passes
into the concave. We may find it difficult to mark the exact point of
change. But that does not invalidate the fact that the change does
actually take place.
If I be asked how, in the course of mental evolution, the new departure
was rendered possible, I reply--Through language. The first step was, I
imagine, _the naming of predominants_. If Noiré and Professor Max Müller
be correct in their views, language took its origin in the association
of an uttered sound with certain human activities. The action thus named
was, so to speak, floated off by its sign. By diacritical marks attached
to the word, the agent, the action, and the object of the action were
distinguished, and thus came to be differentiated the one from the
other. Inseparable in fact, they came henceforth to be separable in
thought. Here was analysis in the germ. The action or activity was
isolated, and henceforth stood forth as an element in abstract thought.
All the busy world around was interpreted in terms of activities. The
host of heaven and all the powers of earth were named according to their
predominant activities. The moon became the measurer, the sun the
shining one, the wind the one who bloweth, the fire the purifier, and so
forth. Our verbs and nouns, then, being named predominants (agents,
actions, or objects), adjectives and adverbs were subsequently
introduced to qualify these by naming a quality less predominant, or to
indicate the how, the when, and the where.
When once the different activities and different qualities came to be
named or symbolized, they were, as I say, floated off from the agents or
objects, and through isolation entered the conceptual sphere. _The named
predominant became an isolate._ Body and mind became separable in
thought; the self was differentiated from the not-self; the mind was
turned inwards upon itself through the isolation of its varying phases;
and the consciousness of the brute became the self-consciousness of man.
Language, and the analytical faculty it renders possible, differentiates
man from the brute. "If a brute," says Mr. Mivart,[HF] "could think
'is,' brute and man would be brothers. 'Is' as the copula of a judgment
implies the mental separation and recombination of two terms that only
exist united in nature, and can, therefore, never have impressed the
sense except as one thing. And 'is,' considered as a substantive
verb, as in the example, 'This man is,' contains in itself the
application of the copula of judgment to the most elementary of all
abstractions--'thing' or 'something.' Yet if a being has the power of
thinking 'thing' or 'something,' it has the power of transcending space
and time by dividing or decomposing the phenomenally one. Here is the
point where instinct [intelligence] ends and reason begins." I regard
this as one of the truest and most pregnant sentences that Mr. Mivart
has written.
And when once the Logos had entered into the mind of man, and made him
man, it slowly but surely permeated his whole mental being. Hence
language is not only involved in our concepts, but also in our percepts,
in so far as they are ours. Professor Max Müller goes so far as to
question whether an unnamed percept is possible. And adult intellectual
man is so permeated by the Logos that I am not prepared to disagree with
him when he says that he has no unnamed perceptions. Nevertheless, the
actions of the speechless child and our dumb companions show that they
(children and animals) are capable of forming mental products of the
perceptual order. But here, once more, we must not forget that it is in
terms of these adult human percepts that we interpret the percepts of
children and animals; that in doing so we cannot divest ourselves of the
garment of our conceptual thought, that we cannot banish the Logos, and
that, therefore, these percepts other than ours cannot be identical with
ours, though they are of the same order, saving their conceptual
element. We may put the matter thus--
(1) _x_ × dog-mind } { Percepts to be interpreted in terms
(2) _x_ × cat-mind } = { of (4), being analogous thereto but
(3) _x_ × infant-mind } { not identical therewith.
(4) _x_ × adult human mind = the percepts of psychologists,
named or namable.
If the views that I have thus very briefly sketched (for I have no right
to offer an opinion on a question of linguistic science) be correct,
language has made analysis, isolation, and conceptual thought possible.
But there may have been a transitory stage when the word-signs stood for
predominants, not yet for isolates. Granting the possibility or
probability of this, I am prepared to follow Professor Max Müller in his
contention that language and thought, from the close of that stage
onward, are practically inseparable, and have advanced hand-in-hand. It
is true that I can now think out a chemical or physical problem without
the use of words--the stages of the experimental work being visualized,
just as a chess-player may think out a game in pictures of the
successive moves. But, historically, I believe the power to do this has
been acquired through language; and if I am able temporarily to isolate
and analyze without language, thought being at times a little ahead of
naming, yet the fact remains that language is absolutely necessary to
make such advances good, if not for me, at any rate for man.
And here I would make one more suggestion. Professor Max Müller, as the
result of analysis of the Aryan language, finds a comparatively small
number of roots which he says are in all cases symbolic of concepts.
Yes, for us now they symbolize concepts. But in their inception may they
not have been symbolic of predominants? Have we not in them the signs
for predominants not yet converted for the primitive utterers into
isolates? May not these have been the stepping-stones from the
perceptual predominants of animal man, to the conceptual isolates of
rational man? Or, to modify the analogy, may they not have been the
embryonic wings by which the human race were floated off from the things
of sense into the free but tenuous air of abstract thought?
Lastly, before taking leave of the subject of this chapter, I am most
anxious that it should not be thought that, in contending that
intelligence is not reason, I wish in any way to disparage intelligence.
Nine-tenths at least of the actions of average men are intelligent and
not rational. Do we not all of us know hundreds of practical men who are
in the highest degree intelligent, but in whom the rational, analytic
faculty is but little developed? Is it any injustice to the brutes to
contend that their inferences are of the same order as those of these
excellent practical folk? In any case, no such injustice is intended;
and if I deny them self-consciousness and reason, I grant to the higher
animals perceptions of marvellous acuteness and intelligent inferences
of wonderful accuracy and precision--intelligent inferences in some
cases, no doubt, more perfect even than those of man, who is often
distracted by many thoughts.
NOTES
[GD] "Chapters on Animals," p. 9.
[GE] Or perhaps we may say, in the language of analogy, that when the
germinal psychoplasm of some dim form of organic memory is
fertilized by the union therewith of the more active male element
of discrimination, a process of segmentation of the psychoplasm
sets in by which, in process of differentiation, the tissues and
organs of the mind are eventually developed.
[GF] _Nature_, vol. xxxviii. p. 257.
[GG] For examples, see Romanes's "Animal Intelligence," p. 455.
[GH] I use the word "arbitrary" in the sense that they form no part of
the normal construct such as would be formed by the animal.
[GI] "The Senses of Animals," p. 277.
[GJ] As I understand the observations here tabulated, the twelve cards
lay always within Van's reach and sight. An ordinary untrained dog
would have taken no notice of them. But Van, when he wanted food
or tea, went and fetched the appropriate card, and got what he
wanted in exchange. In twelve days he only made two mistakes,
bringing "Nought" once and "Door" once.
[GK] "Mental Evolution in Man," p. 27.
[GL] "Intelligence of Animals," p. 121.
[GM] Mr. Romanes also says ("Mental Evolution in Animals," p. 235),
"This abstract idea of ownership is well developed in many if not
in most dogs." By an abstract idea of ownership I understand a
conception of ownership which, to modify Mr. Romanes's phrase, is
quite apart from any objects or persons of which such ownership
happens to be characteristic. Even if we believe that a dog can
regard this or that man as his owner, or this or that object as
his master's property, still even this seems to me a very
different thing from his possessing an abstract idea of ownership.
[GN] Doubt has recently been thrown on this fact. Mr. Bateson has shown
that some fishes do not hear well, and has suggested that the carp
may be attracted by seeing people come to the edge of the pond.
[GO] Journal of Marine Biological Association, New Series, vol. i. No.
2, p. 214. I should not myself have used the word "explanation."
[GP] Ibid. vol. i. No. 3, p. 240.
[GQ] I have to thank this gentleman for a most interesting account of
the intelligence of his favourite bird.
[GR] Professor Max Müller suggests to me that perhaps the ants were
frightened.
[GS] "Mental Evolution in Animals," p. 82.
[GT] Ibid. p. 48.
[GU] These fall under the "practical intelligence" of Mr. Mivart. All
their intelligent activities, in his view, are performed by the
exercise of merely sensitive faculties, through their
"consentience." I agree to so large an extent with Mr. Mivart in
his estimate of animal intelligence, and in his psychological
treatment, that I the more regret our wide divergence when we come
to the philosophy of the subject. I am with him in believing that
conception and perception, in the sense he uses the words, are
beyond the reach of the brute. But I see no reason to suppose that
these higher faculties differ _in kind_ from the lower faculties
possessed by animals. They differ generically, but not in kind. I
believe that, through the aid of language, the higher faculties
have been developed and evolved from the lower faculties. Here,
therefore, I have to part company from Mr. Mivart.
[GV] Romanes, "Animal Intelligence," p. 401.
[GW] "Animal Intelligence," p. 465.
[GX] "Animal Intelligence," p. 430; and _Nature_, vol. xix. p. 409.
[GY] "Animal Intelligence," p. 497.
[GZ] Mr. Romanes regards it as, in the case of the capuchin, a
_recept_. But when he speaks of a generic idea of causation, and
generic ideas of principles, and of qualities as recepts, I find
it exceedingly difficult to follow him. They seem to me to be
concepts supposed to be formed in the absence of language.
[HA] Page 54.
[HB] Vol. xx. p. 96.
[HC] _Nature_, vol. xxi. p. 34.
[HD] Romanes, "Animal Intelligence," p. 17: Definition of _reason_.
[HE] "Mental Evolution in Animals," p. 318.
[HF] "Lessons from Nature," pp. 226, 227.
CHAPTER X.
THE FEELINGS OF ANIMALS: THEIR APPETENCES AND EMOTIONS.
There is one aspect of the mental processes of men and animals that we
have so far left unnoticed--the aspect of feeling, the aspect of
pleasure and pain. Quite distinct from, and yet intimately associated
with, our perception of a beautiful scene, is the pleasure we derive
therefrom; and quite distinct from, and yet inseparably bound up with,
our perception of a discordant clang, is the painful effect that it
produces.
We have, however, no separate organs for the appreciation of pleasure
and pain. These feelings arise out of, and are bound up with, our
sensations, our perceptions, and especially with the conscious exercise
of our bodily activities. There may be, at any rate in some cases,
separate nerves for the appreciation of the pleasurable and the painful;
but even if this be so, these shades of feeling are so closely
associated with our other activities, mental and bodily, that we may for
the present regard them simply as the accompaniments of these
activities.
The question has been raised and much discussed whether all our
activities are accompanied by some shade or colouring of feeling,
pleasurable on the one hand, or painful on the other; or whether some of
these activities may not be indifferent in this respect, affording us
neither pleasure nor pain. Put in this way, I think we may say that
there may be activities which are thus indifferent. But if it be asked
whether, in addition to the pleasurable and painful feelings, there is a
third class of _feelings_, which we may call indifferent or neutral, I
am inclined to answer it in the negative. I hold that every feeling, as
such, must belong either to the painful or pleasurable class, and that
if the pleasurable and painful, so to speak, exactly balance each other,
then feeling, as such, does not emerge into consciousness at all. For,
as Lotze says, "We apply the name 'feelings' exclusively to states of
pleasure and pain, in contrast with sensations as [the elements of]
indifferent perceptions of a certain content."
The broadest division of the feelings is, therefore, into pleasurable on
the one hand, and painful on the other.
Another general question with regard to the feelings is--With what
condition or state of the bodily organization are they associated? In
answer to this question we may say (1) that any very violent and
abnormal stimulus produces pain; (2) that the conditions of pleasure are
to be sought within the limits of the healthy and normal exercise of the
bodily functions and mental activities; (3) that within these limits the
changes of activity consequent upon the rhythmic flow of normal organic
processes bring with them, in the aggregate, pleasure, the delight of
healthy life; (4) that within these limits, again, we experience
pleasure or pain, enjoyment or weariness, ease or discomfort, happiness
or unhappiness, with the continued rise and fall of our life-tide. For,
as Spinoza says, "We live in perpetual mutation, and are called happy or
unhappy according as we change for the better or the worse." So long as
our activities remain at a dead level, there is indifference--neither
pleasure nor pain. A rise of the tide of activity brings pleasure, a
fall the reverse. Lastly, we may say (5) that beyond the limits of
healthy and normal exercise there is, on the one hand, excessive
exercise which, carried far enough, may give rise, first to fatigue, and
then to acute pain; and, on the other hand, deficient exercise, which
may produce that dull and numb form of pain which we call discomfort, or
a sense of craving or want.
Pleasures and pains may thus be either massive or acute, diffused or
locally concentrated. On the whole, we may say, with Mr. Grant
Allen,[HG] that "the acute pains, as a class, arise from the action of
surrounding destructive agencies; the massive pains, as a class, from
excessive function or insufficient nutriment." But since massive pains,
when pushed to an extreme, merge into the acute class, "the two classes
are rather indefinite in their limits, being simply a convenient working
distinction, not a natural division." "Massive pleasure can seldom or
never attain the intensity of massive pain, because the organism can be
brought down to almost any point of innutrition or exhaustion; but its
efficient working cannot be raised very high above the average.
Similarly, any special organ or plexus of nerves can undergo any amount
of violent disruption or wasting away, giving rise to very acute pains;
but organs are very seldom so highly nurtured and so long deprived of
their appropriate stimulant as to give rise to very acute pleasure." The
amount of pleasure varies, according to Mr. Grant Allen, whose
discussion of the subject is, perhaps, the best and clearest we have,
directly as the number of nerve-fibres involved, and inversely as the
natural frequency of their excitation. No doubt the principles above
sketched out are somewhat vague and general; but we are scarcely
justified in formulating any that are more precise and exact.
Accepting now the theory of evolution, we may say, furthermore, that
during the long process of the moulding of life to its environment,
there has been a constant tendency to associate pleasure with such
actions as contribute towards the preservation and conservation of the
individual and the race, and to associate pain with such actions as tend
to the destruction or detriment of the individual or the race. For there
can be little doubt that pleasure and pain are the primary incentives to
action. Without the association of pleasure with conservative action,
and pain with detrimental action, it is difficult to conceive how the
evolution of conscious creatures would be possible. Conservative action,
if it is to be persisted in by a conscious creature, must be associated
directly or indirectly with pleasurable feelings; nay, more, if it is to
be persistently persevered in, its non-performance must be associated
with that dull form of pain which we call a craving or want. Only under
such conditions could activities which tend to the survival of the
individual and the race be fostered and furthered.
It must be remembered, however, that such association is founded on
experience, and has no necessary validity beyond experience. That
quinine, though unpleasant to the taste, is, under certain
circumstances, beneficial to the individual, and that acetate of lead,
though sweet-tasted, is harmful, cannot be fairly urged in opposition to
this principle, since the effects of these drugs form no part of the
normal experience of the individual and the race. Nor can it be fairly
objected that animals transported to new countries often eat harmful and
poisonous plants presumably because they are nice; for these plants form
part of an unwonted environment. Nor, again, is the fact that the
association of pleasure with conservative action and pain with harmful
action is not always perfect, in any sense fatal to the general
principle. For the establishment of the association is still in
progress; and with the increase in the complexity of life its accurate
establishment is more and more difficult. No one is likely to contend
that what appears to be a general principle must also be an invariable
rule. The general principle is that under the joint influence of
pleasure (attractive) and pain (repellent) the needle of animal life
sets towards the pole of beneficial action. That the needle does not
always point true only illustrates the fact that life-activities are
still imperfect.
Let us notice that it is under the joint action of pleasure and pain
that the needle sets. We must not think only of the positive aspect, and
neglect the negative. What we know as wants, cravings, appetites,
desires, and dissatisfactions, are dull and continuous pains,[HH] which
tend to drive us to actions by which they shall be annulled, and the
performance of which shall give us the pleasures of gratification. Dr.
Martineau regards a felt want as a mainspring of our energy. "Life," he
says,[HI] "is a cluster of wants, physical, intellectual, affectional,
moral, each of which may have, and all of which may miss, the fitting
object. Is the object withheld or lost? There is pain: is it restored or
gained? There is pleasure: does it abide or remain constant? There is
content. The two first are cases of disturbed equilibrium, and are so
far dynamic that they will not rest till they reach the third, which is
their posture of stability and their true end." To this I would only add
that the content which follows on the keen pleasure of satisfaction is
evanescent, and ere long lapses into indifference, on which in due time
follows the dull pain resulting from the recurrent pressure of the want
or desire.
It is clear that, in introducing these wants and desires, we are
entering the sphere of the emotions, and it is sometimes said that the
emotions have their basis in pleasure and pain. If by this it is meant
that the emotions often exhibit more or less prominently one or other of
these two aspects of feeling, we may agree with the statement. It will
be well, however, to lead up to our consideration of the emotions by
taking a general review of the manner in which the organism responds to
external stimuli.
A dog is lying dreamily on the lawn in the sunshine. Suddenly he raises
his head, pricks his ears, scents the air, looks fixedly at the hedge,
and utters a low growl. Place your hand upon his shoulder, and you will
find that his muscles are all a-tremble. He can restrain himself no
longer, and darts through the hedge. You follow him, look over the
hedge, and see that it is his old enemy, the butcher's cur. They are
moving slowly past each other, head down, teeth bared, back roughened.
You whistle softly. Such a whistle would generally bring him bounding to
your feet. But now it is apparently unheard. The two dogs have a short
scuffle, and the cur slinks off. Your dog races after him; but after a
few minutes returns, jumps up at you playfully, and then lies down again
on the grass. But every now and then, for ten minutes or so, he raises
his head and growls softly.
Let us briefly analyze the dog's actions, reading into them,
conjecturally, the accompaniments in consciousness. As he lies on the
lawn, he receives a sense-stimulus, auditory or olfactory, which gives
rise to the construction of the percept dog (perhaps particularized
through olfactory discrimination). About the formation of constructs or
percepts, however, we have already said enough; we have now to consider
their effects. The head is raised, the ears pricked, and so on. The dog
is on the alert. His attention is roused. What are the physiological
effects? Certain motor-activities or tendencies to activity. These are
of two kinds--first, in connection with the sense-organs, the muscles of
which are brought into play in such a way as to bring the organs to bear
upon the exciting object; secondly, in connection with many other
muscles, which are innervated, so as to be ready to act rapidly and
forcibly. The first motor-effect, that on the muscles of the
sense-organs, is a very characteristic physical concomitant of the
psychological state which we term "attention;" the second effect, the
incipient innervation of muscles likely to be called into play, is
equally characteristic of the psychological state we call alertness.
Meanwhile an emotional state is rising in the mind of the dog. We may
call it, conjecturally, anger and combativeness. But what we name it
does not much signify for our present purpose. It has a growing tendency
to work itself out in a series of definitely directed actions. And this
reaches its point of culmination when the dog rushes through the hedge
and stands with bared teeth before his antagonist. A whole set of
appropriate muscles are now strongly innervated. There is probably a
double innervation--an innervation prompting to activity and an
innervation inhibiting or restraining from activity. The attention is so
concentrated that he heeds not, probably hears not, his master's
whistle. He is keenly on the alert. Then he sees his chance; the
inhibition or restraint is withdrawn, and he flies at his opponent. The
emotional tendency works itself out in action. Even after he has resumed
his place on the lawn, memories of the emotional state return, and lead
him to lift his head, slightly bare his teeth, and growl.
Now, with regard to the emotional state here indicated, we may notice,
first, that it is initiated by a percept; secondly, that associations of
pleasure or pain are by no means the most important or predominant
characteristics; thirdly, that the motor-tendencies seem to be
essential, the emotional state being the psychological aspect of these
motor-tendencies; and, fourthly, that we should perhaps be justified in
speaking of a presentative emotion when the percept which gives rise to
the emotion is presentative; and a representative emotion where the
originating percept is represented in memory. And with regard to the
attention which was incidentally introduced, we may notice that it, too,
has motor-concomitants, and that it is directly associated with the
emotional state. If no emotional state is aroused by a percept,
attention is not specially directed to the object. The concentration of
the attention is directly proportional to the intensity of the emotion
evoked.
Emotions, then, would seem from this illustration to be certain
psychological states which accompany activities or tendencies to
activity. They are evoked by appropriate objects perceived or
remembered. Where the tendency is towards the object, as in the sexual
emotions, we may speak of it as an _appetence_; where it is away from
the object, as in the emotion of fear, we may speak of it as an
_aversion_. Appetences are normally pleasurable; aversions, painful.
It is clear that the organism must be in a condition fitting it to carry
out its various activities. And this condition is more or less variable.
In the terms of our previous analogy (Chapter II.) the tissues are
"explosive." After a series of explosions have taken place in a tissue,
its store of explosive material becomes exhausted, and a powerful
stimulus is required to liberate further energy in the exhausted tissue.
A period of rest is required to enable the plasmogen to generate a fresh
store of explosive material. As this store increases to its maximum
pitch, the tissue becomes more and more ready to respond at the
slightest touch. Responsiveness to external stimuli is spoken of as
_sensitiveness_; emotional responsiveness is called _sensibility_. What
we have before spoken of as a want or craving is a state of heightened
sensibility, which often gives rise to a painful state of general
uneasiness. It may also give rise to perceptual representations in
memory, as may be seen in the dreams experienced during a state of
extreme sexual sensibility. If we seek a basis for the emotional states,
therefore, we shall find it in sensibility rather than in pleasure and
pain.
The motor-accompaniments of the emotional states have long been known
under the title of the "expression" of the emotions. The term is too
deeply rooted to be altered; but we may notice that what is called the
expression of an emotion is really _its partial fulfilment in action_.
Some psychologists, dissatisfied with the term "expression of the
emotions," as seeming to imply that the emotion is one thing and its
expression another, go so far as to say that the motor-accompaniments
are the objective aspect of what, under its subjective aspect, is the
emotion. It is quite possible, however, to experience an emotion without
any motor-accompaniments at all. Nevertheless, there is, I believe, in
such cases an unfulfilled tendency to action.
A most important feature in general physiology and psychology is _the
postponement or suppression of action_. The physiological faculty on
which it is based is inhibition. I do not propose to discuss the
somewhat conflicting views on the physiological mechanism of inhibition.
It is, however, a fact of far-reaching importance which no one is likely
to deny. In its higher ranges it is the objective basis and aspect of
self-restraint.
A stimulus gives rise to sensation and perception; the perception gives
origin to an emotional state; and the emotional state is fulfilled in
appropriate motor-activities. The process is a continuous one, and, in
the absence of inhibition, would in all cases inevitably fulfil itself.
But through the faculty of inhibition, the final state of activity may
be postponed or suppressed. We may place side by side the physiological
series and the accompanying psychological series thus--
Stimulus of } --> nervous processes in brain --> { Stimulus of
sense-organ } { motor-organs.
Consciousness of } <-- perception, emotion --> { Consciousness of
sense-stimulus } { activity.
The arrows pointing away from perception and emotion are intended to
indicate the fact that the consciousness of sense-stimulus on the one
hand, and of activity on the other hand, are accompaniments of the
nervous processes in the brain, and are referred outwards to the
sense-organ or the motor-organ, as the case may be. It must be
remembered that the two series, physiological and psychological, belong
to distinct phenomenal orders. If one speaks of emotion being fulfilled
in activity, and thus seems to jump from the psychological to the
physiological series, one does so merely to avoid the appearance of
pedantry.
Now, by the postponement or suppression of action, the process is either
arrested in its middle phase, the motor-organs not being innervated at
all, or, as I believe to be more probable, the motor-organs are doubly
innervated, a stimulus to activity being counteracted by an inhibitory
stimulus, the two neutralizing each other either in the motor-organ or
the efferent nerves which convey the stimuli. In any case, there is no
consciousness[HJ] of activity. And the mind occupies itself more and
more completely with the central processes, perception, and emotion, and
also, in human beings, conceptual thoughts and emotions. Nevertheless,
at any rate _so long as we confine ourselves to the perceptual sphere_,
these processes have their normal fulfilments in action, and, if they
become sufficiently intense, actually do so fulfil themselves.
Now, since the emotions with which we are now dealing (we may call them
emotions in the perceptual sphere) are stages in the fulfilment of
activities (though the activities themselves may be suppressed), it is
clear that there may be as many emotional states as there are modes of
activity. Hence, no doubt, the extreme difficulty of anything like a
satisfactory classification of these emotions, especially when the
activities are regarded as a merely extraneous expression.
Moreover, when certain emotions reach a high pitch of intensity, they
may defeat their own object, and give rise, not to definite
well-executed motor-activities, but to helpless contradictory actions,
affections of glandular and other organs, and a general condition of
collapse. The emotion of fear, for example, will lead to
motor-activities tending to remove a man from the source of danger; but
when it reaches the degree of dread, or its culmination terror, the
effects are markedly different. The countenance pales, the lips tremble,
the pupils of the eyes become dilated, and there is an uncomfortable
sensation about the roots of the hair. The bowels are often strongly
affected, the heart palpitates, respiration labours, the secretions of
the glands are deranged, the mouth becomes dry, and a cold sweat bursts
from the skin. The muscles cease to obey the will, and the limbs will
scarcely support the weight of the body. Here we have all the effects of
a prolonged struggle to escape. Just as such a prolonged struggle will
at length produce these motor and other effects accompanied by the
emotion of terror; so, if the emotion of terror be produced directly,
these motor and other effects are seen to accompany it.
Mr. Charles Richardson, the well-known engineer of the Severn Tunnel,
has recorded several instances of railway servants and others being so
affected by the approach of a train or engine that they have been unable
to save themselves by getting out of the way, though there was ample
time to do so. This may have been through the effect of terror. But one
man, who was nearly killed in this way, only just saving himself in
time, informed me that he experienced no feeling of terror; he was
unable to explain why, but he couldn't help watching the train as it
darted towards him. In this case it seems to have been a sort of
hypertrophy of attention. His attention was so rivetted that he was
unable to make, or rather he felt no desire to make, the appropriate
movements. He said, "I had to shake myself, and only did so just in
time. For in another moment the express would have been on me. When it
had passed, I came over all a cold sweat, and felt as helpless as a
baby. I was frightened enough _then_." Cases of so-called fascination in
animals may be due in some cases to terror, but more often, perhaps, to
a hypertrophy of attention, such as is seen in the hypnotic state.
Speaking of the effects of artificial light on fish, Mr. Bateson
says,[HK] "Bass, pollack, mullet, and bream generally get quickly away
at first, but if they can be induced to look steadily at the light with
both eyes, they generally sink to the bottom of the tank, and on
touching the bottom commonly swim away.... In the case of mullet,
effects apparently of a mesmeric character sometimes occur, for a mullet
which has sunk to the bottom as described will sometimes lie there quite
still for a considerable time. At other times it will slowly rise in the
water until it floats with its dorsal fin out of the water, as though
paralyzed.... When the light is first shown, turbot generally take no
notice of it, but after about a quarter of an hour I have three times
seen a turbot swim up, and lie looking into the lamp steadily. It seemed
to be seized with an irresistible impulse like that of a moth to a
candle, and throws itself open-mouthed at the lamp." As a boy I used
frequently to "mesmerize" chickens by making them look at a chalk mark.
They would then lie for some time perfectly motionless. Some such effect
has, perhaps, led to the instinct displayed by some animals of "shamming
dead."
Returning now to the emotions as displayed in man, we may take one more
example in anger. This is an emotion that arises from the idea of evil
having been inflicted or threatened. "Under moderate anger," says
Darwin, "the action of the heart is a little increased, the colour
heightened, and the eyes become bright. The respiration is likewise a
little hurried; and as all the muscles serving for this purpose act in
association, the wings of the nostrils are sometimes raised to allow of
a free draught of air; and this is a highly characteristic sign of
indignation. The mouth is commonly compressed, and there is almost
always a frown on the brow. Instead of the frantic gestures of extreme
rage, an indignant man unconsciously throws himself into an attitude
ready for attacking or striking his enemy, whom he will, perhaps, scan
from head to foot in defiance. He carries his head erect, with his chest
well expanded, and the feet planted firmly on the ground. With Europeans
the fists are generally clenched." "Under rage the action of the heart
is much accelerated, or, it may be, much disturbed. The face reddens, or
it becomes purple from the impeded return of the blood, or may turn
deadly pale. The respiration is laboured, the chest heaves, and the
dilated nostrils quiver. The whole body often trembles. The voice is
affected. The teeth are clenched or ground together, and the muscular
system is commonly stimulated to violent, almost frantic, action. But
the gestures of a man in this state usually differ from the purposeless
writhings and struggles of one suffering from an agony of pain; for they
represent more or less plainly the act of striking or fighting with an
enemy."
These examples will serve to remind the reader of the nature of those
complex aggregates of organized feelings which we call emotions, and
will also show the close connection of these emotions with the
associated bodily movements and activities which constitute their normal
fulfilment. So close is this connection, that the assumption of the
appropriate attitude will conjure up a faint revival of the associated
emotion. Let any one stand with squared shoulders, clenched fists, and
set muscles, and he will find the respiration affected, and perhaps also
the heart-beat, and will experience a faint revival of the emotion of
anger. Very different will be his feelings as he reseats himself,
abandons his limbs to a posture of leisurely repose, and allows a
pleasant smile to steal over his features.
The next point to notice about these emotions is that they are to a
large extent instinctive, and are evidenced in the infant at so early a
period that individual acquisition is out of the question. In any case,
the basis of sensibility is innate. As Mr. Sully says,[HL] "There are
instinctive capacities of emotion of different kinds, answering to such
well-marked classes of feeling as fear, anger, and love. These emotions
arise uniformly when the appropriate circumstances occur, and for the
most part very early in life. Thus there is an instinctive disposition
in the child to feel in the particular way known as anger or resentment
when he is annoyed or injured."
In this, as in other cases of instinctive action, of which we shall have
more to say in the next chapter, it is, of course, impossible to say for
certain how far the activities observed are associated with
psychological states. The activities are undoubtedly instinctive. And
their performance by an adult would be accompanied by an emotional
state. It is, therefore, probable that in the very young child they have
their emotional concomitants. Still, we must remember that oft-repeated
actions tend to become automatic, that the accompanying consciousness
sinks into evanescence, and that it is, therefore, _possible_ that the
emotional state may not have that vividness which the activities seem to
bespeak.
There only remains, before passing on to consider the feelings and
emotions of animals, to indicate what Mr. Sully terms[HM] "the three
orders of emotion." The first order comprises the individual and
personal emotions--those which are self-interested and have sole
reference to the individual who feels, enjoys, or suffers. They take
origin in percepts, either in presentations of sense or representations
in memory. The second order introduces the sympathetic emotions. They
are evoked on sight of the sufferings or emotional states of others. If
we see a woman insulted, we are filled with indignation; and this
emotion has a sympathetic origin. The third order comprises the complex
feelings known as _sentiments_. They have reference to certain qualities
of objects or activities of individuals which inspire admiration or
disapprobation. They are abstract in their nature, and belong to the
conceptual sphere. Such are love of truth, beauty, virtue, liberty,
justice. To become operative on conduct, however, they need, at any rate
in the case of most people, to be particularized and individualized, or
brought within the perceptual sphere, ere they arouse anything that is
emotional in much more than in name. As Dr. McCosh has well said, "No
man ever had his heart kindled by the abstract idea of loveliness, or
sublimity, or moral excellence, or any other abstraction. That which
calls forth our admiration is a lovely scene; that which raises wonder
or awe is a grand scene; that which calls forth love is not loveliness
in the abstract, but a lovely and loving person; that which evokes moral
approbation is not virtue in the abstract, but a virtuous agent
performing a virtuous act. The contemplation of the beautiful and the
good cannot evoke deep or lively emotion. He who would create admiration
for goodness must exhibit a good being performing a good action."
* * * * *
Turning now to the lower animals, the first question that suggests
itself is--What are their capacities for pleasure and pain? A very
difficult question to answer. We cannot, I think, hope to know how much
or how little the invertebrates feel--to what degree they are
psychologically sensitive. Even among the higher vertebrates we are very
apt, I imagine, to over-estimate the intensity of their feelings. Among
human-folk it is not he who halloas loudest that is necessarily most
hurt. And it is only through the expression of their feelings in cries
and gestures that we can conjecture the feelings of animals. There are
grounds for supposing that savages are far less keenly sensitive than
civilized people. And we have some reason for believing and hoping that
our dumb companions are less sensitive to pain than we are. Mr. G. A.
Rowell, for example, in his "Essay on the Beneficent Distribution of the
Sense of Pain," tells us that "a post-horse came down on the road with
such violence that the skin and sinews of both the fore fetlock joints
were so cut that, on his getting up again, the bones came through the
skin, and the two feet turned up at the back of the legs, the horse
walking upon the ends of its leg-bones. The horse was put into a field
close by, and the next morning it was found quietly feeding about the
field, with the feet and skin forced some distance up the leg-bones,
and, where it had been walking about, the holes made in the ground by
the leg-bones were three or four inches deep." Mr. Lamont gives a
somewhat similar observation in the case of the reindeer. "On one
occasion," he says, "we broke one of the fore feet of an old fat stag
from an unseen ambush; his companions ran away, and the wounded deer,
after making some attempts to follow them, which the softness of the
ground and his own corpulence prevented him doing, looked about him a
little, and then, seeing nothing, actually began to graze on his three
remaining legs, as if nothing had happened of sufficient consequence to
keep him from his dinner." Colonel Sir Charles W. Wilson, in his work
"From Korti to Khartoum," gives similar instances with regard to camels.
"The most curious thing," he says,[HN] "was that they showed no alarm,
and did not seem to mind being hit. One heard a heavy thud, and, looking
round, saw a stream of blood oozing out of the wound, but the camel went
on chewing his cud as if nothing at all had happened, not even giving a
slight wince to show he was in pain." And, again,[HO] "I heard the rush
of the shot through the air, and then a heavy thud behind me. I thought
at first it had gone into the field-hospital; but, on looking round,
found it had carried away the lower jaw of one of the artillery camels,
and then buried itself in the ground. The poor brute walked on as if
nothing had happened, and carried its load to the end of the day."
With regard to this question, then, of the susceptibility of animals to
pleasure and pain, no definite answer can be given. That they feel more
or less acutely we may be sure; how keenly they feel we cannot tell; but
it is better to over-estimate than to under-estimate their
sensitiveness. In any case, whether their pain be acute or dull, whether
their pleasures be intense or the reverse, we should do all in our power
to increase the pleasures and diminish the pains of the dumb creatures
who so meekly and willingly minister to our wants.
That the bodily feelings and wants occupy a large relative space in the
conscious life of brutes can scarcely be questioned. On the one hand are
the dull pains resulting from the organic wants and appetences, and
driving the animal to their gratification; the keen pleasure that
accompanies this gratification, when intelligence is so far developed
that it can be foreseen, being a pull in the same direction. And on the
other hand are the pleasures of the normal and healthy exercise of the
sense-organs and bodily activities giving rise to the pleasures of
existence, the joys of active and vigorous life. In the main, these
bodily feelings, or sense-feelings, as they are sometimes called, seem
to cluster round three chief centres--food, sex, and the free exercise
of the bodily activities, including in some cases what seems to be play.
Give a wild creature liberty and the opportunity of gratifying its
appetites; allow its bodily functions the alternating rhythm of healthy
and vigorous exercise and restorative repose; and its life is happy and
joyous. It is not troubled by the pressure of unfulfilled ideals. The
very struggle for existence, keen as it often is, by calling into play
the full exercise of the activities, ministers to the health and
happiness of brutes as well as men. Sir W. R. Grove has preached [HP]
the advantages of antagonism. Speaking of the rabbit, he says, "To keep
itself healthy, it must exert itself for its food; this, and perhaps
avoiding its enemies, gives it exercise and care, brings all its organs
into use, and thus it acquires its most perfect form of life. An estate
in Somersetshire, which I once took temporarily, was on the slope of the
Mendip Hills. The rabbits on one part of it, that on the hillside, were
in perfect condition, not too fat nor too thin, sleek, active, and
vigorous, and yielding to their antagonists, myself and family,
excellent food. Those in the valley, where the pasturage was rich and
luxuriant, were all diseased, most of them unfit for human food, and
many lying dead on the fields. They had not to struggle for life; their
short life was miserable and their death early; they wanted the sweet
uses of adversity--that is, of antagonism." Without endorsing the view
that these rabbits were unhealthy _only_ because they had too much food
and comfort--for the food, though abundant, may have been in some way
noxious, and the damp situation may have been prejudicial--we may still
believe that a struggle for life is better for animals (and men) than
unlimited ease and plenty.
Under the influence, then, of these bodily pleasures and wants, the
activities of animals are drawn out and guided. As Darwin says, in his
autobiography,[HQ] "An animal may be led to pursue that course of action
which is most beneficial to the species by suffering, such as pain,
hunger, thirst, and fear; or by pleasure, as in eating and drinking, and
in the propagation of the species; or by both means combined, as in the
search for food. But pain or suffering of any kind, if long continued,
causes depression, and lessens the power of action, yet it is adapted to
make a creature guard itself against any great or sudden evil.
Pleasurable sensations, on the other hand, may be long continued without
any depressing effect; on the contrary, they stimulate the whole system
to increased action. Hence it has come to pass that most or all sentient
beings have been developed in such a manner, through natural selection,
that pleasurable sensations serve as their habitual guides. We see this
in the pleasure from exertion, even occasionally of great exertion, of
the body or mind--in the pleasure of our daily meals, and especially in
the pleasure derived from sociability, and from loving our families. The
sum of such pleasures as these, which are habitual or frequently
recurrent, give, as I can hardly doubt, to most sentient beings an
excess of happiness over misery, although they occasionally suffer much.
Such suffering is quite compatible with belief in natural selection;
which is not perfect in its action, but tends only to render each
species as successful as possible in the battle for life with other
species, in wonderfully complex and changing circumstances."
Passing now from the bodily feelings and wants to the emotions, there
can be no question that the simpler emotions, of which I have taken fear
and anger as typical, are shared with us by the dumb brutes. And the
interesting observations of Mr. Douglas Spalding showed beyond doubt
that they are instinctive--their manifestation being prior to, and not
the outcome of, individual experience. Writing in _Macmillan's
Magazine_, he says, "A young turkey, which I had adopted when chirping
within the uncracked shell, was, on the morning of the tenth day of its
life, eating a comfortable breakfast from my hand, when the young hawk
in a cupboard just beside us gave a shrill 'Chip! chip! chip!' Like an
arrow, the poor turkey shot to the other side of the room, and stood
there, motionless and dumb with fear, until the hawk gave a second cry,
when it darted out at the open door right to the extreme end of the
passage, and there, silent and crouched in a corner, remained for ten
minutes. Several times during the course of that day it again heard
these alarming sounds, and in every instance with similar manifestations
of fear." And as an example of combined fear and anger, Mr. Spalding
says, "One day last month, after fondling my dog, I put my hand into a
basket containing four blind kittens three days old. The smell my hand
had carried with it sent them puffing and spitting in a most comical
fashion."
A remarkable instance of inherited antipathy in the dog was communicated
by Dr. Huggins to Mr. Darwin. He possessed an English mastiff, Kepler,
which was brought when six weeks old from the stable in which he was
born. The first time Dr. Huggins took him out he started back in alarm
at the first butcher's shop he had ever seen, and throughout his life he
manifested the strongest and strangest antipathy to butchers and all
that pertained to them. On inquiry, Dr. Huggins ascertained that in the
father, in the grandfather, and in two half-brothers of Kepler the same
curious antipathy was innate. Of these, Paris, a half-brother, on one
occasion, at Hastings, sprang at a gentleman who came into the hotel at
which his master was staying. The owner caught the dog, and apologized,
saying he had never known him to behave thus before except when a
butcher came into the house. The gentleman at once said that was his
business.
That many animals display affection towards their offspring and their
mates, towards man and towards other companions, is a matter of familiar
observation. Often the attachments are strange, as of cats and horses,
or contrary to instinctive tendencies, as between cats and dogs.
Sometimes they are capricious, as when Mr. Romanes's wounded widgeon
conceived a strong, persistent, and unremitting attachment to a
peacock;[HR] or even insane, as where a pigeon became the victim of an
infatuation for a ginger-beer bottle. Strong attachment to man is often
exhibited. Every one knows the story which Mr. Darwin tells[HS] of the
little monkey who bravely rushed at the dreaded baboon which had
attacked his keeper. A friend of my own (the Rev. George H. R. Fisk, of
Capetown) tells me the following story (which may be added to the many
similar cases reported of dogs) concerning a favourite cat he had as a
boy. It happened that the children of the house, my friend among the
number, were confined to their room by measles. Their mother remained
with the children by day and night until they were convalescent. She
then came down and resumed her usual daily life, but was shocked at the
appearance of the cat, which was little more than skin and bones, and
would not touch food or milk. The cat seemed to know that Mrs. Fisk
could help her, and gave her no peace till she had taken her upstairs to
the convalescent patients. To Mrs. Fisk's surprise, the cat snarled and
beat the young master with her paws. Why the cat chose this peculiar
method of venting her feelings it is difficult to say. But immediately
afterwards she went down into the kitchen, ate the meat and drank the
milk which she had before refused to touch. Early next morning she mewed
outside the young master's room; and, having gained admittance, sat at
the foot of the bed until he woke, and then licked his face and hair.
This leads us on to the class of sympathetic emotions. For the
sympathetic emotions are those which centre, not round the self, but
round some other self in whose welfare an interest is, in some way and
for some reason, aroused. Not long ago, at the Hamburg Zoological
Gardens, I saw two baboons fighting savagely. One at last retreated
vanquished, with his arm somewhat deeply gashed. He climbed to a corner
of the cage and sat down, moodily licking his wound. Thither followed
him a little capuchin, and, though his bigger friend took mighty little
notice of his overtures, seemed anxious to comfort him, nestling against
him, and laying his head against his side. So far as one could judge, it
was not curiosity, but sympathy, that prompted his action.
The following example of sympathetic action on the part of a dog towards
a stranger-dog is communicated to me by Mrs. Mann, a friend of mine at
the Cape. Carlo was a favourite black retriever, and a highly
intelligent animal. "One day," says Mrs. Mann, "a miserable-looking
white dog came into our yard. Carlo went up to him, looking displeased,
dog-fashion, and ready to fly at the intruder. It was clear, however,
that some communication passed between them, for Carlo's wrath seemed
disarmed, and he trotted into the kitchen, coming out again with a
chop-bone (one with a good deal of meat on it) which the cook had given
him. On looking into the yard, the miserable cur was seen enjoying the
bone, Carlo sitting straight up watching him with a look of
satisfaction."[HT]
That dogs feel sympathy with man will scarcely be questioned by any one
who has known the companionship of these four-footed friends. At times
they seem instinctively to grasp our moods, to be silent with us when we
are busy, to lay their shaggy heads on our knees when we are worried or
sad, and to be quickened to fresh life when we are gay and glad--so keen
are their perceptions. Their life with man has implanted in them some of
the needs of social beings; and as they are ever ready to sympathize
with us, so do they rejoice in our sympathy. To be deprived of that
sympathy, to be neglected, to have no attention bestowed on them, is to
some dogs a punishment more bitter than direct reproof. Mr. Romanes
quotes[HU] an account given him by Mrs. E. Picton of a Skye terrier who
had the greatest aversion to being washed, snarling and biting during
the operation. Threats, beating, and starvation were all of no avail;
but the animal was reduced to submission by persistent neglect on the
part of his mistress. At the end of a week or ten days he looked
wretched and forlorn, and yielded himself quite quietly and patiently to
one of the roughest ablutions it had ever been his lot to experience.
So far I have been content to credit animals with very general and
simple forms of emotion--anger, fear, antipathy, affection, and some
form of sympathy. If, on the perusal of familiar anecdotes, we also
credit them with jealousy, envy, emulation, pride, resentment, cruelty,
deceitfulness, and other more complex emotional states, we must remember
that every one of these, as we know them, is essentially human. It is
necessary to insist on the need of caution and the danger of
anthropomorphism. This is, perhaps, even more necessary in the case of
the emotions than in that of the perceptions, which we have before
considered. Even among men, different individuals and different races
probably vary far more in their emotions than in their perceptions. The
emotions of civilized man have assumed their present form in the midst
of complex social surroundings. They one and all bear ineffaceably
stamped upon them the human image and superscription. In terms of these
complex human emotions we have to decipher the simpler emotional states
of the lower animals. We call them by the same names; we think of them
as like unto those that we experience. And we can do no otherwise, if we
are to consider them at all. But let us not lose sight of the fact that
all we can ever hope to see in the mirror of the animal mind is a
distorted image of our own mental and emotional features. And since the
mirrors are of varying and unknown curvature, we can never hope to be in
a position accurately to estimate the amount of distortion.
Remembering this, it is always well to look narrowly at every anecdote
of animal intelligence and emotion, and endeavour _to distinguish
observed fact from observer's inference_. If we take the great number of
stories illustrative of revenge, consciousness of guilt, an idea of
caste, deceitfulness, cruelty, and so forth, in the higher mammalia, we
shall find but few that do not admit of a different interpretation from
that given by the narrator. A cat's treatment of a mouse is adduced by a
number of witnesses as illustrative of cruelty; but others see in this
conduct, not cruelty, but practice and training in an important branch
of the business of cat-life. That is to say, the act, though objectively
cruel from the human standpoint, is not on this view performed from a
motive of cruelty. Some time ago I ventured to stroke the nose of a
little lion-cub which had tottered, kitten-like, to the bars of its
cage. "I wish," I said shortly afterwards to a distinguished animal
painter, "you could have caught the look of conscious dignity (I speak
anthropomorphically) with which the lioness turned and seemed to say,
'How dare you meddle with my child!'" "I have seen such a look and
attitude," said Mr. Nettleship; "but I attributed it, not to pride, but
to fear." Mr. Romanes quotes,[HV] as typically illustrative of an "idea
of caste," the case of Mr. St. John's retriever, which struck up an
acquaintance with a rat-catcher and his cur, but at once cut his humble
friends, and denied all acquaintanceship with them, on sight of his
master. I, on the other hand, should regard this case as parallel with
that which I have noted a hundred times. My dogs would go out with the
nurse and children when I was busy or absent; but if I appeared within
sight, they raced to me. The stronger affection prevailed. A dog is
described[HW] as "showing a deliberate design of deceiving," because he
hobbled about the room as if lame and suffering from pain in his foot. I
would suggest that there was no pretence, no "deliberate design of
deceit," in this case, but a direct association of ideas between a
hobbling gait and more sympathy and attention than usual. I am not
denying objective deceitfulness to the dog any more than I deny
objective cruelty to the cat. My only question is whether the _motive_
is deceit. We must not forget that the deceitful intent is a piece, not
of the observed fact, but of the observer's inference. Mr. Romanes, for
example, tells[HX] of a black retriever who was asleep, or apparently
asleep, in the kitchen of a certain dignitary of the Church. The cook,
who had just trussed a turkey for roasting, was suddenly called away.
During her temporary absence, "the dog carried off the turkey to the
garden, deposited it in a hollow tree, and at once returned to resume
his place by the fire, where he pretended to be asleep as before."
Unfortunately, a perfidious gardener had watched him, and brought back
the turkey, so that the retriever did not enjoy the feast he had
reserved for a quiet and undisturbed moment. Assuming that the gardener
and cook were accurate in their statement of fact, the deceitful intent
is an inference on their part, or that of the dignitary of the Church,
or Mr. Romanes. I do not deny its correctness from the objective
standpoint. Deceitfulness is apparently exhibited by children at a very
tender age. But for us civilized adults deceit and its converse,
truthfulness in action, mean something a good deal more definite than
for dogs and infants.
Animals are often described as harbouring feelings of revenge and
vindictiveness. To test this in the elephant, Captain Shipp gave an
elephant a sandwich of cayenne pepper. "He then waited," says Mr.
Romanes,[HY] "for six weeks before again visiting the animal, when he
went into the stable, and began to fondle the elephant as he had
previously been accustomed to do. For a time no resentment was shown, so
that the captain began to think that the experiment had failed; but at
last, watching an opportunity, the elephant filled his trunk with dirty
water, and drenched the captain from head to foot." Here the facts are
that an injury was received, and that the retaliation followed after an
interval of six weeks. The inference seems to be that the elephant
harboured feelings of revenge or vindictiveness during this period. It
may have been so. It may be, however, that the elephant never once
pictured the captain during the six weeks; but, on seeing him again,
remembered the injury, and, as we say, paid him out. But what we
understand by revenge and vindictiveness is the keeping of an injury
before the mind for the express purpose of ultimately avenging it. And
this the elephant, to say the least of it, may not have done.
In Miss Romanes's interesting observations on the Cebus monkey, she
says,[HZ] "He bit me in several places to-day when I was taking him away
from my mother's bed after his morning's game there. I took no notice;
but he seemed ashamed of himself afterwards, hiding his face in his
arms, and sitting quiet for a time." But, in a footnote, we read, "On
subsequent observation, I find this quietness was not due to shame at
having bitten me; for whether he succeeds in biting any person or not,
he always sits quiet and dull-looking after a fit of passion, being, I
think, fatigued." I quote this to illustrate the difference which I am
endeavouring to insist upon between observed fact and observer's
inference.
Mr. Romanes comments[IA] on the remarkable change which has been
produced in the domestic dog as compared with wild dogs, with reference
to the enduring of pain. "A wolf or a fox will sustain the severest
kinds of physical suffering without giving utterance to a sound, while a
dog will scream when any one accidentally treads upon its toes. This
contrast," says Mr. Romanes, "is strikingly analogous to that which
obtains between savage and civilized man: the North American Indian, and
even the Hindoo, will endure without a moan an amount of physical
pain--or, at least, bodily injury--which would produce vehement
expressions of suffering from a European. And, doubtless, the
explanation is in both cases the same; namely, that refinement of life
engenders refinement of nervous organization, which renders nervous
lesions more intolerable." I cannot accept this as the most probable
explanation. In the first place, the human beings referred to have
different ideals in the matter of conduct under pain and suffering. The
American Indian and the Hindoo have a stoic ideal, which does not
influence the average European. On the other hand, the dog, from his
association with man, has learnt more and more to give expression to his
feelings in barks, whines, and yelpings. To howl at every little pain
would do a wolf no good, but rather advertise him to his enemies; to
howl when his toes are trodden on makes most men look where they are
stepping, and probably pet the sufferer for his pains. In the one case,
to howl is disadvantageous; in the other, it is advantageous. I do not,
however, put forward my own explanation as necessarily more correct than
that given by Mr. Romanes (though I regard it myself as more probable).
My object is to show that it is possible for two observers to regard the
same activities of animals, and read into them different psychological
accompaniments. Throughout the sections of Mr. Romanes's work which deal
with the emotions, I feel myself forced at almost every turn to question
the validity of his inferences.
From all that I have said in the last chapter, it will be gathered that
I am not prepared to credit our dumb companions with a single
_sentiment_. A sense of beauty, a sense of the ludicrous, a sense of
justice, and a sense of right and wrong,--these abstract emotions or
sentiments, _as such_, are certainly impossible to the brute, if, as I
have contended, he is incapable of isolation and analysis. But, as we
have already seen, even with us these emotions have to be particularized
and brought within the perceptual sphere ere they are strongly operative
on conduct. We are not roused to indignation by an abstract sense of
injustice, but by the particular performance of an unjust deed. Even so,
however, the emotional state aroused carries with it in us some of the
spirit of the conceptual sphere from which it has descended. The
analogous emotions in animals cannot possess, if I am right, any
tincture of this conceptual spirit. And since we cannot divest ourselves
of our conceptual spirituality, we cannot justly estimate what these
emotional states, in dog or ape, are like. Remembering this, let us see
what can be said in favour of a perceptual sense of injustice, guilt,
the ludicrous, and the beautiful. In evidence of a sense of justice, we
have the oft-quoted case of the turnspit-dog reported by Arago the
astronomer.[IB] This dog refused, with bared teeth, to enter out of his
turn the drum by the revolution of which the spit was rotated. M. Arago,
for whom the pullet on the spit was being dressed, requested that the
dog's companion, after turning the spit for a short time, should be
released. Whereupon the dog who had before been so refractory seemed
satisfied that his turn for drudgery had come, and, entering the wheel
of his own accord, began without hesitation to turn it as usual. Many
will be prepared to maintain that dogs resent unjust chastisement. A
gentleman I met near Rio de Janeiro possessed a dog whose sensitiveness
was such that, after a reproof, he would leave the house, and sometimes
not return for several days. His owner assured me of his belief that in
such cases the reproof had always been undeserved; and he told me of one
definite instance in which the reproof--never more than verbal--had been
for a theft which was afterwards found to have been committed by his
garden-boy. On this occasion the dog was away for three days, and
returned in a wretched and miserable condition. What shall we say of
such cases? Seeing how complex is what we call a sense of justice, I am
not prepared to credit the dog therewith; and I am disposed to regard
such actions as I have just described as the result of a breach of
normal association. Dogs, like men, are creatures of habit; and breaches
of normal association--occurrences contrary to expectation--give rise to
uneasiness, dissatisfaction, and consequent resentment.
Conversely, many of the cases where dogs and other animals are said to
know when they have done wrong, and to suffer the pricks of conscience,
may probably be satisfactorily explained by association. When my friend,
coming down into his drawing-room, sees Tim's "guilty" look, he suspects
that the dog has, contrary to rule, been taking a nap on one of the
chairs; and his suspicions are not a little strengthened by the
unnatural warmth of the easiest armchair. "Ah! Tim always knows when he
has done wrong," says my friend. But not improbably the association in
Tim's mind is a direct one between a nap on that chair and his master's
displeasure. What Tim knows is, perhaps, not that he _has_ done wrong,
but that he will "catch it." It is the expectation of a reproof, or
something more, that gives rise to his look of conscious guilt. In the
same way, the look of "conscious rectitude" we often see in some dogs
may be due to the anticipation of a word of commendation. And, in
general, I fancy that the association in an animal's mind is between the
performance of a given act and the occurrence of certain consequences.
When this association becomes definite it must, I imagine, draw after it
a dislike of such actions as have been accompanied by evil consequences,
and a delight in such actions as have been accompanied by pleasant
consequences. And eventually this dislike or delight is transferred from
his own actions to the similar actions of others. Thus dogs punish their
puppies for acts of uncleanliness, while cats are even more particular
in this respect. A correspondent in _Nature_[IC] gives a case of a cat
chastising by a violent blow with her paw her kitten, who was about to
enjoy a herring which had been set down before the fire to keep hot. So,
too, according to Mr. Darwin,[ID] "when the baboons in Abyssinia plunder
a garden, they silently follow their leader, and, if an imprudent young
animal makes a noise, he receives a slap from the others to teach him
silence and obedience." And Mr. Schaub communicated to Professor
Nipher[IE] a case of a black-and-tan terrier bitch, whose pup had stolen
a stocking from his bedroom, and who followed the young offender, took
the stocking from him, and returned it to the owner. Her action gave
evidence, he says, of displeasure at the action of the pup. And Mr.
Schaub contrived to have the offence committed on many successive
mornings, the same performance being repeated each time.
In this connection I will give two anecdotes of Carlo, communicated to
me by Mrs. Mann. "Once I came upon Carlo sitting in the dining-room
doorway, Dulceline, the cat, angrily watching him from the stairs, and
also evidently having an eye on a leg of mutton half dragged off the
dish on the dining-table. Carlo had clearly caught the thief in the act.
He was on guard; and he seemed much relieved when higher powers came on
the scene. Honesty seemed part of Carlo's nature. In this matter we
never had to give him any lessons. Nor could he bear to see dishonesty
in others. One Sunday, one of the little girls saw Carlo coming along
looking so anxiously at her that she knew he wanted her to come. She
therefore followed him, and Carlo took her to the store-room, the door
of which her sister had left open. In the doorway Carlo stopped, and
looked first up at his mistress and then into the store-room, as much as
to say, 'What can we think of this?' And truly there was a certain
little black-and-tan terrier, whose principles were by no means of a
high order, regaling himself with some cold meat that he had dragged on
to the floor. Toby knew he was in the wrong, and tried to flee. But
Carlo stopped him as he endeavoured to fly past. And when Toby was
thereupon duly slapped, Carlo sat straight up, with a face of conscious
rectitude."
These anecdotes, communicated to me by a lady of culture and
intelligence, illustrate how, in describing the actions of animals,
phraseology only, in strictness, applicable to the psychology of man, is
unwittingly and almost unavoidably employed. Toby's "_principles_ were
not of a high order," yet he "_knew he was in the wrong_," while Carlo
watched him receive his punishment, and "sat straight up, with a face of
_conscious rectitude_."
Coming now to a sense of humour or a sense of the ludicrous, Darwin
himself said,[IF] "Dogs show what may fairly be called a sense of
humour, as distinguished from mere play; if a bit of stick or other such
object be thrown to one, he will often carry it away for a short
distance; and then, squatting down with it on the ground close before
him, will wait until his master comes close to take it away. The dog
will seize it and rush away in triumph, repeating the same man[oe]uvre,
and evidently enjoying the practical joke." Mr. Romanes had a dog who
used to perform certain self-taught tricks, "which clearly had the
object of exciting laughter. For instance, while lying on his side and
violently grinning, he would hold one leg in his mouth. Under such
circumstances, nothing pleased him so much as having his joke duly
appreciated, while, if no notice was taken of him, he would become
sulky." To these I may add an observation of my own. I used sometimes,
when staying at Lancaster with a friend, to take his dog Sambo, a highly
intelligent retriever, to the seashore. His chief delight there was to
bury small crabs in the sand, and then stand watching till a leg or a
claw appeared above the surface, upon which he would race backwards and
forwards, giving short barks of keen enjoyment. This I saw him do on
many occasions. He always waited till a helpless leg appeared, and then
bounded away as if he could not contain the canine laughter that was in
him. Who shall say, however, what was passing through the mind of the
dog in any of these three cases? The motive of Mr. Darwin's dog may have
been to prolong the game, though I expect there was something more than
this. Mr. Romanes's dog exemplified, perhaps, the sense of satisfaction
at being noticed. Sambo's performance is now, as it was years ago,
beyond me. But a sense of humour, involving a delicate appreciation of
the minor incongruities of life, is, I imagine, too subtle an emotion
for even Sambo.
I pass now to the sense of beauty, and I shall consider this at greater
length, because of its bearing on sexual selection and the origin of
floral beauty.
The interesting experiments of Sir John Lubbock already alluded to seem
to establish the fact that bees have certain colour-preferences. Blue
and pink are the most attractive colours; yellow and red are in less
favour. No doubt these preferences have arisen in association with the
flowers from which the bees obtain their nectar. They have a practical
basis of biological value. But there seems no doubt that certain colours
are now for them more attractive than others. Bees and other insects
are, undoubtedly, attracted by flowers; these flowers excite in us an
æsthetic pleasure; the bees are, therefore, supposed to be attracted to
the flowers through their possession of an æsthetic sense. Now, this
does not necessarily follow. It is the nectar, not the beauty of the
flower, that attracts the bee. So long as the flower is sufficiently
_conspicuous_ to be rapidly distinguished by the insect, the conditions
of the case are met so far as insect psychology is concerned. The fact
remains, however, that the flowers thus conspicuous to the insect are
fraught with beauty _for us_.
In the case of sexual selection among birds, again, I believe that the
gorgeous plumage has its basis of origin in that pre-eminent vitality
which Mr. Tylor and Mr. Wallace have insisted on. But, as before
indicated, this will not serve to explain its special character for each
several species of birds. Here, again, conspicuousness and recognition
are unquestionably factors. But that the bright plumage of male birds
awakens emotional states in the hens, that it probably also arouses
sexual appetence, seems to be shown by the manner in which the finery is
displayed by the male before the female. I think it is probable, also,
that pleasure, becoming thus associated with bright colours in the mate,
is also aroused by bright colours in other associations. Thus the
gardener bower-bird, described by Dr. Beccari,[IG] collects in front of
its bower flowers and fruits of bright and varied colours. It removes
everything unsightly, and strews the ground with moss, among which it
places the bright objects from among which the cock bird is said to
select daily gifts for his mate's acceptance! Dr. Gould states that
certain humming-birds decorate their nests "with the utmost taste,"
weaving into their structure beautiful pieces of flat lichen. If by
crediting birds with a sense of beauty we mean that in them pleasurable
emotions may be aroused on sight of objects which we regard as
beautiful, I am not prepared to deny them such a sense of beauty, nay, I
fully believe that such pleasurable feelings are aroused in them. When,
however, it is said that the gorgeous plumage of male birds has been
produced by the æsthetic choice of their mates, I am not so ready to
agree. A consciously æsthetic motive has not, I believe, been a
determining cause. The mate selected has been that which has excited the
strongest sexual appetence; his beauty has probably not, as such, been
distinctly present to consciousness. Here, then, we have again the
question which arose in connection with floral beauty--How is it that
the sight of the mates selected by hen birds excites in us, in so many
cases, an æsthetic pleasure?
It is clear that this is a matter rather of human than of animal or
comparative psychology. As such, except for purposes of illustration, it
does not fall within the scope of this work. I can, therefore, say but a
few words on the subject. The view that I think erroneous is that either
floral beauty or the beauty of secondary sexual characters has been
produced on æsthetic grounds, that is to say, for the sake of the beauty
they are seen by man to possess. It is, therefore, to the point to draw
attention to the fact that many of the objects and scenes which excite
in us this æsthetic sense have certainly not been produced for the sake
of their beauty. Their beauty is an adjunct, a by-product of rarest
excellence, but none the less a by-product.
Nothing can be more beautiful in its way than a well-grown beech or lime
tree; and yet it cannot be held to have been produced for its beauty's
sake. The leaves of many trees, shrubs, and plants are scarcely less
beautiful than the flowers. But _they_ cannot have been produced by the
æsthetic choice of insects. From the depth of a mine there may be
brought up a specimen of ruby copper ore, or malachite, or a nest of
quartz crystals, or an agate, or a piece of veined serpentine, which
shall be at once pronounced a delight to the eye. But for the eye it was
not evolved. The grandeur of Alpine scenery, the charm of a winding
river, the pleasing undulations of a flowing landscape,--no one can say
that these were evolved for the sake of their beauty. The fact of their
being beautiful is, therefore, no proof that the blue gentian, or the
red admiral, or the robin redbreast were evolved for the sake of, or by
means of, the beauty that they possess. Again, one leading feature in
the beauty of flowers is their symmetry. The beauty is, so to speak,
kaleidoscopic beauty. It is not so much the single veined or marbled
petal that is so lovely, as the group of similar petals symmetrically
arranged. But this symmetry can hardly be said to have been selected for
its æsthetic value; it is rather part of the natural symmetry of the
plant. Even with butterflies and birds and beasts the symmetrical
element is an important one in their beauty.[IH]
I must not attempt to analyze our sense of beauty or endeavour to trace
its origin. It appears to involve a pleasurable stimulation of the
sense-organs concerned, together with perceptions of symmetry, of
diversity and contrast, and of proportion, with a basis of unity. It is
rich in suggestions and associations. It is heightened by sympathy. A
beautiful scene is doubly enjoyable if a congenial companion is by our
side.
"The whole effect of a beautiful object, so far as we can explain it,"
says Mr. Sully,[II] "is an harmonious confluence of these delights of
sense, intellect, and emotion, in a new combination. Thus a beautiful
natural object, as a noble tree, delights us by its gradations of light
and colour, the combination of variety with symmetry in its contour or
form, the adaptation of part to part, or the whole to its surroundings;
and, finally, by its effect on the imagination, its suggestions of
heroic persistence, of triumph over the adverse forces of wind and
storm. Similarly, a beautiful painting delights the eye by supplying a
rich variety of light and shade, of colour, and of outline; gratifies
the intellect by exhibiting a certain plan of composition, the setting
forth of a scene or incident with just the fulness of detail for
agreeable apprehension; and, lastly, touches the many-stringed
instrument of emotion by an harmonious impression, the several parts or
objects being fitted to strengthen and deepen the dominant emotional
effect, whether this be grave or pathetic on the one hand, or light and
gay on the other. The effect of beauty, then, appears to depend on a
simultaneous presentment in a single object of a well-harmonized mass of
pleasurable material or pleasurable stimulus for sense, intellect, and
emotion."
This, too, is what I understand by an æsthetic sense of beauty; and if a
hen bird has her sexual appetence evoked by the bright display of her
mate, the emotional state she experiences is something very different
from what we know as a sense of beauty. The adjective "æsthetic" should
in any case, I think, be resolutely excluded in any discussion of sexual
selection.
Æsthetics, like conceptual thought, accompany the suppression or
postponement of action. As we have already seen, the normal and
primitive series is (1) sense-stimulus; (2) certain nerve-processes in
the brain which are associated with perception and emotion; and (3)
certain resulting activities. By the suppression of action the mind
comes to occupy itself more and more completely with the central
processes. Perception blossoms forth into conceptual thought; emotion
blossoms forth into æsthetics.
"'Throughout the whole range of sensations, perceptions, and emotions
which we do not class as _æsthetic_,'[IJ] says Mr. Herbert Spencer, 'the
states of consciousness serve simply as aids and stimuli to guidance and
action. They are transitory, or, if they persist in consciousness some
time, they do not monopolize the attention; that which monopolizes the
attention is something ulterior, to the effecting of which they are
instrumental. But in the states of mind we class as æsthetic the
opposite attitude is maintained towards the sensations, perceptions, and
emotions. These are no longer links in the chain of states which prompt
and guide conduct. Instead of being allowed to disappear with merely
passing recognition, they are kept in consciousness and dwelt upon,
their natures being such that their continued presence in consciousness
is agreeable.' The action which is the normal consequent on sensation is
here postponed or suppressed; and thus we are enabled to make knowledge
or beauty an end to be sought for its own sake; and thus, too, we are
able to make progress, otherwise impossible, in science and in art.
Sensations and perceptions are the roots from which spring the sturdy
trunk of action, the expanded leaves of knowledge, and the fair blossoms
of art. The leaves and the flowers are the terminal products along
certain lines of development; but the function of the leaves is to
minister to the growth of the wood, and the function of the flowers is
to minister to the continuance and well-being of the race. So, too, in
human affairs. Knowledge and art are justified by their influence on
conduct; truth and beauty must ever guide us towards right living; and
æsthetics are true or false according as they lead towards a higher or a
lower standard of moral life."[IK]
* * * * *
To sum up, then, concerning this difficult subject, the following are
the propositions on which I would lay stress: (1) What we term an
æsthetic sense of beauty involves a number of complex perceptual,
conceptual, and emotional elements. (2) The fact that a natural object
excites in us this pleasurable emotion does not carry with it the
implication that the object was evolved for the sake of its beauty. (3)
Even if we grant, as we fairly may, that brightly coloured flowers, in
association with nectar, have been objects of appetence to insects; and
that brilliant plumage, in association with sexual vigour, has been a
factor in the preferential mating of birds;--this is a very different
thing from saying that, either in the selection of flowers by insects,
or in the selection of their mates by birds, a consciously æsthetic
motive has been a determining cause. (4) In fine, though animals may be
incidentally attracted by beautiful objects, they have no æsthetic sense
of beauty. A sense of beauty is an abstract emotion. Æsthetics involve
ideals; and to ideals, if what has been urged in these pages be valid,
no brute can aspire.
What applies thus to æsthetics applies also to ethics. Few, however,
will be found to contend that animals can be moral or immoral, or have
any moral ideas properly so called. Mr. Romanes does indeed state, in
the table he prefixes to his works on Mental Evolution, that the
anthropoid apes and dogs are capable of "indefinite morality." He leaves
this to be explained, however, in a future work. In the published
instalment of "Mental Evolution in Man" he seems to contend,[IL] or, at
least, admit, "that the fundamental concepts of morality are of later
origin than the names by which they have been baptized." But he says
nothing of indefinite morality, which still remains for consideration in
another work. In the mean while we may, I think, confidently assume that
ethics, like conceptual thought and æsthetics, are beyond the reach of
the brute. Morality is essentially a matter of ideals, and these belong
to the conceptual sphere.
* * * * *
I have now said enough[IM] to indicate what I mean by advocating the
exercise of extreme caution in our inferences concerning the emotional
states of animals. We must remember, first, how liable to error are our
inferences in these matters; we must remember, next, how complex and
essentially human are our own emotions. I do not for one moment deny
that in animals are to be found the perceptual germs of even the higher
emotional states. Nevertheless, if we employ, in our interpretation of
the actions of animals, such terms as "consciousness of guilt," "sense
of right and wrong," "idea of justice," "deceitfulness," "revenge,"
"vindictiveness," "shame," and the rest, we must not forget that these
terms stand for human products, that they are saturated with conceptual
thought, and that they must be to a large extent emptied of their
meaning before they can become applicable to the emotional consciousness
of brutes.
NOTES
[HG] "Physiological Æsthetics:" chapter on "Pleasure and Pain."
[HH] All of these, at any rate, satisfy Mr. Herbert Spencer's
definition. Pleasure he describes as a feeling which we seek to
bring into consciousness and retain there; pain, as a feeling
which we seek to get out of consciousness and keep out.
[HI] "Types of Ethical Theory," vol. ii. p. 350.
[HJ] Such consciousness of activity is probably associated with the
innervation of afferent, not efferent, nerves.
[HK] Journal of Marine Biological Association, New Series, vol. i. No.
2, pp. 216, 217.
[HL] "Outlines of Psychology," p. 481.
[HM] Ibid. p. 494.
[HN] Page 70.
[HO] Page 104.
[HP] _Nature_, vol. xxxvii. p. 619.
[HQ] Vol. i. p. 310, under date 1876.
[HR] "Mental Evolution in Animals," p. 318.
[HS] "Descent of Man," pt. i. chap. iii.
[HT] Miss Nellie Maclagan describes how her Newfoundland similarly took
a roll to a hungry pauper-friend (_Nature_, vol. xxviii. p. 150).
Mr. Duncan Stewart gives (_Nature_, vol. xxviii. p. 31) the case
of a cat who used frequently to provide her blind mother with
food. Sir Harry Lumsden states that during the cold autumn of 1878
some tame partridges in Aberdeenshire brought two wild coveys to
be fed near the doorstep of the house. And a case has been
communicated to me by Miss Agnes Tanner, of Clifton, of a thrush
that pulled up worms on the lawn for a lame companion.
[HU] "Animal Intelligence," p. 440.
[HV] "Animal Intelligence," p. 442.
[HW] Ibid. p. 444.
[HX] Ibid. p. 451.
[HY] "Animal Intelligence," p. 387.
[HZ] "Animal Intelligence," p. 486.
[IA] Ibid. p. 141.
[IB] "Animal Intelligence," p. 443.
[IC] Mr. Alexander Mackennal, vol. xxi. p. 397.
[ID] "Descent of Man," pt. i. chap. iii., quoted from Brehm's
"Thierleben."
[IE] _Nature_, vol. xxviii. p. 32.
[IF] "Descent of Man," quoted by Romanes, p. 445.
[IG] _Nature_, vol. xl. p. 327.
[IH] Another example of beauty which can hardly be said to have been
evolved for beauty's sake is to be seen in birds' eggs. Mr. Henry
Seebohm regards the bright colours of some birds' eggs as a
difficulty in the way of the current interpretation of organic
nature. "Few eggs," he says (_Nature_, vol. xxxv. p. 237), "are
more gorgeously coloured [than those of the guillemot], and no
eggs exhibit such a variety of colour. [They are sometimes of a
bluish green, marbled or blotched with full brown or black;
sometimes white streaked with brown; sometimes pale green or
almost white with only the ghosts of blotches and streaks; and
sometimes the reddish brown extends so as to form the ground-tint
which is blotched with deeper brown.] It is impossible to suppose
that protective selection can have produced colours so conspicuous
on the white ledges of chalk cliffs; and sexual selection must
have been equally powerless. It would be too ludicrous a
suggestion to suppose that a cock guillemot fell in love with a
plain-coloured hen because he remembered that last season she laid
a gay-coloured egg."
If we connect colour with metabolic changes, its occurrence in
association with the products of the highly vascular oviduct will
not be surprising. Some _guidance_ is, however, on the principles
advocated in Chapter VI., required to maintain a standard of
coloration. In many cases such guidance is found in protective
selection, as in the plover's eggs in our frontispiece. In the
guillemot's egg such protective selection seems to be absent, and,
as Mr. Seebohm himself says, "no eggs exhibit such a variety of
colour."
In our present connection, however, the point to be noticed is that
many eggs are undoubtedly beautiful. But they cannot have been in
any way selected for the sake of their beauty.
[II] "Outlines of Psychology," p. 537.
[IJ] I should add, "or as _conceptual thought_."
[IK] This paragraph is quoted from the author's "Springs of Conduct,"
p. 263.
[IL] Page 347.
[IM] I have said nothing about the emotions of invertebrates, because I
have nothing special to say. They have, no doubt, emotions
analogous to fear, anger, and so on. But it is difficult to
interpret their actions. The "angry" wasp is, perhaps, a good deal
more frightened than furious. Sir John Lubbock's interesting
experiments seem to show that ants have what is termed the
instinct of play. But this admirable observer has rendered it
probable that sympathy and affection in ants and bees have been
somewhat exaggerated.
CHAPTER XI.
ANIMAL ACTIVITIES: HABIT AND INSTINCT.
So soon as one of the higher animals comes into the world a number of
simple vital activities are already in progress or are at once
initiated. Some of these are what are termed "automatic actions," or
actions which take their origin within the organ which manifests the
activity; such are the heart-beat and the rhythmical contractions of the
intestines by which the food is pushed onwards through the alimentary
canal. Some are reflex, or responsive, actions, taking origin from a
stimulus coming from without; such are the contraction of the pupil of
the eye under bright light, the pouring forth of the secretions on the
presence of food in the alimentary canal, taking the breast, sneezing,
and so forth. Some are partly automatic and partly reflex; such is the
rhythm of respiration.
In addition to these vital activities, there is a vast body of more
complex activities, for the performance of which the animal brings with
it innate capacities. Some of these, which we term "instinctive," are
performed at once and without any individual training, as when a chicken
steps out into the world, runs about, and picks up food without learning
or practice. Others, which we term "habitual," are more or less rapidly
learnt, and are then performed without forethought or attention. The
store of innate capacity is often very large; and a multitude of
activities are ere long performed with ease and certainty so soon as the
animal has learnt to use the organization it thus inherits. And lastly,
built upon this as a basis, by recombining of old activities in new
modes, and by special application of the activities to special
circumstances, we have the activities which we term "intelligent;" and
here again the activities are sometimes divided into two classes,
answering respectively to the reflex and the automatic, but on a higher
plane, according as they are responsive to stimuli coming more or less
directly from without, or spontaneous and taking their origin from
within. But it is probably rather the remoteness and indirectness of the
responsive element than its absence that characterizes these spontaneous
activities.
Another classification of activities is into voluntary and involuntary.
Voluntary actions are consciously performed for the attainment of some
more or less definite end or object. Involuntary actions, though they
may be accompanied by consciousness, and though they may be apparently
purposive, are performed without intention. Notwithstanding the
conscious element, they may, perhaps, be regarded as rather
physiological than psychological. The simple vital activities belong to
this class. But some are much more complex. If, when I am watching the
cobra at the Zoo, it suddenly strikes at the glass near my face, I
involuntarily start back. The action is apparently purposive, that is to
say, an observer of the action would perceive that it was performed for
a definite end, the removal from danger; it is also accompanied by
consciousness; but it is unintentional, no representation of the end to
be gained or the action to be performed being at the moment of action
framed by the mind. On the other hand, if I perform a voluntary act,
such as selecting and lighting a cigar, there is first a desire or
motive directed to a certain end in view, involving an ill-defined
representation of the means by which that end may be achieved; and this
is followed by the fulfilment of the desire through the application of
the means to the performance of the act.
In the carrying out of voluntary activities, then, both perception and
emotional appetence are involved. There are construction and
reconstruction, memory and anticipation, and interwoven therewith the
motive elements of appetence or aversion. It is emotion that gives force
and power to the motive. And this must be regarded as the dynamic
element in voluntary activity, while intelligence is the directive
element. Feeling is the horse in the carriage of life, and Intelligence
the coachman.
Let us here note that, in speaking of the activities of animals and the
motives by which they are prompted, we are forced, if we would avoid
pedantry, to leap backwards and forwards across the chasm which
separates the mental from the physical. Motives, as we know them, are
mental phenomena; the activities, as we see them, are physical
phenomena. The two sets of phenomena belong to distinct phenomenal
categories. In ordinary speech, when we pass and repass from motives to
actions, and from actions to the feelings they may give rise to, we are
apt to be forgetful of the depth of the chasm we so lightly leap. And
this is no doubt because the chasm, though so infinitely deep, is so
infinitely narrow. There are, however, no physical analogies by which we
can explain the connection between the physical and the mental, between
body and mind. The so-called connection is, in reality, as I believe,
identity. Viewed from without, we have a series of physical and
physiological phenomena; felt from within, we have a series of mental
and psychological phenomena. It is the same series viewed from different
aspects. This is no explanation; it is merely a way, and, as I believe,
the correct way, of stating the facts. Why certain physiological
phenomena should have a totally different aspect to the organism in
which they occur from that which they offer to one who watches them from
without, is a question which I hold to be insoluble. All we have to
remember, however, is that, in passing from the mental to the physical,
we are changing our point of view. The series may be set down thus--
_External aspect_:
Physical stimulus--> interneural processes--> activities.
\ /
\ /
_Inner aspect_: \ /
\ /
Accompanying consciousness <--mental states--> accompanying consciousness
The physical stimulus and the resulting activities are occurrences in
the external world, and more or less lie open to our view. But the
intervening physical and physiological neural processes are hidden from
us. As occurring in ourselves, however, the mental states which are the
inner aspects of these neural processes stand out clearly in the light
of consciousness. When, therefore, we are watching the life-activities
of others, we naturally fill in between the physical stimulus and the
activities, not the neural processes of which we are so ignorant, but
mental states analogous to those of which we are conscious under similar
conditions. Thus we leap from the physical to the mental, and back again
to the physical, as represented by the diagonal lines in the above
scheme. And there can be no objection to our doing so if we bear in mind
that we are thus changing our point of view.
The human organism, then--for at present we may regard the matter from
man's own position--is a wonderfully delicate piece of organization,
with mental (inner) and physical (outer) aspects. It is in a condition
of the most delicate equipoise. Under the influence of a perception
associated with an appetence, or of a conception accompanied by a
desire, it is thrown into a state of unstable equilibrium; the
performance of the action which leads to the fulfilment or satisfaction
of the appetence or the desire restores the stability of the system. The
instability is caused by the conjoint action of an attraction towards
some state represented as desirable, and a repulsion from the existing
state which is relatively undesirable. In some cases the attraction, and
in others the repulsion, is predominant. When we are in an uncomfortable
position, the discomfort is predominant, and we seek relief by changing
our attitude. When the bright sunshine tempts us to go out for a walk,
the attraction is predominant. But if the uncomfortable attitude is
enforced and prolonged, we have a mental representation of the relief we
long for; and this is attractive. And if we have work which keeps us
indoors, the irksome restraint brings with it an aversion to our present
lot.
Inseparably associated with the appetence or aversion there is a
representation of the activity which constitutes the fulfilment of the
emotion. On the physiological side this is probably an incipient
excitation of the muscles or other organs concerned in the requisite
actions. The miser's fingers itch to clutch the gold, the possession of
which he desires. Our muscles twitch as we long to join in the race or
the active contention of a game of football. Our horse grows restive as
the hunt goes by. Our dog can scarce restrain himself from racing after
the rabbits in the park. Under the influence of emotion, then, the body
is prepared for activity, the organs and muscles are beginning to be
innervated, and, if the appetence or desire be sufficiently strong, the
appropriate actions are initiated, and the organism tends to pass from
the state of unstable equilibrium arising out of a pressing need to the
stable condition of satisfied appetence. The function of the will in
this process we shall have briefly to consider presently.
Let us here notice, with regard to the activities, what we have before
seen with regard to the process of perceptual construction. We there
noticed that, at the bidding of a relatively simple suggestion, a
complex object may be constructed by the mind. This presupposes a highly
complex mental organization ready to be set in motion by the appropriate
stimulus. The organization has been established by association and
through evolution in the individual and his ancestors. It is the same
with the activities. They, too, are the outcomes of associations and
experiences established and registered during generations of ancestral
predecessors. At the bidding of the appropriate stimulus arousing
impulse or appetence, a train of activities of great intricacy may be
set agoing with remarkable accuracy and precision. It is true that a
certain amount of individual education is required to draw out and
establish the latent powers of the body, as also of the mind; but _the
ability is inborn_, and only requires to be cultivated. Every one of us
inherits an organization rendering him capable of performing a vast
amount of mental construction and a great number of bodily activities.
All he has to do is to learn how to use it and to make himself master of
the powers that are given him.
At first, the acquisition of this mastery over the innate powers, even
in the performance of comparatively simple muscular adjustments, may
require a good deal of attention and practice. But, as time goes on, the
frequent repetition of the ordinary activities of everyday life leads to
their easier and easier performance. In simple responsive actions the
appropriate activity follows readily on the appropriate stimulus. And,
ere long, many acts which at first required intelligent attention are
performed easily and without consciousness of effort or definite
intention. A close association between certain oft-recurring stimuli and
the appropriate response in activity is thus established, and the action
follows on the stimulus without hesitation or trouble. With fuller
experience and further practice in the ordinary avocations of life, the
responsive activities link themselves more and more closely in
association, become more and more complex, are combined in series and
classes of activity of greater length and accuracy, and thus become
organized into _habits_. Under this head fall those activities which we
learn with difficulty in childhood, and perform with ease in after-life.
At first voluntary and intentional, they have become, or are becoming,
through frequency and uniformity of performance, more or less
involuntary and unintentional.
"The work of the world is," we are told, "for the most part done by
people of whom nobody ever hears. The political machine and the social
machine are under the ostensible control of personages who are well to
the front; but these brilliant beings would be sorely perplexed, and the
machinery would soon come to a standstill, but for certain experienced,
unambitious, and unobtrusive members of society." So is it also in the
economy of animal life. The work of life is--to paraphrase Mr. Norris's
words--for the most part done by habits of which nobody ever thinks. The
bodily organization is ostensibly under the control of intellect and
reason; but these brilliant qualities would be sorely perplexed, and the
machinery would soon come to a standstill, but for certain unobtrusive,
habitual activities which are already as well trained in the routine
work of life as are the permanent clerks in the routine work of a
Government office.
The importance of the establishment of these habitual activities is
immense. As the muscular and other responses of ordinary everyday life
become habitual, the mind is, so to speak, set free from any special
care with regard to their regulation and co-ordination, and can be
concentrated on the end to be attained by such activities. The cat that
is creeping stealthily upon the bird has all her attention rivetted on
the object of her appetence, and has not to trouble herself about the
movements of her body and limbs. When the swallows are wheeling over our
heads in the summer air, their sweeping curves and graceful evolutions
are not the outcome of careful planning, but are just the normal
exercise of activities which from long practice have become habitual. To
swim, to skate, to cycle, to row, to play the piano or the violin,--all
these require our full attention at first. But with practice they become
habitual, and during their performance the attention may be devoted to
quite other matters. This is a great gain. Without it complex trains of
activities could not be performed with ease by man or beast.
When once habits have been firmly established, their normal performance
is accompanied by a sense of satisfaction. But if their performance is
prevented or thwarted, there arises a sense of want or dissatisfaction.
The pining of a caged wild animal for liberty is a craving for the free
performance of its habitual activities. In an animal born into captivity
the craving is probably less intense, though, for reasons which will
presently become evident, it is presumably by no means absent. Animals
are, to a very large extent, creatures of habit. Much of the pleasure of
their existence lies in the performance of habitual activities. Our
zoological gardens, interesting as they are to us, are probably centres
of an amount of misery and discomfort, from unfulfilled promptings of
habit and instinct, which we can hardly realize.
From habitual activities we may pass by easy steps to those which are
instinctive. Both habits and instincts, or, to use a more convenient and
satisfactory mode of expression for our present purpose, both habitual
and instinctive activities, are based upon innate capacity. But whereas
habitual activities always require some learning and practice, and very
often some intelligence, on the part of the individual, instinctive
activities are performed without instruction or training, through the
exercise of no intelligent adaptation on the part of the performer, and
either at once and without practice (perfect instincts) or by
self-suggested trial and practice (incomplete instincts).[IN]
There is some little difficulty in distinguishing between instinctive
activities and reflex actions. Mr. Herbert Spencer defines or describes
instinct as compound reflex action. Mr. Romanes defines instinct as
reflex action into which there is imported the element of consciousness.
But, on the one hand, many instincts involve something more than
compound reflex action, since there is an organized sequence of
activities; and, on the other hand, the difficulty (which Mr. Romanes
admits) or impossibility (as I contend) of applying the criterion of
consciousness renders unsatisfactory the introduction of the mental
element as distinctive. I would say, therefore, that (1) reflex actions
are those comparatively isolated activities which are of the nature of
organic or physiological responses to more or less definite stimuli, and
which involve rather the several organs of the organism than the
activities of the organism as a whole; and that (2) instinctive
activities are those organized trains or sequences of co-ordinated
activities which are performed by the individual in common with all the
members of the same more or less restricted group, in adaptation to
certain circumstances, oft-recurring or essential to the continuance of
the species.
These instinctive activities may, as I have said, be performed at once
and without practice (perfect instincts) or by self-suggested trial and
practice (incomplete instincts). Most young mammals require some little
practice in the use of their limbs before they are able to walk or run.
But young pigs run about instinctively so soon as they are born.
Thunberg, the South African traveller, relates, on the testimony of an
experienced hunter, the case of a female hippopotamus which was shot the
moment she had given birth to a calf. "The Hottentots," he said, "who
imagined that after this they could catch the calf alive, immediately
rushed out of their hiding-place to lay hold of it; but, though there
were several of them, the new-born calf got away from them, and at once
made the best of its way to the river."
Even in cases where some practice is apparently necessary, the
activities may be, and often are, perfectly instinctive. They cannot,
however, be performed immediately on birth, because the nervous and
muscular mechanism is not at that time sufficiently developed. They
might, perhaps, with advantage be termed "deferred instincts." If time
be given for this development, the activities are carried out at once
and without practice. Throw a new-born puppy into the river, and, after
some helpless floundering, he will be drowned. Throw his brother when
fully grown into the river, and, though he may never have been in the
water in his life, he will swim to shore. He has not to learn to swim;
this is with him an instinctive activity. The dog inherits the power
which the boy must with some little difficulty acquire. He probably has
to pay no special attention to the muscular adjustments involved. The
act is accompanied by consciousness, but not that directed consciousness
we call "attention." When the boy has acquired the habit, he is scarcely
conscious of the special muscular co-ordinations as he swims across the
river; he is only conscious of a desire to pick the water-lilies near
the further bank.
Birds, especially those which are called pr[oe]coces, in
contradistinction from the altrices, which are hatched in a helpless,
callow condition, come into the world prepared at once to perform
complex activities. Mr. Spalding writes,[IO] "A chicken that had been
made the subject of experiments on hearing [having been blindfolded at
birth] was unhooded when nearly three days old. For six minutes it sat
chirping and looking about it; at the end of that time it followed with
its head and eyes the movements of a fly twelve inches distant; at ten
minutes it made a peck at its own toes, and the next instant it made a
vigorous dart at the fly, which had come within reach of its neck, and
seized and swallowed it at the first stroke; for seven minutes more it
sat calling and looking about it, when a hive-bee, coming sufficiently
near, was seized at a dart, and thrown some distance much disabled. For
twenty minutes it sat on the spot where its eyes had been unveiled
without attempting to walk a step. It was then placed on rough ground,
within sight and call of a hen with a brood of its own age. After
standing chirping for about a minute, it started off towards the hen,
displaying as keen a perception of the qualities of the outer world as
it was ever likely to possess in after-life. It never required to knock
its head against a stone to discover that there was 'no road that way.'
It leaped over the smaller obstacles that lay in its path, and ran round
the larger, reaching the mother in as nearly straight a line as the
nature of the ground would permit. This, let it be remembered, was the
first time it had ever walked by sight."[IP]
Mr. Spalding's experiments also proved that, even among the altrices,
young birds do not require to be taught to fly, but fly instinctively so
soon as the bodily organization is sufficiently developed to render this
activity possible. He kept young swallows caged until they were fully
fledged, and then allowed them to escape. They flew straight off at the
first attempt. They exhibited the instinctive power of flight in a
perfect but deferred form.
It is, however, among the higher invertebrates--especially among the
insects, and of them pre-eminently in the social hymenoptera, ants and
bees, that the most remarkable and complete instincts are seen. There
is, however, a tendency to ascribe all the habits of ants and bees to
instinct, often, as it seems to me, without sufficient evidence that
they are performed without instruction, and through no imitation or
intelligent adjustment. This is, perhaps, a survival of the
old-fashioned view that all the mental activities of the lower animals
are performed from instinct, whereas all the activities of human beings
are to be regarded as rational or intelligent. In popular writings and
lectures, for example, we frequently find some or all of the following
activities of ant-life ascribed to instinct: recognition of members of
the same nest; powers of communication; keeping aphides for the sake of
their sweet secretion; collection of aphid eggs in October, hatching
them out in the nest, and taking them in the spring to the daisies, on
which they feed, for pasture; slave-making and slave-keeping, which, in
some cases, is so ancient a habit that the enslavers are unable even to
feed themselves; keeping insects as beasts of burden, e.g. a kind of
plant-bug to carry leaves; keeping beetles, etc., as domestic pets;
habits of personal cleanliness, one ant giving another a brush-up, and
being brushed-up in return; habits of play and recreation; habits of
burying the dead; the storage of grain and nipping the budding rootlet
to prevent further germination; the habits described by Dr. Lincecum,
and to a large extent confirmed by Dr. McCook,[IQ] that Texan ants go
forth into the prairie to seek for the seeds of a kind of grass of which
they are particularly fond, and that they take these seeds to a clearing
which they have prepared, and then sow them for the purpose, six months
afterwards, of reaping the grain which is the produce of their
agriculture; the collection by other ants of grass to form a kind of
soil on which there subsequently grows a species of fungus upon which
they feed; the military organization of the ecitons of Central America;
and so forth. Now, the description of the habits of ants forms one of
the most interesting chapters in natural history. But to lump them
together in this way, as illustrations of instinct, is a survival of an
old-fashioned method of treatment. That they have to a very large extent
_an innate basis_ may be readily admitted. But at present we are hardly
in a position to say how far they are instinctive, that is, performed by
each individual straight off, and without imitation, instruction, or
intelligence; how far habitual, that is, performed after some little
training and practice; how far there is the intelligent element of
special adaptation to special circumstances; how far they are the result
of imitation; to what extent, if any, individual training and
instruction are factors in the process.
To put the matter in another way. Suppose that an intelligent ant were
to make observations on human activities as displayed in one of our
great cities or in an agricultural district. Seeing so great an amount
of routine work going on around him, might he not be in danger of
regarding all this as evidence of blind instinct? Might he not find it
difficult to obtain satisfactory evidence of the establishment of our
habits, of the fact that this routine work has to some extent to be
learnt? Might he not say (perhaps not wholly without truth), "I can see
nothing whatever in the training of the children of these men to fit
them for their life-activities. The training of their children has no
more apparent bearing upon the activities of their after-life than the
feeding of our grubs has on the duties of ant-life. And although we must
remember," he might continue, "that these large animals do not have the
advantage which we possess of awaking suddenly, as by a new birth, to
their full faculties, still, as they grow older, now one and now another
of their instinctive activities are unfolded and manifested. They fall
into the routine of life with little or no training as the period proper
to the various instincts arrives. If learning thereof there be, it has
at present escaped our observation. And such intelligence as their
activities evince (and many of them do show remarkable adaptation to
uniform conditions of life) would seem to be rather ancestral than of
the present time; as is shown by the fact that many of the adaptations
are directed rather to past conditions of life than to those which now
hold good. In the presence of new emergencies to which their instincts
have not fitted them, these poor men are often completely at a loss. We
cannot but conclude, therefore, that, although shown under somewhat
different and less favourable conditions, instinct occupies fully as
large a space in the psychology of man as it does in that of the ant,
while their intelligence is far less unerring and, therefore, markedly
inferior to our own."
Of course, the views here attributed to the ant are very absurd. But are
they much more absurd than the views of those who, on the evidence which
we at present possess, attribute all the varied activities of ant-life
to instinct? Take the case of the ecitons, or military ants, or the
harvesting ants, or the ants that keep draught-bugs as beasts of burden:
have we sufficient evidence to enable us to affirm that these activities
are purely instinctive and not habitual? That they are to a large extent
innate, few are likely to deny; but then our own habitual acts have a
basis that is, to a very large extent, innate. The question is not
whether they have an innate basis, but whether all the varied
man[oe]uvres of the military ants, for example, are displayed to the
full without any learning or imitation, without teaching and without
intelligence on the part of every individual in the army.[IR]
That in some cases there is something very like a training or education
of the ant when it emerges from the pupa condition is rendered probable
by the observations of M. Forel. As Mr. Romanes says,[IS] "The young ant
does not appear to come into the world with a full instinctive knowledge
of all its duties as a member of a social community. It is led about the
nest and 'trained to a knowledge of domestic duties, especially in the
case of larvæ.' Later on, the young ants are taught to distinguish
between friends and foes. When an ants' nest is attacked by foreign
ants, the young ones never join in the fight, but confine themselves to
removing the pupæ; and that the knowledge of hereditary enemies is not
wholly instinctive in ants is proved by the following experiment, which
we owe to Forel. He put young ants belonging to three different species
into a glass case with pupæ of six other species--all the species being
naturally hostile to one another. The young ants did not quarrel, but
worked together to tend the pupæ. When the latter hatched out, an
artificial colony was formed of a number of naturally hostile species,
all living together after the manner of the 'happy families' of the
showmen."
I have said that the varied activities of ants, though they may not in
all cases be truly instinctive, are nevertheless the outcome of certain
innate capacities. It seems to me necessary to distinguish carefully
between innate capacity and instinct. Every animal comes into the world
with an innate capacity to perform the activities which have been
necessary for the maintenance of the normal existence of its ancestors.
This is part of its inherited organization. Only when these activities
are performed at the bidding of impulse, through no instruction and from
no tendency to imitation, can they, strictly speaking, be termed
instinctive. The more uniform the conditions of ancestral life, and the
more highly developed the organism when it enters upon the scene of
active existence, the more likely are the innate capacities to manifest
themselves at once and without training as perfect instincts. Among
birds, the pr[oe]coces, which reach a high state of development within
the egg, and among insects, those which undergo complete metamorphosis,
and emerge from the pupa or chrysalis condition fully formed and fully
equipped for life, display the greatest tendency to exhibit activities
which are truly and perfectly instinctive. But man, whose ancestors have
lived and worked under such complex conditions, and who comes into the
world in so helpless and immature a state, though his innate capacities
are enormous, exhibits but few and rudimentary instincts.
One marked characteristic of many of the habits and instincts of the
lower animals is the large amount of blind prevision (if one may be
allowed the expression) which they display. By blind prevision I mean
that preparation for the future which, if performed through intelligence
or reason, we should term "foresight," but which, since it is performed
prior to any individual experience of the results, is done, we must
suppose, in blind obedience to the internal impulse. The sphex, a kind
of wasp-like insect, forms a little mud chamber in which she lays her
eggs. She goes forth, finds a spider, stings it in such a way that it is
paralyzed but not killed, and places it in the chamber for her unborn
young, which she will never see. The hen incubates her eggs, though she
may never have seen a chicken in her life. The caterpillars of an
African moth weave a collective cocoon as large as a melon. All unite to
weave the enveloping husk; each forms its separate cocoon within the
shell, and all these separate cocoons are arranged round branch-passages
or corridors, by which the moths, when they emerge from the chrysalis
condition, may escape. Another caterpillar, that of a butterfly
(_Thekla_) feeds within the pomegranate, but with silken threads
attaches the fruit to the branch of the tree, lest, when withered, it
should fall before the metamorphosis is complete. An ichneumon fly,
mentioned by Kirby and Spence, "deposits its eggs in the body of a larva
hidden between the scales of a fir-cone, which it can never have seen,
and yet knows where to seek;" and thus provision is made for young which
it will never know. Instances of such blind prevision might be quoted by
the score. It is idle to speculate as to the accompaniments of
consciousness of such acts. If it be asked--May there not be associated
with the performance of the instinctive activity of incubation an
inherited memory of a generalized chick? we can only answer that we do
not know, but that we guess not.[IT]
There is, however, one association, in the case of these and other
instincts, which we may fairly surmise to be frequent, though, for
reasons to be specified hereafter, it is probably not invariable. Just
as we saw to be the case with habits, so too with instinctive
activities, their performance is not infrequently associated with
pleasurable feeling, their non-performance with pain and discomfort and
a sense of craving or want. The animal prevented from performing its
instinctive activities is often apparently unquiet, uneasy, and
distressed. Hence I said that the animals in our zoological gardens,
even if born and reared in captivity, may exhibit a craving for freedom
and a yearning to perform their instinctive activities. This craving may
be regarded as a blind and vague impulse, prompting the animal to
perform those activities which are for its own good and for the good of
the race to which it belongs. The satisfaction of the craving, the
gratification of the blind impulse, is accompanied by a feeling of
relief and ease. Thus where a motive emerges at all into consciousness,
that from which we may presume that instinctive activities are performed
is not any foreknowledge of their end and purpose, but the gratification
of an immediate and pressing need, the satisfaction of a felt want.
* * * * *
We have, so far, been concerned merely with the various kinds of
activity presented by men and animals, and with some of their
characteristics. The organism, in virtue of its organization, has an
inherited groundwork of innate capacity. Surrounding circumstances and
commerce with the world draw out and develop the activities which the
innate capacity renders possible. First, there are automatic and reflex
actions, which are comparatively isolated activities in response to
definite stimuli, external or internal. Secondly, there are those
organized trains or sequences of co-ordinated activities which are
performed by the individual in common with all the members of the same
more or less restricted group, in adaptation to certain circumstances,
oft-recurring or essential to the continuance of the species. These are
the instinctive activities. But no hard-and-fast line can be drawn
between them and reflex actions. The instinctive activities may be
either perfect or relatively imperfect, according to the accuracy of
their adaptation to the purpose for which the activity is performed; but
in either case they are carried out without learning or practice. In
some cases, however, they cannot be performed until the organization is
more perfectly developed than it is at birth; but when the proper time
arrives they are perfect, and require no practice; these may be termed
"deferred instincts." Where some practice, but only a little, is
required, the instinctive activities may be regarded as incomplete; and
these pass into those activities which require at first a good deal of
practice, learning, and attention, but eventually run off smoothly and
without special attention, at times almost or quite unconsciously. These
are habitual activities. Finally, we have those activities which are
performed in special adaptation to special circumstances. These are
intelligent activities.
All of these may be, and the last, the intelligent actions, invariably
are, accompanied by consciousness. The habitual activities, and those
which are incompletely instinctive, are also, we may presume,
accompanied by consciousness during the process of their organization
and establishment. It is possible, however, that some of the perfectly
instinctive activities may be performed unconsciously. When we consider
how perfectly organized such activities are, and when we also remember
that perfectly organized habitual activities are frequently in us
unconscious, we shall see cause for suspecting that instinctive
activities may, at any rate in some cases, be unconscious. No doubt the
conditions of consciousness are not well understood. But let us accept
Mr. Romanes's suggestion, that a physiological concomitant is ganglionic
delay. "Now what," he asks,[IU] "does this greater consumption of time
imply? It clearly implies," he answers, "that the nervous mechanism
concerned has not been fully habituated to the performance of the
response required, and therefore that, instead of the stimulus merely
needing to touch the trigger of a ready-formed apparatus of response
(however complex this may be), it has to give rise in the nerve-centre
to a play of stimuli before the appropriate response is yielded. In the
higher planes of conscious life this play of stimuli in the presence of
difficult circumstances is known as indecision; but even in a simple act
of consciousness--such as signalling a perception--more time is required
by the cerebral hemispheres in supplying an appropriate response to a
non-habitual experience, than is required by the lower nerve-centres for
performing the most complicated of reflex actions by way of response to
their habitual experience. In the latter case the routes of nervous
discharge have been well worn by use; in the former case these routes
have to be determined by a complex play of forces amid the cells and
fibres of the cerebral hemispheres. And this complex play of forces,
which finds its physiological expression in a lengthening of the time of
latency, finds also a psychological expression in the rise of
consciousness." Now, since in many instinctive activities the stimulus
"merely needs to touch the trigger of a ready-formed apparatus of
response," I think that they _may_ be unconscious. And Mr. Romanes thus
himself supplies the reason for rejecting his own definition of instinct
as "reflex action into which there is imported the element of
consciousness." Of course, logically, Mr. Romanes can reply, "It is
merely a question of where we draw the line; if the activity is
unconscious, it is a reflex action; if conscious, it is an instinct." I
think this unsatisfactory, (1) because the criterion of consciousness,
from its purely inferential nature, is practically impossible of
application with accuracy; (2) because the same series of activities may
probably at one time be unconscious and at another time conscious; and
(3) because many actions which are almost universally regarded as reflex
actions may at times be accompanied by consciousness, and would then
have, on Mr. Romanes's view, to be regarded as instincts.
Having made this initial criticism, I may now state that I regard Mr.
Romanes's treatment of instinct as most admirable and masterly. Building
upon the foundation laid by Charles Darwin, he has worked out the theory
of instinct in a manner at once broad and yet minute, lucid and yet
close, definite in doctrine and yet not blind to difficulties. If I say
that it is a piece of work worthy of the great master whose devoted
disciple Mr. Romanes has proved himself, I am according it the highest
praise in my power. I have ventured in this volume to criticize some of
Mr. Romanes's conclusions in the field of animal intelligence. And lest
I should seem to undervalue his work, lest our few divergences should
seem to hide our many parallelisms, I take this opportunity of
testifying to my great and sincere admiration of the results of his
careful and exact observations, his patient and thoughtful inferences,
and his lucid and often luminous exposition.
I do not propose to go over the ground so exhaustively covered by Mr.
Romanes in his discussion of instinct. I shall first endeavour shortly
to set forth his conclusions, and then review the subject in the light
of modern views of heredity.
Admitting that some instincts may have arisen from the growth,
extension, and co-ordination of reflex actions, Mr. Romanes regards the
majority of instincts as of two-fold origin--first, from the natural
selection of fortuitous unintelligent activities which chanced to be
profitable to the agent (primary instincts); and, secondly, from the
inheritance of habitual activities intelligently acquired. These are the
secondary instincts, comprising activities which have become instinctive
through lapsed intelligence. In illustration of primary instincts, Mr.
Romanes cites the instinct of incubation. "It is quite impossible," he
says,[IV] "that any animal can ever have kept its eggs warm with the
intelligent purpose of hatching out their contents, so that we can only
suppose that the incubating instinct began by warm-blooded animals
showing that kind of attention to their eggs which we find to be
frequently shown by cold-blooded animals.... Those individuals which
most constantly cuddled or brooded over their eggs would, other things
equal, have been most successful in rearing progeny; and so the
incubating instinct would be developed without there ever having been
any intelligence in the matter."
Many of the instincts which exhibit what I have termed above "blind
prevision" must, it would seem, belong completely or in the main to this
class. The instincts of female insects, which lead them to anticipate by
blind prevision the wants of offspring they will never see; the
instincts of the caterpillars, which lead them to make provision for the
chrysalis or imago condition of which they can have no experience; the
instinct of a copepod crustacean, which lays its eggs in a brittle-star,
that they may therein develop, probably in the brood-sac, and may even
destroy the reproductive powers of the host for the future good of her
own offspring--these and many others would seem to have no basis in
individual experience.
In illustration of the second class of instincts, those due to lapsed
intelligence, Mr. Romanes cites the case of birds living on oceanic
islands, which at first show no fear of man, but which acquire in a few
generations an instinctive dread of him--for the wildness or tameness
may become truly instinctive. "If," says Dr. Rae,[IW] "the eggs of a
wild duck are placed with those of a tame one under a hen to be hatched,
the ducklings from the former, on the very day they leave the egg, will
immediately endeavour to hide themselves, or take to the water if there
is any water, should any person approach, whilst the young from the tame
duck's eggs will show little or no alarm, indicating in both cases a
clear instance of instinct or 'inherited memory.'"
It must not be supposed that these two modes of origin are mutually
exclusive, and that any particular instinct must belong either to the
one class or the other. On the contrary, many instincts have, as it
were, a double root--the principle of selection combining with that of
lapsing intelligence in the formation of a joint result. Intelligence
may thus give a new direction to a primary instinct, and, the
intelligent modification being inherited, what is practically a new
instinct may arise. Conversely, selection may tend to preserve those
individuals which perform some intelligent action, and may, therefore,
aid the lapsing of intelligence in establishing and stereotyping an
instinct.
Referring the reader to Mr. Romanes's work for the examples and
illustrations by which he enforces his views, we may now proceed to
consider the subject in the light of recently developed theories of
heredity.
We have seen that a school of biologists has arisen who deny the
inheritance of acquired characters. But Mr. Romanes's secondary
instincts depend upon the inheritance of habits intelligently acquired.
By the school of Professor Weismann, therefore (if we may so call it
without injustice to Mr. Francis Galton), secondary instincts, in so far
as any individual acquisition is concerned, are denied. Opposed to this
school are those who lay great stress on the inheritance of acquired
characters. Some of them seem driven to the opposite extreme in the
matter of instinct, and appear to hold that instincts are entirely (or
let us say almost entirely) due to lapsed intelligence. Professor Eimer,
of Tübingen, for example, says,[IX] "I describe as automatic actions
those which, originally performed consciously and voluntarily, in
consequence of frequent practice, come to be performed unconsciously and
involuntarily.... Such acquired automatic actions can be inherited.
Instinct is inherited faculty, especially is inherited habit." In his
discussion of the subject, Professor Eimer seems to make no express
allusion to primary instincts. And he regards at any rate some of those
which are classed by Mr. Romanes as primary, as due to lapsed
intelligence. "Every bird," he says,[IY] "must, from the first time it
hatches its eggs, draw the conclusion that young will also be produced
from the eggs which it lays afterwards, and this experience must have
been inherited as instinct." He says[IZ] that the infant takes the
breast and sucks "in accordance with its acquired and inherited
faculties." He believes[JA] that "the original progenitors of our
cuckoo, when they began to lay their eggs in other nests, acted by
reflection and with design." Regarding the mason-wasps and their allies,
which sting larvæ in the ganglia which govern muscular action, and thus
provide their young with paralyzed but living prey, he exclaims,[JB]
"What a wonderful contrivance! What calculation on the part of the
animal must have been necessary to discover it!" Of the storing
instincts of bees he remarks,[JC] "Selection cannot here have had much
influence, since the workers do not reproduce. In order to make these
favourable conditions constant, insight and reflection on the part of
the animals, and inheritance of these faculties, were necessary." And he
concludes,[JD] "Thus, according to the preceding considerations,
automatic action may be described as habitual voluntary action;
instinct, as inherited habitual voluntary action, or the capacity for
such action."
Professor Eimer would not probably deny the co-operation of natural
selection in the establishment of these instincts, but he throws it
altogether into the background. Now, such a view seems to me wholly
untenable. Many of the instincts of insects are performed only once in
the course of each individual life. Can it be supposed that the weaving
of a cocoon by the caterpillar is mainly a matter of lapsed
intelligence? Even if we credit the hen bird with the amount of
reflection supposed by Professor Eimer, can we grant to the ancestors of
the ichneumon fly such far-reaching observation and intelligence as
really to foresee (not by blind prevision, but through intelligent
foresight) the future development of the eggs which she lays in a
caterpillar? Are we to suppose that the instinctive action of the young
cuckoo, which, _the day after it is hatched_, will eject all the other
occupants of a hedge-accentor's nest,[JE] can have had its origin in
lapsed intelligence? If, because of their purposive character, we are to
regard such instincts as of intelligent origin, may we not be told that
through intelligent design the pike has beset its jaws, palate, and
gill-arches with innumerable teeth, all backwardly directed for the
purpose of holding its slippery prey; and the eagle has protected its
eye with a bony ring of sclerotic plates, like the holder of an
optician's watch-glass? If mimicry in form and colour is due to natural
selection, why not mimicry in habits and activities? If _structures_ of
a wonderfully purposive character have been evolved without the
intelligent co-operation of the organisms which possess them, why not
some of the highly purposive _activities_?
And here the disciple of the school of Professor Weismann will echo and
extend the question, and will say, "Yes! why not _all_ instinctive
activities? You are ready to admit," he will continue, "that many
instincts, wonderfully purposive in their nature, are of primary origin,
that is due to natural selection; why, then, invoke any other mode of
origin? If lapsed intelligence be excluded in these cases, why introduce
it at all? Why not admit, what our theory of heredity demands, that[JF]
'all instinct is entirely due to the operation of natural selection, and
has its foundation, not upon inherited experiences, but upon the
variations of the germ'?"
Professor Weismann's contention needs much more serious consideration
than that of Professor Eimer. I think there is force in the _à priori_
argument (as an _à priori_ argument) that since very complex instincts
are probably of primary origin, there is no _à priori_ necessity for the
introduction of the hypothesis of lapsed intelligence. Let me first
illustrate this further.
A certain beetle (_Sitaris_) lays its eggs at the entrance of the
galleries excavated by a kind of bee (_Anthophora_), each gallery
leading to a cell. The young larvæ are hatched as active little insects,
with six legs, two long antennæ, and four eyes, very different from the
larvæ of other beetles. They emerge from the egg in the autumn, and
remain in a sluggish condition till the spring. At that time (in April)
the drones of the bee emerge from the pupæ, and as they pass out through
the gallery the sitaris larvæ fasten upon them. There they remain till
the nuptial flight of the anthophora, when the larva passes from the
male to the female bee. Then again they await their chance. The moment
the bee lays an egg, the sitaris larva springs upon it. "Even while the
poor mother is carefully fastening up her cell, her mortal enemy is
beginning to devour her offspring; for the egg of the anthophora serves
not only as a raft, but as a repast. The honey, which is enough for
either, would be too little for both; and the sitaris, therefore, at its
first meal, relieves itself from its only rival. After eight days the
egg is consumed, and on the empty shell the sitaris undergoes its first
transformation, and makes its appearance in a very different form.... It
changes into a white, fleshy grub, so organized as to float on the
surface of the honey, with the mouth beneath and the spiracles above the
surface.... In this state it remains until the honey is consumed;"[JG]
and, after some further metamorphoses, develops into a perfect beetle in
August.
Now, it seems to me difficult to understand how, at any stage of this
long series of highly adaptive, instinctive activities, lapsed
intelligence can have been a factor. And therefore I say, if such a
complex series[JH] can have resulted from natural selection and
non-intelligent adaptation, I see no _à priori_ reason why any instinct,
no matter how complex, should not have had a like origin.
Let us, however, next consider whether Professor Weismann's theory of
the origin of instincts necessarily altogether excludes intelligence as
a co-operating factor. The essential point on which that theory is
absolutely insistent is that what is handed on through inheritance is
_an innate, and not an individually acquired, character_. Now, since
intelligent actions are characteristically individual, and performed in
special adaptation to special circumstances, it would seem, at first
sight, that the intelligent modification of an instinct could not, on
Professor Weismann's view, be handed on. Let us consider whether this
must be so.
Speaking of ants and bees, Darwin pointed out that their instincts could
not possibly have been acquired by inherited habit, since they are
performed by neuter insects, that is, by undeveloped females incapable
of laying eggs and continuing their race. For a habit to pass into an
instinct by inheritance, it is obviously necessary that the organism
which performs the habitual actions should be capable of producing
offspring by which these actions might be inherited. But in this case
the parental forms do not possess these instincts, while the neuter
insects which do possess them are sterile.
And how does Mr. Darwin meet this difficulty? "It is lessened, or, as I
believe, disappears," he says,[JI] "when it is remembered that selection
may be applied to the family as well as to the individual. Breeders of
cattle wish the flesh and fat to be well marbled together; an animal
thus characterized has been slaughtered, but the breeder has gone with
confidence to the same stock, and has succeeded. Such faith may be
placed in the power of selection, that a breed of cattle always yielding
oxen with extraordinarily long horns could, it is probable, be formed by
carefully watching which individual bulls and cows, when matched,
produced oxen with the longest horns; and yet no one ox would ever have
propagated his kind.... Hence we may conclude that slight modifications
of structure or of instinct, correlated with the sterile condition of
certain members of the community, have proved advantageous;
consequently, the fertile males and females have flourished, and
transmitted to their fertile offspring a tendency to produce sterile
members with the same modifications. This process must have been
repeated many times, until that prodigious amount of difference between
the fertile and sterile females of the same species has been produced
which we see in many social insects."
Now let us apply this illustration to the case of habits intelligently
acquired. Instead of the possession of long horns, suppose the
performance of some habitual action be observed in the oxen. Then, by
carefully watching which individual bulls and cows, when matched,
produced oxen which performed this intelligent habitual action, a breed
of cattle always yielding oxen which possessed this habit might, on
Darwin's principles, be produced. The intelligence of oxen might in this
way be enhanced. Such faith may be placed in the power of selection that
a breed of cattle always yielding oxen of marked intelligence could, it
is possible, be formed by carefully watching which individual bulls and
cows, when matched, produced the most intelligent oxen; and yet no ox
would ever have propagated its kind. Regarding, then, a nest of ants or
bees as a social community, mutually dependent on each other, and
subject to natural selection, that community would best escape
elimination in which the queen produced two sets of offspring--one set
in which the procreative faculty was predominant to the partial
exclusion of intelligence, and another in which intelligent activities
were predominant to the exclusion of propagation.
It is possible that I have weakened my case by introducing such a
difficult problem as the instincts of neuter insects. And I would beg
the reader to remember that this is only incidental. What I wish to
indicate is that among the many variations to which organisms are
subject, there are variations in their intelligent activities; that
these are of elimination value, those animals which conspicuously
possess them escaping elimination in its several modes; that those
survivors which thus escape elimination are likely to hand on, through
inheritance, that intelligence which enabled them to survive; that if,
throughout a series of generations, such intelligence be applied to some
definite end, nervous channels will tend to be definitely established,
and the intelligent activity will more and more readily become habitual;
that eventually, through the lapsing of intelligence, these habitual
activities may become so fixed and stereotyped as to become instinctive;
that intelligence has thus been a factor in the establishment of these
instinctive activities; that throughout the sequence there is no
inheritance of anything individually acquired, the intelligent
variations being throughout of germinal origin; and that, therefore, in
the origin of instincts, the co-operation of intelligence and the
lapsing of intelligence are not excluded on the principles advocated by
Professor Weismann.
What, then, is excluded? Any _individually acquired increment_, either
in the intelligence displayed or the stereotyping process. The subject
of instinct and of animal intelligence has not at present been
considered at any great length by Professor Weismann, but, judging by
the general tenor of his writings, I take it that what he demands is
definite proof that such individually acquired increment _is actually
inherited_.
As before indicated in the chapter on "Heredity," such proof it is, from
the nature of the case, almost impossible to produce. Suppose that we
find evidence of a gradually increasing application of intelligence to
some important life-activity, or a more and more defined stereotyping of
some incompletely habitual or instinctive action; how are we to prove
that the increment in either case is due to the inheritance of
individual acquisitions, not to the selection of favourable innate (that
is to say, germinal) variations? Such a hopeless task may at once be
abandoned.
Are we, then, to leave the question as insoluble? I think not. It is
still open to us to consider whether there are any cases in which the
inheritance of acquired modifications is a more probable hypothesis than
the selection of favourable germinal variations. Now, the acquisition of
an instinctive dread of man, and the loss of this instinctive timidity
under domestication, seem to be of this kind. And yet I doubt whether
the evidence on this head is _convincing_. For the loss of instinctive
timidity, Professor Weismann may invoke the aid of panmixia. But if
there is truth in what I have already urged on this head, panmixia will
not adequately account for the facts. On the other hand, he may contend
that the instinctive dread is not due to the inheritance of individually
acquired experience, but to the selection of the wilder birds and
animals through the persistent elimination of those which are tame. And
in support of this view, he may quote Darwin himself, who says,[JJ] "It
is surprising, considering the degree of persecution which they have
occasionally suffered during the last one or two centuries, that the
birds of the Falklands and Galapagos have not become wilder; it shows
that the fear of man is not soon acquired." It is questionable, however,
whether this persecution, admittedly occasional, can have much
elimination value. There is, however, the element of imitation and
instruction to be taken into account, and the difficulty of proving that
the timidity is really instinctive. It has frequently been observed that
birds become, after a while, quite fearless of trains. Here elimination
is practically excluded; but it has to be proved that this fearlessness
is truly instinctive. Professor Eimer says,[JK] "In my garden every
sparrow and every crow know me from afar because I persecute these
birds. Once, in the presence of a friend, I shot a crow from the roof of
my house, while the pigeons and starlings on the same roof, to the great
astonishment of my friend, to whom I had predicted it, remained
perfectly quiet. They had learned by frequent experience at what my gun
was aimed, and knew that it did not threaten them." There is nothing in
this interesting observation, however, to show that what the pigeons had
learnt had, by _inherited_ experience, become instinctive. And Professor
Weismann will not, in all probability, be prepared to accept as a
logical inference "that this instinct of fear, because it can be
dispelled by experience, must be founded on inherited, acquired
experience."[JL]
Fully admitting, then, that this is a matter of relative probability,
and that the observations and inferences in this matter are not by
themselves convincing, I still think that the balance of probability is
here on the side of some inheritance of experience. Take next such an
instinctive habit as that which dogs display of turning round in a
narrow circle ere they lie down. In its origin the instinct probably
arose with the object of preparing a couch in the long grass. Now, is
this habit of elimination value? Can we suppose that it arose through
the elimination of those ancestral animals which failed to perform this
habit? I find it difficult to accept this view, though it is just
possible that the animals which did this thereby escaped the observation
of their enemies. It is also possible that this originally was a merely
purposeless habit, a strange trick of manner, which has been inherited,
and rendered constant and fixed. Here again, however, I think the
balance of probability is that the habit was intelligently acquired and
inherited.
I have before drawn attention to the more or less incompletely
instinctive avoidance, by birds and lizards, of insects with warning
coloration. That the avoidance is not perfectly instinctive is shown by
the fact that young birds sometimes taste these caterpillars or insects.
But a very small basis of experience, often a single case, is sufficient
to establish the association. And in young chicks the avoidance of bees
and wasps seems to be perfectly instinctive. The effects on the young
birds, however, can hardly be of elimination value. Mr. Poulton offered
unpalatable insects "to animals from which all other food was withheld.
Under these circumstances, the insects were eaten, although often after
many attempts, and evidently with the most intense disgust."[JM] I have
caused bees to sting young chickens; the result was extreme discomfort,
but in no cases permanent injury or death. If, then, the instinct is not
of elimination value, that is to say, not such as to save the possessors
from elimination, how can it have been established by natural selection?
And if not due to natural selection, to what can it be due, save
inherited antipathy?
Natural selection is such a far-reaching and ubiquitous factor in
organic evolution, that it is not likely that many cases can be found in
which the play of elimination can be rigidly excluded. But there are not
a few in which elimination does not appear to be the most important
factor. Mr. G. L. Grant has recently observed that the sparrows near
Auckland, New Zealand, have taken to burrowing holes in sand-cliffs,
like the sand-martin. The cliff-swallow of the Eastern United States has
almost ceased to build nests in the cliffs, like its progenitors, and
now avails itself of the protection afforded by the eaves of houses. The
surviving beavers in Europe are said to have abandoned the instinct of
building huts and dams. The race being no longer sufficiently numerous
to live in communities, the survivors live in deep burrows. In Russian
Lapland, under the persecution of hunters, the reindeer are reported to
be abandoning the tundras, or open lichen-covered tracts, for the
forests. The kea (_Nestor notabilis_), a brush-tongued parrot of New
Zealand, which normally feeds on honey, fruits, and berries, has, since
the introduction of sheep, taken to a carnivorous diet. It is said to
have begun by pecking at the sheep-skins hung out to dry; subsequently
it began to attack living sheep; and now it has learnt to tear its way
down to the fat which surrounds the kidneys. This habit, far from being
the result of elimination, is rapidly leading to the elimination of the
bird that has so strangely adopted it.
Now, although in these cases elimination has, I think, been a quite
subordinate factor, I do not adduce them as convincing evidence that
acquired habits are hereditary. Instruction and imitation in each
successive generation may well have come into play. There is no proof
that they are even incompletely instinctive. But I think that these are
the kinds of activities, renewed and careful observations and, if
possible, experiments on which, may lead to more decisive results. It
would probably not be difficult to ascertain how far the carnivorous
habit of the kea has become hereditary, and how far it is performed in
the absence of instruction and without the possibility of imitation.
I confess that when I look round upon the varied habits of birds and
mammals, when I see the frigate bird robbing the fish-hawk of the prey
that it has captured from the sea, the bald-headed chimpanzee adopting a
diet of small birds, a _Semnopithecus_ in the Mergui Archipelago eating
crustacea and mollusca, and the koypu, a rodent, living on shell-fish;
when I consider the divergence of habits in almost every group of
organisms, the ground-pigeons, rock-pigeons, and wood-pigeons,
seed-eating pigeons and fruit-eating pigeons; the carrion-eating,
insect-eating, and fruit-eating crows; the aquatic and terrestrial
kingfishers, some living on fish, some on insects, some on reptiles;[JN]
the divergent habits of the ring-ousel and the water-ousel; and the
peculiar habits of blood-sucking bats;--when I see these and a thousand
other modifications and divergences of habit, I question whether the
theory that they have all arisen through the elimination of those forms
which failed to possess them may not be pushed too far; I am inclined to
believe that the inheritance of acquired modifications has been a
co-operating factor. It is not enough to say that these habits are all
useful to their several possessors. _It has to be shown that they are of
elimination value_--that their possession or non-possession has made all
the difference between survival and elimination.
On the whole, then, as the result of a careful consideration of the
subject of instinctive and habitual activities, and in accordance with
my general view of organic evolution as set forth in previous chapters,
I am disposed to accept the inheritance of individually acquired
modifications of habit as a working hypothesis. I do not think that
absolutely convincing evidence thereof can at present be produced. But
to the best of my judgment, the probabilities are in favour of the
inheritance of modifications of existing activities, due to
intelligence, instruction, and imitation; always provided that the
exercise of these modified activities is sufficiently frequent and
definite to give rise to habits in the individual.
I recognize three factors in the origin of instinctive activities--
1. Elimination through natural selection.
2. Selection through preferential mating.
3. The inheritance of individually acquired modifications.
Of these I consider the first quite incontrovertible; the second as
highly probable; and the third as probable in a less degree. In all
three, intelligence may or may not have been a factor. Some of the
habits which have survived elimination under the first factor may have
been originally intelligent, some of them from the first unintelligent.
Some of the love-antics (so called), which, through their tendency to
excite sexual appetence in the female, have been selected under the
second factor, may have had a basis in intelligence; many of them
probably have not. And though the great majority of individually
acquired modifications of habits have owed their origin to intelligent
direction, still it is conceivable that some of them have not. An animal
may have been forced by circumstances to modify its habits, without any
exercise of intelligence; and this modification, forced, through changed
conditions, upon all the members of a species, may, through inheritance,
have passed into the stereotyped condition of an instinct. Under each
factor, then, we have two several categories.
1. Elimination { _a._ of unintelligent activities.
{ _b._ of intelligent activities.
2. Selection { _a._ of unintelligent activities.
{ _b._ of intelligent activities.
3. Inheritance { _a._ of unintelligent activities.
{ _b._ of intelligent activities.
In all cases, however, where intelligence has been a co-operating
factor, this intelligence has lapsed so soon as the activity became
truly instinctive.
From the co-operation of the factors it is almost impossible to give
examples which shall illustrate the exclusive action of any one. The
following table must therefore be regarded as indicating the probable
predominance of the factor indicated:--
1. { _a._ Caterpillars spinning cocoons.
{ _b._ Instincts of social hymenoptera.
2. { _a._ Drumming of snipe.
{ _b._ Procedure of Queensland bower-bird.
3. { _a._ Ants forming nests in trees in flooded parts of Siam.
{ _b._ Instinctive fear of man.
In speaking of the instinct of caterpillars spinning cocoons as
unintelligent, I am regarding the final purpose of the activity.
Intelligence may very possibly have come into play in modifying the
details of procedure. In giving the drumming of snipe as an example of
unintelligent activities furthered by selection, I am assuming that it
has a sexual import, and that the activity correlated with a narrowing
of the tail-feathers was not, in its inception, intelligently performed
with the object of exciting sexual appetence in the hen. The case of the
ants of Siam is given by Mr. Romanes,[JO] on the authority of Lonbière,
who says "that in one part of that kingdom, which lies open to great
inundations, all the ants made their settlements upon trees; no ants'
nests are to be seen anywhere else." Now, this modification of habits
may have been the result of intelligence; or it may have been forced
upon the ants by circumstances. The floods drove them on to the trees;
the instinctive impulse to build a settlement was imperative; hence the
settlement had to be formed on the trees, because the ground was
flooded. The difficulty of ascertaining whether intelligence has or has
not been a factor is simply part of the inherent difficulty of
comparative psychology--a difficulty on which sufficient stress has
already been laid in an earlier chapter.
The great majority of the instinctive activities of animals have arisen
through a co-operation of the factors, and it is exceedingly difficult
in any individual case to assign to the factors their several values.
And here we must once more notice that the separation off of the
instinctive activities from the other activities of animals is merely a
matter of convenience in classification. In the living organism the
activities--automatic actions, reflex actions, incompletely and
perfectly established instincts, habits, and intelligent activities--are
unclassified and commingled. They are going on at the same time, shading
the one into the other, untrammelled by the limits imposed by a
scientific method of treatment.
Once more, too, we must notice that the activities of animals are
essentially the outcome and fulfilment of emotional states. When the
emotional sensibility is high, the resulting activities are varied and
vigorous. As we have before seen, this high state of emotional
sensibility is correlated with a highly charged and sensitive condition
of the organic explosives elaborated by the plasmogen of the cells.
After repose, and at certain periodic times, this state of exalted
sensibility is apt to occur. It is exemplified in the so-called instinct
of play, which manifests itself in varied activities in the early
morning, in early life, and in the returning warmth of spring--at such
times, in fact, as the life-tide is in full flood.
But perhaps the activities which result from a highly wrought state of
sensibility are best seen at the periodic return of sexual appetence or
impulse in animals of various grades of life and intelligence. Many
organisms, at certain periods of the year, and in presence of their
mates, are thrown into a perfect frenzy of sexual appetence. The
love-antics of birds have been so frequently described that I will
merely quote from Darwin[JP] Mr. Strange's account of the satin
bower-bird: "At times the male will chase the female all over the
aviary, then go to the bower, pick up a gay feather or a large leaf,
utter a curious kind of note, set all his feathers erect, run round the
bower, and become so excited that his eyes appear ready to start from
his head; he continues opening first one wing, and then the other,
uttering a low, whistling note, and, like the domestic cock, seems to be
picking up something from the ground, until at last the female goes
gently towards him." Instances might be quoted from almost all classes
of the animal kingdom. Many fish display "love-antics," for example, the
gay-suited, three-spine stickleback, whose excitement is apparently
intense. Newts display similar activities. Even the lowly snail makes
play with its love-darts (_spiculæ amoris_), practical tangible darts of
glistening carbonate of lime. Mr. George W. Peckham has recently
described[JQ] the extraordinary "love-dance" of a spider (_Saitis
pulex_). "On May 24 we found a mature female, and placed her in one of
the larger boxes; and the next day we put a male in with her. He saw her
as she stood perfectly still, twelve inches away; the glance seemed to
excite him, and he at once moved towards her; when some four inches from
her he stood still, and then began the most remarkable performances that
an amorous male could offer to an admiring female. She eyed him eagerly,
changing her position from time to time, so that he might be always in
view. He, raising his whole body on one side by straightening out the
legs, and lowering it on the other by folding the first two pairs of
legs up and under, leaned so far over as to be in danger of losing his
balance, which he only maintained by sidling rapidly towards the lowered
side. The palpus, too, on this side was turned back to correspond to the
direction of the legs nearest it. He moved in a semicircle for about two
inches, and then instantly reversed the position of the legs, and
circled in the opposite direction, gradually approaching nearer and
nearer to the female. Now she dashes towards him, while he, raising his
first pair of legs, extends them upward and forward as if to hold her
off, but withal slowly retreats. Again and again he circles from side to
side, she gazing towards him in a softer mood, evidently admiring the
grace of his antics. This is repeated until we have counted a hundred
and eleven circles made by the ardent little male. Now he approaches
nearer and nearer, and when almost within reach whirls madly around and
around her, she joining and whirling with him in a giddy maze. Again he
falls back and resumes his semicircular motions, with his body tilted
over; she, all excitement, lowers her head and raises her body, so that
it is almost vertical; both draw nearer; she moves slowly under him, he
crawling over her head, and the mating is accomplished."
It can scarcely be doubted that such antics, performed in presence of
the female and suggested at sight of her, serve to excite in the mate
sexual appetence. If so, it can, further, scarcely be doubted that there
are degrees of such excitement, that certain antics excite sexual
appetence in the female less fully or less rapidly than others; yet
others, perhaps, not at all. If so, again, it can hardly be questioned
that those antics which excite most fully or most rapidly sexual
appetence in the female will be perpetuated through the selection of the
male which performs them. This is sexual selection through preferential
mating. And, I think, the importance of these activities, their wide
range, and their perfectly, or at any rate incompletely instinctive
nature, justifies me in emphasizing this factor in the origin of
instinctive activities. It has hitherto, I think, not received the
attention it deserves in discussions of instinct.
A few more words may here be added to what has already been said on the
influence of intelligence on instinct. The influence may be twofold--it
may aid in making or in unmaking instincts. We have seen that instincts
may be modified through intelligent adaptation. A little dose of
judgment, as Huber phrased it, often comes into play. The cell-building
instinct of bees is one which is remarkably stereotyped; and yet it may
be modified in intelligent ways to meet special circumstances. When, for
example, honey-bees were forced to build their comb on the curve, the
cells on the convex side were made of a larger size than usual, while
those on the concave side were smaller than usual. Huber constrained his
bees to construct their combs from below upwards, and also horizontally,
and thus to deviate from their normal mode of building. The
nest-construction of birds, again, may be modified in accordance with
special circumstances. And, perhaps, it is scarcely too much to say
that, whenever intelligence comes on the scene, it may be employed in
modifying instinctive activities and giving them special direction.
Now, suppose the modifications are of various kinds and in various
directions, and that, associated with the instinctive activity, a
tendency to modify it _indefinitely_ be inherited. Under such
circumstances intelligence would have a tendency to break up and render
plastic a previously stereotyped instinct. For the instinctive character
of the activities is maintained through the constancy and uniformity of
their performance. But if the normal activities were thus caused to vary
in different directions in different individuals, the offspring arising
from the union of these differing individuals would not inherit the
instinct in the same purity. The instincts would be imperfect, and there
would be an inherited tendency to vary. And this, if continued, would
tend to convert what had been a stereotyped instinct into innate
capacity; that is, a general tendency to certain activities (mental or
bodily), the exact form and direction of which is not fixed, until by
training, from imitation or through the guidance of individual
intelligence, it became habitual. Thus it may be that it has come about
that man, with his enormous store of innate capacity, has so small a
number of stereotyped instincts.
But while intelligence, displayed under its higher form of originality,
may, in certain cases, lead to all-round variation, tending to undermine
instinct and render it less stereotyped, intelligence, under its lower
form of imitation, has the opposite tendency. For young animals are more
likely to imitate the habits of their own species than the foreign
habits of other species, and such imitation would therefore tend towards
uniformity.
Imitation is probably a by no means unimportant factor in the
development of habits and instincts. Mr. A. R. Wallace, in his
"Contributions to the Theory of Natural Selection," contends that the
nest-building habit in birds is, to a large extent, kept constant by
imitation. The instinctive motive is there, but the stereotyped form is
maintained through imitation of the structure of the nest in which the
builders were themselves reared. Mr. Weir, however, writing to Mr.
Darwin, in 1868, says in a letter, which Mr. Romanes quotes,[JR] "The
more I reflect on Mr. Wallace's theory, that birds learn to make their
nests because they have themselves been reared in one, the less inclined
do I feel to agree with him.... It is usual with canary-fanciers to take
out the nest constructed by the parent birds, and to place a felt nest
in its place, and, when the young are hatched and old enough to be
handled, to place a second clean nest, also of felt, in the box,
removing the other. This is done to prevent acari. But I never knew that
canaries so reared failed to make a nest when the breeding-time arrived.
I have, on the other hand, marvelled to see how like a wild bird's the
nests are constructed. It is customary to supply them with a small set
of materials, such as moss and hair. They use the moss for the
foundation, and line with the finer materials, just as a wild goldfinch
would do, although, making it in a box, the hair alone would be
sufficient for the purpose. I feel convinced nest-building is a true
instinct." On the other hand, Mr. Charles Dixon, quoted[JS] in Mr.
Wallace's "Darwinism," speaking of chaffinches which were taken to New
Zealand and turned out there, says, "The cup of the nest is small,
loosely put together, apparently lined with feathers, and the walls of
the structure are prolonged for about eighteen inches, and hang loosely
down the side of the supporting branch. The whole structure bears some
resemblance to the nests of the hang-birds (_Icteridæ_), with the
exception that the cavity is at the top. Clearly these New Zealand
chaffinches were at a loss for a design when fabricating their nest.
They had no standard to work by, no nests of their own kind to copy, no
older birds to give them any instruction, and the result is the abnormal
structure I have just described."
There is more evidence in favour of the view that the song of birds is,
in part at least, imitative. That it has an innate basis is certain; and
that it may be truly instinctive is shown by Mr. Couch's observation of
a goldfinch which had never heard the song of its own species, but which
sang the goldfinch-song, though tentatively and imperfectly. On the
other hand, imitation is undoubtedly a factor. The Hon. Daines
Barrington says (1773), "I have educated nestling linnets under the
three best singing larks--the skylark, woodlark, and titlark--every one
of which, instead of the linnet's song, adhered entirely to that of
their respective instructors. When the note of the titlark linnet was
thoroughly fixed, I hung the bird in a room with two common linnets for
a quarter of a year. They were in full song, but the titlark linnet
adhered steadfastly to that of the titlark." Mr. Wallace, who quotes
this, adds,[JT] "For young birds to acquire a new song correctly, they
must be taken out of hearing of their parents very soon, for in the
first three or four days they have already acquired some knowledge of
the parent's notes, which they afterwards imitate." Dureau de la Malle,
as quoted by Mr. Romanes,[JU] describes how he taught a starling the
"Marseillaise," and from this bird all the other starlings in a canton
to which he took it are stated to have learned the air!
That dogs, monkeys, and other mammalia have powers of imitation needs no
illustration. And when we remember that it is only the imitation of
strange and unusual actions that arrests our attention, while the
imitation of normal activities is likely to pass unnoticed, we may, I
think, fairly surmise that imitation is by no means an unimportant
factor in the acquisition and development of habits. And where the young
animal is surrounded during the early plastic and imitative period of
life by its own kith and kin, imitation will undoubtedly have a
conservative tendency.
The education of young animals by their parents has also a conservative
tendency. Mr. Spalding's observations show that the flight of birds is
instinctive; but the parent birds normally aid the development of the
instincts by instruction. Ants, as we have seen, are instructed in the
business of ant-life. Dogs and cats train their young. And Darwin tells
us, on the authority of Youatt,[JV] that lambs turned out without their
mothers are very liable to eat poisonous herbs.
We may say, then, with regard to the influence of intelligence on
instinctive activities, that it may lead them to vary along certain
definite lines of increased adaptation; that it may, in some cases, lead
them to vary along divergent lines, and hence tend to render stereotyped
instincts more plastic; and that, through imitation and instruction, it
may tend to render instinctive habits more uniform in a community, and
hence, if the habits are tending to vary under changed circumstances in
a given direction, may tend to draw the habits of all the members of the
community in that given direction.
And with regard to the more general question of the variation of habits
and instincts, we may say that, in addition to those variations in the
origin and direction of which intelligence is a factor, there are other
variations which take their origin without the influence of intelligence
under the stress of changing circumstances, and yet others which may
arise as we say "fortuitively" or "by chance," that is, from some cause
or causes whereof we are at present ignorant, and which do not appear to
be evoked directly by the stress of environing circumstances.
Granting, however, the existence of these variations in whatsoever way
arising, and granting the influence of natural selection, of sexual
selection, and perhaps of the inheritance of individually acquired
modifications, those variations which are for the good of the race or
species in which they occur will have a tendency to be perpetuated,
while those which are detrimental will be weeded out and will tend to
disappear.
Passing on now to consider the characteristics of those activities which
we term "intelligent," we may first notice what Mr. Charles Mercier, in
"The Nervous System and the Mind," calls the four criteria of
intelligence. Intelligence is manifested, he says, first, in the novelty
of the adjustments to external circumstances; secondly, in the
complexity; thirdly, in the precision; and fourthly, in dealing with the
circumstances in such a way as to extract from them the maximum of
benefit.
Now, I think it is clear that, when it is our object to distinguish
intelligent from instinctive activities, the precision of the adjustment
cannot be regarded as a criterion of intelligence. Many instinctive acts
are wonderfully precise. The sphex is said to stab the spider it desires
to paralyze with unerring aim in the central nerve-ganglion. Other
species, which paralyze crickets and caterpillars, pierce them in three
and nine places respectively, according to the number of the ganglia.
And yet this seems to be a purely instinctive action. So, too, to take
but one more example, there is surely no lack of precision in the
cell-making instinct of bees. We may say, then, that, granting that an
action is intelligent, the precision of the adjustment is a criterion of
the level of intelligence; but that, since there may be instinctive
actions of wonderful precision, this criterion is not distinctive of
intelligence. Nay, more, there are many reflex actions of marvellous
precision and accuracy of adjustment; and there can be no question of
intelligence, individual or ancestral, in many of these.
Nor can we regard prevision (which is sometimes advanced as a criterion
of intelligence) as specially distinctive of intelligent acts regarded
objectively in the study of the activities of animals. For, as we have
already seen, there are many instincts which display an astonishing
amount of what I ventured to term "blind prevision"--instance the
instinctive regard for the welfare of unborn offspring, and the
instinctive preparation for an unknown future state in the case of
insect larvæ.
Nor, again, is the complexity of the adjustment distinctive of
intelligence as opposed to instinct. The case of the sitaris, before
given, the larva of which attaches itself to a male bee, passes on to
the female, springs upon the eggs she lays, eats first the egg and then
the store of honey,--this case, I say, affords us a series of
sufficiently marked complexity. This instinct, the paralyzing, but not
killing outright, of prey by the sphex; the marvellous economy of wax in
the cell-building of the honey-bee; the affixing to their body, by
crabs, of seaweed (_Stenorhynchus_), of ascidians (an Australian
_Dromia_), of sponge (_Dromia vulgaris_), of the cloaklet anemone
(_Pagurus prideauxii_); and other cases too numerous for
citation;--these show, too, that the circumstances may be dealt with in
such a way as to extract from them the maximum of benefit, probably
without intelligence. It would be quite impossible intelligently to
improve upon the manner of dealing with the circumstances displayed in
many instinctive activities, even those which we have reason to believe
were evolved without the co-operation of intelligence.
There remain, therefore, the novelty of the adjustment and the
individuality displayed in these adjustments. And here we seem to have
the essential features of intelligent activities. The ability to perform
acts in special adaptation to special circumstances, the power of
exercising individual choice between contradictory promptings, and the
individuality or originality manifested in dealing with the complex
conditions of an ever-changing environment,--these seem to be the
distinctive features of intelligence. On the other hand, in instinctive
actions there seems to be no choice; the organism is impelled to their
performance through impulse, as by a stern necessity; they are so far
from novel that they are performed by every individual of the species,
and have been so performed by their ancestors for generations; and, in
performing the instinctive action, the animal seems to have no more
individuality or originality than a piece of adequately wound clockwork.
It may be said that, in granting to animals a power of individual
choice, we are attributing to them free-will; and surely (it may be
added), after denying to them reason, we cannot, in justice and in
logic, credit them with this, man's choicest gift. I shall not here
enter into the free-will controversy. I shall be content with defining
what I mean by saying that animals have a power of individual choice.
Two weather-cocks are placed on adjoining church pinnacles, two clouds
are floating across the sky, two empty bottles are drifting down a
stream. None of these has any power of individual choice. They are
completely at the mercy of external circumstances. On the other hand,
two dogs are trotting down the road, and come to a point of divergence;
one goes to the right hand, the other to the left hand. Here each
exercises a power of individual choice as to which way he shall go. Or,
again, my brother and I are out for a walk, and our father's dog is with
us. After a while we part, each to proceed on his own way. Pincher
stands irresolute. For a while the impulse to follow me and the impulse
to follow my brother are equal. Then the former impulse prevails, and he
bounds to my side. He has exercised a power of individual choice. If any
one likes to call this yielding to the stronger motive an exercise of
free-will, I, for one, shall not say him nay. What I wish specially to
notice about it is that we have here a sign of individuality. There is
no such individuality in inorganic clouds or empty bottles. Choice is a
symbol of individuality; and individuality is a sign of intelligence.
But though I decline here to enter into the free-will controversy, I may
fairly be asked where I place volition in the series between external
stimulus and resulting activity; and what I regard as the concomitant
physiological manifestation. I doubt whether I shall be able to say
anything very satisfactory in answer to these questions. I shall have to
content myself with little more than stating how the problem presents
itself to my mind.
I believe that volition is intimately bound up and associated with
inhibition. I go so far as to say that, without inhibition, volition
properly so called has no existence. When the series follows the
inevitable sequence--
Stimulus: perception: emotion: fulfilment in action
--the act is involuntary. And such it must ever have remained, had not
inhibition been evolved, had not an alternative been introduced, thus--
/fulfilment in action.
Stimulus: perception: emotion
\inhibition of action.
At the point of divergence I would place volition. Volition is the
faculty of the forked way. There are two possibilities--fulfilment in
action or inhibition. I can write or I can cease writing; I can strike
or I can forbear. And my poor little wounded terrier, whose gashed side
I was sewing up, clumsily, perhaps, but with all the gentleness and
tenderness I could command, could close his teeth on my hand or could
restrain the action.
I have here, so to speak, reduced the matter to its simplest expression.
It is really more complex. For volition involves an antagonism of
motives, one or more prompting to action, one or more prompting to
restraint. The organism yields to the strongest prompting, acts or
refrains from acting according as one motive or set of motives or the
other motive or set of motives prevails; in other words, according as
the stimuli to action or the inhibitory stimuli are the more powerful.
And then we must remember that the perceptual volition of animals
becomes in us the conceptual volition of man. An animal can choose, and
is probably conscious of choosing. This is its perceptual volition. Man
not only chooses, and is conscious of choosing, but can _reflect upon
his choice_; can see that, under different circumstances, his choice
would have been different; can even fancy that, under the same
circumstances (external and internal), his choice might have been
different. This is conceptual volition. Just as Spinoza said that desire
is appetence with consciousness of self; so may we say that the volition
of contemplative man is the volition of the brute with consciousness of
self. No animal has consciousness of self; that is to say, no animal can
reflect on its own conscious states, and submit them to analysis with
the formation of isolates. Self-consciousness involves a conception of
self, persistent amid change, and isolable in thought from its states.
It involves the isolation in thought of phenomena not isolable in
experience. We can think about the self as distinct from its conscious
states and the bodily organization; but they are no more separable in
experience than the rose is separable from its colour or its scent. Such
isolation is impossible to the brute. An animal is conscious of itself
as suffering, but the consciousness is perceptual. There is no
separation of the self as an entity distinct from the suffering which is
a mere accident thereof; no conception of a self which may suffer or not
suffer, may act or may not act, may be connected with the body or may
sever that connection. Just as there is a vast difference between the
perception of an object as here and not there, of an occurrence as now
and not then, of a touch as due to a solid body; and the conception of
space, time, and causation; so is there a vast difference between a
perception of an injury as happening to one's self, and a conception of
self as the actual or possible subject of painful consciousness. This
difference is clearly seen by Mr. Mivart, who therefore speaks of the
_consentience_ of brutes as opposed to the _consciousness_ of man.
Consciousness he regards as conceptual; consentience as perceptual.[JW]
And, as before stated, I should be disposed to accept his nomenclature,
were it not for its philosophical implications. For Mr. Mivart regards
the difference between consciousness and consentience as a difference
_in kind_, whereas I regard it as a generic difference. I believe that
consentience (perceptual consciousness) can pass and has passed into
consciousness (conceptual consciousness); but Mr. Mivart believes that
between the two there is a great gulf fixed, which no evolutionary
process could possibly bridge or span.
The perceptual volition of animals, then, is a state of consciousness
arising when, as the outcome of perception and emotion, motor-stimuli
prompting to activity conflict with inhibitory stimuli restraining from
activity. The animal chooses or yields to the stronger motive, and is
conscious of choosing. But it cannot reflect upon its choice, and bother
its head about free-will. This involves conceptual thought. When
physiologists have solved the problem of inhibition, they will be in a
position to consider that of volition. At present we cannot be said to
know much about it from the physiological standpoint.
Still, as before indicated, the fact of inhibition is unquestionable and
of the utmost importance. It has before been pointed out that through
inhibition, through the suppression or postponement of action, there has
been rendered possible that reverberation among the nervous processes in
the brain which is the physiological concomitant of æsthetic and
conceptual thought. We have just seen that, in association with
inhibition, the faculty of volition has been developed. And we may now
notice that the postponement or suppression of action is one of the
criteria of intelligent as opposed to instinctive or impulsive
activities. This is, however, subordinate to the criterion of novelty
and individuality.
Granting, then, that an action is shown to be intelligent from the
novelty of the adjustments involved, and from the individuality
displayed in dealing with complex circumstances (instinctive adjustments
being long-established and lacking in originality), we may say that the
level of intelligence is indicated by the complexity of the adjustments;
their precision; the rapidity with which they are made; the amount of
prevision they display; and in their being such as to extract from the
surrounding conditions the maximum of benefit.
* * * * *
Before closing this chapter, I will give a classification of involuntary
and voluntary activities:--
---------------------------------------------------------------------
| |Initiation. |Motive. |Result. |
---------------------------------------------------------------------
|A. Involuntary |Sense-stimulus |Unconscious |Automatic or|
| (automatic and | | reaction |reflex act |
| reflex) | | of nerve-centres |reflex act |
---------------------------------------------------------------------
|B. Involuntary |Percept |Impulse (perhaps |Involuntary |
| (habitual and |(perhaps |lapsed) |activity |
| instinctive) |lapsed) | | |
---------------------------------------------------------------------
|C. Voluntary |Percept |Appetence |Voluntary |
|(perceptual) | | |activity |
---------------------------------------------------------------------
|D. Voluntary |Concept |Desire |Conduct |
|(conceptual) | | | |
---------------------------------------------------------------------
In the involuntary acts classed as automatic and reflex, the initiation
and the result may be accompanied by consciousness, but the intermediate
mental link which answers to the motive in higher activities is, I
think, unconscious. In habitual and instinctive activities the
consciousness of the percept and the impulse may in some cases have
become evanescent, or, to use G. H. Lewes's phrase, have lapsed. In the
case of some instincts, originating by the natural selection of
unintelligent activities, the perceptual element may never have emerged,
and the initiation may have been a mere sense-stimulus.
The division of voluntary activities into perceptual and conceptual
follows on the principles adopted and developed in this work. As to the
terminology employed, I agree with Mr. S. Alexander[JX] that it is
convenient to reserve the terms "desire" and "conduct" for use in the
higher conceptual plane. Animals, I believe, are incapable of this
higher desire and this higher conduct. It only remains to note that it
is within the limits of the fourth class (of voluntary activities
initiated by concepts) that morality takes its origin. Morality is a
matter of ideals. Moral progress takes its origin in a state of
dissatisfaction with one's present moral condition, and of desire to
reach a higher standard. The man quite satisfied with himself has not
within him this mainspring of progress. The chief determinant of the
moral character of any individual is the _ideal self_ he keeps steadily
in view as the object of moral desire--the standard to be striven for,
but never actually attained.
NOTES
[IN] I use the term "incomplete," and not "imperfect," because Mr.
Romanes, in his admirable discussion of the subject, applies the
term "imperfect instinct" to cases where the instinct is not
perfectly adapted to the end in view (see "Mental Evolution in
Animals," p. 167).
[IO] _Macmillan's Magazine_, February, 1873. Professor Eimer, in his
"Organic Evolution" (English translation, p. 245), narrates
similar experiences.
[IP] Mr. W. Larden states, in _Nature_ (vol. xlii.), that his brother
extracted, from the oviduct of a Vivora de la Cruz snake in the
West Indies, two young snakelets six inches long. Both, though
thus from their mother's oviduct untimely ripped, threatened to
strike, and made the burring noise with the tail, characteristic
of the snake.
[IQ] Dr. McCook confirms the observation that the clearings are kept
clean, that the ant-rice alone is permitted to grow on them, and
that the produce of this crop is carefully harvested; but he
thinks that the ant-rice sows itself, and is not actually planted
by the ants (see Sir John Lubbock's "Scientific Lectures," 2nd
edit., p. 112).
[IR] The experiments, both of Sir John Lubbock and Mr. Romanes, show
that the homing instinct of bees is largely the result of
individual observation. Taken to the seashore at no great distance
from the hive, where the objects around them, however, were
unfamiliar (since the seashore is not the place where flowers and
nectar are to be found), the bees were nonplussed and lost their
way. Similarly, the migration of birds "is now," according to Mr.
Wallace, "well ascertained to be effected by means of vision, long
flights being made on bright moonlight nights, when the birds fly
very high, while on cloudy nights they fly low, and then often
lose their way" ("Darwinism," p. 442). This, of course, does not
explain the migratory instinct--the internal prompting to
migrate--but it indicates that the carrying out of the migratory
impulse is, in part at least, intelligent.
[IS] "Animal Intelligence," p. 59.
[IT] The American expression, "I guess," is often far truer to fact
than its English equivalent, "I think."
[IU] "Mental Evolution in Animals," pp. 73, 74.
[IV] "Mental Evolution in Animals," p. 177.
[IW] _Nature_, vol. xxviii. p. 271, quoted in "Mental Evolution in
Animals," footnote, p. 196.
[IX] "Organic Evolution," pp. 223, 224.
[IY] Ibid. p. 263.
[IZ] Ibid. p. 303.
[JA] Ibid. p. 258.
[JB] Ibid. p. 279.
[JC] Ibid. p. 276.
[JD] "Organic Evolution," p. 298. The late G. H. Lewes held somewhat
similar views.
[JE] See Mr. John Hancock, Natural History Transactions,
Northumberland, Durham, and Newcastle-on-Tyne, vol. viii. (1886);
and _Nature_, vol. xxxiii. p. 519.
[JF] Weismann, "On Heredity," p. 91.
[JG] M. Fabre, as interpreted by Sir John Lubbock, "Scientific
Lectures," 2nd edit., p. 45.
[JH] In further illustration of the fact that purposiveness and complex
adaptation of activities is no criterion of present or past
direction by intelligence, we may draw attention to the action of
the leucocytes, or white blood-corpuscles. Metchnikoff found that
in the water-flea (_Daphnia_), affected by spores of _Monospora
bicuspidata_, a kind of yeast which passes from the intestinal
canal into the body-cavity, the leucocytes attacked and devoured
the conidia. If a conidium were too much for one cell, a
plasmodium, or compound giant-cell, was formed to repel the
invader. The same thing occurs in anthrax, the bacilli being
attacked and devoured by the leucocytes. "If we summarize," says
Mr. Bland Sutton ("General Pathology," pp. 127, 128), "the story
of inflammation as we read it zoologically, it should be likened
to a battle. The leucocytes are the defending army, their roads
and lines of communication the blood-vessels. Every composite
organism maintains a certain proportion of leucocytes as
representing its standing army. When the body is invaded by
bacilli, bacteria, micrococci, chemical or other irritants,
information of the aggression is telegraphed by means of the
vaso-motor nerves, and leucocytes rush to the attack;
reinforcements and recruits are quickly formed to increase the
standing army, sometimes twenty, thirty, or forty times the normal
standard. In the conflict, cells die and often are eaten by their
companions; frequently the slaughter is so great that the tissue
becomes burdened by the dead bodies of the soldiers in the form of
pus, the activity of the cell being testified by the fact that its
protoplasm often contains bacilli, etc., in various stages of
destruction. These dead cells, like the corpses of soldiers who
fall in battle, later become hurtful to the organism they were in
their lifetime anxious to protect from harm, for they are fertile
sources of septicæmia and pyæmia--the pestilence and scourge so
much dreaded by operative surgeons." Now, if the leucocytes were
separate organisms, whose habits were being described, some might
suppose that they were actuated by intelligence, individual or
inherited. But in this case the activities are purely
physiological. The marshalling of the cells during the growth of
tissue (e.g. the antler of a stag before described) is of like
import. And Dr. Verworn has shown that when a (presumably weak)
electric current is passed through a drop of water containing
protozoa, they will, when the current is closed, flock towards the
negative pole, and when the current is opened will travel towards
the positive pole. The implication of all this is that vital
phenomena may be intensely purposive, and yet afford no evidence
or indication of the present or ancestral play of intelligence.
[JI] "Origin of Species," p. 230.
[JJ] See Appendix to Mr. Romanes's "Mental Evolution in Animals," p.
361.
[JK] "Organic Evolution," p. 227.
[JL] Ibid. p. 228.
[JM] "Colours of Animals," p. 180.
[JN] Wallace's "Darwinism," p. 109.
[JO] "Mental Evolution in Animals," p. 244.
[JP] "Descent of Man," pt. ii. chap. xiii.
[JQ] George W. and Elizabeth G. Peckham, "Occasional Papers of the
Natural History of Wisconsin," vol. i. (1889), p. 37.
[JR] "Mental Evolution in Animals," p. 226.
[JS] "Darwinism," p. 76, from _Nature_, vol. xxxi. p. 533.
[JT] "Contributions," etc., p. 222.
[JU] "Mental Evolution in Animals," p. 222.
[JV] "On Sheep," p. 404.
[JW] In the sense in which I have used the word; not as he uses it
himself.
[JX] "Moral Order and Progress."
CHAPTER XII.
MENTAL EVOLUTION.
The phrase "mental evolution" clearly implies the existence of somewhat
concerning which evolution can be predicated; and the adjective "mental"
further implies that this somewhat is that which we term "mind." What is
this mind which is said to be evolved? And out of what has it been
evolved? Can we say that matter, when it reaches the complexity of the
grey cortex of the brain, becomes at last self-conscious? May we say
that mind is evolved from matter, and that when the dance of molecules
reaches a certain intensity and intricacy consciousness is developed? I
conceive not.
"If a material element," says Mr. A. R. Wallace,[JY] "or a combination
of a thousand material elements in a molecule, are alike unconscious, it
is impossible for us to believe that the mere addition of one, two, or a
thousand other material elements to form a more complex molecule could
in any way tend to produce a self-conscious existence. The things are
radically distinct. To say that mind is a product or function of
protoplasm, or of its molecular changes, is to use words to which we can
attach no clear conception. You cannot have in the whole what does not
exist in any of the parts; and those who argue thus should put forth a
definite conception of matter, with clearly enunciated properties, and
show that the necessary result of a certain complex arrangement of the
elements or atoms of that matter will be the production of
self-consciousness. There is no escape from this dilemma--either all
matter is conscious, or consciousness is something distinct from matter;
and in the latter case, its presence in material forms is a proof of the
existence of conscious beings, outside of and independent of what we
term 'matter.'"
There is a central core of truth in Mr. Wallace's argument which I hold
to be beyond question, though I completely dissent from the conclusion
which he draws from it. I do not believe that the existence of conscious
beings, outside of and independent of what we term "matter," is a
tenable scientific hypothesis. In which case, Mr. Wallace will reply,
"You are driven on to the other horn of the dilemma, and must hold the
preposterous view that all matter is conscious."
Now, I venture to think that the use here of the word "conscious" is
prejudicial to the fair consideration of the view which I hold in common
with many others of far greater insight than I can lay claim to. And it
seems to me that we cannot fairly discuss this question without the
introduction of terms which, from their novelty, are devoid of the
inevitable implications associated with "mind" and "consciousness" and
their correlative adjectives. Such terms, therefore, I venture to
suggest, not with a view to their general acceptance, but to enable me
to set forth, without arousing at the outset antagonistic prejudice,
that hypothesis which alone, as it seems to me, meets the conditions of
the case.
According to the hypothesis that is known as _the monistic hypothesis_,
the so-called connection between the molecular changes in the brain and
the concomitant states of consciousness is assumed to be identity.
Professor Huxley suggested the term "neuroses" for the molecular changes
in the brain, and "psychoses" for the concomitant states of
consciousness. According to materialism, psychosis is a product of
neurosis; but according to monism, neither is psychosis a product of
neurosis, nor is neurosis a product of psychosis, but _neurosis is
psychosis_. They are identical. What an external observer might perceive
as a neurosis of my brain, I should at the same moment be feeling as a
psychosis. The neurosis is the outer or objective aspect; the psychosis
is the inner or subjective aspect.
It is almost impossible to illustrate this assumption by any physical
analogies. Perhaps the best is that of a curved surface. The convex side
is quite different from the concave side. But we cannot say that the
concavity is produced by the convexity, or that the convexity is caused
by the concavity. The convex and the concave are simply different
aspects of the same curved surface. So, too, are molecular brain-changes
(neuroses) and the concomitant states of consciousness (psychoses)
simply different aspects of the same waves on the troubled sea of being.
Again, we may liken the brain-changes to spoken or written words, and
the states of consciousness to the meaning which underlies them. The
spoken word is, from the physical point of view, a mere shudder of sound
in the air; but it is also, from the conceptual point of view, a
fragment of analytic thought.
Now, we believe that the particular kind of molecular motion which we
call neurosis, or brain-action, has been evolved. Evolved from what?
From other and simpler modes of molecular motion. Complex neuroses have
been evolved from less complex neuroses; these from simple neuroses;
these, again, from organic modes of motion which can no longer be called
neuroses at all; and these, once more, from modes of motion which can no
longer be called organic. And from what have psychoses, or states of
consciousness, been evolved? Complex psychoses have been evolved from
less complex psychoses; these from simple psychoses; these, again,
from--what? We are stopped for want of words to express our meaning. We
believe that psychoses have been evolved. Evolved from what? From other
and simpler modes of--something which answers on the subjective side to
motion. We can hardly say "of consciousness;" for consciousness answers
to a _particular_ mode of motion called neurosis. So that unless we are
prepared to say that all modes of motion are neuroses, we can hardly say
that all modes of that which answers on the subjective side to motion
are conscious. I shall venture, therefore, to coin a word[JZ] to meet my
present need.
It is generally admitted that physical phenomena, including those which
we call physiological, can be explained (or are explicable) in terms of
energy. It is also generally admitted that consciousness is something
distinct from, nay, belonging to a wholly different phenomenal order
from, energy. And it is further generally admitted that consciousness is
nevertheless in some way closely, if not indissolubly, associated with
special manifestations of energy in the nerve-centres of the brain. Now,
we call manifestations of energy "kinetic" manifestations, and we use
the term "kinesis" for physical manifestations of this order. Similarly,
we may call concomitant manifestations of the mental or conscious order
"metakinetic," and may use the term "metakinesis" for all manifestations
belonging to this phenomenal order. According to the monistic
hypothesis, _every mode of kinesis has its concomitant mode of
metakinesis, and when the kinetic manifestations assume the form of the
molecular processes in the human brain, the metakinetic manifestations
assume the form of human consciousness_. I am, therefore, not prepared
to accept the horn of Mr. Wallace's dilemma in the form in which he
states it. All matter is not conscious, because consciousness is the
metakinetic concomitant of a highly specialized order of kinesis. But
every kinesis has an associated metakinesis; and _parallel to the
evolution of organic and neural kinesis there has been an evolution of
metakinetic manifestations culminating in conscious thought_.
Paraphrasing the words of Professor Max Müller,[KA] I say, "Like
Descartes, like Spinoza, like Leibnitz, like Noiré, I require two orders
of phenomena only, but I define them differently, namely, as kinesis and
metakinesis. According to these two attributes of the noumenal,
philosophy has to do with two streams of evolution--the subjective and
the objective. Neither of them can be said to be prior.... The two
streams of evolution run parallel, or, more correctly, the two are one
stream, looked at from two opposite shores." And again,[KB] "Like Noiré,
I would go hand-in-hand with Spinoza, and carry away with me this
permanent truth, that metakinesis can never be the product of kinesis
(materialism), nor kinesis the product of metakinesis (spiritualism),
but that the two are inseparable, like two sides of one and the same
substance."
According to this view, the two distinct phenomenal orders, the kinetic
and the metakinetic, are distinct only as being different phenomenal
manifestations of the same noumenal series. Matter, the unknown
substance[KC] of kinetic manifestations, disappears as unnecessary;
spirit, the unknown substance of metakinetic manifestations, also
disappears; both are merged in the unknown substance of being--unknown,
that is to say, in itself and apart from its objective and subjective
manifestations.
It will, no doubt, be objected that the final identity of neuroses and
psychoses is an assumption. It is pure assumption, it will be said, that
these molecular nervous processes, and those percepts and emotions which
are their concomitants, are simply different aspects, outer and inner,
objective and subjective, physiological and psychological, of the same
noumenal series. This must fully and freely be admitted. Any and every
explanation of the connection of mind and body is based on an
assumption. The common-place view of two distinct entities, a mind which
can act on the body and a body which influences the mind, is a pure
assumption. The philosophic view, that there are two entities, body and
mind, that neither can act on the other, but that there is a
pre-established harmony between the activities of the one and the
activities of the other, is, again, a pure assumption. The materialistic
view, that matter becomes at last self-conscious, is a pure assumption.
The idealistic view, that the world of phenomena has no existence save
as a fiction of my own mind, is, once more, a pure assumption. It is not
a question of making or of not making an initial assumption; _that we
must do in any case_. The question is--Which assumption yields the most
consistent and harmonious results?
Again, an answer will, no doubt, be demanded by some people to the
question--_How_ does that which, objectively considered, is neurosis
become subjectively felt as psychosis? Is not the identification of
neurosis and psychosis a begging of the question, unless the _how_, the
_modus operandi_, is explained? If, in the latter query, by "begging the
question" the adoption of an initial assumption is meant, I have already
answered it in the affirmative. To the direct question--How does the
objective neurosis become conscious as a subjective psychosis?--while
freely admitting that I do not know, I enter the protest that it is
philosophically an illegitimate question; for an answer is impossible
without transcending consciousness. An illustration will, perhaps, make
my meaning clear. Suppose that a sentient being be enclosed within a
sphere of opaque but translucent ground glass, into the substance of
which there are wrought certain characters. Suppose that external to
this there is another similar but larger sphere, similarly inscribed,
and that a second sentient being is enclosed in the space between the
two spheres. By an attentive study of the two spheres, this second
sentient being arrives at the conclusion that the markings on the convex
surface of the inner sphere answer to the markings on the concave
surface of the outer sphere; and he is led to the conviction that what
_he_ sees as markings on the convex, the being within the sphere sees as
markings on the concave. He is, however, perplexed by the question--How
can this be? He is acquainted with a certain inner surface and a certain
outer surface. He is led to correlate the markings of the one with the
markings of the other. But the question how the two can have such
different aspects is beyond his solution. Puzzle as he may, he can never
solve it. It can only be solved (and how simple then the solution!) by a
being _outside both spheres_, who can see what the enclosed being,
"cabin'd, cribb'd, confined," could never see, namely, that the
characters were wrought in the translucent glass of the spheres. By
which parable, imperfect as it is, I would teach that we can never learn
how kinetic manifestations have a metakinetic aspect without getting
outside ourselves to view kinesis and metakinesis from an independent
standpoint. Or, in the words of Sir W. R. Hamilton,[KD] "How
consciousness in general is possible; and how, in particular, the
consciousness of self and the consciousness of something different from
self are possible ... these questions are equally unphilosophical, as
they suppose the possibility of a faculty exterior to consciousness and
conversant about its operations."
The only course open to us, then, in this difficult but important
problem is to make certain assumptions, and see how far a consistent
hypothesis may be based upon them. I make, therefore, the following
assumptions: First, that there is a noumenal system of "things in
themselves" of which all phenomena, whether kinetic or metakinetic, are
manifestations. Secondly, that whenever in the curve of noumenal
sequences kinetic manifestations (convexities) appear, there appear also
concomitant metakinetic manifestations (concavities). Thirdly, that when
kinetic manifestations assume the integrated and co-ordinated complexity
of the nerve-processes in certain ganglia of the human brain, the
metakinetic manifestations assume the integrated and co-ordinated
complexity of human consciousness. Fourthly, that what is called "mental
evolution" is the metakinetic aspect of what is called brain or
interneural evolution.
It would require far more space than I can here command to deal
adequately with these assumptions, and meet the objections which have
been and are likely to be raised against them. I must content myself
with drawing attention to one or two which seem at once obvious and yet
easily met.
It may be asked--What advantage has such a view over realistic
materialism? Why not assume that neural processes, when they reach a
certain complexity, give rise to or produce consciousness?
First of all, I think, the objection raised by Mr. Wallace, in the
passage before quoted, to materialism is unanswerable. Secondly,
realistic materialism ignores the fact that kinetic manifestations for
us human-folk are phenomena of consciousness. To this we will return
presently. Thirdly, realistic materialism, and any view which regards
the physical series as one which is independent of the psychical
accompaniments, and which regards consciousness as in any sense a
by-product of neural processes, are open to an objection which was
forcibly stated by the late Professor Herbert.[KE] "It is clearly
impossible," he says, "for those ... who teach that consciousness is [a
by-product and] never the cause of physical change, to dispute that the
actions, words and gestures of every individual of the human race would
have been exactly what they have been in the absence of mind; had mind
been wanting [had the by-product never emerged], the same empires would
have risen and fallen, the same battles would have been fought and won,
the same literature, the same masterpieces of painting and music would
have been produced, the same religious rites would have been performed,
and the same indications of friendship and affection given. To this
absurdity physical science [realistic materialism] stands committed." I
believe that Professor Herbert's argument, of which this passage is a
summary, is, as against realistic materialism, sound and unanswerable.
Finally, as Professor Max Müller has well observed,[KF] "Materialism may
in one sense be said to be a grammatical blunder; it is a misapplication
of a word which can be used in an oblique sense only, but which
materialists use in the nominative. In another sense it is a logical
blunder, because it rests on a confusion between the objective and the
subjective. Matter can never be a subject, it can never know, because
the name was framed to signify what is the object of our knowledge or
what can be known." Materialism, then, for more than one sufficient
reason, stands condemned.
It should be stated, however, that Professor Herbert seems to regard the
monistic view I am advocating as committed to the absurdity indicated in
the passage I have quoted. I am convinced that he was here in error.
Indeed, he seems to have failed to see the full bearing of the monistic
hypothesis; for while he combats it, he comes very near adopting it
himself. With this, however, I have no concern. I have only to show
that, on the assumptions above set down, we are not committed to the
"absurdity" of supposing that intelligence and consciousness have had no
influence on the course of events in organic evolution--that they have
only felt the inevitable sequence of physical phenomena without in any
way influencing it. According to the monistic hypothesis, kinesis and
metakinesis are co-ordinate. The physiologist may explain all the
activities of men and animals in terms of kinesis. The psychologist may
explain all the thoughts and emotions of man in terms of metakinesis.
They are studying the different phenomenal aspects of the same noumenal
sequences. It is just as absurd to say that kinetic manifestations would
have been the same in the absence of metakinesis, as to say that the
metakinetic manifestations, the thoughts and emotions, would have been
the same in the absence of kinesis. It is just as absurd to say that the
physical series would have been the same in the absence of mind, as to
say that the mental series would have been the same in the absence of
bodily organization. For on this view consciousness is no mere
by-product of neural processes, but is simply one aspect of them. You
cannot abstract (except in thought and by analysis) metakinesis from
kinesis; for when you have taken away the one, you have taken the other
also. To speak of the organic activities being conceivably the same in
the absence of consciousness, is like saying that the outer curve of a
soap-bubble would be the same in the absence of the inner curve.
Whatever hypothetical existences this statement may be true of, it
assuredly is not true of soap-bubbles.
To pass on from this point to another, it is possible--I trust not
probable, but still not impossible--that some one may say, "But how, on
this view, can perception be accounted for? Granted that in the neural
processes of the individual organism kinesis is accompanied by those
metakinetic manifestations which we term 'consciousness,' how will this
account for our perception of a distant object? Yonder scarlet geranium
is a centre of kinetic manifestations; it is fifty yards and more away.
How can I here, by any metakinetic process, perceive the kinesis that is
going on out there?"
For one who can ask this question, I have written the chapter on "Mental
Processes in Man," and have used the term "construct," in vain. In vain
have I endeavoured to explain that the seat of all mental processes is
somewhere within the brain; in vain have I indicated the nature of
localization and outward projection; in vain have I reiterated that the
object is a thing we construct through a (metakinetic) activity of the
mind; in vain have I insisted that our knowledge is merely _symbolic_ of
the noumenal existence; and perhaps in vain shall I again endeavour to
make my meaning clear.
When we say that we perceive an object, the mental process (perception)
is the metakinetic equivalent of certain kinetic changes among the
brain-molecules. The object, _as an object_ (as a phenomenon or
appearance), is there generated. As before stated, I assume the
existence of a noumenal system of which the noumenal existence,
symbolized as object, is a part. But what we term the object is a
certain phase of metakinesis accompanying certain kinetic
nerve-processes in the brain. In other words, phenomena are states of
consciousness, and cannot, for the percipient, be anything else.
"It comes to this, then," an idealist will interpose: "states of
consciousness are metakinetic; phenomena are states of consciousness;
therefore phenomena are metakinetic. Your kinesis vanishes, and you are
one with us, a pure idealist."
Before showing _wherein_ I am not a pure idealist, let me state _why_ I
am not. For the pure idealist, phenomena being states of consciousness,
_and nothing more_, the world around resolves itself into an individual
dream. Were I to hold this view, this pen which I hold, this table at
which I write, the spreading trees outside my window, my little sons
whose merry voices I can hear in the garden, my very body and limbs, all
are merely states of my own consciousness. This I am not prepared to
accept. Do what I will, I cannot believe that such an interpretation of
the facts is true.
For this reason I make my first assumption that there is a noumenal
system of things in themselves, of which all phenomena, whether kinetic
or metakinetic, are manifestations. I differ from the pure idealist in
that I believe that phenomena, besides being states of consciousness,
_have another, namely, a kinetic, aspect_. What are for me states of
consciousness are for you neural processes in my brain. These are,
again, for you states of consciousness; but still for some one else they
are kinetic processes. And an ordinary extraneous object, like this
table, is the phenomenal aspect to me of a noumenal existence; and since
that noumenal existence appears to you also in like phenomenal guise,
the table is an object for you as well as for me, and not only for us,
but for all sentient beings similarly constituted. The world we live in
is a world of phenomena; and it has a phenomenal reality every whit as
valid as the noumenal reality which underlies it. And that phenomenal
reality has two aspects--an inner aspect as metakinesis, and an outer
aspect as kinesis.
I must not here further develop the manner in which the hypothesis of
monism presents itself to my mind. I will only, before passing on to
consider mental or metakinetic evolution, draw passing attention to two
matters. We have seen that Professor Hering and Mr. Samuel Butler have
suggested "organic memory" as a conception useful for the comprehension
of embryonic reconstruction in development and other such matters (see
p. 62). On the hypothesis of monism, this may be regarded as a kinetic
manifestation of that which in memory rises to the metakinetic level of
consciousness.
The other matter is of far wider import. Monism affords a consistent and
comprehensible theory of the ego, or conscious self--that which endures
amid the flux and reflux of our conscious states. The ego, or self, is
that metakinetic unity which answers to, or is the inner aspect of, the
kinetic unity of the organism.[KG] Only here and there, in fleeting and
changing series, does the metakinesis rise to the level of
consciousness. But the metakinetic unity is as completely one,
indivisible, and enduring, as is the physical organism which is its
kinetic counterpart. No one questions that there is an enduring organism
of which certain visible activities are occasional manifestations; no
one who has adequately grasped the teachings of monism can question that
the enduring ego, of which certain states of consciousness are
occasional manifestations, is the metakinetic equivalent of the organic
kinesis. This solution of a problem which baffles alike materialists and
idealists is, as it seems to me, as satisfactory as it is simple.
And now let us pass on to consider the question of mental or metakinetic
evolution. What, on the principles above laid down, can we be said to
know or have learnt about it?
The inevitable isolation of the individual mind has long been
recognized. "Such is the nature of spirit, or that which acts," says
Bishop Berkeley, "that it cannot be itself perceived, but only by the
effects that it produceth." "Thinking things, as such," writes Kant,
"can never occur in the outward phenomena; we can have no outward
perception of their thoughts, consciousness, desires; for all this is
the domain of the inward sense." How comes it, then, that there is
nothing of which, practically speaking, we are more firmly convinced
than that our neighbours have each a consciousness more or less similar
to our own? Certain it is that no one can come into sensible contact
with his brother's personality and essential spirit. My brother's soul
can never stand to me in the relation of object. Subject he never can be
to any but himself. What, then, is he--his metakinetic self, not his
kinetic material body--to me? In Clifford's convenient phrase, he is an
eject. And what is an eject? An eject is a more or less modified image
of myself, that I see mirrored, as in a glass darkly, in the human-folk
around me. Into every human brother I breathe the spirit of this eject,
and he becomes henceforth to me a living soul. Or, if this mode of
presentation does not meet with approval, I will say that an eject is
that metakinetic unity I infer as identically associated with the
organic and kinetic unity of my brother's living body. And I base the
close metakinetic correspondence that I infer on the close kinetic
correspondence that I observe. But since the only form or kind of
metakinesis that I know is that of human self-conscious personality, it
is certain that the metakinetic eject is an image of myself; it is and
must be, in a word, anthropomorphic.
Too much stress can scarcely, I think, be laid on the human, nay, even
the individual, nature of the eject. All other-mind I am bound to think
of in terms of my own mind. The men and women I see around me are like
curved mirrors, in which I see an altered reflection of my own mental
features. By certain signs I may be able to infer in this or that human
mirror graces or imperfections that I lack. But throughout my survey of
human nature, every estimate of intellectual or moral elevation or
degradation that I form must ever be measured in terms of my own
subjective base-line. My conception of humanity must always be, not only
anthropomorphic, but idiomorphic.
Once more, let it be remembered that the metakinesis that rises to the
level of consciousness is that which forms the inner aspect of the
neural kinesis of my brain or yours. For each of us, then, that
metakinesis is the only possible metakinesis which we can know as such
and at first-hand. And for the pure idealist it is the only metakinesis
which he can know at all. Not so with us. We have assumed a noumenal
system of "things in themselves," of which all phenomena, whether
kinetic or metakinetic, are manifestations. We have assumed that kinesis
cannot emerge into the light of being without casting its inseparable
metakinetic shadow. We have assumed that when the kinetic manifestations
assume the integrated and co-ordinated complexity of nerve-processes in
certain ganglia of the human brain, the metakinetic manifestations
assume the integrated and co-ordinated complexity of human
consciousness. Human physiology is teaching us more clearly every day
that all human activities are, physically speaking, the outcome of
neural processes. Such neural processes are in us conscious. Therefore,
granting our assumptions, the conclusion that my neighbour is a
conscious self, just as I am, is not only legitimate, but (as we see
from the daily conduct of men) inevitable. In other words, certain
kinetic phenomena have for us inevitable metakinetic implications.
Now, when we pass from man to the lower animals, the metakinetic
implications become progressively less inevitable and less forcible as
the kinesis becomes more dissimilar from that which obtains in the human
organism. The only metakinesis that we know directly is our own human
consciousness. In terms of this we have to interpret all other forms of
metakinesis.
It is unnecessary to go over again the ground that has already been
covered in previous chapters, in which we have endeavoured to give some
account of what seem to us the legitimate inferences concerning the
mental processes in animals. The point on which I wish here to insist is
that, outside ourselves, we can only know metakinesis in and through its
correlative kinesis. Underlying kinetic evolution, we see that, on the
hypothesis of monism, there must have been metakinetic evolution. But of
this mental or metakinetic evolution we neither have nor can have
independent evidence. Such evolution is the inevitable monistic
corollary from kinetic evolution. More than this it is not and cannot
be. And only on the monistic hypothesis, as it seems to me, is it
admissible to believe in mental evolution,[KH] properly so called.
But does not, it may be asked, the hypothesis of monism, if carried to
its logical conclusion, involve the belief in a world-consciousness on
the one hand, and a crystal-consciousness on the other? If, according to
the hypothesis, every form of kinesis has also its metakinetic aspect,
"must we not maintain," in the words of Mr. J. A. Symonds, "that the
universe being in one rhythm, things less highly organized than man
possess consciousness in the degree of their descent, less acute than
man's? Must we not also surmise that ascending scales of existence, more
highly organized, of whom we are at present ignorant, are endowed with
consciousness superior to man's? Is it incredible that the globe on
which we live is vastly more conscious of itself than we are of
ourselves; and that the cells which compose our corporeal frame are
gifted with a separate consciousness of a simpler kind than ours?" To
such questions W. K. Clifford replied with an emphatic negative. "Unless
we can show," he said, as interpreted by Mr. Romanes,[KI] "in the
disposition of the heavenly bodies some morphological resemblance to the
structure of a human brain, we are precluded from rationally
entertaining any probability that self-conscious volition belongs to the
universe."
I conceive that both parties, opposed as they seem, are logically right;
and I venture to think that the terms I have suggested will help us
here. Mr. Symonds used the word "consciousness" to signify metakinesis
in general; Clifford used it to signify that particular kind of
metakinesis which in the human brain rises to the level of
consciousness. Not only is it not inconceivable, but it is a logical
necessity on the hypothesis of monism, that answering to the kinetic
rhythm of the universe there is a metakinetic rhythm; but unless the
gyrations of the spheres have some kinetic resemblance to the dance of
molecules in the human brain, the metakinesis cannot be inferred to be
similar to the consciousness of man.
Similarly, with regard to the supposed self-consciousness of the
so-called social organism. Mr. Romanes, in his article on "The World as
an Eject,"[KJ] leads up to his conception of a world-eject through the
conception of a society-eject--an eject, he tells us, that, for aught
that any one of its constituent personalities can prove to the contrary,
may possess self-conscious personality of the most vivid character. Its
constituent human minds may be born into it, and die out of it, as do
the constituent cells of the human body; it may feel the throes of war
and famine, rejoice in the comforts of peace and plenty; it may
appreciate the growth of civilization in its passage from childhood to
maturity.
This, of course, may be so; or it may not. Who can tell? But Clifford
was on firm monistic ground when he maintained that, unless the kinesis
be similar, we have no grounds for inferring similarity of metakinesis.
The study of kinesis leads us to recognize different kinds or modes of
its manifestation. There is one mode of kinesis in the circling of the
planets around the sun, another mode of kinesis in the orderly
evolutions of a great army, another mode in the throb of a great
printing-press; there is one mode of kinesis in the quivering molecules
of the intensely heated sun, another in the wire that flashes our
thought to America, and yet another in the molecular vibrations of the
human brain. All are of the same order, all are kinetic. But they differ
so widely in mode that each requires separate, patient, and
long-continued study. So is it, we may conclude, with metakinesis. There
may be, nay, there must be, many modes. But our knowledge is confined to
one mode--that in which the metakinesis assumes the form of human
consciousness.
I have been led to discuss this matter in order further to indicate the
inevitable limits of our knowledge of metakinetic evolution. Our
conclusions may be thus summarized: First, we can know directly only one
product of metakinetic evolution--that revealed in our own
consciousness. Secondly, the process of metakinetic evolution must be
reached, if reached at all, indirectly through a study of kinetic
evolution. Thirdly, we have no right to infer a mode of metakinesis
analogous to human consciousness, unless the mode of kinesis is
analogous to that which is observed in neural processes. And, fourthly,
the closer the kinetic resemblance we observe, the closer the
metakinetic resemblance we may infer.
* * * * *
The last point we have to notice, and it is by no means an unimportant
one, is that, just as the kinetic evolution of the organism must be
studied in reference to its kinetic environment, so, too, must the
metakinetic evolution of mind be studied in reference to its metakinetic
or mental environment.
Of course, in ordinary speech, and even in careful scientific
description, we are forced, if we would avoid pedantry, to skip
backwards and forwards from the kinetic to the metakinetic. We speak of
a kinetic cow giving rise to metakinetic fear, and this determining
certain kinetic activities. Why we thus interpose a mental link in a
physical series has already been explained. The physical cow we know,
the physical activities we know, the physical neuroses we scarcely know
at all. On the other hand, fear we have ourselves experienced, and know
well. Hence we introduce the mental link that we know in place of the
physical link of which we are ignorant. And there can be no harm in our
doing so when we are working on the practical, and not the philosophical
plane. But when we are striving to go deeper, and are employing that
gift of analysis which is man's prerogative, in order to proceed to a
higher and more complete synthesis,--then we must be careful to keep
separate those processes which analysis discloses to be distinct. And I
repeat that, on the philosophical plane of thought, we must remember
that _metakineses are determined by other metakineses, and by them
alone_.
The reader who has kept his head among these slippery places will at
once see that this is and must be so; for, as we have already seen (p.
474), all phenomena are states of consciousness, whatever else they may
also be. The cow, as a phenomenon, is a _construct_, a product of mental
activity, and woven out of states of consciousness. For the pure
idealist she is this and nothing more. But for us she is a real external
entity, manifested through phenomenal kineses. Hence in ordinary speech
we separate the kinetic cow from its metakinetic symbols in
consciousness (the convex from the concave aspect), and call the former
the cow itself, and the latter our idea of the cow. But, as before
maintained, my idea of an object is for me the object. And this is now
justified by our deeper analysis.
The physiologist, dealing with organic phenomena in terms of motion
(kinesis), proclaims that the physical series is complete, that there is
no necessity for the introduction of feeling which is at best but a
by-product. The idealist, dealing with the processes of thought and
emotion in terms of consciousness, proclaims that his series is
complete--an external material universe is an unnecessary encumbrance.
Each proclaims a half-truth; each sees that half of the truth which
alone is visible from his special standpoint. Monism combines the two
(and is, of course, scouted by both). It sees not only that the one
series does not in any case interfere with the other, but that the
conception of such an interference involves an impossibility and
incongruity. As soon could one speak of the convexities of one side of a
curved surface interfering with the corresponding concavities of the
other side, as of the metakinetic series interfering with the kinetic
series, which is its other aspect. But if the one cannot interfere with
the other, neither can the one exist without the other. To apply the
same analogy, as well might one speak of the convexities of a curved
surface existing without the concavities of its other side, as of the
kinetic phenomena of organic life as being conceivably the same in the
absence of conscious intelligence.
Remembering, then, that just as the environment of kinetic phenomena is
itself kinetic, with which consciousness can in no wise interfere, so is
the environment of metakinetic phenomena, perception, thought, and
emotion, itself metakinetic. Let us now proceed to consider some of the
implications.
We have already seen that, in what we may regard as the earlier phases
of organic and mental life, the series between stimulus and activity is
a simple one, which may be kinetically represented thus--
Stimulus-->neural processes-->motor-activities;
but that when inhibition is developed, there arises an alternative, thus--
/ motor-activities.
Stimulus-->neural processes
\ inhibition thereof.
And we further saw that, as a result of this inhibition, the entering
stimuli, instead of, as it were, rapidly running out of the organism in
motor-activities, set up a more and more complex series of diffused and
reverberating neural processes in the brain or other central ganglia.
From the metakinetic view-point these diffused and reverberating neural
processes in the brain culminate in consciousness as thought, æsthetic
emotion, and the higher conceptual mental activities. Deeply as these
influence conduct, they are, to a large extent, independent of conduct.
A man's thoughts and æsthetic yearnings may be of the truest and purest;
but in the moment of temptation and action, when stimuli crowding in run
through rapidly to action, he falls away. His conduct belies his ideals.
Nevertheless, the ideals were there, but too far away in the region of
thought and abstract æsthetics to be operative in action.
Now, we may divide the metakinetic concomitants of neural processes into
two categories: first, those which are intimately associated with neural
processes directly leading to motor-activities; secondly, those which
are, so to speak, floated off from these into the region of thought and
æsthetic emotion, and which are therefore associated with neural
processes only indirectly or remotely leading to motor-activities. Both
have, of course, kinetic equivalents in neural processes, but the former
are directly associated with activities and conduct, and the latter are
not.
Let me exemplify. Interpretations of nature, theories, hypotheses,
belong to the latter class. Their association with activities is in the
main indirect. Whether we believe in materialism, idealism, or monism,
our conduct is much the same. People got out of the way of falling
stones, and guarded against being caught by the incoming tide, before
science comprised both phenomena under the theory of gravitation. The
conduct of human-folk was not much altered by the replacement of the
geocentric by a heliocentric explanation of the solar system. It matters
not much how a man explains the lightning's flash so long as he avoids
being struck. The bird continues to soar quite irrespective of man's
prolonged discussion of how it can be explained on mechanical
principles. And in general the practical activities of mankind remain
much the same (I do not say quite the same, for there are remote and
indirect results of the greatest importance in the long run) whatever
their particular theory of the universe may be.
Now, let us note the implication. We have said a good deal in earlier
chapters about natural elimination and selection. To which category of
neural kineses do they apply--to those associated with practical
results; or to those associated with theoretical results (supposing
these to obtain below the level of man); or to both? Clearly to those
associated with practical results. It matters not what theories a lion,
or an adder, or a spider hold (supposing, again, that they are capable
of theorizing, which I doubt). Its practical activities determine
whether it survives or not. So, too, with men, _so far as they are
subject to natural elimination_. It matters not what may be the nature
of their thoughts, their æsthetic yearnings, their ideals. According to
their practical conduct, they are eliminated or escape elimination. In
other words, elimination or natural selection applies only remotely or
indirectly to the human race regarded as theorists, æsthetes, or
interpreters of nature.
Before proceeding to indicate to what laws our theories and
interpretations of nature and moral ideals are subject, we may note that
there are sundry activities of man, the outcome of his conceptual
thought and emotion, which are also, under the conditions of social
life, to a large extent beyond the pale of elimination. I refer to the
æsthetic activities--music, painting, sculpture, and the like; in a
word, the activities associated with art, literature, and pure science.
These, in the main, take rank alongside the ideas of which they are the
outward expression. Natural selection, which deals with practical,
life-preserving, and life-continuing activities, has little to say to
them. They are neutral variations which, so far as elimination is
concerned, are neither advantageous nor disadvantageous, and, therefore,
remain unmolested.
We may, therefore, fully agree with Mr. Wallace, when he says,[KK] "We
conclude, then, that the present gigantic development of the
mathematical faculty [as also of the musical and artistic faculties] is
wholly unexplained by the theory of natural selection, and must be due
to some altogether distinct cause." Nay, we may go further, and say that
it is only by misunderstanding the range of natural selection as an
eliminator that any one could suppose that these faculties could be
explained by that theory.
We must admit, then, that there are certain neural kineses which, from
the fact that they are unassociated with life-preserving and
life-continuing activities, are not subject to the law of elimination;
and in the development of which natural selection cannot have been an
essential factor. These, in their metakinetic aspect, are conceptual
thoughts, emotions, and ideas. Remembering the distinction drawn in the
chapter on "Organic Evolution" between _origin_ and _guidance_, let us
proceed to inquire, first, how these ideas have been guided to their
present development; and, secondly, how we may suppose these special
variations to have originated.
To understand their development, we must understand their environment.
The environment of metakineses is, as we have already seen, constituted
by other metakineses. What we have now to note is that the environment
of conceptual ideas, as such, is constituted by other ideas. The
immediate environment of an hypothesis is other hypotheses; of a moral
ideal, other moral ideals; of an æsthetic thought, other æsthetic
thoughts; of a religious conception, other religious conceptions. But
not only are ideas environed by ideas of their own order; they are
environed by ideas of other orders. Thus a scientific hypothesis or a
moral ideal may be in harmony or conflict with religious conceptions,
and its fate may be thereby determined; or a religious conception may be
in harmony or conflict with psychological principles, and its acceptance
or rejection thereby determined. So that we may say, in general, that
_the environment of an idea is the system of ideas among which it is
introduced_.
Of course, it must be clearly understood that it is with the individual
mind that we are dealing. The scientific ideas, moral ideals, æsthetic
standards, religious conceptions, of a tribe, nation, or other
community, are simply representative, either of the general views of the
majority of the individuals, or more frequently of a majority among a
cultivated minority. In any case, we have seen that metakineses are and
must be an individual matter. For each individual there is a separate
ideal world.
Through certain activities, notably language spoken or written, men can
symbolize to each other the ideas that are taking metakinetic shape in
their own minds. All-important, however, as is this power of
intercommunication by means of language, it does not a whit alter the
fact that the idea and its environment have to work out their relations
to each other separately in each individual mind. My neighbour may
symbolize, through language, his ideas in such a form that similar ideas
may be called up in my mind; but it is there that they have to make good
their claim for acceptance in the environment of the system of ideas
among which they are introduced.
Now, what is the guiding principle of the evolution and development of
ideas in the world of their metakinetic environment? Is there any
principle analogous to that of elimination which we have seen to be of
such high importance in organic evolution? I believe that there is. _An
idea is accepted or rejected according to its congruity or incongruity
with the system of ideas among which it is introduced._ The process has,
perhaps, closer analogy with elimination than with selection, inasmuch
as it would seem to proceed by the rejection of the incongruous, leaving
both the congruous and the neutral. An idea or hypothesis may be
accepted, at any rate provisionally, so long as it is not in
contradiction to the theories and beliefs already existing in the mind.
It may, however, be objected that this view is at variance with the
familiar observation that there are many excellent people who hold and
maintain theories which are exceedingly incongruous, which seem, indeed,
to us mutually antagonistic. Yes, _to us_. Brought into the environment
of _our_ system of ideas, one or other of these antagonistic views would
be eliminated through incongruity. Not so, however, with those who hold
both. Amid the environment of a less logical and less coherent system of
ideas, both can find admission, if not as congruous, still as neutral. A
sense of their incongruity is not aroused.
But there are some people, it may be said, who consciously hold views
which they admit to be incongruous; who base all their scientific
reasonings on a continuity of causation, but who, nevertheless, believe
in miraculous interruptions of that continuity. In this case, however,
the incongruity is made congruous in a higher synthesis. They belie
themselves when they suppose that they are holding incongruous views.
Stated at length, what they admit is that miraculous interventions are
incongruous, not for them, but for those whose whole system of thought
is cast in another mould than theirs--for the materialist and the
infidel.
I cannot discuss the matter further here. This is not the place to show,
or attempt to show, how the evolution of systems of thought has caused,
or is causing, certain ideas, such as that of slavery, religious
persecution, the moral and physical degradation of our poor, to reach
that degree of incongruity which we signify as abhorrent; or how that
evolution has caused yet more primitive ideas to seem positively
repulsive. Nor is it the place to show, or attempt to show, how the
advance of scientific knowledge has been constantly accompanied by the
elimination of incongruous conceptions. I must content myself with the
brief indication I have given of the principle of elimination through
incongruity as applied to ideas.
It may be said that such a principle does not account for the origin of
the new congruous ideas, but only for the getting rid of old incongruous
ideas. Quite true. But I have grievously failed in my exposition of
natural selection through elimination if I have not made it evident that
this objection (if that can be called an objection which, in truth, is
none) lies also at the door of Darwin's generalization.[KL]
Now, from all that has been said in this chapter, it will be seen that,
on the hypothesis of monism, we cannot regard organic and mental
evolution as continuous the one into the other, but rather as parallel
the one with the other--as the kinetic and metakinetic manifestations of
the same process. Organic evolution is a matter of structure and
activity. If the structure or the activity be not attuned to the
environing conditions, it will be eliminated, those sufficiently well
attuned surviving. Turning to the metakinetic aspect, we have seen that
there are certain mental processes which are directly and closely
associated with activities. Their evolution will be intimately
associated with organic evolution. For if these processes lead to
ill-attuned activities, the organism will be eliminated; and thus the
evolution of well-attuned activities and their corresponding mental
states will proceed side by side. We may, therefore, say, not
incorrectly, that these lower phases of mental evolution are subject to
the law of natural selection.
But when the neural processes which intervene between stimulus and
activity become more complex and more roundabout; when, instead of being
directly and closely associated with life-preserving activities, they
are associated indirectly and remotely;--then they become, step by step,
removed from their subjection to natural selection. And when, in man,
the metakineses associated with these neural kineses assume the form of
hypotheses, theories, interpretations of nature, moral ideals, and
religious conceptions, these are, except in so far as they lead to
activities which may conduce to elimination, no longer subject to the
law of natural selection, unless we use this term in a somewhat
metaphorical, or at least extended, sense. They are subject, as we have
seen, to a new process of elimination through incongruity.
Similarly with that wide range of conduct in man which is the outcome of
his conceptual life, and is removed from those merely life-preserving
activities which are still, to some extent, under the influence of
natural elimination. Conduct is here modified in accordance with the
conceptual system of which it is the outcome and outward expression. And
this higher conduct is subject, not to elimination through natural
selection, but to elimination through incongruity. Slavery would never
have been abolished through natural selection; by this means the modest
behaviour of a chaste woman could not have been developed. To natural
selection neither the Factory Acts nor the artistic products in this
year's Academy were due; by this process were determined neither the
conduct of John Howard nor that of Florence Nightingale. Some
evolutionists have done no little injury to the cause they have at heart
by vainly attempting to defend the untenable position that natural
selection has been a prime factor in the higher phases of human conduct.
I believe that natural selection has had little or nothing to do with
them as such. They are the outcome of conceptual ideas, and are subject
to the same process of elimination through incongruity.
So soon as, in the course of mental evolution, the idea of slavery
became incongruous, and in certain minds abhorrent and repulsive, steps
were taken to check the conduct which was the outward expression of this
idea. So, too, in other cases. The reformer must not, however, be too
far in advance of his generation, if his reform is to be practically
carried out. When his ideas are so "advanced" as to be incongruous with
those of all but a very small minority of his contemporaries, even they
are forced to confess that the nation is not yet ripe for the changes
they contemplate.
No one will question that artistic products are the outcome of artistic
ideas. In the slow and difficult progress of a new school of painting or
of music, we see exemplified the rejection of the new ideas through
their incongruity with the old-fashioned artistic systems. Only
gradually do there grow up new generations for whom these new ideas are
not incongruous. For them the old-fashioned systems become incongruous;
and if the school becomes dominant, artistic products embodying the old
ideas are eliminated through incongruity.
We are not all alike. Our mental systems are different. One artist will
introduce into his canvas effects which, to the eye of another, will at
once strike a jarring note of incongruity. To some minds the institution
of slavery presents no incongruity. There are not wanting men for whom
the degrading moral and physical conditions under which many of our poor
are forced to live and work present little or no incongruity. To the
Russian, English fidelity to the marriage vow is said to be as
incongruous as, to an English woman, is the harem of an Eastern
potentate.
In the higher phases of human conduct, then, the activities are subject
to the law of the ideas of which they are the outcome--the law of
elimination through incongruity.
I have said that natural selection has little or nothing to do with
these higher phases of conduct. But has not human selection through
preferential mating? I believe that it has; and I trust that it will
have a still greater influence in the future. It is one of the noblest
privileges of woman, for with her mainly lies the choice, that she may
aid in raising humanity to a higher level. If once the idea of marrying
for anything but pure affection could become utterly incongruous to
woman's mental nature; and if once the idea of perpetuating any form of
moral, intellectual, or physical deformity could become equally
incongruous; the bettering of humanity, through the exclusion of the
deformed in body and mind from any share in its continuance must
inevitably follow. Here, again, ideas would determine conduct.
And what, we may now proceed to ask, is the physiological or kinetic
aspect of this metakinetic process? The answer to this question involves
the conception of what I would term "interneural evolution." Just as the
environment of a conceptual idea is constituted by other conceptual
ideas, so is the environment of its neural concomitant constituted by
the other neural processes in the brain. Just as no idea can get itself
accepted if it be in incongruity with the system of ideas among which it
is introduced, so, too, can no neural process become established if it
be not in harmony with the other neural processes of the cerebral
hemispheres. The brain is a microcosm; its neural processes are
interrelated; and _the environment of any neural process is constituted
by other neural processes_.
A little consideration will show that this must be so; that it is only
the physical or kinetic aspect of what is freely admitted when the
mental or metakinetic aspect is under consideration. If it be admitted
that states of consciousness are determined by other states of
consciousness, and that states of consciousness are the concomitants of
certain neural processes in the brain, it follows as a logical necessity
that brain-neuroses, however originating, are determined in their
evolution by other brain-neuroses; and that there has been a brain or
interneural evolution, distinct from and yet intimately associated with
the evolution of other bodily structures and activities. The more
closely and directly brain-neuroses are associated with immediate
activities, the more closely implicated is interneural evolution in the
process of organic elimination through natural selection. But when long
trains of neuroses take place in only remote and distant connection with
other bodily activities, they are removed from the process of
elimination through natural selection, and interneural evolution is
allowed to proceed comparatively untrammelled.
I have already indicated my belief that abstraction (isolation),
analysis, and conceptual ideas have been rendered possible through
language, and are excellences unto which the lower animals do not
attain. Hence I regard this comparatively untrammelled phase of
interneural evolution as something essentially human, something which
differentiates man from brute. And I would correlate man's greatly
developed brain--inexplicable, I think, by natural selection alone--with
this later and special phase of interneural evolution. Even in the
lowest savage this brain-evolution has proceeded a long way. I am not
fitted in this matter to offer an opinion which would carry much weight.
But from all that I have read I gather that savages have in all cases
elaborated a complex--often a highly complex--interpretation of nature
and theory of things. The interpretation may seem _bizarre_ and
incongruous enough _to us_, full of fetishism and strange superstitions,
but it is an interpretation; to the savage it presents no incongruity;
to him the incongruity is in the oddly assorted beliefs of the
missionary. His system of ideas is, in fact, one of the many possible
systems to which mental evolution may give rise.
For what we call systems of thoughts, interpretations of nature,
theories of things, are so many genera and species which have resulted
from this later phase of metakinetic evolution. Our methods are at
present too coarse, our powers too limited, to enable us to determine
these species from their kinetic aspect. The brains of Kaffir and Boer,
of ploughboy and merchant, of materialist and idealist, are too subtly
wrought to enable us to trace the systems of kineses which were the
concomitants of their scheme of beliefs. But we can learn something of
the genera and species from their metakinetic aspect as symbolized
through language and other bodily activities. They fall into certain
groups, fetishistic, spiritualistic, materialistic, idealistic,
monistic, and so on, and within these groups there are sub-divisions.
This is not the place to consider them or discuss their characteristics.
What I wish to note about them is that, diverse as they seem and are,
each is a coherent product of mental evolution. In each, all that is
incongruous to itself has been or is being eliminated.
There are some people, however, who are surprised at the incongruity of
interpretations of nature among each other. Fetishism, they say, has
been proved to be utterly false. It constitutes a hideous and grotesque
delirium. How can that which is utterly and completely false to nature
have had a natural evolution? Now, for the _élite_ of the Aryan race,
whose systems of ideas have been moulded in accordance with the
conceptions of modern science, no doubt the fetishism of the poor savage
seems sufficiently incongruous and grotesque. So, too, does the system
of ideas of the Right Rev. Bishop of ---- appear no doubt, to the
learned and eminent Professor ----, and _vice versâ_. And so, too, no
doubt, does the system of ideas of the white man (who introduces
firearms and firewater, and preaches the gospel of forgiveness and
temperance) appear to the poor savage. Each in his degree wonders how
this falsity, this incongruity, can have had a natural genesis. But in
each case the falsity and the incongruity is not within the system
itself, but between different systems.
Once more, I repeat that if the individual nature of the systems of
ideas be not adequately grasped, the nature of mental evolution will not
be apprehended. States of consciousness can only be determined by other
states of consciousness; and states of consciousness are for the
individual subject, and for him alone. Conceptual ideas are states of
consciousness; and "falsity to nature" means, and can only mean,
incongruity with the environing states of consciousness in the
individual mind. For the savage there is no falsity to nature in his
fetishism. The idea presents no incongruity with his system of ideas; no
more incongruity than filed teeth, flattened head, or pierced nose do to
his standard of beauty. It is with _our_ system of ideas (i.e. mine or
yours) that his fetishism is false and incongruous. The falsity or
incongruity, I repeat, is not within the system itself, but between
different systems.
It may still, however, be said--Only one interpretation of nature can be
true; all others must be false. And the falsity is not merely
incongruity with other ideas in other systems of thought or belief; it
is falsity to the plain and obvious facts of nature.
We may freely admit that only one interpretation of nature can be true.
But who is to determine which? Who can decide the question between
monist and materialist? Who dare arbitrate between the bishop and the
professor? The criterion of fitness in this case, as in others, is
survival; and who can say what existing interpretation of nature (if
any) shall outlive all its competitors? Who can say what will be the
nature of the further evolution of any existing philosophical creed? The
elimination of the false is a slow and gradual process; and many
degenerate systems of ideas may linger on in the darker corners of the
world of men. False or out of harmony as they seem to be with the higher
phases of development; false or out of harmony as they would be with a
different and more exalted environment; they are not false or out of
harmony with the environment in the midst of which we find them; they
are not false or out of harmony with "the plain and obvious facts of
nature," as these exist for the ill-developed or savage mind.
The plain and obvious facts of nature, as interpreted by men of science
in 1890, have simply no existence for the untutored or the savage
intellect. For him they have not emerged into the light of
consciousness. But while we cannot blame the savage for entertaining
ideas which are false to facts which for him have no existence, we may
none the less believe that his system of ideas is not among those which
are destined to become predominant species. So far as we can judge, the
winning species among systems of ideas and interpretations of nature are
those in which the greatest number of ideas are fused into harmonious
synthesis; in which all the ideas are congruous, few or none neutral;
and in which the abstract or conceptual ideas, when brought into contact
with concrete or perceptual states of consciousness, are found to be in
harmony and congruity therewith.
There is one more question in this connection on which I must say a few
words. How, it may be asked, has the world become peopled, for many
primitive and savage folk, with a crowd of immaterial spiritual
essences, so that it is scarcely too much to say that, for some of these
peoples, everything has its double; and there is no material existence
that has not its spiritual counterpart?
I would connect this almost universal tendency with the origin of
abstract ideas (isolates) through language. When the named predominant
gave rise to the isolate (see p. 374), it could scarcely fail that the
primitive speakers and thinkers should tend to regard those qualities or
properties which they could isolate in thought (conceptually) as also
isolable in fact (perceptually). And we may well suppose, though this
is, of course, hypothetical, that one of the earliest severances to be
thus effected through isolation was the severance of mind and body. The
first phenomena that the nascent reason would endeavour to explain would
probably be those of daily life and almost hourly experience. Many
familiar facts would seem to point to the temporary or permanent divorce
of the part which is conscious and feels, from the part which is
tangible and visible. During wakeful life the two are closely
associated. The visible part, or body, is conscious. But during sleep,
or under the influence of a heavy blow, the visible part, which before
was conscious, is conscious no longer. The conscious part is, therefore,
absent, but returns again after a while. On death the conscious part
returns no more. The divorce of the two has become permanent.
And then comes in the confirmatory testimony of dreams. In dreams the
savage has seen his enemy, though that enemy's body was far away. Here,
then, is the spirit which has left the body during sleep. In dreams also
the slain enemy or the dead chief appears. The spirit, permanently
divorced from the body, still walks the earth in spirit-guise.
Many occurrences would seem like the fulfilled threats of dead enemies
or the fulfilled promises of dead ancestors. How can these be explained?
Are they not produced by the ghost of the departed enemy, by the spirit
of the deceased ancestor? And if these spirits are still powerful to
act, why not petition them to act in certain ways?
Probably primitive man would explain all activities anthropomorphically.
What knows he of gravitation or the laws of the winds? He knows himself
as agent, and attributes his activities to the immaterial spirit within
him; for when this is absent during sleep or in death these activities
cease. All acting things might, therefore, come to be regarded as dual
in their nature--possessed of a sensible material bodily part, and an
insensible active spiritual part. And thus the whole world might be
peopled with living existences of the spiritual order.
Now, whether the fetishistic faith arose in some such way as this or
not--and we can never know how it arose, but can only guess--there would
be nothing in such primitive explanations which would violate the law of
congruity. They would have, therefore, a perfectly natural genesis. The
attempted interpolation at such a stage of primitive reason of any
modern scientific conception would be futile. It would at once be
rejected through incongruity.
The history of scientific conceptions seems to show that they were first
adopted with regard to phenomena on the very horizon of thought--in
regions, that is to say, most remote from the central citadel of the
soul. Only gradually have they, little by little, encroached upon this
centre; and the application of them to physiology and psychology is a
matter of quite modern times. Even to-day only a minority, but an
increasing minority, of thinkers are prepared indissolubly to unite the
mind and body, so long divorced in thought, so completely united, as
many of us believe, in their essential being.
I have now, I trust, illustrated at sufficient length the principle of
elimination through incongruity in interneural and its associated
metakinetic or mental evolution. This, however, like natural selection,
is a matter of guidance; we have still to consider the question of
origin.
In truth, we know too little on the subject to enable us to discuss it
with much profit. From the kinetic or organic point of view, neural
variations take their place among the other variations, the origin of
which, as we have already found, is so hard to account for. There may be
a tendency for neural vibrations to mutually influence each other (like
two clocks placed side by side), and thus gradually to drag each other
into one harmonious and congruous rhythm. But this, though not
improbable, is purely hypothetical. There is the hypothesis of the
inheritance of acquired variations, the increased congruity acquired by
the parent being in some degree transmitted to the offspring. There is
the view which Mr. Wallace adopts[KM] with regard to the origin of
accessory plumes, that such variations may be due to "a surplus of
strength, vitality, and growth-power, which is able to expend itself in
this way without injury," and not without profit. The development of the
social habit, the mutual aid and protection thus afforded, may well have
left a balance of the life-energy, previously employed in individual
self-preservation, available for this purpose. And then there is always
the hypothesis of favourable fortuitous variations to fall back upon.
On only one of these points do I propose to say a few words--that of the
possible inheritance of acquired variations.
Let us restate the problem here for the sake of clearness. There is,
according to the suggestion put forward in this chapter, an interneural
evolution, leading to an harmonious development of the neuroses in the
individual brain. But this special evolution of the brain is nowise
independent of the more general evolution of the body. The human being,
as an organism, is still subject to natural elimination and human
selection. Elimination through the action of surrounding physical
conditions, although it has played some part in the evolution of man, is
not a factor of the first importance. Elimination through enemies is
more important, but has not much bearing on the question at present
before us--the evolution of the conceptual. Elimination by competition,
again, though a factor of yet greater importance in human evolution,
has, nevertheless, so far as individuals are concerned, but little
bearing on our present question. Few are eliminated through the absence
of the conceptual faculty. Natural elimination, then, is, as Mr. Wallace
well pointed out, practically excluded in this matter. No doubt, in the
struggle between tribes and nations, that community is most likely to be
successful in which there is rational guidance. No doubt, during the
earlier phases of the development of man on our islands, the elimination
of the irrational was a factor in progress. But if we take the last
three centuries of English history, I doubt whether it can be shown that
there has been much elimination determined by the relative absence of
conceptual ideas and emotions.
Human selection has been a much more important factor. Those individuals
which showed the higher types of intellectual thought have been
constantly selected. Riches, rank, and social position have been
bestowed upon them. Of course, there have been exceptions; great
intellects have been allowed to languish in their lifetime, and have
only obtained recognition through their works after death. But every day
there is less chance of a genius dying in a garret. And the best
intellects, being thus selected and chosen out from among their
fellow-men, form to some extent a distinct social class. Segregation is
thus effected; and intermarriage takes place within this intellectual
caste, with the result that the conditions are eminently favourable for
the inheritance of intellectual qualities.
Now, is this process of selection of the intellectual, this segregation
into a caste, and the inheritance of innate intellectual qualities
sufficient to account for the facts of intellectual progress; or must we
call in to our aid the inheritance of individual increments? I confess I
cannot say. Direct and satisfactory evidence, one way or the other, is
almost impossible to obtain.
Must we, then, leave the question undecided? I think we must so far as
direct evidence is concerned. I may have a general belief that there has
been some transmission of acquired increment of intellectual faculty.
But unless I can substantiate it by definite facts, I cannot expect to
convince any one who holds the opposite view. And definite facts of
sufficient cogency I am unable to adduce. It is practically impossible
to exclude the influence of human selection; and unless we can do this
the followers of Dr. Weismann will not be satisfied.
Still, general belief--which means the net result of one's consideration
of the subject--counts for something. We must remember the question is
one of origin, and not of guidance. The guidance of human selection is
unquestioned and unquestionable. But when we consider the intellectual
progress of the last three centuries, and ask whether all this has
originated in fortuitous brain-variations, which human selection has
simply picked out from the total mass of available material, an
affirmative answer seems to me a little difficult of acceptance. There
seems to have been a definite tendency to vary in this particular
direction, a general raising of the intellectual level, which is
difficult to account for unless it be due to the persistent employment
of the intellectual faculties.
To put the matter in another way. I do not think that, during the last
three centuries, there has been a large amount of elimination of the
unintellectual. Such elimination as there has been of this nature has
probably been more than compensated by the slower rate of multiplication
of the intellectual classes. Elimination, then, in this matter may be
practically disregarded. But it is obvious that selection, without the
removal or exclusion of the non-selected, does nothing to alter the
_general level_[KN] with regard to the particular quality or faculty
concerned. It is merely a classification of the individuals in
order of merit in this particular respect. It is, in a word, a
segregation-factor. It arranges the individuals in classes, but it does
not alter the position of the mean around which they vary.
Let me explain by means of an analogous case. Fifty boys, who have been
admitted to a public school, await examination in a class-room. They are
at present unclassified, but there is a mean of ability among the whole
fifty. A week afterwards they are distributed in different forms. Some
are selected for a higher form, others have to take a lower place. But
though selection has classified the material, it has not altered the
position of the mean of ability among the fifty boys. This can only be
done by expelling a certain number or excluding them from the school.
Granted, therefore, that elimination is practically excluded, human
selection can at most classify the individuals according to their
intellectual faculties. It cannot raise the mean standard of
intellectuality. If, therefore, this mean standard has been raised
during the last three centuries, there has been a tendency to vary in
this particular direction, which _may_,[KO] to say the least of it, be
due to the inheritance of individual increment.
I am, of course, aware that the matter is complicated by the increased
and increasing diffusion of knowledge through the printing-press and by
the extension and improvement of education. But education, to take that
first, though it may raise the level of each generation, can have no
cumulative effect. For the effects of education cannot, on Professor
Weismann's hypothesis, be inherited. You may educate brain and muscle in
the individual, but his heir will inherit no good or ill effects
therefrom. Each generation goes back and starts from the old level.
There is no summation of effect; or, if there is, it tells so far
against Professor Weismann.
And with regard to the diffusion of knowledge, this, though it brings
more grist to the intellectual mill, can have no effect in raising the
mean standard of excellence in the mill itself. There is more to grind;
but this does not improve the grinding apparatus; or, if it does, it
tells so far against Professor Weismann's hypothesis. To vary the
analogy, the diffusion of knowledge increases the store of available
food; but it does not bring with it any additional power of digesting
the food; or, if it does, it may be through inherited increments of mean
digestive power.
It may, however, be maintained that there is no conclusive proof that
the mean intellectual level of Englishmen to-day is any higher than it
was in the days of the Tudors. If so, of course, my argument falls to
the ground. I have no desire to dogmatize on the subject. I merely set
down the reasons, such as they are, and for what they are worth, which
lead me to entertain a general belief that the intellectual progress of
Englishmen during the past three hundred years has been in part due to
the inheritance of individually acquired faculty.
* * * * *
Mental evolution, then, is the metakinetic equivalent of interneural,
or, in us vertebrates, brain-evolution. The brain forms a kinetic system
in some sense independent of, and yet in constant touch with, the
kinetic system of the world around. Its kineses, though they do not
resemble, yet more or less accurately represent or symbolize, the
kineses of the surrounding universe. As the kineses of the world around
are interdependent and harmonious, so are the neural kineses of the
brain interdependent and harmonious. And no modification of this kinesis
which is out of harmony with the kinetic system already established in
the brain can be incorporated with that existing system. Such attempted
modification is eliminated through incongruity.
Associated with this brain-kinesis, and forming its inner aspect, is a
metakinetic system in which the higher manifestations rise to the level
of full consciousness; others form sub-conscious states; others are
unconscious. But the whole form a coherent system answering to the
coherent kinetic system.
Consciousness is thus associated only with the phenomena of that kinetic
microcosm which we call the brain (or other interneural system).
Obviously, therefore, it does not and cannot deal directly with anything
outside the brain. Its knowledge is solely and entirely a knowledge of
the representative occurrences of the interneural system. But out of
these occurrences a surrounding world of phenomena is constructed in
mental symbolism.
The brain itself, however, is part of the world of phenomena thus
constructed in mental symbolism; and the world, therefore, dissolves in
pure idealism, leaving only a fleeting series of states of
consciousness, if we do not assume the existence of a system of "things
in themselves" (noumena), of which kineses and metakineses are the
phenomenal manifestations. Whether the "things in themselves" in any
sense resemble their phenomenal manifestations, we cannot say. It is as
difficult philosophically to conceive that they can as it is practically
to conceive that they do not. And since, whether they do or do not, the
world we live in is phenomenal; since it is to phenomena that we have to
adapt our conduct; since it is with phenomena that all our thoughts and
emotions have reference; since the world we construct in mental
symbolism is the world in which we live and move and have our being; it
is not only convenient, but logically justifiable, to call this world of
phenomena the really existing world for us human-folk and other sentient
organisms.
As in the kinetic interneural system, or brain, so, too, in the
metakinetic system, no modification of the metakinesis which is out of
harmony with the existing metakinesis can be incorporated therewith.
Such attempted modification is eliminated through incongruity.
In the lower stages of mental evolution, those which belong to the
perceptual sphere, where the neuroses are closely connected with the
life-preserving activities of the organism, the survival or non-survival
of the system of neuroses is largely dependent on the fitness of the
associated activities to the conditions of life. But in the higher
stages of mental evolution, those which belong to the conceptual sphere,
the connection of certain brain-neuroses with life-preserving
motor-activities becomes less close and direct. The corresponding ideas,
thoughts, and emotions become floated off into a more abstract region.
Here the system of ideas, as such, that is to say, so far as they are
removed from life-preserving activities, is determined mainly by the law
of congruity. But there are several such systems. There are, indeed, as
many systems as there are minds; but these may be classified in several
distinct groups, which we may liken to genera and species. These are the
various interpretations of nature, theories of things, and the like; the
systems of ideas, thoughts, conceptions, emotions, beliefs, which, as we
say, belong to us, each and all, and which determine to which
metakinetic species we belong. These are the highest products of mental
evolution; and among them there is, so to speak, a struggle, if not for
existence, at any rate for prevalence. Which shall eventually prevail--a
spiritual interpretation of nature, a material interpretation, a
monistic interpretation, or other, who shall say? But, so far as we can
judge, the winning species among systems of ideas and interpretations of
nature are likely to be those in which the greatest number of ideas are
fused into harmonious synthesis; in which all the ideas are congruous;
and in which the abstract or conceptual ideas, when brought into contact
with concrete or perceptual states of consciousness, are found to be in
harmony and congruity therewith.
NOTES
[JY] "Contributions to the Theory of Natural Selection," p. 365.
[JZ] I consider that an apology is needed for the coinage of this and
of two or three other words, such as "construct," "isolate," and
"predominant." I can only say that in each case I endeavoured to
avoid them, but found that I could not make my meaning clear, or
bring out the point I wished to emphasize without them.
[KA] "Science of Thought," pp. 286, 287.
[KB] "Science of Thought," p. 279.
[KC] I use "substance" here in its philosophical sense.
[KD] Quoted in Professor Veitch's "Hamilton," p. 77.
[KE] T. M. Herbert, "The Realistic Assumptions of Modern Science
Examined," 2nd edit., p. 123.
[KF] "Science of Thought," p. 571.
[KG] Strictly speaking, of the brain; but since the brain has no
organic independence of the body, it is best here to focus
attention on the unity of the organism.
[KH] I ought not to pass over without notice the "psychological scale"
which Mr. Romanes introduces in a table prefixed to "Mental
Evolution in Animals." It would be unjust to criticize this too
closely, for it is admittedly provisional and tentative. If such a
scheme is to be framed, I would suggest that the various phyla of
the animal kingdom be kept distinct. I question, however, whether
any one can produce a scheme which any other independent observer
will thoroughly endorse. And I am inclined to think that the
wisest plan is to tabulate the kinetic manifestations which we can
actually observe rather than the metakineses of which we can have
no independent knowledge.
[KI] _Contemporary Review_, July, 1886. See Clifford's "Lectures and
Essays," vol. i. pp. 72 and 248; vol. ii. p. 67.
[KJ] _Contemporary Review_, July, 1886.
[KK] "Darwinism," p. 467.
[KL] In both cases, the question to which an answer is suggested is
not--What variations will arise? but--What variations will
survive?
[KM] "Darwinism," p. 293. It is strange that Mr. Wallace did not apply
this view to the mathematical and artistic faculties discussed in
his last chapter. It is true that such application tends to
undermine the argument there developed. But Mr. Wallace is far too
great and conscientious a thinker to be influenced by such a
consideration.
[KN] If elimination of the unintellectual (not necessarily of the
unintelligent) may be excluded, and if the unintellectual increase
by natural generation more rapidly than the intellectual, the
general level of intellectuality must, on Professor Weismann's
principles, be steadily _falling_.
[KO] It _may_ also, in part, be due to "organic combination."
INDEX.
A
Abstract ideas, 322, 363
Acceleration, sense of, 269
Acceleration and retardation, 221
_Achirus pellucidus_, 83
Acquired characters, are they transmitted? 147;
habits, are they inherited? 436;
variations in the intellectual sphere, 497
_Acræa_, 203
Activities, organic basis of comparative psychology, 337;
of animals, 415;
voluntary and involuntary, classification of, 462
Adaptation, analogous, 117;
modes of, 119;
special, examples of, 179;
to varying environment, 183
Advantage must be particular, 184;
must be immediate and not prospective, 186;
must be "available," 188, 211
_Æschna_, 289
Æsthetic preferences in insects and birds, 207;
aspect of sensation, not primary, 243;
motive not present to animal consciousness, 409
ALEXANDER, Mr. S., "Moral Order and Progress," 463
ALLEN, Mr. Grant, on evolution of flowers, 206;
on pleasure and pain, 380
ALLEN, Mr. J. A., on colour and humidity, 164
Alternation of generations, 46
_Amblyopsis spelæus_, 271
American school of evolutionists, 221
Am[oe]ba, how it feeds, 5;
reproduction of, 12, 38;
diagram of, 12;
protoplasmic functions of, 142
Amphibia, labyrinthodont, 288
Anabolism, constructive process, 32
Analysis (mental), 321
Ancon sheep, 226
ANDERSON, Mr., on one-eared rabbits, 226
Anemone, sea, reproduction of, 41;
marginal beads of, 298;
discrimination by, 359
Anger and rage, 389
Animal life, nature of, 1;
diversity of, 177
Animal intelligence, differs generically from man's reason, 350
Animals, characteristics of, 1;
divided into protozoa and metazoa, 15;
and plants, their relation to food-stuffs, the atmosphere,
and energy, 15;
intelligent not rational, 373;
capacities for pleasure and pain, 391
Animistic ideas of savages, how developed, 494
_Anisognathus_, 226
_Anomia_, 265
Ant, sauba, of South America, 213;
sense of taste in, 253;
sense of smell in, 258;
auditory organ of, 267;
intelligence of, 357;
activities often described as instinctive, 425;
neuter insects, 440;
Siamese, 449
Antagonism, advantages of, 394
Antennæ of insects, modifications of, 178;
of emperor moth, 199;
organ of hearing in, 267;
modified hairs of, 297
Antennule of crayfish, 259
_Anthophora_, 438
Anticipation, 327
Antlers of deer in illustration of growth, 28
Aphides, absence of fertilization in reproduction, 44
Appetence and aversion, 343, 384
_Apus_, 46
Aquatic organisms, respiration in, 4;
sense of smell in, 256
ARAGO, M., observation on turnspit dog, 404
Arctic hare and fox, 84;
animals, colours of, 165;
fox, cunning of, 366
ARGYLE, Duke of, on humming-birds, 110
_Artemia salina_ and _milhausenii_, 164
Artistic faculties and natural selection, 484;
products, evolution of, 489
Association a tendency to integration, 183;
perceptual and mimicry, 202;
and recognition marks, 203
_Ateles_, 210
Atmosphere, relations of animals and plants to, 15
Attacus, 179
Attention, 342
_Attidæ_, 208
Auditory apparatus in man, 262
Aurelia, life-cycle of, 45
Australian mammals and others convergent, 117
Automatic action, 415
Available advantage, 188, 211
Aversion and appetence, 343, 384
B
Baboon, experiments with, 352
Bacilli attacked by leucocytes, 439
_Bacillus violaceus_, 80
BAILEY, Mr. E. H. S., on taste, 251
BALBIANI on _Chironomus_, 137
_Balistes_, 179
BARRETT, Mr. W. F., on sensitive-flame experiment, 298
Barrier, geographical, 99;
time, in physiological isolation, 105
BARRINGTON, The Hon. Daines, on song of linnet, 454
BATESON, Mr. W., on lateral line, 252;
on fishes hunting by scent, 256;
on smell in shrimps, etc., 260;
on hearing in fishes, 264;
on hearing in _Anomia_, 265;
on sight in fishes, 286;
on rockling and sole, 352;
on fascination in fishes, 388
Bats, tabulated measurements of wing-bones of, 65-73;
wings, fortuitous variations in, 235;
experiment with, 247
Beauty, standard of, 206;
sense of, 407
Beaver, change of habit in, 445
BECCARI on gardener bower bird, 408
BECKER, Alexander, on variations in the balance of life, 112
Bees, divergent development of, 58;
cuckoo, 90;
latency in, 228;
sense of taste, 253;
sense of smell, 257;
smell-hollows, 259;
eyes and eyelets of, 289;
intelligence of, 357;
colour preferences in, 408;
homing faculty in, 428;
neuter insects, 440
Beetles of Madeira, 81;
stag-, variability of male, 180;
observations on dung-, 368
Begging in dogs, 345
BERKELEY, Bishop, quoted, 475
BERT, M. Paul, limits of sensibility to light, 296
BIDIE, Mr. George, anecdote of cat, 370
BINET, M., "Psychic Life of Micro-organisms," 360
Birds, influence of food-yolk on development of, 56;
divergence among, 97;
breeding area of comparatively restricted, 101;
humming, Duke of Argyle on, 110;
destruction of eggs of, 189;
game-, white and black crossed, 225;
taste in, 251;
smell in, 256;
hearing in, 264;
sight in, 284;
colour-vision in, 285;
gardener bower, 408;
humming, nests of, 408;
perfect instincts of pr[oe]coces, 424;
love antics of satin bower, 450;
nests of, 453;
song of, 454
BLOCHMANN on the development of the drone, 153
Blood, circulation of, 22
Body as distinguished from reproductive cells, 131
BOLL and KÜHNE, Messrs., on retinal purple, 276
BOLTON, Miss Caroline, on the bat, 247
_Bombus muscorum_, 90;
_lapidarius_, 91
_Bombyx quercus_, 258
Bower bird, 408, 450
Brain, 31;
decreased, of rabbits and ducks, 171;
a microcosm, 491
BREHM'S, Thierleben, quotation from, 405
Brine shrimp, modified by salinity of water, 164
BROOKS, Prof. W. K., his modification of pangenesis, 134;
on the greater variability of the male, 237
BROWN, Prof. Crum, on sense of acceleration, 270
BROWNE, Sir J. Crichton, on ducks, 171
Budding, reproduction by, 42;
in relation to heredity, 128
Bull, "Favourite," prepotent, 227;
reversion in, 229
BUNYAN, John, on gateways of knowledge, 311
BUTLER, Mr. Samuel, on organic memory, 62, 475
Butterfly, protective resemblance in, 86;
mimicry in, 87
C
Camel, wounded, 392
Canary, crested, 225;
nest building of, 453
Capon, taking to sitting, 228
Capuchin monkey, Miss Romanes's observation on, 367;
sympathy in, 397
CARLYLE, quoted, 331, 335
Carp at Potsdam, 265
CARTER, Dr. Brudenell, quoted, 285
Caste, idea of, in dog, 400
Cat, effect of African climate on, 164;
defining its percept, 339;
communication, 345;
intelligence of, 370;
and mouse, 399;
punishing kitten, 405
Caterpillars, protective resemblance in, 82
Cattle of Falkland Islands, 203
Causation, 327
Cell, diagram of animal, 10;
controlled explosions in, 31
Cessation of selection, effects of, 172
_Chætodon_, 83
_Chætogaster limnæi_, reproduction of, 42
Chaffinch, nest of New Zealand, 454
Chamæleon, 286
Chance, 236
Change of conditions, 163
Characters, specific, 110
CHARBONNIER, Mr, Henry, measurements of bats, 63
CHATTOCK, Mr. A. P., his experiments on colour-vision, 280;
letter to, on dog and picture, 341
CHESHIRE, Mr., on smell-hollows in bees, 259
Chickens' aversion to protected caterpillars, 352;
perfectly instinctive activities, 424
_Chironomus_, reproductive cells of, 137
Choice, 458
Circulation of the blood, 22
Classification, 323
CLIFFORD, W. K., on human consciousness, 341;
on the eject, 476;
on "world-consciousness," 479
Clover and bees, 113
_Clytus arietis_, 87
Cockchafer, smell-hollows of, 259
COCKERELL, Mr., on variations in snails, 75;
on effects of moisture, 239
Cockroach, diagram of trachea or air-tubes of, 3;
sense of taste in, 253;
sense of smell in, 258
Cocoon, collective, 429
_Colobus_, 210
Colour, protective resemblance in, 82;
warning of inedibility, 82;
dependent on humidity, 164;
direct action of climate on, 164;
development of, 202;
blindness, 273, 279;
phenomena of, 278
Combination, organic, hypothesis of, 150, 240
Communication in dogs, 345;
in bees, 358
Compensation of growth, 155
Competition, elimination through, 89
Concept, 325, 326
Conception, 325
Conceptual conduct and evolution, 488
Condor, rate of increase of, 57
Conduct, 463;
influence of thought and æsthetics on, 483;
conceptual, and natural selection, 488
Congruity, principle of, 486
Conjugation in protozoa, 39;
of ovum and sperm-cell, 42
Consciousness, 32;
and consentience, 326, 362;
as a criterion of instinct, 432
Consentience, 326, 362
Construct and construction (mental), 312;
three stages of, 324;
inevitable nature of, 332;
in mammals, 338
Continuity of reproductive cells, 131;
germ-plasm, 138;
cellular, 142;
in mental development, 373
Convergence, phenomena of, 117
Co-ordinants, 303
COPE, Prof., on the effects of use, 210;
and HYATT, Prof., on retardation and acceleration, 221
Correlated variation, 59, 216
CORTI, organ of, 263
_Coryne_, Prof. Weismann on, 139
COUCH, Mr., on goldfinch song, 454
Crab, protective resemblance in, 87;
hermit, 195;
habit of decking itself, 457
Crayfish, smell in, 259;
auditory organ of, 266
Crossing, effect on reversion, 230
Cruelty in cat, objective, 400
Crustacea, eyes of, 292
_Ctenomys_, 194
Cuckoo, the name onomatopoetic, 322;
habits intelligent, 436;
ejecting young birds, 437
Curiosity in prong-horn, 339
Cuttlefish, eyes of, 293
_Cyclas_, 265
_Cycloptera speculata_, locust resembling leaf, 86
D
DALLINGER, Dr., his temperature-experiments on monads, 147
_Danais_, 203
Daphnids, absence of fertilization in reproduction of, 45;
colour-vision in, 292, 296;
leucocytes of, 439
DARWIN, Charles. Natural selection and the struggle for existence, 77;
divides the principle of selection into three kinds, 78;
on selection of flowers and fruits by insects, 93;
on sexual selection, 94;
on prevention of free crossing in breeding, 99;
on differential fertility, 104;
on London rats, 106;
on Galapagos archipelago, 109;
on diverse adaptation, 111;
on the influence of old maids on clover crops, 113;
on the influence of parent on offspring, 122;
on the co-ordinating
power of her organization, 125;
hypothesis of pangenesis, 131;
on fur of arctic animals, 165;
changes of structure attributed to use and disease, 171;
on blindness of tuco-tuco, 194;
on the principle of economy, 194;
on sexual selection, 198;
on preferential mating, 204;
on evolution of flowers, 205;
on co-ordinated variations in the elk, 213;
on acceleration, 222;
on ancon sheep, 226;
on prepotency, 227;
on reversion, 229;
on the effects of crossing, 230;
on fortuitous variation, 236;
on the subordination of the conditions to the organism, 236;
on the greater variability of male, 237;
on attention in monkeys, 342;
on brain of ant, 358;
on gestures of anger and rage, 389;
on pleasures and pains of animals, 394;
on bravery of a monkey, 396;
on Abyssinian baboons, 405;
on sense of humour in the dog, 406;
on neuter insects, 440;
on selection of oxen, 441;
on acquisition of fear of man by birds, 443;
on satin bower bird, 450
Death, natural introduction of, 186, 193
Deceit in dogs, 400
Degeneration, 183
Desert animals, inconspicuousness of, 89
DESCARTES on pineal gland, 288
Desire, 460, 463
Destruction, indiscriminate, as opposed to elimination, 76
Development of organisms distinct from growth, 6;
reproduction and, 36;
is differential growth, 49;
of a vertebrate, diagrammatic account of, 51;
comparative, of some vertebrates, 220
DE VRIES, 132, 159
Differentiation in protozoa, 40;
in metazoa, 41;
during development, 49;
of reproductive cells, 143;
and integration, 183;
of tissues, 232
_Difflugia_, 360
Dimorphism in larvæ, 187
Discrimination in the sense of touch, 245;
hearing, 262;
sight, 275;
its fundamental nature, 338;
in sea-anemone, 359
Disease, elimination by, 80
Display, 207
Disuse, panmixia and, 189;
negative and not positive, 196;
use and, 209
Divergence among birds, illustrated
from Wallace, 97;
through diverse adaptation, 111
DIXON, Mr. Charles, effects of climate on the colours of birds, 164;
on chaffinch nests, 454
Dog, effect of Indian climate on, 164, 167;
greyhounds in Mexico, 167;
sense of smell in, 255, 338;
vague percept of, 339;
and the feelings of other animals, 340;
and pictures, 341;
powers of communication, 344;
swimming rivers, 365;
cleverness of, 367;
sympathy in, 397;
idea of caste, deceit, 400;
endurance of pain, 402;
sense of justice in, 404;
punishing pup, 405;
sense of humour in, 406;
swimming a deferred instinct in, 423;
turning round to make a couch, 444
Dog-fish, sense of smell in, 257
Domestication, variations effected by, 171, 215;
crossing and reversion, 230
_Doris tuberculata_, 84
Dreaming, 341;
and the animistic hypothesis, 495
_Dromia vulgaris_, 457
Drones developed from unfertilized ova, 45;
second polar cell extruded, 153
DUBOIS, M., on _Proteus_, 294
Ducks, Sir J. Crichton Browne on, 171;
Dr. Rae on instinctive wildness of, 435
Duration of life, 186
E
Eagle, sclerotic plates of, 437
Ear, 263
Earthworm, respiration in, 4, 24;
regeneration of lost parts, 41;
sensitive to light, 293;
outward projection in, 359
EATON, Rev. A. E., on insects of Kerguelen Island, 81
Ecitons, 427
Economy, principle of, 194
Education of ants, 428;
of young animals, 455
Egg and hen, problem of, 130
Egg-cell and sperm-cell, diagram of, 13;
conditions which determine production of, 60
Eggs, influence of food-yolk on mode of development of, 56;
destruction of birds, 189
Ego, or self, 475
EIMER, Prof., on inhabitants of Nile valley, 165;
on _Helix hortensis,_ 226;
on instinct, 436;
on differential dread in birds, 444
Eject, meaning of, 476
Elaboration, 183
Elephant, rate of increase of, 57;
intelligence of, 363, 369;
use of tools by, 370;
vindictiveness in, 401
Elimination, as opposed to selection, 79;
its three modes, 80;
as a factor in the origin of instinct, 447;
of ideas through incongruity, 486;
as applied to the intellectual faculties, 497
Embryology negatives preformation, 50
Emotions exemplified, 382;
the expression of, 385;
three orders of, 391;
in vertebrata, 395
Encystment, 38, 49
Ends and means, 371
Energy, relations of animals and plants to, 16
_Ennomos tiliaria_, caterpillar, protective resemblance of, 85
Environment, direct effects of on the organism, 163;
changes of, in relation to the organism, 183;
are effects of direct or indirect? 233;
instances of effects of, 238
_Equus_, 118
_Eristalis tenax_, 87
Ethics in animals, 413
_Euplæa_, 203
Evolution of older writers, 50;
and revolution, 119;
organic, 177;
meaning of term, 182;
mental, 464;
organic and mental not continuous, 488;
interneural, 490
Excrement of birds, resemblance of spider to, 90
Excretion, an essential life-process, 3, 29
Expectation, 327
Experience dependent on memory, 305
Expression of the emotions, 385
Eye, structure of in man, 274;
in mole, 284;
pineal, 287;
in insects, 288;
facetted, 289;
in crustacea, 292;
in molluscs, 292;
four types of, 294
F
FABRE, M., on _Sitaris_, 439
Facetted eye, 289
Factors of phenomena, laws of, 61
Falkland Islands, cattle of, 102;
birds of, 443
Fear, dread and terror, 387;
instinct of, 443
Feelings of animals, 8, 378
Female. _See_ Sex-differentiation.
Female and male insects, differences between, 179;
vigour expended on offspring, 238
Fertilization, nature of, 42;
absent in parthenogenetic forms, 44
Fertility, differential, Darwin and Romanes on, 104;
of hybrids, 105
Fetishism, its natural genesis, 492
FISCHER, Dr. Emil, on smell, 254
Fish, respiration in, 24;
protective resemblance in, 83;
amount of food-yolk in eggs of, 220;
skate and turbot compared, 220;
sense of taste in, 252;
sense of smell in, 256;
sense of hearing in, 264;
sense of sight in, 286;
fascination in, 388;
love-antics of, 450
FISK, Rev. G. H. R., on sympathy in cat, 397
Fission, a process of cell-division, 37;
in protozoa, 38;
in metazoa, 41
Flight, instinctive nature of, 425
FLOURENS, M., on function of semicircular canals, 269
Flowers and fruits, selection of, 93;
evolved through insect agency, 206
_Folliculina_, 360
Food-stuffs, relations of animals and plants to, 15;
nature of and digestion of, 25
Food-yolk, influence of, on development, 55;
the result of parental sacrifice, 57
FORBES, H. O., on Javan spiders, 90
FOREL, M., on taste of ants, 253;
on vision of daphnids, 296;
on happy family of ants, 428
Form-characteristics of animals, 2
Fortuitous variation, 235
Fosterage and protection, 219;
result of female self-sacrifice, 238
FOTHERGILL, Mr., on dogs swimming rivers, 364
Fowl, variations in, attributed by Darwin to use, 171;
crossing of, 227, 230
Fox, cunning of, 366
FRANCIS, Mr. H. A., 90
FRITSCH, Dr., Fig. of skull of _Melanerpeton_, 288
Frog, development of, 6;
arrest of life in, 21;
respiration in, 24;
fishing, or angler-fish, 91;
modified development of, 214;
effects of simple stimulus on, 305
Fruits and flowers, selection of, 93
G
GABET, Messrs. HUC and, on Llama cow, 333
Galapagos Archipelago, species and varieties in, 99;
climate of, 109
_Gallus bankiva_, 230
GALTON, Mr. Francis, on the coloration of the zebra, 84;
his modification of pangenesis, 135;
numerical estimate of inheritance, 150, 192;
his investigations on twins, 169;
on blended characters, 225;
on the steps of evolution, 227
Ganglia, 31
Gannet, rate of increase of, 57
Gas-engine, analogy of, 30
GAUTIER, Théophile, his cat, 264
GEDDES, Prof. Patrick, and THOMSON, J. A., on anabolism and
katabolism, 44;
quoted, 50, 137, 237
Gemmules, pangenetic, 131
Generations, alternation of, 46
Generic idea, 326
Geographical barriers a means of segregation, 99
Geological changes, influence on natural selection, 113
Germ-plasm, continuity of, 138;
convenience of, 140
Gills of mussel, 4;
as respiratory organs, 24
Giraffe, co-ordinated variations in, 212
Glacial epoch, effects of, 113
Gland, pineal, 288
Goldfinch, song of, 454
GOLDSCHNEIDER, on temperature-sense, 249
GOULD, Dr., on humming-birds' nests, 408
GRABER, Dr., on colour-sensitiveness of earthworm, 293
GRANT, Mr. G. L., on New Zealand sparrows, 445
Grasshopper, auditory organ of, 266
_Gregarina_, reproduction in, 38
GRENACHER, Dr., experiment on moth's eye, 290
Grouse, white plumage in, due to reversion, 229
GROVE, Sir W. R., on antagonism, 394
Growth of organisms, 5;
illustration of a deer's antler, 28;
law of, after mutilation, 126
Guidance distinguished from origin, 242
Guillemot, eggs of, 410
GULICK, Rev. J. T., on landshells of Sandwich Islands, 109;
on tendency to divergence, 151
GUPPY, Mr., on crab of Solomon Islands, 87
H
Habits of animals, 415
Habitual activities, 420;
sense of satisfaction in performance of, 421
HAECKEL, Prof., plastidules of, 125;
theory of perigenesis, 159
_Halictus cylindricus_, 90
HAMERTON, Mr. P. G., on the ignorance of animals, 333
HAMILTON, Sir Wm., quoted, 470
HANCOCK, Mr. John, on instinct of cuckoo, 437
HASSE, E., on bumble-bees, 259
HAUSER, on cockchafer, 259
HAYCROFT, Mr. J. B., on taste, 250
Hearing, sense of, 261
_Heliconia_, 203
_Helix_, _nemoralis_ and _hortensis_, variation of, 75, 217, 226, 239
HELMHOLTZ, Von, on colour, 277;
on local signs of retina, 308
Hen and egg, problem of, 130
HENSEN, on shrimps, 266
HERBERT, Prof. T. M., quoted, 471
HERDMAN, Prof., on sea-slug (_Doris_), 84;
his modification of pangenesis, 135;
on warning coloration in nudibranchs, 252
Heredity, an organic application of the law of persistence, 62;
and the origin of variations, 122;
in protozoa, 123;
and regeneration of lost parts, 124;
failure of, 192;
and instinct, 435
HERING, Edward, on organic memory, 62, 475
HERON, Sir R., on crossing rabbits, 225
HERSCHELL, Sir John, on colour, 277
HERTWIG, Richard, observations on Infusoria, 39
HICKS, on Capricorn beetle, 267
HICKS' organ, 267
HICKSON, Dr., Fig. of eye of fly, 290
_Hipparion_, 118
Hippopotamus, instinctive activities in, 423
HOLLAND, Sir Henry, on inheritance, 223
Homing faculty of bees, 428
Horse, two different evolutions of, 118;
effects of use on digits of, 210;
sense of pain in, 392
HOWSE, Prof., antennule of crayfish, 259
HUBER, Pierre, on smell in bees, 257;
judgment and instinct, 452
HUC and GABET, Messrs., on Llama cow, 333
HUGGINS, Dr., his dog Kepler, 396
Humming-birds, 110
Humour, sense of, in dog, 406
HUXLEY, T. H., on limitation of variations, 151;
on neurosis and psychosis, 465
HYATT, Prof., on acceleration and retardation, 221
Hybrids, fertility of, 105
Hydra, reproduction of, 14, 41;
diagram of, 43;
artificial division of, 124;
budding in, 128;
sexual reproduction of, 129
Hydra tuba, and medusa of aurelia, 45
Hydroids, development of, 46;
Weismann on, 139
Hymenoptera, antennary structures of, 297;
instincts of social, 441, 448
I
Ichneumon fly, instinct of, 430
_Ichthyosaurus_, pineal eye of, 288
_Icteridæ_, 454
Idea of an object, 313
Ideas, conceptual, their environment, 485;
the law of their evolution, 486
Idealism, 474
Ignorance of animals, 333
Image, inverted in retina, 311
Imagination, constructive, 325
Imitation as a factor in habit or instinct, 443, 453
Immortality of protozoa, 12
Incongruity, elimination by, 486
Increase, law of, 58
Incubation, instinct of, 434
Individuality, a tendency to differentiation, 183
Inference, conscious and unconscious, 328;
in animals, 361
Infertility of isolated forms, 108
Infusoria, reproduction in, 39
Inheritance, exclusive, a means of isolation, 104;
of variations, 223;
of acquired habits, 435;
of acquired increments of intellectual faculty, 497
Inhibition, 385;
as a condition of volition, 459
Innate capacity, 422;
its importance, 429
Insects, tracheal respiration of, 3, 24;
wingless, of Madeira, 81;
of Kerguelen Island, 81;
mimicry and protective resemblance in, 85, 88;
segregation by colour, 101;
antennæ of, 178;
mouth-organs of, 179;
and the evolution of flowers, 206;
sense of touch in, 248;
taste in, 253;
smell in, 257;
hearing in, 266;
sight in, 288;
perceptual powers of, 357;
neuter, 440
Instinct and available advantage, 211;
consideration of, 415;
perfect, imperfect, and incomplete, 422;
deferred, 423;
blind prevision in, 429;
gratification in performance of, 430;
consciousness and, 432;
primary and secondary, 434;
three factors in the origin of, 447;
as influenced by intelligence, 452;
by imitation, 453;
by education, 455;
as distinguished from intelligence, 457
Instinctive emotion, 390, 395
Integration and differentiation, 183
Intellectual development, 486
Intelligence involved in selection, 95;
distinguished from reason, 330, 365;
lapsed, 435
involved in instinct, 440;
as influencing instinct, 452;
criteria of, 456
Interbreeding and intercrossing, 97
Interneural evolution, 490
Interpretations of nature, genera and species of, 492
Isle of Man, tortoiseshell butterfly of, 81
Isolates, 322, 364
Isolation, organic, or segregation, 99;
mental, or abstraction, 322
J
JAEGER, Dr., on crossing of pigs, 230
JENKINS, Mr. H. L., on the elephant, 363
Judgment, 330
K
_Kallima paralecta_, leaf-butterfly, 86
KANT, quoted, 476
Katabolism, a disruption or explosive process, 32
Kea, of New Zealand, 446
Keimplasma. _See_ Germ-plasm
Kentish plover, 83, 217
Kepler, Dr. Huggins's dog, 396
Kerguelen Island, wingless insects of, 81
Kinesis, 467
Kingfishers, 446
KIRBY and SPENCE, localization of smell in insects, 258;
on hearing in a moth, 267;
on instinct of ichneumon fly, 430
Kittens, instinctive antipathy to dog, 396
KLEIN, Mr. S., on _Bombyx quercus_, 258
KÜHNE, Messrs. BOLL and, on retinal purple, 276
L
Labyrinthodont amphibia, pineal eye in, 288
LAMONT, on reindeer, 392
LANE, Dr. Arbuthnot, on influence of certain trades on structure, 169
LANGLEY, Prof., On ætherial vibrations, 299
Language, 322;
the instrument of analysis, 349;
its origin and effects, 374
LANKESTER, Prof. E. Ray, his description of perigenesis, 159;
on blind cave-fish, 194
Lapsing of intelligence, 435
LARDEN, W., on the Rhea, 89;
on instinct in a snakelet, 424
Larmarckian school, 209
Larvæ, dimorphism in, 187
Latency, phenomena of, 227
Lateral line of fishes, 252
Leaf-butterfly, 86
LEE, Mr. Arthur, on communication in cat, 345
_Leptalis_, 87
LEROY, on abstract notion of danger in fox, 348
Leucocytes, _role_ of, 439
LEWES, G. H., 437, 462
LEYDIG, on antennule of crayfish, 259
Life, duration of, due to natural selection, 186
Life-area, expansion and contraction of, 114
Limits of vision, 281; of sensation, 299
_Limnæus truncatulus_, 48
LINCECUM, Dr., on habits of Texan ants, 425
Linnet, song of, 454
Lion, observation on, 400
Liver-fluke, life-history of, 47
Local signs, 308
Localization, 307;
in animals, 338;
in medusa, 359
LOCKE, on difference between man and brute, 349
Logos makes man human, 375
LONBIÉRE, on instincts of Siamese ants, 449
LOTZE, quoted, 379
LUBBOCK, Sir J., "Senses of Animals," 246;
sense of smell in ants, 258;
auditory organ of ant, 267;
on Hicks's organ, 267;
on colour-sense in dog, 283;
in insects, 291;
in Daphnia, 292;
on limits of colour-vision, 296;
on antennary structures in hymenoptera, 297;
on power of communication
in dog, 345;
in ants, 358;
on colour preferences in bees, 407;
on instinct of play and sympathy in ants, 414;
on homing faculty in bees, 428;
on sitaris, 439
_Lucanus cervus_, 180
Ludicrous, sense of, in dog, 406
LUMSDEN, Sir Harry, on partridges, 398
LYELL, the necessary precursor of Darwin, 121
M
MACH, Prof., on Macula acustica, 271
_Machetes pugnax_, 110, 178
MACKENNAL, Mr. Alexander, observation on a cat, 405
MACLAGAN, Miss Nellie, on sympathetic action in dog, 398
Madeira, wingless insects of, 81
Male, _See_ Sex-differentiation
Male and female insects, differences between, 179;
greater variability in, 237;
vigour and vitality of, in secondary sexual characters, 237
MALLE, Dureau de la, on starling, 455
Mammals, respiration in, 21;
early nutrition of, the result of parental sacrifice, 57;
convergence in, 117;
sense of smell in, 255;
hearing in, 263;
sight in, 283;
perceptions of, 338
Man, elimination by physical circumstances, 81;
alternation of good and bad times, 117;
reversion in, 229
MANN, Mrs., on sympathetic action of dog, 397;
anecdotes of dogs, 406
Mantis, protective and aggressive resemblance in, 90
Marsupials of Australia, 117
MARTINEAU, Dr., on wants, 382
Materialism, 464, 471
Mathematical faculty and natural selection, 484
MAUPAS, M., observations on infusoria, 39
MAYER, on mosquito, 267
MCCOOK, Dr., sense of smell in ants, 258;
habits of Texan ants, 425
MCCOSH, Dr., quoted, 391
Means and ends, 371
Medusa, 46;
sense of hearing in, 265;
eyes of, 293;
localization by, 359
_Melanerpeton_, 288
MELDOLA, Prof. R., 239
Memory, the revival of past impressions, 304;
organic, Butler and Hering on, 62
Mental evolution, 464
MERCIER, Dr. Charles, on the criteria of intelligence, 456
MERRIFIELD, Mr., experiments on moths, 238
Metabolism, 32
Metakinesis, 467
Metamorphosis and transformation, 7
Metaphyta, 15
Metazoa, 15
_Methona_, 87
MIALL, Prof., Fig. of touch-hair of an insect, 248
Mice, white and grey, crossed, 225
Microbes, elimination among, 80
_Micrococcus prodigiosus_, 81
_Microstomum lineare_, reproduction in, 42
Mimicry, 87;
as evidence of perceptual association, 202, 351
Mind, out of what evolved? 464
Mineral crystals, analogy of, 240
MITCHELL, James, his delicate sense of smell, 255
MIVART, Prof. St. George, on Saturnia, 163;
on common-sense realism, 316;
on ideas, etc., 320;
on "practical intelligence," 362;
on man and brute, 374;
on consciousness and consentience, 461
Modifiability of individual organism, 163
Modifications of antennæ and mouth-organs of insects, 178
Mole, eye of, 284
Mollusks, variety of, 178;
sense of smell in, 260;
hearing in, 265;
sight in, 292
Monads, reproduction of, 38;
temperature experiments with, 147
Mongrelization, 168
Monistic hypothesis, 465
Monkey, _ateles_ and _colobus_ digits of, 210;
examining marsupial pouch, 340;
attention in, 342;
capuchin, intelligence of, 367
_Monospora bicuspidata_, 439
MOORE, Mr. Thomas, on hybrids between Amherst and golden pheasants, 106
Mosaic vision, 291
Mouth-organs of insects, 179
Muciparous canals of fishes, 298
MÜLLER, Prof. Max, "Science of Thought," 325;
on percepts, 375;
on language and thought, 376;
paraphrased, 467;
on materialism, 471
_Murex_, 292
_Mus rex_ and _imperator_, 100
Musical and artistic faculty, 484
Mussel, freshwater, gills of, 4;
olfactory organ of, 260
Mutilation, law of growth after, 126;
not the best kind of evidence of transmitted modifications, 162
N
NÄGELI, 159
NAISH, Mr. John G., on the cockatoo, 354
Natural selection, variation and, 61;
two modes, elimination and selection proper, 79;
and the effects of use and disuse, 174;
not to be used as a magic formula, 184;
and instinct, 445;
and human thought, 484
Nerves, briefly described, 246;
afferent and efferent, 303
_Nestor notabilis_, 446
Nests of bower-bird and humming-bird, 408;
instinctive building of, 453
NETTLESHIP, Mr., on a lion, 400
Neural processes, environment of, 491
Neurosis and psychosis, 465
Neuter insects, 440
New Zealand sparrow, 445;
parrot, 446;
chaffinch, 454
NICHOLS, on taste, 251
Noctule, 66
NOIRÉ, on concepts, 325
_Nomada solidaginis_, 90
NORRIS, Mr. W. E., quoted, 420
Noumena, or "things in themselves," 470
Nucleus of animal cell, 10;
as controlling formative process in, 124
Nutrition in illustration of the process of life, 25
O
Object, nature of, 313, 437
Ocelli in insects, 288
_Oecodoma cephalotes_, 213
_Onchidium_, 293
Optogram, 276
Organic combination, hypothesis of, 150, 240
Organic evolution, 177;
as basis of comparative psychology, 336
Organic growth, 5
Organism, unity of, as regards body and germ, 161;
relation of, to environment, 183
Organization, co-ordinating power of, 125;
of bodily and mental activities, 419
Origin, distinguished from guidance, 242
Origin of species, 242
Origin of organic variations, 231;
of metakinetic or mental variations, 496
_Ornithoptera_, 179
Otoliths, 265, 271
OWEN, Sir Richard, suggested germinal continuity, 135
Oyster-embryo set free early, 56;
variation of Mediterranean, 164
P
_Pachyrhyncus orbifex_, 87
_Pagurus prideauxii_, 457
Pain, massive and acute, 379;
capacities of animals for, 391
Pangenesis, 182
Panmixia and disuse, 189
_Papilionidæ_, 202
Paradise, birds of, 202
Paranucleus in protozoa, 39
_Param[oe]cium_, reproduction in, 39
Parasites, how they feed, 5
Parental sacrifice in birds and mammals, 57;
its limits, 186
Parrot, intelligence of, 353
Parthenogenetic forms, no second polar cell in, 153;
the drone an exception, 153
_Parus palustris_, 164
PEAL, Mr. S., on use of tools by elephant, 370
PECKHAM, Mr. G. W., on love-antics of a spider, 208, 450
_Pecten_, 293
Pelagic animals, colours of, 83
PENZOLDT, Dr., on smell, 254
Percept, 325, 326
Perception, 311, 324;
in animals, 339
Perceptual association, 202
Perigenesis of the plastidule, 159
_Peripatus_, 142
Persistence, law of, 61
Pheasant, hybrids between Amherst and golden, 106;
golden, hen with cock's plumage, 228
_Phengodini_, 223
Phenomenal nature of object, 315, 320, 331
Photographic psychology, 320, 326
_Phrynocephalus mystaceus_, 90
Physiological isolation, 104
Physiological and psychological activities, 304;
series, 386, 417
PICTON, Mrs. E., on Skye terrier, 398
Pigeons, correlated variations in, 216;
silky fantail prepotent, 227
Pigs, intestines of, 171;
crossing of, 226, 230
Pike, teeth of, 437
Pineal gland, 196, 288
Pipistrelle, wing of, 64
Pipits as illustrating divergence, 97
Pitch, musical, 261
Plasm, 10
Plasmogen, 10
_Platyglossus_, 83
Play, instinct of, 450
Pleasure and the special senses, 243;
massive and acute, 379;
capacities of animals for, 391
_Plecotus auritus_, 68
_Plesiosaurus_, pineal eye of, 288
PLOSS, Herr, on sex-differentiation in man, 59
Plover, Kentish, 83, 217
Polar cells, extrusion of, 51;
and variation, 153
Postponement of action, 385
POULTON, Mr. E. B., on colours of animals, 84;
on _Phrynocephalus mystaceus_, 90;
on caterpillars and chrysalids, 165;
dimorphism in larvæ, 187;
observations on edibility of caterpillars, 212;
"Theories of Heredity," quotation from, 214;
on the eating of unpalatable insects, 445
Predominant defined, 349;
and language, 374
Preferential mating, a means of segregation, 102;
and sexual selection, 197
Preformation and evolution of older writers, 50
Prepotency, 227
Presentations of sense, 318
Previous sire, effect of, 168
Prevision as a criterion of intelligence, 457
Principles, mechanical, 368
Process of life, 20
Progress, or continuous adaptation, 119;
adaptation to more complex circumstances, 183
Pronghorn, curiosity in, 339
Proposition, 329
Protective resemblance and mimicry, 82;
general resemblance, 83;
variable resemblance, 84;
special resemblance, 86;
to another organism, 87;
coloration, a means of segregation, 101
Protection, fosterage and, 219
_Proteus_, sensitive to light, 294
Protista, 15
_Protohippus_, 118
Protophyta, 15
Protoplasm, 10
Protozoa, nature of, 15;
transmission of acquired faculty in, 147;
origin of metazoan variations in, 156;
psychology of, 360
_Psithyrus rupestris_, 90
Psychological and physiological activities, 304;
series, 386, 417
Psychoses and neuroses, 465
Ptarmigan, on colour of, 165
R
Rabbit, brain of, 171;
Angora crossed, 225;
one-eared, 226;
deprived of long lip-hairs, 247;
_papilla foliata_ of, 250;
effects of superabundant food on, 394
RAE, Dr., on dogs swimming rivers, 364;
on "abstract reasoning" in the fox, 366;
on wild and tame ducklings, 435
Rage and anger, 389
RAMSAY, Dr. Wm., on smell, 255
Rats of Solomon Islands, 100;
of the London Docks, 106;
at South Kensington, 115
RAYLEIGH, Lord, on colour-blending, 283;
on sensitive-flame experiments, 298;
Reality, meaning of term, 314
Reason distinguished from intelligence, 330, 365;
as defined by Mr. Romanes, 372
Recepts, 326, 368
Recognition-marks, 103;
involve perception, 351
Reconstructs and reconstruction (mental), 318
Reflex action, 415;
and instinct, 422
Regeneration of lost parts, 41;
in relation to heredity, 124;
law of growth concerned in, 126
Reindeer wounded, 392;
change of habit in, 445
Remnants or vestiges, 196
Reproduction, nature of, 13;
and development, 36;
in the protozoa, 38;
in the metazoa, 41;
by budding, 42;
sexual, 42;
peculiar modifications of, 45;
developmental, 143
Reproductive cells, continuity of, 131
Resemblance, protective, 82;
aggressive, 90
Respiration an essential life-process, 3;
in illustration of the process of life, 21
Retardation and acceleration, 221
Retina of man, 274; of birds, 284
Retinal purple, 276
Revenge, 401
Reversion, 191
Revolution and evolution, 119
Rhea, neck resembling snake, 88
_Rhinolophus ferri-equinum_, _hipposideros_, 65
Rhyme-association in parrot, 356
RIBOT, M., on attention, 343
RICHARDSON, Mr. Charles, on railway servants killed by train, 388
RILEY, Prof., on _Phengodini_, 223
ROMANES, Prof. G. J., on physiological isolation, 104;
on the cessation of selection, 190;
on the failure of heredity, 192;
on the reversal of selection, 193;
on sense of smell in dog,
on colour-sense in chimpanzee, 283;
on ideas, 326;
on dog cowed by noise, 340;
on abstract ideas in animals, 348;
on parrot, 353;
on localization and discrimination, 359;
examples of animal intelligence considered, 362;
on abstract ideas in the capuchin, 368;
definition of reason, 372;
on strange attachments in birds, 396;
on some emotions in animals, 400;
on endurance of pain in dogs and wolves, 402;
on sense of humour in dog, 407;
on indefinite morality in animals, 413;
definition of instinct, 422;
on education of ant, 428;
on homing faculty of bees, 428;
on consciousness and instinct, 432;
summary of his conclusions on instinct, 434;
on instincts of Siamese ants, 449;
his psychological scale, 478;
on the world as an eject, 479
Rotation, sense of, 269
Rotifers, absence of fertilization in reproduction, 45
Roux, on extirpation of cleavage-cell of frog's egg, 214
ROWELL, G. A., on "Beneficent Distribution of Pain," 392
Ruffs, variability of males, 110, 178
RUSSELL, Mr. W. J., on smell in the dog, 255
S
_Saitis pulex_, 450
Salinity of water, effects of, on brine-shrimp, 164
Salmon, new variety of, in Tasmania, 99
_Saturnia_, modification of, by changed food, 163;
_carpini_ (emperor moth), 258
Savages, fetishistic belief in, 494
SCHAUB, Mr., observations on a terrier, 405
SCHMANKEWITSCH on Artemia, 164
SCLATER, Mr. W. L., on mimicry in an insect, 88
SEDGWICK, Mr. Adam, on development of peripatus, 142
SEEBOHM, Mr. H., on birds' eggs, 410
Segregation, 99
Selection, as compared with elimination, 79;
illustrated, 92;
artificial, 172;
cessation of, 190;
reversal of, 193;
sexual, or preferential mating, 197, 452;
as a factor in the origin of instinct, 447;
as applied to the intellectual faculties, 498
_Selenia_, _illunaria_, and _illustraria_, 238
Self, the, or ego, 475
Self-consciousness, 460
Semicircular canals, 262, 269
Senility, introduction of, 184
Sensation defined, 305, 324
Sense-feelings of animals, 393
Senses of animals, 243;
organic and muscular, 244;
touch, 245;
temperature-sense, 249;
taste, 250;
smell, 253;
hearing, 261;
sight, 272;
contact and telæsthetic, 249;
problematical, 297
Sensibility, 385;
variations of, 449
Sensitive, special use of the term, 9
Sensitiveness and sensibility, 385
Sentiments, 391;
in animals, 403
Sex-differentiation, 58
Sexual union of ovum and sperm a source of variations, 149;
characters, secondary, 197;
selection, 197
Shame in monkey, 402
Sheep, YOUATT on, quoted, 455
Shells, land, of Sandwich Islands, 99
SHIPP, Captain, experiment on an elephant, 401
Sight, sense of, 272
_Sitaris_, instinct of, 438
SKERTCHLY, Mr. S. B. J., on leaf-butterfly, 86
Slave-making ants, 425
Smell, sense of, 253
_Smerinthus ocellatus_, 165
SMITH, Mr. G. Munro, on elimination among microbes, 80
Snail, variations in banding of shells, 75;
sense of smell in, 260;
auditory sac, 265;
eye of, 292;
_spiculæ amoris_ of, 450
Snakes, mimicry in, 88
Snipe, drumming of, 448
SOLLAS, Dr. W. J., on regeneration of tentacle in snail, 127
Somatic, or body-cells, 193
SOMMERING, Fig. of semicircular canals, 270
SPALANZANI, his experiments on bats, 248
SPALDING, Douglas, on instinctive emotions, 395;
on perfect instincts of chicken, 424;
on deferred instinct in swallow, 425
Sparrows in New Zealand, 445
Specific characters, utility of, 110;
constancy of, 111
SPENCER, Mr. Baldwin, Fig. of pineal eye, 288
SPENCER, Mr. Herbert, law associated with his name, 37;
physiological units, 125, 153;
on lap-dogs, 195;
on the Irish elk and giraffe, 212;
on diminution in ear-muscles, 215;
definition of pleasure and pain, 381;
on æsthetics, 412;
on instinct and reflex action, 422
Sperm-cell and egg-cell, 13;
conditions which determine production of, 60
Sphex, instinct of, 429, 456
Spiders, hunting, mimicry in, 89;
Javan, Mr. H. O. Forbes on, 90;
love-antics of, 208, 450;
ocelli of, 289
SPINOZA, quoted, 61, 379, 460
Sponges, reproduction of, 41, 42
_Spongilla_, reproduction of, 46
Spore-formation, reproduction by, 38
Squirrel of Sarepta, 113
Stag-beetles, variation in males of, 180
Star-fish, embryo set free early, 56
Starling, modified song of, 455
ST. JOHN, observations on a retriever, 400
_Stenorhynchus_, 457
Sterility, how developed, 108
STEWART, Mr. Duncan, on sympathy in cat, 398
Stimuli, 302
STRANGE, Mr., on love-antics of satin bower-bird, 450
Striped ancestor of Equidæ, 230
Struggle for existence, 79;
variations in the intensity of, 112
STURGE, Miss Mildred, on the parrot, 355
_Stylonichia_, observations of M. Maupas on, 39
SULLY, Mr. James, on concepts, 325;
on propositions, 329;
on judgment and reason, 330;
on emotion, 390;
on æsthetic sense of beauty, 411
SUTTON, Mr. Bland, on hen pheasant like the male, 228;
on the action of leucocytes, 439
Swallow and swift, convergence in, 117;
cliff, of United States, 445
SWAYNE, Mr. S. H., on the elephant, 369
Symbolic nature of mental products, 314
SYMONDS, Mr. J. A., on "world-consciousness," 478
Sympathy in animals, 397
T
Tameness, instinctive, 435
TANNER, Miss Agnes, on a thrush, 398
Tasmanian salmon, 99
Taste, standard of, 95, 205;
sense of, 250
Teeth of pike, 437
Temperature-sense, 249
Terror, 387
_Thaumalia picta_ and _amherstiæ_, 106
_Thekla_, instinct of, 430
"Things in themselves," or noumena, 470
THOMAS, Mr. Oldfield, on rats of Solomon Islands, 100
THOMSON, Mr. J. A., Prof. Patrick GEDDES, and, on anabolism and
katabolism, 44;
quoted, 50, 137, 237;
his "History and Theory of Heredity," 35
Thought, 482
Thrush, hearing in, 264;
sympathy in, 398
THUNBERG on young hippopotamus, 423
Tissues of the body, 20
TOOKE, Mr. Hammond, on egg-eating snake, 88
Tools, use of, by animals, 370
Touch, sense of, 245
Transformation and metamorphosis, 7
Transparency of some marine organisms, 83
TREAT, Mrs., her experiments on caterpillars, 59
Tricks, 355
_Trionyx_, 181
_Trochus_, 292
Tuco-tuco, 194
TURNER, Sir Wm., on New Guinea natives, 169
Turkey, instinctive emotion in the, 395
Twins, Mr. Galton's investigations on, 169
TYLOR, Alfred, on coloration in animals and plants, 201
U
Udders, enlarged, of cows, 215
Ultra-violet rays, 296
Unicellular organism. _See_ Protozoa
Unity of organism, 161, 234
Use and disuse, 146, 209
Utility of specific characters, 110
V
_Vanessa urticæ_, 165
_Varanus benegalensis_, 288
Variation, correlated, 59;
and natural selection, 61;
tabulated by A. R. Wallace, 63;
in wing-bones of bats, 63;
advantageous, neutral, and disadvantageous, 95;
in climatal and geographical conditions, 112;
secular, in climate and life area, 113;
effect of good times and hard times on, 114;
heredity and the origin of, 122;
a source of, in use and disuse, 146;
sexual union, a mode of origin of, 149;
in definite directions, 151;
produced by extrusion of second polar cell, 153;
protozoan origin of, 156;
due to the action of environment, 163;
to the effects of use and disuse, 168;
to domestication, 171;
in male stag-beetles, 180;
in mating preferences, 205;
co-ordinated in Irish "elk" and giraffe, 212;
nature of, 216;
in amount of developmental capital, 221;
inheritance of, 223;
origin of, 231;
limitations of, 232;
fortuitous, in bat's wing, 235;
definite direction of, 238;
in limits of colour-vision, 281;
in habits and instincts, 445, 456;
in mental evolution, 496
Vertebrata, diagrammatic account of development of, 51
VERWORN, Dr., on protozoa, 440
_Vespertilio mystacinus_, 70
_Vesperugo leisleri_, 65
_Vesperugo noctula_, 67
_Vesperugo pipistrellus_, 69
Vigour and vitality, application of, in male, 237;
in female, 238
Vindictiveness, 401
Vision, 272; mosaic, 291
Volition, 459
_Volucella bombylans_, 90
Voluntary and involuntary activities, 416
_Vorticella_, 38
W
WAELCHLI, Dr., on colour-globules in birds, 284
WALLACE, Mr. A. R., tabulations of variations, 63;
on tortoiseshell butterfly of Isle of Man, 81;
on protective colours in fishes, 83;
on divergence among birds, 97;
on recognition-marks, 102;
on papilionidæ of Celebes, 165;
on the dull colours of hen birds, 199;
on origin of secondary sexual characters, 200;
and A. Tylor on physiological guidance, 201;
on preferential mating, 203;
on reversion in grouse, 229;
on migration in birds, 428;
on nest-building in birds, 453;
on the song of birds, 455;
on materialism, 464;
on mathematical and artistic faculties, 484, 497
WALKER, R., on reversion in bull, 229
WARD, Mr. J. Clifton, on dog, 345
Warning-coloration, 82;
involves perception, 351
WARREN, Mr. Robert Hall, a dog anecdote, 344
Wasp, use of antennæ, 291
Waste and repair essential life-processes, 8
Water, changes of salinity in, 164
Water-ousel, 446
WATERTON, Charles, 256
WATSON, "Reasoning Power of Animals," 369
WEBB, Dr., his operation on an elephant, 369
WEBER, on musical discrimination, 309;
on muscular sensation in eye, 310
WEIR, Mr. Jenner, on nest-building in birds, 453
WEISMANN, Dr., on continuity of germ-plasm, 138;
on distinctness of germ-plasm from body-plasm, 140;
on meaning of second polar cell, 153;
on protozoan origin of variations 156;
on the introduction of senility and death, 184;
on the distinction of birds' eggs, 189;
on the effects of panmixia, 190;
on acceleration, 222;
his views applied to instinct, 438;
the intellectual faculties, 497
WESTLAKE, Miss Mabel, on the parrot, 353
Whiskered bat, 70
White, in arctic forms, 165;
Mr. Poulton on production of, 202;
in grouse, instance of reversion, 229
Wildness of birds, instinctive, 435
WILL, F., on taste in bees, 253
WILSON, Sir Charles W., on wounded camels, 392
WILSON, Edward, measurements of bats, 63
Wing-bones of bats, measurement of, in illustration of variation, 63
Words, "understanding" of, by animals, 347
Wrasse, keenness of vision of, 287
X
Xiphocera, 179
Y
YOUATT "On Sheep," 455
YOUNG, Thomas, his colour-vision theory, 277
YUNG, his experiments on tadpoles, 59
Z
Zebra, inconspicuousness of, in dusk, 84
Zuyder Zee, new variety of herrings in, 99
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