| By Author | [ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z | Other Symbols ] |
| By Title | [ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z | Other Symbols ] |
| By Language |
|
Download this book: [ ASCII | HTML | PDF ] Look for this book on Amazon Tweet |
Title: The Making of Species
Author: Finn, Frank, Dewar, Douglas, 1875-1957
Language: English
As this book started as an ASCII text book there are no pictures available.
*** Start of this LibraryBlog Digital Book "The Making of Species" ***
http://www.pgdpcanada.net (This file was produced from
images generously made available by The Internet
Archive/American Libraries.)
[Illustration: HEX CURASSOW FEEDING YOUNG BIRD, WITH PLUMAGE OF THE
GLOBOSE CURASSOW]
THE MAKING
OF SPECIES
BY DOUGLAS DEWAR, B.A. (Cantab), I.C.S., F.Z.S.
AND FRANK FINN, B.A. (Oxon), F.Z.S., M.B.O.U.
WITH FIFTEEN ILLUSTRATIONS
LONDON: JOHN LANE THE BODLEY HEAD
NEW YORK: JOHN LANE COMPANY MCMIX
_Turnbull & Spears, Printers, Edinburgh_
PREFACE
Post-Darwinian books on evolution fall naturally into four classes. I.
Those which preach Wallaceism, as, for example, Wallace’s _Darwinism_,
Poulton’s _Essays on Evolution_, and the voluminous works of Weismann.
II. Those advocating Lamarckism. Cope’s _Factors of Evolution_ and the
writings of Haeckel belong to this class. III. The writings of De Vries,
forming a group by themselves. They advocate the theory that species
spring suddenly into being; that new species arise by mutations from
pre-existing species. IV. The large number of books of a more judicial
nature, books written by men who decline to subscribe to any of the above
three creeds. Excellent examples of such works are Kellog’s _Darwinism
To-Day_, Lock’s _Recent Progress in the Study of Variation, Heredity, and
Evolution_, and T. H. Morgan’s _Evolution and Adaptation_.
All four classes are characterised by defects.
Books of the two first classes exhibit the faults of ardent partisanship.
They formulate creeds, and, as Huxley truly remarked, “Science commits
suicide when it adopts a creed.” The books which come under the third
category have the defects of extreme youth. De Vries has discovered a new
principle, and it is but natural that he should exaggerate its
importance, and see in it more than it contains. But, as time wears on,
these faults will disappear, and the theory of mutations will assume its
true form and fall into its proper place, which is somewhere between the
dustbin, to which Wallaceians would relegate it, and the exalted pinnacle
on to which De Vries would elevate it.
In the present state of our knowledge, books of Class IV. are the most
useful to the student, since they are unbiassed, and contain a judicial
summing-up of the evidence for and against the various evolutionary
theories which now occupy the field. Their chief defect is that they are
almost entirely destructive. They shatter the faith of the reader, but
offer nothing in place of that which they have destroyed. T. H. Morgan’s
_Evolution and Adaptation_, however, contains much constructive matter,
and so is the most valuable work of this class in existence.
Zoological science stands in urgent need of constructive books on
evolution—books with leanings towards neither Wallaceism, nor Lamarckism,
nor De Vriesism; books which shall set forth facts of all kinds,
concealing none, not even those which do not admit of explanation in the
present state of our knowledge.—It has been our aim to produce a book of
this description.
We have endeavoured to demonstrate that neither pure Lamarckism nor pure
Wallaceism affords a satisfactory explanation of the various phenomena of
the organic world. We have further, while recognising the very great
value of the work of De Vries, tried to show that that eminent botanist
has allowed his enthusiasm to carry him a little too far into the realm
of speculation. We have followed up the exposure of the weak points of
the theories, which at present occupy the field, with certain
suggestions, which, we believe, throw new light on many biological
problems.
Our aim in writing this book has been twofold. In the first place we have
attempted to place before the general public in simple language a true
statement of the present position of biological science. In the second
place, we have endeavoured to furnish the scientific men of the day with
food for reflection.
Even as the British nation seems to be slowly but surely losing, through
its conservatism, the commercial supremacy it had the good fortune to
gain last century, so is it losing, through the unwillingness of many of
our scientific men to keep abreast of the times, that scientific
supremacy which we gained in the middle of last century by the labours of
Charles Darwin and Alfred Russell Wallace. To-day it is not among
Englishmen, but among Americans and Continentals, that we have to look
for advanced scientific ideas.
Even as the Ultra-Cobdenites believe that Free Trade is a panacea for all
economic ills, so do most English men of science believe that natural
selection offers the key to every zoological problem. Both are living in
a fool’s paradise. Another reason why Great Britain is losing her
scientific supremacy is that too little attention is paid to bionomics,
or the study of live animals. Morphology, or the science of dead
organisms, receives more than its due share of attention. It is in the
open, not in the museum or the dissecting-room, that nature can best be
studied. Far be it from us to deprecate the study of morphology. We wish
merely to insist upon the fact, that the leaders of biological science
must of necessity be those naturalists who go to the tropics and other
parts of the earth where nature can be studied under the most favourable
conditions, and those who conduct scientific breeding experiments.
Natural selection—the idea which has revolutionised modern biological
science—came, not to professors, but to a couple of field-naturalists who
were pursuing their researches in tropical countries. It is absurd to
expect those who stay at home and gain most of their knowledge
second-hand to be the pioneers of biological science.
We fear that this book will come as a rude shock to many scientific men.
By way of consolation we may remind such that they will find themselves
in much the same position as that occupied by theologians immediately
after the appearance of the _Origin of Species_.
At that time theological thought was cramped by dogma. But the clergy
have since reconsidered their position, they have modified their views,
and thus kept abreast of the times. Meanwhile scientific men have lagged
behind. The blight of dogma has seized hold of them. They have adopted a
creed to which all must subscribe or be condemned as heretics. Huxley
said that the adoption of a creed was tantamount to suicide. We are
endeavouring to save biology in England from committing suicide, to save
it from the hands of those into which it has fallen.
We would emphasise that it is not Darwinism we are attacking, but that
which is erroneously called Neo-Darwinism. Neo-Darwinism is a
pathological growth on Darwinism, which, we fear, can be removed only by
a surgical operation.
Darwin, himself, protested in vain against the length to which some of
his followers were pushing his theory. On p. 657 of the new edition of
the _Origin of Species_ he wrote: “As my conclusions have lately been
much misrepresented, and as it has been stated that I attribute the
modification of species exclusively to natural selection, I may be
permitted to remark that in the first edition of this work, and
subsequently, I placed in a most conspicuous position—namely, at the
close of the Introduction—the following words: ‘I am convinced that
natural selection has been the main but not the exclusive means of
modification.’ This has been of no avail. Great is the power of steady
misrepresentation; but the history of science shows that this power does
not long endure.”
Notwithstanding this protest the Wallaceians continue on their course,
and give to the world a spurious Darwinism. It is our belief that were
Darwin alive to-day his sympathies would be with us, and not with those
who call themselves his followers. It was one of Darwin’s strong points
that he never avoided facts. If new facts came to light which were
incompatible with a theory of his, he promptly modified his theory. Since
his death a number of new facts have come to light which, in our opinion,
plainly indicate that the theory of natural selection as enunciated by
Darwin needs considerable modification.
We have in this book set forth certain of these facts and indicated the
directions in which the Darwinian theory seems to require modification.
This volume originated as the result of several conversations we, the
joint authors, had last summer. We discovered that we had a great many
ideas in common on the subject of evolution. This seemed strange, seeing
that our education had not been on the same lines. One of us took a
degree in natural science at Cambridge, and subsequently entered His
Majesty’s Indian Civil Service, but continued his zoological studies in
India as a hobby. The other, a naturalist from childhood, nevertheless
took a classical degree at Oxford, then received a technical zoological
training, adopted zoology as a profession, and held for some years a
position in the Natural History Museum at Calcutta.
Our conversations revealed that we were both of opinion that biology is
in an unhealthy condition, especially in England, and that the science
sorely needs some fresh impetus. Neither of us had the time to attempt,
single-handed, to give the required impetus, but as one of us happened to
be home on eighteen months’ leave, we thought we might undertake the task
in collaboration.
We felt that we might collaborate the more successfully because the large
number of facts collected by the one of us form the necessary complement
to the philosophical studies of the other.
We have endeavoured, so far as possible, to avoid technical terms, and
have made a special point of quoting, wherever practicable, familiar
animals as examples, in order that the work may make its appeal not only
to the zoologist but to the general reader.
It may, perhaps, be urged against us that we have quoted too freely from
popular writings, including those of which we are the authors. Our reply
to this is that the study of bionomics, the science of living animals,
occupies so small a place in English scientific literature that we have
been compelled to have recourse to popular works for many of our facts;
and we would, moreover, point out that a popular work is not necessarily
inaccurate in its information.
In conclusion, we would warn the reader against the danger of confounding
Inference with Fact. The failure to distinguish between the two has
vitiated much of the work of the Wallaceian school of biologists.
Facts are always to be accepted. Inferences should be scrutinised with
the utmost care.
In making our deductions, we have endeavoured to act without bias. We
shall, therefore, welcome any new facts, be they consistent with, or
opposed to, our inferences.
D. D.
F. F.
CONTENTS
PAGE
CHAPTER I 1
Rise of the Theory of Natural Selection and its Subsequent Development
Pre-Darwinian Evolutionists—Causes which led to the speedy triumph
of the theory of Natural Selection—Nature of the opposition which
Darwin had to overcome—Post-Darwinian biology—Usually accepted
classification of present-day biologists as Neo-Lamarckians and
Neo-Darwinians is faulty—Biologists fall into three classes rather
than two—Neo-Lamarckism: its defects—Wallaceism: its
defects—Neo-Darwinism distinguished from Neo-Lamarckism and
Wallaceism—Neo-Darwinism realises the strength and weakness of the
theory of Natural Selection, recognises the complexity of the
problems which biologists are endeavouring to solve.
CHAPTER II 30
Some of the more Important Objections to the Theory of Natural Selection
Brief statement of Theory—Objections to the Theory fall into two
classes—Those which strike at the root of the Theory—Those which
deny the all-sufficiency of Natural Selection—Objections which
strike at root of Theory are based on misconception—Objections to
Wallaceism—The Theory fails to explain the origin of
Variations—Natural Selection called on to explain too much—Unable
to explain beginnings of new organs—The Theory of change of
function—The co-ordination of variations—The fertility of races of
domesticated animals—Missing links—Swamping effects of
intercrossing—Small variations cannot have a survival value—Races
inhabiting same area—Excessive specialisation—Chance and Natural
Selection—Struggle for existence most severe among young
animals—Natural Selection fails to explain mimicry and other
phenomena of colour—Conclusion, that scarcely an organism exists
which does not possess some feature inexplicable on the theory of
Natural Selection as held by Wallace and his followers.
CHAPTER III 52
Variation
The assumption of Darwin and Wallace that variations are haphazard
in origin and indefinite in direction—If these assumptions be not
correct Natural Selection ceases to be the fundamental factor in
evolution—Darwin’s views regarding variation underwent
modification—He eventually recognised the distinction between
definite and indefinite variations, and between continuous and
discontinuous variations—Darwin attached but little importance to
either definite or discontinuous variations—Darwin’s views on the
causes of variations—Criticism of Darwin’s views—Variations appear
to occur along certain definite lines—There seems to be a limit to
the extent to which fluctuating variations can be accumulated—De
Vries’ experiments—Bateson on “discontinuous variation”—Views held
by De Vries—Distinction between continuous and discontinuous
variations—The work of De Vries—Advantages enjoyed by the botanist
in experimenting on the making of species—Difficulties encountered
by the animal breeder—Mutations among animals—The distinction
between germinal and somatic variations—The latter, though not
transmitted to offspring, are often of considerable value to their
possessor in the struggle for existence.
CHAPTER IV 111
Hybridism
The alleged sterility of hybrids a stumbling-block to
evolutionists—Huxley’s views—Wallace on the sterility of
hybrids—Darwin on the same—Wallace’s theory that the infertility of
hybrids has been caused by Natural Selection so as to prevent the
evils of intercrossing—Crosses between distinct species not
necessarily infertile—Fertile crosses between species of
plants—Sterile plant hybrids—Fertile mammalian hybrids—Fertile bird
hybrids—Fertile hybrids among amphibia—Limits of
hybridisation—Multiple hybrids—Characters of hybrids—Hybridism does
not appear to have exercised much effect on the origin of new
species.
CHAPTER V 133
Inheritance
Phenomena which a complete theory of inheritance must explain—In
the present state of our knowledge it is not possible to formulate
a complete theory of inheritance—Different kinds of
inheritance—Mendel’s experiments and theory—The value and
importance of Mendelism has been exaggerated—Dominance sometimes
imperfect—Behaviour of the nucleus of the sexual
cell—Chromosomes—Experiments of Delage and Loeb—Those of Cuénot on
mice and Castle on guinea pigs—Suggested modification of the
generally-accepted Mendelian formulæ—Unit characters—Biological
isomerism—Biological molecules—Interpretation of the phenomena of
variation and heredity on the conception of biological
molecules—Correlation—Summary of the conception of biological
molecules.
CHAPTER VI 170
The Colouration of Organisms
The theory of protective colouration has been carried to absurd
lengths—It will not bear close scrutiny—Cryptic colouring—Sematic
colours—Pseudo-sematic colours—Batesian and Müllerian
mimicry—Conditions necessary for mimicry—Examples—Recognition
markings—The theory of obliterative colouration—Criticism of the
theory—Objections to the theory of cryptic colouring—Whiteness of
the Arctic fauna is exaggerated—Illustrative tables—Pelagic
organisms—Objectors to the Neo-Darwinian theories of colouration
are to be found among field naturalists—G. A. B. Dewar, Gadow,
Robinson, F. C. Selous quoted—Colours of birds’ eggs—Warning
colouration—Objections to the theory—Eisig’s theory—So-called
intimidating attitudes of animals—Mimicry—The case for the
theory—The case against the theory—“False mimicry”—Theory of
recognition colours—The theory refuted—Colours of flowers and
fruits—Neo-Darwinian explanations—Objections—Kay Robinson’s
theory—Conclusion that Neo-Darwinian theories are untenable—Some
suggestions regarding the colouration of animals—Through the
diversity of colouring of organisms something like order runs—The
connection between biological molecules and colour—Tylor on colour
patterns in animals—Bonhote’s theory of pœcilomeres—Summary of
conclusions arrived at.
CHAPTER VII 297
Sexual Dimorphism
Meaning of the term—Fatal to Wallaceism—Sexual Selection—The law of
battle—Female preference—Mutual Selection—Finn’s
experiments—Objections to the theory of Sexual Selection—Wallace’s
explanation of sexual dimorphism stated and shown to be
unsatisfactory—The explanation of Thomson and Geddes shown to be
inadequate—Stolzmann’s theory stated and criticised—Neo-Lamarckian
explanation of sexual dimorphism stated and criticised—Some
features of sexual dimorphism—Dissimilarity of the sexes probably
arises as a sudden mutation—The four kinds of mutations—Sexual
dimorphism having shown itself, Natural Selection determines
whether or not the organisms which display it shall survive.
CHAPTER VIII 345
The Factors of Evolution
Variation along definite lines and Natural Selection are undoubtedly
important factors of evolution—Whether or not sexual selection is a
factor we are not yet in a position to decide—_Modus operandi_ of
Natural Selection—Correlation an important factor—Examples of
correlation—Correlation is a subject that requires close
study—Isolation a factor in evolution—Discriminate
isolation—Indiscriminate isolation—Is the latter a factor?—Romanes’
views—Criticism of these—Indiscriminate isolation shown to be a
factor—Summary of the methods in which new species arise—Natural
Selection does not make species—It merely decides which of certain
ready-made forms shall survive—Natural Selection compared to a
competitive examination and to a medical board—We are yet in
darkness as to the fundamental causes of the Origin of Species—In
experiment and observation rather than speculation lies the hope of
discovering the nature of these causes.
Footnotes 389
Index 389
LIST OF ILLUSTRATIONS
FACING PAGE
Heck’s Curassow feeding Young Bird, which has the Plumage of the Hens
of the Globose Curassow, its Father’s Species _Frontispiece_
_By permission of the Avicultural Society._
A Turbit belonging to Mr H. P. Scatliff 92
_From “The Modern Turbit,” published by “The Feathered World,” London._
Yellow-Rumped and Chestnut-Breasted Finches, with Specimens in
Transitional State 98
On the left, the yellow-rumped finch; on the right, the
chestnut-breasted; birds in state of change in the middle.
_By permission of the Avicultural Society._
Male Amherst Pheasant 122
The chief colours of this species (_Chrysolophus amherstiæ_) are
white and metallic green, so that it is very different in
appearance from its near ally the gold pheasant.
Harlequin Quail (_Coturnix delegorguei_) 124
_By permission of the Avicultural Society._
Rain Quail (_Coturnix coromandelica_) 124
The markings on the throats of these quails are of the type usually
put down as “recognition marks,” but as the Harlequin Quail is
African and the Rain Quail Indian, the two species cannot possibly
interbreed. The pattern, then, can have no “recognition”
significance.
_By permission of the Avicultural Society._
Bouru Friar-Bird 222
Like most of the group to which it belongs, this honey-eater
(_Tropidorhynchus bouruensis_) is a soberly coloured bird, but is
noisy, active, and aggressive.
_By permission of Messrs Hutchinson & Co._
Bouru Oriole 222
This “mimicking” oriole (_Oriolus bouruensis_) is of the same tone
of colour as its supposed model the Friar-bird of the same island.
_By permission of Messrs Hutchinson & Co._
King-Crow or Drongo 232
This very conspicuous black bird (_Dicrurus ater_), ranging from
Africa to China, is a striking feature of the landscape wherever it
occurs.
_By permission of Messrs Hutchinson & Co._
Drongo-Cuckoo 232
The fork of the tail in this bird is unique among cuckoos, but is
nevertheless much less developed than in the supposed model, and
may be an adaptation for evolutions in flight, as such tails
usually appear to be.
_By permission of Messrs Hutchinson & Co._
Shikra Hawk 236
The upper surface of the tail, not shown in this drawing, exactly
corresponds with that of the cuckoo “mimic.”
_By permission of Messrs Hutchinson & Co._
Hawk-Cuckoo 236
This species (_Hierococcyx varius_) is commonly known in India as
the “Brain-fever bird.”
_By permission of Messrs Hutchinson & Co._
Brazilian Troupial 284
This species (_Icterus vulgaris_) is that most frequently seen in
captivity; the pattern of colour is found in several other allied
forms.
_By permission of Messrs Hutchinson & Co._
Indian Black-Headed Oriole 284
Several other orioles besides this (_O. melanocephalus_) have the
black head.
_By permission of Messrs Hutchinson & Co._
Queen Whydah 298
This species (_Tetraenura regia_) is a typical example of seasonal
sexual dimorphism, the male being long-tailed and conspicuously
coloured only during the breeding season, and at other times
resembling the sparrow-like female.
_By permission of the Foreign Bird Club._
Courtship of Skylark 314
Illustrating display by a species with no decorative colouring or
sex difference.
THE MAKING OF SPECIES
CHAPTER I
RISE OF THE THEORY OF NATURAL SELECTION AND ITS SUBSEQUENT DEVELOPMENT
Pre-Darwinian Evolutionists—Causes which led to the speedy triumph of
the theory of Natural Selection—Nature of the opposition which Darwin
had to overcome—Post-Darwinian biology—Usually accepted classification
of present-day biologists as Neo-Lamarckians and Neo-Darwinians is
faulty—Biologists fall into three classes rather than
two—Neo-Lamarckism: its defects—Wallaceism: its defects—Neo-Darwinism
distinguished from Neo-Lamarckism and Wallaceism—Neo-Darwinism realises
the strength and weakness of the theory of Natural Selection,
recognises the complexity of the problems which biologists are
endeavouring to solve.
Darwinism and evolution are not interchangeable terms. On this fact it is
impossible to lay too much emphasis. Charles Darwin was not the
originator of the theory of evolution, nor even the first to advocate it
in modern times. The idea that all existing things have been produced by
natural causes from some primordial material is as old as Aristotle. It
was lost sight of in the mental stagnation of the Middle Ages. In that
dark period zoological science was completely submerged. It was not until
men shook off the mental lethargy that had held them for many generations
that serious attention was paid to biology. From the moment when men
began to apply scientific methods to that branch of knowledge the idea of
evolution found supporters.
Buffon suggested that species are not fixed, but may be gradually changed
by natural causes into different species.
Goethe was a thorough-going evolutionist; he asserted that all animals
were probably descended from a common original type.
Lamarck was the first evolutionist who sought to show the means whereby
evolution has been effected. He tried to prove that the efforts of
animals are the causes of variation; that these efforts originate changes
in form during the life of the individual which are transmitted to its
offspring.
St Hilaire was another evolutionist who endeavoured to explain how
evolution had occurred. He believed that the transformations of animals
are effected by changes in their environment. These hypotheses were
considered, and rightly considered, insufficient to explain anything like
general evolution, so that the idea failed for a time to make headway.
Strength of Darwin’s Position
As knowledge grew, as facts accumulated, the belief in evolution became
more widespread. Hutton, Lyell, Spencer, and Huxley were all convinced
that evolution had occurred, but they could not explain how it had
occurred.
Thus, by the middle of last century, all that was needed to make
evolution an article of scientific belief was the discovery of a method
whereby it could be effected. This Darwin and Wallace were able to
furnish in the shape of the theory of natural selection. The discovery
was made independently, but Darwin being the older man, the more
influential, and the one who had gone the more deeply and carefully into
the matter, gained the lion’s share of the credit of the discovery. The
theory of natural selection is universally known as the Darwinian theory,
notwithstanding the fact that Darwin, unlike Wallace, always recognised
that natural selection is not the sole determining factor in organic
evolution.
From the moment of the enunciation of his great hypothesis, Darwin’s
position was an exceedingly strong one. Everything was in his favour.
As we have seen, the theory was enunciated at the psychological moment,
at the time when zoological science was ripe for it. Most of the leading
zoologists were evolutionists at heart, and were only too ready to accept
any theory which afforded a plausible explanation of what they believed
to have occurred.
Hence the rapturous welcome accorded to the theory of natural selection
by the more progressive biologists.
Another point in Darwin’s favour was the delightful simplicity of his
hypothesis. Nothing could be more enticingly probable. It is based on the
unassailable facts of variation, heredity, and the tendency of animals to
multiply in numbers. Everybody knows that the breeder can fix varieties
by careful breeding. Darwin had simply to show that there is in nature
something to take the part played among domesticated animals by the human
breeder. This he was able to do. As the numbers of species remain
stationary, it is evident that only a small portion of the animals that
are born can reach maturity. A child can see that the individuals most
likely to survive are those best adapted to the circumstances of their
life. Even as the breeder weeds out of his stock the creatures not suited
to his purpose, so in nature do the unfit perish in the everlasting
struggle for existence.
In nature there is a selection corresponding to that of the breeder.
It is useless to deny the existence of this selection in nature, this
natural selection. The only disputable point is whether such selection
can do all that Darwin demanded of it.
The man in the street, then, was able to comprehend the theory of natural
selection. This was greatly in its favour. Men are usually well disposed
towards doctrines which they can readily understand.
The nineteenth century was a superficial age. It liked simplicity in all
things. If Darwin could show that natural selection was capable of
producing one species, men were not only ready but eager to believe that
it could explain the whole of organic evolution.
The simplicity of the Darwinian theory has its evil side. It has
undoubtedly tended to make modern biologists superficial in their
methods. It has, indeed, stimulated the imagination of men of science;
but the stimulation has not in all cases been a healthy one.
So far from adhering to the sound rule laid down by Pasteur, “never
advance anything that cannot be proved in a simple and decisive manner,”
many modern naturalists allow their imagination to run riot, and so
formulate ill-considered theories, and build up hypotheses on the most
insecure foundations. “A tiny islet of truth,” writes Archdale Reid, “is
discovered, on which are built tremendous and totally illegitimate
hypotheses.”
Another source of Darwin’s strength was the vast store of knowledge he
had accumulated. For twenty years he had been steadily amassing facts in
support of his hypothesis. He enunciated no crude theory, he indulged in
no wild speculations. He was content to marshal a great array of facts,
and to draw logical conclusions therefrom. He was as cautious in his
deductions as he was careful of his facts. He thus stood head and
shoulders above the biologists of his day. He was a giant among pigmies.
So well equipped was he that those who attempted to oppose him found
themselves in the position of men, armed with bows and arrows, who seek
to storm a fortress defended by maxim guns.
Nor was this all. The majority of the best biologists of his time did not
attempt to oppose him. They were, as we have seen, ready to receive with
open arms any hypothesis which seemed to explain how evolution had
occurred. Some of them perceived that there were weak points in the
Darwinian theory, but they preferred not to expose these; they were
rather disposed to make the best of the hypothesis. It had so many merits
that it seemed to them but reasonable to suppose that subsequent
investigation would prove that the defects were apparent rather than
real.
Opponents of Darwin
We hear much of the “magnitude of the prejudices” which Darwin had to
overcome, and of the mighty battle which Darwin and his lieutenant Huxley
had to fight before the theory of the origin of species by natural
selection obtained acceptance. We venture to say that statements such as
these are misleading. We think we may safely assert that scarcely ever
has a theory which fundamentally changed the prevailing scientific
beliefs met with less opposition. It would have been a good thing for
zoology had Darwin not obtained so easy a victory.
Sir Richard Owen, a distinguished anatomist, certainly attacked the
doctrine in no unmeasured terms, but his attack was anonymous and so
cannot be considered very formidable. Far more important was the
opposition of Dr St George Mivart, whose worth as a biologist has never
been properly appreciated. His most important work, entitled the _Genesis
of Species_, might be read with profit even now by many of our modern
Darwinians.
For some time after the publication of the _Origin of Species_ Mivart
appears to be almost the only man of science fully alive to the weak
points of the Darwinian theory. The great majority seem to have been
dazzled by its brilliancy.
The main attack on Darwinism was conducted by the theologians and their
allies, who considered it to be subversive of the Mosaic account of the
Creation. Now, when one whose scientific knowledge is, to say the best of
it, not extensive, attacks a man who has studied his subject
dispassionately for years, and invariably expresses himself with extreme
caution, the onslaught can have but one result—the attacker will be
repulsed with heavy loss, and the onlookers will have a higher opinion of
his valour than of his common sense.
The theologians were in the unfortunate position of warriors who do not
know what it is against which they are fighting; they confounded natural
selection with evolution, and directed the main force of their attack
against the latter, under the impression that they were fighting the
Darwinian theory.
It was the misfortune of those theologians that it is possible to prove
that evolution, or, at any rate, some evolution has occurred; they thus
kicked against the pricks with disastrous results to themselves. When
this attack had been repulsed men believed that the theory of natural
selection had been demonstrated, that it was as much a law of nature as
that of gravitation. What had really happened was that the fact of
evolution had been proved, and the theory of natural selection obtained
the credit. Men thought that Darwinism was evolution. Had the theologians
admitted evolution but denied the ability of natural selection to explain
it, the Darwinian theory, in all probability, would not have gained the
ascendency which it now enjoys.
Evolution and Natural Selection
To us who are able to look back dispassionately upon the biological
warfare of the last century, Darwin’s opponents—or the majority of
them—appear very foolish. We must, however, bear in mind that at the time
of the publication of the _Origin of Species_ both natural selection and
evolution were comparatively unknown ideas. Darwin had to fight for both.
He had to prove evolution as well as natural selection. Many of the facts
adduced by him supported both. It is, therefore, not altogether
surprising that many of his opponents failed to distinguish between them.
A glance at the _Origin of Species_ will suffice to show how considerable
is the portion of the book that deals with the evidence in favour of
evolution rather than of natural selection.
Of the fourteen chapters which make up the book no fewer than nine are
devoted to proving that evolution has occurred. It has been truly said,
that for every one fact biologists have found in support of the special
theory of natural selection they have found ten facts supporting the
doctrine of evolution. Darwin, then, was in the position of a skilled
barrister who has a plausible case and who knows the ins and outs of his
brief, while his opponents stood in the shoes of inexperienced counsel
who had but recently received their brief, and who had not had the time
to master the details thereof. In such circumstances it is not difficult
to predict which way the verdict of the jury will go.
Darwin, moreover, had a charming personality. Never was a man with a
theory less dogmatic. Never was the holder of a theory more careful of
the expressions he used. Never was a scientific man more ready to give
ear to his opponents, to meet them half way, and, where necessary, to
compromise. Darwin was not afraid of facts, and was always ready to alter
his views when they appeared to be opposed to facts. The average
scientific man of to-day makes facts fit his theory; if they refuse to
fit it he ignores or denies them.
Darwin continually modified his views; when he found himself in a tight
place he did not hesitate to resort to Lamarckian factors, such as the
inheritance of the effects of use and disuse and of the effects of
environment. He conceded that natural selection was insufficient to
account for all the phenomena of organic evolution, and advanced the
theory of sexual selection in order to account for facts which the major
hypothesis seemed to him incapable of explaining.
Darwin, moreover, having ample private means, was not obliged to work for
a living, and was therefore able to devote the whole of his time to
research. The advantages of such a position cannot be over-estimated,
and, perhaps, have not been sufficiently taken into account in
apportioning the praise between Darwin and Wallace for their great
discovery.
Huxley
To all these factors in Darwin’s favour we must add his good fortune in
possessing so able a lieutenant as Huxley.
Huxley was an ardent evolutionist, an able writer, and a brilliant
debater. A man of his mental calibre was able, like a clever barrister,
to make out a plausible case for any theory which he chose to take up.
While nominally a strong supporter of the Darwinian theory, he was in
reality fighting for the doctrine of descent. Had _any_ plausible theory
of evolution been enunciated, Huxley would undoubtedly have fought for it
equally earnestly.
A firm believer in evolution, Huxley was, as Professor Poulton says,
confronted by two difficulties,—first, the insufficiency of the evidence
of evolution, and, secondly, the absence of any explanation of how the
phenomenon had occurred. The _Origin of Species_ solved both these
difficulties. It adduced much weighty evidence in favour of evolution,
and suggested a _modus operandi_. Small wonder, then, that Huxley became
a champion of Darwinism. But, as Poulton writes, on page 202 of _Essays
on Evolution_, “while natural selection thus enabled Huxley freely to
accept evolution, he was by no means fully satisfied with it.” “He never
committed himself to a full belief in natural selection, and even
contemplated the possibility of its ultimate disappearance.” To use
Huxley’s own words: “Whether the particular shape which the doctrine of
evolution, as applied to the organic world, took in Darwin’s hands, would
prove to be final or not, was, to me, a matter of indifference.”
The result of the fortuitous combination of the circumstances which we
have set forth was that in a surprisingly short time the theory of
natural selection came to be regarded as a law of nature on a par with
the laws of gravitation. Thus, paradoxical though it seems, practical
certainty was given to a hitherto uncertain doctrine by the addition of a
still more uncertain theory.
“At once,” writes Waggett, “the theory of development leapt from the
position of an obscure guess to that of a fully-equipped theory and
almost a certainty.”
Darwin thus became a dictator whose authority none durst question. A
crowd of slavish adherents gathered round him, a herd of men to whom he
seemed an absolutely unquestionable authority. Darwinism became a creed
to which all must subscribe. It still retains this position in the
popular mind.
Growing Opposition to Darwinism
The ease with which the theory of natural selection gained supremacy was,
as we have already said, a misfortune to biological science. It produced
for a time a considerable mental stagnation among zoologists. Since
Darwin’s day the science has not made the progress that might reasonably
have been expected, because the theory has so captivated the minds of the
majority of biologists that they see everything through Darwinian
spectacles. The wish has been in many cases the father to the
observation. Zoologists are ever on the lookout for the action of natural
selection, and in consequence frequently imagine they see it where it
does not exist. Many naturalists, consciously or unconsciously, stretch
facts to make them fit the Darwinian theory. Those facts which refuse to
be so distorted are, if not actively ignored or suppressed, overlooked as
throwing no light upon the doctrine. This is no exaggeration. A perusal
of almost any popular book dealing with zoological theory leaves the
impression that there is nothing left to be explained in the living
world, that there is no door leading to the secret chambers of nature to
which natural selection is not an “open sesame.”
But the triumph of natural selection has not been so complete as its more
enthusiastic supporters would have us believe. Some there are who have
never admitted the all-sufficiency of natural selection. In the British
Isles these have never been numerous. In the United States of America and
on the Continent they are more abundant. The tendency seems to be for
them to increase in numbers. Hence the recent lamentations of Dr Wallace
and Sir E. Ray Lankester. Modern biologists are commonly supposed to fall
into two schools of thought—the Neo-Darwinian and the Neo-Lamarckian.
The former are the larger body, and pin their faith absolutely to natural
selection. They deny the inheritance of acquired characters, and preach
the all-sufficiency of natural selection to explain the varied phenomena
of nature. The Neo-Lamarckians do not admit the omnipotency of natural
selection. Some of them allow it no virtue. Others regard it as a force
which keeps variation within fixed limits, which says to each organism,
“thus far shalt thou vary and no farther.” This school lays great stress
on the inheritance of acquired characters, especially on the inheritance
of the effects of use and disuse.
The above statement of the recent developments of Darwinism is
incomplete, for it fails to include those who occupy a middle position.
If it be possible to classify a large number of men of which scarcely any
two hold identical views, it is into three, rather than two, classes that
they must be divided.
Speaking broadly, evolutionists of to-day may be said to represent three
distinct lines of thought. For the sake of classification we may speak of
them as falling into three schools, which we may term the Neo-Lamarckian,
the Wallaceian, and the Neo-Darwinian, according as their views incline
towards those held by Lamarck, Wallace, or Darwin.
The Neo-Lamarckian School
As adherents of the Neo-Lamarckian school, we cite Cope, Spencer, Orr,
Eimer, Naegeli, Henslow, Cunningham, Haeckel, Korchinsky, and a number of
others. It may almost be said of these Neo-Lamarckians that each holds a
totally distinct theory of evolution. So heterogeneous are their views
that it is difficult to find a single article common to the evolutionary
belief of all. It is commonly asserted that all Neo-Lamarckians are
agreed, firstly, that acquired characters are transmissible; and,
secondly, that such transmission is an important factor in the production
of new species. This assertion is certainly true of the great bulk of
Neo-Lamarckians, but it does not appear to hold in the case of those who
believe that evolution is the result of some unknown inner force. So far
as we can see, a belief in the inheritance of acquired characters is not
necessary to the theories of orthogenesis held by Naegeli and Korchinsky.
For that reason it would possibly be more correct to place those who hold
such views in a fourth school. Since, however, a number of undoubted
Neo-Lamarckians, as, for example, Cope, believe in an inner growth-force,
it is convenient to regard Naegeli as a Neo-Lamarckian. His views need
not detain us long. Those who wish to study them in detail will find them
in his _Mechanisch-physiologische Theorie der Abstammungslehre_.
Naegeli believes that there is inherent in protoplasm a growth-force,
which makes each organism in itself a force making towards progressive
evolution. He holds that animals and plants would have become much as
they are now even if no struggle for existence had taken place. “To the
believers in this kind of . . . orthogenesis,” writes Kellog (_Darwinism
To-day_, p. 278), “organic evolution has been, and is now, ruled by
unknown inner forces inherent in organisms, and has been independent of
the influence of the outer world. The lines of evolution are immanent,
unchangeable, and ever slowly stretch toward some ideal goal.” It is easy
to enunciate such a theory, impossible to prove it, and difficult to
disprove it.
It seems to us that the fact that, so soon as organisms are removed from
the struggle for existence, they tend to degenerate, is a sufficient
reason for refusing to accept theories of the description put forth by
Naegeli. More truly Lamarckian is Eimer’s theory of orthogenesis,
according to which it is the environment which determines the direction
which variation takes; and the variations which are induced by the
environment are transmitted to the offspring.
Orr’s Views
Spencer and Orr preach nearly pure Lamarckism. The former, while fully
recognising the importance of natural selection, considered that
sufficient weight has not been given to the effects of use and disuse, or
to the direct action of the environment in determining or modifying
organisms.
The similarity of the views of Orr and Lamarck is best seen by comparing
their respective explanations of the long neck of the giraffe. Lamarck
thought that this was the direct result of continual stretching. The
animal continually strains its neck in the search for food, hence it
grows longer as the individual grows older, and this elongated neck has
been transmitted to the offspring. Orr writes, on page 164 of his
_Development and Heredity_: “The giraffe seems to present the most
remarkable illustration of the lengthening of the bones as the result of
the frequent repetition of such shocks. As is well known, this animal
feeds on the foliage of trees. From the earliest youth of the species,
and the earliest youth of each individual, it must have been stretching
upwards for food, and, as is the custom of such quadrupeds, it must have
constantly raised itself off its forefeet, and, as it dropped, must have
received a shock that made itself felt from the hoofs through the legs
and vertical neck to the head. In the hind legs the shock would not be
felt. It is impossible to imagine that an animal which, during the
greater part of every day of its life (both its individual and racial
life), performed motions so uniform and constant, would not be peculiarly
specialised as a result. The forces acting upon such an animal are widely
different from the forces acting upon an animal which eats the grass at
its feet like an ox, or one which must run and climb like a goat or a
deer, and the resultant modifications of growth in the several cases must
also be different. The principle of increased growth in the direction of
the shock, resulting from superabundant repair of the momentary
compression, explains how the giraffe acquired the phenomenal length of
the bones of its forelegs and neck; and the absence of the shock in the
hind-quarters shows why they remained undeveloped and absurdly
disproportionate to the rest of the body.”
Inheritance of Acquired Characters
It seems to us that a fatal objection to all these Neo-Lamarckian
theories of evolution is that they are based on the assumption that
acquired characters are inherited, whereas all the evidence goes to show
that such characters are not inherited. In these days, when scientific
knowledge is so widely diffused, it is scarcely necessary to say that all
the characteristics which an organism displays are either congenital or
inborn, or acquired by the organism during its lifetime. Thus a man may
have naturally a large biceps muscle, and this is a congenital character;
or he may by constant exercise develop or greatly increase the size of
the biceps. The large biceps, in so far as it has been increased by
exercise, is said to be an acquired character, for it was not inherited
by its possessor, but acquired by him in his lifetime. We must bear in
mind that the period in the life history of an organism at which a
character appears, is not necessarily a test as to whether it is
congenital or acquired, for a great many congenital characters, such as a
man’s beard, do not appear until some years after birth. As we have seen,
the Neo-Lamarckians believe that it is possible for an organism to
transmit to its offspring characters which it has acquired during the
course of its existence. But, as we have already said, the evidence goes
to show that such characters are not inherited. For example, the tail of
the young fox-terrier is not shorter than that of other breeds of dogs,
notwithstanding the fact that its ancestors have for generations had the
greater portion of their caudal appendage removed shortly after birth.
We do not propose to discuss at any great length the vexed question of
the inheritance of acquired characters, for the simple reason that the
Neo-Lamarckians have not brought forward a single instance which
indubitably proves that such characters are inherited.
Mr J. T. Cunningham, in a paper of great value and interest, entitled
“The Heredity of Secondary Sexual Characters in relation to Hormones: a
Theory of the Heredity of Somatogenic Characters,” which appeared in vol.
xxvi., No. 3, of the _Archiv für Entwicklungsmechanik des Organismen_,
states: “The dogma that acquired characters cannot be inherited . . . is
founded not so much on evidence, or the absence of evidence, as on _a
priori_ reasoning, on the supposed difficulty or impossibility of
conceiving a means by which such inheritance could be effected.” Such
appears certainly to be true of some zoologists, but we trust that Mr
Cunningham will do us the justice to believe that our opinion that the
inheritance of acquired characters does not play an important part in the
evolution of, at any rate, the higher animals, is based, not on the
ground of _a priori_ reasoning, but on facts. All the evidence seems to
show that such characteristics are not inherited. If, as Mr Cunningham
thinks, all secondary sexual characters are due to the inheritance of the
effects of use, etc., how is it that no Neo-Lamarckian is able to bring
forward a clear case of the inheritance of a well-defined acquired
character? If such characteristics are habitually inherited, countless
examples should be forthcoming. Fanciers in their endeavours are
constantly “doctoring” the animals they keep for show purposes; and it
seems to us certain that if acquired characters are inherited, breeders
would long ago have discovered this and acted upon the discovery. If
Neo-Darwinians are charged with refusing to believe that acquired
characters are inherited because they “cannot conceive the means by which
it could be effected,” may it not be said with equal justice that many
Neo-Lamarckians believe that acquired characters are inherited, not on
evidence thereof, but because if such characters are not inherited it is
very difficult to account for many of the phenomena presented by the
organic world?
In many of the lower animals, as, for example, the hydra, the germinal
material is diffused through the organism, so that a complete individual
can be developed from a small portion of the creature. In such
circumstances it seems not improbable that the external environment may
act directly on the germinal substance, and induce changes in it which
may perhaps be transmitted to the offspring. If this be so, it would seem
that some acquired characters may be inherited in such organisms. Very
many plants can be propagated from cuttings, buds, etc., so that we might
reasonably expect some acquired characters to be hereditary in them. The
majority of botanists appear to hold Lamarckian views; but on the
evidence at present available, it is doubtful whether such views are the
correct ones.
Plants are so plastic, so protean, so sensitive to their environment that
their external structure appears to be determined by the external
conditions in which they find themselves quite as much as by their
inherited tendencies. In this respect they differ very considerably from
the higher animals. The peacock, for example, presents the same outward
appearance[1] whether bred and reared in Asia or Europe, in a hot or
cold, a damp or a dry climate. The same plant, on the other hand, differs
greatly in outward appearance according as it is grown in a dry or a damp
soil, a hot or a cold country. In his recent book _The Heredity of
Acquired Characters in Plants_, the Rev. G. Henslow cites several
examples of the celerity with which plants react to their environment. On
page 32 he writes: “The following is an experiment I made with the common
rest-harrow (_Ononis spinosa, L._) growing wild in a very dry situation
by a roadside. I collected some seeds, and also took cuttings. These I
planted in a garden border, keeping this well moist with a hand-light
over it, and a saucer of water, so that the air should be thoroughly
moist as well. Its natural conditions were thus completely reversed. They
all grew vigorously. The new branches of the first year’s growth bore
spines, proving their hereditary character, but instead of their being
long and stout, they were not an inch long, and like needles. This proved
the spines to be a hereditary feature. In the second year there were none
at all; moreover, the plants blossomed, and, taken altogether, there was
no appreciable difference from _O. repens, L._”
From this experiment Professor Henslow draws the inference that acquired
characters tend to be inherited in plants. In our opinion the experiment
affords strong evidence against the Lamarckian doctrine. Here we have a
plant which has, perhaps, for thousands of generations developed spines
owing to its dry environment. If acquired characters are inherited we
should have expected this spiny character to have become fixed and
persisted under changed conditions, for some generations at any rate. But
what do we find? By the second year the thorns have entirely disappeared.
All the years during which the plant was exposed to a dry environment
have left no stamp upon it. The fact that the new branches of the first
year’s growth bore small spines is not, as Professor Henslow asserts,
proof of their hereditary character. It merely shows that the initial
stimulus to their development occurred while the plant was still in its
dry surroundings.
In the same way all other so-called proofs of the heredity of acquired
characters break down when critically examined.
In our opinion “not proven” is the proper verdict on the question of the
possibility of the inheritance of acquired characters in the higher
animals. One thing is certain, and that is that acquired characters are
not commonly inherited in those organisms in which there is a sharp
distinction between the germinal and the somatic cells.
It is nothing short of a misfortune that Haeckel’s _History of Creation_,
which seems to be so widely read in England, should be built on a
fallacious foundation. It seems to us that this work is calculated to
mislead rather than to teach.
Our attitude is not quite that of the Wallaceian school, which denies the
possibility of the inheritance of acquired characters. In practice,
however, the attitude we adopt is as fatal to Lamarckism in all its forms
as the dogmatic assertions of the Wallaceians. It matters not whether
acquired characters are very rarely or never inherited. In either case
their inheritance cannot have played an important part in evolution. All
those theories which rely on use-inheritance as a factor in evolution are
therefore in our opinion worthless, being opposed to facts. Our attitude,
then, is that the inheritance of acquired characteristics, if it does
occur, is so rare as to be a negligible quantity in organic evolution.
We may add that the position which we occupy will not be affected even if
the Lamarckians do succeed eventually in proving that some acquired
characters are really inherited. Such proof would merely help to
elucidate some of the problems which confront the biologist. Thus the
question of the inheritance of acquired characters, while full of
interest, has no very important bearing on the question of the making of
species.
The Wallaceian School
The Wallaceians hold the doctrines which have been set forth above as
those of the Neo-Darwinian school. It is incorrect to call those who pin
their faith to the all-sufficiency of natural selection Neo-Darwinians,
because Darwin at no time believed that natural selection explained
everything. Darwin moreover was a Lamarckian to the extent that he was
inclined to think that acquired characteristics could be inherited. His
theory of inheritance by gemmules involved the assumption that such
characters are inherited. It is Wallace who out-Darwins Darwin, who
preaches the all-sufficiency of natural selection. For this reason we dub
the school which holds this article of belief, and to which Weismann,
Poulton, and apparently Ray Lankester belong, the Wallaceian school.
Weismann has put forth a theory of inheritance, that of the continuity of
the germ plasm, which makes this inheritance a physical impossibility. We
believe that the Wallaceians have erred as far from the truth as the
Lamarckians have, because, as we shall show hereafter, a great many of
the organs and structures displayed by organisms cannot be explained on
the natural selection hypothesis. Those who pin their faith to this,
needlessly increase the difficulty of the problem which they have to
face.
There remains the third school, to which we belong, and of which Bateson,
De Vries, Kellog and T. H. Morgan appear to be adherents. This school
steers a course between the Scylla of use-inheritance and the Charybdis
of the all-sufficiency of natural selection. It may seem surprising to
some that we should class De Vries as a Neo-Darwinian, seeing that he is
the originator of the theory of evolution by means of mutations, which we
shall discuss in Chapter III. of this work. As a matter of fact the
theory of mutations should be regarded, not as opposed to the theory of
Darwin, but as a theory engrafted upon it. De Vries himself writes:—“My
work claims to be in full accord with the principles laid down by
Darwin.” Similarly Hubrecht writes in the _Contemporary Review_ for
November 1908: “Paradoxical as it may sound, I am willing to show that my
colleague, Hugo de Vries, of Amsterdam, who a few years ago grafted his
_Mutations Theorie_ on the thriving and very healthy plant of Darwinism,
is a much more staunch Darwinian than either Dr Wallace himself, or the
two great authorities in biological science whom he mentions, Sir William
Thistleton Dyer and Professor Poulton.”
Complexity of the Problem
Having classified ourselves, it remains for us (the authors of the
present work) to define our position more precisely. Like Darwin we
welcome all factors which appear to be capable of effecting evolution. We
have no axe to grind in the shape of a pet hypothesis, and consequently
our passions are not roused when men come forward with new ideas
seemingly opposed to some which already occupy the field. We recognise
the extreme complexity of the problems that confront us. We look facts in
the face and decline to ignore any, no matter how ill they fit in with
existing theories. We recognise the strength and the weakness of the
Darwinian theory. We see plainly that it has the defect of the period in
which it was enunciated. The eighteenth century was the age of
cocksureness, the age in which all phenomena were thought to be capable
of simple explanation.
This is well exemplified by the doctrines of the Manchester school as
regards political and economic science. The whole art of legislation was
thought to be summed up in the words _laissez faire_. The whole sphere of
legitimate government was asserted to be the keeping of order and the
enforcing of contracts. Experience has demonstrated that a State guided
solely by these principles is wretchedly governed. A large proportion of
recent Acts of Parliament limits the freedom of contract. Such
limitations are necessary in the case of contracts between the weak and
the strong. Similarly the earlier economists considered political economy
a very simple affair. They asserted that men are actuated by but one
motive—the love of money. All their men were economic men, men devoid of
all attributes save an intense love of gold. Experience has shown that
these premises are not correct. Love of family, pride of race, caste
prejudices are more or less deeply implanted in men, so that they are
rarely actuated solely by the love of money.
The Aim of the Biologist
Thus it is that the political economy of to-day as set forth by Marshall
is far more complex and less dogmatic than that of Ricardo or Adam Smith.
Similarly the political philosophy of Sidgwick is very different to that
of Herbert Spencer. So is it with the theory of organic evolution. The
theory of natural selection is no more able to explain all the varied
phenomena of nature than is Ricardo’s assumption that all men are
actuated solely by the love of money capable of accounting for the
multifarious existing economic phenomena. Even as the love of wealth is
an important motive of human actions, so is natural selection an
important factor in evolution. But even as the majority of human actions
are the resultant of a variety of motives, so are the majority of
existing organisms the resultant of a complex system of forces. Even as
it is the duty of the economist to discover the various motives which
lead to human actions, so is it the duty of the biologist to bring to
light the factors which are operative in the making of species.
CHAPTER II
SOME OF THE MORE IMPORTANT OBJECTIONS TO THE THEORY OF NATURAL SELECTION
Brief statement of Theory—Objections to the Theory fall into two
classes—Those which strike at the root of the Theory—Those which deny
the all-sufficiency of Natural Selection—Objections which strike at
root of Theory are based on misconception—Objections to Wallaceism—The
Theory fails to explain the origin of Variations—Natural Selection
called on to explain too much—Unable to explain beginnings of new
organs—The Theory of change of function—The co-ordination of
variations—The fertility of races of domesticated animals—Missing
links—Swamping effects of intercrossing—Small variations cannot have a
survival value—Races inhabiting same area—Excessive
specialisation—Chance and Natural Selection—Struggle for existence most
severe among young animals—Natural Selection fails to explain mimicry
and other phenomena of colour—Conclusion, that scarcely an organism
exists which does not possess some feature inexplicable on the theory
of Natural Selection as held by Wallace and his followers.
“The burden of proof is on him who asserts” is a rule of evidence which
the man of science should apply as rigidly as does the lawyer.
It is therefore incumbent upon us to prove our assertion that the theory
of natural selection does not afford an adequate explanation of all the
varied phenomena observed in the organic world.
Theory of Natural Selection
The theory of natural selection is so generally understood, that to set
it forth in detail in this place would be quite superfluous.
Darwin, it will be remembered, based his great hypothesis on the
following observed facts:—
1. No two individuals of a species are exactly alike. This is sometimes
called the law of variation.
2. All creatures tend in a general way to resemble their parents in
appearance more closely than they resemble individuals not related to
them. This may be termed the law of heredity.
3. Each pair of organisms produces in the course of a lifetime, on an
average, many more than two young ones.
4. On an average the total number of each species remains stationary.
From (3) and (4) follows the doctrine of Malthus, namely, that many more
individuals are born than can reach maturity.
Darwin applied this doctrine to the whole of the animal and the vegetable
kingdoms.
In his introduction to _The Origin of Species_ he writes:—“As many more
individuals of each species are born than can possibly survive; and as,
consequently, there is a frequently recurring struggle for existence, it
follows that any being, if it vary, however slightly, in any manner
profitable to itself, under the complex and sometimes varying conditions
of life, will have a better chance of surviving, and thus be naturally
selected. From the strong principle of inheritance, any selected variety
will tend to propagate its new and modified form.”
In other words, the struggle for existence amongst all organic beings
throughout the world, which inevitably follows from the high geometrical
ratio of their increase, results in the survival of the fittest, that is
to say, of those best adapted to cope with their enemies and to secure
their food. Since organisms are thus naturally selected in nature, we may
speak of a natural selection which acts in much the same way as the human
breeder does. Darwin’s theory, then, is that all the variety of organisms
which now exist have been evolved from one or more forms by this process
of natural selection.
Various Anti-Darwinian Views
The objections which have been urged against the theory of natural
selection fall into two classes.
I. Those which strike at its root, which either deny that there is any
natural selection, or declare that it is not capable of producing a new
species.
II. Those which are directed against the all-sufficiency of natural
selection to account for organic evolution.
Those of the first class need not detain us long, although among those
who formulate them are to be found some eminent men of science.
Delage alleges that selection is powerless to form species, its function
is, according to him, limited to the suppression of variations radically
bad, and to the maintaining of a species in its normal character. It is
thus an inimical factor in evolution, a retarder rather than an
accelerator of species-change. It merely acts by preserving the type at
the expense of the variants, and so acts as a brake on evolution.
Korschinsky, while possibly not denying that selection occurs in nature,
declares that its influence on evolution is _nil_, or, if it has any
influence, that it is a hindering one.
Eimer similarly denies any capacity on the part of natural selection to
create species.
Pfeffer urges a very different objection. He says that if such a force as
natural selection existed it would transform species much more rapidly
than it does!
Now, in order that the above objections can carry any weight, one of two
sets of conditions must be fulfilled.
Either all organisms must be perfectly adapted to their environment, and
this environment must never change, or there must be inherent in each
species a kind of growth-force which impels the species to develop in
certain fixed directions. In either of these circumstances natural
selection will be an inhibitory force, for if the normal organism is
perfectly adapted to its environment, all variations from the type must
be unfavourable, and natural selection will weed out the individuals that
display them. No careful student of nature can maintain, either that all
animals are perfectly adapted to their environment, or that this never
changes. Hence those who deny that natural selection is a factor in the
making of species, assume the second set of conditions, that species
develop in certain fixed directions, being impelled either by internal or
external forces. How far these ideas are founded on fact we shall
endeavour to determine when speaking of variation. It must suffice at
present to say that even if any of these views of orthogenesis be
established, natural selection will have, so to speak, a casting vote, it
will decide which series of species developing along preordained lines
shall survive and which shall not survive.
Thus we reach by a different line of argument the conclusion we arrived
at in the last chapter: namely, there is no room for doubt that natural
selection is a factor in the making of species.
We must now pass on to the second class of objections, those which are
urged against the all-sufficiency of natural selection. So numerous are
these that it is not feasible to consider them all. A brief notice of the
more important ones should suffice to satisfy any unbiassed person;
firstly, that natural selection is an important factor in evolution;
secondly, that the position taken up by Wallace and his followers, that
natural selection, acting on minute variations, is the one and only
factor in organic evolution, is untenable.
Darwinism does not explain Variation
1. It has been urged that the Darwinian theory makes no attempt to
explain variation, and that, until we know what it is that causes
variations, we are not in a position to explain evolution. This of course
is quite true, but the objection is scarcely a fair one, since, as we
have seen, Darwin freely admitted that his theory made no attempt to
explain the origin of variations. It is not reasonable to object to a
theory because it fails to explain phenomena with which it expressly
states that it is not concerned. On the other hand, the objection is one
that must be reckoned with, for, as we shall see, it makes a great
difference to the importance of natural selection as a factor in
evolution if variations appear indiscriminately in all directions, as
Darwin tacitly assumed they do, or whether, as some biologists believe,
they are determinate in direction, being the result of a growth-force
inherent in all organisms.
2. Very similar to the above-mentioned objection is that which points out
that it is a long journey from Amoeba to man. It is difficult to believe
that this long course of development from the simple to the complex is
due to the action of a blind force, to the survival of those whose
fortuitous variations happen to be best adapted to the environment. The
result seems out of all proportion to the cause. There must be some
potent force inherent in protoplasm, or behind organisms, impelling them
upwards. This objection is as difficult to refute as it is to establish.
It is purely speculative.
3. A very serious objection to the Darwinian theory is that the
beginnings of new organs cannot be explained by the action of natural
selection on fortuitous minute variations, and natural selection can act
on an organ only when that organ has attained sufficient size to be of
practical utility to its possessor. When once an organ has come into
being it is not difficult to understand how it can be improved, modified
and developed by natural selection. But how can we explain the origin of
an organ such as a limb by the action of natural selection on minute
variations?
Theory of Change of Function
The theory of the change of function goes some way towards meeting the
difficulty, for by means of it we are able to understand how certain
organs, as, for example, the lung of air-breathing animals, might have
come into existence. This is said to have been developed from the
swimming-bladder of fishes. This bladder is, to use the words of Milnes
Marshall, “a closed sac lying just underneath the vertebral column. In
many fish it acquires a connection by a duct with some part of the
alimentary canal. It then becomes an accessory breathing organ,
especially in those fish which are capable of living out of water for a
time, _e.g._ the _Protopterus_ of America. An interesting series of
modifications exists connecting the air-bladder with the lung of the
higher vertebrates, which is undoubtedly the same organ.”
This theory, however, does not seem adequate to explain the origin of all
organs. It does not explain, for example, how limbs developed in a
limbless organism. Wallace tried to avoid the difficulty by asserting
that it is unreasonable to ask a new theory that it shall reveal to us
exactly what took place in remote geological ages and how it took place.
To this the obvious reply is, firstly, that we ought not to give
unqualified acceptance to any theory of evolution until it does afford us
such explanations, and, secondly, that the theory of the origin of
species by means of natural selection is no longer a new one.
Latterly, however, Wallace appears to have given up all hope of being
able to account for the origin of new organs by means of natural
selection, for he states on page 431 of the issue of the _Fortnightly
Review_ for March 1909: “It follows—not as a theory but as a fact—that
whenever an advantageous variation is needed, it can only consist in an
increase or decrease of some power or faculty already existing.” Now, in
order for an increase or decrease to occur, there must be something in
existence to be increased or diminished. Wallace, it is true, speaks here
only of powers and faculties; but it can scarcely be supposed that he
believes that variations as to structure are intrinsically different from
those relating to powers and faculties.
4. Herbert Spencer urges, as an objection to the theory of natural
selection, that favourable variations in one organ are likely to be
counterbalanced by unfavourable variations in some other organ. He
maintains that the chances are enormous against the occurrence of the
“many coincident and co-ordinated variations” that are necessary to
create a life or death determining advantage.
This objection was urged by a writer in the _Edinburgh Review_ in January
1909, and even by Wallace himself in the _Fortnightly Review_ last March
against the mutation theory. This objection, strong though it appears on
paper, exists only in the imagination of the objector.
Those who urge it display a misunderstanding of the manner in which
natural selection acts, and ignorance of the phenomenon of the
correlation of organs.
Correlation
Natural selection deals with an organism as a whole. Its effect is to
permit those creatures to survive which, taken as a whole, are best
adapted to their environment.
Physiologists insist with ever-increasing emphasis that there is more or
less correlation and inter-connection between the various parts of an
organism.
The several organs of an animal are not so many isolated units. It is
impossible to act on one organ without affecting some or all of the
others.
Variations in a given direction of one organ are usually accompanied by
correlated variations in some of the other organs. If strength be of
paramount importance to an animal, natural selection will tend to
preserve those individuals which exhibit strength to a marked degree, and
this exhibition of strength may be accompanied by other peculiarities,
such as short legs or a certain colour, so that natural selection will
indirectly tend to produce individuals with short legs and having the
colour in question, and it may happen that this particular colour is one
that renders the animal more conspicuous than the normal colour does.
Nevertheless, on account of the all-needful strength which accompanies
it, those animals so coloured may survive while those of a more
protective hue perish. Thus, paradoxical though it seems, natural
selection may indirectly be responsible for characteristics which in
themselves are injurious to the individual. This is probably the case as
regards the decorative plumage of some male birds. The phenomenon of
correlation was recognised by Darwin, and has, we believe, played an
important part in the making of species. We shall deal more fully with
the subject in a later chapter.
5. An oft-urged objection to the theory of natural selection, and one
which weighed very strongly with Huxley, is that breeders have hitherto
not succeeded in breeding a variety which is infertile with the parent
species. If, Huxley asked, breeders cannot produce such a thing, how can
we say we consider it proved that natural selection produces new species
in nature? This objection, however, loses much of its force in view of
the fact that many perfectly distinct species are quite fertile when bred
together. We shall recur to this in Chapter IV.
6. The fact that palæontology has hitherto failed to yield links
connecting many existing species is a classical objection to the theory
of the origin of species by gradual evolution.
Missing Links
Wallace states this objection as follows, on page 376 of his _Darwinism_:
“Many of the gaps that still remain are so vast that it seems incredible
to these writers that they could ever have been filled up by a close
succession of species, since these must have been spread over so many
ages, and have existed in such numbers, that it seems impossible to
account for their total absence from deposits in which great numbers of
species belonging to other groups are preserved and have been
discovered.”
Wallace’s reply is to the effect that in the case of many species
palæontology affords abundant evidence of the gradual change of one
species into another, the foot of the horse being a well-known case. The
genealogy of this noble quadruped can be traced from the Eocene four-toed
_Orohippus_, through the _Mesohippus_, the _Miohippus_, the
_Protohippus_, and the _Pliohippus_, until we reach the one-toed _Equus_.
Wallace further points out that in order that the fossil of any organism
may be preserved, the “concurrence of a number of favourable conditions”
is required, and against this the chances are enormous. Lastly, he urges
the imperfection of our knowledge of the things that lie embedded in the
earth’s crust.
The objection based on the lack of “missing links” loses some of its
force if we accept the theory that species sometimes arise as sports.
Thus, suppose a species with well-developed horns produces as a mutation
a hornless variety, which eventually replaces the horned form, we should
look in vain for any forms intermediate between the parent and the
daughter species. On the other hand, it is significant that just where
the links are most needed they are missing. For example, the splint bones
of the horse, taken in conjunction with the feet of existing tapirs,
which have four toes in front and three behind, would have led us to
infer, without the help of the geological record, that the horse was a
descendant of a polydactyle ancestor. When, however, we come to the
origin of birds, bats, and whales, palæontology fails to give us any
assistance, so that we are in the dark as to the origin of such really
important modifications.
7. The swamping effects of inter-crossing is an objection which has been
repeatedly urged against the Darwinian theory.
This objection is not so serious as it appears at first sight. Darwin and
Wallace maintain, firstly, that natural selection acts by eliminating all
individuals except those which present favourable variations. The
favoured few alone survive and mate with one another, so that there is
here no question of the swamping effects of inter-crossing, none but
well-adapted individuals being left to mate with one another.
The objection gains greater force when directed against the theory that
evolution proceeds by sudden jumps. But in this connection we must bear
in mind that the experiments of Mendel and his followers have
demonstrated that some of the offspring of crosses may resemble their
pure ancestors and breed true _inter se_. Nor is this all.
Recurrent Mutations
Experience shows that where a mutation, or sport, or discontinuous
variation occurs, it frequently repeats itself; for example, the
black-winged sport of the peafowl has occurred several times over and in
different flocks of birds. The sport or mutation must have a definite
cause. There must be something within the organism, something in the
generative cells, which causes the mutation to arise; and hence, on _a
priori_ grounds, we should expect the same mutation to arise about the
same time in many individuals. It seems legitimate to infer that things
have been quietly working up to a climax. When this is reached there
results a mutation. Therefore we should expect sudden mutations to appear
simultaneously in a number of individuals. To this important subject we
shall return.
8. An almost insuperable objection to the theory that species have
originated by the action of natural selection on minute variations, is
that such small differences cannot be of a life-or-death value, or, as it
is usually called, a survival value to their possessor. But if evolution
is the result of the preservation by natural selection of such slight
variations, it is absolutely necessary that each of these should possess
a survival value.
As D. Dewar has pointed out, on page 704 of vol. ii. of _The Albany
Review_, it is only when the beast of prey and its victim are evenly
matched as regards fleetness and power of endurance that small variations
in these qualities can have a survival value. But in the rough and tumble
of the struggle for existence the victim and its foe are but rarely
well-matched. Take as an example the case of a flycatcher. “This bird,”
writes D. Dewar, “will sometimes take three or four insects in the course
of one flight; all are captured with the same ease, although the length
of wing in each victim varies. So great is the superiority of the bird
that it does not notice the difference in the flying powers of its puny
quarry.” It is unnecessary to labour this point.
9. Species or varieties differing considerably in colour may exist side
by side, as the hooded and carrion crows, the white and dark breasted
forms of the Arctic skua, the pale and dark forms of the fulmar petrel,
the grey and rufous forms of the American scops owl (_Megascops asio_).
It is true that preponderance of one form or another in certain districts
points to some advantage possessed by one over the other, but, for all we
know, it may be due to heredity, and in any case the co-existence of the
two types in part of their range, or at certain seasons, shows that
selection is not at all rigorous.
The same argument applies to the co-existence of very
differently-coloured species with generally similar habits, such as that
of the jaguar and puma in South America, and the five very
differently-coloured flycatchers in the Nilgiri Hills.
Leaf-butterflies
In short, there is abundant evidence to show that considerable
differences in colour do not appear to have any effect on the chances of
survival in the struggle for existence of those that display them. Yet
this is precisely what the supporters of the Darwinian hypothesis cannot
afford to admit, for they then find it impossible to account for the
origin of such a form as _Kallima_, the leaf-butterfly, by the action of
natural selection. As most people are aware, this creature displays a
remarkable resemblance to a decaying leaf. “These butterflies” (there are
several species which show the marvellous imitation), writes Kellog, on
page 53 of _Darwinism To-day_, “have the under sides of both fore and
hind wings so coloured and streaked that when apposed over the back in
the manner common to butterflies at rest, the four wings combine to
resemble with absurd fidelity a dead leaf still attached by a short
petiole to the twig or branch. I say absurd, for it seems to me the
resemblance is over-refined. Here for safety’s sake it is no question of
mimicking some one particular kind of other organism or inanimate thing
in nature which birds do not molest. It is simply to produce the effect
of a dead leaf on a branch. Leaf-shape and general dead-leaf
colour-scheme are necessary for this illusion. But are these following
things necessary? namely, an extra-ordinarily faithful representation of
mid-rib and lateral veins, even to faint microscopically-tapering vein
tips; a perfect short petiole produced by the apposed ‘tails’ of the
hind-wings; a concealment of the head of the butterfly so that it shall
not mar the outlines of the lateral margin of the leaf; and finally,
delicate little flakes of purplish or yellowish brown to mimic spots of
decay and fungus-attacked spots in the leaf! And, as culmination, a tiny
circular clear spot in the fore-wings (terminal part of the leaf) which
shall represent a worm-eaten hole, or a piercing of the dry leaf by
flying splinter, or the complete decay of a little spot due to fungus
growth! A general and sufficient seeming of a dead leaf, object of no
bird’s active interest, yes, but not a dead leaf modelled with the
fidelity of the waxworkers in the modern natural history museums. When
natural selection has got Kallima along to that highly desirable stage
when it was so like a dead leaf in general seeming that every bird
sweeping by saw it only as a brown leaf clinging precariously to a
half-stripped branch, it was natural selection’s bounden duty, in
conformance to its obligations to its makers, to stop the further
modelling of Kallima and just hold it up to its hardly won advantage. But
what happens? Kallima continues its way, specifically and absurdly
dead-leafwards, until to-day it is a much too fragile thing to be
otherwise than very gingerly handled by its rather anxious
foster-parents, the Neo-Darwinian selectionists.” It is obvious that if
natural selection has produced so highly specialised an organism as the
dead-leaf butterfly, every minute variation must be of value and have
been seized upon by natural selection.
A Dilemma
Thus the Wallaceians are on the horns of a dilemma. If they assert, as
they appear to do, that every infinitesimal variation has a survival
value, they find it difficult to explain the existence, side by side of
such forms as the hooded and carrion crows, to say why in some species of
bird both sexes assume a conspicuous nuptial plumage at the very time
when they stand most in need of protective coloration, why the cock
paradise flycatcher is chestnut for the first two years of his life and
then turns as white as snow. If, on the other hand, the Wallaceians
assert that small variations are unimportant and have no survival value,
they are, as Kellog points out, in trouble over the close and detailed
resemblance which the Kallima butterflies bear to dead leaves.
10. An objection to the Darwinian theory which has been advanced by Conn,
Henslow, D. Dewar, and others, is that the selection theory fails to take
into account the effects of chance. “If,” writes D. Dewar on page 707 of
_The Albany Review_, vol. ii., “the struggle for existence were of the
nature of a race at a well-regulated athletic meeting, where the
competitors are given a fair start, where there is no difference in the
conditions to which the various runners are subjected, then indeed would
every variation tell. I would rather liken the struggle for existence to
the rush to get out of a crowded theatre, poorly provided with exits,
when an alarm of fire is given. The people to escape are not necessarily
the strongest of those present. Propinquity to a door may be a more
valuable asset than strength.”
Or again, we may take the imaginary case of some antelopes being pursued
by wolves. The chase, being prolonged, brings the antelopes to a locality
with which they are not familiar. The foremost of the herd, the most
swift, and therefore the individual which should stand the best chance of
survival, suddenly finds himself on soft boggy ground, which, owing to
the depth to which his feet sink into the soil, seriously impedes his
progress. His fellow antelopes, now outdistanced, seeing his predicament,
take another course and soon leave him behind, to fall an easy prey to
his foes. Here we have a case of the perishing of the most fit as regards
the important point of speed.
The Effects of Chance
Writing of plants, Professor Henslow says, on page 16 of _The Heredity of
Acquired Characters in Plants_: “As the whole of the animal kingdom
ultimately lives upon the vegetable, plants must supply the entire
quantity of food supplied, not to add innumerable vegetable parasites as
well, for both young and old. Myriads of germinating seeds perish
accordingly, being destroyed by slugs and other mollusca, and ‘mildews,’
etc. But far more seeds and spores—about 50,000,000 of these it is
calculated can be borne in a single male-fern—never germinate at all.
They fall where the conditions of life are unfavourable and perish. This
misfortune is not due to any inadaptiveness in themselves, but to the
surrounding conditions which will not let them germinate. Thus thousands
of acorns and other fruits, as of elder, drop upon the ground in and by
our hedges, road-sides, copses, and elsewhere; but scarcely any or even
no seedlings are to be seen round the trees.”
Every year thousands of birds perish in the great migratory flight,
others succumb in a cyclone, a fierce tropical storm, a prolonged
drought, a severe frost. Here death overtakes multitudes, all that dwell
in a locality, the weak and the strong, the swift and the slow alike.
This objection may be met by saying that in the long run it is the
fittest that will survive. This is true. The objection is nevertheless of
importance in showing how exceedingly uncertain must be the action of
natural selection if it have but small variations upon which to work. In
such circumstances the mills of natural selection may grind surely, but
they must grind very slowly.
11. We must bear in mind that the struggle for existence is most severe
among young animals, among creatures that are not fully developed. Nature
pays no attention to potentialities. The weak go to the wall in the
conflict, even though, if allowed time, they might develop into prodigies
of strength.
Moreover, and this is an important point, death in the case of young
creatures overtakes broods and families rather than individuals.
The above-cited objections to the theory that species have originated by
the action of natural selection on minute variations, are mostly of a
general nature; let us now notice briefly a few more concrete objections.
We shall not devote much space to these in the present chapter, since we
shall be continually confronted with them when dealing with the subject
of animal colouring.
The Origin of Mimicry
12. Natural selection, as we shall see, fails to account for the origin
of what is known as protective mimicry. Some insects look like inanimate
objects, others resemble other insects which are believed or known to be
unpalatable. Those creatures displaying this resemblance to other objects
or creatures, and deriving profit therefrom, are said to “mimic” the
objects or creatures they copy. They are also called “Mimics.” It is easy
to understand the profit that these mimics derive from their mimicry.
When once the disguise has been assumed we can comprehend how natural
selection will tend to improve it by eliminating those that mimic badly;
but it seems to us that the theory fails utterly to account for the
origin of the likeness.
13. Similarly, the Neo-Darwinian theory fails to explain the colours of
the eggs of birds laid in open nests, why, for example, the eggs of the
accentor or hedge-sparrow are blue and those of the doves are white.
14. The theory fails to give a satisfactory explanation of the phenomena
of sexual dimorphism. Why, for example, in some species of doves and
ducks, the sexes are alike, while in other species with similar habits
they differ in appearance.
15. It fails to explain why the rook is black and why the jackdaw has a
grey neck.
These and many other objections we shall deal with more fully in the
chapter on animal colouration. It must suffice here to mention them, and
to say that our experience teaches us that scarcely a single species of
bird or beast exists which does not display some characteristic which is
inexplicable on the theory that natural selection, acting on small
variations, is the one and only cause of organic evolution.
CHAPTER III
VARIATION
The assumption of Darwin and Wallace that variations are haphazard in
origin and indefinite in direction—If these assumptions be not correct
Natural Selection ceases to be the fundamental factor in
evolution—Darwin’s views regarding variation underwent modification—He
eventually recognised the distinction between definite and indefinite
variations, and between continuous and discontinuous variations—Darwin
attached but little importance to either definite or discontinuous
variations—Darwin’s views on the causes of variations—Criticism of
Darwin’s views—Variations appear to occur along certain definite
lines—There seems to be a limit to the extent to which fluctuating
variations can be accumulated—De Vries’ experiments—Bateson on
“discontinuous variation”—Views held by De Vries—Distinction between
continuous and discontinuous variations—The work of De Vries—Advantages
enjoyed by the botanist in experimenting on the making of
species—Difficulties encountered by the animal breeder—Mutations among
animals—The distinction between germinal and somatic variations—The
latter, though not transmitted to offspring, are often of considerable
value to their possessor in the struggle for existence.
Nature of Variation
As we have already seen, the Darwinian theory, unlike that of Lamarck,
does not attempt to explain the origin of variations. It is content with
the fact that variations do occur.
Although Darwin did not try to explain how it is that variation occurs,
and was very guarded in the expressions he used concerning it, he assumed
that variations are indefinite in variety and occur indiscriminately in
all directions, as the following quotations from the _Origin of Species_
will show: “But the number and diversity of inheritable deviations of
structure . . . are endless” (page 14, ed. 1902). “The variations are
supposed to be extremely slight, but of the most diversified nature.” “I
have hitherto sometimes spoken as if the variations so common and
multiform with organic beings under domestication, and in a lesser degree
to those under nature, were due to chance. This, of course, is a wholly
incorrect expression, but it serves to acknowledge plainly our ignorance
of the cause of each particular variation” (page 164).
Wallace is far less guarded in his expressions. On page 82 of his
_Darwinism_ he speaks of “the constant and large amount of variation of
every part in all directions . . . which must afford an ample supply of
favourable variations whenever required.”
The double assumption that variations are for all practical purposes
haphazard in origin and indefinite in direction is necessary if natural
selection is to be the main factor in evolution. For if variations be not
haphazard, if they are definite, if there be a directive force behind
them, like fate behind the classical gods, then selection is not the
fundamental cause of evolution. It can at most effect, not the origin of
species, but the survival of certain species which have arisen as the
result of some other force. Its position is changed; it is no longer a
cause of the origin of new organisms, but a sieve determining which of
certain ready-made forms shall survive. Evidently, then, we shall not be
able to fully understand the evolutionary process until we have
discovered how it is that variations are caused. In other words, we must
go considerably farther than Darwin attempted to do.
Before proceeding to inquire into the true nature of variations, it
behoves us to set forth briefly the ideas of Darwin on the subject. We
shall then be in a position to see how much progress has been made since
the days of that great biologist.
It is not at all easy to discover exactly what were Darwin’s views on the
subject of variation. A perusal of his works reveals contradictions, and
gives one the impression that he himself scarcely knew his own mind upon
the subject. This should not be a matter for surprise.
We must remember that Darwin had to do pioneer work, that he had to deal
with altogether new conceptions. Such being the case, his ideas were of
necessity somewhat hazy; they underwent considerable modification as
fresh facts came to his knowledge.
Definite and Indefinite Variability
Towards the end of his life Darwin recognised that variability is of two
kinds—definite and indefinite. Indefinite variation is indiscriminate
variation in all directions around a mean, variation which obeys what we
may perhaps call the law of chance. Definite variation is variation in a
determinate direction—variation chiefly on one side of the mean. Darwin
believed that these determinate variations were caused by external
forces, and that they are inherited. He thus accepted Lamarckian factors.
“Each of the endless variations,” he writes, “which we see in the plumage
of our fowls, must have had some efficient cause, and if the same causes
were to act uniformly during a long series of generations on many
individuals, all probably would be modified in the same direction.”
But Darwin was always of opinion that this definite variability, this
variability in one direction as the result of some fixed cause, is far
less important, from an evolutionary point of view, than indefinite
variability, that it is the exception rather than the rule, that the
usual result of changed conditions is to let loose a flood of indefinite
variability, that it is almost exclusively upon this that natural
selection acts.
Darwin also recognised that variations differ in degree, even as they do
in kind. He perceived that some variations are much more pronounced than
others. He recognised the distinction between what are now known as
continuous and discontinuous variations. The former are slight departures
from the normal; the latter are considerable deviations from the mean or
mode; great jumps, as it were, taken by nature, as, for example, the pea
and the rose combs of fowls, which were derived from the normal single
comb.
Monstrosities
“At long intervals of time,” wrote Darwin, “out of millions of
individuals reared in the same country and fed on nearly the same food,
deviations of structure so strongly pronounced as to deserve to be called
monstrosities arise, but monstrosities cannot be separated by any
distinct line from slighter variations.” Therefore it is evident that he
regarded the difference between continuous and discontinuous variations
as not one of kind, but merely of degree. To the discontinuous variations
Darwin attached very little importance from an evolutionary point of
view. He looked upon them as something abnormal.
“It may be doubted,” he wrote, “whether such sudden and considerable
deviations of structure such as we occasionally see in our domestic
productions, more especially with plants, are ever permanently propagated
in a state of nature. Almost every part of every organic being is so
beautifully related to its complex conditions of life that it seems as
improbable that any part should have been suddenly produced perfect, as
that a complex machine should have been invented by a man in a perfect
state. Under domestication monstrosities sometimes occur which resemble
normal structures in widely different animals. Thus pigs have
occasionally been born with a sort of proboscis, and if any wild species
of the same genus had naturally possessed a proboscis, it might have been
argued that this had appeared as a monstrosity; but I have as yet failed
to find, after diligent search, cases of monstrosities resembling normal
structures in nearly allied forms, and these alone bear on the question.
If monstrous forms of this kind ever do appear in a state of nature and
are capable of reproduction (which is not always the case), as they occur
rarely and singly, their preservation would depend on unusually
favourable circumstances. They would, also, during the first and
succeeding generations cross with the ordinary form, and thus their
abnormal character would almost inevitably be lost.” But, in a later
edition of the _Origin of Species_, Darwin seems to contradict the above
assertion: “It should not, however, be overlooked that certain rather
strongly marked variations, which no one would rank as mere individual
differences, frequently recur owing to a similar organisation being
similarly acted on—of which fact numerous instances could be given with
our domestic productions. In such cases, if the varying individual did
not actually transmit to its offspring its newly acquired character, it
would undoubtedly transmit to them, as long as the existing conditions
remained the same, a still stronger tendency to vary in the same manner.
There can also be little doubt that the tendency to vary in the same
manner has often been so strong that all the individuals of the same
species have been similarly modified without the aid of any form of
selection. Or only a third, fifth, or tenth part of the individuals may
have been thus affected, of which fact several instances could be given.
Thus Graba estimates that about one-fifth of the guillemots in the Faroe
islands consist of a variety so well marked, that it was formerly ranked
as a distinct species under the name _Uria lacrymans_. In cases of this
kind, if the variation were of a beneficial nature, the original form
would soon be supplanted by the modified form, through the survival of
the fittest.” Here we seem to have a plain statement of the origin of new
forms by mutation.
Minute Variations
Again, we read (page 34): “Some variations useful to him (_i.e._ man)
have probably arisen suddenly, or by one step; many botanists, for
instance, believe that the fuller’s teasel, with its hooks, which cannot
be rivalled by any mechanical contrivance, is only a variety of the wild
Dipsacus; and this amount of change may have suddenly arisen in a
seedling. This is known to be the case with the turnspit dog.”[2] But, as
we have already said, Darwin at no time attached much importance to these
jumps made by nature as a factor in evolution. He pinned his faith to the
minute, indefinite variations which he believed could be piled up, one
upon another, so that, if allowed sufficient time, either nature or the
human breeder could, by a continued selection of these minute variations,
call into being any kind of organism. The importance of selection, he
writes, “consists in the great effect produced by the accumulation in one
direction, during successive generations, of differences absolutely
inappreciable by an uneducated eye” (page 36). On page 132 he writes: “I
can see no limit to the amount of change, to the beauty and complexity of
the coadaptations between all organic beings . . . which may have been
effected[3] in the long course of time by nature’s power of selection.”
He expressly states, on page 149, that he sees no reason to limit the
process to the formation of genera alone.
Although the theory of natural selection does not attempt to explain the
causes of variation, Darwin paid some attention to the subject. He
believed that both internal and external causes contribute to variation,
that variations tend to be inherited whether the result of causes within
the organism or outside it. He believed that the inherited effect of use
and disuse was a cause of variation, and cited, as examples, the lighter
wing-bones and heavier leg-bones of the domestic duck and the drooping
ears of some domestic animals. He supposed that animals showed a greater
tendency to vary when under domestication than when in their natural
state, attributing the supposed greater variability to the excess of food
received, and the changed conditions of the life of domestic animals.
Nevertheless, he was fully alive to the fact that “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.” In other words, the nature
of organisms appeared to Darwin to be a more important factor in the
origin of variations than external conditions. Evidence of this is
afforded by the fact that some animals are more variable than others.
Finally, he frankly admitted how great was his ignorance of the causes of
variability. Variability is, he stated, governed by unknown laws which
are infinitely complex.
Lines of Variation
It will be convenient to deal with each of Darwin’s main ideas on
variation separately, and to consider to what extent they seem to require
modification in the light of later research.
Firstly, Darwin believed that variations arise in what appears to be a
haphazard manner, that they occur in all directions, and seem to be
governed by the same laws as chance. It is our belief that we are now in
a position to make more definite statements regarding variation than
Darwin was able to.
Biologists can now assert definitely that variations do not always occur
equally in all directions. The results of many years of the efforts of
practical breeders demonstrate this. These men have not been able to
produce a green horse, a pigeon with alternate black and white feathers
in the tail, or a cat with a trunk, for the simple reason that the
organisms upon which they operated do not happen to have varied in the
required direction. It may perhaps be objected that breeders have no
desire to produce such forms; had they wished to do so, they would
probably have succeeded. To this objection we may reply that they have
not managed to produce many organisms, which would be highly desirable
from a breeder’s point of view, as, for example, a blue rose, hens that
lay brown eggs but do not become broody at certain seasons of the year,
or a cat that cannot scratch.
As Mivart well says, on page 118 of his _Genesis of Species_, “Not only
does it appear that there are barriers which oppose change in certain
directions, but that there are positive tendencies to development along
certain special lines. In a bird which has been kept and studied like the
pigeon, it is difficult to believe that any remarkable spontaneous
variations would pass unnoticed by breeders, or that they would not have
been attended to and developed by some fancier or other. On the
hypothesis of indefinite variability, it is then hard to say why pigeons
with bills like toucans, or with certain feathers lengthened like those
of trogons, or those of birds of paradise, have never been produced.”
There are certain lines along which variation seems never to occur. Take
the case of the tail of a bird. Variable though this organ be, there are
certain kinds of tail that are seen neither in wild species nor
domesticated races. A caudal appendage, of which the feathers are
alternately coloured, occurs neither in wild species nor in artificial
breeds. For some reason or other, variations in this direction do not
occur. Similarly, with the exception of one or two of the “Noddy” terns,
whenever a bird has any of its tail feathers considerably longer than the
others, it is always the outer pair or the middle pair that are so
elongated. It would thus appear that variations in which the other
feathers are especially lengthened do not usually occur. The fact that
they are elongated in two or three wild species is the more significant,
because it shows that there is apparently nothing inimical to the welfare
of a species in having, say, the third pair of tail feathers from the
middle exceptionally prolonged.
Breeders’ Boasts
This is a most important point, and one which seems to be ignored by the
majority of scientific men, who appear to be misled by the boastful talk
of certain successful breeders. Thus, on page 29 of the _Origin of
Species_, Darwin quotes, with approval, Youatt’s description of selection
as “the magician’s wand, by means of which he may summon into life
whatever form and mould he pleases.” Darwin further cites Sir John
Sebright as saying, with regard to pigeons, that he would “produce any
given feather in three years, but it would take him six years to obtain
head and beak.”
If it were possible absolutely to originate anything by selection,
horticulturists would almost certainly ere this have produced a pure
black flower. The fact that not a single mammal exists, either in nature
or under domestication, with scarlet, blue, or green in its hair, appears
to show that, for some reason or other, mammals never vary in any of
these directions.
The fact that so few animals have developed prehensile tails seems to
indicate that variation does not often occur in that direction, for
obviously a prehensile tail is of the very greatest utility to its
possessor; so that there can be little room for doubt that it would be
seized upon and preserved by natural selection, whenever it occurred.
As E. H. Aitken very truly says, “so early and useful an invention
should, one would think, have been spread widely in after time; but there
appears to be some difficulty in developing muscles at the thin end of a
long tail, for the animals that have turned it into a grasping organ are
few and are widely scattered. Examples are the chameleon among lizards,
our own little harvest mouse, and, pre-eminent among all, the American
monkeys” (_Strand Magazine_, Nov. 1908).
Even as there are many variations which seem never to occur in nature, so
are there others which occur so frequently that they may be looked for in
any species. Albinistic forms appear now and again in almost every
species of mammal or bird; while melanistic sports, although not so
common, are not by any means rare.
Every complete manual on poultry gives for each breed a note of the
faults which constantly appear, and which the fancier has to watch
carefully for and guard against. The fact that these “faults” occur so
frequently in each breed shows how strong is the tendency to vary in
certain definite directions. It is true that some of these faults are in
the nature of reversions, as, for example, the appearance of red hackles
in the cocks of black breeds of poultry. On the other hand, some
certainly are not reversions, such as the appearance of a white ring in
the neck of the female of the Rouen duck, which should resemble the
Mallard as regards the plumage of the neck. Again, the tendency of Buff
Orpingtons to assume white in the wings and tail must be regarded as a
variation which is not in the nature of a reversion. In short, the
efforts of all breeders are largely directed to fighting against the
tendencies which animals display towards variation in certain directions.
Albinistic Variations
This tendency to vary in the direction of whiteness may account for many
of the white markings which occur in nature, as, for example, the white
tails of the Sea Eagle (_Haliaetus albicilla_) the Nicobar Pigeon
(_Caloenas nicobarica_), and many hornbills. Provided that such
variations are not too great a handicap to their possessors in the
struggle for existence, natural selection will allow them to persist.
It was the belief of Linnæus, based on experience, that every blue or
red-coloured flower is likely to produce a white variety, hence he held
that it is not safe to trust to colour for the identification of a
botanical species.
On the other hand, white flowers are not likely to produce red varieties,
and we believe we may positively assert that they never produce a blue
sport. Similarly, white animals appear not to give rise to colour
varieties.
We are never surprised to find that an ordinary upright plant produces as
a sport or mutation a pendulous, or fastigiate form. These aberrant
varieties, be it noted, occur in species which belong to quite different
orders.
De Vries points out that laciniated leaves appear in such widely
separated trees and shrubs as the walnut, the beech, the hazel-nut, and
the turnip.
Another example of the definiteness of variation is furnished by what
Grant Allen calls the “Law of Progressive Colouration” of flowers.
On pp. 20, 21 of _The Colours of Flowers_, he writes, “All flowers, as we
know, easily sport a little in colour. But the question is, do their
changes tend to follow any regular and definite order? Is there any
reason to believe that the modification runs from any one colour toward
any other? Apparently there is. . . . All flowers, it would seem, were in
their earliest form yellow; then some of them became white; after that a
few of them grew to be red or purple; and finally a comparatively small
number acquired the various shades of lilac, mauve, violet, or blue.”
Over-development
So among animals there are many colour patterns and structures that
appear in widely different genera, as, for example, the magpie colouring
in birds. With this phenomenon we shall deal more fully when speaking of
animal colouration. There is certainly no small amount of evidence which
seems to indicate that, from some cause or other, an impetus has been
given to certain organs to develop along definite lines. The reduction of
the number of digits in several mammalian families which are not nearly
related is a case in point. This phenomenon is, as Cope points out,
observed in Marsupials, Rodents, Insectivores, Carnivores, and Ungulates.
He, being a Lamarckian, ascribes this to the inherited effects of use.
Wallaceians attribute it solely to the action of natural selection. The
assumption of a growth-force or tendency for the development of one digit
at the expense of the others, would explain the phenomenon equally well.
And it is significant that many palæontologists are believers in some
kind of a growth-force. In the case of certain extinct animals we seem to
have examples of the over-development of organs. “Palæontology,” writes
Kellog on p. 275 of his _Darwinism To-day_, “reveals to us the one-time
existence of animals, of groups of animals, and of lines of descent,
which have had characteristics which led to extinction. The unwieldiness
of the giant Cretaceous reptiles, the fixed habit of life of the
crinoids, the coiling of the ammonities and the nautili, the gigantic
antlers of the Irish stag—all these are examples of development along
disadvantageous lines, or to disadvantageous degrees. The statistical
studies of variation have made known numerous cases where the slight, as
yet non-significant (in a life-and-death struggle) variation in pattern
of insects, in dimensions of parts, in relative proportions of
superficial non-active areas, are not fortuitous, that is, do not occur
scattered evenly about a mean or mode according to the law of error, but
show an obvious and consistent tendency to occur along certain lines, to
accumulate in certain directions.”
It seems to us that the only proper attitude to adopt in the present
state of our knowledge is, not to call in to our aid an unknown
growth-force, but simply to say that there is evidence to show that
variations frequently occur along certain definite lines only.
Speed of Racehorses
Darwin’s second assumption was that there is no limit to which variations
may be accumulated in any direction; that by adding one minute variation
to another through countless generations new species, new genera, new
families may arise. This assumption, if applied to continuous or
fluctuating variations, seems opposed to facts. All the evidence
available goes to show that there is a definite limit to which minute
variations can be accumulated in any given direction. No one has
succeeded in breeding a dog as large as a horse, or a pigeon with a beak
as long as that of a snipe. In the case of racehorses, which have been
selected so carefully through a long period of time, we seem to have
reached the limit of speed which can be attained by the multiplication of
insignificant variations. We do not wish to dogmatise, but we believe
that of late years there has not been any material increase in the speed
of our racehorses.
Mr S. Sidney says, on page 174 of _Cassell’s Book of the Horse_: “As far
as form went (_pace_ Admiral Rous), the British racehorse had reached
perfection in 1770, when ‘Eclipse’ was six years old.” He quotes the
measurements of the skeleton of “Eclipse” in the Museum of the Royal
College of Surgeons as evidence of this. All the efforts of breeders,
then, have failed appreciably to improve the form of the British
racehorse in the course of over a century and a quarter.
Experiments of De Vries
De Vries has made some important experiments with a view to determining
whether or not there is a limit to the amount of change which can be
induced by the selection of fluctuating or continuous variations as
opposed to mutations. “I accidentally found,” he writes, on page 345 of
_Species and Varieties: their Origin by Mutation_, “two individuals of
the ‘five-leaved’ race (of clover); by transplanting them into my garden
I have isolated them and kept them free from cross-fertilisation with the
ordinary type. Moreover, I brought them under such conditions as are
necessary for the full development of their character; and last, but not
least, I have tried to improve their character as far as possible by a
very rigid and careful selection. . . . By this method I brought my
strain within two years up to an average of nearly 90 per cent. of the
seedlings with a divided primary leaf (such seedlings averaging five
leaves in the adult). . . . This condition was reached by the sixth
generation in the year 1894, and has since proved to be the limit, the
figures remaining practically the same through all the succeeding
generations. . . . I have cultivated a new generation of this race nearly
every year since 1894, using always the strictest selection. This has led
to a uniform type, but has not been adequate to produce further
improvement.” Similarly, De Vries found in the bulbous buttercup
(_Ranunculus bulbosus_) a strain varying largely in the number of petals;
therefore he tried by means of continuous selection of those flowers
having the largest number of petals to produce a double flower, but was
not able to do so. He succeeded in evolving a strain with an average
number of nine petals, some individuals having as many as twenty or
thirty; but even by breeding only from these last he could not increase
the average number of petals in any generation beyond nine. This was the
limit to be obtained by the most rigorous selection of fluctuating
variations.
Selection, based on fluctuating variation, does not, asserts De Vries,
conduce to the production of improved races. “Only temporary
ameliorations are obtained, and the selection must be made in the same
manner every year. Moreover, the improvement is very limited, and does
not give any promise of further increase.” Notwithstanding prolonged
efforts, horticulturists have not yet succeeded in breeding a biennial
race of either beetroots or carrots that does not continually give rise
to useless annual forms. Writing of the beet, De Vries says useless
annual varieties “are sure to return each year. They are ineradicable.
Every individual is in the possession of this latent quality, and liable
to convert it into activity as soon as the circumstances provoke its
appearance, as is proved by the increase of annuals in the early
sowings”—that is to say, in circumstances favourable to the annual
variety.
It will be urged perhaps that these experiments, which seem to show that
there is a limit to which a species can be modified by the accumulation
of fluctuating variations, cannot have been properly carried out, because
all the various breeds of pigeons and other domestic animals clearly show
that extraordinary differences not only can, but have actually been
produced by the selection of such variations. This objection is based
upon the assumption that breeders have in the past dealt only with
fluctuating variations. This assumption does not appear to be justified.
It is exceedingly probable that most, if not all, the varieties of
domesticated animals have originated in mutations. Take, for instance,
the modern turbit pigeon; this has been derived from the old Court-bec,
described and figured over two centuries ago by Aldrovandus.
De Vries goes so far as to assert that the various races of pears are all
mutations; that each distinct flavour is a mutation, and that it is
impossible to produce a new flavour by selecting fluctuating variations.
Thus it would appear that in every case of the production of a new breed
a mutation has occurred which has attracted the fancy of some breeder,
and he has seized upon this and perpetuated it.
All the evidence available tends to show that there is a limit—and one
which is quickly reached—to the amount of change that can be produced by
the selection of fluctuating or continuous variations. We, therefore,
seem driven to the belief that evolution is based on the kind of
variation which Professor Bateson terms “discontinuous variation” and
Professor De Vries calls “mutation.”
Bateson on Variation
As long ago as 1894 Bateson published his _Materials for the Study of
Variation_, in which he set forth a large number of cases of
discontinuous variation which he had collected. He pointed out that
species are discontinuous, that they are sharply separated one from
another, whereas “environments often shade into one another and form a
continuous series.” How, then, he asked, if variations are minute and
continuous, have these discontinuous species arisen? May not variation
prove to be discontinuous, and thus make it clear why species are
discontinuous?
On page 15 of the above-cited work we find: “The preliminary question,
then, of the degree of continuity with which the process of evolution
occurs has never been decided. In the absence of such a decision, there
has nevertheless been a common assumption, either tacit or expressed,
that the process is a continuous one. The immense consequence of a
knowledge of the truth as to this will appear from a consideration of the
gratuitous difficulties which have been introduced by this assumption.
Chief among these is the difficulty which has been raised in connection
with the building up of new organs in their initial and imperfect stages,
the mode of transformation of organs, and, generally, the selection and
perpetuation of minute variations. Assuming, then, that variations are
minute, we are met by this familiar difficulty. We know that certain
devices and mechanisms are useful to their possessors; but from our
knowledge of natural history we are led to think that their usefulness is
consequent on the degree of perfection in which they exist, and that if
they were at all imperfect, they would not be useful. Now it is clear
that in any continuous process of evolution such stages of imperfection
must occur, and the objection has been raised that natural selection
cannot protect such imperfect mechanisms so as to lift them into
perfection. Of the objections which have been brought against the theory
of natural selection this is by far the most serious.”
Bateson further pointed out that chemical compounds are not continuous,
that they do not merge gradually each into the next, and suggested that
we might expect a similar phenomenon in the organic world.
Elsewhere he says: “Let the believer in the efficacy of selection
operating on continuous fluctuations try to breed a white or a black rat
from a pure strain of black-and-white rats, by choosing for breeding the
whitest or the blackest; or to raise a dwarf sweet pea from a tall race
by choosing the shortest. It will not work. Variation leads and selection
follows.”
Work of Bateson and De Vries
But Bateson’s views fell upon stony ground, because zoologists are mostly
men of theory and not practical breeders. They laboured under the
delusion that mutations or “sports” are rare in nature, and that when
these do happen to occur they must of necessity be swamped by
inter-crossing.
However, the discovery of the Abbé Mendel’s account of his experiments on
breeding mongrel sweet peas has opened the eyes of many zoologists, so
that they have at last learned what practical breeders have known for
untold years—namely, that sports have a way of perpetuating themselves.
Moreover, Mendel was able to give a theoretical explanation of his
discoveries, with the result that the believers in discontinuous
variation have largely increased in number of late.
While we are unable to see eye to eye with Professor Bateson in all
things, we gladly recognise the immense value of his work. Had his
statements in 1894 received the attention they merited, zoological theory
would to-day be considerably more advanced than it actually is.
Professor De Vries has gone farther than Bateson, having engrafted upon
the Darwinian hypothesis the theory of mutations. He has done no small
amount of experimental work, and has undoubtedly thrown much new light on
the ways in which species arise. He is purely a botanist, so that he
argues only from plants. Nevertheless, we believe that some of his
conclusions are applicable to animals. We are far from accepting his
theory of mutations _in toto_. We are, however, convinced that he, like
Bateson, is on the right track. There can be no doubt that a great many
new forms have originated suddenly, by jumps, and not by imperceptibly
slow degrees. Before giving a list of the names of some of the races,
both plant and animal, which appear to have come into existence suddenly,
it will be of advantage to consider for a little some of the more
important conceptions of De Vries.
Varieties and Elementary Species
That eminent botanist, as we have already seen, insists on the
distinction between fluctuating variations and mutations. The former
correspond, for all practical purposes, to the continuous variations of
Bateson, and the latter seem to be equivalent to his discontinuous
variations.
According to De Vries, all plants display fluctuating variation, but only
a small percentage exhibit the phenomenon of mutation. The most daring of
his conceptions is, that the history of every species is made up of
alternating periods of inactivity, when only fluctuating variations
occur, and of activity when “swarms of species” are produced by mutation,
and of these only a few at the most survive; natural selection, which De
Vries likens to a sieve, determining which shall live and which shall
perish.
As we have seen, De Vries does not believe that new species can arise by
the accumulation of fluctuating variations. By means of these the race
may be greatly improved, but nothing more can be accomplished. These
variations follow Quetelet’s law, which says that, for biological
phenomena, deviations from the average comply with the same laws as the
deviations from the average in any other case, if ruled by chance alone.
Very different in character are mutations. By means of these, new forms,
quite unlike the parent species, suddenly spring into being. Mutations
are said by De Vries to be of two kinds—those that produce varieties and
those which result in new elementary species.
According to De Vries, those species of plants which are in a state of
mutation (he refers to the species of the systematic botanists) are of a
composite nature, being made up of a collection of varieties and
elementary species. His conception of a variety is a plant that differs
from the parent plant in the loss or suppression of one or more
characters, while an elementary species differs from the parent form in
the possession of some new and additional character. But we will allow
him to speak for himself: “We can consider (page 141 _Species and
Varieties_) the following as the principal difference between elementary
species and varieties: that the first arise by the acquisition of
entirely new characters, and the latter by the loss of existing
qualities, or by the gain of such peculiarities as may already be seen in
other allied species. If we suppose elementary species and varieties
originated by sudden leaps and bounds, or mutations, then the elementary
species have mutated in the line of progression, some varieties have
mutated in the line of retrogression, while others have diverged from the
parental types in a line of digression or in the way of repetition. . . .
The system (of the vegetable kingdom) is built up of species; varieties
are only local and lateral, never of real importance for the whole
structure.”
De Vries asserts that these elementary species, when once they arise,
breed true, and show little or no tendency to revert to the ancestral
form. We can, says De Vries, ascertain only by experiment which plants
are in the mutating state and which are not. The great majority, however,
are not at present in the mutating state.
Mutations
The distinction between fluctuating variation and mutation has been
roughly illustrated by the case of a solid block of wood having a number
of facets, on one of which it stands. If the block be tilted slightly it
will, when the force that has tilted it is removed, return to its old
position. Such a gentle tilt may be compared to a fluctuating variation
in an organism. If, however, the block be tilted to such an angle that
when left to itself the block does not return to its old position, but
tips over and comes to rest on another facet, we have a representation of
the kind of change indicated by a mutation.
The analogy is far from perfect, for it makes it appear that the smallest
mutation must of necessity involve a departure from the normal type more
considerable than that of the largest fluctuating variation. Now,
although mutations ordinarily consist in considerable deviations from the
mean or mode of the type, while continuous variations are usually minute
deviations, it sometimes happens that the extreme fluctuations are more
considerable than some mutations. Hence “fluctuating” describes this
latter kind of variation more accurately than “continuous” does.
The test, then, of a mutation is not so much the amount of deviation as
the degree in which it is inherited. Mutations show no tendency to a
gradual return to the mean of the parent species; fluctuating variations
do display such a tendency. A mutation consists, as M. E. East says, in
the production of a new mode or centre for linear fluctuation; it is, as
it were, a shifting of the centre of gravity; the centre about which
those fluctuations which we call continuous variations occur.
As it is of considerable importance thoroughly to grasp the true nature
of mutations or discontinuous variations, and as some writers do not
appear to realise wherein lies the essential difference between the two
kinds of variation, we will, at the risk of appearing tedious, give a
further illustration. Let A be a species of bird of which the average
length of the wing is 20 inches, and let us suppose that individuals
belonging to that species occur in which the length of the wing varies as
much as 3 inches each side of the mean; thus it is possible to find
individuals of this species with a wing as short as 17 inches, or as long
as 23 inches. Let B be another species of which the average length of the
wing is 17 inches, and let us suppose that a 3-inch variation on each
side of the mean be found to occur. Individuals belonging to species B
will occur which have a wing as short as 14 inches, or as long as 20
inches. Thus some individuals of the short-winged species will have
longer wings than certain individuals of the long-winged species.
Similarly, certain individuals of a species which display a mutation may
show less deviation from the mean than some individuals showing a very
pronounced fluctuating variation. In other words, even as by measuring
the length of wing in the above example it was not always possible to say
whether a given individual belonged to species A or B, so is it not
always possible to say by looking at an individual that shows a
considerable departure from the mean whether that departure is due to a
mutation or a fluctuating variation.
Law of Regression
It is only by watching the effect of the peculiarity on the offspring of
its possessor that we are able to determine the nature of the variation.
Where the peculiarity is due to a fluctuating variation the offspring
will display the peculiarity in a diminished degree; but if the
peculiarity be due to a mutation, the offspring are likely to display it
in as marked a degree as the parent.
Fritz Müller and Galton conducted independently enquiries into the amount
of the regression shown by the progeny of parents which have deviated
from the average by fluctuating variation.
Müller experimented with Indian corn; Galton with the sweet pea.
Each found that where the deviation of the parents is represented by the
figure 5, that of their offspring is usually 2, that is to say, the
deviation they display is, on the average, less than half that of their
parents.
Applying this rule to the hypothetical case given above, if two
individuals of species A having a length of wing of 20 inches be bred
together, their offspring will, on an average, have a length of wing of
20 inches, since neither parents showed any deviation from the mean. On
the other hand, the offspring of 20-inch-wing individuals of species B
would show, on an average, a length of wing of only about 18¼ inches.
They tend to return to that mode from which their parents had departed.
But suppose that the deviation of the parents in this case had been due,
not to fluctuating variation, but to a mutation; this would mean that,
owing to some internal change in the egg that produced each parent, 20
inches became the normal length of wing; that the normal length of wing
had suddenly shifted from 17 inches to 20 inches.
The result of this would be that their offspring would have on an average
a wing-length of 20 inches instead of 18¼ inches, that the centre of
variation as regards length of wing had suddenly shifted from 17 to 20,
that, in future, all fluctuating variations would occur on either side of
20 inches, instead of on either side of 17 inches as heretofore.
Thus a variation is a fluctuating one or a mutation according as it does
or does not obey Galton’s Law of Regression.
De Vries’s Dictum
De Vries says that it is of the essence of mutations that they are
completely inherited. This statement, although substantially true, fails
to take into consideration the factor of fluctuating variation. For
example, in the above instance if the two individuals of species B had
mutated into forms with a 20-inch wing, their offspring will nevertheless
vary _inter se_, some of them will have wings shorter than 20 inches and
others wings more than 20 inches in length. But the average wing-length
of the offspring of the two mutating individuals will be 20 inches.
So much, then, for the practical difference between a mutation and a
fluctuating variation. In Chapter V. we shall discuss the possible causes
of the difference. By way of anticipation we may say that the suggestion
we shall make is that a mutation is due to some rearrangement in the
particles which represent that part of the organism in the fertilised
egg, whereas a fluctuating variation is caused by variations in the
particles themselves.
De Vries, it should be noted, bases his theory largely on experimental
evidence. His dictum is “the origin of species is an object of
experimental observation.” He has, we consider, proved conclusively that
among plants mutations sometimes occur, and, further, that in a mutating
plant the same mutation tends to occur again and again. This latter is a
most important fact, because it goes some way towards overcoming the
difficulty urged by Darwin that isolated sports must be swamped by
continual crossing with the normal type. If mutations arise in swarms, as
De Vries asserts they do, then any particular mutation is likely, sooner
or later, to cross with a similar mutation and so be able to perpetuate
itself.
Mutating Plants
The classical example of a mutating plant is the evening primrose of the
species _Oenothera lamarckiana_. This is described by De Vries as a
stately plant, with a stout stem, attaining often a height of 1.6 metres
or more. The flowers are large and of a bright yellow colour, attracting
immediate attention, even from a distance. “This striking species,” he
writes, in _Species and Varieties_ (p. 525), “was found in a locality
near Hilversum, in the vicinity of Amsterdam, where it grew in some
thousands of individuals. Ordinarily biennial, it produces rosettes in
the first, and stems in the second year. Both the stems and the rosettes
were seen to be highly variable, and soon distinct varieties could be
distinguished among them.
“The first discovery of this locality was made in 1886. Afterwards I
visited it many times, often weekly or even daily, and always at least
once a year up to the present time. This stately plant showed the
long-sought peculiarity of producing a number of new species every year.
Some of them were observed directly in the field, either as stems or
rosettes. The latter could be transplanted into my garden for further
observation, and the stems yielded seeds to be sown under like control.
Others were too weak to live a sufficiently long time in the field. They
were discovered by sowing seed from indifferent plants of the wild
locality in the garden. A third and last method of getting still more new
species from the original strain was the repetition of the sowing
process, by saving and sowing the seed which ripened on the introduced
plants. These various methods have led to the discovery of over a dozen
new types, never previously observed or described.” Some of these De
Vries regards as varieties, in the sense in which he uses the words;
others, he maintains, are real progressive species, some of which are
strong and healthy, others weaker and apparently not destined to be
successful. All these types proved absolutely constant from seed.
“Hundreds of thousands of seedlings may have arisen, but they always come
true and never revert to the original _O. lamarckiana_ type. But some of
them, however, are, like their parent form, liable to mutations.” The
case of the evening primrose is by no means an isolated one. De Vries
cites several other instances of plants in a mutating state. “The common
poppy,” he says (p. 189), “varies in height, in colour of foliage and
flowers; the last are often double or laciniated. It may have white or
bluish seeds, the capsules may open themselves or remain closed, and so
on. But every single variety is absolutely constant, and never runs into
another when the flowers are artificially pollinated and the visits of
insects excluded.” Similarly the garden carnation sometimes gives rise to
the wheat-ear form. “In this variety,” writes De Vries (p. 228), “the
flower is suppressed, and the loss is attended by a corresponding
increase in the number of pairs of bracts. This malformation results in
square spikes, or somewhat elongated heads, consisting only of the
greenish bracts. As there are no flowers, the variety is quite sterile,
and, as it is not regarded by horticulturists as an improvement on the
ordinary bright carnations, it is seldom multiplied by layering.
Notwithstanding this it appears from time to time, and has been seen in
different countries and at different periods, and what is of great
importance for us, in different strains of carnations. Though sterile,
and obviously dying out as often as it springs into existence, it is
nearly two centuries old. It was described in the beginning of the
eighteenth century by Volckamer, and afterwards by Jaeger, De Candolle,
Weber, Masters, Magnus, and many other botanists. I have had it twice at
different times and from different growers.” Similarly, the long-headed
green dahlia arose twice over some years ago in the nursery of Messrs
Zocher & Co.
Further, the peloric Toad-flax (_Linaria vulgaris peloria_) is, De Vries
informs us, “known to have originated from the ordinary type at different
times and in different countries under more or less divergent
conditions.” And, as this variety is wholly barren, it must in each
instance have had an independent origin. Lastly, the purple beech seems
to be a mutation which has originated at least three times over.
Mutation Theory Criticised
Every one interested in biological theory should read both _Species and
Varieties_ and _Plant Breeding_ by De Vries, works which are of
incalculable value to the horticulturist and agriculturist as well as to
the biologist.
While not wishing to detract in any way from the truly splendid work done
by De Vries, we feel constrained to bring several charges against him.
Firstly, he suffers from the complaint that seizes nine out of ten
originators of new theories. He pushes his theory to extreme lengths; he
allows his imagination to run away with him. We do not think that on the
evidence available he is justified in asserting that every species passes
through alternating periods of comparative quiescence and periods in
which it throws off, as mutations, swarms of elementary species. He is
justified in asserting that discontinuous variation is by no means an
uncommon phenomenon, but further than this it does not seem safe to go at
present.
Secondly, he ought to lay more stress on the fact that _Oenothera
lamarckiana_ is a plant which does not appear to be known in the wild
state, and that it is therefore possibly a hybrid plant, and the
so-called elementary species which it gives off may be merely the
varieties out of which it has been built up. Boulenger and Bailey have
both studied this plant, and they have not been able to witness all the
mutations of which De Vries speaks, so that the former says, “The fact
that _Oenothera lamarckiana_ was originally described from a garden
flower, grown in the Paris _Jardin des Plantes_, and that, in spite of
diligent search, it has not been discovered wild anywhere in America,
favours the probability that it was produced by crossing various forms of
the polymorphic _Oenothera biennis_, which had been previously introduced
in Europe.”
Definition of a Species
It has further been objected that, even if these various forms which
Lamarck’s evening primrose throws off are true mutations, they ought not
to be called new species, for they do not differ sufficiently from the
parent species to deserve the name of new species. The reply to this
criticism is that De Vries asserts that mutations produce new elementary
species, which are not the same things as new species in the ordinary
sense of the term. Most Linnæan species differ from one another to a far
greater extent than do elementary species. It seems to us quite plain
that new species arise, not by a single mutation, but by two or three
successive mutations which occur in various parts of an organism.
First arises a well-marked variety, by a single mutation. Subsequent
mutations follow, so that a distinct race is produced. And, finally,
fresh mutations occur, so that a new species is eventually produced.
What De Vries calls an elementary species the majority of systematists
would call a well-marked variety.
We may take this opportunity of remarking that the definition of a
species is one on which naturalists seem unable to agree.
So vast is the field of biology, that now-a-days biologists are compelled
to specialise to some extent. Thus we have botanists, ornithologists,
those who devote themselves to the study of mammals, those who confine
themselves to reptiles, or insects, or fishes, or crustaceans, or
bacteria, etc.
Now each class of systematists has its own particular criterion of what
constitutes a species. Ornithologists do not seem very exacting. Most of
them appear to consider a constant difference of colour sufficient for
the formation into a species of the birds that display such a variation.
Those who study reptiles, on the other hand, do not allow that a mere
difference in colour is sufficient to promote its possessor to specific
rank. Into these nice questions we cannot enter. For our purpose a
species is a group of individuals that differ from all other individuals
in displaying certain well-marked and tolerably constant characters,
which they transmit to their offspring.
Our contention, then, is that new species, in the ordinarily-accepted use
of the term, do not arise as a rule by one sudden bound (although they
may sometimes do so), but are the result of the accumulation of several
mutations or discontinuous variations. Some of these mutations are
exceedingly well marked, while others are so small as to be
indistinguishable from the more extreme fluctuating variations. Before
passing on to consider some cases of well-marked mutations which have
occurred among animals and plants, we should like to take this
opportunity of pointing out that as regards experiments in evolution the
botanist is far more favourably situated than the zoologist.
The botanist is able to reproduce many species vegetatively, _e.g._ by
cuttings, and is thus easily able to multiply examples of mutation. He
can also reproduce the great majority of plants by self-fertilisation,
and so experiences no difficulty in “fixing” a new form. Again, plants
are far easier to control than animals; as a rule they can be
transplanted without any impairment of their capacity for breeding.
Moreover, they produce a greater number of offspring than the most
prolific of the higher animals. The animal breeder is thus at an obvious
disadvantage as compared with the horticulturist. It is only with great
difficulty that he can fix the mutations which appear in his stock.
“Scatliff Strain” of Turbit
The history of the production of the “Scatliff strain” of turbit affords
a good example of the kind of difficulties that confront the breeder.
Pigeon fanciers require that the ideal turbit shall have, among other
things, an unbroken “sweep,” that is to say the line of the profile from
the tip of the beak to the back of the head should be the arc of a
circle. As a rule this line is broken by the overgrowth of the wattle at
the base of the beak. Mr Scatliff, however, has succeeded in breeding a
strain which possesses the required description of profile.
“In the year 1895,” writes Mr H. P. Scatliff on page 25 of _The Modern
Turbit_, “I visited Mr Houghton’s lofts and purchased three or four extra
stout and short-beaked stock birds. . . . The following year I mated one
of these to one of my own black hens, and reared one of the most
successful show birds ever bred, viz. ‘Champion Ladybird,’ a black hen. .
. . Most of the leading judges and many turbit breeders remarked upon
this hen’s wonderful profile, which seemed to improve as she got older
instead of getting worse, as is usual in rather coarse-wattled birds. I,
too, had remarked this, and it opened my eyes to a point in turbit
breeding which I had never heard mentioned by any turbit judges or
breeders, and which I believe I am now pointing out for the first time in
print, viz. that the feathers over her beak wattle which formed her front
_grew from the top and right to the front of her wattle, and not from
slightly behind_, as in almost every other turbit of her day; thus, as
the wattle developed and grew coarser, the front became more developed,
and made her head larger without in any way spoiling the sweep of the
profile.
“The same year ‘Ladybird’ was bred I bred eight others from the same
pair, and with one exception all turned out to be hens. There was only
one other hen, however (a dun), that had this same point, but in a lesser
degree than ‘Ladybird,’ and from these two hens nearly all my blacks, and
several of my blues are descended.”
[Illustration: A TURBIT BELONGING TO MR. H. P. SCATLIFF]
Mr Scatliff, having “spotted” this point, looked about him for another
bird having the peculiarity, with the object, if possible, of fixing the
same in his strain. He discovered this point in a pigeon belonging to Mr
Johnston of Hull, and purchased the bird for £20. But it died in the
following spring without producing for Mr Scatliff a single young one.
The next year Scatliff found that a bird belonging to a Mr Brannam had
the required peculiarity and so purchased him for £20. But that cock,
too, died before anything was bred from him. Nothing daunted, Scatliff
found that another of Brannam’s cocks displayed the same peculiarity, so
purchased him in 1899 for £15, but he also died before the year was out.
Meanwhile Scatliff had, by mating up “Ladybird” with the most likely of
his own cocks, succeeded in producing one or two young cocks with the
desired point. By breeding these with their mother “Ladybird” and their
offspring again with “Ladybird,” Scatliff eventually succeeded in
breeding some turbits, both blacks and duns, with the required
peculiarity fully developed, but not before he had spent a further sum of
£55 on two other cocks, both of which died before they could be mated
with the famous “Ladybird.” However, amid all his misfortunes, Scatliff
informs us that he bought one bird, by name “Amazement,” which did assist
him in fixing his strain. Thus Scatliff spent considerably over £100 in
purchases, and took eight years fixing the peculiarity in question. Had
“Ladybird” been a flower, the peculiarity could probably have been fixed
in one generation by self-fertilisation.
This furnishes an excellent example of the trouble which breeders will
take, and the expense to which they will go in order to produce a desired
result. Nevertheless, it appears to be the fashion for scientific men to
decry the work of the breeder.
Let us now pass on to consider the cases of mutations which are known to
have occurred among animals.
Mutations among Animals
Some instances of great and sudden variation in domesticated animals have
become classical, and been detailed in almost every work on evolution.
These are, firstly, the celebrated hornless Paraguay cattle. This
hornless breed, or rather the ancestor of the breed, arose quite
suddenly.
Many domestic horned breeds of animals, especially sheep and goats, throw
off hornless sports. Were a hornless breed of buffalo found in nature, it
would undoubtedly be ranked a new species, and the Wallaceians would
doubtless exercise much ingenuity in explaining how natural selection had
brought about the gradual disappearance of the horns; and
palæontologists, being baffled in their search for intermediaries between
the hornless species and their horned ancestors, would complain of the
imperfection of the geological record.
It may, perhaps, be argued that this hornless mutation was a direct
result of the unnatural conditions to which the Paraguay cattle were
subjected, it may be asserted that since there are no species of hornless
cattle in nature, such mutations have never occurred under natural
conditions, and hence the Paraguay cattle prove nothing. As a matter of
fact, we know that in nature a great many mutations occur which are not
perpetuated because not beneficial to the species. A hornless individual
in the wild state would stand but little chance in fighting for females
against his horned brethren. We must keep clearly in mind that the theory
of mutation does not seek to abolish natural selection; it merely affords
that force something substantial to work upon.
The second classical example of a leap taken by nature is furnished by
the Franqueiro breed of long-horned cattle in Brazil. These furnish us
with an example of a mutation in the other direction. Then there is the
Niata or bull-dog breed of cattle, which are also South American. These
instances would seem to indicate that cattle are what De Vries would call
“in a mutating state” in that part of the world.
The other classical examples of great and sudden variations are the Ancon
sheep of Massachusetts, the Mauchamp breed of Merino sheep, the tufted
turkeys, and the long-haired race of guinea-pigs.
The “wonder horses,” whose manes and tails grow to an extraordinary
length, so as to trail on the ground, may perhaps be cited as a race
which originated in a sudden mutation. They are all descendants of a
single individual, Linus I., whose mane and tail were respectively
eighteen and twenty-one feet long. But in this case it is important to
note that the parents and grandparents of Linus I. had exceptionally long
hair.
Mutations among Birds
Coming now to birds we find several undoubted examples of mutations, or
new forms which have come suddenly into being.
The black-winged peafowl, whose peculiarities were commented on by
Darwin, afford a striking example of this phenomenon. These birds breed
true when mated together, and are known to have arisen from common
peafowl in no less than nine instances. The cocks have the wings (except
the primary quills), black glossed with blue and green, and have the
thighs black, whereas, in the ordinary peacock, the same part of the wing
is nearly all mottled black and pale buff, and the thighs are drab. The
black-winged hen, on the other hand, is nearly white, but has a black
tail and black speckling on the upper surface of the body, while her
primary quills are cinnamon coloured as in male peafowl, not drab as in
the normal hens. The young are white when hatched, the young cock
gradually assuming the dark colour as he matures.
This mutation, which, in one case quoted by Darwin, increased among a
flock of peafowl until the black-winged supplanted the ordinary kind, is
so distinct in appearance in all stages that it was formerly supposed to
be a true species (_Pavo nigripennis_), of which the wild habitat was
unknown.
The Golden Pheasant (_Chrysolophus pictus_) produces, in domestication,
the dark-throated form (_C. obscurus_), in which the cock has the throat
sooty-black instead of buff, and the scapulars or shoulder feathers black
instead of red. Moreover, the two middle-tail-feathers are barred with
black and brown like the lateral ones, while in the ordinary form they
are spotted with brown on a black ground. The hens have a chocolate-brown
ground-colour instead of yellow-ochre as in the normal type. The chicks
are likewise darker.
The common duck, in domestication, when coloured like the wild mallard,
sometimes produces a form in which the chocolate breast and white collar
of the drake are absent, the pencilled grey of the abdomen reaching up to
the green neck. In this mutation the duck has the head uniformly speckled
black and brown, and lacks the light eye-brow and cheek-stripes found in
the normal duck. Both sexes have the bar on the wing dull black instead
of metallic blue.
The ducklings which ultimately bear this plumage are sooty-black
throughout, not black and yellow like normal ones.
The phenomenon of mutation is not confined to animals in a state of
domestication. The common Little Owl of Europe (_Athene noctua_) has
produced the mutation _A. chiaradiæ_ in the wild state. In this the
irides are dark, instead of yellow as in the normal type, and the plumage
of the back of the wings is longitudinally streaked with white instead of
barred. Several examples of this form were found, along with normal
young, in the nest of one particular pair of little owls in Italy, but
the whole family were foolishly exterminated by local ornithologists.
The reed bunting (_Emberiza schœniclus_) exists in two distinct forms—one
having a much stouter bill than the other (_E. pyrrhuloides_). This
probably is an example of a mutation.
The rare yellow-rumped Finch (_Munia flaviprymna_), of Australia, has
displayed a tendency to change into the allied and far commoner
chestnut-breasted Finch (_M. castaneithorax_) during the lifetime of the
individual (_Avicultural Magazine_, 1907). Conversely, the male of the
common Red-billed Weaver (_Quelea quelea_) of Africa has been found in
its old age to assume the characters of the comparatively rare _Q.
russi_, its black throat becoming pale buff as in that form.
Everyone is familiar with the chequered variety of the common blue-rock
pigeon, in which the wings are regularly mottled with black instead of
being barred. This form sometimes occurs among wild birds, so that it has
been described as a distinct species. It is important to note that there
are red, dun, and silver chequers as well as blue ones.
[Illustration: YELLOW-RUMPED AND CHESTNUT-BREASTED FINCHES, WITH
TRANSITIONAL SPECIMENS]
A well-marked mutation which appears regularly in nature is the
red-headed variety of the beautiful Gouldian Finch (_Pöephila mirabilis_)
of North Australia. Normally the head of the cock is black, but in about
ten per cent. of the individuals the cock has a crimson head, while that
of the hen is dull crimson and black.
Mutations which occur with such regularity are certainly rare. On the
other hand, there are certain mutations which we may expect to see appear
in any species of plant or animal.
Albinistic forms are a case in point, and less frequently we see white
varieties which are not pure albinos, because the eye retains some at
least of the normal pigment. As examples, we may cite white dogs, cats,
fowls, horses, ducks, geese, and Java sparrows among domesticated
animals, and the white forms of the Amazonian dolphin and of the giant
Petrel of the South seas (_Ossifraga gigantea_) among wild creatures.
In a white mutation the eye may lose all its pigment, and then we have a
true albino. Such forms on account of their imperfect vision cannot
survive in a state of nature, hence no wild pink-eyed species are known.
Or the eye may display a partial loss of pigment, as, for example, in the
white domestic forms of the common goose, the Chinese goose, and the
Muscovy duck. Finn saw a case in which the eyes of a pink-eyed rabbit
changed after death into this type of eye—that is, with the pupil black
and the iris blue. It is to be observed that this kind of eye sometimes
occurs in coloured horses, rabbits, and dogs. Finally, we have white
mutations in which the eye loses none of the pigment. These are abundant
in nature, and probably most of the white species of birds—as, for
example, some egrets, swans, etc.—arose in this way.[4] Pure white
species are comparatively uncommon in nature, because, except in
snow-clad regions, white creatures are easily seen by their adversaries.
Most white birds are of considerable size, and well able to look after
themselves.
Similarly black mutations occur frequently among animals, both under
domestication and in a state of nature. All are familiar with black dogs,
cats, horses, fowls, ducks, pigeons. Black mutations, however, do not
occur nearly so frequently as white ones. So far as we are aware no black
mutation has been recorded among canaries, geese, guinea-fowl, ferrets,
Java sparrows or doves, all of which produce white mutations.
On the other hand, in the wild state black species occur more frequently
than normal-eyed white forms. This is probably because such creatures are
less conspicuous than white ones. As examples of black mutations which
occur in nature, we may cite black leopards, water rats, squirrels,
foxes, barking deer (_Cervulus muntjac_), hawk-eagles, harriers, peppered
moth (_Amphidasys betularia_), etc.
That many black species have arisen as sudden mutations from
lighter-coloured animals seems tolerably certain from the facts that in
Malacca the black leopard forms a local race; that some of the Gibbon
apes are as often black as light coloured; that the American black bear
is sometimes brown, while the other bears, when not brown, are almost
invariably black.
Color Mutations
Not uncommon, although rarer than black or melanistic forms, are reddish
or chestnut varieties. These occur both among tame and wild animals.
Among domesticated creatures, sandy cats, “red” pigeons, buff fowls,
chestnut horses, red guinea pigs afford examples of this mutation. Among
wild animals many of the species of squirrel, not naturally red, produce
red mutations; and some of the grey owls—as, for example, the Indian race
of the Scops (_Scops giu_)—throw off a red or chestnut form. As everyone
knows, some species are normally red.
Green or olive species not unfrequently throw off yellow mutations. As
examples of these we may cite yellow canaries, yellow budgerigars
(_Melopsittacus undulatus_), goldfish, golden tench, and the golden form
of the common carp among captive animals; and among animals in a state of
nature, yellow forms have been recorded of the rose-ringed Paroquet
(_Palæornis torquatus_), the green woodpecker, the pike, and the eel.
These lutinistic forms usually have normally coloured eyes. Sometimes,
but only very rarely, these yellow forms throw off white sports—as, for
example, the “silver” form of the goldfish. Finn has seen a white variety
of the common carp. White canaries are excessively rare, while white
budgerigars are unknown.
It is worthy of note that entirely yellow species of birds and fish are
unknown. We would suggest that the explanation of this is that yellowness
is correlated with some physical characteristic unfavourable to an
organism exposed to the struggle for existence; hence individuals which
are yellow are not permitted to survive. In some species of moths
individuals occur in which the parts normally red are yellow. According
to Bateson, a chalk pit at Madingly, near Cambridge, has long been known
to collectors as a habitat of a yellow-marked form of the six-spot Burnet
Moth (_Zygæna filipendulæ_). These lutinistic forms are not confined to
one genus of Butterflies. Moreover, in the Pin-tailed Nonpareil Finch
(_Eythrura prasina_) of the Eastern Archipelago the red tail and other
red parts of the plumage are not infrequently replaced by yellow in wild
individuals of either sex and of any age. In the blue-fronted Amazon
parrot (_Chrysotis æstiva_)—a most variable bird—the normally red edge of
the pinion is sometimes yellow. Bateson, in his _Materials for the Study
of Variation_, gives other examples of this kind of variation.
Mutations among Invertebrates
As further instances of mutations among animals which have been observed
in nature, we may mention the _valezina_ form of the female of the
Silver-washed Fritillary Butterfly (_Argynnis paphia_) and the _helice_
form of the female Clouded-yellow Butterfly (_Colias edusa_).
The common jelly-fish is an organism which frequently throws off sports,
and some zoologists are of opinion that the medusoid _Pseudoclytia
pentata_ arose by a discontinuous variation from _Epenthesis folleata_ or
a closely allied form. Thomson discusses this particular case at some
length on pages 87-89 of his _Heredity_, and gives it as his opinion that
the evidence in favour of this latter having arisen as a mutation is
“exceedingly strong.”
Mutating Species
It is our belief that many species of birds which occur in nature have
been derived from other species which still exist, but as no one has ever
seen the mutation take place, we cannot furnish any proof thereof. We
merely rely on the fact that the species in question differ so slightly
from one another that there seems every likelihood that they have
suddenly arisen and managed to establish themselves alongside of the
parent species.
The Curassows, _Crax grayi_, _C. hecki_, each of which is only known by a
very few specimens, appear to be mutations of the female of the globose
Curassow, _Crax globicera_. The fact that when a female _hecki_ bred in
the London Zoological Gardens with a male _globicera_, the solitary young
one which lived to grow up was a pure _globicera_, renders the assumption
almost certain.
The Chamba Monaul (_Lophophorus chambanus_) seems to be a mutation of the
male of the common Monaul or Impeyan Pheasant (_Lophophorus impeyanus_),
the common species of the Himalayas.
The Three-coloured Mannikin (_Munia malacca_) of South India is probably
simply a white-bellied form of the widely-ranging Black-headed Mannikin
(_M. atricapilla_), which has the abdomen chestnut like the back.
Intermediate wild-caught forms have been recorded.
The African Cordon-bleu (_Estrelda phœnicotis_) and Blue-bellied Waxbill
(_E. cyanogastra_) would also seem to be mutations, as almost the only
difference between them lies in the fact that the male of the former has
a crimson cheek-patch, which is wanting in the latter.
The Ringed Finch (_Stictoptera annulosa_) of Java, and Bicheno’s Finch
(_S. bichenovii_) of Australia, only differ in the former having the rump
black, while in the latter it is white, and this difference appears to be
of the nature of a mutation.
So, it might be urged, is the pure white breast of the male Upland Goose
(_Chloëphaga magellanica_), which part, in the very similar _C. dispar_,
is barred as in the females, the latter form being probably the ancestor.
The differences between the silver-grey-necked Crowned Crane of the Cape
(_Balearica chrysopelargus_) and the dark-necked species of West Africa
(_B. regulorum_) seem also to be not more than could be accounted for by
mutation.
Peculiar forms, such as a rabbit with a convoluted brain or a mouse with
a peculiar pattern of molar teeth, have been come upon by anatomists.
The above-cited mutations are all very considerable ones, and we do not
profess to have mentioned a tenth part of those which have actually been
recorded.
We trust that we have collected and set forth sufficient evidence to show
that the phenomenon of discontinuous variation is a very general one, and
this would seem to tell against the hypothesis of De Vries that species
pass through alternate periods of comparative stability and periods when
swarms of mutations appear. We think it more probable that all species
throw off at greater or less intervals discontinuous variations, and that
it is upon these that natural selection acts.
We further hope that we have succeeded in making clear what we believe to
be the very sharp distinction between continuous and discontinuous
variations, even when the latter are inconsiderable, as frequently
happens.
Somatic and Germinal Variations
Before leaving the subject of variation it is necessary to notice the
distinction, which Weismann was the first to emphasise, between somatic
and germinal variations.
Every adult organism must be regarded as the result of two sets of
forces; inherited tendencies or internal forces, and the action of
environment or external forces. The differences which the various members
of a family show are due in part to the initial differences in the
germinal material of which they are composed, and in part to the
differences of their environment. The former differences are the result
of what we may call germinal variations, and the latter the result of
somatic variations. It is scarcely ever possible to say of any particular
variation that it is a germinal or a somatic one, because even before
birth a developing organism has been subjected to environmental
influences. One of a litter may have received more nourishment than the
others. Nevertheless, any marked variation which appears at birth is
probably largely germinal. According to Weismann and the majority of
zoologists, there is a fundamental difference between these germinal and
somatic variations, in that the former tend to be inherited, while the
latter are never inherited. Weismann believes that very early in the
formation of the embryo the cells which will form the generative organs
of the developing organism are separated off from those cells which will
go to build up the body, and become as much isolated from them as if they
were contained in a hermetically-sealed flask, so that they remain
totally unaffected by any changes which the environment effects in the
somatic cells. Therefore, says Weismann, acquired characters cannot be
inherited.
While the majority of zoologists believe that acquired characters are not
inherited, probably not many will go so far as Weismann and declare that
the environment cannot exercise _any_ effect whatever on the germ cells.
Somatic Variations
Even though acquired characters or variations are not inherited, it does
not follow that they do not play an important part in evolution. Acquired
variations are the result of the way in which an organism reacts to its
environment. If an organism is unable to react to its environment it must
inevitably perish. If it is able to react, it matters not, so far as the
chances of survival of the organism are concerned, whether the adaptation
is the result of a congenital variation or a somatic one. This will be
rendered clear by a hypothetical example. Let us suppose that a certain
mammal is forced, owing to the intensity of the struggle for existence,
to migrate into the Arctic regions. Let us further suppose that this
organism is preyed upon by some creature that hunts by sight rather than
by scent. Let us yet further imagine that this predacious species is
swifter than our animal, on which it preys. It is obvious that, other
things being equal, the more closely the creature preyed upon assimilates
to its surroundings the more likely is it to escape the observation of
its foes, and so to survive and give birth to offspring. Now suppose that
the glare from the snow-covered ground bleaches its coat. This whitening
of the fur is a somatic variation, one which is induced by the
environment. Such an animal will be as difficult to see, if the bleaching
is such as to render it snow-white, as if its whiteness were due to a
germinal variation. Thus, as regards its chances of survival, it matters
not whether its whiteness be the result of germinal or somatic variation.
But if the whiteness is due to a somatic variation, its offspring will
show no tendency to inherit the variation; they will have in turn to
undergo the bleaching process. If, on the other hand, the whiteness is
due to a germinal variation, the offspring will tend to inherit this
peculiarity and to be born white. In such a case, it is unlikely that the
fur of an organism which is naturally coloured will be completely
bleached by the snow, and, even if it be, the bleaching process will take
time, meanwhile the creature will be comparatively conspicuous. So that
those which are naturally whiter than the average, that is to say, those
in which the tendency to whiteness appears as a germinal variation, will
be less conspicuous than those which tend to be the ordinary colour. Thus
the former will enjoy a better chance of survival, and will be likely to
transmit their whiteness to their offspring in so far as it is due to a
germinal or congenital variation.
Thus, although none of the whiteness due to somatic variations is
transmitted to the offspring, such variations are of considerable
importance to the species, as they enable it to survive and allow time
for the germinal variations in the required direction to appear.
That this case need not be purely hypothetical is shown by the fact that
dun domestic pigeons, which are of an earthy-brown colour when fresh
moulted, soon fade in the sun to a dull creamy hue. Thus a coloration
adapted to an ordinary soil could soon be suited to a desert environment.
The ruddy sheldrake also, normally a bright chestnut-coloured bird, and
one that haunts exposed sunny places, in many cases fades very much,
becoming almost straw-coloured.
Many variations which organisms display are of a mixed kind, being in
part the result of inner forces and in part due to the action of the
environment. In so far as they are due to this latter they do not appear
to be inherited.
Thus, although we cannot say of many variations whether they are
germinal, or somatic, or of a mixed kind, it is of great importance to
keep continually in mind the fundamental differences between the two
kinds.
Some somatic variations are due to the direct action of the environment;
they are merely the expression of the manner in which an organism
responds to external stimuli.
What is the cause of germinal variations? This is a question to which we
are not yet in a position to give a satisfactory answer.
The attempt to explain their origin plunges us into the realm of theory.
This doubtless is a realm full of fascination, but it is an unexplored
region of extreme darkness, in which, we believe, it is scarcely possible
to take the right road until more of the light of fact has been shed upon
it.
In the chapter dealing with inheritance we shall indicate the lines along
which it is likely that future progress will be made.
CHAPTER IV
HYBRIDISM
The alleged sterility of hybrids a stumbling-block to
evolutionists—Huxley’s views—Wallace on the sterility of hybrids—Darwin
on the same—Wallace’s theory that the infertility of hybrids has been
caused by Natural Selection so as to prevent the evils of
intercrossing—Crosses between distinct species not necessarily
infertile—Fertile crosses between species of plants—Sterile plant
hybrids—Fertile mammalian hybrids—Fertile bird hybrids—Fertile hybrids
among amphibia—Limits of hybridisation—Multiple hybrids—Characters of
hybrids—Hybridism does not appear to have exercised much effect on the
origin of new species.
The alleged sterility of the hybrids produced by crossing different
species has long proved a great stumbling-block to evolutionists. Huxley,
in particular, felt the force of this objection to the Darwinian theory.
If the hybrids between natural species are sterile, while those of all
the varieties which the breeder has produced are perfectly fertile, it is
obviously quite useless for evolutionists to point with pride to the
results obtained by the breeder, and to declare that his products differ
from one another to a greater extent than do many well-recognised
species.
“After much consideration, and with no bias against Mr Darwin’s views,”
wrote Huxley to the _Westminster Review_ in 1860, “it is our clear
conviction that, as the evidence now stands, it is not absolutely proven
that a group of animals having all the characters exhibited by species in
nature, has ever been originated by selection, whether natural or
artificial. Groups having the morphological nature of species, distinct
and permanent races, in fact, have been so produced over and over again;
but there is no positive evidence at present that any group of animals
has, by variation and selective breeding, given rise to another group
which was in the least degree infertile with the first. Mr Darwin is
perfectly aware of this weak point, and brings forward a multitude of
ingenious and important arguments to diminish the force of the objection.
We admit the value of these arguments to the fullest extent; nay, we will
go so far as to express our belief that experiments, conducted by a
skilful physiologist, would very probably obtain the desired production
of mutually more or less infertile breeds from a common stock in a
comparatively few years; but still, as the case stands at present, this
little ‘rift within the lute’ is not to be disguised or overlooked.”
Alleged Sterility of Hybrids
Similarly Wallace writes, at the beginning of chapter vii. of his
_Darwinism_: “One of the greatest, or perhaps we may say the greatest, of
all the difficulties in the way of accepting the theory of natural
selection as a complete explanation of the origin of species, has been
the remarkable difference between varieties and species in respect of
fertility when crossed. Generally speaking, it may be said that the
varieties of any one species, however different they may be in external
appearance, are perfectly fertile when crossed, and their mongrel
offspring are equally fertile when bred among themselves; while distinct
species, on the other hand, however closely they may resemble one another
externally, are usually infertile when crossed, and their hybrid
offspring absolutely sterile. This used to be considered a fixed law of
nature, constituting the absolute test and criterion of a species as
distinct from a variety; and so long as it was believed that species were
separate creations, or at all events had an origin quite distinct from
that of varieties, this law could have no exceptions, because if any two
species had been found to be fertile when crossed and their hybrid
offspring to be also fertile, this fact would have been held to prove
them to be not species but varieties. On the other hand, if two varieties
had been found to be infertile, or their mongrel offspring to be sterile,
then it would have been said—These are not varieties, but true species.
Thus the old theory led inevitably to reasoning in a circle, and what
might be only a rather common fact was elevated into a law which had no
exceptions.”
Thus the sterility of hybrids was a zoological bogey which had to be
demolished. The plan of campaign adopted by Darwin and Wallace was,
firstly, to try to disprove the assertion that the hybrids between
different species are always sterile, and secondly, to find a reason for
the alleged sterility of these hybrids.
Fertile Hybrids
Darwin succeeded in obtaining some examples of crosses between botanical
species which were said to be fertile. These he quotes in chapter viii.
of _The Origin of Species_. As regards animals, he met with less success.
“Although,” he writes, “I do not know of any thoroughly
well-authenticated cases of perfectly fertile hybrid animals, I have some
reason to believe that the hybrids from _Cervulus vaginalis_ and
_reevesii_, and from _Phasianus colchicus_ and _P. torquatus_ and with
_P. versicolor_ are perfectly fertile. There is no doubt that these three
pheasants, namely, the common, the true ring-necked, and the Japan,
intercross, and are becoming blended together in the woods of several
parts of England. The hybrids from the common and Chinese geese (_A.
cygnoides_), species which are so different that they are generally
ranked in distinct genera, have often been bred in this country with
either pure parent, and in one single instance they have bred _inter se_.
This was effected by Mr Eyton, who raised two hybrids from the same
parents but from different hatches; and from these two birds he raised no
less than eight hybrids (grandchildren of the pure geese) from one nest.
In India, however, these cross-bred geese must be far more fertile; for I
am assured by two eminently capable judges, namely, Mr Blyth and Captain
Hutton, that whole flocks of these crossed geese are kept in various
parts of the country; and as they are kept for profit, where neither pure
parent species exists, they must certainly be highly fertile.[5] . . . So
again there is reason to believe that our European and the humped Indian
cattle are quite fertile together; and from facts communicated to me by
Mr Blyth, I think they must be considered as distinct species.”
Darwin does not seem to have been very satisfied with the evidence he had
collected, for he said: “Finally, looking to all the ascertained facts on
the intercrossing of plants and animals, it may be concluded that some
degree of sterility, both in first crosses and in hybrids, is an
extremely general result; but that it cannot, under our present state of
knowledge, be considered as absolutely universal.”
Similarly Wallace writes: “Nevertheless, the fact remains that most
species which have hitherto been crossed produce sterile hybrids, as in
the well-known case of the mule; while almost all domestic varieties,
when crossed, produce offspring which are perfectly fertile among
themselves.”
Darwin resorted to much ingenious argument in his attempt to explain what
he believed to be the almost universal sterility of hybrids, as opposed
to mongrels or crosses between varieties. He pointed out that changed
conditions tend to produce sterility, as is evidenced by the fact that
many creatures refuse to breed in confinement, and believed that the
crossing of distinct wild species produced a similar effect on the sexual
organs. He expressed his belief that the early death of the embryos is a
very frequent cause of sterility in first crosses.
Wallace thus summarises Darwin’s conclusions as to the cause of the
sterility of hybrids: “The sterility or infertility of species with each
other, whether manifested in the difficulty of obtaining first crosses
between them or in the sterility of the hybrids thus obtained, is not a
constant or necessary result of species difference, but is incidental on
unknown peculiarities of the reproductive system. These peculiarities
constantly tend to arise under changed conditions owing to the extreme
susceptibility of that system, and they are usually correlated with
variations of form or of colour. Hence, as fixed differences of form and
colour, slowly gained by natural selection in adaptation to changed
conditions, are what essentially characterise distinct species, some
amount of infertility between species is the usual result.”
A Biological Bogey
But Wallace has not been content to let the matter remain where Darwin
left it. He has boldly tried to make an ally of this bogey of the
infertility of hybrids. On page 179 of _Darwinism_ he argues, most
ingeniously, that the sterility of hybrids has been actually produced by
natural selection to prevent the evils of the intercrossing of allied
species. We will not reproduce his argument for the simple reason that it
is now well-known, or should be well-known, that hybrids between allied
species are by no means always sterile. The doctrine of the infertility
of hybrids seems to have been founded on the fact that the hybrids best
known to breeders, namely the cross between the ass and the horse, and
those between the canary and other finches, are sterile.
Fertile Crosses between Species of Plants
In the case of plants the number of fertile hybrids between species is so
large that we cannot attempt to enumerate them. De Vries cites several
instances in Lecture IX of his _Species and Varieties: Their Origin by
Mutation_.
One of these—the hybrid between the purple and the yellow species of
Lucerne which is known to botanists as _Medicago media_ is, writes De
Vries, “cultivated in some parts of Germany on a large scale, as it is
more productive than the ordinary lucerne.” Other examples of perfectly
fertile plant hybrids cited by De Vries are the crosses between _Anemone
magellanica_ and _A. sylvestris_, between _Salix alba_ and _Salix
pentandra_, between _Rhododendron hirsutum_ and _R. ferrugineum_.
He gives an instance of a hybrid—_Ægilops speltæformis_, which, though
fertile, is not so fertile as a normal species would be. It is worthy of
note that Burbank of California has obtained a hybrid between the
blackberry and the raspberry, which is not only fertile, but quite
popular as producing a novel fruit.
Sterile Plant Hybrids
De Vries does not cite nearly so many examples of sterile hybrids,
presumably because they are not so easy to find. He mentions the sterile
“Gordon’s currant,” which is considered to be a hybrid between the
Californian and the Missouri species. He also gives _Cytisus adami_ as an
absolutely sterile hybrid, this being a cross between two species of
Labernum—the common and the purple.
In the case of animals the known hybrids are so much less numerous that
we are able to furnish a list which may be taken as fairly exhaustive.
Fertile Mammalian Hybrids
Taking the mammals first, we find that, in addition to those cited by
Darwin, there are several recorded cases of crosses between well-defined
species which are fertile.
There is the hybrid between the brown bear and the polar bear, which is
perfectly fertile. In the London Zoological Gardens there is a specimen
of this hybrid, also one of this individual’s offspring by a pure polar
bear.
The stoat has been crossed with the domestic ferret, a descendant of the
polecat, a very distinct species; the resulting hybrids have nevertheless
proved fertile.
The bull American bison produces with the domestic cow hybrids known as
“cataloes,” which are fertile. The reverse cross of the domestic bull
with the bison cow does not, however, succeed at all, which reminds us of
what happens in the case of finch-hybrids.
Bird fanciers when crossing the canary with wild species of finch, almost
invariably use a hen canary as the female parent, because domesticated
female animals breed more readily than do captive wild ones.
The domestic yak breeds frequently in the Himalayas with the perfectly
distinct zebu or humped cow of India, and the hybrids are fertile. Yet
the zebu and the Indian buffalo, living constantly side by side in the
plains of India, never interbreed at all.
Among wild ruminants of this hollow-horned family, the Himalayan Argali
(_Ovis ammon_) ram, a giant sheep of the size of a donkey, has been known
to appropriate a herd of ewes of the Urial (_O. vignei_), a very distinct
species of the size of a domestic sheep. Many hybrids were born, and
these, in turn, bred with the pure urials of the herd.
In our parks the little Sika deer of Japan (_Cervus sika_), a species
about the size of the fallow-deer, with an even more marked seasonal
change of colouration and antlers having only three tines, breeds with
the red deer, and the hybrids are fertile.
In certain parts of Asia Minor the natives cross the female one-humped
camel with the male of the bactrian or two-humped species. The hybrids
(which are one-humped) will breed with the pure species; but, although
the hybrids are strong and useful, the three-quarter bred beasts are
apparently of little value.
Fertile Bird Hybrids
Coming to birds, we are confronted by a longer list of fertile hybrids.
This is the natural outcome of the fact that a greater number of bird
species have been kept in captivity.
The oldest known fertile hybrid is that between the common and Chinese
geese above cited, but many others have since been recorded. Even among
birds so seldom bred, comparatively, as the parrot family, a fertile
hybrid has been produced, that between the Australian Rosella Parrakeet
(_Platycercus eximius_) and Pennant’s Parrakeet (_P. elegans_). The
hybrid was first described as a distinct species, the Red-mantled
Parrakeet (_P. erythropeplus_). These two parrakeets, though nearly
allied, are very distinct; Pennant’s being coloured red, blue, and black,
with a distinct young plumage of uniform dull green; the rosella in
addition to the above colours displays much yellow and some white and
green. It is, moreover, considerably smaller and has no distinct youthful
dress.
The Amherst Pheasant (_Chrysolophus amherstiæ_) and the Gold Pheasant
(_C. pictus_) have long been known as producing hybrids which are fertile
either _inter se_ or with the parents. Here the species are still more
distinct; not only are the leading colours of the Amherst white and
green, instead of red and gold, but it is a bigger bird with a larger
tail and smaller crest, and a bare patch round the eyes.
The Pintail Duck (_Dafila acuta_) and the Mallard or Wild Duck and its
domestic descendants (_Anas boscas_), when bred together, produce hybrids
which have been proved fertile between themselves and with the pure
pintail. Any sportsman or frequenter of our parks can see for himself the
distinctness of the species concerned.
The Pied Wagtail (_Motacilla lugubris_) and the Grey Wagtail (_M.
melanope_) have produced hybrids in aviaries, which have proved fertile.
The two species are distinct in every way, as all British ornithologists
know.
The Cut-throat Finch (_Amadina fasciata_) and Red-headed Finch (_A.
erythrocephala_) of Africa have hybridised in aviaries, and the produce
has proved fertile. The red-headed finch, among other differences, is far
larger than the cut-throat, and the males have the head all red, not
merely a throat-band of that colour.
The Japanese Greenfinch (_Ligurinus sinicus_) which is not green, but
brown and grey, with bolder yellow wing- and tail-markings than our
larger European greenfinch, has produced fertile hybrids with this latter
bird.
[Illustration: MALE AMHERST PHEASANT]
The Red Dove of India (_Oenopopilia tranquebarica_) has produced hybrids
with the tame Collared Dove (_T. risorius_) and these have bred again
when paired with the red species. _O. tranquebarica_, although presenting
a general similarity to the collared dove, is truly distinct, being much
smaller, with a shorter tail, and displaying a marked sex-difference (the
male only being red, and the female drab). Its voice is also utterly
unlike the well-known penetrating and musical _coo_ of the Collared Dove.
There is a large class of fertile wild hybrids produced between forms
differing only in colour, such as those between the Hooded Crow (_Corvus
cornix_) and Carrion Crow (_Corvus corone_), the various species of
_Molpastes_ bulbuls, and the Indian Roller (_Coracias indica_) and
Burmese Roller (_C. affinis_). Indeed, it may be said that wherever two
such colour-species meet they hybridize and become more or less fused.
In this connection sportsmen, as mentioned by Darwin, performed
unconsciously a most interesting experiment when, more than a century
ago, they introduced largely into their coverts the Chinese Ring-necked
Pheasant (_Phasianus torquatus_) and the Japanese _P. versicolor_. So
freely has the former bred with the common species already present there
(_Phasianus colchicus_) that nowadays nearly all our English pheasants
show traces of the cross in the shape of white feathers on the neck, or
the green tinge of the plumage of the lower back. The influence of the
Japanese Green Pheasant (_P. versicolor_) has been very slight.
It is, of course, open to anyone to assert that such crosses are not true
hybrids, as the species are not fully distinct, but mere
colour-mutations.
The fact of the intermingling, however, is a fatal blow to the theory of
recognition marks, since it demonstrates that merely distinctive
colouring is not a preventative of cross-breeding. To this matter we
shall return later.
Fertile Hybrids among Amphibia
Our Crested Newt (_Molge cristata_) and the Continental Marbled Newt (_M.
marmorata_) interbreed in France, in the wild state, and the resulting
hybrid was at first described as a distinct species, under the name of
_Molge blasii_. These two newts differ greatly in appearance. In the
Marbled Newt the colouration is brilliant green and black above, and
shows no orange below, thus differing much from that of the Crested Newt,
which is black above and mottled with orange beneath, while the crest of
the breeding-male of this species lacks the notches which are so
conspicuous in that of the Crested Newt.
[Illustration: HARLEQUIN QUAIL (Coturnix delegorguei)]
[Illustration: RAIN QUAIL (Coturnix coromandelica)]
Insects
Among insects, M. de Quatrefages states that the hybrid progeny of the
silk-moths _Bombyx cynthia_ and _B. arrindia_ are fertile for eight
generations when bred _inter se_.
Limits to the Possibilities of Hybridisation
Hybrids can apparently only be produced between species of the same
natural family. The stories of cat-rabbits, deer-ponies, fowl-ducks, and
similar distant crosses invariably break down on close examination. A
belief in such remote crosses characterized the ancient “bestiaries,” and
still lingers, as witness the falsely-reputed crosses alluded to above.
This belief has no doubt arisen from the fact that the domestic breeds of
dogs, fowls, etc., are popularly confounded with truly distinct species.
Mongrels are well known to be readily produced, and hence the notion
arises that hybrids between the most widely-separated species are
possible.
In practice, the most remote cross of which authenticated specimens exist
is that between the red grouse and the domestic fowl (bantam cock). It is
true that the grouse are commonly ranked by ornithologists as a family
distinct (_Tetraonidae_) from that of the pheasants and partridges
(_Phasianidae_), to which the fowl belongs; but the relationship is
admittedly very close, and we doubt if general zoologists would
countenance the maintenance of the families as distinct. Ornithologists
are notoriously apt to over-rate small differences when drawing up a
classification. It would be therefore safe to say, in the present state
of our knowledge, that species belonging to different natural families
cannot hybridize.
In some cases multiple hybrids have been produced. Thus, at the London
Zoological Gardens, many years ago, a hybrid between the Gayal of India
(_Bos frontalis_) and the Indian humped cow mentioned above was put to an
American bison, and produced a double hybrid calf.
M. G. Rogeron of Angers bred many hybrids from a male pochard and a duck
bred from a Mallard and a Gadwall.
More recently, Mr J. L. Bonhote has succeeded in combining the blood of
five wild species of ducks in one individual.
Mr J. T. Newman has also bred turtle-doves containing the blood of three
distinct species.
A cross, which usually results in sterile offspring, may in very rare
cases produce a fertile individual; thus, Mr A. Suchetet once succeeded
in obtaining a three-quarter-bred bird from the not uncommon hybrid of
the tame pigeon and tame collared dove (_Turtur risorius_), which is
usually barren, by pairing it with a dove; but the bird thus produced,
when again paired with a dove, was itself sterile. Some of the cases here
given seem to encourage Darwin’s view that domestication tends to
eliminate sterility; but it is doubtful if this can be upheld. The hybrid
between the Muscovy duck (_Cairina moschata_) and common duck is usually,
at all events, sterile, like that between the pigeon and dove; yet all
these birds have been long domesticated. The hybrid between the fowl and
the guinea-fowl is likewise barren, nor has the long domestication of the
horse and ass lessened the sterility of the mule.
Characters of Hybrids
Some facts may be noted respecting the characters of hybrids. In the
first place, it is important to notice that the characters of the hybrid
vary according to the sexes of the species concerned; thus, the “hinny,”
which is bred from a horse and a she-ass, is a different animal from the
true “mule,” which is bred from the jackass and mare, and is inferior to
it.
Similarly, Mr G. E. Weston, a great authority on British cage-birds and
their hybrids, informs us that when hybrids are bred from a male canary
and a hen goldfinch or siskin—contrary to the almost universal practice
of using the hen canary for crossing—the progeny are inferior in size and
colour to the hybrids obtained in the ordinary way.
Hybrids, in animals at all events, differ from crosses between mutations
or colour-variations in not exhibiting the phenomenon of alternative
inheritance; they do not follow one parent or the other exclusively, but
always exhibit some blending of the characters of both, which is, after
all, what might have been expected, since well-defined species usually
differ in more than one character.
Thus, the cross between the Amherst and gold pheasants chiefly resembles
the latter, but has the ruff white as in the Amherst, while the crest,
though in form it resembles that of the gold species, is not yellow as in
that species, nor red as in the Amherst, but of an intermediate tint,
brilliant orange.
The mule between the horse and ass, as all know, combines the shapes of
the two parents, though in colour it follows the horse rather than the
ass.
When two remote species, one or each of which possesses some distinctive
structural peculiarity, are crossed, the hybrid does not inherit such
points. The guinea-fowl has a helmet, and a pair of wattles on the upper
jaw; the common fowl a comb, and a pair of wattles on the lower jaw; but
in the hybrid no comb, helmet, or wattles are present.
The Muscovy drake has a bare red eye-patch, and the male of the common
duck curled middle-tail feathers; in the hybrid neither of these
peculiarities is reproduced.
In a cross between nearly-related forms, the peculiarity of one species
may be reproduced in a modified form in the hybrid; for instance, in that
between the blackcock (_Tetrao tetrix_) and the capercailzie (_T.
urogallus_), the forked tail of the former reappears to a small extent in
the hybrid.
Very interesting are those cases in which the hybrid resembles neither
parent, but tends to be like an altogether distinct species, or to have a
character of its own. Thus the hybrids between the pied European and
chestnut African sheldrakes (_Tadorna cornuta_ and _Casarca cana_), now
in the British Museum, bear a distinct resemblance to the grey Australian
sheldrake (_C. tadornoides_). In pheasants, also, the crosses between the
common and gold, common and Amherst, gold and Japanese, and gold and
Reeves’ pheasants, widely different as all these birds are in
colouration, are remarkably alike, being all chestnut-coloured birds with
buff median tail-feathers. These may be seen in the British Museum. This
phenomenon, together with the above-noted disappearance of specialised
features in hybrids, is possibly comparable to the “reversion” observed
when widely-distinct domestic breeds are crossed, and so may give us an
idea of the appearance of the ancestors of the groups of species
concerned.
In the few cases wherein several generations of hybrids have been bred
_inter se_, there seems to have been no reversion to the original pure
types, such as happens when colour-forms are crossed.
M. Suchetet bred hybrid gold = Amherst pheasants for four generations,
and they retained the hybrid character. The young bred by Darwin from a
pair of common = Chinese geese hybrids “resembled,” he says, “in every
detail their hybrid parents.”
Wild Hybrids
When hybrids have been—as has far more usually been the case—bred back to
one of the pure stocks, the hybrid characters have shown, as might be
expected, a tendency quickly to disappear. The three-quarter-bred polar
bear now in the London Zoological Gardens is a pure polar save for a
brown tinge on the back. A three-quarter Amherst = gold pheasant in the
British Museum is a pure Amherst save for the larger crest, and a patch
of red on the abdomen. When three-quarter-bred pintail = common duck
hybrids were bred back to the pintail, the offspring “lost all
resemblance to the common duck.” In the case of the Argali-urial herd of
wild sheep above-mentioned, after the usurping Argali ram had been killed
by wolves, the hybrids bred with the urials, with the result that the
herd renewed the appearance of pure urial.
Thus, except in the very improbable case of a family of hybrids going off
and starting a colony by themselves, the effect of hybridism on the
evolution of species seems likely to have been _nil_. It is, however,
curious that three-quarter-bred animals have rarely, if ever, been
recorded in a state of nature, though a good many wild-bred hybrids are
on record.
This points to some unfitness for the struggle for existence even in a
fertile hybrid. It is necessary to emphasise the fact that wild hybrids
are always exceedingly rare as individuals, in spite of what has been
said as to the number of recorded crosses.
More hybrid unions have been noted among the duck family than anywhere
else in the animal kingdom. Nevertheless Finn never once saw a hybrid
duck for sale in the Calcutta market, although for seven years he was
constantly on the look-out for such forms; nor does Hume record any such
specimen in his _Game Birds and Wild Fowl of India_.
The hybrid which occurs most commonly as an individual is that between
the blackcock and capercailzie, which is recorded yearly on the
Continent; but it appears to be sterile, and so has no influence on the
species.
Wild hybrids between mammals are far rarer even than bird hybrids, the
only ones which seem to be on record being those between the Argali and
Urial above alluded to; those between the brown and blue hares and the
common and Arctic foxes.
A consideration of the phenomena of hybridism thus leads us to the
conclusion that, although many hybrids are fertile, the crossing of
distinct species has exercised little or no effect on the origin of
species. Even where allied species, like the pintail and the mallard
ducks, whose hybrid offspring is known to be fertile, inhabit the same
breeding area and occasionally interbreed in nature, such crossing does
not, for some reason or other, appear to affect the purity of the
species.
Very different, of course, is the effect of crossing a mutation within a
species with the parent form; the offspring are, as we shall see, likely
to resemble one or other of the parents; so that, if the mutation occur
frequently enough and be favourable to the species, the new form may in
course of time replace the old one.
CHAPTER V
INHERITANCE
Phenomena which a complete theory of inheritance must explain—In the
present state of our knowledge it is not possible to formulate a
complete theory of inheritance—Different kinds of inheritance—Mendel’s
experiments and theory—The value and importance of Mendelism has been
exaggerated—Dominance sometimes imperfect—Behaviour of the nucleus of
the sexual cell—Chromosomes—Experiments of Delage and Loeb—Those of
Cuénot on mice and Castle on guinea pigs—Suggested modification of the
generally-accepted Mendelian formulae—Unit characters—Biological
isomerism—Biological molecules—Interpretation of the phenomena of
variation and heredity on the conception of biological
molecules—Correlation—Summary of the conception of biological
molecules.
We have seen that variations may be, firstly, either acquired or
congenital, and, secondly, fluctuating or discontinuous. We have further
seen that acquired variations—at all events in the higher animals—do not
appear to be inherited, and therefore have not played a very important
part in the evolution of the animal world. Discontinuous congenital
variations or mutations are the usual starting points of new species. It
is not unlikely that fluctuating congenital variations, although they do
not appear to give rise directly to new species, may play a considerable
part in the making of new species, inasmuch as they may, so to speak,
pave the way for mutations.
We are now in a position to consider the exceedingly difficult question
of inheritance. We know that offspring tend to resemble their parents,
but that they are always a little different both from either parent and
from one another. How are we to account for these phenomena? What are the
laws of inheritance, whereby a child tends to inherit the peculiarities
of its parents, and what are the causes of variation which make children
differ _inter se_ and from their parents?
Scores of theories of inheritance have been advanced. It is scarcely
exaggerating to assert that almost every biologist who has paid much
attention to the subject has a theory of inheritance which differs more
or less greatly from the theory held by any other biologist.
As regards the phenomena of heredity we may say _Tot homines tot
sententiæ_.
Phenomena of Inheritance
For this state of affairs there is a good and sufficient reason. We are
not yet in possession of a sufficient number of facts to be in a position
to formulate a satisfactory theory of inheritance. A complete theory of
heredity must explain, among other things, the following phenomena:—
1. Why creatures show a general resemblance to their parents.
2. Why they differ from their parents.
3. Why the members of a family display individual differences.
4. Why the members of a family tend to resemble one another more closely
than they resemble individuals belonging to other families.
5. Why “sports” sometimes occur.
6. Why some species are more variable than others.
7. Why certain variations tend to occur very frequently.
8. Why variations in some directions seem never to occur.
9. Why a female may produce offspring when paired with one male of her
species and not when paired with another male of the species.
10. Why organisms that arise by parthenogenesis appear to be as variable
as those which are sexually produced.
11. Why certain animals possess the power of regenerating lost parts,
while others have not this power.
12. Why most plants and some of the lower animals can be produced
asexually from cuttings.
13. Why mutilations are not inherited.
14. Why acquired characters are rarely, if ever, inherited.
15. Why the ovum puts forth the polar bodies.
16. Why the mother-cell of the spermatozoa produces four spermatozoa.
17. Why differences in the nature of the food administered to the larvæ
of ants determines whether these shall develop into sexual or neuter
forms.
18. Why the application of heat, cold, etc., to certain larvæ affects the
nature of the imago, or perfect insect, to which they will give rise.
19. Why the females in some species lay eggs which can produce young
without being fertilised.
20. Why some species exhibit the phenomena of sexual dimorphism, while
others do not.
21. In addition to all the above, a satisfactory theory of inheritance
must account for all the varied phenomena which are associated with the
name of Mendel. It must explain the various facts with which we have
dealt in the chapter on hybridism, why some species produce sterile
hybrids when intercrossed, while others give rise to fertile hybrids, and
yet others form no offspring when crossed; why the hinny differs in
appearance from the mule, etc.
22. It must explain all the facts which constitute what is known as
atavism.
23. It must account for the phenomenon of prepotency.
24. It must explain the why and the wherefore of correlation.
25. It must tell us the meaning of the results of the experiments of
Driesch, Roux, and others.
26. It must render intelligible the effects of castration on animals.
Existing Theories Unsatisfactory
Now, no existing theory of heredity can give anything approaching a
satisfactory explanation of all these phenomena.
It is for this reason that we refrain from critically examining, or even
naming, any of them.
We are convinced that in the present state of our knowledge it is not
possible to formulate anything more than a provisional hypothesis.
It must not be thought that we consider the various theories that have
been enunciated to be of no value. Erroneous hypotheses are often of the
greatest utility to science, for they set men thinking and suggest
experiments by means of which important additions to knowledge are made.
We now propose to set forth certain facts of inheritance, and from these
to make a few deductions—deductions which seem to be forced upon us.
We would ask our readers to distinguish carefully between the facts we
set forth, and the conclusions we draw therefrom. The former, being
facts, must be accepted.
The interpretations we suggest should be rigidly examined, we would say
regarded with suspicion, and all possible objections raised. It is only
by so doing that any advance in knowledge can be made.
By inheritance we mean that which an organism receives from its parents
and other ancestors—all the characteristics, whether apparent or dormant,
it inherits or receives from its parents. Professor Thomson’s
definition—“all the qualities or characters which have their initial
seat, their physical basis, in the fertilised egg cell”—seems to cover
all cases except those where eggs are parthenogenetically developed.
The first fact of heredity which we must notice is that inheritance may
take several forms. This is apparent from what was set forth in the
chapter dealing with hybrids.
Types of Crosses
In considering the phenomena of inheritance it is convenient to deal with
crosses in which the parents do not closely resemble one another, because
by so doing we are able readily to follow the various characters
displayed by each parent. It may, perhaps, be urged that such crosses
occur but rarely in nature. This is true. But we should bear in mind that
any theory of inheritance must explain the various facts of
cross-breeding, so that, from the point of view of a theory of
inheritance, crosses are as important as what we may term normal
offspring. As inheritance is so much easier to observe in the former, it
is but natural that we should begin with them. Our deductions must, if
they be valid ones, fit all cases of ordinary inheritance, _i.e._ all
cases where the offspring results from the union of parents which closely
resemble one another. Now, when two unlike forms inter-breed, their
offspring will fall into one of six classes.
I. They may exactly resemble one parent, or rather the type of one
parent, for, of course, they will never be exactly like either parent;
they must of necessity display fluctuating variations. The cases in which
the offspring exactly resemble one parent type in all respects are
comparatively few. They occur only when the parents differ from one
another in one, two, or at the most three characters. Thus when an
ordinary grey mouse is crossed with a white mouse the offspring are all
grey, that is to say, they resemble the grey parent type. Although they
are mongrels or hybrids, they have all the appearance of pure grey mice.
This is what is known as unilateral inheritance.
II. The offspring may resemble one parent in some characters and the
other in other characters. They may have, for example, the colour of one
parent, the shape of the other, and so on. Thus if a pure, albino,
long-haired, and rough-coated male guinea-pig be crossed with a coloured,
short-haired and smooth-coated female, all the offspring are coloured,
short-haired, and rough-coated. That is to say, they take after the
father in being rough-coated, but after the mother in being pigmented and
short-haired. This form of inheritance is usually seen only in crosses
between two types which differ in but few of their characters.
III. The offspring may display a blend of the characters of the two
parents. They may be intermediate in type. They are not of necessity
midway between the two parents; one of the parents may be prepotent. The
crosses between the horse and the ass show this well. Both the mule,
where the ass is the sire, and the hinny, where the horse is the sire,
are more like the ass than like the horse; but the hinny is less ass-like
than the mule. The offspring between a European and a native of India
furnishes a good case of blended inheritance; Eurasians are neither so
dark as the Asiatic nor so fair as the European.
IV. The offspring may show a peculiarity of one parent in some parts of
the body and the peculiarity of the other parent in other parts of the
body. This is known as particulate inheritance. The piebald foal, which
is the result of a cross between a black sire and a white mare, is a good
example of such inheritance. This does not appear to be a common form of
inheritance.
V. The usual kind of inheritance is perhaps a combination between the
forms II. and III. In such cases the offspring display some paternal
characters and some maternal ones, and some characters in which the
maternal and paternal peculiarities are blended. An example of
inheritance of this description is furnished by a cross between the
golden and the amherst pheasants.
VI. The offspring may be quite unlike either parent. For example, Cuénot
found that sometimes a grey mouse when crossed with an albino produces
black offspring.
Mendel’s Experiments
The first two kinds of inheritance were carefully investigated by Gregor
Johann Mendel, Abbot of Brunn. The results of his experiments were
published in the Proceedings of the Natural History Society of Brunn, in
1854, but attracted very little notice at the time.
Mendel experimented with peas, of which many varieties exist. He took a
number of varieties, or sub-species, which differed from one another in
well-defined characters, such as the colour of the seed coat, the length
of the stem, etc. He made crosses between the various varieties, being
careful to investigate one character only at a time. He found that the
offspring of such crosses resembled, in that particular character, one
only of the parents, the other parent apparently exerting no influence on
it. Mendel called the character that appeared in the off-spring dominant,
and the character which was suppressed, recessive. Thus when tall and
short varieties were crossed the offspring were all tall. Hence Mendel
said that tallness is a dominant character, and shortness a recessive
character. Mendel then bred these crosses among themselves, and found
that some of the offspring resembled one grandparent as regards the
character in question while some resembled the other, and he found that
those that showed the dominant character were three times as numerous as
those that displayed the recessive character. He further found that all
those of the second generation of crosses which displayed the recessive
character bred true; that is to say, when they were bred together all
their descendants exhibited this characteristic. The dominant forms,
however, did not all breed true; some of them produced descendants that
showed only this dominant character, others, when crossed, gave rise to
some forms having the dominant character and some having the recessive
character.
It is thus evident that organisms of totally different ancestry may
resemble one another in external appearance. In other words, part of the
material from which an organism is developed may lie dormant.
Mendelism
From the above results Mendel inferred, in the case of what he called
alternating characters, that only one or other of the pair can appear in
the offspring, that they will not blend. If both parents display one of
the opposing characters, the offspring will of course show it. But if one
parent display one character and the other the opposing character, the
hybrid offspring will display one only, and that which is dominant. The
other character is suppressed for the time being. When, however, these
hybrids are bred _inter se_, their gametes or sexual cells split up into
their component parts, and then the recessives are free to unite with
other recessives and thus produce offspring which show the recessive
character.
His results can be set forth in symbols.
Let T stand for the tall form and D for the dwarf form. Since the
offspring are composed of both the paternal and maternal gamete, we may
represent them as TD. But dwarfness is, as we have seen, recessive, so
that the offspring all look as though they were pure T’s. When, however,
we come to breed these TD’s _inter se_, the gamete or sex-cell of each
individual crossed breaks up into its component parts T and D, which
unite with other free T or D units to form TD’s or TT’s or DD’s. What are
the possible combinations? A D of one parent may meet and unite with a D
of the other parent, so that the resulting cells will be pure D, _i.e._
DD, and will give rise to pure dwarf offspring. Or the D gamete from one
parent may unite with a T gamete from the other parent, and the result
will be a TD cross, but this, as we have seen, will grow up to look like
a pure T, _i.e._ will become a tall organism. Similarly, a T gamete from
one parent may unite with a T gamete of the other, and produce a pure
tall form, or it may unite with a D and produce a hybrid TD, which gives
rise to a tall form. Thus the possible combinations of offspring are DD,
DT, TD, TT, but all these three last contain the dominant T gamete, and
so develop into tall offspring; therefore, _ex hypothesi_, we shall have
three tall forms produced to one dwarf form, but of these three tall
forms two are not pure, and do not breed true. Mendel’s experimental
results accorded with what we should expect to obtain if the above
explanation were correct. Hence the inference that there is such a
splitting of the gametes in the sexual act seems a legitimate one.
Mendel’s experiments are of great importance, for they give us some
insight into the nature of the sexual act. But, as is usual in such
cases, Mendel’s disciples have greatly exaggerated the value and
importance of his work. It is necessary to bear in mind that Mendel’s
results apply only to a limited number of cases—to what we may call
balanced characters. In the case of characters which do not balance one
another, which are, so to speak, not diametrically opposed to one
another, Mendel’s law does not hold. A second important point is, that
the dominance is in many cases not nearly so complete as it should be if
the Mendelian formula correctly represented what actually occurs in
nature. Further, the segregation of the gametes does not appear to be so
complete as the above hypothesis requires it to be. The phenomena of
inheritance seem to be far more complex than the thorough-going Mendelian
would have us believe.
Let it be noted that it is not to the facts of Mendelism, but to some
portions of what we may call the Mendelian theory, that we take
exception.
Maturation of the Germ-cells
Before passing on to consider some of the later developments of
Mendelism, it is necessary for us to set forth briefly certain of the
more important facts regarding the sexual act which the microscope has
brought to light. We propose to state these only in the merest outline.
Those who are desirous of pursuing the subject farther are referred to
Professor Thomson’s _Heredity_.
The germ cells, like all other cells, consist of a nucleus lying in a
mass of cytoplasm. The nucleus is composed of a number of rod-like
bodies, which are called chromosomes, because they are readily stainable.
These chromosomes appear, under ordinary circumstances, to be joined
together end to end, and then look like a rope in a tangle.
When a cell is about to divide into two, these chromosomes become
disjoined and can then be counted, and it is found that each cell of each
species of animal or plant has a fixed number of these chromosomes. Thus
the mouse and the lily have twenty-four chromosomes in each cell, while
the ox is said to have sixteen of them per cell.
When a cell divides into two, each of these chromosomes splits by a
_longitudinal_ fissure into two halves, which appear to be exactly alike.
One-half of every chromosome passes into each of the daughter cells, so
that each of these is furnished with exactly half of each one of the
rod-like chromosomes. In the cell division, which takes place immediately
before the male gamete or generative cell meets the female gamete, the
chromosomes do not divide into equal halves, as is usually the case. In
this division half of them pass into one daughter cell and half into the
other daughter cell, so that, prior to fertilisation both the male and
the female gametes contain only half the normal number of chromosomes. In
the sexual act the male and the female chromosomes join forces and then
the normal number is again made up, each parent contributing exactly one
half.
Experiments of Delage and Loeb
Biologists, with a few exceptions, seem to be agreed that these
chromosomes are the carriers of all that which one generation inherits
from another. Thus the cardinal facts of the sexual act are, firstly,
prior to fertilisation the male and the female gamete each part with half
their chromosomes; and, secondly, the fertilised cell is composed of the
normal number of chromosomes, of which one-half have been furnished by
each parent. Thus the microscope shows that the nucleus of the fertilised
egg is made up of equal contributions from each parent. This is quite in
accordance with the observed phenomena of inheritance.
But Delage has shown that a non-nucleated fragment of the ovum in some of
the lower animals, as, for example, the sea-urchin, can give rise to a
daughter organism with the normal number of chromosomes when fertilised
by a spermatozoon. Conversely, Loeb showed that the nucleus of the
spermatozoon can be dispensed with. Thus it seems that either the egg or
the spermatozoon of the sea-urchin contains all the essential elements
for the production of the perfect larva of a daughter organism. We are,
therefore, driven to the conclusion that the fertilised ovum contains two
sets of fully-equipped units. Only one of these seems to contribute to
the developing organism. If this set happens to be composed of material
derived from one only of the parents, we can see how it is that we get
unilateral inheritance in the case of a cross. Where, however, the units
from the two parents intermingle, although only one set is active in
development, the result will be blended inheritance. Thus, we may regard
the fertilised egg as made up of two sets of characters—a dominant set,
which is active in the production of the resulting organism, and a
recessive set, which appears to take little or no part in the production
of the organism.
This is quite in accordance with Mendelian conceptions.
Let X be an organism having the unit characters A _B_ C D _E_ F _G_, and
let Y be another organism having the unit characters _a_ b _c_ _d_ e _f_
g.
Now suppose that these behave as opposed Mendelian units, and that the
unit characters in italics are dominant ones. Then the resulting
individual will resemble each parent in certain unit characters. It may
be represented by the formula a B c d E f G, but it will contain the
characters A b C D e F g in a recessive form, so that its complete
formula may be written
a B c d E f G}
A b C D e F g
When these hybrids are paired together it will be _possible_ to get such
forms as
A B C D E F G
A B C D E F G
and
a b c d e f g
a b c d e f g
which exactly resemble the
respective grandparents, and these should breed
absolutely true, if the segregation of the
gametes is as pure as the Mendel’s law seems
to require.
Experiments of Cuénot and Castle
There are, however, certain facts, which recent experimenters have
brought to light, that seem to show that the segregation is not so
complete as the law requires. For example, the so-called pure extracted
forms may be found, when bred with other varieties, to have some latent
characters. Thus Cuénot observed that extracted pure albino mice, that is
to say, those derived from hybrid forms, did not all behave alike when
paired with other mice. Those which had been bred from grey × white
hybrids behaved, on being crossed, differently to those that had been
bred from black × white hybrids; and further, those derived from yellow ×
white hybrids yielded yet other results on being intercrossed. Castle
records similar phenomena in the case of guinea-pigs, and accordingly
draws a distinction between recessive and latent characters. Recessive
characters are those which disappear when they come into contact with a
dominant character, but reappear whenever they are separated from the
opposing dominant character. Latency is defined by Castle as “a condition
of activity in which a normally dominant character may exist in a
recessive individual or gamete.”
The ordinary Mendelian pictures a unit character in a cross that obeys
Mendel’s law, as follows:—
D
R,
the dominant character only
showing. It seems to us that each unit character
should be represented as a double entity, thus
D(D), the portion within the bracket being
latent. The cross would appear to be represented
by the formula
D(R)
R(D),
since the union
appears to take the form of the transfer of
the dormant latent characters. Now an extracted
pure recessive will, on this hypothesis,
bear the formula
R(D)
R(D).
When such recessives
are crossed the two dormant portions will
ordinarily change places, and never appear, so
that these extracted recessives will, under
ordinary circumstances, appear to be as pure
as the true pure recessives, which are represented
by the formula
R(R)
R(R).
Now, suppose that, from some cause or other,
it is possible for the latent D to change places
with the visible R, it is obvious that the impure
nature of the extracted and hitherto apparently
pure recessives will become manifest. This
seems to be what happens under certain circumstances
to the extracted albino mice. They
possess latent the character of their dominant
ancestor.
Unit Characters
Mendelian phenomena force upon us the conclusion that organisms display a
number of unit characters, each of which behaves in much the same way as
a radicle does in chemistry, inasmuch as for one or more of these
characters others can be substituted without interfering with the
remaining unit characters. For example, it is possible to replace the
chemical radicle NHࠣ by the radicle Naࠢ; _e.g._ (NHࠣ)ࠢSOࠤ (ammonium
sulphate) may be transformed into NaࠢSOࠤ (sodium sulphate).
The conclusion that each organism is composed of a number of unit
characters, which sometimes behave more or less independently of one
another, is one which most biologists who have studied the phenomena of
inheritance appear to have arrived at. Zoologists are mostly of opinion
that these characters, or rather their precursors, exist as units in the
fertilised egg. Very varied have been the conceptions of the nature of
these biological units. Almost every biologist has given a name to his
particular conception of them. Thus we have the gemmules of Darwin, the
unit characters of Spencer, the biophors of Weismann, the micellæ of
Naegeli, the plastidules of Haeckel, the plasomes of Wiesner, the
idioblasts of Hertwig, the pangens of De Vries, and so on. It is
unnecessary to extend this list. It must suffice that almost every
investigator of the phenomena of inheritance believes in these units, and
calls them by a different name. Moreover, each clothes them with
characteristics according to his taste or the fertility of his
imagination.
Chemical Molecules
These units behave in such a way as to suggest to us an analogy between
them and the chemical molecules. The sexual act would appear to resemble
a chemical synthesis in some respects. One of the most remarkable
phenomena of chemistry is that of isomerism. It not infrequently happens
that two very dissimilar substances are found, upon analysis, to have the
same chemical composition, that is to say, their molecules are found to
be composed of the same kind of atoms and the same number of these. Thus
chemists are compelled to believe that the properties of a molecule are
dependent, not only on the nature of the atoms which compose it, but also
on the arrangement of these within the molecule. To take a concrete
example: Analysis shows that both alcohol and ether are represented by
the chemical formula CࠢHࠦO. In other words, the molecule of each of these
compounds is made up of two atoms of the element Carbon, six of the
element Hydrogen, and one of the element Oxygen. Now, every chemical atom
possesses the property which chemists term valency, in other words, the
number of other atoms with which it can directly unite is strictly
limited. All atoms of the same element have the same valency. Monovalent
atoms are those which can, under no circumstances, unite with more than
one other atom. The Hydrogen atom is an example of such an atom. Divalent
atoms, as, for example, that of Oxygen, can unite with one other atom of
similar valency or with two monovalent atoms. Similarly, a trivalent
atom, such as that of Nitrogen, can unite with three monovalent atoms. A
tetravalent atom, such as that of Carbon, can combine with four
monovalent atoms. There are also pentavalent and hexavalent atoms. Now,
by indicating the valency of any given atom by a stroke for each
monovalent atom with which it is able to combine, chemists have been able
to represent the molecule of every compound, or, at any rate, of every
inorganic compound, by what is known as a graphic or structural formula.
Thus, ethylic alcohol is represented by the formula:—
H H
| |
H––C––C––O––H = CࠢHࠦO,
| |
H H
and methylic ether by the structural formula:—
H H
| |
H––C––O––C––H = CࠢHࠦO.
| |
H H
The formulæ indicate a very different arrangement of the nine atoms which
compose the molecule in each case. And to this different arrangement the
differing properties of the two compounds are supposed to be due. A rough
illustration of the phenomenon of isomerism is furnished by written
language. Thus, three different words can be made from the letters t, a,
and r, _e.g._ tar, art, and rat. They also form tra, which does not
happen to be an English word, although it might have been one.
Experiments of Gräfin von Linden
Among organisms we sometimes observe a phenomenon which looks very like
isomerism. The classical example of this is furnished by the butterflies
_Vanessa prorsa_ and _Vanessa levana_.
At one time these were supposed to belong to different species, since
they differ so greatly in appearance. _Vanessa levana_ is red, with black
and blue spots. _Vanessa prorsa_ is deep black, with a broad
yellowish-white band across both wings. It is now known that the _levana_
is the spring form and the _prorsa_ the summer and autumn form of the
same species. The pupæ of _levana_ produce the _prorsa_ form, but
Weismann found that after being placed in a refrigerator they emerged,
not as _prorsa_, but partly as _levana_ and partly as another form
intermediate in many respects between _levana_ and _prorsa_. Weismann
also succeeded, by exposing the winter pupa to a high temperature, in
making it give rise to the _prorsa_ form, and not to the _levana_ form,
as it would ordinarily do.
Similar results have been obtained with the seasonally dimorphic _Pieris
napi_. Standfuss, the Gräfin von Linden, and others have obtained like
results in the case of other seasonally dimorphic butterflies. In some
instances it has been proved that the change in the pigment is a purely
chemical one; a similar transformation can be effected in the extracted
pigment. But, we must bear in mind that the changes which are induced in
this way are not confined to colour; they occur in the marking and shape
of the wing.
Even more remarkable is the fact that in some sexually dimorphic species
a change of temperature alters the female, so as to cause her to have the
outward appearance of the male. For example, it has been found that
warmth changes the colours of the female _Rhodocera rhamni_ and
_Parnassius apollo_ into the colours of the male.
By applying rays of strong light, electric shock, or centrifuge, the
Gräfin von Linden was able to change the colours of the butterflies to
which the caterpillars gave rise. Pictet experimented on twenty-one
species of butterflies, or rather on their caterpillars, and found that
in nearly all cases when the caterpillars ate unusual food, they
developed into butterflies with abnormal colouring. Schmankewitsch made
the discovery that, in the case of the crustacean _Artemia_, he could
produce either of two species according to the amount of salt in the
water in which these creatures were placed. He declared that the
anatomical differences between the species _Artemia salina_ and _Artemia
milhausenii_ depended solely on the percentage of the salt in the
surrounding water. He further stated that by adding still more salt he
could change the _Artemia_ into a new genus—_Branchipus_. More recent
observers have cast doubt upon these results of Schmankewitsch. They,
however, admit that the degree of salinity of the water has some effect
on the form of the _Artemia_, although they suggest that factors other
than concentration affect the result. In any case, it is now well-known
that changes in the environment effect changes in the colouring of many
crustacea. Pictet has shown that the alternating wet and dry seasons in
some tropical countries are the cause of, or stimulus that induces,
seasonal dimorphism in some butterflies. He was able to effect changes in
the colouring of certain species by means of humidity.
The most important cases, from our point of view, are those in which the
application of heat or cold to a pupa has affected the colour, shape,
etc., of the emerging butterfly. Here we have but one factor, that of
temperature. All the material for the formation of the butterfly is
already stored up in the pupa. The unit characters, or their precursors,
are all there, and they take one form or another according to the
stimulus applied.
Biological Isomerism
Phenomena of this kind can, we think, be accounted for only on the
assumption that the unit characters affected are each developed from a
definite portion of the fertilised egg, that each of these portions,
these precursors of the unit characters, is, like a chemical molecule,
made up of a number of particles, and that upon the arrangement of these
particles in its precursor in the egg depends the form that the unit
character derived from it will take. One arrangement of these particles
gives rise to one form of unit character, while another arrangement will
give rise to a totally different form of unit character.
Thus, some organisms seem to display a biological isomerism akin to
chemical isomerism, save that the particles which in organisms take the
place of chemical atoms are infinitely more complex.
In other words, the precursors in the fertilised egg of each of these
unit characters behave in some respects like chemical molecules.
In order to avoid the manufacture of fresh terms we may speak
figuratively of the germ cells as being composed of biological molecules,
which in their turn are built up of biological radicles and atoms. These
behave in some ways like chemical molecules, radicles, and atoms, as the
case may be.
Biological Molecules
It seems legitimate to regard each unit character in the adult as the
result of the development of one or more of the biological molecules
which compose the nucleus of the fertilised egg. These biological
molecules are, of course, a million-fold more complex than chemical
molecules. Each biological atom must contain within itself a number of
the very complex protoplasmic molecules. This view of the structure of
the germ cell seems to force itself upon the observer. Notwithstanding
this, the conception will have no value unless it seems to throw light on
the various phenomena of heredity, variation, etc.
Let us then try to interpret some of these.
Each chemical element is made up of atoms which are all of the same kind,
but no two elements are made up of the same kind of atoms, although
chemists are now inclined to conceive of all the various kinds of atoms
as made up of varying amounts of some primordial substance. In any case,
the molecules of chemical compounds are made up of various kinds of
atoms. With biological atoms the case would seem to be different. All
would appear to be made up of the same kind of substance, and the
differences shown by the various unit characters that go to make up an
organism would seem to be due to the different numbers and the varying
arrangement of the biological atoms which compose the molecules from
which unit characters are derived. This would be quite in accordance with
the chemical notion of allotropy. Thus, the graphite and the diamond
molecules are both made up of the same kind of atoms.
But the biological atoms are living, that is to say, they are continually
undergoing anabolism and katabolism, growth and decay. They exhibit all
the phenomena of life, they must grow and divide, and they must absorb
nourishment; hence it is not surprising that they should differ slightly
among themselves, that they should exhibit the phenomenon of variation.
Although probably all are composed of the same living material, no two
are exactly alike, hence the molecules formed by them will also differ
from one another. Thus we can see why it is that all organisms exhibit
fluctuating variations.
Very different are the discontinuous variations or mutations. These would
seem to be due to either a rearrangement of the biological atoms in the
biological molecule or the splitting up of the latter into two or more
molecules. This, of course, is pure hypothesis. Let us take an imaginary
example. Suppose that a biological molecule contains eighteen biological
atoms, and that these are arranged in the form of an equilateral
triangle, six of them going to each side. Suppose now, that from some
cause or other they rearrange themselves to form an isosceles triangle,
so that only four form the base and seven go to each of the remaining
sides. Such an arrangement would give rise to a mutation. Suppose now
that, from some cause or other, this triangular biological molecule were
to split up into two triangles, each having three atoms to each side, we
should obtain a still more marked mutation. We are far from saying that
the atoms in the organic molecule ever take such forms. We have merely
attempted to give rough but simple illustrations of the kind of processes
which on this hypothesis might be expected to take place in the germ
cells or the fertilised eggs.
Let us now consider the sexual act from this aspect. The various
molecules (we speak, of course, of biological molecules) of the male
parent meet those of the female parent, and a synthesis occurs, which
results in the formation of a new organism. When these two sets of
gametes meet one another, one of several events may happen. The gametes
may refuse to combine. This will occur whenever they are of very
different constitution; thus it is that widely differing species will not
interbreed. But it may even happen that gametes of individuals of the
same species may refuse to coalesce on account of some peculiarity in the
composition of one or other of them. Secondly, they may be able to form
some sort of a union, but, owing to their diverse nature, the resulting
molecules may be so complex that they cannot be broken up into equal
halves, and as this seems to be necessary for the sexual act, the
resulting organism will be sterile. Thirdly, the two sets of gametes may
enter into a proper union, that is to say, form new molecules, but these
may be of such different structure to the molecules of the gametes, that
the resulting offspring will be quite unlike their parents in appearance.
Fourthly, some or all the groups of radicles in each gamete may be united
so closely that in the sexual act they do not break up, but enter bodily
into the new resulting organism. In these circumstances the inheritance
of the offspring will follow Mendel’s law. Fifthly, there may be some
slight disturbance of the molecule, perhaps one or only a few atoms will
be replaced by those of the other gamete. This would give us impure
dominance.
Thus this hypothesis appears to be compatible with the various modes of
inheritance.
The curious phenomenon known as prepotency would seem also to be quite in
accordance with the conception.
In chemical reactions the tendency is for the most stable combinations to
be formed, so in nature.
We may probably go farther and say, not only will the most stable
biological molecules be formed, but the most stable radicles will
dominate the molecule. Hence, if any two animals are crossed and the
offspring show alternate inheritance, the resulting organism will, in the
case of each unit character, display the most stable of the pair; in
other words, it will take after the parent which happens to have the
greater stability as regards that particular character. The difference
between the mule and the hinny would seem to be explicable on this
supposition. If the union were like a simple chemical synthesis it should
not make any difference which way the cross were made. But if the species
crossed are of varying stability, and if their respective degrees of
stability vary with the sex, it is easy to see that it will make a
difference how the animals are crossed.
In the cases of creatures that obey Mendel’s law, the most stable form of
a unit character will presumably be the dominant one.
One of the most curious of the phenomena of inheritance is that of
correlation. We shall deal with this more fully in Chapter VIII. It will
suffice here to say that certain characters appear to be linked together
in organisms. Such seem to be transmitted in pairs. The offspring never
exhibits one of such a correlated couple without exhibiting the other
also.
It would thus seem that certain combinations of biological atoms, certain
molecules, can only exist in conjunction with certain other combinations.
This is quite in accordance with the teaching of physiologists regarding
the interdependence of the various organs of the body. We have now
reached the stage of the fertilised ovum. According to our conception it
is a series or conglomeration of the precursors of the unit characters of
the adult. These precursors we call biological molecules. Each is of a
very complex nature. Each seems to be composed of several portions, only
one of which will take part in the building up of the body of the
offspring, the other portions remaining latent. We further conceive that
it is possible for the various radicles which compose these molecules to
arrange themselves in various manners, and with each new arrangement a
different form of unit character will be developed. These molecules,
then, are built up from radicles derived from both parents, the most
stable combinations being formed and one portion of the molecule
dominating the whole. Under normal circumstances this dominant portion of
the molecule will give rise to a character of a definite type. But it
seems that other factors may come into play and cause a rearrangement of
the radicles which compose it, and this will result in the formation of a
unit character different from that to which it would ordinarily give
rise.
But, it may be objected, if the colour of an organism be derived from one
of these so-called biological molecules, how is it that it affects the
whole organism, or, at any rate, several of the other unit characters?
The objection may be met in several ways. In the first place, the
colour-forming molecules may split up into as many portions as there are
units which it affects, and each portion may attach itself to a unit. Or
the property which we call colouration may not be derived from a
molecule, it may be an expression in the relative positions of the
various molecules in the fertilised egg. Or the colour-determining
molecule may secrete a ferment or a hormone, and this may be the cause of
the particular colouring of the resulting organism. We do not pretend to
say which (if any) of these alternative suppositions is the correct one.
But it seems to us that some such conception as that which we have set
forth is forced upon us by observed facts. This conception should be
regarded not as a theory, but rather as an indication of the lines along
which we believe the study of inheritance could best be made.
The fertilised ovum has nothing of the shape of the creature to which it
will give rise. It is merely a potential organism, a something which
under favourable conditions will develop into an organism.
Phenomenon of Sex
In the higher animals each individual is either of the male or the female
sex. A vast amount of ingenuity has been expended by zoologists in the
attempt to ascertain what it is that determines sex. Many theories have
been advanced, but no one of them has obtained anything like general
acceptance, because its opponents are able to adduce facts which appear
to be incompatible with it.
It is tempting to try to interpret the phenomenon of sex on the
assumption that the female-producing biological molecule or unit is an
isomeride of the male-producing cell. Certain facts, however, seem to
negative the idea, as, for example, the occasional appearance in an
individual of one sex of characteristics of the other sex.
Possibly the attempts to explain the phenomena of sex-production on a
Mendelian basis may prove to be more successful. It seems not impossible
that each fertilised egg contains material which is capable of developing
into male generative organs and material which is capable of developing
into female generative organs, but that only one kind of material, that
which dominates, succeeds in developing. The number of what are known as
“X-elements” that happen to be present in the fertilised egg appear to
decide which kind of material is to be dominant.
But the problem of the determination of sex, fascinating though it be, is
not one that can be discussed adequately in a general work on evolution.
Those interested in the subject are referred to Professor Thomson’s
_Heredity_, and to the address given by Professor E. B. Wilson, of
Columbia University, before the American Association for the Advancement
of Science, which was fully reported in the issue of _Science_, dated
January 8, 1909.
Stated briefly, then, our conception is, that the fertilised egg is
composed of a number of entities, to which we have given the name
“biological molecules,” because in certain respects their behaviour is
not unlike that of chemical molecules.
The units which compose these molecules, being made up of protoplasm, are
endowed with all the properties of life, including the inherent
instability which characterises all living matter.
We suggest that the continuous or fluctuating variations that appear in
the adult organism may be the result of individual differences in the
biological “atoms” that compose the molecule.
Discontinuous variations, or mutations, on the other hand, may be the
result of a rearrangement of the atoms within the biological molecule.
Upon what causes this rearrangement it would not be very profitable to
speculate in the present state of our knowledge. To do this would be to
inquire into the cause of a re-grouping of entities of the existence of
which we are not certain! For aught we know there may be an intracellular
struggle for nourishment among the various molecules and among the atoms
which compose the molecules. If one molecule enjoys any special advantage
over the others the result may be an unusual degree of development of the
resulting unit character; in other words, the result will be a variation
in the organism. This variation may prove favourable or unfavourable to
its possessor.
Struggle for Nourishment
Certain phenomena seem to point to a struggle for nourishment between the
germinal and the somatic portions of the egg, between the parts from
which the sexual cells of the resulting organism are produced and those
which give rise to the body of the organism. Each molecule may strive, so
to speak, to increase at the expense of the others. Thus, great size in
an organism is likely to be produced at the expense of the germinal
cell-forming molecules. In other words, great size in an organism would
be incompatible with excessive fecundity. This is what we observe in
nature. On the other hand, poor development of bodily tissue, as in the
case of intestinal parasites, would be correlated with great fecundity.
Some organisms are mere sacs full of eggs.
Success in the struggle for nourishment of one molecule might be shared
by the other molecules near to it, hence the phenomena of correlation.
It is thus conceivable that, in a brood consisting of several
individuals, a particular molecule or set of molecules in one of the
individuals may receive more than its share of nourishment, and this will
result in the organs of that individual which spring from the
well-nourished molecules being exceptionally well developed. Thus arises
the phenomenon of differences between the members of a litter or brood.
Natural selection will tend to eliminate those individuals in which the
resulting variation is an unfavourable one. If the environment is such,
as in the case of an internal parasite, that the production of germ cells
is the most necessary function of the organism, then those individuals in
which the germ-forming molecules increase at the expense of the
body-forming ones will tend to be preserved. This would cause the
phenomenon which biologists term degeneration. The nourishment of the
various biological molecules may possibly depend on their relative
positions in the egg. Those in a favourable position will then tend to
develop at the expense of the others. This will result in variation along
definite lines. Each succeeding generation will tend to an increased
development of that particular organ to which the favourably-situated
molecule gives rise. This process may continue, as in the case of the
horns of the Irish elk, until the development of that particular organ
becomes so excessive as to be positively injurious; then natural
selection will step in and eliminate the species. But before this
happens, something may cause a rearrangement of the biological molecules
in the fertilised egg, and thus a mutation may arise, which, so to speak,
strikes out a new line.
Origin of Mutations
Finally, on this conception there may be some sort of connection between
fluctuating variations and mutations. We can picture the fluctuating
variations being piled up, one upon the other, until there results a
rearrangement of the atoms in one or more of the biological molecules
which, in turn, causes a mutation.
Occasionally this remodelling, as it were, of one biological molecule may
affect certain of the other molecules, and thus lead to correlated
mutations.
CHAPTER VI
THE COLOURATION OF ORGANISMS
The theory of protective colouration has been carried to absurd
lengths—It will not bear close scrutiny—Cryptic colouring—Sematic
colours—Pseudo-sematic colours—Batesian and Müllerian
mimicry—Conditions necessary for mimicry—Examples—Recognition
markings—The theory of obliterative colouration—Criticism of the
theory—Objections to the theory of cryptic colouring—Whiteness of the
Arctic fauna is exaggerated—Illustrative tables—Pelagic
organisms—Objectors to the Neo-Darwinian theories of colouration are to
be found among field naturalists—G. A. B. Dewar, Gadow, Robinson, F. C.
Selous quoted—Colours of birds’ eggs—Warning colouration—Objections to
the theory—Eisig’s theory—So-called intimidating attitudes of
animals—Mimicry—The case for the theory—The case against the
theory—“False mimicry”—Theory of recognition colours—The theory
refuted—Colours of flowers and fruits—Neo-Darwinian
explanations—Objections—Kay Robinson’s theory—Conclusion that
Neo-Darwinian theories are untenable—Some suggestions regarding the
colouration of animals—Through the diversity of colouring of organisms
something like order runs—The connection between biological molecules
and colour—Tylor on colour patterns in animals—Bonhote’s theory of
pœcilomeres—Summary of conclusions arrived at.
Since the publication of _The Origin of Species_, naturalists have paid
much attention to the colouration of animals and plants, with the result
that a large majority of scientific men to-day hold the belief that all,
or nearly all, the colours displayed by animals are of direct utility to
them, and are therefore the direct result of natural selection; a few
would add, “and of sexual selection.”
“Among the numerous applications of the Darwinian theory,” writes
Wallace, “in the interpretation of the complex phenomena, none have been
more successful than those which deal with the colours of animals and
plants.”
Robinson on Protective Colouring
We readily admit that the Darwinian theory has thrown a great deal of
light on the phenomenon of animal colouration; it has reduced to
something like order what was before Darwin’s time chaos. While admitting
this we feel constrained to say that many naturalists, especially Dr
Wallace and Professor Poulton, have pushed the various theories of animal
colouration to absurd lengths. As Dr H. Robinson truly says (_Knowledge_,
January 1909), “It seems to have been taken for granted, and some even of
Dr Wallace’s writings may be interpreted in this sense, that protective
colouring is necessary to the continued existence of every species, and
that, sexual colouration apart, it is incumbent on naturalists to offer
ingenious speculations in this sense to account for the appearance even
of the most bizarre and conspicuous beasts. Thence it has been but a
short step to the announcement of those speculations as further evidence
in favour of natural selection, and of various assumptions made in the
speculative process as indisputable facts.”
The result of this is that men have ceased to regard the Neo-Darwinian[6]
theories of protective colouration, mimicry, and recognition markings as
mere hypotheses which seem to throw light on certain phenomena in the
organic world. These theories have assumed the rank of laws of nature. To
dispute them would seem to be as futile as to assert that the earth is
flat. To take exception to them would appear to be as ridiculous as to
object to Mont Blanc. To dare to criticise them is heresy of the worst
type.
Be this as it may, scientific dogma or no scientific dogma, scientific
opinion or no scientific opinion, we have dared to weigh these theories
in the balance of observation and reason, and have found them wanting. We
have examined these mighty images of gold, and silver, and brass, and
iron, and found that there is much clay in the feet.
We shall devote this chapter to lifting the hem of the garment of
sanctity that envelopes each of these images, and so expose to view the
clay that lies concealed.
We propose, first, to set forth in outline what we trust will be
considered a fair statement of the various theories of animal colouration
which are generally accepted to-day, then to show up the various weak
points in these, and lastly, to endeavour to ascertain whether there are
not some alternative explanations in certain cases to which the
generally-accepted theory does not apply.
Cryptic Colouring
Neo-Darwinians divide the various forms of colouration into three great
classes:—(1) Cryptic colouring, or protective and aggressive
resemblances; (2) sematic colours, or warning and recognition colours;
and (3) pseudo-sematic colours, or mimicry. A tabular statement of this
scheme of colouring will be found on pp. 293-7 Professor Poulton’s
_Essays on Evolution_.
As regards class (1), Neo-Darwinians point out that the great majority of
animals are so coloured as to make them very difficult to see in their
natural environment, hence the whiteness of the creatures which inhabit
the snow-bound Arctic regions, the sandy colour of desert animals, the
spotted coats of creatures which live among trees, the striped markings
of animals which spend their lives amid long grass, and the transparent
blueness of pelagic animals. The theory is that all kinds of animals,
whether those that hunt or those that are hunted, derive much advantage
from being coloured like their environment. The hunted creatures are
thereby the better able to elude the vigilance of their foes, while those
that hunt are in a position to take their quarry by surprise; so that
natural selection has caused them all to assimilate to the hues of their
surroundings. Neo-Darwinians point to the fact that some Arctic animals
are brown in the summer to match the ground from which the snow has
melted, and turn white in winter to assimilate with their snowy
background. Naturalists further cite, as evidence in favour of this
theory, the case of those creatures which imitate inanimate objects, such
as leaves and twigs, and thereby escape the observation of their foes.
Thus, the great majority of animals are supposed to be cryptically
coloured, that is to say, coloured so as to be, if not quite invisible,
at least very inconspicuous in their natural habitat.
Warning Colouration
It is, however, generally admitted that many creatures are not
cryptically coloured. Some, indeed, seem to be coloured in such a way as
to render them as conspicuous as possible. The Neo-Darwinians declare
that there is a reason for this. “If,” writes Professor Milnes Marshall
(page 133 of his _Lectures on the Darwinian Theory_), “an animal,
belonging to a group liable to be eaten by others, is possessed of a
nauseous taste, or if an animal, such as a wasp, is specially armed and
venomous, it is to its advantage that it should be recognised quickly,
and so avoided by animals that might be disposed to take it as food.
“Hence arises warning colouration, the explanation of which is due to
Wallace. Darwin, who was unable to explain the reason for the gaudy
colouration of some caterpillars, stated his difficulty to Wallace, and
asked for suggestions. Wallace thought the matter over, considered all
known cases, and then ventured to predict that birds and other enemies
would be found to refuse such caterpillars if offered to them. This
explanation, first applied to caterpillars, soon extended to adult forms,
not only of insects, but of other groups as well. . . . Insects afford
many admirable examples of warning colours, and many well-known instances
occur among butterflies. The best examples of these are found in three
great families of butterflies—the _Heliconidæ_, found in South America,
the _Danaidæ_, found in Asia and tropical regions generally, and the
_Acræidæ_ of Africa. These have large but rather weak wings, and fly
slowly. They are always very abundant, all have conspicuous colours or
markings, and often a peculiar form of flight, characters by which they
can be recognised at a glance. The colours are nearly always the same on
both upper and under surfaces of the wings; they never try to conceal
themselves, but rest on the upper surfaces of leaves and flowers.
Moreover, they all have juices which exhale a powerful scent; so that, if
they are killed by pinching the body, a liquid exudes which stains the
fingers yellow, and leaves an odour which can only be removed by repeated
washing. This odour is not very offensive to man, but has been shown by
experiment to be so to birds and other insect-eating animals.
“Warning colours are advertisements, often highly coloured
advertisements, of unsuitability as food. Insects are of two kinds—those
which are extremely difficult to find, and those which are rendered
prominent through startling colours and conspicuous attitudes. Warning
colours may usually be distinguished by being conspicuously exposed when
the animal is at rest. Crude patterns and startling contrasts in colour
are characteristically warning, and these colours and patterns often
resemble each other; black combined with white, yellow, or red, are the
commonest combinations, and the patterns usually consist of rings,
stripes, or spots.”
We trust that we shall be forgiven for this lengthy quotation. Our object
in reproducing so large an extract is to allow the Neo-Darwinians to
speak for themselves. Were we to state their theory in our own words, we
might perhaps be charged with stating it inaccurately. We should add
that, even as natural selection is supposed to have been the cause of
conspicuous colouring in some organisms, so has it caused others to
assume intimidating attitudes or emit warning sounds, such as a hiss,
when attacked.
Batesian Mimicry
We now come to the third great class of animal colours—mimetic colours.
Mimicry is of two kinds, known respectively as Batesian and Müllerian
mimicry, after their respective discoverers.
It has been found that some apparently warningly coloured butterflies and
other creatures are palatable to insectivorous animals. The explanation
given of this is that these showy but edible butterflies “mimic,” that is
to say, have the appearance of, show a general resemblance to, species
which are unpalatable. This is known as Batesian mimicry. “Protective
mimicry,” writes Professor Poulton (_Essays on Evolution_, p. 361), “is
here defined as an advantageous superficial resemblance of a palatable
defenceless form to another that is specially defended so as to be
disliked or feared by the majority of enemies of the groups to which both
mimic and model belong—a resemblance which appeals to the senses of
animal enemies . . . but does not extend to deep-seated characters,
except when the superficial likeness is affected thereby.”
As Wallace has pointed out, five conditions must be satisfied before such
protective mimicry can occur:—
“1. That the imitative species occur in the same area and occupy the same
station as the imitated. 2. That the imitators are always the more
defenceless. 3. That the imitators are always less numerous in
individuals. 4. That the imitators differ from the bulk of their allies.
5. That the imitation, however minute, is external and visible only,
never extending to internal characters or to such as does not affect the
external characters.” (_Darwinism_, Chap. ix.)
Thus the mimic is supposed to deceive his enemies by deluding them into
the belief that he is the inedible species which they once tried to eat
and vowed never again to touch, so nasty was it. The mimic, then, may be
compared to the ass in the lion’s skin. Needless to say, this mimicry is
quite unconscious. It is supposed to have been developed by natural
selection. Every popular book on Evolution cites many examples of such
mimicry. We may therefore content ourselves with mentioning but a few.
Examples of Mimicry
Our common wasps are copied by a beetle (_Clytus arietis_), active in
movement and banded black and yellow, and by several yellow-barred
hover-flies (_Syrphidæ_); and the bumble-bee by a clear-winged moth
(_Sesia fuciformis_). There is, indeed, a whole group of these
clear-winged moths, resembling bees, wasps, and other stinging
hymenoptera. The common Indian Danaid butterfly, _Danais chrysippus_, is
marvellously reproduced by the female of _Hypolimnas misippus_, a form
allied to our Purple Emperor. The male of this is black, with white
blue-bordered patches, the female chestnut, edged with black and with
white spots at the tips of the wings, as in the _Danais_. Finn has shown
experimentally that this species is liked by birds.
Another common Indian Danaid (_D. limniace_), black, spotted with pale
green, is imitated, though not very closely, by the female of one of the
“white” group, _Nepheronia hippia_. Finn found that this insect was eaten
freely by birds, and that the common jungle-babbler (_Crateropus
canorus_) was deceived by the mimicry of the female. The very nauseous
Indian swallow-tail (_Papilio aristolochiæ_) is closely imitated by
another swallow-tail (_P. polites_), both having black wings marked with
red and white; _P. aristolochiæ_, however, has a red abdomen. This
difference was not noticed by two species of Drongo-shrikes (_Dicrurus
ater_ and _Dissemurus paradiseus_), to which the butterflies were
offered; but the Pekin robin (_Liothrix luteus_)—a very intelligent
little bird—did not fail to pick out and eat the mimic, though it was
deceived by the marvellously perfect imitation of _Danais chrysippus_, by
the female of the _Hypolimnas_.
Such resemblances can therefore be effective.
The cases of mimicry usually quoted include very few among mammals,
probably, as Beddard suggests, because the species of that class are
relatively few.
The insectivorous genus _Tupaia_ is supposed to mimic the squirrels,
which it much resembles as regards form in all respects save the long
muzzle; the idea being that squirrels are so active that carnivorous
animals find it hopeless to pursue them.
On the other hand, there is a squirrel (_Rhinosciurus tupaioides_) which
is supposed to mimic the tupaias! It has a similar long muzzle, and the
light shoulder-stripe which is a common marking in tupaias. But why the
squirrel, one of the group imitated, should in turn become an imitator is
not explained.
The true interpretation of the resemblance is probably that both
squirrels and tupaias are adapted to a life in trees. Like profession
begets like appearance: the ground-living shrews much resemble mice, and
the moles find representatives in mole-like rodents.
Another case, however, wherein true mimicry may have come into play is
that of the South American deer (_Cervus paludosus_) which singularly
resembles in colouration the long-legged wolf or _Aguara-guazu_ (_Canis
jubatus_). Both these species are chestnut in colour, with the front of
the legs black, and the ears lined with white hair; both inhabit the same
regions in South America.
Müllerian Mimicry
The second kind of mimicry—Müllerian mimicry—is where one unpalatable
creature resembles another. This form of mimicry is named after Fritz
Müller, who suggested the explanation now usually accepted, namely, that
“Life is saved by a resemblance between the warning colours in any area,
inasmuch as the education of young inexperienced enemies is facilitated,
and insect life saved in the process.” “It is obvious,” writes Poulton
(p. 328 of _Essays on Evolution_), “that the amount of learning and
remembering, and consequently of injury and loss of life involved in
these processes, are reduced when many species in one place possess the
same aposematic colouring, instead of each exhibiting a different danger
signal. . . . The precise statement of advantage was made by Mr Blakiston
and Mr Alexander, of Tokio. ‘Let there be two species of insects equally
distasteful to young birds, and let it be supposed that the birds would
destroy the same number of individuals of each before they were educated
to avoid them. Then if these insects are thoroughly mixed and become
undistinguishable to the birds, a proportionate advantage accrues to each
over its former state of existence. These proportionate advantages are
inversely in the duplicate ratio of the respective percentages that would
have survived without the mimicry.’”
This is rather a cumbrous method of saying that if there are in a
locality a number of young birds, and each of these has to learn by
experience which insects are edible and which are not, each will, if it
learns by one example, devour one insect of any given pattern. Now, if
two species of inedible insects have this pattern, they will between them
lose only one member in the educating process of each bird, whereas if
each species of insect had a colouration peculiar to itself, each species
would lose a whole individual instead of half a one. There can be no
doubt that such a livery of unpalatability is of some advantage to its
possessors.
It has been shown experimentally that hand-reared young birds have to
acquire their knowledge of flavours and colours by experiment.
It is well known that in many species the male and the female are not
coloured alike. Such species are said to exhibit sexual dimorphism. In
these cases it is usually the male that is more conspicuously coloured.
Darwin felt that the theory of natural selection could not satisfactorily
account for this phenomenon, so put forward the supplementary theory of
sexual selection. On this hypothesis the females are supposed to be able
to pick and choose their mates, and to select the most beautiful and
ornamental ones, hence the greater showiness of these in most sexually
dimorphic species. Wallace does not accept this theory. He thinks it
unnecessary. He looks upon the brilliant colouring of the males as due to
their superior vigour; moreover, he says that it is the hen that sits
upon the eggs, and so requires a greater degree of protection than the
male, and therefore natural selection has not permitted her to develop
all the ornaments displayed by the cock. With the phenomenon of sexual
dimorphism we shall deal at length in the next chapter.
Danger Signals
Dr Wallace recognizes yet another exception to the rule that animals are
cryptically coloured. Many creatures possess on the body markings which
tend to render them conspicuous rather than difficult to see. Where such
markings occur on gregarious animals, Wallace believes that they have
been evolved by natural selection, either to enable their possessors to
recognize one another, or to act as a danger signal to their fellows. The
white tail of the rabbit is believed by Wallace to serve as a danger
signal. The first member of the company to espy the approaching foe takes
to his heels, and, as he moves, his white tail catches the eye of his
neighbour, who at once follows him, so that, in less time than it takes
to tell, the whole company of rabbits is scampering towards the burrow,
thanks to the white under-surface of the tail.
Even as Wallace out-Darwin’s Darwin, so does Mr Abbott Thayer, an
American naturalist and artist, out-Wallace Wallace. That gentleman seems
to be of opinion that _all_ animals are cryptically or, as he calls it,
concealingly or obliteratively coloured. Even those schemes of colour
which have hitherto been called conspicuous are, he asserts, “purely and
potently concealing” when looked at properly, that is to say, with the
eye of the artist.
Lest it be thought unnecessary to criticize a hypothesis which appears to
be based upon the assumption that animals see with the eye of the artist,
we may say that Professor Poulton writes approvingly of Thayer’s theory.
He frequently alludes to it in his _Essays on Evolution_, and he
published an account of it in the issue of _Nature_, dated April 24,
1902. Moreover the hypothesis has been enunciated in such scientific
journals as _The Auk_ (1896) and _The Year-Book of the Smithsonian
Institution_ (1897).
Thayer asserts that all animals, or at any rate the great majority,
including many that are usually supposed to be conspicuously coloured,
are in reality obliteratively coloured—that is to say, coloured in such a
way that the effects of light and shade are completely counteracted, with
the result that they are invisible.
Obliterative Colouring
It is possible, says Mr Thayer, to almost obliterate a statue in a
diffused light, by putting white paint on the surfaces in darkest shadow
and dark paint on the most brightly lighted parts, all in due proportion.
Now this is precisely what nature is supposed by Mr Thayer to have done
for all her creatures.
It is well known that a great many animals, as for example the Indian
black-buck and the hare, are coloured on the upper side and white below.
This is called by Mr Thayer the principle of the gradation of colour. It
runs, he declares, all through the animal world, and is “the main
essential step toward making animals inconspicuous under the descending
light of the sky.”
Animals, he contends, are not protectively coloured to look like clods or
stumps or like surrounding objects, they are simply obliteratively
coloured—coated, as it were, with invisible paint.
To quote from _The Century Magazine_ (1908): “Whales, lions, wolves,
deer, hares, mice; partridges, quails, sandpipers, larks, sparrows;
frogs, snakes, fishes, lizards, crabs; grasshoppers, slugs,
caterpillars—all these animals, and many thousands more, crawl, crouch,
and swim about their business, hunting and eluding, under cover of this
strange obliterative mask, the smooth and perfect balance between shades
of colour and degrees of illumination.”
Nature having thus visually unsubstantialized the bodies of animals, so
that, if seen at all, they look flat and ghostly, does not stop there.
From solid-shaded bodies they have been converted, as it were, into flat
cards or canvases, and, to complete the illusion of obliteration,
pictures of the background—veritable pictures of the more or less distant
landscape—have been painted on their canvases! Such in effect are the
elaborate “markings of field and forest birds.”
Again he writes: “Brilliantly changeable or metallic colours are usually
supposed to make the birds that wear them conspicuous, but nothing could
be further from the truth. Iridescence is, indeed, one of the strongest
factors of concealment. The quicksilver-like intershifting of many lights
and colours, which the slightest motion generates on an iridescent
surface, like the back of a bird or the wing of a butterfly, destroys the
visibility of that wing or back as such and causes it to blend
inextricably with the gleaming and scintillating labyrinthine-shadowed
world of wind-swayed leaves and flowers.”
According to Thayer, the skunk, which for years has been an important
item of the stock-in-trade of the advocates of the theory of warning
colouration, is an excellent example of obliterative colouring, since its
enemies are supposed to mistake for the sky-line the line of junction
between the white fur of the back and the dark fur of the sides.
Similarly the crocodiles are supposed to mistake a flamingo for the sky
at sunrise or at sunset!
There is doubtless something in this theory of obliterative colouration.
Any one can see, by paying a visit to the South Kensington Museum, that
an animal which is of a lighter colour below than above, is less
conspicuous in a poor light than it would be were it uniformly coloured.
There is then no doubt that this scheme of colour, which is so common in
nature, has some protective value.
To this extent has Mr Thayer made a valuable contribution to zoological
science. But when he informs us that obliterative colouring is a
“universal attribute of animal life,” we feel sorely tempted to poke fun
at him.
We would ask all those who believe in the universality of obliterative
colouring to observe a flock of rooks wending their way to their
dormitories at sunset.
Let us now pass on to the examination of the more orthodox theories of
animal colouration.
Objections to the Theory of Cryptic Colouring
Before criticising the theory of cryptic colouring, we desire to state
distinctly that we admit that, where other things are equal, it is of
advantage to all creatures which hunt or which are preyed upon to be
inconspicuous. If difficult to distinguish amid their natural
surroundings, the former are likely to secure their prey readily, and the
latter have a chance of escaping from their enemies. Our quarrel is with
the theory of cryptic colouring as it is enunciated by many
Neo-Darwinians, with the theory that every hue, every marking, every
device displayed by an organism is of utility to the organism and has
been directly developed by natural selection.
The extreme advocates of the theory of cryptic colouring have greatly
exaggerated the degree in which animals are assimilated to their natural
environment.
Fauna of Polar Regions
We grant that a great many creatures, which when seen in a menagerie
appear very conspicuous, are the reverse of conspicuous when standing
motionless amid their natural surroundings. As Beddard has pointed out,
it is often not easy to find a sixpenny piece which has been dropped on
the carpet, but the reason for this is, not that the coin is protectively
coloured, but that any small object, no matter how coloured, is difficult
to distinguish amid a variegated environment. The assumption of a white
winter coat by many organisms that live in northern latitudes has been
cited, again and again, as showing how important it is for an animal to
be protectively coloured. If, it is urged, those creatures that live in
lands which are covered in snow for half of the year have become white in
winter by the action of natural selection in order to escape their foes,
it is obviously of paramount importance to all creatures that they should
be cryptically coloured. Popular books on natural history convey the
impression that during winter the snow-clad, ice-bound Arctic regions are
peopled by a fauna whose fur or hair rivals in whiteness the snowy mantle
of the earth. The impression thus conveyed is misleading. It is true that
an unusually large percentage of the animals that inhabit the polar
regions are white in winter, but the majority of the creatures which
dwell there do not assume the white garb of winter.
As the fauna of the polar regions is a small one, we are able to give
lists of all the birds and mammals which dwell in the Arctic and the
Antarctic regions. We have arranged these in in three columns. In the
first are placed those creatures which are white throughout the year, in
the third those that retain their colour through the winter, while the
middle column contains those forms which change their colouring with the
season.
ARCTIC FAUNA.
Mammals.
White.
Polar Bear.
Arctic Fox (some individuals).
White Whale or Beluga.
Changing with the Seasons.
Arctic Fox (most individuals).
Arctic Lemming.
Stoat.
Weasel.
Blue Hare.
Coloured.
Arctic Fox (sometimes).
Reindeer.
Musk-ox.
Glutton.
Moose.
Sable.
Seals.
Walrus.
Narhwal.
Greenland Whale.
Birds.
White.
Ivory Gull.
Snowy Owl.
Gyrfalcon.
Snow Goose.
Changing with the Seasons.
Black Guillemot.
Ptarmigans.
Snow Bunting (whitest in summer!)
Razorbill.
Little Auk (throat only becomes white).
Coloured.
Sea Eagle.
Greenland Redpoll (very pale).
All Arctic Geese and Ducks other than Snow Goose.
Raven.
Cormorant.
Brunnich’s Guillemot.
Puffin.
Fulmar Petrel.
Ross’s Gull.
Glaucous Gull (very pale).
Sandpipers.
ANTARCTIC FAUNA.
Mammals.
White.
Antarctic White Seal (_Lobodon carcinophaga_), in some cases.
Changing with the Seasons.
None.
Coloured.
Other Seals than _Lobodon._
Whales.
Birds.
White.
Sheathbill.
Snowy Petrel.
Giant Petrel (some individuals).
Chick of Emperor Penguin.
Changing with the Seasons.
None.
Coloured.
Penguins.
Cormorant.
Skua Gull.
Giant Petrel (usually).
Other Petrels.
It will be observed that the third column contains the largest number of
forms. It is thus evident that the whiteness of the Arctic and Antarctic
faunas in winter has been greatly exaggerated.
The Arctic fox appears in all three columns, as the creature seems to
fall into three races—a permanently white race, a permanently coloured
race, and a seasonally dimorphic race.
Of the creatures set forth in the middle column of the above tables all
are whiter in winter than in summer with the exception of the snow
bunting, who sets at naught the theory of cryptic colouring by turning
darker in winter! The same may be said of the Alpine chamois.
The advocates of the theory of protective colouring assert that the
creatures which do not turn white in winter are strong and active animals
which have no enemies to fear.
This contention is met by F. C. Selous as follows (_African Nature Notes
and Reminiscences_, p. 9): “According to the experience of Arctic
travellers, large numbers of young musk oxen are annually killed by
wolves. . . . Nothing, I think, is more certain than that a far smaller
percentage of so-called protectively coloured giraffes are killed
annually by lions in Africa than of musk oxen by wolves in Arctic
America.”
Another difficulty which confronts the Neo-Wallaceian school is that, _ex
hypothesi_, the assumption of the white coat was gradual. Hence the
change in the direction of whiteness cannot, in its first beginning, have
been of perceptible utility to an organism. How then can natural
selection have operated on it?
Pelagic Organisms
The transparency of pelagic organisms is frequently cited as exemplifying
cryptic colouring. We all know that the common jelly-fish is as
transparent as glass. Floating on the surface of the ocean are millions
of tiny organisms, so transparent as to be invisible to the human eye. At
first sight this certainly appears to be a remarkable case of protective
colouring. Unfortunately, nearly all the more highly developed forms
display conspicuous pigment (as in most jelly-fish) in some part of the
body.
“An animal floating about in the sea,” writes Beddard, “perfectly
transparent, but decked with dense black patches, of the size of saucers,
would betray its whereabouts even to the least observant; if the observer
were stimulated by hunger or fear, the conspicuousness would not be
lessened. . . . Besides the internecine warfare which is continually
going on amongst the smaller surface organisms, they are devoured
wholesale by the larger pelagic fish, and by whales and other Cetacea. A
whale, rushing through the water with open mouth and gulping down all
before him, is not the least inconvenienced by the invisibility of the
organisms devoured in such enormous quantities; nor do a solid phalanx of
herring or mackerel stop to look carefully for their food: they take what
comes in their way, and get plenty in spite of ‘protective absence of
colouration.’
“If the transparency of the pelagic organisms be due entirely to natural
selection, it is remarkable that there is so little modification in this
direction among the species inhabiting the bottom at such depths as are
accessible to the sun’s rays; the advantage gained by this transparency
and consequent invisibility would be equally great. And yet this is not
the case; the bulk of the bottom fauna of the coasts are brilliantly
coloured animals, and those that show any protective colouring at all
appear to be coloured so as to resemble stones or sea-weeds.”[7]
Before leaving the subject of marine animals, we may point out that the
majority of the creatures that live in the everlasting blackness of the
depths of the ocean display exceedingly conspicuous colouring, and this
colouring seems to be constant. In such cases the colouring cannot be
useful as such to its possessors. The same may be said of the colour of
blood, or of the colouring of the internal tissues of all organisms. We
must not lose sight of the fact that every organism, and every component
part thereof, must of necessity be either of some colour or perfectly
transparent. It seems to us that since the appearance of _The Origin of
Species_ zoologists have tended to exaggerate the importance of colouring
to organisms; they frequently speak of it as though it were the one and
only factor in the struggle for existence. It is on this account that
they feel it incumbent upon them to find ingenious explanations for every
piece of colouring displayed by every plant or animal.
Unimportance of Colour
The tendency to exaggerate the importance to an animal of its colouring
is doubtless in large part due to the fact that many zoologists are
content to study nature in museums rather than in the open. Some of those
who observe organisms in their natural surroundings, especially in such
favourable localities as the tropics, seem to be of opinion that natural
selection has but little influence on the colouration of organisms.
Thus D. Dewar writes (_Albany Review_, 1907): “Eight years of
bird-watching in India have convinced me that, so far as the struggle for
existence is concerned, it matters not to a bird whether it be
conspicuously or inconspicuously coloured, that it is not the necessity
for protection against raptorial foes which determines the colouring of a
species; in short, that the theory of protective colouration has but
little application to the fowls of the air.”
Similarly, F. C. Selous writes, on page 13 of _African Nature Notes and
Reminiscences_: “Having spent many years of my life in the constant
pursuit of African game, I have certainly been afforded opportunities
such as have been enjoyed by but few civilised men of becoming intimately
acquainted with the habits and life-history of many species of animals
living in that continent, and all that I have learned during my long
experience as a hunter compels me to doubt the correctness of the now
very generally accepted theories that all the wonderfully diversified
colours of animals—the stripes of the zebra, the blotched coat of the
giraffe, the spots of the bushbuck, the white face and the rump of the
bontebok, to mention only a few—have been coloured either as means of
protection from enemies or for the purpose of mutual recognition by
animals of the same species in times of sudden alarm.”
So also G. A. B. Dewar—a very close observer of nature in England—writes,
in _The Faery Year_: “Few theories in natural history have received more
attention of late years than protective or aggressive colour, ‘mimicry,’
and harmony with environment. . . . To doubt this use of colour to
animals seems like inviting back chaos in place of cosmos—for abandon the
theory, and a world of colour is straightway void of purpose, a muddle of
chance. So we all like the theory. Some, however, perceive plans to aid
the wearer in every colour, tint, shade, and pattern. We may be sceptical
of a good many of the cases they cite in support of colour aid, though
attracted by the main idea.”
Writing of the commoner British butterflies, he says: “After a little
practice, any man furnished with good eyesight can easily distinguish
these butterflies—blues, coppers, small heaths, and meadow browns—from
their perches; and so we may be sure that the small beast, bird, or
insect of prey, with sense of colour or form, could also distinguish
them. . . . Quite often, without even searching for them, I can see
cabbage whites and other butterflies asleep on perches to which they by
no means assimilate.” Mr G. A. B. Dewar suggests that the safety of the
resting butterfly lies in “the position, the couch on high, . . . not the
mask of colour or marking.”
Gadow on Coral Snakes
Two short visits to Southern Mexico sufficed to show Dr Hans Gadow that
some of the commonly accepted explanations of colour phenomena are not
the correct ones.
Thus writing of coral snakes, he says, on page 95 of _Through Southern
Mexico_: “They are usually paraded as glaring instances of warning
colouration, but I am not at all sure whether this is justifiable.
Certainly these _Elaps_ are most conspicuous and beautiful objects. Black
and carmine or coral red, in alternate rings, are the favourite pattern;
sometimes with narrow golden-yellow rings between them, as if to enhance
the beautiful combination. But these snakes are inclined to be nocturnal
in their habits, and, except when basking, spend most of their time under
rotten stumps, in mouldy ground, or in ants’ nests in search of their
prey, which must be very small, to judge from the size of the mouth.”
Dr Gadow goes on to show that although black and red are very strong
contrasts in the day-time, the combination ceases to be effective in the
dark. He suggests that red and black is a self-effacing rather than a
warning pattern. He further points out that several kinds of harmless
snakes have the same colouring and pattern. “There seems,” he says, “to
be no reason why we should not call these cases of mimicry; and yet this
is most likely a wrong interpretation, since such harmless snakes are
also found in districts where the _Elaps_ does not occur, not only in
Mexico, but likewise in far-distant parts of the world, where neither
elapines nor any other similarly coloured poisonous snakes exist. To
interpret this as an instance of ‘warning colours’ in a perfectly
harmless snake, which has no chance of mimicry, amounts in such cases to
nonsense, and we have to look for a different explanation upon
physiological and other grounds.”
It is, to say the least of it, significant that all the opposition to the
theory of protective colouration comes from those who observe nature
first hand, while the warmest supporters of the theory are cabinet
naturalists and museum zoologists.
In the case of nocturnal creatures, as Dr H. Robinson very sagely points
out (_Knowledge_, January 1909), the value for protective purposes of any
given colouration must depend very largely on the state of the moon. “It
was,” he writes, “a common experience in the South African War that on
overcast or moonless nights the nearly black army great-coat made a
picquet sentry invisible at a distance of a few feet. In strong moonlight
this garb could be seen at a great distance, whereas a khaki pea jacket,
useless on a dark night, answered the requirements of invisibility very
well.” It is thus evident that the dark colour of the buffalo and sable
antelope cannot be protective on both dark and moonlight nights.
The theory of protective colouration is based on the tacit assumption
that beasts of prey rely on eyesight for finding their quarry. Raptorial
birds certainly do use their eyes as the means of discovering their
victims; but the great majority of predaceous mammals trust almost
entirely to their power of smell as a means for tracking down their prey.
F. C. Selous Quoted
“Nothing,” writes F. C. Selous, on page 14 of _African Nature Notes and
Reminiscences_, “is more certain than that all carnivorous animals hunt
almost entirely by scent until they have closely approached their quarry,
and usually by night, when all the animals on which they prey must look
very much alike as far as colour is concerned.”
The herbivora—the quarry for the beast of prey—too, have a keen sense of
smell, so that they trust their noses rather than their eyes for safety.
No observer of nature can have failed to remark how the least movement on
the part of an animal will betray its whereabouts, even though in
colouring it assimilates very closely to the environment. So long as the
hare squats motionless in the furrow, it may remain unobserved, even
though the sportsman be searching for it; but the least movement on its
part at once attracts his eye. Thus, in order that protective colouration
can be of use to its possessor, the latter must remain perfectly
motionless. But, in tropical countries, where flies, gnats, etc., are a
perfect scourge, no large animal is, when awake, motionless for ten
seconds at a time. The tail is in constant motion, flicking off the flies
that attempt to settle on the quadruped. The ears are used in a similar
manner. Thus the so-called protective colouring of herbivora cannot
afford them much protection. It is further worthy of note that the
brush-like tip to the tail of many mammals is not of the same colour as
the skin or fur. It is very frequently black. Thus we have the spectacle
of a protectively coloured creature continually moving, as if to attract
attention, almost the only part of its body that is not protectively
coloured!
Sexual Dimorphism
Many species of birds display what is known as seasonal dimorphism, still
more display sexual dimorphism.
Seasonally dimorphic birds very often assume a bright livery at the
breeding season; this nuptial plumage is by no means invariably confined
to the cock, so that we are brought face to face with the fact that some
hen birds, that are normally inconspicuously coloured, become showy and
easy to see at the nesting time, that is to say, precisely at the season
when they would seem to be most in need of protection.
In the great majority of cases of sexual dimorphism among birds the cock
is the more showily coloured. Now, if it be a matter of life-and-death
importance to a bird to be protectively coloured, we should expect the
showily coloured cock birds to be far less numerous than the
dull-plumaged hens, since the former are, _ex hypothesi_, exposed to far
greater danger than the inconspicuous hens. As a matter of fact, cock
birds in practically all species appear to be at least as numerous as the
hens. Nor can it be said that this is due to their more secretive habits.
As a general rule, cock birds show themselves as readily as the hens;
indeed, in the case of the familiar blackbird, the conspicuous cock is
less retiring in his habits than the more sombre hen. It may, perhaps, be
thought that the greater danger to which the sitting bird is exposed
accounts for the fact that hens, notwithstanding their protective
colouration, are not more numerous than the cocks. Unfortunately for the
supposition, in many sexually dimorphic hens, as, for example, the
paradise fly-catcher (_Terpsiphone paradisi_), the showy cock shares the
burden of incubation equally with the hen.
It frequently happens that allied species of birds are found in
neighbouring countries. The Indian robins, for example, fall into two
species. The brown-backed robin (_Thamnobia cambayensis_) occurs north of
Bombay, while the black-backed species (_T. fulicata_) is found south of
Bombay. The hens of these two species are almost indistinguishable, but
the cocks differ, in that one has a brown back, while the other’s back is
glossy black. The Wallaceian theory of colouration seems quite unable to
explain this phenomenon—the splitting up of a genus into local
species—which is continually met with in nature. Equally inimical to the
theory of protective colouration is the existence, side by side, of
species which obtain their living in much the same manner. On every
Indian lake three different species of kingfisher pursue their profession
cheek by jowl; one of these—_Ceryle rudis_—is speckled black and white,
like a Hamburg fowl; the second is the kingfisher we know in England; and
the third is the magnificent white-breasted species—_Halcyon
smyrnensis_—a bright-blue bird with a reddish head and a white wing bar.
It is obvious that all three of these diversely plumaged species cannot
be protectively coloured. It may perhaps be objected that the piscatorial
methods of these kingfishers differ in detail. We admit that this is the
case, but would maintain, at the same time, that these comparatively
slight differences in habit do not account for the very striking
differences in plumage. We may also cite the yellow and pied wagtails of
our own country, which may be seen feeding in the same meadows. Most
familiar and striking of all is the everyday sight of a blackbird and
thrush plying their respective avocations within a few yards of each
other on the same lawn, differently coloured though they be.
Another weighty objection to the generally accepted theory of protective
colouration is that some of the creatures which assimilate most closely
to their environment are those which appear to be the least in need of
such protection.
Precis Artexia
The butterfly _Precis artexia_, writes F. C. Selous, “is only found in
shady forests, is seldom seen flying until disturbed, and always sits on
the ground amongst dead leaves. Though handsomely coloured on the upper
side, when its wings are closed it closely resembles a dead leaf. It has
a little tail on the lower wing, which looks exactly like the stalk of a
leaf, and from this tail a dark-brown line runs through both wings (which
on the under side are light brown) to the apex of the upper wing. One
would naturally be inclined to look upon this wonderful resemblance to a
dead leaf in a butterfly sitting with closed wings on the ground amongst
real dead leaves as a remarkable instance of protective form and
colouration. And of course it may be that this is the correct
explanation. But what enemy is this butterfly protected against? Upon
hundreds of different occasions I have ridden and walked through forests
where _Precis artexia_ was numerous, and I have caught and preserved many
specimens of these butterflies, but never once did I see a bird
attempting to catch one of them. Indeed, birds of all kinds were scarce
in the forests where these insects were to be found.”
Similarly D. Dewar writes (_Albany Review_, 1907): “If a naturalist be
asked to cite a perfect example of protective colouring, he will, as
likely as not, name the sand grouse (_Pteroclurus exustus_). This species
dwells in open, dry, sandy country, and its dull brownish-buff plumage,
with its soft dark bars, assimilates so closely to the sandy environment
as to make the bird, when at rest, practically invisible, at any rate to
the human eye. Unfortunately for the theory, this bird stands less in
need of protective colouration than any other, for it has wonderful
powers of flight. Even a trained falcon is unable to catch it, because it
can fly upwards in a straight line as though it were ascending an
inclined plane, with the result that the pursuing hawk is never able to
get above it to strike.”
Striped Caterpillars
Lord Avebury, who is a typical Wallaceian, points out the connection that
exists between longitudinal stripes on caterpillars and the habit of
feeding either on grass or low-growing plants among grass. The inference,
of course, is that birds mistake these caterpillars for leaves, or, at
any rate, fail to observe them when feeding, not only because they are
green in colour, but because their longitudinal stripes look like the
parallel veins on the blades of grass. But the butterflies of the family
_Satyridæ_, as Beddard points out, _all_ possess striped larvæ, and these
feed chiefly by night, when neither their colouring nor marking is
visible, while during the day many of them lie up under stones; other
caterpillars of this family feed inside the stems of plants. “Now,”
writes Beddard (_Animal Colouration_, p. 101), “in these cases the colour
obviously does not matter: if, therefore, the longitudinal striping is
kept up by constant selection on account of its utility, and has no other
signification, we might expect that in these two species (_Hipparchia
semele_ and _Œnis_), and in others with similar habits, the cessation of
natural selection would have permitted the high standard required in the
other cases to be lowered—perhaps, even, as has been suggested in the
case of cave animals, the colours being useless to their possessors,
might have disappeared altogether—but they have not.”
Many exceedingly conspicuous birds—as, for example all the crow-tribe,
the egrets, the kingfishers—flourish in spite of their showy plumage.
Such creatures, while scarcely constituting a valid objection to the
theory of protective colouration, serve to show that protective colouring
is not a necessity. An animal otherwise able to take care of itself can
afford to dispense with cryptic colouration. “An ounce of good solid
pugnacity is a more effective weapon in the struggle for existence than
many pounds of protective colouration.”
There used to live in the gardens of the Zoological Society of London a
black cat belonging to the manager of one of the restaurants. This animal
used to catch birds on the lawn. We believe that not even Mr Thayer will
maintain that a black cat is cryptically coloured when stalking on a
well-watered lawn! Nevertheless the nigritude of that cat did not prevent
it securing a meal.
Colours of Eggs
The case of birds’ eggs furnish an excellent example of the lengths to
which Wallace and his followers have pushed the theory of protective
colouration.
D. Dewar maintains that it is possible to divide birds’ eggs that are
coloured, as opposed to those that are white, into two classes—those
which are protectively coloured and those which are not. The former class
includes all those which are laid in shingle or on the bare ground, as,
for example, the eggs of the ring-plover and the lap-wing.[8] He
maintains that the variously coloured and speckled eggs that are laid in
cup-shaped nests are not protectively coloured at all; he declares that
they are usually very conspicuous when in the nest, and, moreover, it
would be futile for them to be cryptically coloured, for a bird or lizard
that habitually sucks eggs will examine carefully the interior of each
nest it discovers.
Needless to say, this view does not appeal to the so-called
Neo-Darwinians. Wallace writes, on page 215 of _Darwinism_: “The
beautiful blue or greenish eggs of the hedge-sparrow, the song-thrush,
the blackbird, and the lesser redpole seem at first sight especially
calculated to attract attention, but it is very doubtful whether they are
really so conspicuous when seen at a little distance among their usual
surroundings. For the nests of these birds are either in evergreen, or
holly, or ivy, or surrounded by the delicate green tints of early spring
vegetation, and may thus harmonise very well with the colours around
them. The great majority of the eggs of our smaller birds are so spotted
or streaked with brown or black on variously tinted grounds that, when
lying in the shadow of the nest and surrounded by the many colours and
tints of bark and moss, of purple buds and tender green or yellow
foliage, with all the complex glittering lights and mottled shades
produced among these by the spring sunshine and sparkling rain-drops,
they must have quite a different aspect from that which they possess when
we observe them torn from their natural surroundings.”
The obvious comment on this is that it is very fine and poetic English,
but it is not science. It is futile to deny what should be obvious to
every field naturalist, namely, that the majority of eggs laid in open
nests are most conspicuous.
D. Dewar thus summarises the main facts which show that eggs in nests (as
opposed to those laid on the bare ground) are not protectively coloured:—
“1. Allied species of birds, even though their nesting habits are very
different, as a rule lay similarly coloured eggs.
“2. Eggs laid in domed nests certainly do not need protective colouring,
yet many of these are coloured.
“3. The same is true of many eggs laid in holes in trees or in buildings.
“4. The protective resemblances of eggs which are laid in the open are
apparent to everyone, which certainly is not true of those deposited in
nests.
“5. Many birds lay eggs which exhibit very great variations.
“6. Some birds lay eggs of different types, and these sometimes differ
from one another so greatly that it is difficult to believe that they
could have been laid by the same species.”[9]
7. It not infrequently happens that one species lays in the disused nest
of another, and the eggs of the latter are often very different in
colouring from those of the former.
We have up to the present considered the theory of general cryptic
colouration, which declares that the majority of creatures are so
coloured as to be inconspicuous. We have still to deal with the
hypothesis of special cryptic colouring.
Certain animals look, when resting, very like an inanimate object, such
as a dead leaf or a twig. This resemblance is said to be the result of
natural selection, since it enables its possessors to escape destruction;
they are seen, but mistaken for something else.
The classical examples of this kind of protective colouring are furnished
by the _Kallimas_ or leaf-butterflies, which display an extraordinary
resemblance to dead leaves.
Other examples are the stick-insects and the lappet moth, which looks
like a bunch of dry leaves. It is needless to multiply instances. In
every work on animal colouration numbers of such cases are cited.
We may grant that in some cases, at any rate, the resemblance is of value
to its possessor, in that it deceives predatory creatures. But it does
not follow from this that the likeness has originated through the action
of natural selection. In order that there can be selection there must be
varying degrees of a tolerable resemblance to select from. How did the
initial similarity arise? This is a matter upon which Wallaceians are
silent. As Poulton truly says, in discussing the degree of protection
afforded by such resemblances, we tacitly endow animals with senses
exactly similar to our own. Are we justified in so doing? Most certainly
not in the case of the invertebrate animals, especially as regards the
arthropods, of which the eyes are constructed very differently from those
of human beings.
D. Dewar has often seen a toad shoot out its tongue and touch a lighted
cigarette end, apparently mistaking it for an insect. Similarly, he has
again and again induced a gecko lizard to chase and try to swallow a
piece of black cotton, one end of which was rolled up into a ball. It is
only necessary to take hold of the unrolled end of the cotton and place
the rolled-up end a few inches from the lizard, and gradually draw it
away in order to induce the lizard to attempt to seize it.
Eyesight of Birds
It would therefore seem that all these elaborate “protective” devices are
unnecessary refinements if regarded as a protection against invertebrate,
reptilian, and amphibian foes. Birds, on the other hand, appear to have
exceedingly sharp eyesight, so that in order to deceive them the
resemblance requires to be very close. Indeed, as regards those birds
which systematically hunt for their prey among leaves and grass, it seems
doubtful whether the alleged “protective” resemblances of caterpillars to
twigs, etc., are sufficient to be of much use to them. Thus Beddard
writes (on page 91 of _Animal Colouration_): “Judging of birds by our own
standard—which is the way in which nearly all the problems relating to
colour have been approached—does it seem likely that we should fail to
see a caterpillar, perhaps as long or longer than the arm, of an
obviously different texture from the branches, and displaying in many
cases through its semi-transparent skin the pulsation of the heart, for
which we were particularly searching?”
Now, birds certainly feed very largely on caterpillars, while they are
but rarely seen to eat butterflies. If, therefore, the aim and object of
these special resemblances is the protection of the species, we should
expect to see them in a nearly perfect state in caterpillars on which
birds feed very largely, and poorly developed in butterflies, which do
not appear to be greatly preyed upon by birds, but have to fear chiefly
the comparatively dull-eyed lizards and mammals, of which the latter hunt
mainly by scent. As a matter of fact, the most striking cases of
resemblance to inanimate objects are seen among butterflies, which seem
to stand least in need of them.
We have already cited the case of the butterfly _Precis artexia_. Even
more marked does the unnecessary elaboration of the likeness seem to be
in the Kallima butterflies.
The Theory of Warning Colouration
All biologists admit that there exist some organisms which are not
coloured so as to be inconspicuous. Indeed, the colouring of certain
species is such as to render them particularly conspicuous. Such species
are said to be warningly coloured. They are supposed to be inedible, or
to have powerful stings or other weapons of defence, or to resemble in
appearance organisms which are thus protected. In the first two cases
they are said to be warningly coloured, and in the last they are cited as
examples of protective mimicry. With the theory of mimicry we shall deal
shortly. We must first discuss the hypothesis of warning colouration.
When animals are unpalatable, or when they possess a sting or
poison-fangs, it is, to use the words of Wallace, “important that they
should not be mistaken for defenceless or eatable species of the same
class or order, since in that case they might suffer injury, or even
death, before their enemies discovered the danger or the uselessness of
the attack. They require some signal or danger-flag which shall serve as
a warning to would-be enemies not to attack them, and they have usually
obtained this in the form of conspicuous or brilliant colouration, very
distinct from the protective tints of the defenceless animals allied to
them” (_Darwinism_, page 232).
Examples of Warning Colouration
For examples of so-called warningly coloured animals, we may refer the
reader to Wallace’s _Darwinism_, Poulton’s _Essays on Evolution_, or
Beddard’s _Animal Colouration_. An instance familiar to all is our
English ladybird. “Ladybirds,” says Wallace, “are another uneatable
group, and their conspicuous and singularly spotted bodies serve to
distinguish them at a glance from all other beetles.”
In order to establish the theory of warning colouration, it is necessary
to prove that all, or the great majority of conspicuously-coloured
organisms, are either unpalatable or mimic unpalatable forms. If this be
so, we are able to understand that the possession of gaudy colouring may
be of advantage to the individual. But even if this be satisfactorily
proved, we must bear in mind that it does not necessarily follow that
these warning colours can be accounted for on the theory of natural
selection. For, in order to explain the existence of any organ by the
action of natural selection, we must be able to demonstrate the utility,
not only of the perfected organ, but of the organ at its very beginning,
and at each subsequent stage of development. This, as we shall show, is
precisely what the Neo-Darwinians are unable to do. We shall have no
difficulty in proving that it would be more advantageous even to a highly
nauseous creature to have remained inconspicuously coloured rather than
to have gradually become more and more conspicuous.
In the first place, let us briefly examine the evidence on which rests
the assertion that all gaudily-coloured insects, etc., are unpalatable,
or possess stings, or mimic forms which are thus armed.
In England wasps, bees, and ladybirds are familiar examples of
conspicuous insects.
The banded black and yellow pattern of the common wasp and the humble bee
are regarded as advertisements or danger signals of the powerful sting.
The red-coat with its black spots is similarly believed to be a warning
that the ladybird is not fit to be eaten.
Caterpillars are usually coloured grey or brown, so as to be
inconspicuous; but numerous exceptions occur which are brightly coloured,
and of these individuals many have been experimentally proved to be
objectionable as food to most insect-eating animals, being either
protected by an unpleasant taste, or covered with hairs or spines.
Familiar cases are those of the abundant and conspicuous black and yellow
mottled caterpillars of the European Buff-tip Moth (_Pygæra bucephala_),
which are much disliked by birds; and the gaily—coloured Vapourer Moth
caterpillar (_Orgyia antiqua_), with its conspicuous tufts of hair.
Readers will remember that a few years back these caterpillars were a
perfect plague in London, in spite of the abundance of sparrows, which
feed freely on smooth green and brown caterpillars.
Oft-cited examples of warning colouration, are the three great groups of
mainly tropical butterflies—the _Heliconidæ_ of America, the _Acræidæ_ of
Africa, and the _Danainæ_ found all over the world. In all of these the
sexes are alike. They are, every one, strikingly coloured, displaying
patterns of black and red, chestnut, yellow, or white. In most
butterflies the lower surface of the wings is of a quiet hue, in order to
render the organism inconspicuous when at rest, but in these warningly
coloured groups the under surface of the wings is as gaudy as the upper
surface. Their flight is slow. They are tough, and exhale a
characteristic odour.
Belt showed that, in Nicaragua, birds, dragonflies, and lizards seem to
avoid the Heliconine butterflies, as the wings of these last are not
found lying about in places where insectivorous creatures feed, whereas
wings of the edible forms are to be found. Moreover, a Capuchin monkey,
kept by Belt, always refused to eat Heliconine butterflies.
Finn investigated the palatability of a number of Indian insects. He
found that most of the birds with which he experimented objected to the
Danaine butterflies; but they disliked still more intensely two
butterflies belonging to groups not universally protected—a swallowtail
(_Papilio aristolochiæ_) and a white (_Delias eucharis_).
Finn further experimented with the tree-shrew or Tupaia (_Tupaia
ellioti_), which feeds largely on insects. He found that this creature
refused most emphatically all these warningly-coloured butterflies. It
would under no circumstances eat the _Danainæ_, whereas the birds would
do so if no more palatable insects were offered to them at the time.
Colonel A. Alcock found that a tame Himalayan bear indignantly refused to
eat a locust (_Aularches militaris_) gaily coloured with black, red, and
yellow, and exhaling an unpleasant-smelling froth; but this bear readily
devoured ordinary brown or green species.
Among cold-blooded vertebrates the common European salamander, with its
bright black and yellow markings, is a striking example of warning
colouration; its skin exudes, on pressure, a very poisonous secretion.
Colonel A. Alcock has described a small siluroid sea-fish, brightly
banded with black and yellow, and armed with poison spines.
A well-known Indian poisonous snake, the banded Krait (_Bungarus
cœruleus_), is conspicuously barred with wide bands of black and yellow;
and in South America there occur numerous species of coral snakes, in
which red is added to these conspicuous colours.
The only known poisonous lizard—the Heloderm of Mexico—is conspicuously
blotched with black and salmon-colour.
Among birds, no instances of warning colouration have been recorded,
though Professor Poulton has suggested that possibly the striking and
contrasted tints of many tropical species may be due to this cause. The
suggestion is an ingenious one, but is at present totally unsupported by
evidence.
The skunks are often cited as an excellent example of warning colouration
among mammals. Skunks are most conspicuously arrayed in black and
white—the latter above, not below, as is usual—and have bushy tails,
which they carry erect. Although less powerful and ferocious than other
members of the weasel family, to which they belong, skunks are
notoriously protected by their abundant secretion of a very fetid liquid.
For further examples of warning colouration we would refer the reader to
Beddard’s illuminating book, entitled _Animal Colouration_.
It should be noticed that in all the cases which we have cited the
colouration is not only conspicuous, but is found in both sexes, whereas
in many undefended animals the male may be just as strikingly coloured,
but the female is not.
We may take it as proved that there is a very general relation between
gaudy colouring and inedibility, or rather unpalatability, among insects.
It may safely be said that any species of insect which lives, either as
an adult or as a larva, in the open will perish in the struggle for
existence if, being conspicuously coloured, it is neither inedible nor
armed with a weapon such as sting, nor provided with a thick cuticle, nor
resembles in appearance some creature which is protected.
Warning Colouring a Drawback
But from this it is not legitimate to conclude, as Neo-Darwinians do,
that these brilliant colours have been slowly brought into being by
natural selection.
Why should any creature, having by the “luck” of variation and heredity
acquired some quality—be it strength, pugnacity, sting, or unpleasant
taste—which renders it comparatively immune from persecution, proceed to
advertise the fact by assuming a gaudy or striking colour? It would
surely be better for such an organism to remain inconspicuous. By
becoming showy it is visible to every young bird who, not having yet
learned that the creature in question is unfit for food, seizes and
perhaps kills it. It is true that the young bird vows that never again
will it touch another such organism. But of what avail to the dying
example of warning colouration is the resolution of the young bird?
Moreover, the organism in question, by being conspicuous, also advertises
itself to those few enemies which will eat it. There are always, as
Professor Poulton justly remarks, animals which are enterprising enough
to take advantage of prey which has at least the advantage of being
easily seen and caught.
Conspicuous Animals Attacked
It is possible to cite cases where animals, notwithstanding the fact that
they possess natural defences, become the prey of others in some
exceptional cases.
The salamander can be eaten with comparative impunity by the toad, a
creature very likely to meet with it.
The toad itself may be eaten; Finn saw the Indian toad (_Bufo
melanostictus_) eat another of its own kind. He further observed that the
Indian water-snake (_Tropidonotus piscator_) and the “Crow pheasant”
cuckoo (_Centropus sinensis_), in the free state, and the Indian Roller
(_Coracias indica_) and the Pied Hornbill (_Anthracoceros_), in
captivity, eat the warningly-coloured toad. On the other hand, a captive
Racket-tailed drongo rejected toads when offered to it. The common cuckoo
is well known to feed on hairy and “warningly-coloured” caterpillars.
Finn has also seen the glossy cuckoo in Zanzibar devouring
black-and-yellow caterpillars. Moreover, in America crows are found to
select deliberately highly polished and strongly flavoured beetles. Yet
again, wasps are preyed upon by bee-eaters, and also eaten by our common
toad. In India, Finn found, by many experiments, that the common garden
lizard, or “bloodsucker” (_Calotes versicolor_), would eat, both in
captivity and in freedom, all “warningly-coloured” butterflies, not only
the _Danainæ_, but even _Delias eucharis_ and the pre-eminently nauseous
_Papilio aristolochiæ_. That this reptile is a great enemy to butterflies
is rendered probable by the frequent occurrence of specimens of these
insects with its semicircular bites in their wings.
Further, Finn found that bulbuls, the commonest garden birds in India,
ate the _Danainæ_ readily in captivity, even when other butterflies could
be had, which was not the case with most other birds. Bulbuls did,
however, usually refuse the _Delias_ and _Papilio_ mentioned above.
The Skunk is preyed upon in America by the Eagle-owl (_Bubo virginianus_)
and the Puma.
Thus, animals provided with natural defences are not immune from attack.
Hence natural selection cannot have encouraged the survival of
individuals which displayed a conspicuous colour, for the sake of the
“warning.”
We must not forget that many creatures armed with powerful weapons
possess the unobtrusive drab, brown, or green colouration which is
associated with concealment from foes.
There can be little doubt that, but for the fact that the hive-bee can
inflict a sting more severe than that of the wasp, this useful insect
would have been cited as a case of a protectively coloured creature.
Notwithstanding its sober brown colouring, the hive-bee is recognised and
avoided.
Professor Poulton records that the dull inconspicuous caterpillar of the
moth (_Mænia typica_) is rejected by reptiles. It must be admitted,
however, that these cases among insects are very rare.
The smooth newt (_Molge vulgaris_), a relation of the salamander, is
protected by a poisonous skin; nevertheless the creature has a dark brown
back and spends most of its time on land. Its black-spotted, yellow
under-surface may have some protective value in the water. Neither the
pike nor the common European water-tortoise will eat this newt.
Toads are nearly all very inconspicuous; nevertheless they are well
protected by the acrid secretion from the skin glands; moreover, they are
both recognised and avoided by those predacious creatures to whom they
are distasteful. Hawks, although as a rule plainly coloured, are
certainly recognised by all other birds. It would seem, therefore, that
“warning colours,” like the similar striking hues of many domestic
animals, are incidental attributes. It has been possible for their owners
to develop them, because for the most part let alone.
Eisig, long ago, pointed out that the brightly coloured pigment in the
skin of these warningly coloured insects is in certain cases of an
excretory nature. Therefore the inference which should be drawn is, as
Beddard points out on page 173 of his _Animal Colouration, “that the
brilliant colours_ (i.e. _the abundant secretion of pigment_) _have
caused the inedibility of the species, rather than that the inedibility
has necessitated the production of bright colours as an advertisement_.”
In other words, Neo-Darwinians put the cart before the horse!
[Illustration: BOURU FRIAR-BIRD]
[Illustration: BOURU ORIOLE]
In some cases these brilliantly coloured insects may be survivals of an
age in which there were no birds. When these came into being and began to
prey upon insects, the conspicuously coloured species which were not
inedible or very unpalatable would soon become extinct, while those that
were inedible would survive as warningly-coloured insects. In other cases
it is not improbable that these warningly-coloured creatures have arisen
by mutations from more soberly-hued insects. It is conceivable that every
now and again a mutation occurs which renders its possessor conspicuous.
This will result in the early destruction of these aberrant individuals
unless their newly-acquired gaudiness is either correlated with, or the
result of, distastefulness.
Aposematic Sounds
In the case of warning colouration, the Neo-Darwinians have, as usual,
pursued their theory to absurd lengths. Professor Poulton, for example,
extends it to sounds and attitudes. “Sound,” he writes, on page 324 of
_Essays on Evolution_, “may be employed as an Aposematic character, as in
the hiss of some snakes and some lizards. Certain poisonous snakes when
disturbed produce by an entirely different method a far-reaching sound
not unlike the hiss. Thus the rattle-snake (_Crotalus_) of America
rapidly vibrates the series of dry, horny, cuticular cells, movably
articulated to each other and to the end of the tail. The stage through
which the character probably arose is witnessed in another genus which
vibrates its tail among dry leaves, and thus produces a warning sound.
The deadly little Indian snake (_Echis carinata_) (‘the Kuppa’) makes a
penetrating swishing sound by writhing the coils of its body one over the
other. Special rows of the lateral scales are provided with serrated
keels which cause the sound when they are rubbed against each other.
Large birds, when attacked, often adopt a threatening attitude,
accompanied by an intimidating sound which usually suggests more or less
closely the hiss of a serpent, and thus includes an element of mimicry. .
. . The cobra warns an intruder chiefly by attitude and by the broadening
of its flattened neck, the effect being heightened in some species by the
‘spectacles.’ In such cases we often witness a combination of cryptic and
Aposematic methods, the animal being concealed until disturbed, when it
instantly assumes a warning attitude.
“The benefit of such intimidating attitudes is clear: a venomous snake
gains far more advantage by terrifying than by killing an animal it
cannot eat. By striking, the serpent temporarily loses its poison, and
with this a reserve of defence. Furthermore, the poison does not cause
immediate death, and the enemy would have time to injure or destroy the
snake.”
Intimidating Attitudes
At first sight this reasoning may seem very convincing. But consider for
a moment the process by which the hiss originated and gradually increased
by natural selection. We must suppose that the rattle-snake was formerly
incapable of making any sound. One day a variety appeared in which the
skin was slightly hardened, so that when the creature moved its body
rapidly there issued a slight sound. This must have caused an enemy to
refrain from attack; it thus lived to transmit this peculiarity to its
offspring, and those which made more noise than their ancestors escaped,
while those that made less succumbed to their enemies. For ourselves, we
find it quite impossible to believe that the rattle was thus gradually
evolved by means of natural selection. Indeed, we are inclined to think
that neither the hiss of the cobra nor its “intimidating attitude” has
any terrifying effect on its adversary. In the case of the cobra we are
able to cite positive evidence that dogs and cattle show no alarm at the
attitude.
“Dogs,” writes D. Dewar of this display, “regard it as a huge joke. Of
this I have satisfied myself again and again, for when out coursing at
Muttra we frequently came across cobras, which the dogs used invariably
to chase, and we sometimes had great difficulty in keeping the dogs off,
since they seemed to be unaware that the creature was venomous.”
Colonel Cunningham writes, on page 347 of _Some Indian Friends and
Acquaintances_: “Sporting dogs are very apt to come to grief where cobras
abound, as there is something very alluring to them in the sight of a
large snake when it sits up nodding and snarling; and it is often
difficult to come up in time to prevent the occurrence of irreparable
mischief.”
Colonel Cunningham also states that many ruminants have a great animosity
to snakes, and are prone to attack any that they may come across.
We may therefore well be sceptical as to the value of intimidating
attitudes to those creatures which are in the habit of striking them.
Mimicry
In a work of this kind it is neither possible nor necessary to consider
in great detail the mass of evidence which has been advanced in favour of
the theory of mimetic resemblance.
Chapters vii. and viii. of Professor Poulton’s _Essays on Evolution_
contain an up-to-date statement of the facts in favour of the theory.
Professor Poulton believes that in all cases mimetic resemblance is the
result of the action of natural selection.
He admits that there is no direct evidence in its favour, but asserts
that “the facts of the cosmos, so far as we know them, are consistent
with the theory, and none of them inconsistent with it” (page 271).
Theory of Protective Mimicry
We are not at all sure that no facts are against the theory of protective
mimicry. We shall presently set forth some which to us seem, if not
actually inconsistent with the theory, at least to point to the
conclusion that the phenomenon may be explained otherwise than as a
product of natural selection.
Evidence for the Theory
Let us first briefly state the case for the theory of protective mimicry.
1. It is asserted that the mimicking species and that which is mimicked
are often not nearly related. For example, the unpalatable larva of the
Cinnabar Moth (_Euchelia jacobaeæ_) is said to mimic a wasp, because it
has black and yellow rings round its body.
“The conclusion which emerges most clearly,” writes Poulton (p. 232), “is
the entire independence of zoological affinity exhibited by these
resemblances.” This is supposed to be proof that Darwin was wrong when he
asserted that the original likeness was due to affinity. Says Poulton:
“The preservation of an original likeness due to affinity undoubtedly
explains certain cases of mimicry, but we cannot appeal to this principle
in the most remarkable instances.”
2. It is asserted that species which are mimicked are invariably either
armed with a sting, well defended, or unpalatable, so that it is against
the interest of insectivorous creatures to attack them. It is further
asserted that the species imitated are “even more unpalatable than the
generality of their order.”
3. It is pointed out that the most distasteful groups of butterflies—the
_Danaidæ_, the _Acræinæ_, the _Ithomiinæ_, and the _Heliconinæ_—consist
of large numbers of species which closely resemble one another. This is
said to be due to Müllerian mimicry. Mayer states that in South America
there are 450 species of inedible _Ithomiinæ_ which display only 15
distinct colours, while the 200 species of _Papilio_, which are edible,
exhibit 36 distinct colours. Nevertheless, he says, there is no lack of
individual variability among the former hence their conservatism as
regards colour cannot be attributed to their having but little tendency
to vary.
4. It is asserted that although in many cases the mimetic resemblances
extend to the minutest detail, nevertheless they are not accompanied by
any changes in the mimetic species except such as assist in the
production or strengthening of a superficial likeness.
Pictures illustrating such cases of mimicry are figured on pp. 241, 247,
and 251 of Wallace’s _Darwinism_ (1890 edition).
5. It is stated that mimetic resemblance is not confined to colour, but
extends to pattern, form, attitude, and movement; that deep-seated organs
are affected when the superficial resemblance is intensified, but not
otherwise. Poulton cites _Clytus arietis_, the “wasp-beetle,” as an
example of this.
6. It is asserted that mimetic resemblances are produced in the most
diverse ways; that the modes whereby the similarity in appearance is
brought about are varied, but the result is uniform.
“A lepidopterous insect,” writes Poulton (p. 251), “requires above all to
gain transparent wings, and this, in the most striking cases that have
been studied, is produced by the loose attachment of the scales, so that
they easily and rapidly fall off and leave the wing bare except for a
marginal line and along the veins (_Hemaris_, _Trochilium_).”
7. It is alleged that the imitator and imitated are always found in the
same locality. If they did not do so no advantage would be derived from
the resemblance. It is further alleged that where the mimicking species
is edible it is invariably less abundant where it occurs than the species
it imitates.
8. It is pointed out that it sometimes happens that where in the mimic
the sexes differ in appearance, the male copies one species, the female
quite a different one. This is said to be because the deception would be
liable to be detected if the mimicking species became common relatively
to that which is imitated. “We therefore find that two or more models are
mimicked by the same species” (_Essays on Evolution_, p. 372).
Occasionally the female mimics two other species, _i.e._ she occurs in
two forms, each like a different species.
It sometimes happens that the female alone mimics. This is said by
Wallace to be due to her greater need of protection. When she is laden
with eggs her flight is slow, and therefore she requires a special degree
of protection.
9. It is said that in some species we find a non-mimetic ancestor
preserved on islands where the struggle for existence is less severe,
while on the adjacent continent mimicry has been developed.
10. It is alleged that in the cases where moths resemble butterflies the
former are either as diurnal as the butterflies or are species which
“readily fly by day when disturbed.”
11. It is asserted that some seasonally dimorphic forms are examples of
mimicry only in one state, in the form that comes into being at the time
when the struggle for existence is most severe; that is to say, in the
dry season, in Africa, when insect life is far less abundant than in the
rainy season.
In other cases the mimicry of the dry-weather form is said to be far more
perfect.
Instances of this phenomenon are set forth in Professor Poulton’s _Essays
on Evolution_.
Alternative Theories
It will be observed that we have quoted very largely from Professor
Poulton’s work. Our reason for so doing is that he appears to be the most
prominent advocate of the theory of protective mimicry, and his work,
which was published in 1908, may be taken as the latest Neo-Darwinian
pronouncement on the subject.
Hence if we can show, as we believe we can, that his arguments are not
sound, we may take it that we have demonstrated that the theory in its
present form is untenable.
It is worthy of notice that Professor Poulton sets forth three other
suggestions which have been proposed as substitutes for natural selection
as an explanation of the phenomena of mimicry.
The first is the theory of External Causes, namely, that the resemblance
is due to some external cause, such as food or climate.
The second is the theory of Internal Causes, which states that mimetic
resemblance is due to internal developmental causes.
The third is the suggestion that sexual selection has caused the origin
of these resemblances.
He then proceeds to demolish these to his own satisfaction, and adds
triumphantly, “The conclusion appears inevitable that under no theory,
except natural selection, do the various resemblances of animals to their
organic and inorganic environments fall together into a natural
arrangement and receive a common explanation” (p. 228).
To reasoning of this description there is an obvious reply. Even if it be
granted that the alternatives to the theory of natural selection as set
forth by Professor Poulton are untenable, it does not follow that natural
selection affords an adequate explanation. If A, B, C and D are charged
with theft and the prosecutor proves that neither A nor B nor C committed
the theft, this will not suffice to secure the conviction of D. It is
quite possible that a fifth person, E, may be the culprit.
Much of the popularity of the theory of natural selection is due to the
fact that biologists have not yet been able to discover a substitute for
it.
It seems to us that the proper method of making progress in science is
not to bolster up natural selection by ingenious speculations, but to
look around for other hitherto undiscovered causes.
[Illustration: KING-CROW OR DRONGO]
[Illustration: DRONGO-CUCKOO]
Objections to the Theory that the so-called Cases of Mimicry owe their
Origin to Natural Selection
It is obvious that for one creature to resemble another can be of little
or no benefit to either until the resemblance is tolerably close. It is,
therefore, insufficient to prove the utility of the perfected
resemblance. We may readily grant this and yet maintain that the origin
of the resemblance cannot be due to the action of natural selection.
The Drongo-cuckoo (_Surniculus lugubris_) displays so great a likeness to
the King Crow (_Dicrurus ater_) that it is frequently held up by
Neo-Darwinians as an excellent example of mimicry among birds. But D.
Dewar writes, on page 204 of _Birds of the Plains_: “I do not pretend to
know the colour of the last common ancestor of all the cuckoos, but I do
not believe that the colour was black. What then caused _Surniculus
lugubris_ to become black and assume a king-crow-like tail?
“A black feather or two, even if coupled with some lengthening of the
tail, would in no way assist the cuckoo in placing its egg in the
drongo’s nest. Suppose an ass were to borrow the caudal appendage of the
king of the forest, pin it on behind him, and then advance among his
fellows with loud brays, would any donkey of average intelligence be
misled by the feeble attempt at disguise? I think not. Much less would a
king-crow be deceived by a few black feathers in the plumage of a cuckoo.
I do not believe that natural selection has any direct connection with
the nigritude of the drongo-cuckoo.”
Darwin was fully alive to this difficulty when he wrote: “As some writers
have felt much difficulty in understanding how the first step in the
process of mimicry could have been effected through natural selection, it
may be well to remark that the process probably commenced long ago
between forms not widely dissimilar in colour” (_Descent of Man_, 10th
Ed., p. 324). Such a statement is of course quite inconsistent with the
Neo-Darwinian position. “The conclusion which emerges most clearly,”
writes Poulton (_Essays on Evolution_, p. 232), “is the entire
independence of zoological affinity exhibited by these resemblances; and
one of the rare cases in which Darwin’s insight into a biological problem
did not lead him right was when he suggested that a former closer
relationship may help us to a general understanding of the origin of
mimicry. The preservation of an original likeness due to affinity
undoubtedly explains certain cases of mimicry, but we cannot appeal to
this principle in the most remarkable instances.”
It is unnecessary to labour this point. It is surely evident to everyone
with average intelligence that, until the resemblance between two forms
has advanced a considerable way, the likeness cannot be of utility to
either, or at any rate of sufficient utility to give its possessor a
survival advantage in the struggle for existence. Until it reaches this
stage, natural selection cannot operate on it. It is therefore absurd to
look upon natural selection as the direct cause of the origin of the
likeness. When once a certain degree of resemblance has risen, it is
quite likely that in some cases natural selection has strengthened the
likeness.
The second great objection to the Neo-Darwinian explanation of the
phenomenon known as mimicry is that in many cases the resemblance is
unnecessarily exact. Even as we saw how the Kallimas, or dead-leaf
butterflies, carried their resemblance to dead leaves to such an extent
as to make it appear probable that factors other than natural selection
have had a share in its production, so do we see in certain cases of
mimetic resemblance an unnecessarily faithful likeness.
The Brain-fever Bird
The common Hawk Cuckoo of India (_Hierococcyx varius_) furnishes an
example of this: “The brain-fever bird,” writes Finn, on page 58 of
_Ornithological and Other Oddities_, “is the most wonderful feather copy
of the Indian Sparrow-hawk or Shikra (_Astur badius_). All the markings
in the hawk are reproduced in the cuckoo, which is also of about the same
size, and of similar proportions in the matter of tail and wing; and both
hawk and cuckoo having a first plumage quite different from the one they
assume when adult, the resemblance extends to that too. Moreover, their
flight is so much the same that unless one is near enough to see the
beak, or can watch the bird settle and note the difference between the
horizontal pose of the cuckoo and the erect bearing of the hawk, it is
impossible to tell them apart on a casual view.” Moreover, the tail of
the cuckoo sometimes hangs down vertically, thus intensifying the
likeness to the hawk.
It is quite possible that the brain-fever bird derives some benefit from
the resemblance; indeed, it has been seen to alarm small birds, even as
the hawk-like common cuckoo frightens its dupes, but, as D. Dewar pointed
out, on page 105 of vol. 57 of the _Journal of the Society of Arts_,
“this is not sufficient to explain a likeness which is so faithful as to
extend to the marking of each individual feather. When a babbler espies a
hawk-like bird, it does not wait to inspect each feather before fleeing
in terror; hence all that is necessary to the cuckoo is that it should
bear a general resemblance to the shikra. The fact that the likeness
extends to minute details in feather marking, points to the fact that in
each case identical causes have operated to produce this type of
plumage.” This conclusion is still further strengthened by the fact that
the likeness extends to the immature plumage, that is to say, exists at a
time when it cannot assist the cuckoo in its parasitical work.
Poulton meets this objection as follows:
[Illustration: SHIKRA HAWK]
[Illustration: HAWK-CUCKOO]
Hypertely
“All such criticism is founded on our imperfect knowledge of the struggle
for existence. The impressions and judgments of man are immensely
influenced by the ‘corroborative detail,’ giving ‘artistic verisimilitude
to a bold and unconvincing narrative.’ Indeed, the laughter which is
invariably raised by this passage from _The Mikado_ is, I have always
thought, not only or chiefly due to the humour of the application, but to
the way in which a great and familiar truth breaks in upon the listener
with all the pleasing surprise which belongs to epigram. Birds, the chief
enemies of insects, are known to have powers of sight far superior to
those of man, and, from our experience of them in captivity, it may be
safely asserted that their attention is attracted by excessively minute
detail. Until our knowledge of the struggle for life is far more
extensive than at present, the argument founded on Hypertely may be left
to contend with another argument often employed against the explanation
of cryptic and mimetic resemblance by natural selection. Hypertely
assumes that there are unnecessary details in the resemblance, that the
resemblance is perfect beyond the requirements of the insect; the second
argument maintains that birds are so supremely sharp-sighted that no
resemblance, however perfect, is of any avail against them. In the
meantime the majority of naturalists will probably reject both extremes,
and believe that the enemies are certainly sharp-sighted and successful
in pursuit, but that perfection in detail makes their task a harder one,
and gives to the individuals possessing it in a higher degree than
others, increased chances of escape, and of becoming the parents of
future generations.” (_Essays on Evolution_, p. 302.)
This long quotation requires careful consideration, since to us it
appears to be typical of the kind of reasoning resorted to by
Neo-Darwinians.
Note the reference to our “imperfect knowledge of the struggle for
existence.” This is almost invariably the last refuge of the
Neo-Darwinian when worsted in argument. We fully admit that there is
still much to be learned of the nature of the struggle for existence, but
such a statement sounds very curious when uttered to those who pin their
faith to the theory which sees in the principle of natural selection an
explanation of all the phenomena of the organic world. Natural selection,
be it remembered, is but a name for the struggle for existence.
Birds capturing Butterflies
“Birds,” says Professor Poulton, “are the chief enemies of insects.” This
may be so. But we greatly doubt whether they are the chief enemies of
butterflies and moths, among which the most perfect examples of mimicry
are supposed to occur.
We have watched birds closely for some years, but believe that we could
almost count on our fingers the cases in which we have seen a bird chase
a butterfly.
Professor Poulton, being aware of this objection, sets forth, on pp.
283-292 of _Essays on Evolution_, the evidence he has gathered in favour
of the view that birds are the chief enemies of butterflies and other
lepidoptera.
As the result of five years’ observation in S. Africa, Mr G. A. K.
Marshall was able to record some eight cases of birds capturing
butterflies. In three cases the butterfly seized was warningly coloured,
or, at any rate, conspicuous! In two of these eight cases the bird failed
to capture its quarry!
Says Mr Marshall, “the fact that birds refrain from pursuing butterflies
may be due rather to the difficulty in catching them than to any
widespread distastefulness on the part of these insects.”
During six years’ observation in India and Ceylon, Colonel Yerbury
records some half dozen cases of birds capturing, or attempting to
capture, insects. He writes: “In my opinion an all-sufficient reason for
the rarity of the occurrence exists in the fact that in butterflies the
edible matter is a minimum, while the inedible wings, etc., are a
maximum.”
Colonel C. T. Bingham in Burma states that between 1878 and 1891 he on
two occasions witnessed the systematic hawking of butterflies by birds,
although he observed on other occasions some isolated cases.
This appears to be the sum total of the evidence adduced by Professor
Poulton as regards the capture of butterflies by birds. This seems to us
an altogether insufficient foundation upon which to build the theory that
the cases of resemblance between unrelated species have been effected by
natural selection.
It is, however, to be noted that probably among birds the most dangerous
enemies of butterflies are not those that habitually catch insect prey on
the wing. Such are experts in the art of fly-catching, and would despise
the comparatively meatless butterfly. One often comes across butterflies
with an identical notch in each wing, which leaves little room for doubt
that those particular butterflies had been snapped at, _while resting_,
by a bird. Among birds the chief enemies of butterflies and moths are
probably to be found in those that hunt for their food in bushes and
trees.
Thus, what we do know of the nature of the struggle for existence offers
but poor support to the Neo-Darwinian explanations of the cases of
so-called mimicry in nature.
Observing-powers of Birds
Professor Poulton’s idea of pitting the argument of Hypertely against
that of the alleged supreme sharp-sightedness of birds is ingenious, but
is not likely to satisfy very many people save those content to live in a
fools’ paradise. If birds are supremely sharp-sighted, and pay attention
to excessively minute detail, the difficulty of accounting for the
_origin_ of protective mimicry on the natural selection hypothesis
becomes all the greater.
The question whether or not birds are good observers is a most
interesting one. Unfortunately, hitherto, but little attention has been
paid to the subject. The evidence available seems to point to the fact
that birds, like savages, have sharp eyes only for certain objects—that
is to say, for the things they are accustomed to look out for. All
observers of nature must have noticed how quick a butcher-bird is to
catch sight of a tiny insect upon the ground at a distance of some yards
from his perch.
On the other hand, it is said that when there is snow upon the ground
wood pigeons will approach quite close to a man wearing white clothes and
a white hat, provided he keep perfectly still. Finn once witnessed in
Calcutta a sparrow pick up a very young toad, obviously by mistake, for
it dropped it at once with evident distaste. Birds of prey are supposed
to have remarkably good eyesight; yet they can readily be caught by a net
stretched out before their quarry. They are not trained to be on the
watch for such things as nets, and so do not appear to notice one when
erected.
It is thus our belief that the very perfection and detail of some
so-called mimetic resemblances are a very serious objection to the theory
of protective mimicry as enunciated by Professor Poulton and other
Neo-Darwinians.
There is yet a further objection to this theory, one which, in our
opinion, is fatal to the hypothesis in its generally accepted form.
A number of cases occur where two species, in no way related, show close
resemblance to one another under such circumstances that neither can
possibly derive any benefit from the likeness. The theory of protective
mimicry is quite unable to explain these cases. This fact leads to a
suspicion that, in the instances where the theory does at first sight
appear to offer an explanation, the resemblance may also be due to mere
coincidence.
We may perhaps call the cases which the theory of mimicry is unable to
account for “false mimicry,” but in so doing we must bear in mind the
possibility that some, at any rate, of the examples of so-called mimicry
may, on further investigation, prove to be nothing of the kind.
“False” Mimicry among Mammals
The Cacomistle of Mexico (_Bassaris astuta_), one of the raccoon family,
has a grey body and long black-and-white ringed tail, just like the
ring-tailed Lemur of Madagascar (_Lemur catta_); both are arboreal and
about the same size, and this lemur’s colouration is exceptional in its
family.
The banded Duiker-buck of West Africa (_Cephalophus doriae_), has the
same very unusual colouration as the thylacine or marsupial wolf of
Tasmania, light brown, with bold black bands across the hinder part of
the back, and the animals are about the same size.
The dormouse of Europe closely resembles a small American Opossum
(_Didelphys murina_), and a larger opossum (_D. crassicaudata_) is very
like the Siberian Mink (_Mustela sibirica_).
The Flying Squirrel of North America (_Sciuropterus volucella_) is
closely copied by the Flying Phalanger (_Petaurus breviceps_) of
Australia.
It will be readily seen that in no one of these cases can the likeness be
of utility to either the “model” or the “copy.”
False Batesian Mimicry among Birds
There are many instances of this phenomenon among birds. The New Zealand
Cuckoo (_Urodynamis tritensis_) shows a far closer resemblance to the
American Sparrow-hawk (_Accipiter cooperi_) than to any New Zealand hawk,
and in fact closely mimics this quite alien bird.
The stormy petrel, a purely oceanic bird, closely resembles in size,
colour, and style of flight the Indian Swift (_Cypselus affinis_), a
purely inland creature; both are sooty black, with a conspicuous white
patch on the lower back.
The Pied Babbling Thrush (_Crateropus bicolor_) of Africa is singularly
like the Pied Myna (_Græulipica melanoptera_) of Java, both being of
about the same size, with white body and black wings and tail quills.
This, we may add, is a very unusual colouration among small birds.
The black-headed Oriole (_Oriolus melanocephalus_) of India is very
similar in appearance to the common Troupial (_Icterus vulgaris_) of
Brazil; indeed, the troupials, a purely American group, are so like the
old world orioles in colour that they usurp their name in America.
The little insectivorous Iora (_Ægithina tiphia_) of India strongly
resembles in size and colour a Siskin (_Chrysomitris colambiana_) from
South America, the males in both being black above and yellow below,
while in the females the black is replaced by olive-green.
Another Indian babbler (_Cephalopyrus flammiceps_), yellowish-green, with
orange forehead, is closely copied by, or copies, the well-known
Brazilian Saffron-finch (_Sycalis flaveola_).
In Fergusson Island, near New Guinea, there is a ground pigeon
(_Otidiphaps insularis_) which is black with chestnut wings, like several
of the powerful ground cuckoos of the genus _Centropus_, but no species
of these cuckoos so coloured appears to inhabit the island.
In Africa there is a tit (_Parus leucopterus_) which has the same very
unusual colouration as an East-Indian bulbul (_Micropus melanoleucus_),
both being black with a white patch on the wing-coverts. These two birds
are about the same size. As showing the purely coincidental character of
such resemblances, we may mention that this same rare pattern occurs
again in our Black Guillemot (_Uria grylle_) and in the Muscovy Duck
(_Cairina moschata_).
We have already quoted Gadow (p. 198) on “false mimicry” among snakes. He
also gives, on p. 110 of _Through Southern Mexico_, an example of this
phenomenon among amphibia. It is, he writes, “impossible to distinguish
certain green tree-frogs of the African genus _Rappia_ from a _Hyla_,
unless we cut them open. If they lived side by side, which they do not,
this close resemblance would be extolled as an example of mimicry.”
We should be very greatly surprised if abundant examples of “false
mimicry” are not found among insects. We trust that this remark will
stimulate some entomologist to pay attention to the subject.
It is the essence of Müllerian mimicry that both model and copy are
immune from attack from enemies. Unfortunately for the theory, similar
resemblances occur among birds of prey, where neither party can benefit
from the association. This gives rise to what we may perhaps call false
Müllerian mimicry. Thus the goshawk and peregrine falcon resemble each
other in being brown above and streaked below in immature plumage, and
having barred underparts and a grey upper plumage when adult.
Theory of Mimicry Criticised
Having stated the more important objections to the theory of protective
mimicry, it now remains for us to deal specifically with each head of
evidence offered in its favour.
1. With regard to the assertion that the model and its copy are often not
nearly related, we have shown that among mammals and birds instances of
resemblance between widely-separated groups occur under such
circumstances that neither party can derive any benefit therefrom.
2. As regards the assertion that species which are mimicked are either
well-defended or unpalatable, this certainly does not hold good with
regard to some at any rate of the coincidental resemblances among birds
which we have pointed out; even if these pairs of similar species lived
in the same country it would require considerable ingenuity to say why
one should mimic the other.
3. As regards the argument that the inedible species of _Ithomiinæ_,
etc., display only fifteen colours, while the less numerous edible
_Papilios_ display more than double this number of colours, we may draw
attention to the fact that those birds which are most immune from attack
are precisely those which display the smallest range as regards colour,
e.g., hawks, owls, crows, gulls, storks, and cranes. As we have already
submitted, no question of Müllerian association comes in here.
On the other hand, the eminently edible families of game-birds and ducks
display great variety of colour, in the males at all events.
4. As regards the statement that although in many cases the mimetic
resemblances extend to the minutest detail, they are not accompanied by
any structural changes except such as assist in the production of a
superficial likeness, we may refer to the case we have already cited of
the New Zealand cuckoo, which, though it so closely copies an American
hawk, is typically cuculine in structure. Here, of course, there can be
no question of advantage to the “mimicking” cuckoo in the resemblances.
5. In answer to the argument that mimetic resemblance extends to form,
attitude, and movement, as well as colour, and that deep-seated organs
are affected only when the superficial resemblance is thereby
intensified, we may draw attention to such cases as the following:—
(_a_) The harmless Indian Snake (_Lycodon aulicus_) is closely similar to
the well-known Krait (_Bungarus cœruleus_), also Indian; but the
resemblance extends to a structural detail which can hardly have mimetic
value—namely, the harmless snake has long, fang-like front teeth, though
these are unconnected with poison-glands. Animals which come into contact
with the krait and its mimic are hardly likely to inspect their teeth.
(_b_) A considerable number of birds of the shrike group—known as
Cuckoo-Shrikes (_Campophaga_)—closely resemble cuckoos in plumage; but
even if they derive any benefit from mimicking birds which are credited
with being mimics already, they cannot profit by the fact that the shafts
of the rump-feathers in both groups are stiffened; this being a
peculiarity which would not be perceptible until the bird was in the
grasp of an aggressor.
(_c_) As a third case of coincidence we may refer to the tubercle in the
nostril of the Brain-fever-bird (_Hierococcyx varius_), as a minute
detail of hawk-like appearance, though not present in the particular
species imitated.
6. The argument that mimetic resemblances are produced in the most
diverse ways, but the result is uniform, loses much of its force when we
consider the various methods by which short-tailed birds appear to have
long caudal appendages.
In the peacock it is the upper tail coverts which are elongated; in the
Stanley Crane (_Tetrapteryx paradisea_) it is the innermost or tertiary
quills of wing; in one of the egrets some of the feathers of the upper
back grow to a great length and form a train; in the Bird of Paradise
(_Paradisea apoda_) the long flank plumes are commonly mistaken for the
tail.
In these cases there can be no question of mimicry.
7. We have shown that the idea that imitator and imitated are always
found in the same area is absolutely fallacious. In birds, for example,
the most striking resemblances appear to occur between species that dwell
far apart.
8. We can cite, as parallel to the case of a mimicking species of which
the male copies one model and the female another, the strange similarity
between the barred brown plumage of the female blackcock and that of the
female eider-duck. The males of these species, although both black and
white, differ greatly in appearance; but the male blackcock is admittedly
very like the male of another species of sea-duck—the scoter.
9. Against the supposed ancestral non-mimetic forms existing on islands
we can pit the “mimetic” orioles in small islands and their non-mimetic
cousins on the mainland. In Australia an oriole of what appears to be an
ancestral style lives beside, but declines to mimic, a friar bird of a
very pronounced type.
10. The case of certain diurnal moths mimicking butterflies appears to be
explicable without the aid of the theory of protective mimicry. When two
species adopt the same method of obtaining food, it not infrequently
happens that a professional likeness springs up between them. Of this the
swifts and swallows afford a striking illustration.
11. As a set-off to the cases where the alleged mimicry is confined to
certain seasons of the year, we may cite the case of the pheasant-tailed
Jaçana (_Hydrophasianus chirurgus_), which in its winter plumage might
easily be mistaken, when on the wing, for the paddy bird or Pond Heron
(_Ardeola grayii_), both being of like size and having a brown back, long
green legs, and white wings. Moreover, they are to be found in the same
localities in India. At the breeding season, however, they are absolutely
different in plumage.
Yet another argument commonly adduced in favour of the theory of
protective mimicry is that local variations of the imitated species are
sometimes followed by the imitator; thus the butterfly _Danais
chrysippus_ shows a white patch on the hind wings in Africa, and this is
followed by its mimic.
But the same thing occurs, quite irrationally, so to speak, among birds.
The peregrine falcon and hobby of Europe are only winter migrants to
India, where they are replaced as residents by the Shaheen (_Falco
peregrinator_) and Indian Hobby (_F. severus_). Both these differ from
the migratory forms by being blacker above and chestnut below, instead of
cream colour. Thus the resemblance occurs in each race. A similar
distinction, as noted by Blyth, exists between the Common Swallow
(_Hirundo rustica_) and the Swallow (_H. tytleri_) of Eastern Asia, the
latter having the whole ventral surface rufous instead of only the
throat. Yet no one will suggest that swallows mimic falcons, or that
there is mimicry between the peregrine and hobby. It is obvious that such
parallel changes occur independently of mimicry.
The Water-rail (_Rallus aquaticus_) and Baillon’s Crake (_Porzana
bailloni_) of Europe are distinguished from their allies of Eastern Asia
by having the sides of the head plain grey, whereas the Eastern Asiatic
forms (_R. indicus_ and _P. pusilla_) have a brown streak along each side
of the face. Here, again, we have an instance of birds of the same family
varying together with geographical distribution.
“Recognition” Colours
One of the prettiest conceits of the Wallaceian school of zoologists is
the theory of recognition markings.
“If,” writes Wallace, on page 217 of _Darwinism_, “we consider the habits
and life-histories of those animals which are more or less gregarious,
comprising a large proportion of the herbivora, some carnivora, and a
considerable number of all orders of birds, we shall see that a means of
ready recognition of its own kind, at a distance or during rapid motion,
in the dusk of twilight or in partial cover, must be of the greatest
advantage and often lead to the preservation of life. Animals of this
kind will not usually receive a stranger in their midst. While they keep
together they are generally safe from attack, but a solitary straggler
becomes an easy prey to the enemy; it is therefore of the highest
importance that, in such a case, the wanderer should have every facility
for discovering its companions with certainty at any distance within the
range of vision.
“Some means of easy recognition must be of vital importance to the young
and inexperienced of each flock, and it also enables the sexes to
recognise their kind and thus avoid the evils of infertile crosses; and I
am inclined to believe that its necessity has had a more widespread
influence in determining the diversities of animal colouration than any
other cause whatever. To it may probably be imputed the singular fact
that whereas bilateral symmetry of colouration is very frequently lost
among domesticated animals, it almost universally prevails in a state of
nature; for if the two sides of an animal were unlike, and the diversity
of colouration among domestic animals occurred in a wild state, easy
recognition would be impossible among numerous closely allied forms.”
As examples of recognition colouration, Wallace cites, among others, the
white upturned tail of the rabbit—a “signal flag of danger,” the
conspicuous white patch displayed by many antelopes, the white marks on
the wing- and tail-feathers of the British species of butcher-birds, the
stone-chat, the whin-chat, and the wheat-ear.
Wallace therefore asserts, firstly, that recognition marks not only help
herbivorous animals to keep together, but act as a danger signal; the
member of a flock which first catches sight of the enemy takes to its
heels, displaying its white flag, which is the signal of danger to the
other members of the flock. Secondly, that recognition marks prevent the
evils of infertile crosses. Thirdly, that the necessity of being able to
recognise one another has rigidly preserved bilateral symmetry among
animals in a state of nature.
As regards assertion number one, we would point out that where a flock of
herbivora is being stalked by a beast of prey, the member of the flock
nearest to the enemy—that is to say, the hindmost member—will probably be
the first to observe him. As that creature will be more unfavourably
situated for escape than the rest of the herd, it will not be to their
advantage to follow the line it has taken. Moreover, being at the rear of
the flock, it is not in a good position to take the lead, and its pursuer
is likely to see the danger signal before its friends do. It would thus
seem that “danger signals,” while possibly sometimes of service to their
possessors, are on the whole ornaments which might profitably be
dispensed with. Natural selection can scarcely be charged with the
production of a character of such doubtful utility to the organism.
Moreover, flourishing species of many gregarious animals do not possess
any “signal flag of danger,” while, on the other hand, a great many
solitary species display markings that render them very conspicuous when
in motion. Take the case of the famous Indian Paddy Bird (_Ardeola
grayii_). This, when at rest, is coloured so as to be very difficult to
distinguish from its surroundings, but flight transforms it, for it then
displays its milk-white pinions, which would make a perfect danger
signal, if only it were not peculiarly solitary in its habits. Its
gregarious brethren, the Cattle Egrets (_Bubulcus coromandus_), on the
other hand, display no danger signal.
Interbreeding of Allied Species
That these recognition marks prevent the intercrossing of allied species
and the production of infertile hybrids appears to be pure fiction. As we
have already shown, hybrids between allied species are by no means always
infertile. Moreover, species which differ only in colour seem usually to
interbreed in those parts where they meet.
“This interbreeding,” writes Finn, on page 14 of _Ornithological and
Other Oddities_, “occurs where the carrion crow (_Corvus corone_) meets
the hooded crow (_Corvus cornix_), where the European and Himalayan
goldfinches (_Carduelis carduelis_ and _C. caniceps_) encounter each
other, and where the blue rollers of India and Burma (_Coracias indicus_
and _C. affinis_) come into contact, to say nothing of other cases.”
Of these other cases, the Indian bulbuls of the genus _Molpastes_ form a
very remarkable one. In all places where two of the so-called species
meet they appear to interbreed, and so freely do they interbreed that at
the points where the allied species run into one another it is not
possible to refer the bulbuls to either species. Thus William Jesse
writes of the Madras Red-vented Bulbul (_Molpastes hæmorrhous_) (page 487
of _The Ibis_ for July 1902): “This bird, although I have given it the
above designation, is not the true _M. hæmorrhous_. I have examined
numbers of skins and taken nests and eggs time after time, and have come
to the conclusion that our type is very constant, and at the same time
differs from all the red-vented bulbuls hitherto described. The
dimensions tally with those given by Oates for _M. hæmorrhous_, while the
black of the crown terminates rather abruptly on the hind neck, and is
not extended along the back, as is the case with _M. intermedius_ and _M.
bengalensis_. On the other hand, as in the two last species, the ear
coverts are chocolate. Furthermore, I may add—although I attach little
importance to this—that the eggs of the Lucknow bird which I have seen
are, without exception, far smaller than my eggs of genuine _M.
intermedius_ from the Punjab. My own opinion is that the Lucknow race is
the result of a hybridisation between the other three species.”
Further, in Bannu, Mr D. Donald saw _M. intermedius_ and _M. leucogenys_
paired at the same nest. That gentleman could not possibly be mistaken on
the point, as the latter species has white cheeks and yellow under
tail-coverts, while the cheeks of the former species are dark-coloured
and the patch of feathers under the tail is red. Similarly, Whitehead and
Magrath, writing of the birds of the Kurram Valley (_Ibis_, January
1909), record that the former shot no fewer than twelve bulbuls, which
undoubtedly appear to be hybrids between these two species. As these
hybrids differ considerably _inter se_, there seems no room for doubt
that they breed with one another and with the parent species.
Symmetry in Nature
Wallace’s third statement, that if the two sides of animals in a state of
nature were alike, easy recognition would be impossible among numerous
closely allied forms, reminds us forcibly of the sad case of the boy
whose tailor was his mother. _Humanum est errare_: she made her son one
pair of trousers that fastened up behind, so that the poor boy when
wearing them never knew whether he was going to or coming home from
school! If animals are able to recognise their mates, their bilateral
symmetry does not seem necessary to enable them to distinguish their
fellows from allied species.
It is, indeed, true that asymmetrically marked animals are very rarely
seen in the wild state, while they are the rule rather than the exception
among domesticated species. But this appears to be due, not to the
necessity of recognition markings in nature, but to the fact that those
animals that display a tendency to massed pigment perish in the struggle
for existence, since this massing of pigment appears to be correlated
with weakness of constitution. In other words, this massing of pigment is
an unfavourable variation, which under natural conditions dooms its
possessor. In the easier circumstances of domestication, animals which
are irregularly pigmented are able to survive, so that, among them, the
almost universal tendency to the massing of pigment can be followed
without let or hindrance.
It is unnecessary to say more upon this subject. The few facts we have
set forth suffice to destroy this particular excrescence on the Darwinian
theory.
The Colouring of Flowers and Fruits
Extremely interesting though the subject be, we are unable to consider at
length the generally accepted theory that the colour markings and
perfumes of wild flowers are the result of the unconscious selection
exercised by insects.
While not denying that many flowers profit by their colouring, that these
colours may sometimes serve to attract the insects, by means of which
cross-fertilisation is effected, we are not prepared to go to the length
of admitting that all the colours, etc., displayed by flowers and floral
structures are due to the unconscious selection exercised by insects. It
is one thing to admit that the colour of its flowers is of direct utility
to a plant; it is quite another to assert that the colour in question
owes its origin and development to natural selection. Our attitude
towards the generally accepted explanation of the colours of flowers is
similar to that which we adopt towards the theory of protective mimicry
among animals. In certain cases we are prepared to admit that the
mimicking organism derives benefit from the likeness; but this, we
assert, is no proof that natural selection has originated the likeness.
Cross- versus Self-fertilisation
The theory that flowers have developed their colours in order to attract
insects to them, and thus secure cross-fertilisation, is based on the
assumption that cross-fertilisation is advantageous to plants. It is
questionable whether this assumption is justified. True it is that
numbers of experiments have been performed, which show that, in many
cases, flowers which are artificially self-fertilised yield comparatively
few seeds. But experiments of this kind do not prove very much.
To place on the stigma pollen from the anthers of the same flower, in
case of a plant which for many generations has been cross-fertilised, is
to subject the plant in question to a novel experience—an experience
which may be compared to transplanting it to another soil. The immediate
effect may appear to be unfavourable, although, if the experiment be
persisted in, the ultimate results may prove beneficial to the plant.
That this is the case with some flowers that are artificially fertilised
is asserted by the Rev. G. Henslow. This observer states, that had Darwin
pursued his investigations further, he would probably have modified his
views regarding the benefits of self-fertilisation. Darwin’s statement
that “Nature abhors perpetual self-fertilisation” seems to be as far from
the truth as that which declares “Nature abhors a vacuum.”
From the mere fact that cross-fertilised flowers yield a greater quantity
of seed than they do when self-fertilised, it does not necessarily follow
that cross-fertilisation is advantageous. The amount of seed produced is
probably not always a criterion as to the advantages of the crossing to
the plant. Some flowers yield most seed when fertilised by the pollen
from flowers belonging to a different species!
It is significant that some plants produce cleistogamous flowers, that is
to say, flowers which invariably fertilise themselves. Such flowers never
open; so that the visits of insects are precluded.
According to Bentham, the Pansy (_Viola tricolor_) is the only British
species of _Viola_ in which the showy flowers produce seeds. The other
species are all propagated by their cleistogamous flowers. The genus
_Viola_ is an advanced species: it would therefore seem that the
production of cleistogamous flowers is an advance on the production of
entomophilous flowers. Cleistogamous blossoms are obviously more
economical.
Insects and Flowers
In the case of the malvas, epilobias and geraniums, where we see, side by
side, races of which the individuals produce insect-fertilised flowers
and those that are characterised by self-fertilised flowers, the latter
are quite as thriving as the former.
The common groundsel, which, according to Lord Avebury, is “rarely
visited by insects,” flourishes like the green bay tree, as many
gardeners know to their cost. The same may be said of the pimpernels. In
this connection it is important to bear in mind that the anemophilous, or
wind-fertilised, angiosperms, as, for example, the grasses, are believed
to be descendants of insect-fertilised or entomophilous forms.
A weighty objection to the theory that the colours of flowers have been
developed because they attract insects has been urged by Mr E. Kay
Robinson, namely, that among wild flowers the most highly coloured ones
are the least attractive to insects.
“Show me,” writes he, on page 222 of _The Country-Side_ for March 20,
1909, “the insect-collector who will seek for specimens among the
brilliant scarlet poppies. Of what use is the dog rose, with its large
discs of pinky-white, to him? On the other hand, does he not find that by
far the most attractive flowers are the almost invisible spurge laurel
blossoms in February and March, the fuzzy sallow catkins in March and
April, the bramble blossom in midsummer, and the ivy’s small green
flowers in autumn? Of these only the bramble has any pretensions to
colour, and if you try, as I have tried, the experiment of picking off
every petal from sprays of bramble blossoms you will find that its
attraction to moths does not appear diminished.
“The fact that insects do visit many conspicuously coloured flowers does
not show that the colour attracts them, when the fact is borne in mind
that they neglect others which are equally coloured, while the flowers
which they particularly haunt are inconspicuous. Conspicuous flowers
_which have abundance of nectar_ attract insects, of course, but so do
inconspicuous flowers which have nectar. If they have no nectar, neither
the conspicuous nor the inconspicuous flowers attract insects other than
pollen or petal eaters, whose visits are not good for the plant. This
shows that the nectar attracts the insects and that the colour of the
flowers makes no difference.”
In autumn many leaves assume bright and beautiful tints. These are not
believed to be in any way useful to the plant. The autumnal hues and
shades are regarded, and rightly regarded, as the garb of death and
decay. Such colours are the result of the oxidation of the chlorophyll or
green colouring matter of the leaves. Why should not the colours of the
petals of the flowers, which wither and fade long before the green leaves
do, be due to a similar cause? The bright colours of fruits are supposed
to have been effected by natural selection in order to attract
fruit-eating animals. Surely a hungry animal does not require that its
food be brightly coloured in order to find it! We must remember that
during the greater part of the year most animals have no occupation save
that of finding their food. Inconspicuously coloured fruits, like those
of the ivy, are frequently eaten by birds. The bright colours of some
ripening fruits are undoubtedly the colours of decay. Many fungi and
seaweeds have bright colours. It is never hinted that these are of any
direct utility to their possessor.
Every flower, every plant, every organism must be of some colour.
Honey
Many flowering plants produce honey. This is said by some botanists to
have been directly caused by natural selection, because the honey
attracts insects. Possibly those who take up this attitude are putting
the cart before the horse. It is probable that honey, like oxygen, is an
ordinary product of the metabolism of the plant, and that the visits of
bees and other insects to such plants are the result rather than the
cause of the honey being there. Boisier found that some plants, for
example, _Potentilla tormentilla_ and _Geum urbanum_, gave honey in
Norway, but very little near Paris.
He further discovered that by supplying certain plants copiously with
water he could induce them to produce more than their normal output of
honey.
As is their habit, Neo-Darwinians have pushed their pet theory to absurd
lengths in its application to flowers. They assert that the visits of
insects are responsible for not merely the general colour of every
flower, but also the various lines, spots, and other markings of flowers.
The lines that frequently occur on the petals are supposed to guide the
insects to the honey! This particular refinement of Neo-Darwinism, to
quote Kay Robinson, “needs little discussion. Insects have very poor
sight. You can see this when a bee or a butterfly flies bang against a
whitewashed wall; when a wasp pounces upon a black spot on a sunlit
floor, mistaking it for a fly; or when a settled dragon-fly will allow
you to poke it in the face with the end of a walking-stick, although it
will be off like a flash if you raise your arm. There is, therefore,
large reason to doubt whether insects can even see the fine lines in the
throats of flowers which are supposed to guide them to the nectar. It is
rather absurd, too, to suppose that such lines can be needed, since
insects come in swarms to inconspicuous and apparently scentless flowers
or to ‘sugared’ tree-trunks in the dark. Where there is nectar, insects
which have come to the feast from a distance need no pencilled lines to
guide them over the last quarter of an inch of their journey.”
Scents of Flowers
Neo-Darwinians further assert that the scents of flowers have been
developed by natural selection because they serve to attract insect
visitors to the flowers. In support of this contention it is urged that
the most highly scented flowers are not usually the most conspicuous
ones, since it is not necessary for a flower to be both highly coloured
and strongly scented. Again, those flowers which open at night are
usually very highly scented.
Plausible though this view seems, there are weighty objections to it.
These are so admirably summarised by Kay Robinson in the issue of _The
Country-Side_ for March 27, 1909, that we feel we cannot do better than
reproduce his words:—
“It is true that many flowers which are strongly scented are visited by
insects, but these flowers have abundance of nectar, and the insects come
in spite of the scent, and not on account of it. They visit unscented
flowers, provided that they have nectar, equally freely; and they do not
visit flowers which have scent without nectar.
“Moreover, fruits are more generally scented even than flowers; but what
explanation have those, who attribute the scents of flowers to the tastes
of insects, for the scents of fruits? Insects which visit fruits are only
robbers. Therefore, if we say that plants have scents for the purpose of
attracting insects, we accuse all plants which have scented fruits of
attempted suicide.
“There are hosts of plants, again, with scented leaves. Here also the
insects are only robbers, and it is quite clear that the scent is not
useful in attracting insects. If, therefore, you adopt the insect theory
to explain the scents of flowers, you must invent entirely new theories
to explain the scents of fruits and leaves.”
It is thus evident that the ordinarily accepted explanation of the
colours, scents, and markings of flowers is far from satisfactory.
Kay Robinson’s Theory
Mr E. Kay Robinson has put forth in recent issues of _The Country-Side_
(March 20, 27, and April 3, 1909) quite a new explanation of the
phenomena, and one which deserves careful consideration. He maintains
that “the real, primary, and original meaning of the colours, markings,
nectar and scents of flowers is not to attract insects, but to deter
grazing and browsing animals.”
“I say,” he writes, “that grazing and browsing animals avoid eating
conspicuous flowers. I have watched a flock of five hundred sheep pass
across a yard-wide strip of close-nibbled turf on the Norfolk coast,
grazing as they passed, and the number of open daisy blossoms after they
had passed seemed the same as before they came. Every one of five hundred
sheep had eaten something from that yard of grass, and not one had eaten
any of the hundred and thirty odd daisies.
“Every summer the farm horses are turned into the same old pasture, and
as the summer wanes the field always presents the same appearance—the
green grass close-grazed, the tall buttercups left standing high.
“Once, leaning over a gate with friends, I pointed out that a flock of
sheep grazing in a sainfoin field were nibbling the greenstuff close, but
were not eating the flowery stalks, when one sheep near us accidentally
pulled up a whole sainfoin plant by the roots and proceeded to munch it
upwards. Inch by inch the stem passed into its jaws, and I began to be
afraid that it was going to establish an ‘exception’ to my rule. But,
just when the bright cluster of pink sainfoin blossom was within two
inches of its teeth, it gave an extra nip, and the flower head fell to
the ground, and the sheep resumed its search for greenstuff.
“I do not say that this would always happen—I should be sorry for any
theory which depended upon the intelligence of a sheep—but it was a very
striking object-lesson to my two companions; and any one who looks around
during this summer with an inquiring mind will find plenty of evidence
that grazing, browsing, and nibbling animals avoid flowers, and stick to
greenstuff when they can get it.
“I do not say that all animals avoid the same flowers. Horses, for
instance, may dislike large flowers like roses and conspicuous yellow
flowers like buttercups, but they will bite off flat clusters of minute
white or pale yellow flowers, such as yarrow or wild parsnip. These
distinctions made by certain kinds of beasts will probably in the future
be found to afford valuable evidence as to the regions of origin of our
flowers and animals. Such plants as the yarrow and the wild parsnip, for
instance, probably did not originate in the home of the wild horse,
because they are not protected against it.
“As a general rule, however, there is abundance of evidence that plants
with conspicuous flowers gain a large advantage in the struggle for
existence, because grazing and browsing animals avoid them; while there
is no real evidence at all that conspicuous flowers attract insects.”
Kay Robinson extends this explanation to the shape, the scent, and the
nectar of flowers. He admits that many flowers are adapted to the visits
of insects, but this is, he asserts, but a secondary result. The “real,
primary meaning” of the shapes of flowers of curious configuration is, he
insists, “a deterrent to grazing or browsing animals.”
According to him plants, like the snap-dragon, which have “blossoms in
the semblance of a mouth,” are avoided by grazing animals, because they
mistake such flowers for mouths, and have no wish to be bitten! Orchids,
he asserts, “are strongly deterrent to grazing and browsing animals,
which are looking for greenstuff, and regard these gaudy, spidery, winged
blossoms as live creatures.” “If this is not the truth,” he asks, “will
any adherent of the theory that we owe the shapes of flowers to insects
explain why some of our common British orchids are so like bees, spiders,
etc.? Some which have no particular resemblance to any insect still
exhibit weird shapes, suggestive to the human mind of living things, such
as lizards, etc. The reason why they look like bees, spiders, lizards,
and various unclassed creatures is quite simple. Grazing animals are
looking for greenstuff, and do not wish to eat living creatures which may
bite or sting or taste nasty. Thus the orchids have acquired the power of
looking like creatures.
“Every one,” he continues, “who is familiar with the blossom of the wild
carrot—a flat head of minute, dull-white blossoms—must have noticed how
very often the centre blossom in each head is purplish or reddish-black.
This makes it very conspicuous in the middle of the flat white flower
head. Now what conceivable use can this barren little blackish
blossom—scarcely bigger than a pin’s head—be to the wild carrot plant if
we regard the flat head of white flowers as an attraction to the sight of
insects? If, on the other hand, we rightly regard the flat head of white
blossoms as an advertisement to grazing animals that it is not wholesome
greenstuff, but innutritious blossoms liable to be infested with ants and
other stinging insects, we see at once the great use of this small
blackish flower in the middle. It looks like an insect, and possibly in
the home of the wild carrot there is some minute blackish insect with a
peculiarly villainous smell or taste—or perhaps a potent sting—which
grazing animals carefully avoid whenever they can see it. Thus the wild
carrot flourishes; though here in Britain—where the wild carrot has
established itself now—we may fail at first to see the exact meaning of
the trick. I think, however, that, when we understand it, it fits
admirably into the theory that the shapes and colours of flowers are
primarily useful as deterrents to grazing and browsing animals and not as
attractions to insects.
“Thus we see,” he concludes, “that the queer shapes of these orchids,
which are a great stumbling-block in the way of those who preach that we
owe the shapes of flowers to the tastes of insects, become a strong
confirmation of my theory that we owe the shapes of flowers to grazing
and browsing animals.”
Of the nectar of flowers, Kay Robinson writes: “Since this is eagerly
sought for by hosts of insects, whose visits are in most cases useful to
the flowers, it seems only natural to suppose that we see cause and
effect in this connection.
“Here, however, I will outline my theory of the origin of nectar and of
flowers in general.
“I think there is no doubt whatever that all the parts of a flower are
modified leaves. The original type of flowering plant—I think we may
safely assume—had a single stem and produced its seed at the summit, as
the crown of its year’s endeavour. The flower, before it became what we
would recognise as a flower, was a cluster of protecting leaves round the
seed-making parts of the plant. To the production of the seed the whole
energies of the plant were devoted, and into the cluster of leaves at the
top of the stem all the essences of the plant were concentrated. If
during the coming spring you handle and examine the leaves at the end of
the strong shoots of thorns or fruit bushes, you will find that the
surface of the young leaves is quite sticky. If you observe browsing
animals also, you will discover that—contrary to expectation—they do not
like strong-growing, juicy shoots, evidently preferring mature leaves
lower down the branch. This shows, I think, that plants have the power of
protecting their new shoots by crowding into them the volatile oils and
essences which they produce as a protection against animals. Now nectar
appears always to be distasteful to grazing and browsing animals; and
they also dislike scented flowers. I think, therefore, that it is
reasonable to suppose that the nectar and scents which now distinguish so
many flowers were first produced as an exudation of concentrated sap upon
the surfaces of the protecting leaves round the seed-making parts of the
original flowers. As these leaves became more efficiently protective by
assuming colours, shapes, and markings which warned animals of their
character, so their apparatus for producing scent and honey became
specialised; and at this point the insect appeared upon the scene as a
factor in the life’s success of the plant.”
Such, then, is Kay Robinson’s bold and original theory. In some respects
it seems far-fetched. The natural inclination is to ask, “Is it possible
that cattle can be so stupid, so blind, as to really believe that a
snap-dragon is the mouth of an animal, or that an orchid is a spider?”
At present we know so little of animal psychology that we are not yet in
a position to give an answer to this question. Horses, we know, are apt
to be frightened by the most harmless things, such as a piece of brown
paper lying on the road. Mr Robinson’s theory should give a stimulus to
the study of the mind of animals—a study which, if properly undertaken,
will probably throw a flood of light upon some of the problems of
evolution. Mr Robinson’s theory equally with the ordinarily-accepted
hypothesis, utterly fails to explain the first origins of colours,
scents, etc. When once a flower has acquired a certain amount of colour,
it is easy to understand how that flower may attract insects or repel
grazing animals. But how can the origin of the colour or other
characteristic be explained?
We asked Mr Kay Robinson how he would account for the great success in
the struggle for existence of some species of grasses on which
herbivorous animals feed so largely. He replied, in the issue of _The
Country-Side_, dated April 3, 1909:—
“The grass has a manner of growth which defies the grazing animal. Its
long, thin leaves are constantly pushing upwards from the ground, and, if
they are grazed down one day, they will have pushed up again the next.
Moreover, when the outside blade of grass has exhausted its power of
growing, there is another blade inside it with many inches still to grow,
and another inside that which has scarcely begun to grow, and yet another
further in which has not yet seen daylight; and so on. In a state of
nature grazing animals are nowhere so numerous on any given patch of
ground from day to day as to keep down the grass. If they were,
carnivorous animals would stay there to eat the grazing animals, and grow
fat and multiply. Thus the grazing herds are scattered and wandering,
followed wherever they go by the beasts of prey; and in their absence the
grass pushes ahead, so that when the grazing animals return its clump is
larger and its roots are stronger, and it is better able to survive
attack than before.
“The method of the clovers and trefoils is quite different. When
circumstances are favourable and enemies few, they will form large-leaved
luxuriant clumps, with fine heads of blossom; but where grazing animals
abound they have the power of adapting themselves to altered
circumstances. They creep so closely along the ground that the teeth of
the grazing animal cannot pick them up between the surrounding grass, and
they produce leaves so small and short-stalked that to eat them would be
like nibbling the pile off velvet. Any clover or trefoil thus growing in
self-defence is accepted as the ‘shamrock’ of Ireland; and it is
certainly a fine emblem for a race which regards itself as surviving in
spite of incessant oppression.
“These are the reasons, however, why the grasses and clovers or trefoils
continue to enrich old pastures when most of the other plants disappear,
with the exception of daisies and buttercups, and the acid sorrels.”
We should be glad to hear how Mr Robinson accounts for the conspicuous
flowers in the species of “prickly pear” (_Euphorbia_), which is so
abundant in India, and which is not browsed upon by animals.
We regret that we are not able to devote more space to this most
interesting theory. We can only add that, even if it fail to become
widely accepted, it is of great value as showing that it is possible to
offer a plausible explanation of a large number of phenomena, which nine
out of ten botanists explain in a very different way.
So satisfied are the majority of naturalists with the “insect theory,”
that they seem of late years to have paid but little attention to the
subject of floral colouration. This affords a striking instance of the
pernicious influence which Neo-Darwinism is exercising on the minds of
men to-day. It tends to stifle research instead of stimulating it.
Accepted Theories Unsatisfactory
We have now dealt with the theory of protective colouration, the theory
of warning colouration, the theory of mimicry, and the theory of
recognition markings. We have shown that although many organisms
undoubtedly derive profit from the fact that they are difficult to see in
their natural surroundings or from their resemblance to other organisms,
the hypothesis that this inconspicuousness or the mimicry of these
animals has been caused by the natural selection of small variations is
untenable.
Warning colours, we have shown, although a disadvantage to their
possessors, are sometimes seen in nature because they are accompanied by
unpalatability. The theory of recognition markings must, we fear, be laid
to rest in the burial ground of exploded hypotheses.
The extreme popularity of the existing theories regarding animal
colouration and their very general acceptance are to be attributed,
firstly, to their simplicity; secondly, to the fact that they have thrown
light on many phenomena which previously had seemed inexplicable;
thirdly, that if we assume, as the great majority of biologists do, that
evolution has been effected by the accumulation of numerous variations,
small in degree and indefinite in direction, we seemed forced either to
accept Neo-Darwinism or admit that the whole subject of animal
colouration baffles us, in other words, to reject what appears like
cosmos and substitute for it chaos.
With a few exceptions, books that deal with the colours of organisms,
while emphasising the evidence in favour of the generally-accepted
theories, seem almost entirely to ignore the host of facts that do not
appear to fit in with them.
This is largely due to the almost unavoidable bias of the human mind when
obsessed by a pet theory. There are none so blind as those who will not
see. It is also, in part, the consequence of the prevalent neglect of the
scientific method of comparison which leads men to theorise on
insufficient evidence. This, of course, is a natural result of
specialisation in biology. Naturalists are in the habit of confining
their study to the habits of the animals of one particular country and
then making far-reaching generalisations therefrom.
As an example of the kind of theorising to which this method leads, we
may cite the often-quoted theory which ascribes the green colouring of
some arboreal fruit-eating pigeons to adaptation to an existence among
tropical foliage, and ignores the fact that in America tree-haunting
pigeons are never of this colour, and that it is not by any means
universal even among the old-world pigeons.
White Down of Nestlings
Similarly, a theory has been advanced (W. P. Pycraft, _Knowledge_, 1904,
p. 275) that the white down of some nestling birds, is an adaptation to
resisting the heat of the sun in open nests. This is at once negatived by
the fact that young owls, usually hatched in shaded places, are also
generally white, while young cormorants, living in open nests, are black;
yet the allied darters, with the same breeding haunts in some cases, have
white young. Lest it should be thought that black has some especial value
in a nestling living exposed, we may mention that young petrels, which
are born in holes, have black or dark down.
As we have already pointed out, naturalists in too readily accepting the
theory that variation is minute in degree and indefinite in direction,
have raised quite unnecessary difficulties, even for the selection
hypothesis. We have cited certain facts, which seem to show that
variations, as a rule, are not indefinite in direction; of these the most
striking is furnished by birds in which the tail feathers are greatly
elongated. Were variations indeterminate, we might reasonably expect to
find that the elongation occurred in one particular feather or pair of
feathers in one species, in another pair in a second species, in a third
pair in a third species, and so on. But this is not the case; no bird has
one _single_ long feather in its tail, and when two are elongated, as is
so commonly the case, these are almost invariably the middle or the
outside pair; _e.g._, in the European bee-eater and pheasant it is the
former, in the swallow and blackcock, the latter.
Exceptions are so rare that they may almost be said to prove the rule;
_e.g._, although most terns have the outer-tail feathers elongated, in
some of the Noddy Terns (_Anous_, _Gygis_) the third pair, in others the
fourth pair, of tail feathers are the longest. This must mean one of two
things, either that the variation, as regards length in tail feathers,
other than middle or outer, does not ordinarily occur, or that it occurs,
but is, in some way, inimical to the welfare of the species. The latter
hypothesis does not seem probable, as the Noddies are particularly
abundant birds where they occur, that is to say, in the tropical seas;
therefore, we can only conclude that that particular variation has not
occurred in birds as a whole.
We have adduced abundant evidence to show that mutations or discontinuous
variations occur in nature; and as these afford much more favourable
material on which natural selection can act, it is reasonable to suppose
that they have played a considerable part in evolution.
When discussing the phenomena of inheritance, we attempted to show that,
not improbably, these discontinuous variations are due to some
re-arrangement in the constituent parts of the unit characters, or
biological molecules, as we have called them.
Cranes
In this connection we may mention the apparently singular phenomenon of
different species in the same natural group, exhibiting either a definite
excess or deficiency of plumage on the head. Among cranes, most species
are more or less bald; but the Demoiselle (_Anthropoides virgo_) has a
fully-feathered head with long side-plumes, while the head of the Stanley
Crane (_A. paradisea_) appears to be swollen, so abundantly is it
feathered. The crowned cranes, although bare-cheeked, have double crests,
the two parts of which have been respectively compared to a pen-wiper and
a bunch of toothpicks!
Among the guinea-fowls, several species are crested, while others, as,
for example, the domestic one, are bare-headed. Now, on the theory of
evolution, by accumulation of minute variations, phenomena such as these
are difficult of explanation; but, on the assumption that a slight
rearrangement of the biological atoms in the molecule may produce very
diverse results, as we see in the case of chemical molecules, and of
seasonally dimorphic butterflies, there is no particular ground for
surprise at such a phenomenon.
In this connection we may cite the significant fact, so well known to
canary breeders, that two crested birds when mated tend to produce a
bald-headed one.
If the colour of any part of an organism be due to the internal
arrangement of the constituent parts of the biological molecule from
which it is derived, we should expect any rearrangement of the component
parts to produce quite a different colour. In other words, we should
expect occasionally to see colour-mutations. These are precisely what we
do see. Similarly, if the scheme of colouring of an organism be due to a
certain grouping of biological molecules, we should expect the same
scheme of colouring to occur in organisms which are not nearly related.
This, too, we observe in nature.
Many of the phenomena of mimicry, and all the cases which we have cited
as pseudo-mimicry, seem to us to be referable to this.
Magpie Colouring
Take, for example, the magpie colouration in birds—that is to say, a
scheme of colouring in which the body is white, and head, wings, and tail
black. This occurs in the following birds belonging to the most diverse
groups:—
The Magpie.
The Magpie Tanager (_Cissopis leveriana_).
The Magpie Robin (_Copsychus saularis_), cock only; in the hen the black
is replaced by brownish grey.
The Pied Honeyeater (_Entomophila picata_).
The Chaplain Crow (white-bodied form of the hoodie crow).
The New Ireland Swallow Shrike (_Artamus insignis_).
The Magpie Goose (_Anseranas melanoleucus_).
Combinations of this kind, in which the black is replaced by brown or
grey, are excessively rare.
On the other hand, we see in several birds the combination in which the
white is replaced by yellow:—
The Common Troupial (_Icterus vulgaris_).
The Black-headed Oriole (_Oriolus melano cephalus_).
The Black-and-yellow Grosbeak, male only.
What we may call imperfect magpie colouration, _i.e._ where the head
becomes white, occurs in several species of birds. The head of a black
species sometimes becomes white as a mutation; in the domestic Muscovy
duck, for example, an individual is sometimes produced having a white
head, although the black of the remainder of the plumage remains
unchanged.
As examples of this scheme of colouration we may cite—
Black-and-white Fruit Pigeons (_Myristicivoræ_).
Several Gannets (_Sula capensis_, _S. serrator_, etc.)
Swallow-tailed Kite (_Elanoides furcatus_).
Several Storks (_Euxenura maguari_, _Anastomus oscitans_, _Pseudotantalus
cinereus_).
Moreover, a common variety of the barn-door fowl has also a white body
and black primaries and tail, showing that this scheme of colour may
arise as a mutation.
A further elimination of black in the tail and body leads us to white
birds with more or less black wings:—
White Storks (_Ciconia alba_, _C. boyciana_, and _Euxenura maguari_).
The White Crane (_Grus leucogeranus_).
The Snow Geese (_Chen nivalis_, _C. rossi_).
The Common Gannet (_Sula bassana_).
The White Buzzard (_Leucopternis_).
The Scavenger Vultures (_Neophron_).
A recurring combination in mammals is black, with a white marking on the
breast.
Most of the bears, even young brown bears, show a tendency to this. It is
also found in the Tasmanian devil, and in varieties of our domestic cats,
rats, and dogs; also in the domestic duck.
The white-spotted pelage, not uncommon in deer, especially fawns, is
curiously repeated in the Australian carnivorous marsupials, known as
Native Cats (_Dasyurus_).
In domestic animals we frequently find the following localisation of
white—white socks, collar, breast, and muzzle. The arrangement occurs in
cats, dogs, rabbits, guinea-pigs and mice, also in the horse and pig, but
without the collar. The arrangement is not seen in goats, cattle, or
sheep, nor in wild animals of any kind. This would lead to the conclusion
that the combination is correlated with some character unfavourable to
survival under natural conditions.
Many variations which frequently occur among both wild and domestic
animals do not persist in nature.
Albinos
As instances of such variations we may mention pure albino forms, that is
to say those in which pigment does not occur in the eyes.
It is easy to see why this variation is not allowed to persist in nature.
Its possessors are handicapped by bad eyesight, and so have no chance of
surviving in the struggle for existence. It is thus that natural
selection acts. On the other hand, white species with pigmented eyes are
fairly numerous. These enjoy normal eyesight, but labour under the
disadvantage of being easily seen by their foes. Hence we find that white
species generally either occur in a snowy habitat, or are powerful and
both able and ready to defend themselves. In this connection it is
interesting to notice that in New Zealand all birds, whether introduced
or indigenous, are particularly liable to albinism. Owing to the fewness
of their enemies these albinistic forms are able to persist.
A variation, or rather a mutation, that frequently occurs among
domesticated birds, but which is seen in very few wild species, is that
which takes the form of white primary feathers on the wing. This
variation must often occur in nature, but it rarely establishes itself,
apparently because white feathers do not resist wear so well as coloured
ones do.
Biological Molecules and Colour
Black-and-yellow colouration occurs in several widely separated species
of birds. The arrangement of the two colours follows to some extent the
same rules as the black-and-white combination.
Several birds have a yellow body with black head, wings, and tail, such
as—
The Black-headed Oriole (_Oriolus melanocephalus_).
The Black-and-Yellow Grosbeaks (_Pycnorhamphus icteroides_, _P. affinis_)
(cock).
The Common Troupial (_Icterus vulgaris_).
In others the black on the head is nearly or quite suppressed, that on
the tail remaining to a greater or less extent; such are—
The Golden Orioles (_Oriolus galbula_, _O. kundoo_, etc.).
Several species of _Icterus_.
Several fly-catchers of the genus _Piezorhynchus_ (males only).
[Illustration: BRAZILIAN TROUPIAL]
[Illustration: INDIAN BLACK-HEADED ORIOLE]
We have said sufficient to show that certain combinations of colours
recur in nature in species which are neither nearly related to one
another nor subjected to similar environment. For such phenomena it is
difficult, if not impossible, to account on the theory that natural
selection, acting on minute variations, is responsible for all the varied
colouring of the animal kingdom. The facts, however, are in accordance
with the supposition that the organism is the result of the growth and
development of a number of units or biological molecules which exist in
the fertilised egg.
If there be any truth in the supposition, the colouration of every animal
must be due to the development of one or more of these molecules.
Colouration may be expression of the arrangement of all the molecules in
the fertilised egg, or it may be due to the development of a number of
molecules whose function is to determine the colouring of an organism, or
it may be the result of the development of one such molecule, which
perhaps splits up in such a way that a portion attaches itself to each of
the other molecules.
But it is idle to speculate on this point. As we have already insisted,
the tendency to build up elaborate theories on very slender foundations
is a too frequent failing of zoologists. We desire merely to emphasise
the fact that the phenomena of animal colouration almost force us to the
conclusion that the colouring of each organism is the result of the
development of a number of units.
It may be objected that, if this be the case, the number of the units
which contribute to the colour of any organism must be exceedingly large,
since we see in nature an almost limitless number of different schemes of
colouring. If the colour of each animal be the result of the development
of a few units, it might be thought, firstly, that the diversity of
schemes of colouration which we observe in nature could not possibly
occur; and secondly, that, under such circumstances, the colour pattern
of a bird or beast should be of the nature of a mosaic, each colour being
sharply defined and separated from every other colour, instead of the
colours shading one into the other, as is so frequently the case.
Such objections would be based on a misconception as to the nature of the
units which combine to produce the colouration of an organism. _These
units show themselves as centres of development of colour_, as points
from which the colour or colouring they represent spreads, until it meets
and mingles with other patches of colour which are being developed from
other centres. The colour produced at one centre may spread more rapidly
than that which forms at another; this, of course, will result in a
preponderance in the organism of the colour which is produced at the
former centre.
Further, we must bear in mind that the development of each
colour-producing unit is largely affected by conditions external to it,
as we shall see when dealing with Sexual Dimorphism.
More than one naturalist, who has paid careful attention to the subject
of animal colouration, has perceived that through the apparently endless
diversity of the colouring of organisms something like order runs.
Mr Tylor Quoted
Over thirty years ago Mr Alfred Tylor called attention to this important
fact. That observer, whose views met with the approval of Wallace, was of
opinion that colour follows structure, and that in a many-hued animal it
changes at points where the function changes.
“If,” writes Mr Tylor, “we take highly decorated species—that is, animals
marked by alternate dark or light bands or spots, such as the zebra, some
deer, or the carnivora, we find, first, that the region of the spinal
column is marked by a dark stripe; secondly, that the regions of the
appendages, or limbs, are differently marked; thirdly, that the flanks
are striped or spotted, along or between the regions of the lines of the
ribs; fourthly, that the shoulder and hip regions are marked by curved
lines; fifthly, that the pattern changes, and the direction of the lines,
or spots, at the head, neck, and every joint of the limbs; and, lastly,
that the tips of the ears, nose, tail, and feet, and the eyes are
emphasised in colour.”
More recently Mr J. Lewis Bonhote has devoted much attention to this
important subject. The results of his researches are summarised on page
185 of vol. xxix. of the _Proceedings of the Linnæan Society_, and on
page 258 of the _Proceedings of the Fourth International Ornithological
Congress_, 1905. Mr Bonhote states that the presence or absence of colour
tends almost invariably to make its appearance, first of all, on certain
definite tracts, common to mammals and birds alike, which he calls
_pœcilomeres_.
Pœcilomeres
“Pœcilomeres,” he writes, “are situated on the following parts, viz.,
chin, malar stripe, maxillary stripe, a spot above and slightly in front
of the eye, a spot below or slightly behind the eye, the ear, crown of
the head, occiput, fore-end of sternum, vent, rump, thighs, wrist,
shoulders (above and below).
“Now, there is hardly any species of bird on which one or more of these
pœcilomeres is not ‘picked out’ (to use a painter’s expression) in some
colour different from that of the surrounding parts, and, in fact, most
of the so-called recognition or protective markings will be found on
these patches.
“On the other hand, among many species the differentiation of colour on
the pœcilomeres is not so conspicuous as to attract the eye or to serve
in any way for protection or mimicry, _yet we still find them marked by
differences of colour so slight that, unless especially looked for, they
would never be noticed_.
“Or, again, some species occasionally, but not invariably, show a few
white feathers on certain parts of their body, and, when such is the
case, it will be found that these white feathers appear on the
pœcilomeres. . . . There is hardly a species in which examples of these
pœcilomeres may not be found. . . . The Kingfisher (_Alcedo ispida_)
shows the various head pœcilomeres very clearly, and as examples of
inconspicuous differences on these tracts, the rump of the hen sparrow
(_Passer domesticus_) and hen chaffinch (_Fringilla cœlebs_), the malar
stripe and dark ear-patch of the hen Yellow Bunting (_Emberiza
citrinella_), and the dark ante-orbital patch of the Barn Owl (_Strix
flammea_) are familiar examples. And, lastly, as an instance of the class
where a few white feathers frequently, but not invariably, appear, the
young of the cuckoo (_Cuculus canorus_) forms a good example.
“These spots may, however, appear in a transitory manner, as, for
instance, where a change of plumage (not necessarily moult) is
occurring.”
As an instance of this, Bonhote cites the case of a young male Shoveler
(_Spatula clypeata_), “in which the metallic colour on the head first
showed itself on the post-orbital and auricular pœcilomeres, gradually
meeting and joining up across the head with the crown and occipital
pœcilomeres, and then finally spreading forwards. And it may be well to
note that the joining up of the auricular and post-orbital pœcilomeres
formed a metallic patch similar in size and position to that found in the
male Teal (_Querquedula crecca_), and, further, in the last stage, when
the whole head, except the portion round the beak, was metallic, the
markings are similar to those found permanently in the hen Scaup
(_Fuligula marila_).
“Now, these resemblances taking place in the normal pure-bred wild
shoveler, the question of reversion does not come in, and no one would
suppose these resemblances due to anything more than transitional
variation, and it is the object of this portion of the paper to show that
variation in colour follows along definite lines.”
Biological Molecules
Mr Bonhote continues: “As a further illustration of how widely spread
these lines are throughout the mammalian and avian kingdoms, we may note
the assumption of the brown head in the case of the Black-headed Gull
(_Larus ridibundus_), which invariably follows each year on lines similar
to those related in the case of the shoveler, and . . . the method by
which, on the approach of winter, the stoat assumes his white dress, is
(although the change is from brown to white) again conducted along
precisely similar lines.” Mr Bonhote argues with great force that, as the
process occurs in two animals so widely separated, the fundamental cause
must be a deep-seated one. There can be no doubt that these pœcilomeres
of Bonhote are connected with our biological molecules. Each of these
pœcilomeres is the result of the development of one of these unit
characters; each is to be regarded as the centre of activity, the sphere
of influence of a biological molecule, or the portion of one, which
controls the colouring of a definite region of the organism. In the case
of creatures which display the same colour throughout, these molecules
all give rise to the same kind of colouring; in the case of animals which
display a variety of colours and markings the various molecules give
origin to various colours. But we must bear in mind that the final colour
to which each colour-producing molecule gives rise depends to some extent
on circumstances other than the constitution of the molecule. Thus it is
that the young in most organisms differ in colour and marking from the
adults. On this also depends the phenomena of seasonal and sexual
dimorphism. The same colour-producing molecule may give rise to one
colour under one set of conditions and to a totally different colour
under another set of conditions.
It is a significant fact that under abnormal conditions the feathers of
birds tend to disappear precisely on those spots where the pœcilomeres of
Bonhote occur.
Thus in a sickly cage bird the feathers frequently show a tendency to
fall off on the following spots: crown of head, lores, jaws, head
generally, rump, vent and thighs.
Many wild birds—as, for example, the cranes—display patches of naked skin
on the head, and these are usually situated on pœcilomeres. Similarly,
natural excessive developments of plumage tend to occur on the
pœcilomeres, or, rather, the spots characterised by pœcilomeres—for
example, the train of the peacock. Loral plumage, it is true, is seldom
long, but is often of a peculiar nature.
Colour mutations tend to occur on the pœcilomeres. Thus it is that these
pœcilomeres often form the distinctive characters and markings of allied
species. This is precisely what we should expect if the pœcilomeres
correspond to biological molecules and mutations are the result of the
rearrangement of the constituent parts of these molecules.
Still more significant is the fact that the colour-markings in hybrids
tend to follow pœcilomeres.
Bonhote has performed a large number of experiments in hybridising ducks.
Some of his hybrids were produced from three pure ancestors, as, for
example, the pintail, the spotbill, and the mallard; others from two
ancestors. Some of these hybrids were crossed with other hybrids, and
others with the parent forms, hence Bonhote secured a number of hybrids,
each of which had a distinctive appearance; but _all_ the variations
appearing among the hybrids were found to start on one or more of the
pœcilomeres.
Certain of the hybrids showed a resemblance to one or other of the parent
species, others were unlike either parent, and resembled either no known
species or species other than their parents.
When a hybrid shows a resemblance to a species other than that to which
either parent belongs, it is said to exhibit the phenomenon of atavism or
reversion,—the individual is supposed to have been “thrown back” to an
ancestral form.
The true explanation of the phenomenon would seem to be that, as the
result of the crossing, biological molecules in the fertilised egg have
been formed which, on development, give rise to combinations of colour
like those seen in other species.
Thus the phenomena of “mimicry” and “reversion” are, we believe, due to
the fact that in the fertilised egg of both the pattern and its copy a
similar arrangement of biological molecules obtains. If we regard the
sexual act as resembling in many respects a chemical synthesis, the
phenomenon need not surprise us.
To sum up, the observed facts of animal colouration seem to indicate that
there are in each organism some twelve or thirteen centres of colouring,
which we suggest may correspond with portions of the fertilised egg. From
each of these centres the colour develops and spreads, so that every part
of the organism is eventually coloured. These centres of colouring are
not altogether independent of one another. Sometimes they all give rise
to the same hue, in which case we have a uniformly-coloured organism,
such as the raven. More often from some one colour develops, and from
others another colour; if these two colours happen to be black and white,
the result is a pied organism, which displays a definite pattern due to
the correlation of the various colour-producing biological molecules.
Thus it occasionally happens that two widely different organisms exhibit
very similar markings, and therefore resemble one another. When this
resemblance is believed to be of advantage to one or other of the
similarly-coloured species, naturalists call it mimicry, and assert that
the likeness is due to the action of natural selection; but where neither
organism can profit by the resemblance, zoologists make no attempt to
explain it. What we suggest is that the colouration of an animal depends
upon the structure, or, at any rate, the nature, of the parts of the egg
which produce these centres of colour. But this is not by any means the
only cause that determines the colouration of the organism. If it were,
young creatures in their first plumage would invariably resemble the
parents, the two sexes would always be alike, and there would be no such
phenomenon as seasonal dimorphism.
As a matter of fact, the portions of the egg (we call them, for the sake
of clearness, colour-producing biological molecules) which give rise to
the pœcilomeres exhibit themselves merely in the shape of tendencies; the
ultimate form the colouring will take depends to a large extent upon
other and extraneous circumstances, such as the secretion of hormones.
Thus it is that organisms seem to display an almost endless diversity of
colouration. But beneath all this diversity we see something like order.
It occasionally happens (_why_, we do not know) that one, or more, of the
biological molecules which make up the nucleus of the fertilised ovum
becomes altered in the sexual act, with the result that a discontinuous
variation or mutation appears in the resulting organism. The mutation may
be a favourable one, or one which does not affect in any way the chances
of an organism in the struggle for existence, or an unfavourable one. In
the last of the three cases the organism will perish early and not leave
behind any offspring exhibiting its peculiarity.
It is thus that natural selection acts. Natural selection weeds out
relentlessly all organisms which display unfavourable variations. It is
thus obvious that many species may, and we believe do, exist which
possess characters of no direct utility to them, or even slightly harmful
ones. For this reason Wallace and his followers fail in their attempts to
prove that every patch of colour in every organism is of direct utility.
Natural selection has to take an animal as it finds it—the good with the
bad. If an organism as a whole is not wanting—that is to say, if it is
able to hold its own against other organisms, and is fitted to fill any
place in nature—that organism will probably survive, although it may be
defective in many respects. As its name implies, natural selection is a
mere selecting agency. It has to choose from what is presented to it. It
is not, as many seem to think, a manufacturer or inducer of variations.
Natural selection can no more _make_ an animal vary in any given
direction than the human breeder can. Its power is limited to the
destroying of all variations which do not pass the test prescribed by it.
CHAPTER VII
SEXUAL DIMORPHISM
Meaning of the term—Fatal to Wallaceism—Sexual Selection—The law of
battle—Female preference—Mutual Selection—Finn’s experiments—Objections
to the theory of Sexual Selection—Wallace’s explanation of sexual
dimorphism stated and shown to be unsatisfactory—The explanation of
Thomson and Geddes shown to be inadequate—Stolzmann’s theory stated and
criticised—Neo-Lamarckian explanation of sexual dimorphism stated and
criticised—Some features of sexual dimorphism—Dissimilarity of the
sexes probably arises as a sudden mutation—The four kinds of
mutations—Sexual dimorphism having shown itself, Natural Selection
determines whether or not the organisms which display it shall survive.
In some species the sexes are so similar in appearance that it is not
possible to tell by mere outward inspection to which sex a given
individual belongs.
In other species the sexes differ so widely in external appearance that
it is difficult to believe that the male and the female belong to the
same species. Between these two extremes are a great number of species in
which the sexes are more or less dissimilar. Those species in which the
sexes differ in appearance are said to be sexually dimorphic. The
phenomena of sexual dimorphism are fatal to that form of Neo-Darwinism
which sees in natural selection an explanation of all the peculiarities
of animal structure and colouration.
It is not easy to understand how natural selection can have caused marked
sexual dimorphism in a species where the habits of the sexes are the
same, in the Paradise Flycatcher (_Terpsiphone paradisi_), for example,
where the cock and the hen obtain their food in the same way, and share
equally the duties of nest-building, incubation, and feeding the young.
Of course, in all species where each individual carries only one of the
two kinds of sexual organs, there must of necessity be some slight
difference between the individuals that carry the male organ, which
performs one function, and those that carry the female organ, which
performs another function.
But in many species the sexes display differences which have no direct
connection with the generative organs—for example, the deer, where the
stag alone has horns.
Those characters which differ with the sex, but are not directly
connected with the organs of reproduction, are known as secondary sexual
characters.
[Illustration: QUEEN WHYDAH]
Theory of Sexual Selection
In nearly all species where the male and female differ in beauty, it is
the male who surpasses the female. Natural selection is, in many cases,
not able to explain the origin of these differences, or why, when they
occur, the male should be more beautiful than the female. This Darwin
saw. In order to account for the phenomena of sexual dimorphism, he
formulated the theory of sexual selection. This hypothesis is based on
the assumption that there is, in all species of animals, a competition
among the males to secure females as mates. It is not difficult to
understand how this competition arises in polygamous species. Assuming
that approximately equal numbers of males and females are born (an
assumption which appears to be justified as regards the majority of
species), it is clear that for every male who secures more than one wife,
at least one male will be obliged to live in a state of single
blessedness.
But how can there be competition in the case of monogamous species? The
sexes being approximately equal in number, there are sufficient females
to allow of a mate for every male.
The Law of Battle
Such is the nature of things, said Darwin, that, even under these
circumstances, there is competition among the males for females.
“Let us take any species,” he writes, on page 329 of _The Descent of Man_
(Ed. 1901), “a bird for instance, and divide the females inhabiting a
district into two equal bodies, the one consisting of the more vigorous
and better-nourished individuals, and the other of the less vigorous and
healthy. The former, there can be little doubt, would be ready to breed
in the spring before the others; and this is the opinion of Mr Jenner
Weir, who has carefully attended to the habits of birds during many
years. There can also be no doubt that the most vigorous, best nourished,
and earliest breeders would on an average succeed in rearing the largest
number of fine offspring. The males, as we have seen, are generally ready
to breed before the females; the strongest, and with some species the
best armed of the males, drive away the weaker; and the former would then
unite with the more vigorous and better-nourished females, because they
are the first to breed. Such vigorous pairs would surely rear a larger
number of offspring than the retarded females, which would be compelled
to unite with the conquered and less powerful males, supposing the sexes
to be numerically equal; and this is all that is wanted to add, in the
course of successive generations, to the size, strength, and courage of
the males, or to improve their weapons.”
From this competition among the males there arise, firstly, contests
between the males for mates; secondly, the preference of the females for
favoured males.
It is a matter of common knowledge that at the breeding season the males
of nearly all, if not all, species are very pugnacious. Two males often
engage in desperate fights for one or more females; the victor drives
away his foe and secures the harem. In such contests the stronger male
wins, and thus emerges that particular form of sexual selection which
Darwin termed “the law of battle.”
“There are,” writes Darwin, on page 324 of _The Descent of Man_, “many
other structures and instincts which must have developed through sexual
selection—such as the weapons of offence and the means of defence of the
males for fighting with and driving away their rivals—their courage and
pugnacity—their various ornaments—their contrivances for producing vocal
or instrumental music—and their glands for emitting odours.” The former
characters have, according to Darwin, been developed by the law of
battle, and the latter, since they serve only to allure or excite the
female, by the preference of the female.
“It is clear,” continues Darwin, “that these characters are the result of
sexual and not of ordinary selection, since unarmed, unornamented, or
unattractive males would succeed equally well in the battle for life and
in leaving a numerous progeny, but for the presence of better-endowed
males. We may infer that this would be the case, because the females,
which are unarmed and unornamented, are able to survive and procreate
their kind. . . . Just as man can improve the breed of his game-cocks by
the selection of those birds which are victorious in the cockpit, so it
appears that the strongest and most vigorous males, or those provided
with the best weapons, have prevailed under nature, and have led to the
improvement of the natural breed or species.”
Selection by Females
“With mammals,” says Darwin (_loc. cit._, p. 763), “the male appears to
win the female much more through the law of battle than through the
display of his charms.”
In the case of birds, however, feminine preference comes more into play.
It is well known that cocks display their charms to the hens at the
breeding season, and Darwin believed that the hen selected the most
beautiful of her rival suitors.
“Just as man,” he writes (p. 326 of _The Descent of Man_, new edition,
1901), “can give beauty, according to his standard of taste, to his male
poultry, or, more strictly, can modify the beauty originally acquired by
the parent species, can give to the Sebright bantam a new and elegant
plumage, an erect and peculiar carriage, so it appears that female birds
in a state of nature have, by a long selection of the more attractive
males, added to their beauty or other attractive qualities.”
Thus the theory of sexual selection is based on three assumptions.
Firstly, that there is in all species competition among the males for
females with which to mate. Secondly, that this results in either “the
law of battle” among the males, or selection by the female of one among
several admirers. Thirdly, that the female selects, as a rule, the most
attractive of her suitors.
The evidence upon which Darwin founds this theory may be thus
summarised:—
1. In cases where the sexes differ in appearance, or power of song, it is
almost invariably the cock who is the more beautiful or the better
singer, as the case may be.
2. All male birds that possess accessory plumes or other attractions,
make a most elaborate display of these before the females at the mating
season, hence “it is obviously probable that these appreciate the beauty
of their suitors.”
3. Darwin was able to cite specific instances in which the hens showed
preference.
In the case of polygamous species there can be no doubt that there is
considerable competition among males for their wives. It cannot be said
that the contention is so well established in the case of monogamous
species. D. Dewar suggests that circumstances may occur in which the hens
have to fight for the cock, or in which the male is in the happy position
of being able to select his mate. He states his belief that in many cases
the selection is mutual, as in the case of human beings.
“I have seen,” he writes, on page 13 of _Birds of the Plains_, “one hen
Paradise Flycatcher (_Terpsiphone paradisi_) drive away another and then
go and make up to a cock bird. Similarly, I have seen two hen orioles
behave in a very unladylike manner to one another all because they both
had designs on the same cock. He sat and looked on from a distance at the
contest.”
Darwin quotes, on page 500 of _The Descent of Man_, a case of a male
exercising selection: “It appears to be rare when the male refuses any
particular female, but Mr Wright of Geldersley House, a great breeder of
dogs, informs me that he has known some instances: he cites the case of
one of his own deerhounds who would not take any notice of a particular
female mastiff, so that another deerhound had to be employed.”
Similarly, Finn records, in _The Country-Side_ for August 29th, 1908,
that the male Globose Curassow (_Crax globicera_) in the London
Zoological Gardens, which bred with the female Heck’s Curassow (_C.
hecki_), as related on p. 104, selected the hen of this very distinctly
coloured form or species in preference to any of the typical hens of his
own kind.
Male Attractiveness
The cases on record of cocks being in a position to select their mates
are comparatively rare, while instances of selection on the part of the
hens are far more numerous.
Hence it would seem that the sex, which is in a minority, and so has the
opportunity of selecting a mate, does exert a choice and prefer one
particular individual; and that, for the reasons pointed out by Darwin,
it is in most cases the female who is in the position of being able to
pick and choose her mate. It is, as Darwin truly said, far more difficult
to decide what qualities determine the choice of the female. He believed
that it is “to a large extent the external attractions of the male,
though no doubt his vigour, courage, and other mental qualities come into
play.”
Darwin argued that it is the love of hen birds for “external attractions”
in cock birds that has brought into being all the wonderful plumes that
characterise such birds as the peacock. “Many female progenitors of the
peacock,” he writes, on page 661 of _The Descent of Man_ (ed. 1901),
“during a long line of descent, have appreciated this superiority, for
they have unconsciously, by the continued preference of the most
beautiful males, rendered the peacock the most splendid of living birds.”
This conclusion has been vigorously attacked. It is argued, with some
show of reason, that it is absurd to credit birds with æsthetic tastes
equal, if not superior, to those of the most refined and civilised of
human beings.
Is it likely, it is asked, that a bird, which will nest in an old shoe
cast off by a tramp, can appreciate beauty of plumage?
As Geddes and Thomson say (page 29 of _The Evolution of Sex_), “When we
consider the complexity of the markings of the male bird or insect, and
the slow gradations from one step of perfection to another, it seems
difficult to credit birds or butterflies with a degree of æsthetic
development exhibited by no human being without special æsthetic
acuteness and special training. Moreover, the butterfly, which is
supposed to possess this extraordinary development of psychological
subtlety, will fly naively to a piece of white paper on the ground, and
is attracted by the primary æsthetic stimulus of an old-fashioned
wall-paper, not to speak of the gaudy and monotonous brightness of some
of our garden flowers. Thus we have the further difficulty, that we must
suppose the female butterfly to have a double standard of taste, one for
the flowers which she and her mate both visit, the other for the far more
complex colourings and markings of the males. And even among birds, if we
take those unmistakable hints of real awakening of the æsthetic sense
which are exhibited by the Australian bower-bird or by the common jackdaw
in its fondness for bright objects, how very rude is his taste compared
with the critical examination of infinitesimal variations of plumage on
which Darwin relies. Is not, therefore, his essential supposition too
glaringly anthropomorphic?
“Again, the most beautiful males are often extremely combative; and on
the conventional view this is a mere coincidence, yet a most unfortunate
one for Mr Darwin’s view. Battle thus constantly decides the question of
pairing, and in cases where, by hypothesis, the female should have most
choice, she has simply to yield to the victor.”
Darwin, with characteristic fairness, quotes some instances which appear
to be opposed to the theory that the hen selects the most beautiful of
her suitors. He informs us that Messrs Hewitt, Tegetmeier, and Brent, who
have all had a long experience of domesticated birds, “do not believe
that the females prefer certain males on account of the beauty of their
plumage. . . . Mr Tegetmeier is convinced that a game-cock, though
disfigured by being dubbed and with his hackles trimmed, would be
accepted as readily as a male retaining all his natural ornaments. Mr
Brent, however, admits that the beauty of the male probably aids in
exciting the female; and her acquiescence is necessary. Mr Hewitt is
convinced that the union is by no means left to mere chance, for the
female almost invariably prefers the most vigorous, defiant, and
mettlesome male”; and, in consequence, when there is a game-cock in the
farmyard, the hens will all resort to him in preference to the cock of
their own breed. Darwin thinks that “some allowance must be made for the
artificial state in which these birds have long been kept,” and cites in
his favour the case of Mr Cupples’ female deerhound that thrice produced
puppies, and on each occasion showed a marked preference for one of the
largest and handsomest, but not the most eager, of four deerhounds living
with her, all in the prime of life.
The question what is it that determines the choice of the female is
obviously one of considerable importance, and it was to be expected that
many zoologists would have conducted experiments with a view to deciding
it. This legitimate expectation has not been realised.
The matter of sexual selection remains to-day practically where Darwin
left it. Wallace rejects the whole theory, and believes that natural
selection alone can explain all the phenomena of sexual dimorphism. To
such an extent does the enticing idea of the all-puissance of natural
selection dominate the minds of scientific men that but few of them have
paid any attention to the question of sexual selection. This neglect of
the subject affords an example of the baneful results of the too-ready
acceptance of an enticing theory, “Natural selection explains everything,
why then investigate further?” seems to be the general attitude of our
present-day naturalists.
Edmund Selous and D. Dewar have made some observations on birds, and the
Peckhams on spiders, in a state of nature. Such observations demonstrate
that selective mating occurs in nature, but, for the most part, fail to
show what it is that determines the choice.
D. Dewar, however, states (_Birds of the Plains_, p. 42) that the
coloured peahens in the Zoological Gardens at Lahore show a decided
preference for the white cocks, which are kept in the aviary along with
normally coloured cocks. He gives it as his opinion that “the hens select
the white cocks, not because they are white, but because of the strength
of the sexual instincts of these latter. The white cocks continually show
off before the hens; the sexual desire is developed more highly in them
than in the ordinary cocks, and it is this that attracts the hens.”
Pearson’s Investigations
The only zoologists who have investigated experimentally the question of
sexual selection appear to be Karl Pearson and Frank Finn. The former
tried to determine, by actual measurements, whether there is any
preferential mating among human beings as regards physical
characteristics. “Our statistics,” he writes, on page 427 of _The Grammar
of Science_, “run to only a few hundreds, and were not collected _ad
hoc_. Still, as far as they go, they show no evidence of preferential
mating in mankind on the basis of stature, or of any character _very_
closely correlated with stature. Men do not appear, for example, to
select tall women for their wives, nor do they refuse to mate with very
tall or very short women.” As regards eye-colour, Pearson seems to have
arrived at somewhat more definite results. “We conclude,” he writes (p.
428), “that in mankind there certainly exists a preferential mating in
the matter of eye-colour, or of some closely allied character in the
male; in the case of the female there also appears to be some change of
type due to preferential mating. . . . The general tendency is for
lighter-eyed to mate, the darker-eyed being relatively less frequently
mated.”
But Pearson’s experiments seem to show that as regards stature and
eye-colour there is “a quite sensible tendency of like to mate with
like.” “In fact,” writes Pearson, “husband and wife for one of these
characters are more alike than uncle and niece, and for the other more
alike than first cousins.” He adds, “Such a degree of resemblance in two
mates, which we reasonably assume to be not peculiar to man, could not
fail to be of weight if all the stages between like and unlike were
destroyed by differential selection.”
Two obvious criticisms of the results obtained by Prof. Pearson occur to
us. The first is that his conclusions do not seem to be in accordance
with the popular notion that fair-haired men prefer dark hair in a woman,
while dark-haired men prefer fair-haired women, and _vice versa_. The
second is that the human animal is not a typical one. Husbands and wives
are selected for mental and moral qualities rather than physical ones.
The same may, of course, be to some extent true of animals, but in these
there must of necessity be far less variation as regards mental
attributes. Moreover, the question of income is much bound up with human
matrimonial alliances; a rich man or woman has the same advantage in
selection as is possessed by an animal endowed with more than the average
physical strength of its species.
Finn’s Experiments
Finn adopted the plan of experiment suggested by Prof. Moseley. His
apparatus consisted of a cage divided into three compartments by wire
partitions, so that a bird living in one of them could see its neighbour
in the next compartment. In the middle compartment he placed a hen
Amadavat (_Sporæginthus amandava_), and in each of the other compartments
he put a cock bird. Under such circumstances, the hen in the middle
compartment will sit and roost beside the cock she prefers. The male
amadavat, he writes, in _The Country-Side_, vol. i. p. 142, “is in
breeding plumage red with white spots, and the hen brown. The red varies
in intensity even in full-plumaged birds, and I submitted to the hen
first of all two male birds, one of a coppery and the other of a rich
scarlet tint. In no long time she had made her choice of the latter bird;
the other, I am sorry to say, very soon died; and, as he had appeared
perfectly healthy, I fear grief was accountable for his end—a warning to
future experimenters to remove the rejected suitor as early as possible.
In the present case I took away the favoured bird, and put in the side
compartments he and his rival had occupied two other cocks, which
differed in a similar way, though not to the same extent. Again the hen
kept at the side of the rich red specimen, so, deeming I knew her views
about the correct colour for an amadavat, I took her away too, and tried
a second hen with these two males. This was an unusually big bird, and a
very independent one, for she would not make up her mind at all, and
ultimately I released all three without having gained any result.
“Subsequently I made another experiment with linnets. In this case all
three were allowed to fly in a big aviary-cage together, a method which I
do not recommend.
“In this case, however, the handsomest cock, which showed much richer red
on the breast, had a crippled foot, and proved, as I had expected, to be
in fear of the other; nevertheless, the hen mated with him. It must be
said, in justice to the duller bird, that he did not press the advantage
his soundness gave him, but with a less gentle bird than the linnet this
would have happened.”
It is obvious that there is a wide field for observation on these lines.
In the case of large birds the experiment could be made still more
conclusive by confining the three birds to be experimented on in a single
enclosure, divided into three compartments by fences. The males should be
placed each in a separate compartment, and have a wing clipped so as to
prevent them leaving their respective compartments, while the hen should
be allowed the power of flight so that she can visit at will any
compartment.
Finn has also recorded (_loc. cit._) some other observations bearing on
the question of sexual selection. He writes:—
“One cannot observe or read about the habits of birds very much without
finding out that, whatever may be the value of beauty, strength counts
for a great deal. Male birds constantly fight for their mates, and the
beaten individual, if not killed, is at any rate kept at a distance by
his successful rival, so that, if he be really more beautiful, his beauty
is not necessarily of much service to him. I was particularly impressed
by this about a couple of years ago, when I frequently watched the
semi-domesticated mallards in Regent’s Park in the pairing season. These
birds varied a good deal in colour; in some the rich claret breast was
wanting, and others had even a slate-coloured head instead of the normal
brilliant green. Yet I found these ‘off-coloured’ birds could succeed in
getting and keeping mates when correctly-dressed drakes pined in lonely
bachelorhood; one grey-breasted bird had even been able to indulge in
bigamy. That strength ruled here was obvious from the way in which the
wedded birds drove away their unmated rivals, a proceeding in which their
wives most thoroughly sympathised.
“Evidently, beauty does not count for much with the park duck, and the
same seems to be the case with the fowl. As a boy, I often used to visit
a yard wherein was a very varied assortment of fowls. Among these was one
very handsome cock, of the typical black and red colouring of the wild
bird, and very fully ‘furnished’ in the matter of hackle and sickle
feathers. Yet the hens held him in no great account, while the master of
the yard, a big black bird, with much Spanish blood, provided with a huge
pair of spurs, was so admired that he was always attended by some little
bantam hens, although they might have had diminutive husbands of their
own class.
“It must be remembered, however, that these ducks and fowls had an
unnaturally wide choice. In nature, varieties are rare, and the competing
suitors are likely to be all very much alike; this makes matters very
difficult for the observer, who may easily pass over small differences
which are plain enough to the eyes of the hen birds.”
[Illustration: COURTSHIP OF SKYLARK]
Display of Undecorated Cocks
Finn observed that a young hen Bird of Paradise (_Paradisea apoda_) in
the London Zoological Gardens, mated with a fully adult cock in the next
compartment although a young cock in female plumage in her own
compartment did his best to show off.
It would thus seem that the very limited evidence at present available is
not sufficient to sustain the theory that the hens select the most
attractive of their suitors. It is significant that plainly-coloured
species of birds show off with as much care as their gaily-plumaged
brethren; and, if they be nearly allied, assume similar courting
attitudes. Thus the homely-attired males of the Spotted-bill (_Anas
poecilorhyncha_), Gadwall, and Black Duck (_Anas superciliosa_), show off
in precisely the same way as does the handsome mallard.
Howard describes and figures in his excellent and beautifully illustrated
monograph the elaborate display at the pairing season of some of our
plain-coloured little warblers. The skylark has also a notable display.
The common partridge assumes a nuptial attitude similar to that of the
pheasant, and, although the cock of the former species has nothing
brilliant to show off, the hen partridge pays far more attention to the
display of her suitor than does the hen pheasant.
The fact that some cock birds show off _after_ the act of pairing seems
to tell against the theory of sexual selection, or at any rate to
indicate the purely mechanical nature of the performance. Finn has
witnessed this post-nuptial display at the Zoological Gardens (London) in
the pied wagtail, the peacock, the Andaman Teal (_Nettium albigulare_),
the Avocet, the Egyptian Goose (_Chenatopex ægyptiaca_), and the Maned
Goose (_Chenonetta jubata_).
Another objection to the theory that the bright colours of cock birds are
due to feminine selection is presented by those birds which breed in
immature plumage. Darwin admits that this objection would be a valid one
“if the younger and less ornamental males were as successful in winning
females and propagating their kind as the older and more beautiful males.
But,” he continues, “we have no reason to suppose that this is the case.”
Unfortunately for the theory of sexual selection, there is evidence to
show that the cock Paradise Fly-catcher (_Terpsiphone paradisi_) in
immature plumage is quite as successful in obtaining a mate as is the
cock in his final plumage. The cock of this beautiful species has a
chestnut plumage in his second year, and a white one in the third and
subsequent years of his life. Nevertheless, a considerable proportion of
the nests found belong to chestnut cocks.
Plumage of Herons
Darwin was of opinion that any novelty in colouring in the male is
admired by the female; and in this manner he sought to overcome some
difficulties to his theory which certain birds presented.
Writing of the heron family, he says:—
“The young of the _Ardea asha_ are white, the adults being
slate-coloured; and not only the young, but the adults of the allied
_Buphus coromandus_ in their winter plumage are white, their colour
changing into a rich golden buff during the breeding season. It is
incredible that the young of these two species, as well as of some other
members of the same family, should have been specially rendered pure
white, and thus made conspicuous to their enemies; or that the adults of
one of these two species should have been specially rendered white during
the winter in a country which is never covered with snow. On the other
hand, we have reason to believe that whiteness has been gained by many
birds as a sexual ornament. We may therefore conclude that an early
progenitor of the _Ardea asha_ and the _Buphus_ acquired a white plumage
for nuptial purposes, and transmitted this colour to their young; so that
the young and the old became white like certain existing egrets, the
whiteness having afterwards been retained by the young whilst exchanged
by the adults for more strongly pronounced tints. But if we could look
still further backwards in time to the still earlier progenitors of these
two species, we should probably see the adults dark-coloured. I infer
that this would be the case, from the analogy of many other birds, which
are dark whilst young, and when adult are white; and more especially from
the adult of the _Ardea gularis_, the colours of which are the reverse of
those of _A. asha_, for the young are dark-coloured and the adults white,
the young having retained a former state of plumage. It appears,
therefore, that the progenitors in their adult condition of the _A.
asha_, the _Buphus_, and of some allies have undergone, during a long
line of descent, the following changes of colour: firstly a dark shade,
secondly pure white, and thirdly, owing to another change of fashion (if
I may so express myself), their present slaty, reddish or golden-buff
tints. These successive changes are intelligible only on the principle of
novelty having been admired by the birds for the sake of novelty.”
This reasoning may appear far-fetched and unconvincing. It seems,
however, quite likely that the hen may select as her mate the suitor who
is conspicuously different from the others, not because she admires
novelty, but because his conspicuousness attracts her attention and
enables her to make up her mind quickly to take him and thus rid herself
of the other troublesome admirers, who are all very much alike.
Sexual Dissimilarity
It is perhaps worthy of note that, after the most successful of her
suitors has succeeded in securing the hen, it may happen that a
disappointed rival makes love to her in the absence of her lord and
master and thereby nullifies the effect of her previous selection.
It is to be observed that, even if we take it as proved, as Darwin
believed, that the hens alone exercise a choice of mates, and that they
select the most beautiful of their suitors, we are still far from
arriving at an explanation of the fact that the males alone have acquired
beauty. Admitting that the hens always mate with the most beautiful
cocks, we should expect the offspring of each union to be all more or
less alike in beauty—that is to say, more beautiful than the mother and
less so than the cock. How are we to explain the one-sided inheritance of
this beauty? Why is it confined to the cocks?
In order to meet this objection Darwin had to call to his aid unknown
laws of inheritance. “The laws of inheritance,” he writes (_Descent of
Man_, p. 759), “irrespectively of selection, appear to have determined
whether the characters acquired by males for the sake of ornament, for
producing various sounds, and for fighting together, have been
transmitted to the males alone or to both sexes, either permanently or
periodically, during certain seasons of the year. Why various characters
should have been transmitted sometimes in one way and sometimes in
another is not in most cases known; but the period of variability seems
often to have been the determining cause. When the two sexes have
inherited all characters in common, they necessarily resemble each other;
but, as the successive variations may be differently transmitted, every
possible gradation may be found, even within the same genus, from the
closest similarity to the widest dissimilarity between the sexes.”
This statement, although it does not throw any light upon the problem, is
somewhat damaging to the theory of sexual selection. If it be admitted
that dissimilarity between the sexes is due to the fact that the males
have varied in one way and the females in another way, there seems no
necessity for invoking the aid of feminine preference.
Even greater is the difficulty presented by those species in which the
males alone are provided with horns or antlers. “When,” writes Darwin
(_Descent of Man_, p. 767), “the males are provided with weapons which in
the females are absent, there can hardly be a doubt that these serve for
fighting with other males; and that they were acquired through sexual
selection, and were transmitted to the male sex alone. It is not
probable, at least in most cases, that the females have been prevented
from acquiring such weapons on account of their being useless,
superfluous, or in some way injurious. On the contrary, as they are often
used by the males for various purposes, more especially as a defence
against their enemies, it is a surprising fact that they are so poorly
developed, or quite absent, in the females of so many animals.”
We have, we believe, demonstrated that Darwin’s theory of sexual
selection is unable to account satisfactorily for all the phenomena of
sexual dimorphism. But, as we have seen, it is quite possible that sexual
selection is a real factor of evolution.
We trust that what we have said will stimulate some leisured naturalist
to study the question of male and female preference.
We now pass on to consider briefly some of the other attempts that have
been made to explain the phenomena of sexual dimorphism.
Wallace’s Explanation of Sexual Dissimilarity
Wallace does not accept the theory of sexual selection. He admits that
the form of male rivalry, which Darwin calls “the law of battle,” is “a
real power in nature,” and believes that “to it we must impute the
development of the exceptional strength, size, and activity of the male,
together with the possession of special offensive and defensive weapons,
and of all other characters which arise from the development of these, or
are correlated with them” (_Darwinism_, p. 283). But the view that the
female selects the most beautiful of her suitors has always seemed to
Wallace “to be unsupported by evidence, while it is also quite inadequate
to account for the facts.” For example, the accessory plumes of birds
“usually appear in a few definite parts of the body. We require some
cause to initiate the development in one part rather than in another.”
Wallace considers that natural selection is able to explain all the
phenomena of sexual dimorphism. He points out that, when the sexes are
dissimilar among birds, it is almost invariably the female which is
duller coloured. The reason for this is, he believes, that the hen birds,
while sitting, “are exposed to observation and attack by the numerous
devourers of eggs and birds, and it is of vital importance that they
should be protectively coloured in all those parts of the body which are
exposed during incubation. To secure this, all the bright colours and
showy ornaments which decorate the male have not been acquired by the
female, who often remains clothed in the sober hues which were probably
once common to the whole order to which she belongs. The different
amounts of colour acquired by the females have no doubt depended on
peculiarities of habits and environment, and on the powers of defence and
concealment possessed by the species.”
In support of his contention, Wallace asserts that all species of birds,
of which the hens are as conspicuously coloured as the cocks, nest in
holes or build domed nests. The plumes and other ornaments, which the
cocks of certain species display, Wallace would attribute to a surplus of
strength, vitality, and growth power, which is able to expend itself in
this way without injury.
“If,” he writes, “we have found a _vera causa_ for the origin of
ornamental appendages of birds and other animals in a surplus of vital
energy, leading to abnormal growths in those parts of the integument
where muscular and nervous action are greatest, the continuous
development of these appendages will result from the ordinary action of
natural selection in preserving the most healthy and vigorous
individuals, and the still further selective agency of sexual struggle in
giving to the very strongest and most energetic the parentage of the next
generation.” (_Darwinism_, p. 293.) “Why,” he says, “in allied species
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.”
Wallace’s Theory Criticised
Wallace’s view that the dull plumage of the hen bird is due to her
greater need of protection is based on the assumption that the hen bird
alone takes part in incubation.
Is this assumption a correct one?
It certainly is not in all cases. As D. Dewar has stated in _Birds of the
Plains_, the showy white cock Paradise Fly-catcher (_Terpsiphone
paradisi_) sits in broad daylight on the open nest quite as much as the
hen does. And this may prove to be true of many other species of birds.
Again, the cocks of the various species of Indian sunbirds are brightly
coloured while the hens are dull brown. In these species the hen alone
sits on the eggs, but, as the nest is well covered-in, the hen might
display all the colours of the rainbow without being visible to passing
birds. Moreover, as D. Dewar pointed out in a paper read before the Royal
Society of Arts (_Journal_, vol. lvii., p. 104), although, in most
species of Indian dove, the sexes show little or no dissimilarity, there
is one species (_Œnopopelia tranquebarica_) which exhibits considerable
sexual dimorphism. But the nesting habits of this peculiar species are in
all respects similar to those of the other species of dove. Why then the
marked dissimilarity of the sexes?
Another objection to the theory of Wallace is that urged by J. T.
Cunningham (_Archiv für_ _Entwicklungsmechanik der Organismen_, vol.
xxvi., p. 378), namely, that the secondary sexual characters in those
species which possess them show an entire absence of uniformity in nature
and position. “Why,” asks Cunningham, “should the male constitution of
the stag show itself in bony excrescences of the skull, in the peacock in
excessive growth of the other end of the body? Why should the larynx be
modified in one mammal, the teeth in another, the nose in another? Why is
the male newt distinguished by a dorsal fin, the male frog by a swelling
on the fore foot?”
Another objection to the explanation of sexual dimorphism suggested by
Wallace, is that in many species of bird, as, for example, the house
sparrow and the green paroquets of India, the external differences
between the sexes are so slight that it is unreasonable to believe that
they are the result of natural selection. It seems impossible to hold
that the Rose-ringed Paroquet (_Palæornis torquatus_)—a species which
nests in holes—would have become extinct if the hens had developed the
narrow rose-coloured collar that characterises the cocks.
Darwin pointed out that while Wallace’s hypothesis might appear plausible
if applied to colour, it can scarcely be said to explain the origin of
such structures as the musical apparatus of certain male insects, or the
larger size of the larynx in some birds and mammals. We thus see that
suggestions offered by Wallace, although they contain a modicum of truth,
fail to explain the phenomena of sexual dimorphism.
The fairest possible criticism of these views is that of Darwin:—
“It will have been seen that I cannot follow Mr Wallace in the belief
that dull colours, when confined to the females, have been in most cases
specially gained for the sake of protection. There can, however, be no
doubt, as formerly remarked, that both sexes of many birds have had their
colours modified, so as to escape the notice of their enemies; or in some
instances, so as to approach their prey unobserved, just as owls have had
their plumage rendered soft, that their flight may not be overheard”
(_The Descent of Man_, p. 745).
The Theory of Thomson and Geddes
Thomson and Geddes have attempted to explain sexual dimorphism on the
hypothesis that males are essentially dissipators of energy, while
females tend to conserve energy. They point out that the spermatozoon is
a small intensely active body, which dissipates its energy in motion,
while the ovum is a large inert body—the result of the female tendency to
conserve energy and to build up material. The various ornaments and
excrescences which appear in male organisms are the result of this male
tendency to dissipate energy. In the spermatozoon the dissipated energy
appears in the form of active movement; in the adult organism it takes
the shape of plumes and other ornaments, of song and contests for the
females.
This theory, however, does not explain what we might call the haphazard
nature of sexual dimorphism. If sexual dissimilarity is due to the
tendency of the male to dissipate energy, why do we see very marked
dimorphism in one species, and no dimorphism in a very nearly allied
species? Why are the males larger than the females in some species, and
smaller in other species? Again, how is it that in certain species of
birds—the quails of the genus _Turnix_, the Painted Snipe (_Rhynchæa_),
and the Phalaropes—it is the female who possesses the more showy plumage?
Moreover, this theory, equally with that of Wallace, does not explain why
the excrescences which characterise the male appear in various parts of
the body in different species.
Stolzmann’s Theory
Stolzmann has made an ingenious attempt to explain why in birds the cock
is so frequently more conspicuously coloured than the hen. He asserts
that among birds the males are more numerous than the females, and that
this preponderance is not advantageous to the species. Those males which
have not managed to secure a mate are apt to persecute the females while
sitting on the eggs, to the detriment of these latter. Natural selection,
says Stolzmann, is concerned with the well-being of the species rather
than of the individual. Hence anything that would tend to lessen the
number of males would be a good thing for the species, so that a
peculiarity, such as bright plumage, which renders the males conspicuous,
or ornamental plumes, which cause their flight to be slow, and so leads
to their destruction, will be seized upon and perpetuated by natural
selection. He points out that the cock of one species of
hummingbird—_Loddigesia mirabilis_—has not only longer tail feathers, but
a shorter wing than the female, and must, in consequence, find it
comparatively difficult to obtain food, and be more liable to fall a
victim to birds of prey than the hen. Stolzmann further suggests that the
excessive pugnacity of male birds at the breeding season may lead to the
destruction of some individuals, and so prove of advantage to the
species.
Several objections seem to present themselves to this most ingenious
theory.
In the first place, there does not appear to be any satisfactory evidence
to show that more cocks than hens are born.
We may grant that a superfluity of cocks is injurious to any species,
since the unmated ones are likely to persecute the hens; we may also
grant that many cocks are handicapped in the struggle for existence by
the excessive growth of certain of their feathers, but we fail to see how
this excessive development has been caused by natural selection in the
manner suggested by Stolzmann. Although it may be advantageous to the
species for the cocks to be showy, natural selection can perpetuate this
only by weeding out the least conspicuous of the cocks. But it is the
more gaudy ones, those, according to Stolzmann, whose presence is
beneficial to the species, which will be eliminated by natural selection.
So that, in this case, that force will act in a manner contrary to the
interests of the species, if Stolzmann’s idea is a correct one.
The theory in question would therefore seem to be untenable. Nevertheless
there is doubtless some truth in the notion that too many males spoil the
species. Thus, excessive showiness and high mortality among the males may
be beneficial to the species. But we must not forget that the more
beneficial it is, the stronger must be the tendency of natural selection
to eliminate the males that possess the desired peculiarity.
Neo-Lamarckian Explanation
Cunningham’s Theory
J. T. Cunningham makes an attempt to explain the phenomena of sexual
dimorphism on Neo-Lamarckian principles. His theory is set forth in a
paper entitled _The Heredity of Secondary Sexual Characters in relation
to Hormones_, which was read before the Zoological Society of London, and
published in full in the _Archiv für Entwicklungsmechanik der
Organismen_. “The significant correlation of male sexual characters,” he
writes, “is not with any general or essential property of the male sex,
such as katabolism (or the tendency to dissipate energy, as we have
called it), but with certain habits and functions confined to one sex,
but differing in different animals. . . . In those animals which possess
such (_i.e._ secondary sexual) characters, the parts of the soma (_i.e._
the body) affected differ as much as they can differ; any part of the
soma may show a sexual difference: teeth in one mammal, skull in another;
feathers of the tail in one bird, those of the neck in another, and so
on. But in all cases such unisexual characters correspond to their
functions or use in habits and instincts which are associated, but only
indirectly, with sexual production. These habits are as diverse and as
irregular in their distribution as the characters. The cocks of common
fowls and of the Phasianidæ generally are polygamous, fight with each
other for the possession of the females, and take no part in incubation
or care of the young, and they differ from the hens in their enlarged
brilliant plumage, spurs on the legs, and combs, wattles, or other
excrescences on the head. In the Columbidæ _per contra_ the males are not
polygamous, but pair for life, the males do not fight, and share equally
with the females in parental duties.
“Corresponding with this contrast of sexual habits is the contrast of
sexual dimorphism, which is virtually absent in the Columbidæ.
“I think, then, the only scientific explanation is that the difference of
habits is the cause of the sexual dimorphism, and that the special sexual
habits which occur in some species but not in others are the causes of
the sexual characters. . . . The habits in question always involve
certain definite stimulations applied to those parts of the body whose
modification constitutes the somatic sexual characters. The stimulations
are confined, as the characters are confined, to one sex, to one period
of life, to one season of the year, to those animals which have the
characters, to those parts of the body which are modified.” Mr Cunningham
believes that these stimulations cause hypertrophy or excessive growth of
the part affected, and that this peculiarity is transmitted to the
offspring. And thus he supposes all the ornaments and excrescences of the
males of various species to have arisen.
As evidence in favour of his view, he points out that these excrescences
are, in many species, not only functionless but absolutely injurious, as
in the case of the comb and wattles of the jungle cock and his domestic
descendants, which merely serve as a handle for enemies to seize.
Cunningham asserts that the only objection to his theory is the dogma
that acquired characters cannot be inherited. This assertion is, however,
not correct. It is, indeed, a very serious objection that all the
evidence available seems to show that acquired characters are not
inherited, but this is by no means the only difficulty.
Before mentioning these further objections, let us say a word on the
subject of the inheritance of acquired characters. Mr Cunningham himself
compares the formation of a splint or spavin in a horse as the result of
special strain, to the acquisition of secondary sexual characters.
Unfortunately for Cunningham’s theory, but fortunately for mankind in
general, spavined horses and mares do not beget spavined offspring. If,
then, spavin is not inherited, is it not unreasonable to assert that the
thickening of the bone that develops on the head of a butting animal is
inherited?
Another objection to Cunningham’s theory is that many birds which show
off their plumage most vigorously possess no ornamental plumes. As Howard
has recorded, many of our dull-coloured British warblers show off in the
same manner as bright-coloured birds do. If the exercise has caused the
development and inheritance of plumes in some species, why not in the
others?
Again, Cunningham is not correct in saying that sexual dimorphism is
“virtually absent” in the Columbidæ. Few birds display so striking a
sexual dimorphism as the Orange Dove (_Chrysœna victor_) of Fiji, in
which the male is bright orange and the hen green. We have already cited
the case of the curious sexually dimorphic red turtle-dove. Now, the
courting attitudes and actions of this species are precisely the same as
those of other allied turtle-doves; why, then, have these exercises
caused only one species to become sexually dimorphic?
Existing Theories not Satisfactory
Our survey of the more important attempts which have been made to explain
the phenomena of sexual dimorphism leads to the conclusion that these
still require elucidation. We have weighed each theory in the balance and
found it wanting.
The outstanding feature of sexual dissimilarity is the apparently
haphazard manner of its occurrence.
We have already alluded to the case of the doves in India. In that
country four species are widely distributed—namely, the Spotted Dove
(_Turtur suratensis_), the Ring or Collared Dove (_Turtur risorius_), the
Little Brown Dove (_Turtur cambayensis_), and the Red Turtle-dove
(_Œnopopelia_ _tranqebarica_). The habits of all these four species
appear to be identical, nevertheless in the first three the sexes show
little or no dissimilarity in outward appearance, while in the last the
sexual dimorphism is so great that the cock and hen were formerly thought
to belong to different species.
Another very curious case is that of the South American geese of the
genus _Chloëphaga_, in which some species, as the familiar Upland or
Magellan Goose of our parks (_C. magellanica_), have the sexes utterly
unlike, while in others, as the Ruddy-headed Goose (_C. rubidiceps_),
they are quite similar to each other.
The ducks furnish us with another very good example of the apparently
haphazard nature of sexual dimorphism. In the Common Mallard or Wild Duck
(_Anas boscas_) the cock is far more showily coloured than the hen, but
in all the species most nearly allied to it the males are as
inconspicuous as the females, _e.g._ in the Indian Spotted-bill (_Anas
pœcilorhyncha_), the Australian Grey Duck (_A. superciliosa_), the
African Yellow Bill (_Anas undulata_), and the American Dusky Duck (_A.
obscura_). As the dusky duck inhabits North America, where the mallard is
also found, the case is particularly striking.
Among mammals the lion and the tiger and the sable and roan antelopes
(_Hippotragus niger_ and _H. equinus_) furnish familiar examples of
nearly-related species, in one of which the sexes are alike and in the
other dissimilar in appearance.
Hormones
Another important point to be borne in mind is the intimate correlation
that exists between the reproductive organs and the general appearance of
the organism, more especially of the secondary sexual characters. These
last, in most cases, do not show themselves until the maturity of the
sexual organs. The well-known effects of castration illustrate this
connection. Again, females in which the reproductive organs have ceased
to be functional often assume male characters.
It has lately been proved by experiment that, in many cases at any rate,
the development of the ornaments, etc., characteristic of the sexes is
due to the secretion by the sexual cells of what are known as
hormones—that is to say, secretions which excite development of the
secondary sexual characters. The tendency to produce the external
characteristics of the sex to which an organism belongs is inherited, but
the actual development thereof is in many cases dependent on the
secretion of these hormones. Accordingly, if a male individual be
completely castrated it ceases to develop the external characters of its
sex. The evidence upon which the doctrine of hormones is based is
admirably summarised in the above-quoted paper by Cunningham. Into this
evidence we cannot go. It must suffice that the doctrine is quite in
accordance with all the observed results of castration.
It is worthy of notice that the various features which characterise the
sexes in sexually dimorphic animals are not associated with any
particular organ or parts of the body, nor do they necessarily affect the
same part in allied species. “We cannot say,” writes J. T. Cunningham,
“that any part of the soma (_i.e._ the body tissue) is specially sexual
more than another part, except that such differences between the sexes
are usually external. They usually affect the skin, and especially
epidermic appendages, and the superficial parts of the skeleton, or whole
limbs and appendages; or the difference may be one of size of the whole
soma. In mammals and birds the male is often the larger, sometimes very
much so, but there are cases in which the female is larger. There is no
general rule.”
Another important point is, that females, although they themselves show
no trace of the male character, are capable of transmitting it to their
progeny. This can be proved by crossing a hen pheasant with a cock
barn-door-fowl; the male offspring of the union display the plumes so
characteristic of the cock pheasant. These cannot have been derived from
the barn-door-fowl father; they must have come from the dull-coloured hen
pheasant.
In this connection we may mention the curious fact recorded by Bonhote,
on page 245 of the _Proceedings of the Fourth International
Ornithological Congress_, that in the case of ducks descended from
crosses between the pintail, the mallard, and the spotbill, the drakes in
full breeding plumage showed a mixture of pintail and mallard
characteristics, while, in their non-breeding plumage, the colouring of
the spotbill is predominant.
Eye-colour, Comb, and Spurs
An important point, and one which does not seem to have been pointed out
by any zoologist, is that eye-colour, comb, and spurs in birds and horns
in mammals do not stand in the same relation to the sexual organs as do
the other external characteristics. For example, the castrated Nilgai
(_Boselaphus tragocamelus_) acquires horns, but not the characteristic
male colour. In the common Indian Francolin Partridge (_Francolinus
pondicerianius_), the cock differs from the hen only in the possession of
spurs. The same applies to the various species of Snow Cock
(_Tetraogallus_). There is a breed of game-cocks which display plumage
like that of the hen, but such birds have the comb and spurs developed as
in normally feathered cocks.
The white eye of the white-eyed Pochard Drake (_Nyroca africana_), and
the yellow eye of the cock Golden Pheasant (_Chrysolophus pictus_), which
are purely male characters, show themselves earlier than the male
plumage. Occasionally a hen golden pheasant assumes the plumage of the
cock, but she never acquires the yellow eye.
Many birds when kept in captivity lose some of the beauty of their
plumage, and this is usually attributed to the sexual organs becoming
impaired and reacting on the somatic tissue. But this explanation cannot
in all cases be the correct one, because the linnet, although losing the
male plumage in captivity, lives long and well in a cage and breeds
readily with hen canaries.
Another curious fact is that the male plumage sometimes appears
pathologically in hen birds, more especially in those which have become
sterile from age or disease. This phenomenon occurs comparatively
frequently in the gold pheasant, and more rarely in the common pheasant,
the fowl, and the duck.
Phenomena such as these seem to suggest that in some cases the bright
colours of the male may be pathological, that the hormones which the male
sexual cells secrete may exercise an injurious effect on the somatic or
body tissues. Decay is known to be accompanied by the production of
brightly coloured pigment in the case of leaves. Finn suggests that the
white plumage which the cock paradise fly-catcher assumes in the fourth
year of his existence may be a livery of decay, a sign of senility.
The Four Kinds of Mutations
It is our belief that sexual dimorphism arises frequently, if not
invariably, as a mutation. Mutations may be of four different kinds.
Those which appear only, or especially, in conjunction with the male
organs, for example, whiteness in domesticated geese allowed to breed
indiscriminately.
Those which appear only, or especially, in conjunction with the female
organs; mutations of this description appear to be very rare, but it may
be noted that in fowls allowed to breed indiscriminately, as in India,
completely black hens are common, but completely black cocks are rarely,
if ever, seen. This indicates an association between blackness and
femininity.
Those which appear in the same manner in both sexes. The great majority
of mutations appear to be of this kind.
Lastly, those that appear in both sexes but take a different form in the
case of the two sexes; thus in cats a mutation has given rise to sandy
males and tortoise-shell females. The mutation which has produced the
black-winged peacock shows itself in the form of a black wing in the
cock, while it causes the plumage of the hen to be grizzly white.
We shall deal with the phenomenon of correlation at some length in the
next chapter. It is a subject to which sufficient attention has not been
paid. Even as certain characters are correlated in certain species, so in
some cases are certain characters correlated with sex.
Why this should be so we are not in a position to say; this, however,
does not affect the indisputable fact that such correlation does exist.
Physicians in the course of their practice sometimes come across very
curious cases of correlation in human beings.
Unilateral Transmission
“It is,” writes Thomson (_Heredity_, p. 290), “an interesting fact that
an abnormal element in the inheritance may find expression in the males
only or in the females only. If we could understand this we should be
nearer understanding what sex really means.
“Hæmophilia, or a tendency to bleeding, is a heritable abnormality,
partly associated with weakness in the blood-vessels, which do not
contract as they should and are apt to break, and partly connected with a
lack of coagulating power in the blood. It is usually confined to males.
But as it passes from a father through a daughter to a grandson, and so
on, it must be a latent part of the germinal inheritance of the females,
though for some obscure physiological reason it fails to find expression
in them, or has its expression quite disguised. Colour-blindness or
Daltonism has been recorded (Horner) through the males only of seven
generations. Dejerine cites another case (_fide_ Appenzeller) in which
all the males in a family history had cataract through four generations.
There are other instances of what is sometimes awkwardly called the
unilateral transmission of abnormal qualities. Edward Lambert, born in
1717, is said to have been covered with ‘spines.’ His children showed the
same peculiarity, which began to be manifest from the sixth to the ninth
month after birth. One of his children grew up and handed on the
peculiarity to another generation. Indeed, it is said to have persisted
for five generations, and in the males only—unilateral transmission.”
In our view, these abnormalities are of such a kind that they are only
possible in connection with the male organ; in other words, they are
mutations of the first of the four kinds cited above—those which appear
only in connection with the male organ.
It is a curious fact that the general rule in nature seems to be that the
male is ahead of the female in the course of evolution. The sexes may be
alike at a given period in the life-history of the species. Presently a
mutation appears which is confined to the male alone; thus arises the
phenomenon of sexual dimorphism. The next step in the evolution of the
species is frequently a mutation on the part of the female which brings
her once again into line with the male, and so the sexual dimorphism
disappears, for a time at any rate. A good example of this is furnished
by the sparrows; in the common sparrow of a large part of Africa (_Passer
swainsoni_) both sexes are very plain, like the hen of the house-sparrow;
in this species (_P. domesticus_) as every one knows, the cock, though by
no means brilliant, is noticeably handsomer than his mate; while in the
Tree-sparrow (_P. montanus_) both sexes have a plumage of masculine type,
much like that of the cock house-sparrow.
If we consider in conjunction with one another the various facts we have
cited above, we begin to grasp the nature of the phenomena of sexual
dimorphism.
Let us consider an imaginary case of a defenceless little bird which
builds an open nest. Let us suppose that it is inconspicuously plumaged.
Now suppose that a mutation of the first kind shows itself, a mutation
which affects the cock only and makes him more conspicuous. Let us
further suppose that the cock does not share in the duties of incubation.
It is quite possible that, in spite of this apparently unfavourable
mutation, the species may survive, for, as we have seen, it does not
affect the hen, and she, since she alone incubates, stands the most in
need of protective colouring. Moreover, as Stolzmann has suggested, the
species can possibly afford to lose a few males. But suppose that both
cock and hen share in the duties of incubation, it is then quite likely
that the mutation will cause the species to become extinct, by the
elimination of all the males. Or, let us suppose that the mutation in the
direction of showy plumage affects both sexes, then in such a case the
species will almost certainly become extinct. If, however, the
hypothetical species nested in holes in trees, it is quite possible that
it might survive notwithstanding its showy plumage.
Greater Value of Females
Whether, as Wallace suggests, the hen does most of the incubating, and is
exposed to special danger when sitting on her eggs in an open nest, or,
as Stolzmann urges, it is of advantage to the species that there should
not be too many males, the result is the same, that the species can
afford to allow the cock to be more gaily attired than the hen. In either
case the colouration of the cock becomes a matter of comparatively little
importance to the species, and this, coupled with the fact that the male
tends to mutate more readily than the female, will explain why, in most
species which exhibit sexual dimorphism, it is the cocks that are the
more conspicuous. In certain species the cocks alone incubate, and these
then become more important than the females to the race, so that they
have not been permitted to become showy, while the hens have been allowed
more freedom in this respect. The extreme variability of the Ruff
(_Pavoncella pugnax_) in breeding plumage points to the fact that his
colour is a matter of comparative indifference to the species; in
consequence plenty of latitude is allowed to his tendency to vary.
Our view, then, is that evolution proceeds by mutations, which may be
large or small.
The mutation is the result of a rearrangement in part or parts of the
fertilised egg, and this rearrangement shows itself in the adult organism
as a change in one or more of its characteristics. The mutation may be
correlated with only one of the sexual organs, and when this is the case,
it gives rise to the phenomenon of sexual dimorphism. The appearance in
the adult of certain, if not of all, characteristics is affected by
causes other than the nature of the biological molecules from which they
are derived. The tendency to develop in a certain direction is there, but
something else, such as the secretion of hormones from the sexual cells,
is frequently necessary to enable a given tendency to fully develop
itself. Thus it is that castration often affects the bodily appearance of
those animals operated on. When a mutation appears, natural selection
decides whether or not it shall persist.
CHAPTER VIII
THE FACTORS OF EVOLUTION
Variation along definite lines and Natural Selection are undoubtedly
important factors of evolution—Whether or not sexual selection is a
factor we are not yet in a position to decide—_Modus operandi_ of
Natural Selection—Correlation an important factor—Examples of
correlation—Correlation is a subject that requires close
study—Isolation a factor in evolution—Discriminate
isolation—Indiscriminate isolation—Is the latter a factor?—Romanes’
views—Criticism of these—Indiscriminate isolation shown to be a
factor—Summary of the methods in which new species arise—Natural
Selection does not make species—It merely decides which of certain
ready-made forms shall survive—Natural Selection compared to a
competitive examination and to a medical board—We are yet in darkness
as to the fundamental causes of the Origin of Species—In experiment and
observation rather than speculation lies the hope of discovering the
nature of these causes.
We have so far considered three factors of evolution. The first of these
is the tendency of organisms to vary along definite lines. This is a most
important factor, because, unless variation occurs in any given
direction, there can be no evolution in that direction. Variations are
the materials upon which the other factors, or causes, of evolution work.
The second great factor is natural selection. Natural selection may be
compared to a builder, and variations to his materials. The kind of
building that a builder can construct depends very largely on the
material supplied to him. The Forth Bridge could not have been built had
those who constructed it had no material given them but bricks and
mortar. Wallaceians regard natural selection as a builder who is supplied
with every kind of building material—stone, bricks, wood, iron,
aluminium, in any quantities he may desire. They therefore regard natural
selection as the one and only cause which determines evolution. This,
however, is a wrong idea. Natural selection should rather be likened to a
builder who is supplied with a limited variety of building materials, so
that considerable restrictions are imposed on his building operations.
The doors, windows, fireplaces, etc., are supplied to him ready-made. He
merely selects which of these he will use for each building.
The third factor of evolution which we have considered is sexual
selection. As we have seen, sufficient attention has not been paid to
this subject, so that we are not yet in a position to say how much, if
any, influence it has exercised on the course of evolution.
The Struggle for Existence
In addition to these three factors, there are, we believe, some others.
Before proceeding to a consideration of these, it is important to study
carefully the _modus operandi_ of natural selection, or, in other words,
the nature of the struggle for existence, as many of the statements
contained in recent books on evolution seem to us to be based upon a
mistaken conception of this important factor.
As usual, Darwin’s disciples have failed to improve upon the account he
gave of the nature of the struggle for existence. This is set forth in
Chapter III. of the _Origin of Species_.
“The causes,” writes Darwin (new edition, p. 83), “which check the
natural tendency of each species to increase in number are most obscure.
Look at the most vigorous species; by as much as it swarms in numbers, by
so much will it tend to increase still further. We know not exactly what
the checks are even in a single instance.” This is perfectly true.
Nevertheless elaborate theories of protective and warning colouration and
mimicry have been built up on the tacit assumption that the checks to the
multiplication of all, or nearly all, species are the creatures which
prey upon them. Possibly no Wallaceian asserts this in so many words, but
it is a logical deduction from the excessive prominence each one gives to
the various theories of animal colouration; for, if the chief foes of an
organism are not the creatures which prey upon it, how can the particular
shade and pattern of its coat be of such paramount importance to it?
Checks on Increase
We shall endeavour to show that there are checks on the increase of a
species far more potent than the devastation caused by those creatures
which feed upon it. Let us, however, first briefly set forth some of the
checks on the multiplication of organisms which Darwin mentions in the
_Origin of Species_.
“Eggs, or very young animals,” he says, “seem generally to suffer the
most, but this is not invariably the case.” This is, as we have already
insisted, a most important point to be borne in mind, especially when
considering the various current theories of animal colouration. When once
the average animal has become adult its chances of survival are
enormously increased.
A second check mentioned by Darwin is the limitation of food supply. “The
amount of food for each species,” he writes (p. 84), “of course gives the
extreme limit to which each can increase; but very frequently it is not
the obtaining food, but the serving as prey to other animals, which
determines the average numbers of a species. Thus there seems to be
little doubt that the stock of partridges, grouse, and hares on any large
estate depends chiefly on the destruction of vermin. . . . On the other
hand, in some cases, as with the elephant and rhinoceros, none are
destroyed by beasts of prey.”
We are inclined to think that neither the food limit nor the beasts of
prey are a very important check on the multiplication of organisms. The
lion, for example, was never so numerous as to reach the limit of its
food supply. Before the white man obtained a foothold in Africa vast
herds of herbivores were to be seen in those districts where lions were
most plentiful. This is a most important fact, for, if the numbers of a
species are not determined by those of the animals that prey upon it, the
particular colour of an organism is probably not of any direct importance
to it. This cuts away the foundation of some of the generally accepted
theories of animal colouration.
“Climate,” writes Darwin (p. 84), “plays an important part in determining
the average numbers of a species, and periodical seasons of extreme cold
or drought seem to be the most effective of all checks. I estimated
(chiefly from the greatly reduced numbers of nests in the spring) that
the winter of 1854-55 destroyed four-fifths of the birds in my own
grounds, and this is a tremendous destruction when we remember that 10
per cent. is an extraordinarily severe mortality from epidemics with
man.”
In our opinion, Darwin did not lay nearly enough stress upon the
importance of climate as a check on the increase of species. We have seen
that he stated his belief that it is the most effective of all checks.
But even this is not a sufficiently strong statement of the case. It
seems to us that before this check all other checks pale into
insignificance.
Darwin failed to notice the potent effects of damp. Damp is more
injurious to most species than even cold or drought, as every one who has
tried to keep birds in England knows. All entomologists are aware how
harmful damp is to insects. Caterpillars seem to take cover under leaves
to avoid damp rather than to hide themselves from birds, since these make
a point, when searching for insects, of invariably looking carefully
under leaves.
It is a well-known fact that a wet winter in England causes much
mortality among rabbits. The increase of the rabbit in Australia is
usually attributed to the fact that the little rodent has not so many
predatory creatures to contend with there as it has in Europe. This is
not so. In Australia the rabbit has to fight against eagles, other large
birds of prey, carnivorous marsupials, feral cats, monitor lizards and
large snakes, to say nothing of the well-organised and persistent attacks
of man.
Were predacious creatures the most important foes of the rabbit it would
never have obtained a firm foothold in Australia. Damp appears to be its
chief enemy. In Australia this does not exist. Hence the remarkable
increase of the species. Stronger evidence it would not be possible to
advance of the potency of damp as a check on the increase of a species
and of the comparative powerlessness of the attacks of raptorial
creatures.
The failure of the sandgrouse to establish a footing in England is, we
believe, due to the fact that it is constitutionally unfitted to
withstand our damp climate.
The camel is an animal that revels in dry habitats, hence the difficulty
of keeping camels in damp Bengal, although they seem to thrive well
enough in the drier parts of India.
“When a species,” writes Darwin (p. 86), “owing to highly favourable
circumstances, increases inordinately in numbers in a small tract,
epidemics—at least, this seems generally to occur with our game
animals—often ensue; and here we have a limiting check independent of the
struggle for life. But even some of these so-called epidemics appear to
be due to parasitic worms, which have from some cause, possibly in part
through facility of diffusion amongst the crowded animals, been
disproportionately favoured: and here comes in a sort of struggle between
the parasite and its prey.”
Thus inadequately does Darwin deal with that bar to the increase of
organisms, which is only second in importance to the effect of climate.
The check occasioned by disease and parasites is one to which naturalists
have as yet paid but little attention. The result is a very general
misunderstanding of the true nature of the struggle for existence, in
other words, of the _modus operandi_ of natural selection.
The tsetse-fly in Africa is a far more important check on the increase of
some animals than the lions and other beasts of prey. There are in that
continent large tracts of country, known as tsetse-fly belts, in which
neither horse, nor ox, nor dog can exist. If races of these animals were
to arise which could withstand the bite of the tsetse-fly, these species
might increase more rapidly than the rabbit in Australia has done, nor
would it matter if the creatures in question were bright crimson, or any
other conspicuous colour.
Take the case of the lion in Africa. The chief bar to the increase in
numbers of this species appears to be the teething troubles to which the
whelps are liable. Now suppose that a mutation were to occur in the lion.
Suppose that several members of a litter were all bright blue, and that
these suffered from no teething troubles. They would probably all grow
up, and although at some disadvantage as hunters on account of their
conspicuous colouring, they would nevertheless probably increase at the
expense of the normally coloured lions, because of the immunity of their
offspring from death from teething troubles. Zoologists would then be at
a loss to explain their bright colouring. We should have all manner of
ingenious suggestions raised, namely, that in the moonlight these
creatures were really not at all conspicuous, indeed that they were
obliteratively coloured. In other words, a totally wrong explanation of
their colouring would be given and accepted. It is our belief that many
of the explanations put forward and accepted of the colouration of
existing species are wide of the mark.
As all bee-keepers are aware, the disease known as foul-brood works more
havoc among their bees than all the insectivorous creatures put together.
Similarly throat disease among wood-pigeons does more towards keeping
their numbers down than all the efforts of predacious birds.
A check on multiplication not mentioned by Darwin is that which is
sometimes imposed by the individuals of the species on one another. Thus,
in some animals, as, for example, the hyæna, the male occasionally
devours his own young ones.
A check of a similar nature results from the habit which the Indian House
Crow (_Corvus splendens_) has of interrupting the pairing operations of
its neighbours.
Attributes of Successful Species
We are now in a position to sum up briefly the more important requisites
for success in the struggle for existence.
These are not so much specialised structure as courage, a good
constitution, mental capacity and prolificacy.
Few animals possess all these characteristics in a pre-eminent degree,
for, to use the words of Mr Thompson Seton, “Every animal has some strong
point or it could not live, and some weak point or the other animals
could not live.” Courage may be of two kinds—active courage, like that of
the Englishman, or passive courage, like that of the Jew.
As D. Dewar has said: In the struggle for existence, “An ounce of good
solid pugnacity is worth many pounds of protective colouration.”
It is of course possible for an animal to possess too much courage. An
excessive amount of courage will often cause a creature to fight
unnecessary battles, which may lead to its premature death. This is
perhaps the reason why the pugnacious black form of the leopard is not
more numerous.
Under a good constitution we must include the power of resisting the
rigours of climate, more especially damp, the ability to resist disease,
and the enjoyment of a good digestion. When from any cause the normal
food of a species becomes scarce, the members of that species will have
to starve or supplement the normal diet with food of an unusual nature;
and those that are endowed with a good digestion will be able to digest
the new food and thus survive, while those which cannot assimilate food
to which they are unaccustomed will become emaciated and perish. We see
this in every hard winter in England, when the redwing, which, unlike
other thrushes, cannot thrive on berries, is the first to die. Most of
the more successful birds—the crows and gulls, for example—are
omnivorous—that is to say, they are able to digest all manner of food.
Under mental capacity, we would include cunning and sufficient
intelligence to adapt oneself to changed conditions. It is largely
through man’s superior mental capacity that he has become the dominant
species. It is true that he displays also courage and a good
constitution, being able to adapt himself to life under the most diverse
conditions; but this is, of course, in part due to his mental capacity,
which enables him to some extent to adapt his environment to himself.
The advantages of prolificacy are so apparent that it is unnecessary to
dilate upon them. Nearly as important as excessive fertility is the
ability on the part of the parents to look after their young ones.
Every successful species possesses in a special degree at least one of
the above attributes. It is interesting to take in turn the various
species which are most widely distributed and consider to what extent
they possess these several qualities.
Let us now consider a factor in evolution which is nearly as important as
natural selection itself—we allude to the phenomenon of correlation.
Correlation
We may define correlation as the interdependence of two or more
characters. This phenomenon is far more common than the majority of
naturalists seem to think. It very frequently happens that one particular
character never appears in an organism without being accompanied by some
other character which we should not expect to be in any way related to
it.
Darwin called attention to this phenomenon. “In monstrosities,” he
writes, on page 13 of the _Origin of Species_ (new edition), “the
correlations between quite different parts are very curious, and many
interesting instances are given in Isidore Geoffroy St Hilaire’s great
work on this subject. Breeders believe that long limbs are almost always
accompanied by an elongated head. Some instances of correlation are quite
whimsical: thus cats which are entirely white and have blue eyes are
generally deaf; but it has been lately stated by Mr Tait that this is
confined to the males.
“Colour and constitutional peculiarities go together, of which many
remarkable cases could be given among animals and plants. From the facts
collected by Heusinger, it appears that white sheep and pigs are injured
by certain plants, whilst dark-coloured individuals escape. Professor
Wyman has recently communicated to me a good illustration of this fact:
on asking some farmers in Virginia how it was that all their pigs were
black, they informed him that the pigs ate the paint-root
(_Lachnanthes_), which coloured their bones pink, and which caused the
hoofs of all but the black varieties to drop off; and one of the
‘crackers’ (_i.e._ Virginia squatters) added, “we select the black
members of a litter for raising, as they alone have a good chance of
living.’
“Hairless dogs have imperfect teeth; long-haired and coarse-haired
animals are apt to have, as is asserted, long or many horns; pigeons with
feathered feet have skin between their outer toes; pigeons with short
beaks have small feet, and those with long beaks large feet.
“Hence, if man goes on selecting, and thus augmenting, any peculiarity,
he will almost certainly modify unintentionally other parts of the
structure, owing to the mysterious laws of the correlation of growth.”
The great importance of the principle of the correlation of organs is,
that _natural selection may indirectly cause the survival of unfavourable
variations, or of variations which are of no utility to the organism,
because they happen to_ _be correlated with organs or structures that are
useful_.
Physiologists insist more and more upon the close interdependence of the
various parts of the organism. All recent researches tend to show that
each of the organs has, besides its primary function, a number of
subordinate duties to perform, and that the removal of one organ reacts
on all the others.
In face of these facts we should have expected those zoologists who have
followed Darwin to have paid very close attention to the subject of
correlation. As a matter of fact, the phenomenon seems to have been
almost completely neglected. This is an example of the manner in which
the superficial theories which to-day command wide acceptance have tended
to bar the way to research.
There seems to be, in the case of some organisms, at any rate, a distinct
correlation between their colouring and their constitution or mental
characters. For example, the black forms of the cobra, the leopard, and
the jaguar are notoriously bad-tempered.
“There is,” writes Col. Cunningham, on p. 344 of _Some Indian Friends and
Acquaintances_, “much variation in the temper of different varieties of
cobras, and, as is often so noticeable among other sorts of animals,
there would seem to be a distinct correlation between darkness of colour
and badness of temper. It is probably in part owing to a recognition of
this that the cobras ordinarily seen in the hands of the so-called snake
charmers are of a very light colour, although the choice may also be to
some extent of æsthetic origin, seeing that the paler varieties are
specially ornamental, due to the brilliancy of their markings and the
great development of their hoods.” It would thus appear that there is
also a correlation between the colour of the cobra and the size of its
hood.
Hesketh Pritchard informs us, in _Through the Heart of Patagonia_, that
the Gauchos assert that a “picaso” colt—that is to say, a black one with
white points—is the reverse of docile. Similarly, black mice are said to
be very hard to tame.
We have already called attention to the importance of courage and the
power of resisting the rigours of climate in the struggle for existence.
It is apparently because black is so frequently correlated with courage
that it is seen comparatively often in nature, in spite of the fact that
it is a very bad colour as regards protection from enemies. Those birds
and beasts which are black are usually thriving species. The dominance of
the crow tribe is a case in point. Crows, it is true, are not really
courageous, but they are dangerous owing to their gregarious habits, and
are dreaded by other creatures on account of their power of combination.
In _Birds of the_ _Plains_, D. Dewar records an instance of a number of
crows killing in revenge so powerful a bird as the kite.
Since very many species seem to throw off melanistic variations, it may
perhaps be asked, How is it that more black species do not exist?
The reply is twofold. In the first place, it is quite likely that in some
organisms black variations are not correlated with courage or extreme
pugnacity, and when such is the case the melanistic varieties will be
more likely to be exterminated by foes, on account of their
conspicuousness. It must be remembered that, other things being equal,
the inconspicuously coloured organism has a better chance of survival
than the showily coloured one. This is, of course, a very different
attitude from that which insists on the all-importance to animals of
protective colouration. Secondly, it is not difficult to see how too much
courage may be fatal to an animal in leading it to take risks which a
more timid creature would refrain from doing. This, as we have already
suggested, is probably the reason why the black panther is so scarce. The
black colour is readily inherited, so there must be some cause which
tends to kill off the black varieties of the panther.
Lest it be thought the idea that excessive courage and pugnacity are
harmful is mere fancy, let us quote from the account of the nesting
habits of the White-rumped Swallow (_Tachycineta leucorrhoa_) given by Mr
W. H. Hudson on p. 32 of _Argentine Ornithology_. He says that no matter
how many nesting sites are available, there is always much fighting
amongst these birds for the best places. “Most vindictively,” he writes,
“do the little things clutch each other, and fall to the earth twenty
times an hour, where they often remain struggling for a long time,
heedless of the screams of alarm their fellows set up above them; for
often, while they thus lie on the ground punishing each other, they fall
an easy prey to some wily pussy who has made herself acquainted with
their habits.”
We have already emphasised the importance to many species of possessing
the power of resisting the effects of damp. In the case of some organisms
favourable variations in this direction may possess a greater survival
value than those in the shape of greater speed or physical strength.
Now, if there be any correlation between the power of resisting damp and
the colour an animal bears, it is quite probable that animals of this
colour, whether or no it be conspicuous, are likely to survive in
preference to those who are more protectively coloured. There is some
evidence that in certain cases, at any rate, resistance to climate is
correlated with colour peculiarities. For example, some fanciers assert
that yellow-legged poultry resist cold and damp better than those whose
legs are not yellow. Fowls which have yellow legs have also yellow skins.
In this connection the almost universal assumption of orange feet by
domestic guinea-fowls is significant. Normally the feet of these birds
are black, and their natural African habitat is a dry one.
A grey or white colour appears to be correlated with resistance to cold.
In birds this may perhaps be explained by the fact that the feathers in
some light-coloured varieties are longer than in those of
normally-coloured ones. Thus mealy-coloured canaries have longer feathers
than brightly-coloured ones.
The Arctic Skua, having no enemies to fear, stands in no need of
protective colouration. It would therefore seem that the white-breasted
form of this bird becomes more numerous as it nears the north pole, not
because of the closer assimilation of its plumage to the colour of the
snowy surroundings, but because the bird has to resist the greater degree
of cold the farther north it finds itself. Similarly, in the region of
the south pole the albino form of the Giant Petrel (_Ossifraga gigantea_)
becomes common. Both these birds are themselves predatory and not liable
to be preyed upon.
The curious china-white legs of some desert birds—as, for example,
coursers and larks—would seem to indicate a power of resisting the hot
rays radiating from the sand on which these creatures dwell.
White quills do not wear well either in domestic birds or in wild
albinos. This may explain why it is that when a white wild species of
bird has any black in its plumage the black is almost invariably on the
tips of the wings.
White quill-feathers are one of the commonest variations observed in
domesticated birds, nevertheless they are as rare as complete whiteness
among birds in their natural state.
A chestnut or bay colour in mammals appears to be correlated with a high
rate of speed, as in the thoroughbred horse. This perhaps explains why so
many of the swiftest species of antelope, such as the hartebeests and
sassaby (_Damaliscus lunatus_), are chestnut bay in colour. It is further
a remarkable fact that in the Black-buck (_Antilope cervicapra_) and the
Nilgai (_Boselaphus tragocamelus_) the females, which are faster than the
males, are not black or grey like their respective males, but reddish.
Wild turkeys are bronze; tame ones are black more often than any other
colour. This may be due to the fact that in them nigritude is correlated
with the power to resist damp. Among human beings those races which live
in very swampy districts are often intensely black.
It is a significant fact that those domestic animals which are bred for
speed or for fighting purposes do not assume all the varied hues that
characterise those that are allowed to breed indiscriminately.
Racehorses, greyhounds, and homing pigeons furnish examples of this. Even
more remarkable is the case of the Indian Aseel or game-cock. This is
bred purely for fighting purposes, and is required to display
extraordinary powers of endurance, since the spurs are cut off in order
to prolong the fight. Thus it is that this Indian race of game-cocks
shows little variation when compared with the English breed, which fights
in a more natural manner. The hens of the Indian form seem never to show
the colouration of the wild jungle fowl, although the cocks may do so. It
would appear that hens having the colouration of their wild ancestors
cannot breed cocks possessed of the requisite courage. The Aseel is said
to be of the highest courage only when the legs, beak and iris are white.
There is, we believe, not the least doubt that many other connections
between colour and various characteristics have yet to be discovered. It
is high time that competent naturalists paid attention to this subject. A
study of the question will almost certainly throw much light upon many
phenomena of animal colouration which hitherto have not been
satisfactorily explained. It is quite likely that the sandy hue displayed
by birds and beasts which frequent desert regions may be due to a
correlation with the power of withstanding intense dry heat rather than
to its rendering them inconspicuous to their foes.
As other examples of correlation we may cite the correlation which seems
to obtain between short canine teeth and the absence of a hairy covering
to the body. This phenomenon is observed both in men and pigs. Hairless
dogs almost invariably have their teeth but poorly developed.
Darwin called attention to the connection between a short beak and small
feet in pigeons; we see the same phenomenon in the dwarf breed of ducks
known as call-ducks.
A curious correlation exists between fowls’ eggs with brown shells and
the incubating habit. Fanciers have long tried in vain to produce a hen
that lays brown eggs without becoming “broody” at certain seasons.
Among fowls, long legs are invariably correlated with a short tail, as is
well seen in the Malay breed. This correlation may explain the short
tails of wading birds. Short-legged fowls, like Japanese bantams, have
long tails, and it is significant that the short-legged Weka Rails
(_Ocydromus_) of New Zealand have unusually long tails for the family. In
this connection we may say that the tail-like plumes of the cranes are
not tail-feathers, but the tertiary feathers of the wings. As egrets also
have long trains of plumes growing from the back, it cannot be said that
the short tail of the vast majority of the waders is due to the fact that
these birds would be at a disadvantage were their caudal feathers long.
Isolation
Isolation is a most important factor in the making of species. It is a
factor to which Darwin failed to attach sufficient importance, and one
which has been to a large extent neglected by Wallaceians.
Divergence of Character
We have seen how a species can be improved or changed by natural
selection. All those individuals which have varied in a favourable
direction have been preserved, and allowed to leave behind them offspring
that inherit their peculiarities, while those which have not so varied
have perished without leaving behind any descendants. Thus the nature of
the species has changed. The old type has given place to a new one.
Instead of species A, species B exists. This is what Romanes has called
_monotypic_ evolution—the transformation of one species into another
species. But any theory of the origin of species must be able to answer
the question, Why have species multiplied? How is it that species A has
given rise to species B, C, and D, or, while itself continuing to exist,
has thrown off sister species B and C? How is it that in the course of
evolution, species have not been transmuted in linear series instead of
ramifying into branches? This ramification of a species into branches has
been termed by Romanes _polytypic_ evolution. It is easy to see how
natural selection can bring about monotypic evolution, but how can it
have effected polytypic evolution? To use Darwin’s phraseology, how is it
that divergence of character has come about? Darwin’s reply to this
question is (_Origin of Species_, p. 136), “from the simple circumstance
that the more diversified the descendants from any one species become in
structure, constitution, and habits, by so much will they be better
enabled to seize on many and widely diversified places in the polity of
nature, and so be enabled to increase in numbers.
“We can clearly discern this in the case of animals with simple habits.
Take the case of a carnivorous quadruped, of which the number that can be
supported in any country has long ago arrived at its full average. If its
natural power of increase be allowed to act, it can succeed in increasing
(the country not undergoing any change in its conditions) only by its
varying descendants seizing on places at present occupied by other
animals: some of them, for instance, being enabled to feed on new kinds
of prey, either dead or alive; some inhabiting new stations, climbing
trees, frequenting water, and some perhaps becoming less carnivorous. The
more diversified in habits and structure the descendants of our
carnivorous animal become, the more places they will be enabled to
occupy. What applies to one animal will apply throughout all time to all
animals—that is, if they vary—for otherwise natural selection can effect
nothing.” Darwin was, therefore, of opinion that natural selection is
able to bring about polytypic evolution. Darwin tacitly assumes, in the
illustration he gives, that the various races of the carnivorous animal
are in some way prevented from intercrossing; for if they interbreed
indiscriminately, these races will tend to be obliterated.
Isolation
“That perfectly free intercrossing,” writes Professor Lloyd Morgan (on p.
98 of _Animal Life and Intelligence_), “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 with 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 interbreeding 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. Its
importance, indeed, can 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.”
This is very sound criticism, and is not very materially affected by the
fact that the intercrossing of varieties does not necessarily imply a
blending of their characters in the offspring; for, as we have seen, some
characters do not blend. No matter what form inheritance takes, in order
that natural selection may cause polytypic evolution it must be assisted
by isolation in some form or other.
Thus isolation is an important factor in evolution, though probably not
so important as its more extreme advocates would have us believe. Wagner,
Romanes, and Gulick have, in insisting upon the importance of the
principle of isolation, rendered valuable service to biological science,
but, in common with most men having a new theory, they have pushed their
conclusions to absurd lengths.
As Romanes has pointed out, isolation may be discriminate or
indiscriminate. “If,” he writes, on p. 5 of vol. iii. of _Darwin and
after Darwin_, “a shepherd divides a flock of sheep without regard to
their characters, he is isolating one section from the other
indiscriminately; but if he places all the white sheep in one field, and
all the black sheep in another field, he is isolating one section from
the other discriminately. Or, if geological subsidence divides a species
into two parts, the isolation will be indiscriminate; but if the
separation be due to one of the sections developing, for example, a
change of instinct determining migration to another area, or occupation
of a different habitat on the same area, then the isolation will be
discriminate, so far as the resemblance of instinct is concerned.”
Discriminate Isolation
Other names for indiscriminate isolation are separate breeding and
apogamy. Discriminate isolation is also called segregate breeding and
homogamy. The human breeder resorts to discriminate isolation in that he
separates all those creatures from which he seeks to breed, from those
from which he does not wish to breed. Natural selection itself is,
therefore, a kind of discriminate isolator, since it isolates the fit by
destroying all the unfit, and, inasmuch as it kills off all those
creatures which it fails to isolate, it differs from other forms of
isolation in preventing the inter-breeding of the unisolated forms and
their giving rise to a different race. Thus it is clear that natural
selection, unless aided by some other form of isolation, can give effect
to only monotypic evolution. This is a point on which Romanes rightly
insists strongly.
There are several other forms of discriminate isolation. Sexual selection
would be one of these. Suppose, for example, that in any species there
are large and small varieties formed, and like tends to breed with like,
then the small individuals will breed with other small individuals, while
large ones will mate with large ones; thus two races—a large one and a
small one—will be evolved side by side, provided, of course, natural
selection does not step in and destroy one of them.
Another kind of discriminate isolation may be due to the fact that one
variety is ready to pair before the other; thus two races are likely to
arise which breed at different seasons. It is unnecessary for us to
discourse further on the subject of discriminate isolation; those
interested in the subject should read vol. iii. of _Darwin and after
Darwin_, by Romanes.
Indiscriminate Isolation
It is impossible to deny the importance of discriminate isolation as a
factor in evolution. On this there can be no room for disagreement among
biologists. It is when we come to the subject of indiscriminate isolation
that we enter a region of zoological strife.
Is indiscriminate isolation _per se_ a factor of evolution? Romanes,
Gulick, and Wagner assert that it is, Wallace and his adherents assert
that it is not.
As the burden of proof is on the former, they are entitled to the first
hearing.
“We may well be disposed, at first sight,” writes Romanes (_Darwin and
after Darwin_, p. 10), “to conclude that this kind of isolation can count
for nothing in the process of evolution. For if the fundamental
importance of isolation in the production of organic forms be due to its
segregation of like with like, does it not follow that any form of
isolation which is indiscriminate must fail to supply the very condition
on which all the forms of discriminate isolation depend for their
efficacy in the causing of organic evolution? Or, to return to one’s
concrete example, is it not self-evident that the farmer who separated
his flock into two or more parts indiscriminately, would not effect any
more change in his stock than if he had left them all to breed together?
Well, although at first sight this seems self-evident, it is, in fact,
untrue. For, unless the individuals which are indiscriminately isolated
happen to be a very large number, sooner or later their progeny will come
to differ from that of the parent type, or unisolated portion of the
parent stock. And, of course, as soon as this change of type begins, the
isolation ceases to be indiscriminate; the previous apogamy has been
converted into homogamy, with the usual result of causing a divergence of
type. The reason why progeny of an indiscriminately isolated section of
an originally uniform stock—_e.g._ of a species—will eventually deviate
from the original type is, to quote Mr Gulick, as follows:—‘No two
portions of a species possess exactly the same average character, and the
initial differences are for ever reacting on the environment and on each
other, in such a way as to ensure increasing divergence as long as the
individuals of the two groups are kept from intergenerating.’”
The words of Mr Gulick require close scrutiny. We may admit that “no two
portions of a species possess exactly the same average character,” but
why should the two, if prevented from interbreeding yet subjected to
similar climatic and other conditions, present the phenomenon of
“increasing divergence?” The reason assigned by Romanes is the “Law” of
Delbœuf, which runs:—“_A constant cause of variation_, however
insignificant it may be, changes the uniformity of type little by little,
and diversifies it _ad infinitum_.” From this “Law” it follows, says
Romanes, on p. 13 of vol. iii. _Darwin and after Darwin_, that “no matter
how infinitesimally small the difference may be between the average
qualities of an isolated section of a species compared with the average
qualities of the rest of that species, if the isolation continues
sufficiently long, differentiation of specific type is necessarily bound
to ensue.”
This deduction involves two important assumptions. The first is, that in
each of the separated portions of the given species there is a constant
cause of variation operating in one direction in the case of one portion
and in another direction in the case of the other. This assumption is,
unfortunately, not founded on fact. If we were to take one hundred
race-horses and shut them up in one park and one hundred cart-horses and
shut them up in another park, and prevent the interbreeding of the two
stocks, we should, if Romanes’s tacit assumption be true, see the two
types diverge more and more from one another. We know that as a matter of
fact they will tend, generation after generation, to become more like one
another. Galton’s Law of Regression, of which we have already spoken, and
which is supported by ample evidence, clearly negatives this tacit
assumption made by Romanes and Gulick. The second assumption upon which
their reasoning is based is that there is no limit to the amount of
change which can be effected by the accumulation of fluctuating
variations; but, as we have already seen (on p. 70), there is a very
definite limit and this limit is quickly reached.
Thus the arguments of Romanes and Gulick are fundamentally unsound.
Mollusca of Sandwich Isles
But the fact remains, and has to be accounted for, that, as a general
rule, when two portions of a species are separated, so that they are
prevented from interbreeding, they begin to diverge in character, and the
longer they remain thus separated the greater becomes that divergence.
This is an observed fact which cannot be gainsaid.
It was the observance of this fact which led Gulick to insist with such
emphasis on the importance of geographical isolation as a factor in
evolution. He discovered that the land mollusca of the Sandwich Islands
fall into a great number of varieties.
These islands are very hilly, and Gulick found that each of the varieties
is confined not merely to one island, but to one valley. “Moreover,”
writes Romanes, on p. 16 of _Darwin and after Darwin_, “on tracing this
fauna from valley to valley, it is apparent that a slight variation in
the occupants of valley 2, as compared with those of the adjacent valley
1, becomes more pronounced in the next, valley 3, still more so in 4,
etc., etc. Thus it was possible, as Mr Gulick says, roughly to estimate
the amount of divergence between the occupants of any two given valleys
by measuring the number of miles between them. . . . The variations which
affect scores of species, and themselves eventually run into fully
specific distinctions, are all more or less finely graduated as they pass
from one isolated region to the next; and they have reference to changes
of form or colour, which in no one case presents any appearance of
utility.”
Hitherto three different attempts have been made to explain this and
allied phenomena:—
1. That it is the result of isolation.
2. That it is the result of natural selection.
3. That it is the result of the action of the environment on the
organism.
Let us consider these in inverse order.
Local Species
In the case of some organisms, more especially plants, invertebrates, and
fish, the environment does exert a direct influence on their colouration.
But, as we have seen, the changes in colour, etc., thus induced appear
never to be transmitted to the offspring of the organisms so affected.
They disappear when the offspring are removed to other surroundings.
On the other hand, local races or species—as, for example, the
white-cheeked variety of sparrow found in India—usually retain their
external appearance when the environment is changed. In the one case the
peculiarity is not inherited; in the other it is inherited.
The Wallaceian explanation is, of course, that the phenomenon is the
result of natural selection. There must, say Wallace and his followers,
be some differences in the environment, differences which we poor human
beings cannot perceive, that have caused the divergence between the
various isolated sections of the species. In the case of some local
species this explanation is probably the correct one, but we have no
hesitation in saying that natural selection is unable to offer a
satisfactory explanation in a considerable number of instances. Take, for
example, the case of the land mollusca of the Sandwich Islands. Mr Gulick
worked for fifteen years at them, and states that so far as he is able to
ascertain the environment in the fifteen valleys is essentially the same.
“To argue,” writes Romanes, on p. 17 of vol. iii. of _Darwin and after
Darwin_, “that every one of some twenty contiguous valleys in the area of
the same small island must necessarily present such differences of
environment that all the shells in each are differently modified thereby,
while in no one out of the hundreds of cases of modification in minute
respects of form and colour can any human being suggest an adaptive
reason therefore—to argue thus is merely to affirm an intrinsically
improbable dogma in the presence of a great and consistent array of
opposing facts.”
Men of science not infrequently charge the clergy with adhering to dogma
in face of opposing facts; it seems to us that many of the apostles of
science are in this respect worse offenders than the most orthodox of
Churchmen.
The example of the mollusca of the Sandwich Islands is by no means a
solitary one. D. Dewar cited some interesting cases in a paper recently
read before the Royal Society of Arts (p. 103 of vol. lvii. of the
Society’s Journal):
“The Indian robins present even greater difficulties to those who profess
to pin their faith to the all-sufficiency of natural selection. Robins
are found in nearly all parts of India, and fall into two species, the
brown-backed (_Thamnobia cambaiensis_) and the black-backed Indian Robin
(_Thamnobia fulicata_). The former occurs only in Northern India, and the
latter is confined to the southern portion of the peninsula. The hen of
each species is a sandy brown bird with a patch of brick-red feathers
under the tail, so that we cannot tell by merely looking at a hen to
which of the two species she belongs. The cock of the South Indian form
is, in winter, a glossy black bird, with a white bar in the wing, and the
characteristic red patch under the tail. The cock of the northern
species, as his name implies, has a sandy-brown back, which contrasts
strongly with the glossy black of his head, neck, and under parts. In
summer the cocks of the two species grow more like one another owing to
the wearing away of the outer edges of their feathers; but it is always
possible to distinguish between them at a glance. The two species meet at
about the latitude of Bombay. Oates states that in a certain zone, from
Ahmednagar to the mouth of the Godaveri valley, both species occur, and
they do not appear to interbreed.
“It seems impossible to maintain that natural selection, acting on minute
variations, has brought about the divergence between these two species.
Even if it be asserted that the difference in the colour of the feathers
of the back of the two cocks is in some way correlated with adaptability
to their particular environment, how are we to explain the fact that in a
certain zone both species flourish?
“A similar phenomenon is furnished by the red-vented bulbul. This genus
falls into several species, each corresponding to a definite locality and
differing only in details from the allied species, as, for example, the
distance down the neck to which the black of the head extends. There is a
Punjab Red-vented Bulbul (_Molpastes intermedius_), a Bengal (_Molpastes
bengalensis_), a Burmese (_Molpastes burmanicus_) and a Madras
(_Molpastes hæmorrhous_) species.
“It does not seem possible to maintain the contention that these various
species are the products of natural selection, for that would mean if the
black of the head of the Punjab species extended further into the neck
the bird could not live in that country.”
Thus, natural selection clearly is unable to explain some cases of
divergence of character due to geographical isolation.
There remains the third explanation, that the divergence is the result of
the simple fact of isolation.
We have already shown how insuperable are the objections to the view held
by Romanes and Gulick.
It seems to us that explanation must lie in the fact that mutations occur
every now and again in some species. If two portions of a species are
separated and a mutation occurs in one portion and not in the other, and
if the mutating form succeeds in supplanting the parent form in that
isolated portion of the species in which it has appeared, we should have
the phenomenon of two races or species differing in appearance although
subjected to what appear to be identical environment.
This, of course, is pure conjecture. All that can be said of it at
present is that it is not opposed to observed facts. That mutations do
occur must be admitted. At present we are totally in the dark as to what
causes them. They arise at the most unexpected times.
In favour of the explanation based on “mutation” there is the interesting
fact that geographical isolation does not by any means always cause
divergence of character. This Romanes, with great fairness, freely
admits. “There are,” he writes, on p. 133 of vol. iii. of _Darwin and
after Darwin_, “four species of butterflies, belonging to three genera
(_Lycæna donzelii_, _L. pheretes_, _Argynnis pales_, _Erebia manto_),
which are identical in the polar regions and the Alps, notwithstanding
that the sparse Alpine populations have been presumably separated from
their parent stocks since the glacial period.” Again, there are “certain
species of fresh-water crustaceans (_Apus_), the representatives of which
are compelled habitually to form small isolated colonies in widely
separated ponds, and nevertheless exhibit no divergence of character,
although apogamy has probably lasted for centuries.”
Cormorants
To these examples we may add that of the cormorants. These birds have an
almost worldwide range. One species—our Cormorant (_Phalacrocorax
carbo_)—occurs in every imaginable kind of environment. Isolation has not
effected any changes in the appearance of this species. Yet in New
Zealand there exist no fewer than fourteen other species of cormorant.
New Zealand is a country where climatic conditions are comparatively
uniform, nevertheless it boasts of no fewer than fifteen out of the
thirty-seven known species of cormorant. A possible explanation of this
phenomenon may be found in the comparatively easy conditions under which
cormorants live in New Zealand.[10] Under such circumstances mutants may
be permitted by natural selection to survive, whereas in other parts of
the world such mutants have not been able to hold their own.
Prof. Bateson has likened natural selection to a competitive examination
to which every organism must submit. The penalty for failure is immediate
death. The standard of the examination may vary with the locality.
Isolation, then, is a very important factor in the making of species, for
without it, in some form, the multiplication of species is impossible.
Let us, in conclusion, briefly summarise what we now know of the method
in which new species are made. We have studied the various factors of
evolution—variation and correlation, heredity, natural selection, sexual
selection, and the other kinds of isolation. How do these combine to
bring new species into being, and to establish the same?
Natural Selection
Let us first consider the factor known as natural selection, since this
is the one on which Darwin laid such great stress. Natural selection,
although a most important factor in evolution, is not an indispensable
one. Evolution is possible without natural selection.
Let us suppose that there is no such thing as natural selection; that the
numbers of existing species are kept constant by the elimination of all
individuals born in excess of the number required to maintain the species
at the existing figure, and that the elimination of the surplus is
effected, not by natural selection, but by chance, by the drawing of
lots. Under such circumstances there may be evolution, existing species
may undergo change, but the evolution will be determined solely by the
lines along which variations occur.
If mutations take place along certain fixed lines, and tend to accumulate
in the given directions, evolution will proceed along these lines quite
independently of the utility to the organism of the mutations that occur.
An unfavourable mutation will have precisely the same chance of survival
as a favourable one.
If, on the other hand, mutations occur indiscriminately on all sides of
the mean, then those mutations which happen to occur most frequently will
have the best chance of survival, and they will mark the lines of
evolution. But suppose that no mutation occurs more frequently than the
others. Under such circumstances there will be no evolution, unless, by
some cause or other, portions of the species are isolated, because in the
long run the mutations will neutralise one another.
Let us now suppose that natural selection comes into play. The old method
of determining by lot which forms shall persist is replaced by selection
on the fixed principle that the fittest shall survive. The mutations
appear as before, and as before, of the large number that occur, only a
few are permitted to survive. But now the survivors, instead of being a
motley crowd, are a selected band, composed of individuals having many
characteristics in common—a homogeneous company. Thus one result of
natural selection is to accelerate evolution, by weeding out certain
classes of individuals and preventing them breeding with those it has
selected. On the other hand, natural selection will tend to diminish the
number of species which have arisen through mutation, inasmuch as it
weeds out many mutants which would have perished had their survival been
determined by lot.
Origin of the Fittest
From this the kind of work performed by natural selection should be
obvious. Natural selection does not make new species. These make
themselves, or, rather, originate in accordance with the laws of
variation.
“You can,” runs an old proverb, “bring a horse to the drinking fountain,
but you cannot make him drink.” You may be able to bring a child into the
world, but you cannot secure its survival. Variation brings into being
mutants, which are incipient species, but variation cannot determine
their survival. It is at this stage that natural selection steps in.
But because natural selection allows certain mutations to persist, it is
not correct to say that natural selection has caused these mutations or
made or originated the species to which they give rise.
The Civil Service Commissioners do not make Indian civil servants: they
merely determine which of a number of ready-made men shall become civil
servants. Similarly, natural selection does not make new species, it
simply decides which of a number of ready-made organisms shall survive
and establish themselves as new species. Nor does natural selection
always do as much as this; for it is not the only determinant of
survival. Its position is sometimes comparable to that of the Medical
Board which inspects and rejects the physically unfit of the candidates
which have already been selected by some other authority.
The examination conducted by natural selection may be compared to a
competitive one. A separate, independent examination is held for each
particular locality; consequently the severity of the competition will
vary with the locality.
In each competition some candidates pass with ease: they gain an
unnecessarily high total of marks. So in nature do certain organisms, as,
for example, the Leaf-butterflies (_Kallimas_), appear to be over-adapted
to their environment. Other candidates manage to pass only by a very
narrow margin: these are paralleled in nature by those species which are
barely able to maintain themselves, which become extinct the moment the
competition increases in severity.
The great bulk of the candidates fail to obtain sufficient marks to gain
a place among the chosen few; these unsuccessful candidates correspond to
the mutating forms which perish in the struggle for existence, to those
individuals which happen to have mutated in unfavourable directions.
Even as many candidates have acquired knowledge of subjects in which they
are not examined, so do many organisms possess characteristics which are
of no utility to them in the struggle for existence.
Wallaceians expend much time and energy in misguided attempts to explain
the existence of such characters in terms of natural selection.
Nature’s examination, like that held for entrance to the Indian Civil
Service, is a liberal one, so that the qualifications of the successful
candidates vary considerably. Provided a candidate is able to gain more
marks than the other candidates for a vacancy, it matters not in what
subjects the marks are gained. So is it in nature. Natural selection
takes an organism as a whole. One species may have established itself
because of its fleetness, a second because of its courage, a third
because it has a strong constitution, a fourth because it is protectively
coloured, a fifth because it has good digestive powers, and so on.
We thus perceive the part played by natural selection and other forms of
isolation in the making of species. It is obvious that these do not make
species any more than the Civil Service Commissioners manufacture Indian
civil servants.
The real makers of species are the inherent properties of protoplasm and
the laws of variation and heredity. These determine the nature of the
organism; natural selection and the like factors merely decide for each
particular organism whether it shall survive and give rise to a species.
The way in which natural selection does its work is comparatively easy to
understand. But this is only the fringe of the territory which we call
evolution.
We seem to be tolerably near a solution of the problem of the causes of
the _survival_ of any particular mutation. This, however, is merely a
side issue. The real problem is the cause of variations and mutations,
or, in other words, how species _originate_. At present our knowledge of
the causes of variation and mutation is practically _nil_. We do not even
know along what particular lines mutations occur.
We have yet to discover whether one mutation invariably leads to another
along the same lines—in other words, whether mutating organisms behave as
though they had behind them a force acting in a definite direction. The
solution of these problems seems afar off. The hope of solving them lies,
not in the speculations in which biologists of to-day are so fond of
indulging, but in observation and experiment, especially the last.
The future of biology is largely in the hands of the practical breeder.
FOOTNOTES
[1]The white, pied, and “Japan” individuals are not more different from
the type than some variations occurring in wild birds.
[2]This short-legged type of dog is sometimes seen among the ownerless
and unselected pariah dogs of Indian towns; and a short-legged
variety of the fowl may occur sporadically in Zanzibar, where the
long-legged Malay is the prevalent breed.
[3]“Effected” appears in the earlier editions, but in the later editions
has given place to “affected,” probably a printer’s error.
[4]Some egrets, such as the rock-egrets (_Demiegretta_) of eastern
tropical coasts, are normally grey, but may be white, and this
whiteness may be confined in individuals to the young or adult
states.
[5]After years of observation of these Indian geese, Finn is convinced
they are now, at all events, pure Chinese; it is possible that they
really were hybrids in Blyth’s time, but that fresh importations of
geese from China, such as still occur, may have ultimately swamped
the blood of the common goose. The fertility of the hybrid geese was,
however, known to such early writers as Pallas and Linnæus. Darwin
himself, at a later date, bred five young from a pair of such hybrids
(_Nature_, Jan. 1, 1880, p. 207).
[6]In this chapter we use the word Neo-Darwinism in its usually-accepted
sense, _i.e._ as a name for that which should be called Wallaceism,
for the doctrine of the all-sufficiency of natural selection.
[7]_Animal Colouration_, p. 125. A book full of valuable facts and ideas
on this most interesting subject.
[8]Even these eggs, closely though they resemble in colouring the
shingle, etc., on which they are laid, are discovered and eaten by
gulls, as Mr A. J. R. Roberts points out in _The Bird Book_.
[9]_Journal of the Bombay Natural History Society_, Vol xv. (1903-4), p.
454.
[10]Hutton and Drummond record other examples of this in the valuable
work entitled _The Animals of New Zealand_.
INDEX
A
Accentor, 1
_Accipitcr cooperi_, 243
Acorn, 49
Acquired characters, 10, 14, 15, 18-24, 60, 107-10
_Acræeidæ_, 175, 215, 228
_Ægilops speltæformis_, 118
_Ægithina tiphia_, 244
Æsthetic sense in birds, 306
“African Nature Notes and Reminiscences,” 192, 195, 199
Aggressive resemblance, 173
Aguara-guazu, 181
Aitken, E. H., 64
“Albany Review, The,” 43, 48, 195, 204
Albinism, 64, 65, 99, 283, 284, 362
_Alcedo ispida_, 289
Alcock, Col., 216, 217
Alcohol, 152, 153
Alexander, 181
Allen, Grant, 66
Allotrophy, 159
Alternating characters, 143
Alternative inheritance, 127
Amadavat, 311
_Amandina erythrocephala_, 122
_A. fasciata_, 122
“Amazement,” 93
Amazon parrot, 103
Amazonian dolphin, 99
Ammonites, 67
Ammonium sulphate, 151
Amœba, 35
_Amphidasys betularia_, 101
_Anas boscas_, 123, 334
_A. obscura_, 334
_A. pœcilorhyncha_, 315, 334
_A. superciliosa_, 315, 334
_A. undulata_, 334
_Anastomus oscitans_, 282
Ancon sheep, 95
_Anemone magellanica_, 118
_A. sylvestris_, 118
Anemophilous flowers, 261
“Animal Colouration,” 194, 205, 211, 213, 218, 222
“Animal Life and Intelligence,” 368
“Animals of New Zealand,” 382
_Anous_, 278
_Anser cygnoides_, 114
_Anseranas melanoleucus_, 281
Antarctic fauna, 191
Antelope, 48, 199, 334
_Anthracoceros_, 220
_Anthropoides paradisea_, 279
_A. virgo_, 279
_Antilope cervicapra_, 363
Ape, 101
Apogamy, 370
Appenzeller, 340
_Apus_, 381
“Archiv für Entwicklungsmechanik der Organismen,” 325, 330
Arctic fauna, 173, 174, 190, 191
Arctic regions, 173, 189
_Ardea asha_, 317, 318
_A. gularis_, 318
_Ardeola grayii_, 250, 254
Argali, 120, 130, 131
“Argentine Ornithology,” 361
_Argynnis pales_, 381
_A. paphia_, 103
Aristotle, 1
_Artemia milhausenii_, 156
_A. salina_, 156
Aseel, 364
Asexual reproduction, 135
Asiatic, 140
Ass, 117, 127, 128, 140
_Astur badius_, 235
Atavism, 136, 293
_Athene chiaradiæ_, 97
_A. noctua_, 97
Atoms, biological, 158
“Auk, The,” 190
_Aularches militaris_, 216
Avebury, Lord, 205, 260
“Avicultural Magazine, The,” 98
Avocet, 80
B
Babbler, 244
Bactrian camel, 121
Bailey, 88
Baillon’s crake, 251
Balanced characters, 143
_Balearica chrysopelargus_, 105
_B. regulorum_, 105
_Bassaris astuta_, 242
Batesian mimicry, 177
Bateson, 26, 72, 73, 74, 75, 76, 102, 103, 302
Bats, 42
Bear, 101, 119, 190, 216, 282
Beddard, 180, 188, 194, 205, 211
Bee, 178, 179, 214, 221, 263, 264, 269
Beech, purple, 87
Bee-eater, 220, 278
Beetroots, 71
Belt, 216
Beluga, 190
Bentham, 260
Bestiary, 125
Bicheno’s finch, 105
Bilateral symmetry, 252, 253, 257
Bingham, Col. C. T., 239
Biological atoms, 158-69, 280
Biological molecules, 157-69, 280, 285, 291, 293, 294, 295, 344
Biological radicles, 158-69
Biophors, 153
“Bird Book, the,” 207
“Birds of the Plains,” 233, 303, 309, 359
Bison, 119, 126
Blackcock, 129, 131, 249, 278
Blackberry, 118
Blackbird, 201, 203, 207
Black-buck, 363
Blakiston, 181
Bloodsucker, 220
Blue-bellied waxbill, 104
Blyth, 115, 251
Boisier, 263
_Bombyx arrindia_, 125
_B. cynthia_, 124
Bonhote, 126, 288, 289, 290, 291, 292, 293, 337
Bontebock, 196
_Boselaphus tragocamelus_, 357, 363
_Bos frontalis_, 126
Boulenger, 88
Bower-bird, 306
Brain-fever bird, 235, 236, 248
Bramble, 261
_Branchipus_, 156
Brannam, 92
Brent, Mr, 307
British Museum, 129, 130, 187
_Bubo virginianus_, 221
_Bubulcus coromandus_, 254
Budgerigars, 101
Buffalo, 120, 199
Buffon, 2
Buff Orpingtons, 65
Buff-tip moth, 215
_Bufo melanostictus_, 219
Bulbul, 123, 220, 221, 244, 245, 255, 256, 279
Bull, 119
_Bungarus cœruleus_, 217, 247
Bunting, reed, 98, 190, 289
_Buphus coromandus_, 317, 318
Burbank, 118
Burnet moth, 102
Bush-buck, 196
Butcher-bird, 241, 253
Buttercups, 70, 267, 274
Butterfly, 45, 47, 102, 103, 196, 197, 203, 204, 209, 212, 216,
238, 239, 240, 250, 264, 280, 306, 381
Buzzard, 262
C
Cacomistle, 242
_Cairina moschata_, 127, 245
Californian currant, 119
_Calœnas nicobarica_, 65
_Calotes versicolor_, 220
Camel, 120, 357
_Campophaga_, 248
Canary, 100, 101, 102, 117, 120, 127, 280, 338, 362
_Canis jubatus_, 181
Capercailzie, 129, 131
Capuchin monkey, 216
Carbon, 153
_Carduelis caniceps_, 255
_C. carduelis_, 255
Carnation, 85, 86
Carnivores, 67
Carp, 102
Carrion crow, 123
Carrot, 71, 269, 270
_Casarca cana_, 129
_C. tadornoides_, 129
“Cassell’s Book of the Horse,” 69
Castle, 149
Castration, effects of, 335, 344
Cat, 61, 98, 99, 100, 206, 282, 283, 339, 350, 356, 361
Cat-rabbit, 125
Cataloe, 119
Cataract, 340
Caterpillars, 155, 175, 205, 211, 215, 221, 350
Cattle, 94, 95, 115
_Centropus sinensis_, 220, 244
_Cephalophus doriæ_, 243
_Cephalopyrus flammiceps_, 244
_Cervulus muntjac_, 101
_C. reevesii_, 114
_C. vaginalis_, 114
_Cervus paludosus_, 180
_C. sika_, 120
_Ceryle rudis_, 202
Chaffinch, 289
Chamba monaul, 104
“Champion Ladybird,” 91, 92, 93
Change of function, theory of, 36, 37
_Chen nivalis_, 282
_C. rossi_, 282
_Chenatopex ægyptiaca_, 316
_Chenonetta jubata_, 316
Chinese goose, 99, 114, 121, 130
Chinese pheasant, 123
_Chloëphaga dispar_, 105
_C. magellanica_, 105, 334
_C. rubidiceps_, 105, 334
Chromosomes, 145-7
_Chrysæna victor_, 333
_Chrysolophus amherstiæ_, 121
_C. obscurus_, 97
_C. pictus_, 97, 121, 337
_Chrysomitris colombiana_, 244
_Chrysotis æstiva_, 103
_Ciconia alba_, 282
_C. boyciana_, 282
Cinnabar moth, 227
_Cissopis leveriana_, 281
Civil Service Commissioners, 385, 387
Cleistogamous flowers, 260
Climate as check on multiplication, 349, 350
Clouded-yellow butterfly, 103
Clover, 69, 274
_Clytus arietis_, 178, 229
Cobra, 224, 225, 226, 358, 359
_Colias edusa_, 103
Colour-blindness, 340
Colouration of Flowers, Law of Progressive, 66
—— of Organisms, 170-296
Columbidæ, 331, 333
Concealing colouration, 184-7
Congenital characters, 18, 19
Conn, 47
“Contemporary Review,” 26
Cope, 15, 67
_Copsychus saularis_, 281
_Coracias affinis_, 123, 255
_C. indica_, 123, 220, 255
Cordon-bleu, 104
Cormorant, 190, 191, 277, 381, 382
Corn, Indian, 81
Correlation, 39, 40, 117, 162, 167, 223, 339, 340, 344, 356-65
_Corvus corone_, 123, 255
_C. cornix_, 123, 255
_C. splendens_, 353
“Country-Side, The,” 261, 265, 266, 273, 304, 311, 313
Courser, 362
Court-bec, 72
Cow, 119, 120, 126
Crab, 155
Crane, 105, 247, 248, 279, 282, 292
_Crateropus bicolor_, 242
_C. canorus_, 179
_Crax globicera_, 104, 304
_C. grayi_, 104
_C. hecki_, 104, 304
Crested newt, 124
Cretaceous reptiles, 67
Crinoids, 67
Crocodile, 187
Cross-fertilisation, 69, 258-60
_Crotalus_, 223
Crow, 47, 123, 206, 220, 247, 255, 281, 353, 355, 359, 361
“Crow-pheasant,” 220
Cryptic colouring, 173
Cuckoo, 220, 233, 235, 236, 243, 244, 247, 248, 289
—— shrike, 248
_Cuculus canorus_, 289
Cuénot, 149
Cunningham, Col., 225, 226, 358
—— J. T., 15, 19, 20, 324, 325, 329, 331, 332, 333, 336
Cupples, Mr, 308
Curassow, 104, 304
Currant, 119
Cut-throat finch, 122
_Cypselus affinis_, 243
_Cytisus adami_, 119
D
Dafila acuta, 122
Dahlia, 86
Daisy, 266, 274
Daltonism, 340
_Damaliscus lunatus_, 363
Damp as a check to multiplication of species, 350, 351
_Danaidæ_, 175, 179, 215, 216, 226, 228
_Danais chrysippus_, 179, 250
Danger signal, 183, 214, 253, 254
Darter, 277
Darwin, 1-12, 14, 25-27, 31, 35, 42, 52, 54-7, 59, 60-3, 68, 83,
96, 112, 114-7, 119, 123, 127, 130, 151, 171, 175, 182,
184, 233, 259, 299, 301-8, 316, 319-21, 325, 326, 347
“Darwin and after Darwin,” 370-5, 377, 381
Darwinian theory, 3, 5-8, 11, 13, 27, 28, 35, 42, 45, 52, 75, 111,
171
Darwinism, 1, 7, 8, 11, 14, 26
“Darwinism,” 40, 53, 112, 117, 178, 207, 213, 228, 322, 323
“Darwinism To-day,” 16, 45, 67
_Dasyurus_, 283
De Candolle, 86
Decorative plumage, 40
Deer, 101, 120, 180, 298
Deerhound, 304, 308
Deer-ponies, 125
Degeneration, 168
Dejerine, 340
Delage, 33, 147
Delbœuf, Law of, 373
_Delias eucharis_, 216, 220, 221
_Demiegretta_, 100
Demoiselle crane, 277
“Descent of Man,” 234, 299, 301, 302, 304, 305, 319, 320, 326
Determination of sex, 165
“Development and Heredity,” 17
De Vries, 26, 66, 69-72, 75-8, 82-9, 95, 105, 118, 151
Dewar, D., 43, 44, 47, 48, 195, 204, 206, 208, 210, 225, 233, 236,
303, 308, 309, 354, 360, 378
Dewar, G. A. B., 196, 197
_Dicrurus ater_, 179, 233
_Didelphys nurina_, 243
Dimorphism, sexual, 51, 200, 201
_Dipsacus_, 58
Disease as a check to multiplication of species, 351
_Dissemurus paradiseus_, 179, 220
Divergence of character, 367
Dog, 59, 68, 99, 100, 125, 225, 226, 282, 283, 304, 308, 352, 357,
364, 365
Dog-rose, 261
Dolphin, 99
Dominant characters, 142
Donald, Mr D., 256
Dragon-fly, 216, 264
Driesh, 136
Drongo cuckoo, 233
Drongo-shrikes, 179, 220
Drummond, 382
Duck, 51, 60, 68, 97, 99, 100, 122, 126-8, 190, 247, 249, 282, 292,
314, 315, 334, 337, 338, 365
Duiker-buck, 243
Dyer, Sir William Thistleton, 26
E
Eagle, 65, 190, 350
Eagle-owl, 221
East, M. E., 79
_Echis carinata_, 224
“Eclipse,” 69
“Edinburgh Review, The,” 38
Eel, 102
Eggs, colours of birds’, 206-9
Egret, 100, 206, 254, 365
Eider-duck, 249
Eimer, 15, 16, 33
Eisig, 222
_Elanoides furcatus_, 282
_Elaps_, 197, 198
Elder, 49
Elementary species, 77, 78, 87, 88, 89
Elk, Irish, 67
_Emberiza citrinella_, 289
_E. pyrrhuloides_, 98
_E. schœniclus_, 98
_Entomophila picata_, 281
Entomophilous flowers, 261
_Epenthesis folleata_, 103
Epilobias, 260
_Equus_, 41
_Erebia manto_, 381
_Erythrura prasina_, 102
“Essays on Evolution,” 11, 173, 177, 181, 184, 213, 223, 226, 227,
229, 230, 231, 234, 237, 238, 239
_Estrelda cyanogastra_, 104
_E. phœnicotis_, 104
Ether, 152, 153
_Euchelia jacobacæ_, 227
Eurasian, 140
European, 140
_Euxenura maguari_, 282
Evening primrose, 84, 85, 88
“Evolution of Sex, The,” 306
Existence, struggle for, 31, 32
Eye-colour in human beings, 310
Eyesight of birds, 211, 237-41
—— insects, 264
Eyton, 15
F
“Faery Year, The,” 196
Falcon, 204, 246, 250
_Falco peregrinator_, 251
_F. severus_, 251
False mimicry, 243
Faults in poultry, 64
Ferrets, 100, 119
Finch, 117, 120
—— Bicheno’s, 105
—— chestnut-breasted, 98
—— cut-throat, 122
—— Gouldian, 98
—— Nonpareil, 102
—— red-headed, 142
—— ringed, 104
—— saffron, 244
—— yellow-rumped, 98
Finn, 99, 102, 115, 131, 179, 216, 219, 220, 235, 241, 255, 304,
309, 310, 313, 315, 316, 358
Fittest, survival of the, 32
Flowers, 65, 66
Flowers, colours of, 258-75
Fly-catchers, 44, 45, 47, 285, 338
Flying squirrel, 243
“Fortnightly Review, The,” 37, 38
Foul-brood, 353
Fowl, 56, 58, 61, 64, 65, 99, 101, 125, 127, 128, 282, 301, 302,
307, 314, 330, 336, 338, 339, 361, 362, 364, 365
Fowl-ducks, 125
Foxes, 101, 131, 190, 191
Fox-terrier, 19
Franqueiro cattle, 95
_Francolinus pondicerianus_, 337
Friar-bird, 249
_Fringella coelebs_, 209
Fritillary butterfly, 103
Frog, 325
Fruits, colours of, 258, 275
_Fuligula marila_, 290
Fulmar petrel, 190
Function, change of, 36, 37
Fungi, 263
G
Gadow, Dr, 197, 245
Gadwall, 126, 315
Galton, 81, 82, 374
“Game Birds and Wild Fowl of India,” 131
Gametes, segregation of, 143-5
Gannet, 282
Gayal, 126
Gauchos, 359
Gecko, 210
Geddes, 306, 326
Gemmules, 151
“Genesis of Species,” 7, 61
Geographical isolation, 375
Geological record, imperfection of, 40-2, 94
Geranium, 260
Germ-plasm, continuity of the, 25
Germinal variations, 106-10
_Geum urbanum_, 263
Gibbon ape, 101
Giraffe, 17, 18, 192, 196
_Globicera_, 104
Glutton, 190
Goat, 283
Goethe, 2
Golden pheasant, 97, 129, 149, 337, 338
Golden tench, 101
Goldfinch, 127, 255
Goldfish, 101, 102
Goose, 99, 100, 105, 115, 121, 130, 190, 281, 316, 334, 339
Gordon’s currant, 119
Goshawk, 247
Gouldian Finch, 99
Graba, 58
Gradation of colour, principle of, 185
_Graculipica melanoptera_, 244
“Grammar of Science, The,” 309
Grass, 273
Grasshopper, 185
Greenfinch, 122
Greyhound, 364
Grosbeak, 281, 284
Groundsel, 260
Grouse, red, 125
Growth-force, 15, 16, 68
_Grus leucogeranus_, 282
Guillemot, 58, 190, 245
Guinea-fowl, 100, 127, 128, 279, 362
Guinea-pig, 95, 101, 129, 283
Gulick, 369, 372-7, 380
Gull, 190, 191, 207, 247, 290, 355
_Gygis_, 278
Gyrfalcon, 190
H
Haeckel, 15, 24
Hæmophilia, 340
_Halcyon smyrnensis_, 202
_Haliœtus albicilla_, 65
Hare, 131, 185, 200
Harrier, 101
Hartebeeste, 363
Hawk-cuckoo, 235, 236
Hawk-eagle, 101
Hawks, 222, 235, 236, 247, 277
_Hecki_, 104
Helice, 103
_Heliconidæ_, 175, 215, 216, 228
Heloderm, 217
Henslow, 15, 22, 23, 47, 48, 259
“Heredity,” 103, 145, 166, 340
“Heredity of Acquired Characters in Plants,” 22, 48
“Heredity of Sexual Characters in relation to Hormones,” 19, 330
Heron, 250, 317
Herring, 193
Hertwig, 151
Heusinger, 357
Hewitt, Mr, 307
_Hierococcyx varius_, 235, 248
Hilversum, 84
Himalayan argali, 120
Hinny, 127, 136, 140, 162
_Hipparchia, semele_, 205
_Hippotragus equinus_, 334
_H. niger_, 334
_Hirundo rustica_, 251
_H. tytleri_, 251
“History of Creation,” 24
Hobby, 250, 251
Homogamy, 370
Honeyeater, 281
Hormones, 335, 338
Hornbill, 65, 220
Horner, 340
Horse, 61, 68, 69, 95, 96, 100, 101, 117, 127, 128, 140, 266, 267,
268, 272, 283, 332, 352, 363, 364, 374
Horse, genealogy of, 41
Houghton, 91
Howard, 315, 332
Hubrecht, 26
Hume, 131
Humming-bird, 328
Hutton, 3
Hutton, Captain, 115, 382
Huxley, 3, 6, 11, 40, 100, 111
Hyæna, 353
Hybridism, 111-32, 292, 293
Hydra, 21
Hydrogen, 152, 153
_Hydrophasianus chirurgus_, 250
_Hyla_, 245
Hypertely, 237, 240
_Hypolimnas misippus_, 179, 180
I
“Ibis, The,” 255, 256
_Icterus vulgaris_, 244, 281, 284
Impeyan pheasant, 104
Indian Civil Service, 385, 386, 387
Indian corn, 81
Inheritance, 133-69
—— alternative, 127
—— blended, 140, 148
—— definition of, 138
—— of acquired characters, 10, 14, 15, 18-24, 60, 107-10
—— particulate, 140
—— unilateral, 139, 140, 162
Insectivores, 67
Intercrossing, swamping effects of, 42, 83
Intimidating attitudes, 224, 225
Iora, 244
Iridescence, 186
Irish elk, 67, 168
Isolation, 366-82, 387
Isomerism, biological, 154-8
—— chemical, 152-4, 157
_Ithomiinæ_, 228, 246
Ivy, 261
J
Jacana, 250
Jackdaw, 51, 306
Jaeger, 86
Jaguar, 45, 358
Japanese greenfinch, 122
—— pheasant, 122, 124, 129
Jardin des plantes, 88
Java sparrow, 99, 100
Jelly-fish, 192
Jesse, W., 255
Johnston, 92
“Journal of the Bombay Natural History Society,” 209
“Journal of the Royal Society of Arts,” 236, 324, 378
Jungle-babbler, 179
Jungle fowl, 332
K
Kallima, 45, 47, 209, 212, 235, 386
Kellog, 16, 26, 45, 47, 67
Kingfisher, 202, 203, 206
Kite, 282
“Knowledge,” 171, 198, 277
Korchinsky, 15, 33
Krait, 216, 247
Kuppa, 224
L
Labernum, 119
_Lachnanthes_, 357
Ladybird, 213, 214
Lamarck, 2, 14, 17, 52
Lamarckism, 16, 24, 25
Lambert, Edward, 341
Lankester, Sir E. Ray, 13, 25
Lapwing, 207
Lark, 185, 362
_Larus ridibundus_, 290
Latent characters, 149
Law of battle, 301, 302, 321
Leaf-butterfly, 45, 47, 209, 235, 386
Lemming, 190
Lemur, 242, 243
_Lemur catta_, 242
Leopard, black, 101, 354, 358
_Leucopternis_, 282
_Ligurinus sinicus_, 122
Lily, 146
_Linaria vulgaris peloria_, 86
Linden, Gräfin von, 155
Links, missing, 41, 42
Linnæus, 65, 115
Linnet, 212, 338
“Linus I.,” 95, 96
Lion, 192, 334, 349, 352
_Liothrix luteus_, 179
Lizard, 64, 207, 210, 212, 216, 217, 220, 223, 269, 350
_Loddigesia mirabilis_, 328
Loeb, 147
_Lophophorus chambanus_, 104
_L. impeyanus_, 104
Lucerne, 118
Lung, 36, 37
Lutinism, 102
_Lycæna donzelli_, 381
_L. pheretes_, 381
_Lycodon aulicus_, 247
Lyell, 3
M
Mackerel, 193
Madingly, 102
_Mænia typica_, 221
Magnus, 86
Magpie, 281
Magpie colouring, 66, 67, 280, 281
Magrath, 256
Male-fern, 49
Mallard, 65, 97, 122, 126, 132, 293, 313, 315, 334, 337
Malthus, 31
Malva, 260
Manchester School, 27
Mannikin, 104
Marbled newt, 124, 245
Marshall, 28
—— Mr G. A. K., 239
—— Milnes, 37, 174
Marsupials, 67
Masters, 86
“Materials for the Study of Variation,” 73, 103
Mauchamp sheep, 95
Mayer, 228
“Mechanischphysiologische Theorie der Abstammungslehre,” 15
_Medicago media_, 118
_Megascops asio_, 44
Melanism, 64, 101, 360
_Melopsittacus undulatus_, 101
Mendel, 42, 74, 136, 141, 142, 144, 145
Mendel’s Law, 145, 149, 150, 161
Mendelism, 145
_Mesohippus_, 41
Micellæ, 151
_Micropus melanoleucus_, 245
“Mikado, The,” 237
Mildew, 49
Mimicry, conditions of, 178
Mimicry, protective, 45, 50, 51, 173, 177-82, 226-51, 275, 293, 294
Mink, 243
_Miohippus_, 41
Missing links, 41, 42
Missouri currant, 119
Mivart, Dr St George, 7, 61
Mole, 180
_Molge blasii_, 124
_M. cristata_, 124
_M. marmorata_, 124
_M. vulgaris_, 221
Mollusca, 49
—— of Sandwich Islands, 375, 378
Molpastes, 123, 255
_Molpastes bengalensis_, 256, 379
_M. burmanicus_, 379
_M. hæmorrhous_, 255, 379
_M. intermedius_, 256, 379
_M. leucogenys_, 256
Monaul, 104
Monkey, 64, 213
Monotypic evolution, 366
Monstrosities, 56, 57, 358
Morgan, Prof. Ll., 368
—— T. H., 26
Morse, 190
Moseley, Prof., 311
_Motacilla lugubris_, 122
_M. melanope_, 122
Moth, 101, 102, 124, 209, 215, 227, 238, 240
Mouse, 64, 105, 139, 141, 146, 149, 150, 180, 185, 282, 359
Mule, 127, 136, 140, 160, 162
Müller, Fritz, 81, 180
Müllerian mimicry, 177, 181, 182
_Munia atricapilla_, 104
_M. castaneithorax_, 98
_M. flaviprymna_, 98
_M. malacca_, 104
Muscovy duck, 99, 127, 128, 281
Musk ox, 190, 192
_Mustela sarmatica_, 243
Mutations, 41, 43, 66, 69, 72, 75-105, 124, 127, 134, 159, 160,
169, 223, 280, 281, 284, 292, 295, 339, 341, 342-4, 380-8
Mutations, theory of, 26, 38, 75, 76, 95
Myna, 244
_Myristicivoræ_, 282
N
Naegeli, 15, 16, 151
Nahrwal, 190
Natural selection, theory of, stated, 31, 32
“Nature,” 184
Nautili, 67
Nectar of flowers, 262, 264, 265, 268, 270, 271
Neo-Darwinians, 13, 14, 25, 173, 174, 176, 188, 214, 218, 222, 233,
238, 242, 263, 264
Neo-Darwinism, 51, 172, 234, 235, 264, 275, 276, 297
Neo-Lamarckians, 13, 14, 15
_Neophron_, 282
_Nepheronia hippia_, 179
_Nettium albigulare_, 179
New organs, beginnings of, 36, 73
Newman, 126
Newt, 124, 221, 222
Niata cattle, 95
Nicobar pigeon, 65
Nilgai, 337
Nitrogen, 153
Noddy, 62, 279
Nonpareil finch, 102
_Nyroca africana_, 337
O
Oates, 255, 379
Obliterative colouration, 184-7
_Ocydromus_, 365
_Œnis_, 205
_Œnopopelia tranquebarica_, 122, 123, 324, 333
_Œnothera lamarckiana_, 84, 85, 87, 88
_Ononis repens_, 23
_O. spinosa_, 22
Opossum, 243
Orchid, 268, 269, 270, 272
_Orgyia antiqua_, 215
“Origin of Species, The,” 7, 9, 11, 31, 53, 57, 63, 114, 170, 194,
347, 348, 356, 367
Oriole, 244, 249, 284, 304
_Oriolus galbula_, 282
_O. kundoo_, 282
_O. melanocephalus_, 244, 284
“Ornithological and Other Oddities,” 255
_Orohippus_, 41
Orr, 15-7
Orthogenesis, 15, 16, 34
_Ossifraga gigantea_, 99, 362
_Otidiphaps insularis_, 244
_Ovis ammon_, 120
_O. vignei_, 120
Owen, Sir Richard, 7
Owl, 247, 277, 289
—— little, 97, 98
—— scops, 101
—— snowy, 190
Ox, 146, 352
Oxygen, 152, 153, 263
P
Paddy bird, 254
Paint-root, 357
_Palæornis torquatus_, 102, 325
Pallas, 115
Pansy, 260
Panther, 360
_Papilio_, 228, 246
_P. aristolochiæ_, 179, 216, 220, 221
_P. polites_, 179
Paradise, bird of, 62, 249
Paradise flycatcher, 47, 202, 298, 303, 316, 324, 338
_Paradisea apoda_, 249
Paraguay cattle, 94
_Parnassius apollo_, 155
Paroquet, 102, 121, 325
Parrot, 103
Parthenogenesis, 135, 138
Partridge, 185, 315, 337
_Parus leucopterus_, 245
_Passer domesticus_, 289, 342
_P. montanus_, 342
_P. swainsoni_, 342
Pasteur, 5
_Pavo nigripennis_, 96
_Pavoncella pugnax_, 343
Pea, sweet, 74, 75, 81, 141
Pear, 72
Pearson, Karl, 309, 310
Peckham, 308
Pekin robin, 179
Pelagic animals, 173, 192-4
Penguin, 191
Pennant’s parakeet, 121
_Petaurus breviceps_, 243
Petrel, 44, 190, 191, 277, 337
Pfeffer, 33
_Phalacrocorax carbo_, 381
Phalanger, 243
Phalarope, 327
_Phasianidæ_, 125, 330
_Phasianus colchicus_, 114, 123
_P. torquatus_, 114, 123
_P. versicolor_, 114, 123, 124
Pheasant, 97, 104, 114, 121, 123, 128-30, 141, 315, 336, 338
Pictet, 155, 156
_Pieris napi_, 155
_Piezorhynchus_, 285
Pig, 57, 283, 357, 365
Pigeon, 61, 62, 65, 68, 71, 72, 91, 92, 93, 98, 101, 109, 126, 127,
244, 277, 282, 353, 357, 364, 365
Pigment, massing of, 256
Pike, 102, 222
Pimpernel, 261
Pintail duck, 130, 132, 293, 337
Pintailed nonpareil finch, 102
“Plant Breeding,” 87
Plasomes, 151
Plastidules, 151
_Platycercus elegans_, 121
_P. erythropeplus_, 121
_P. eximius_, 121
_Pliohippus_, 41
Plover, 207
Plumage, decorative, 40
Pochard, 126, 337
Pœcilomeres, 288-95
_Poëephila mirabilis_, 99
Polar bear, 119, 130
Polar bodies, 135
Polecat, 119
Polytypic evolution, 367
Poppy, 82, 261
_Porzana bailloni_, 251
_P. pusilla_, 251
Post-nuptial display, 316
_Potentilla tormentilla_, 263
Poulton, 11, 25, 26, 171, 173, 177, 181, 184, 210, 213, 217, 221,
223-5, 229-35, 238-42
_Precis artexia_, 203, 204, 212
Preferential mating among human beings, 309, 310
Prepotency, 136
Prickly pear, 274
Primrose, evening, 84, 85, 88
Pritchard, Hesketh, 359
“Proceedings of the Fourth International Ornithological Congress,”
288, 337
“Proceedings of the Linnæan Society,” 288
“Proceedings of the Natural History Society of Brunn,” 141
_Protohippus_, 37
_Pseudoclytia pentata_, 103
Pseudo-sematic colours, 173
_Pseudotantalus cinereus_, 282
Ptarmigan, 190
_Pteroclurus exustus_, 204
Puffin, 191
Pugnacity of animals, 206, 360
Puma, 45
Purple beech, 87
Pycraft, W. P., 277
_Pycnorhampus affinis_, 284
_P. icteroides_, 284
_Pygæra bucephala_, 215
Q
Quail, 185
Quatrefages, de, 124
_Quelea quelea_, 98
_Q. russi_, 98
_Querquedula crecca_, 290
Quetelet’s Law, 77
R
Rabbit, 99, 100, 105, 183, 253, 283, 350, 352
Racehorse, 69
Radicles, biological, 159
_Rallus aquaticus_, 251
_R. indicus_, 251
_Ranunculus bulbosus_, 70
_Rappia_, 245
Raspberry, 118
Rat, 74, 282
—— water, 101
Raven, 190
Razorbill, 190
Recessive characters, 142
Recognition colours, 251-7, 275
—— marks, 124
Red-mantled parakeet, 121
Redpole, 207
Redwing, 354
Reed bunting, 98
Reeves’ pheasant, 129
Regression, Law of, 82, 374
Reid, Archdale, 5
Reindeer, 190
Rest-harrow, 22
Reversion, 64, 65, 129, 293
_Rhinosciurus tupaioides_, 180
_Rhodocera rhamni_, 155
_Rhododendron ferrugineum_, 118
_R. hirsutum_, 118
_Rhynchæa_, 327
Ricardo, 28
Ringed finch, 104
Robin, 281, 378
Robin, Indian, 202
Robinson, Dr H., 171, 198
—— E. K., 261, 264, 265, 266, 268, 270, 272-4
Rodents, 67
Rogeron, 126
Roller, 123, 220, 255
Romanes, 366-81
Rook, 51, 187
Rose, 61, 267
Rosella parakeet, 121
Rous, Admiral, 69
Roux, 136
Ruff, 343
S
Sable, 190
Saffron finch, 244
Sainfoin, 267
Salamander, 217, 219, 221
_Salix alba_, 118
_S. pentandra_, 118
Sandgrouse, 204, 351
Sandpipers, 185, 190
Sassaby, 363
_Satyridæ_, 205
Scatliff, H. P., 91-3
Scatliff strain, 91
Scaup, 290
Schmankewitsch, 156
“Science,” 166
_Sciuropterus volucella_, 243
_Scops giu_, 101
Scops owl, American, 44
——, Indian, 101
Scoter, 249
Seal, 190, 191
Sea-urchin, 149
Seaweed, 263
Sebright, Sir John, 63
Secondary sexual characters, 298
Segregation, 369
—— of gametes, 143-5
Selous, Edmund, 308
—— F. C., 192, 195, 197, 203
Sematic colours, 173
_Sesia fuciformis_, 178
Sexual dimorphism, 51, 297-344
Sexual selection, theory of, 299-321
Shaheen, 251
Shamrock, 274
Sheathbill, 191
Sheep, 95, 266, 267, 283, 357, 372
Sheldrake, 109, 129
Shikra, 235, 236
Shoveler, 290
Shrew, 180, 216
Sidgwick, 28
Sidney, 5, 49
Sika deer, 120
Silver-washed fritillary butterfly, 103
Siskin, 127, 244
Skua, Arctic, 44, 362
Skua-gull, 191
Skunk, 186, 217, 221
Skylark, 315
Slug, 49, 185
Smith, Adam, 28
Snake, 185, 197, 198, 217, 220, 223-6, 247, 356
Snap-dragon, 268, 272
Snipe, 69, 327
Sodium sulphate, 151
Somatic variations, 106-10
“Some Indian Friends and Acquaintances,” 225, 358
Sorrel, 274
Sparrow, 213, 241, 341, 342
—— Java, 99, 100
Sparrow-hawk, 235, 243
_Spatula clypeata_, 290
Spavin, 332
“Species and Varieties,” 69, 77, 84, 87, 118
Species, definition of, 89
Species, elementary, 77, 78, 87-9
Spencer, 3, 15, 16, 28, 38, 151
Spider, 269, 272
_Sporæginthus amandava_, 311
Sports, 41, 43, 66, 75, 85, 135
Squirrel, 101, 186, 243
Stag, 325
—— Irish, 67
Standfuss, 155
Stanley crane, 248, 279
St Hilaire, T. G., 2, 356
Stick insect, 209
_Stictoptera annulosa_, 104
Stoat, 119, 190, 290
Stolzmann, 327-9, 342, 343
Stonechat, 353
Stork, 247, 282
“Strand Magazine,” 64
_Strix flammea_, 289
Struggle for existence, 31, 32, 48
—— for nourishment, 167
Suchetet, A., 126, 130
_Sula capensis_, 282
_S. serrator_, 282
Sunbird, 324
_Surniculus lugubris_, 235, 243
Survival of the fittest, 32
Survival value, 33, 34
Swallow, 250, 251, 279, 361
Swallow-shrike, 281
Swallow-tail butterfly, 179
Swan, 100
Swift, 243, 250
Swimming bladder of fishes, 36, 37
_Sycalis flaveola_, 244
_Syrphidæ_, 178
T
_Tachycineta leucorrhoa_, 361
_Tadorna cornuta_, 129
_T. tadornoides_, 129
Tails, 62, 64
Tait, Mr, 356
Tanager, 281
Tapir, 42
Tasmanian devil, 282
Teal, 290, 316
Teasel, fuller’s, 58
Teeth, molar, 105
Tegetmeier, Mr, 307
Tern, 62, 278
_Terpsiphone paradisi_, 202, 298, 304, 316, 324
_Tetraogallus_, 337
_Tetraonidæ_, 125
_Tetrapteryx paradisea_, 249
_Tetrao tetrix_, 129
_T. urogallus_, 129
_Thamnobia cambayensis_, 202, 275
_T. fulicata_, 202, 378
Thayer, Mr Abbot, 184-7
Thompson, Seton, 354
Thomson, 103, 136, 145, 166, 306, 326, 340
Throat disease, 353
“Through Southern Mexico,” 197, 245
“Through the Heart of Patagonia,” 359
Thrush, 203, 207, 355
Tiger, 334
Tit, 245
Toad, 210, 219, 241
Toad-flax, 56
Tortoise, 222
Trefoil, 274
_Trochilium_, 229
Trogon, 62
_Tropidonotus piscator_, 220
Troupial, 244, 281, 284
Tsetse-fly, 352
_Tupaia_, 180, 216
_T. ellioti_, 216
Turbit, 72, 91-3
“Turbit, The Modern,” 91
Turkey, 95, 363
Turnspit dog, 59
_Turtur cambayensis_, 333
_T. suratensis_, 333
_T. risorius_, 33, 123, 126
Tylor, Mr Alfred, 287
U
Ungulates, 67
Unilateral transmission, 341
Unit characters, 148-52
_Uria grylle_, 245
_U. lacrymans_, 58
Urial, 120, 130, 131
_Urodynamis tritensis_, 243
V
Valezina, 103
_Vanessa levana_, 154
_V. prorsa_, 154
Vapourer moth, 215
Variation, 52-110
—— cause of, 59-60
—— continuous, 56, 69, 76, 105
—— definite, 55
—— determinate, 55
—— discontinuous, 43, 56, 72, 73, 76, 78, 79, 87, 105, 106, 133,
159, 295
—— germinal, 106-10, 133
—— indefinite, 55, 59
—— somatic, 106-110
_Viola_, 260
_V. tricolor_, 260
Volckamer, 86
Vulture, 282
W
Waggett, 12
Wagner, 369, 372
Wagtail, 122, 203
Wallace, 3, 10, 13, 14, 25, 26, 35-42, 53, 112, 114, 116, 117, 171,
175, 177, 183, 184, 207, 213, 228, 230, 251, 253, 256, 287,
296, 308, 321-7, 343, 372, 377
Wallaceian school of biologists, 14, 24, 25, 47, 192, 210, 251,
346, 347, 366, 377
Wallaceism, 172, 202
Walrus, 190
Warblers, British, 315, 332
Warning colours, 173, 176, 198, 212-26
Wasp, 174, 178, 179, 214, 227
Wasp-beetle, 229
Water-rail, 251
Waxbill, blue-bellied, 104
Weasel, 190
Weaver, red-billed, 98
Weber, 86
Weir, Mr Jenner, 299
Weismann, 25, 106, 107, 151, 154
Weka rail, 365
“Westminster Review,” 112
Weston, G. E., 127
Whale, 42, 185, 190, 193
Wheatear, 253
Whinchat, 253
Wiesner, 151
Wilson, Prof. E. B., 166
Winter coat, 188
Wolf, 48, 130, 185, 192
Wonder horse, 95, 96
Woodpecker, 102
Wright, Mr, 304
Wyman, Professor, 357
X
X-element, 165
Y
Yak, 120
Yarrow, 268
“Year-book of the Smithsonian Institution,” 184
Yerbury, Col., 239
Youatt, 63
Z
Zebra, 196
Zebu, 120
Zocher & Co., 56
Zoological Gardens, Lahore, 309
——, London, 104, 119, 126, 130, 206, 304, 316
Zoological Society of London, 330
_Zygæna filipendulæ_, 102
_OTHER WORKS BY THE SAME AUTHORS_
By DOUGLAS DEWAR
BOMBAY DUCKS
BIRDS OF THE PLAINS
ANIMALS OF NO IMPORTANCE
Etc. Etc.
By FRANK FINN
ORNITHOLOGICAL AND OTHER ODDITIES
THE WORLD’S BIRDS
WILD BEASTS OF THE WORLD
GARDEN AND AVIARY BIRDS IN INDIA
Etc. Etc.
ORNITHOLOGICAL AND OTHER ODDITIES
BY
FRANK FINN, B.A. (Oxon), F.Z.S.
LATE DEPUTY-SUPERINTENDENT OF THE INDIAN MUSEUM, CALCUTTA
WITH NUMEROUS ILLUSTRATIONS FROM PHOTOGRAPHS
_Demy_ 8_vo._ 10_s._ 6_d. net_
PRESS OPINIONS
_Standard._—“This book, dealing with the courting of birds, how they
fight and mimic, and moult and blush, is one of the most fascinating we
have read for some time. His book will prove as interesting to the
general reader as to the enthusiastic naturalist.”
_Morning Post._—“The book consists of a number of papers—all are
delightfully readable. A very interesting and delightful book. The
style is always clear and free from technicalities; this volume will
certainly prove as entertaining to the general reader as it is
interesting to the naturalist.”
_Globe._—“The pleasantest of reading—produced most charmingly. The book
is illustrated with numbers of beautiful photographs showing bird and
beast life with wonderful truth and charm. We must congratulate Mr Finn
and his publisher on one of the most alluring nature books we have seen
for a long time.”
_Shooting Times._—“The volume is well illustrated, and is certainly a
very amusing and highly instructive publication.”
_Country Side._—“Mr Finn always has something to tell us, and often
something new. He is at home in writing of birds. An eminently readable
book.”
_Bookman._—“Very good. Always worth reading, and is well illustrated.”
_Academy._—“A most readable volume; there is not a dull line in the
whole volume, while the illustrations are remarkably good.”
_Indian Field._—“It is always with the greatest of pleasure that we
pick up a book written by this ever-interesting author. We must
congratulate him on his latest work—a delightful work.”
BOMBAY DUCKS
AN ACCOUNT OF SOME OF THE EVERYDAY BIRDS
& BEASTS FOUND IN A NATURALIST’S EL DORADO
By DOUGLAS DEWAR, F.Z.S., I.C.S.
With Numerous Illustrations From Photographs of
Living Birds by Captain F. D. S. Fayrer, I.M.S.
_Demy_ 8_vo._ 16_s. net._
PRESS OPINIONS
_Spectator._—“Mr Douglas Dewar’s book is excellent. . . . A feature of
the book is the photographs of birds by Captain Fayrer. They are most
remarkable, and quite unlike the usual wretched snapshot and blurred
reproductions with which too many naturalists’ books are nowadays
illustrated.”
_Standard._—“The East has ever been a place of wonderment, but the
writer of ‘Bombay Ducks’ brings before Western eyes a new set of
pictures. . . . The book is entertaining, even to the reader who is not
a naturalist first and a reader afterwards. . . . The illustrations
cannot be too highly praised.”
_Daily News._—“This new and sumptuous book. . . . Mr Dewar gives us a
charming introduction to a great many interesting birds.”
_Pall Mall Gazette._—“Most entertaining dissertations on the tricks and
manners of many birds and beasts in India.”
_Graphic._—“The book is written in a most readable style, light and
easy, yet full of information, and not overburdened with scientific
words and phrases. . . . The habits of the different birds are fully
described, often in a very amusing and interesting manner.”
BIRDS OF THE PLAINS
By DOUGLAS DEWAR, F.Z.S., I.C.S.
AUTHOR OF “BOMBAY DUCKS,” etc.
WITH NUMEROUS ILLUSTRATIONS
_Demy_ 8_vo._ 10_s._ 6_d. net_
PRESS OPINIONS
_Globe._—“Mr Dewar is not only a keen and patient observer, but he is
gifted with the descriptive art in high degree, and his vivacious style
communicates the characters and habits of birds with unerring fidelity
and infinite spirit.”
_Sportsman._—“Mr Dewar has a delightfully simple and quaintly humorous
way of expressing himself, and his clever word pictures of bird life
making charming reading.”
_Truth._—“The volume is handsomely produced, and, like its predecessor,
it has a number of remarkably fine illustrations.”
_Manchester Guardian._—“Those who enjoyed ‘Bombay Ducks’ will welcome
‘Birds of the Plains.’ His breezy style is pleasant and easy reading.
The photographs deserve the highest praise.”
_Daily Chronicle._—“Here is a work worthy of all commendation to those
who love birds, and is ably seconded by Captain Fayrer’s excellent
photographs.”
_NOTICE_
_Those who possess old letters, documents, correspondence, MSS., scraps
of autobiography, and also miniatures and portraits, relating to persons
and matters historical, literary, political and social, should
communicate with Mr. John Lane, The Bodley Head, Vigo Street, London, W.,
who will at all times be pleased to give his advice and assistance,
either as to their preservation or publication._
LIVING MASTERS OF MUSIC
An Illustrated Series of Monographs dealing with Contemporary Musical
Life, and including Representatives of all Branches of the Art. Edited by
Rosa Newmarch. Crown 8vo. Cloth. 2_s._ 6_d._ net each volume.
HENRY J. WOOD. By Rosa Newmarch.
SIR EDWARD ELGAR. By R. J. Buckley.
JOSEPH JOACHIM. By J. A. Fuller Maitland.
EDWARD MACDOWELL. By L. Gilman.
EDVARD GRIEG. By H. T. Finck.
THEODOR LESCHETIZKY. By A. Hullah.
GIACOMO PUCCINI. By Wakeling Dry.
ALFRED BRUNEAU. By Arthur Hervey.
IGNAZ PADEREWSKI. By E. A. Baughan.
RICHARD STRAUSS. By A. Kalisch.
CLAUDE DEBUSSY. By Franz Liebich.
STARS OF THE STAGE
A Series of Illustrated Biographies of the Leading Actors, Actresses, and
Dramatists. Edited by J. T. Grein. Crown 8vo. 2_s._ 6_d._ each net.
∵ _It was Schiller who said: “Twine no wreath for the actor, since his
work is oral and ephemeral.” “Stars of the Stage” may in some degree
remove this reproach. There are hundreds of thousands of playgoers, and
both editor and publisher think it reasonable to assume that a
considerable number of these would like to know something about actors,
actresses, and dramatists, whose work they nightly applaud. Each volume
will be carefully illustrated, and as far as text, printing, and paper
are concerned will be a notable book. Great care has been taken in
selecting the biographers, who in most cases have already accumulated
much appropriate material._
_First Volumes._
ELLEN TERRY. By Christopher St. John.
HERBERT BEERBOHM TREE. By Mrs. George Cran.
W. S. GILBERT. By Edith A. Browne.
CHAS. WYNDHAM. By Florence Teignmouth Shore.
GEORGE BERNARD SHAW. By G. K. Chesterton.
_A CATALOGUE OF MEMOIRS, BIOGRAPHIES, ETC._
_WORKS UPON NAPOLEON_
NAPOLEON & THE INVASION OF ENGLAND: The Story of the Great Terror,
1797-1805. By H. F. B. Wheeler and A. M. Broadley. With upwards of 100
Full-page Illustrations reproduced from Contemporary Portraits, Prints,
etc.; eight in Colour. Two Volumes. 32_s._ net.
_Outlook._—“The book is not merely one to be ordered from the library;
it should be purchased, kept on an accessible shelf, and constantly
studied by all Englishmen who love England.”
_Westminster Gazette._—“Messrs. Wheeler and Broadley have succeeded in
producing a work on the threatened invasion of England by Napoleon,
which treats of the subject with a fulness of detail and a completeness
of documentary evidence that are unexampled.”
DUMOURIEZ AND THE DEFENCE OF ENGLAND AGAINST NAPOLEON. By J. Holland
Rose, Litt.D. (Cantab.), Author of “The Life of Napoleon,” and A. M.
Broadley, joint-author of “Napoleon and the Invasion of England.”
Illustrated with numerous Portraits, Maps, and Facsimiles. Demy 8vo.
21_s._ net.
THE FALL OF NAPOLEON. By Oscar Browning, M.A., Author of “The Boyhood and
Youth of Napoleon.” With numerous Full-page Illustrations. Demy 8vo (9 ×
5¾ inches). 12_s._ 6_d._ net.
_Spectator._—“Without doubt Mr. Oscar Browning has produced a book
which should have its place in any library of Napoleonic literature.”
_Truth._—“Mr. Oscar Browning has made not the least, but the most of
the romantic material at his command for the story of the fall of the
greatest figure in history.”
THE BOYHOOD & YOUTH OF NAPOLEON, 1769-1793. Some Chapters on the early
life of Bonaparte. By Oscar Browning, M.A. With numerous Illustrations,
Portraits, etc. Crown 8vo. 5_s._ net.
_Daily News._—“Mr. Browning has with patience, labour, careful study,
and excellent taste given us a very valuable work, which will add
materially to the literature on this most fascinating of human
personalities.”
_Literary World._—“. . . Mr. Browning has examined all the available
sources of information and carefully weighed his historical evidence.
His discriminating treatment has resulted in a book that is . . . one
that arrests attention by the conviction its reasoned conclusions
carry.”
THE DUKE OF REICHSTADT (NAPOLEON II.) By Edward de Wertheimer. Translated
from the German. With numerous Illustrations. Demy 8vo. 21_s._ net.
(Second Edition.)
_Times._—“A most careful and interesting work which presents the first
complete and authoritative account of the life of this unfortunate
Prince.”
_Westminster Gazette._—“This book, admirably produced, reinforced by
many additional portraits, is a solid contribution to history and a
monument of patient, well-applied research.”
NAPOLEON’S CONQUEST OF PRUSSIA, 1806. By F. Loraine Petre. With an
Introduction by Field-Marshal Earl Roberts, V.C., K.G., etc. With Maps,
Battle Plans, Portraits, and 16 Full-page Illustrations. Demy 8vo (9 x 5¾
inches). 12_s._ 6_d._ net.
_Scotsman._—“Neither too concise, nor too diffuse, the book is
eminently readable. It is the best work in English on a somewhat
circumscribed subject.”
_Outlook._—“Mr. Petre has visited the battlefields and read everything,
and his monograph is a model of what military history, handled with
enthusiasm and literary ability, can be.”
NAPOLEON’S CAMPAIGN IN POLAND, 1806-1807. A Military History of
Napoleon’s First War with Russia, verified from unpublished official
documents. By F. Loraine Petre. With 16 Full-page Illustrations, Maps,
and Plans. New Edition. Demy 8vo (9 x 5¾ inches). 12_s._ 6_d._ net.
_Army and Navy Chronicle._—“We welcome a second edition of this
valuable work. . . . Mr. Loraine Petre is an authority on the wars of
the great Napoleon, and has brought the greatest care and energy into
his studies of the subject.”
NAPOLEON AND THE ARCHDUKE CHARLES. A History of the Franco-Austrian
Campaign in the Valley of the Danube in 1809. By F. Loraine Petre. With 8
Illustrations and 6 sheets of Maps and Plans. Demy 8vo (9 x 5¾ inches).
12_s._ 6_d._ net.
RALPH HEATHCOTE. Letters of a Diplomatist During the Time of Napoleon,
Giving an Account of the Dispute between the Emperor and the Elector of
Hesse. By Countess Günther Gröben. With Numerous Illustrations. Demy 8vo
(9 x 5¾ inches), 12_s._ 6_d._ net.
∵ _Ralph Heathcote, the son of an English father and an Alsatian
mother, was for some time in the English diplomatic service as first
secretary to Mr. Brook Taylor, minister at the Court of Hesse, and on
one occasion found himself very near to making history. Napoleon became
persuaded that Taylor was implicated in a plot to procure his
assassination, and insisted on his dismissal from the Hessian Court. As
Taylor refused to be dismissed, the incident at one time seemed likely
to result to the Elector in the loss of his throne. Heathcote came into
contact with a number of notable people, including the Miss Berrys,
with whom he assures his mother he is not in love. On the whole, there
is much interesting material for lovers of old letters and journals._
MEMOIRS OF THE COUNT DE CARTRIE. A record of the extraordinary events in
the life of a French Royalist during the war in La Vendée, and of his
flight to Southampton, where he followed the humble occupation of
gardener. With an introduction by Frédéric Masson, Appendices and Notes
by Pierre Amédée Pichot, and other hands, and numerous Illustrations,
including a Photogravure Portrait of the Author. Demy 8vo. 12_s._ 6_d._
net.
_Daily News._—“We have seldom met with a human document which has
interested us so much.”
_Athenæum._—“As a record of personal suffering and indomitable
perseverance against opposing circumstances the narrative of De
Cartrie’s escape to the Eastern frontier, in the disguise of a
master-gunner, could not easily be surpassed.”
WOMEN OF THE SECOND EMPIRE. Chronicles of the Court of Napoleon III. By
Frédéric Loliée. With an introduction by _Richard Whiteing_ and 53
full-page Illustrations, 3 in Photogravure. Demy 8vo. 21_s._ net.
_Standard._—“M. Frédéric Loliée has written a remarkable book, vivid
and pitiless in its description of the intrigue and dare-devil spirit
which flourished unchecked at the French Court. . . . Mr. Richard
Whiteing’s introduction is written with restraint and dignity.”
_Daily Telegraph._—“It is a really fascinating story, or series of
stories, set forth in this volume. . . . Here are anecdotes innumerable
of the brilliant women of the Second Empire, so that in reading the
book we are not only dazzled by the beauty and gorgeousness of
everything, but we are entertained by the record of things said and
done, and through all we are conscious of the coming ‘gloom and doom’
so soon to overtake the Court. Few novels possess the fascination of
this spirited work, and many readers will hope that the author will
carry out his proposal of giving us a further series of memories of the
‘Women of the Second Empire.’”
LOUIS NAPOLEON AND THE GENESIS OF THE SECOND EMPIRE. By F. H. Cheetham.
With Numerous Illustrations. Demy 8vo (9 × 5¾ inches). 16_s._ net.
MEMOIRS OF MADEMOISELLE DES ÉCHEROLLES. Translated from the French by
Marie Clothilde Balfour. With an Introduction by G. K. Fortescue.
Portraits, etc. 5_s._ net.
_Liverpool Mercury._—“. . . this absorbing book. . . . The work has a
very decided historical value. The translation is excellent, and quite
notable in the preservation of idiom.”
JANE AUSTEN’S SAILOR BROTHERS. Being the life and Adventures of Sir
Francis Austen, G.C.B., Admiral of the Fleet, and Rear-Admiral Charles
Austen. By J. H. and E. C. Hubback. With numerous Illustrations. Demy
8vo. 12_s._ 6_d._ net.
_Morning Post._—“. . . May be welcomed as an important addition to
Austeniana . . .; it is besides valuable for its glimpses of life in
the Navy, its illustrations of the feelings and sentiments of naval
officers during the period that preceded and that which followed the
great battle of just one century ago, the battle which won so much but
which cost us—Nelson.”
SOME WOMEN LOVING AND LUCKLESS. By Teodor de Wyzewa. Translated from the
French by C. H. Jeffreson, M.A. With Numerous Illustrations. Demy 8vo (9
× 5¾ inches), 7_s._ 6_d._ net.
POETRY AND PROGRESS IN RUSSIA. By Rosa Newmarch. With 6 full-page
Portraits. Demy 8vo. 7_s._ 6_d._ net.
_Standard._—“Distinctly a book that should be read . . . pleasantly
written and well informed.”
THE LIFE OF PETER ILICH TCHAIKOVSKY (1840-1893). By his Brother, Modeste
Tchaikovsky. Edited and abridged from the Russian and German Editions by
Rosa Newmarch. With Numerous Illustrations and Facsimiles and an
Introduction by the Editor. Demy 8vo. 7_s._ 6_d._ net. Second edition.
_The Times._—“A most illuminating commentary on Tchaikovsky’s music.”
_World._—“One of the most fascinating self-revelations by an artist
which has been given to the world. The translation is excellent, and
worth reading for its own sake.”
_Contemporary Review._—“The book’s appeal is, of course, primarily to
the music-lover; but there is so much of human and literary interest in
it, such intimate revelation of a singularly interesting personality,
that many who have never come under the spell of the Pathetic Symphony
will be strongly attracted by what is virtually the spiritual
autobiography of its composer. High praise is due to the translator and
editor for the literary skill with which she has prepared the English
version of this fascinating work . . . There have been few collections
of letters published within recent years that give so vivid a portrait
of the writer as that presented to us in these pages.”
COKE OF NORFOLK AND HIS FRIENDS: The Life of Thomas William Coke, First
Earl of Leicester of the second creation, containing an account of his
Ancestry, Surroundings, Public Services, and Private Friendships, and
including many Unpublished Letters from Noted Men of his day, English and
American. By A. M. W. Stirling. With 20 Photogravure and upwards of 40
other Illustrations reproduced from Contemporary Portraits, Prints, etc.
Demy 8vo. 2 vols. 32_s._ net.
_The Times._—“We thank Mr. Stirling for one of the most interesting
memoirs of recent years.”
_Daily Telegraph._—“A very remarkable literary performance. Mrs.
Stirling has achieved a resurrection. She has fashioned a picture of a
dead and forgotten past and brought before our eyes with the vividness
of breathing existence the life of our English ancestors of the
eighteenth century.”
_Pall Mall Gazette._—“A work of no common interest; in fact, a work
which may almost be called unique.”
_Evening Standard._—“One of the most interesting biographies we have
read for years.”
THE LIFE OF SIR HALLIDAY MACARTNEY, K.C.M.G., Commander of Li Hung
Chang’s trained force in the Taeping Rebellion, founder of the first
Chinese Arsenal, Secretary to the first Chinese Embassy to Europe.
Secretary and Councillor to the Chinese Legation in London for thirty
years. By Demetrius C. Boulger, Author of the “History of China,” the
“Life of Gordon,” etc. With Illustrations. Demy 8vo. Price 24_s._ net.
_Daily Graphic._—“It is sate to say that few readers will be able to
put down the book without feeling the better for having read it . . .
not only full of personal interest, but tells us much that we never
knew before on some not unimportant details.”
DEVONSHIRE CHARACTERS AND STRANGE EVENTS. By S. Baring-Gould, M.A.,
Author of “Yorkshire Oddities,” etc. With 58 Illustrations. Demy 8vo.
21_s._ net.
_Daily News._—“A fascinating series . . . the whole book is rich in
human interest. It is by personal touches, drawn from traditions and
memories, that the dead men surrounded by the curious panoply of their
time, are made to live again in Mr. Baring-Gould’s pages.”
CORNISH CHARACTERS AND STRANGE EVENTS. By S. Baring-Gould. Demy 8vo.
21_s._ net.
THE HEART OF GAMBETTA. Translated from the French of Francis Laur by
Violette Montagu. With an Introduction by John Macdonald, Portraits and
other Illustrations. Demy 8vo. 7_s._ 6_d._ net.
_Daily Telegraph._—“It is Gambetta pouring out his soul to Léonie Leon,
the strange, passionate, masterful demagogue, who wielded the most
persuasive oratory of modern times, acknowledging his idol, his
inspiration, his Egeria.”
THE MEMOIRS OF ANN, LADY FANSHAWE. Written by Lady Fanshawe. With
Extracts from the Correspondence of Sir Richard Fanshawe. Edited by H. C.
Fanshawe. With 38 Full-page Illustrations, including four in Photogravure
and one in Colour. Demy 8vo. 16_s._ net.
∵ _This Edition has been printed direct from the original manuscript in
the possession of the Fanshawe Family, and Mr. H. C. Fanshawe
contributes numerous notes which form a running commentary on the text.
Many famous pictures are reproduced, including paintings by Velazquez
and Van Dyck._
THE LIFE OF JOAN OF ARC.
By Anatole France.
A Translation by Winifred Stephens.
With 8 Illustrations.
Demy 8vo, 9 × 5¾ inches, 2 vols.
Price 25_s._ net.
∵ _Joan of Arc, by her friends accounted a saint, by her enemies a
witch, stands out the one supreme figure of the French 15th century;
that period of storm and stress, that time of birth-giving from which
proceeded the glories of the Renaissance. Bitter controversy raged
round the Maid in her life-time. Round her story to-day literary
polemic waxes high; and her life by Anatole France is the most eagerly
discussed book of the century. That it presents a life-like picture of
the time critics of all parties agree. Its author has well equipped
himself with the best erudition of the last thirty years. To the fruits
of these researches he has added profound philosophy and true
historical insight, and thus into consummate literary art he has
painted a more vivid picture of the French 15th century than has ever
yet been presented in any literature. The Maid herself Monsieur France
regards not as a skilful general or a wily politician as some writers
have endeavoured to make out, but as above all things a saint. It was
by her purity and innate goodness that she triumphed. “It was not Joan
who drove the English out of France . . . And yet the young saint
played the noblest part in the salvation of her country. Hers was the
part of sacrifice. She set the example of high courage and gave to
heroism a new and attractive form._
THE DAUGHTER OF LOUIS XVI.
Marie-Thérèse-Charlotte of France, Duchesse D’Angoulême.
By G. Lenotre.
With 13 Full-page Illustrations.
Demy 8vo.
Price 10_s._ 6_d._ net.
∵ _M. G. Lenotre is perhaps the most widely read of a group of modern
French writers who have succeeded in treating history from a point of
view at once scientific, dramatic and popular. He has made the
Revolution his particular field of research, and deals not only with
the most prominent figures of that period, but with many minor
characters whose life-stories are quite as thrilling as anything in
fiction. The localities in which these dramas were enacted are vividly
brought before us in his works, for no one has reconstructed 18th
century Paris with more picturesque and accurate detail. “The Daughter
of Louis XVI.” is quite equal in interest and literary merit to any of
the volumes which have preceded it, not excepting the famous Drama of
Varennes. As usual, M. Lenotre draws his material largely from
contemporary documents, and among the most remarkable memoirs
reproduced in this book are “The Story of my Visit to the Temple” by
Harmand de la Meuse, and the artless, but profoundly touching narrative
of the unhappy orphaned Princess: “A manuscript written by Marie
Thérèse Charlotte of France upon the captivity of the Princes and
Princesses, her relatives, imprisoned in the Temple.” The illustrations
are a feature of the volume and include the so-called “telescope”
portrait of the Princess, sketched from life by an anonymous artist,
stationed at a window opposite her prison in the tower of the Temple._
HUBERT AND JOHN VAN EYCK: Their Life and Work. By W. H. James Weale. With
41 Photogravure and 95 Black and White Reproductions. Royal 4to. £5 5_s._
net.
Sir Martin Conway’s Note.
_Nearly half a century has passed since Mr. W. H. James Weale, then
resident at Bruges, began that long series of patient investigations
into the history of Netherlandish art which was destined to earn so
rich a harvest. When he began work Memlinc was still called Hemling,
and was fabled to have arrived at Bruges as a wounded soldier. The van
Eycks were little more than legendary heroes. Roger Van der Weyden was
little more than a name. Most of the other great Netherlandish artists
were either wholly forgotten or named only in connection with paintings
with which they had nothing to do. Mr. Weale discovered Gerard David,
and disentangled his principal works from Memlinc’s, with which they
were then confused. During a series of years he published in the
“Beffroi,” a magazine issued by himself, the many important records
from ancient archives which threw a flood of light upon the whole
origin and development of the early Netherlandish school. By universal
admission he is hailed all over Europe as the father of this study. It
is due to him in great measure that the masterpieces of that school,
which by neglect were in danger of perishing fifty years ago, are now
recognised as among the most priceless treasures of the Museums of
Europe and the United States. Fullness and accuracy are the
characteristics of all Mr. Weale’s work._
VINCENZO FOPPA OF BRESCIA, Founder of the Lombard School, His Life and
Work. By Constance Jocelyn Ffoulkes and Monsignor Rodolfo Majocchi, D.D.,
Rector of the Collegio Borromeo, Pavia. Based on research in the Archives
of Milan, Pavia, Brescia, and Genoa, and on the study of all his known
works. With over 100 Illustrations, many in Photogravure, and 100
Documents. Royal 4to. £3. 11_s._ 6_d._ net.
∵ _No complete Life of Vincenzo Foppa has ever been written: an
omission which seems almost inexplicable in these days of
over-production in the matter of biographies of painters, and of
subjects relating to the art of Italy. The object of the authors of
this book has been to present a true picture of the master’s life based
upon the testimony of records in Italian archives; all facts hitherto
known relating to him have been brought together; all statements have
been verified; and a great deal of new and unpublished material has
been added. The authors have unearthed a large amount of new material
relating to Foppa, one of the most interesting facts brought to light
being that he lived for twenty-three years longer than was formerly
supposed. The illustrations will include several pictures by Foppa
hitherto unknown in the history of art, and others which have never
before been published, as well as reproductions of every existing work
by the master at present known._
MEMOIRS OF THE DUKES OF URBINO. Illustrating the Arms, Art and Literature
of Italy from 1440 to 1630. By James Dennistoun of Dennistoun. A New
Edition edited by Edward Hutton, with upwards of 100 Illustrations. Demy
8vo. 3 vols. 42_s._ net.
∵ _For many years this great book has been out of print, although it
still remains the chief authority upon the Duchy of Urbino from the
beginning of the fifteenth century. Mr. Hutton has carefully edited the
whole work, leaving the text substantially the same, but adding a large
number of new notes, comments and references. Wherever possible the
reader is directed to original sources. Every sort of work has been
laid under contribution to illustrate the text, and bibliographies have
been supplied on many subjects. Besides these notes the book acquires a
new value on account of the mass of illustrations which it now
contains, thus adding a pictorial comment to an historical and critical
one._
THE PHILOSOPHY OF LONG LIFE. By Jean Finot. A Translation by Harry
Roberts. Demy 8vo. (9 × 5¾ inches). 7_s._ 6_d._ net.
∵ _This is a translation of a book which has attained to the position
of a classic. It has already been translated into almost every
language, and has, in France, gone into fourteen editions in the course
of a few years. The book is an exhaustive one, and although based on
science and philosophy it is in no sense abstruse or remote from
general interest. It deals with life as embodied not only in man and in
the animal and vegetable worlds, but in all that great world of (as the
author holds) misnamed “inanimate” nature as well. For M. Finot argues
that all things have life and consciousness, and that a solidarity
exists which brings together all beings and so-called things. He sets
himself to work to show that life, in its philosophic conception, is an
elemental force, and durable as nature herself._
THE DIARY OF A LADY-IN-WAITING. By Lady Charlotte Bury. Being the Diary
Illustrative of the Times of George the Fourth. Interspersed with
original Letters from the late Queen Caroline and from various other
distinguished persons. New edition. Edited, with an Introduction, by A.
Francis Steuart. With numerous portraits. Two Vols. Demy 8vo. 21_s._ net.
∵ _This book, which appeared anonymously in 1838, created an enormous
sensation, and was fiercely criticised by Thackeray and in the Reviews
of the time. There is no doubt that it was founded on the diary of Lady
Charlotte Bury, daughter of the 5th Duke of Argyll, and Lady-in-Waiting
to the unfortunate Caroline of Brunswick, when Princess of Wales. It
deals, therefore, with the curious Court of the latter and with the
scandals that occurred there, as well as with the strange vagaries of
the Princess abroad. In this edition names left blank in the original
have been (where possible) filled up, and many notes are given by the
Editor to render it useful to the ever-increasing number of readers
interested in the later Georgian Period._
JUNIPER HALL: Rendezvous of certain illustrious Personages during the
French Revolution, including Alexander D’Arblay and Fanny Burney.
Compiled by Constance Hill. With numerous Illustrations by Ellen G. Hill,
and reproductions from various Contemporary Portraits. Crown 8vo. 5_s._
net.
JANE AUSTEN: Her Homes and Her Friends. By Constance Hill. Numerous
Illustrations by Ellen G. Hill, together with Reproductions from Old
Portraits, etc. Cr. 8vo. 5_s._ net.
THE HOUSE IN ST. MARTIN’S STREET. Being Chronicles of the Burney Family.
By Constance Hill, Author of “Jane Austen, Her Home, and Her Friends,”
“Juniper Hall,” etc. With numerous Illustrations by Ellen G. Hill, and
reproductions of Contemporary Portraits, etc. Demy 8vo. 21_s._ net.
STORY OF THE PRINCESS DES URSINS IN SPAIN (Camarera-Mayor). By Constance
Hill. With 12 Illustrations and a Photogravure Frontispiece. New Edition.
Crown 8vo. 5_s._ net.
NEW LETTERS OF THOMAS CARLYLE. Edited and Annotated by Alexander Carlyle,
with Notes and an Introduction and numerous Illustrations. In Two
Volumes. Demy 8vo. 25_s._ net.
_Pall Mall Gazette._—“To the portrait of the man, Thomas, these letters
do really add value; we can learn to respect and to like him the more
for the genuine goodness of his personality.”
_Morning Leader._—“These volumes open the very heart of Carlyle.”
_Literary World._—“It is then Carlyle, the nobly filial son, we see in
these letters; Carlyle, the generous and affectionate brother, the
loyal and warm-hearted friend, . . . and above all, Carlyle as the
tender and faithful lover of his wife.”
_Daily Telegraph._—“The letters are characteristic enough of the
Carlyle we know: very picturesque and entertaining, full of extravagant
emphasis, written, as a rule, at fever heat, eloquently rabid and
emotional.”
THE NEMESIS OF FROUDE: a Rejoinder to “My Relations with Carlyle.” By Sir
James Crichton Browne and Alexander Carlyle. Demy 8vo. 3_s._ 6_d._ net.
_Glasgow Herald._—“. . . The book practically accomplishes its task of
reinstating Carlyle; as an attack on Froude it is overwhelming.”
_Public Opinion._—“The main object of the book is to prove that Froude
believed a myth and betrayed his trust. That aim has been achieved.”
NEW LETTERS AND MEMORIALS OF JANE WELSH CARLYLE. A Collection of hitherto
Unpublished Letters. Annotated by Thomas Carlyle, and Edited by Alexander
Carlyle, with an Introduction by Sir James Crichton Browne, M.D., LL.D.,
F.R.S., numerous Illustrations drawn in Lithography by T. R. Way, and
Photogravure Portraits from hitherto unreproduced Originals. In Two
Volumes. Demy 8vo. 25_s._ net.
_Westminster Gazette._—“Few letters in the language have in such
perfection the qualities which good letters should possess. Frank, gay,
brilliant, indiscreet, immensely clever, whimsical, and audacious, they
reveal a character which, with whatever alloy of human infirmity, must
endear itself to any reader of understanding.”
_World._—“Throws a deal of new light on the domestic relations of the
Sage of Chelsea. They also contain the full text of Mrs. Carlyle’s
fascinating journal, and her own ‘humorous and quaintly candid’
narrative of her first love-affair.”
_Daily News._—“Every page . . . scintillates with keen thoughts, biting
criticisms, flashing phrases, and touches of bright comedy.”
ÉMILE ZOLA: Novelist and Reformer. An Account of his Life, Work, and
Influence. By E. A. Vizetelly. With numerous Illustrations, Portraits,
etc. Demy 8vo. 21_s._ net.
_Morning Post._—“Mr. Ernest Vizetelly has given . . . a very true
insight into the aims, character, and life of the novelist.”
_Athenæum._—“. . . Exhaustive and interesting.”
_M.A.P._—“. . . will stand as the classic biography of Zola.”
_Star._—“This ‘Life’ of Zola is a very fascinating book.”
_Academy._—“It was inevitable that the authoritative life of Emile Zola
should be from the pen of E. A. Vizetelly. No one probably has the same
qualifications, and this bulky volume of nearly six hundred pages is a
worthy tribute to the genius of the master.”
Mr. T. P. O’Connor in _T.P.’s Weekly_.—“It is a story of fascinating
interest, and is told admirably by Mr. Vizetelly. I can promise any one
who takes it up that he will find it very difficult to lay it down
again.”
MEMOIRS OF THE MARTYR KING: being a detailed record of the last two years
of the Reign of His Most Sacred Majesty King Charles the First,
1646-1648-9. Compiled by Allan Fea. With upwards of 100 Photogravure
Portraits and other Illustrations, including relics. Royal 4to. 105_s._
net.
Mr. M. H. Spielmann in _The Academy_.—“The volume is a triumph for the
printer and publisher, and a solid contribution to Carolinian
literature.”
_Pall Mall Gazette._—“The present sumptuous volume, a storehouse of
eloquent associations . . . comes as near to outward perfection as
anything we could desire.”
MEMOIRS OF A VANISHED GENERATION 1813-1855. Edited by Mrs. Warrenne
Blake. With numerous Illustrations. Demy 8vo. 16_s._ net.
∵ _This work is compiled from diaries and letters dating from the time
of the Regency to the middle of the nineteenth century. The value of
the work lies in its natural unembellished picture of the life of a
cultured and well-born family in a foreign environment at a period so
close to our own that it is far less familiar than periods much more
remote. There is an atmosphere of Jane Austen’s novels about the lives
of Admiral Knox and his family, and a large number of well-known
contemporaries are introduced into Mrs. Blake’s pages._
CÉSAR FRANCK: A Study. Translated from the French of Vincent d’Indy. And
with an Introduction by Rosa Newmarch. Demy 8vo. 7_s._ 6_d._ net.
∵ _There is no purer influence in modern music than that of César
Franck, for many years ignored in every capacity save that of organist
of Sainte-Clotilde, in Paris, but now recognised as the legitimate
successor of Bach and Beethoven. His inspiration “rooted in love and
faith” has contributed in a remarkable degree to the regeneration of
the musical art in France and elsewhere. The now famous “Schola
Cantorum,” founded in Paris in 1896, by A. Guilmant, Charles Bordes and
Vincent d’Indy, is the direct outcome of his influence. Among the
artists who were in some sort his disciples were Paul Dukas, Chabrier,
Gabriel Fauré and the great violinist Ysāye. His pupils include such
gifted composers as Benoît, Augusta Holmès, Chausson, Ropartz, and
d’Indy. This book, written with the devotion of a disciple and the
authority of a master, leaves us with a vivid and touching impression
of the saint-like composer of “The Beatitudes.”_
FRENCH NOVELISTS OF TO-DAY: Maurice Barres, Réné Bazin, Paul Bourget,
Pierre de Coulevain, Anatole France, Pierre Loti, Marcel Prévost, and
Edouard Rod. Biographical, Descriptive, and Critical. By Winifred
Stephens. With Portraits and Bibliographies. Crown 8vo. 5_s._ net.
∵ _The writer, who has lived much in France, is thoroughly acquainted
with French life and with the principal currents of French thought. The
book is intended to be a guide to English readers desirous to keep in
touch with the best present-day French fiction. Special attention is
given to the ecclesiastical, social, and intellectual problems of
contemporary France and their influence upon the works of French
novelists of to-day._
THE KING’S GENERAL IN THE WEST, being the Life of Sir Richard Granville,
Baronet (1600-1659). By Roger Granville, M.A., Sub-Dean of Exeter
Cathedral. With Illustrations. Demy 8vo. 10_s._ 6_d._ net.
_Westminster Gazette._—“A distinctly interesting work; it will be
highly appreciated by historical students as well as by ordinary
readers.”
THE LIFE AND LETTERS OF ROBERT Stephen Hawker, sometime Vicar of
Morwenstow in Cornwall. By C. E. Byles. With numerous Illustrations by J.
Ley Pethybridge and others. Demy 8vo. 7_s._ 6_d._ net.
_Daily Telegraph._—“. . . As soon as the volume is opened one finds
oneself in the presence of a real original, a man of ability, genius
and eccentricity, of whom one cannot know too much . . . No one will
read this fascinating and charmingly produced book without thanks to
Mr. Byles and a desire to visit—or revisit—Morwenstow.”
THE LIFE OF WILLIAM BLAKE. By Alexander Gilchrist. Edited with an
Introduction by W. Graham Robertson. Numerous Reproductions from Blake’s
most characteristic and remarkable designs. Demy 8vo. 10_s._ 6_d._ net.
New Edition.
_Birmingham Post._—“Nothing seems at all likely ever to supplant the
Gilchrist biography. Mr. Swinburne praised it magnificently in his own
eloquent essay on Blake, and there should be no need now to point out
its entire sanity, understanding keenness of critical insight, and
masterly literary style. Dealing with one of the most difficult of
subjects, it ranks among the finest things of its kind that we
possess.”
MEMOIRS OF A ROYAL CHAPLAIN, 1729-63. The correspondence of Edmund Pyle,
D.D., Domestic Chaplain to George II, with Samuel Kerrich, D.D., Vicar of
Dersingham, and Rector of Wolferton and West Newton. Edited and Annotated
by Albert Hartshorne. With Portrait. Demy 8vo. 16_s._ net.
_Truth._—“It is undoubtedly the most important book of the kind that
has been published in recent years, and is certain to disturb many
readers whose minds have not travelled with the time.”
GEORGE MEREDITH: Some Characteristics. By Richard Le Gallienne. With a
Bibliography (much enlarged) by John Lane. Portrait, etc. Crown 8vo.
5_s._ net. Fifth Edition. Revised.
_Punch._—“All Meredithians must possess ‘George Meredith; Some
Characteristics,’ by Richard Le Gallienne. This book is a complete and
excellent guide to the novelist and the novels, a sort of Meredithian
Bradshaw, with pictures of the traffic superintendent and the head
office at Boxhill. Even Philistines may be won over by the
blandishments of Mr. Le Gallienne.”
LIFE OF LORD CHESTERFIELD. An account of the Ancestry, Personal
Character, and Public Services of the Fourth Earl of Chesterfield. By W.
H. Craig, M.A. Numerous Illustrations. Demy 8vo. 12_s._ 6_d._ net.
_Daily Telegraph._—“Mr. Craig has set out to present him (Lord
Chesterfield) as one of the striking figures of a formative period in
our modern history . . . and has succeeded in giving us a very
attractive biography of a remarkable man.”
_Times._—“It is the chief point of Mr. Craig’s book to show the
sterling qualities which Chesterfield was at too much pains in
concealing, to reject the perishable trivialities of his character, and
to exhibit him as a philosophic statesman, not inferior to any of his
contemporaries, except Walpole at one end of his life, and Chatham at
the other.”
A QUEEN OF INDISCRETIONS. The Tragedy of Caroline of Brunswick, Queen of
England. From the Italian of G. P. Clerici. Translated by Frederic
Chapman. With numerous Illustrations reproduced from contemporary
Portraits and Prints. Demy 8vo. 21_s._ net.
_The Daily Telegraph._—“It could scarcely be done more thoroughly or,
on the whole, in better taste than is here displayed by Professor
Clerici. Mr. Frederic Chapman himself contributes an uncommonly
interesting and well-informed introduction.”
_Westminster Gazette._—“The volume, scholarly and well-informed . . .
forms one long and absorbingly interesting chapter of the _chronique
scandaleuse_ of Court life . . . reads like a romance, except that no
romancer would care or dare to pack his pages so closely with startling
effects and fantastic scenes.”
LETTERS AND JOURNALS OF SAMUEL GRIDLEY HOWE. Edited by his Daughter Laura
E. Richards. With Notes and a Preface by F. B. Sanborn, an Introduction
by Mrs. John Lane, and a Portrait. Demy 8vo. (9 × 5¾ inches). 16_s._ net.
_Outlook._—“This deeply interesting record of experience. The volume is
worthily produced and contains a striking portrait of Howe.”
_Daily News._—“Dr. Howe’s book is full of shrewd touches; it seems to
be very much a part of the lively, handsome man of the portrait. His
writing is striking and vivid; it is the writing of a shrewd, keen
observer, intensely interested in the event before him.”
THE LIFE OF ST. MARY MAGDALEN. Translated from the Italian of an Unknown
Fourteenth-Century Writer by Valentina Hawtrey. With an Introductory Note
by Vernon Lee, and 14 Full-page Reproductions from the Old Masters. Crown
8vo. 5_s._ net.
_Daily News._—“Miss Valentina Hawtrey has given a most excellent
English version of this pleasant work.”
_Academy._—“The fourteenth-century fancy plays delightfully around the
meagre details of the Gospel narrative, and presents the heroine in
quite an unconventional light. . . . In its directness and artistic
simplicity and its wealth of homely detail the story reads like the
work of some Boccaccio of the cloister; and fourteen illustrations
taken from Italian painters happily illustrate the charming text.”
MEN AND LETTERS. By Herbert Paul, M.P. Fourth Edition. Crown 8vo. 5_s._
net.
_Daily News._—“Mr. Herbert Paul has done scholars and the reading world
in general a high service in publishing this collection of his essays.”
_Punch._—“His fund of good stories is inexhaustible, and his urbanity
never fails. On the whole, this book is one of the very best examples
of literature on literature and life.”
ROBERT BROWNING: Essays and Thoughts. By J. T. Nettleship. With Portrait.
Crown 8vo. 5_s._ 6_d._ net. (Third Edition.)
A LATER PEPYS. The Correspondence of Sir William Weller Pepys, Bart.,
Master in Chancery, 1758-1825, with Mrs. Chapone, Mrs. Hartley, Mrs.
Montague, Hannah More, William Franks, Sir James Macdonald, Major
Rennell, Sir Nathaniel Wraxall, and others. Edited, with an Introduction
and Notes, by Alice C. C. Gaussen. With numerous Illustrations. Demy 8vo.
In Two Volumes. 32_s._ net.
Douglas Sladen in the _Queen_.—“This is indisputably a most valuable
contribution to the literature of the eighteenth century. It is a
veritable storehouse of society gossip, the art criticism, and the
_mots_ of famous people.”
_Academy and Literature._—“The effect consists in no particular
passages, but in the total impression, the sense of atmosphere, and the
general feeling that we are being introduced into the very society in
which the writer moved.”
_Daily News._—“To Miss Alice Gaussen is due the credit of sorting out
the vast collection of correspondence which is here presented to the
public. . . . Her industry is indefatigable, and her task has been
carried out with completeness. The notes are full of interesting items;
the introduction is exhaustive; and the collection of illustrations
enhances the value of the book.”
_World._—“Sir William Pepys’s correspondence is admirable.”
ROBERT LOUIS STEVENSON, AN ELEGY; AND OTHER POEMS, MAINLY PERSONAL. By
Richard Le Gallienne. Crown 8vo. 4_s._ 6_d._ net.
_Daily Chronicle._—“Few, indeed, could be more fit to sing the dirge of
that ‘Virgil of Prose’ than the poet whose _curiosa felicitas_ is so
close akin to Stevenson’s own charm.”
_Globe._—“The opening Elegy on R. L. Stevenson includes some tender and
touching passages, and has throughout the merits of sincerity and
clearness.”
RUDYARD KIPLING: a Criticism. By Richard Le Gallienne. With a
Bibliography by John Lane. Crown 8vo. 3_s._ 6_d._ net.
_Guardian._—“One of the cleverest pieces of criticism we have come
across for a long time.”
_Scotsman._—“It shows a keen insight into the essential qualities of
literature, and analyses Mr. Kipling’s product with the skill of a
craftsman . . . the positive and outstanding merits of Mr. Kipling’s
contribution to the literature of his time are marshalled by his critic
with quite uncommon skill.”
POEMS. By Edward Cracroft Lefroy. With a Memoir by W. A. Gill, and a
Reprint of Mr. J. A. Symonds’ Critical Essay on “Echoes from Theocritus.”
Photogravure Portrait. Crown 8vo. 5_s._ net.
_The Times._—“. . . the leading features of the sonnets are the
writer’s intense sympathy with human life in general and with young
life in particular; his humour, his music, and, in a word, the quality
which ‘leaves a melody afloat upon the brain, a savour on the mental
palate.’”
_Bookman._—“The Memoir, by Mr. W. A. Gill, is a sympathetic sketch of
an earnest and lovable character; and the critical estimate, by J.
Addington Symonds, is a charmingly, written and suggestive essay.”
APOLOGIA DIFFIDENTIS. By W. Compton Leith. Demy 8vo. 7_s._ 6_d._ net.
∵ _The book, which is largely autobiographical, describes the effect of
diffidence upon an individual life, and contains, with a consideration
of the nature of shyness, a plea for a kindlier judgment of the
inveterate case._
_Daily Mail._—“Mr. Leith has written a very beautiful book, and perhaps
the publisher’s claim that this will be a new classic is not too bold.”
THE TRUE STORY OF MY LIFE: an Autobiography by Alice M. Diehl, Novelist,
Writer, and Musician. Demy 8vo. 10_s._ 6_d._ net.
BOOKS AND PERSONALITIES: Essays. By H. W. Nevinson. Crown 8vo. 5_s._ net.
_Daily Chronicle._—“It is a remarkable thing and probably unique, that
a writer of such personality as the author of ‘Between the Acts’ should
not only feel, but boldly put on paper, his homage and complete
subjection to the genius of one after another of these men. He is
entirely free from that one common virtue of critics, which is
superiority to the author criticised.”
OTIA: Essays. By Armine Thomas Kent. Crown 8vo. 5_s._ net.
BOOKS AND PLAYS: A Volume of Essays on Meredith, Borrow, Ibsen, and
others. By Allan Monkhouse. Crown 8vo. 5_s._ net.
LIBER AMORIS; or, The New Pygmalion. By William Hazlitt. Edited, with an
introduction, by Richard Le Gallienne. To which is added an exact
transcript of the original MS., Mrs. Hazlitt’s Diary in Scotland, and
Letters never before published. Portrait after Bewick, and facsimile
Letters. 400 copies only. 4to. 364 pp. Buckram. 21_s._ net.
TERRORS OF THE LAW: being the Portraits of Three Lawyers—the original
Weir of Hermiston, “Bloody Jeffreys,” and “Bluidy Advocate Mackenzie.” By
Francis Watt. With 3 Photogravure Portraits. Fcap. 8vo. 4_s._ 6_d._ net.
_The Literary World._—“The book is altogether entertaining; it is
brisk, lively, and effective. Mr. Watt has already, in his two series
of ‘The Law’s Lumber Room,’ established his place as an essayist in
legal lore, and the present book will increase his reputation.”
CHAMPIONS OF THE FLEET. Captains and Men-of-War in the Days that Helped
to make the Empire. By Edward Fraser. With 16 Full-page Illustrations.
Crown 8vo. 6_s._
THE LONDONS OF THE BRITISH FLEET: The Story of Ships bearing the name of
Old Renown in Naval Annals. By _Edward Fraser_. With 8 Illustrations in
colours, and 20 in black and white. Crown 8vo. 6_s._
JOHN LANE, THE BODLEY HEAD, VIGO STREET, LONDON.
Transcriber’s Notes
--Retained publisher information from the printed copy (the electronic
edition is in the public domain in the country of publication).
--Corrected some palpable typos.
--Converted page headings into section titles (shifted to an appropriate
paragraph break.)
--Moved all promotional material to the end of the book.
--In the HTML version, split some illustrations, and rotated others to
portrait mode for better display on e-readers.
--In the text versions only, represented text font and size variations
(the HTML version preserves the presentation of the original):
--Text in italics is delimited by _underscores_.
--Subscripted numbers are preceded by an underscore, as in the formula
for water “H_2O”.
--Split genetic tables within paragraphs into separate lines.
*** End of this LibraryBlog Digital Book "The Making of Species" ***
Copyright 2023 LibraryBlog. All rights reserved.