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Title: Are the Effects of Use and Disuse Inherited? - An Examination of the View Held by Spencer and Darwin
Author: Ball, W. P. (William Platt)
Language: English
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_NATURE SERIES_
ARE THE EFFECTS OF USE AND
DISUSE INHERITED?
_AN EXAMINATION OF THE VIEW HELD BY
SPENCER AND DARWIN_
BY
WILLIAM PLATT BALL
LONDON
MACMILLAN AND CO.
AND NEW YORK
1890
_The Right of Translation and Reproduction is Reserved_
RICHARD CLAY AND SONS, LIMITED,
LONDON AND BUNGAY.
PREFACE.
My warmest thanks are due to Mr. Francis Darwin, to Mr. E. B. Poulton
(whose interest in the subject here discussed is shown by his share in
the translation of Weismann's _Essays on Heredity_), and to Professor
Romanes, for the help afforded by their kindly suggestions and
criticisms, and for the advice and recommendation under which this essay
is now published. Encouragement from Mr. Francis Darwin is to me the
more precious, and the more worthy of grateful recognition, from the
fact that my general conclusion that acquired characters are _not_
inherited is at variance with the opinion of his revered father, who
aided his great theory by the retention of some remains of Lamarck's
doctrine of the inherited effect of habit. I feel as if the son, as
representative of his great progenitor, were carrying out the idea of an
appreciative editor who writes to me: "We must say that if Darwin were
still alive, he would find your arguments of great weight, and
undoubtedly would give to them the serious consideration which they
deserve." I hope, then, that I may be acquitted of undue presumption in
opposing a view sanctioned by the author of the _Origin of Species_, but
already stoutly questioned and firmly rejected by such followers of his
as Weismann, Wallace, Poulton, Ray Lankester, and others, to say nothing
of its practical rejection by so great an authority on heredity as
Francis Galton.
The sociological importance of the subject has already been insisted on
in emphatic terms by Mr. Herbert Spencer, and this importance may be
even greater than he imagined.
Civilization largely sets aside the harsh but ultimately salutary action
of the great law of Natural Selection without providing an efficient
substitute for preventing degeneracy. The substitute on which moralists
and legislators rely--if they think on the matter at all--is the
cumulative inheritance of the beneficial effects of education, training,
habits, institutions, and so forth--the inheritance, in short, of
acquired characters, or of the effects of use and disuse. If this
substitute is but a broken reed, then the deeper thinkers who gradually
teach the teachers of the people, and ultimately even influence the
legislators and moralists, must found their systems of morality and
their criticisms of social and political laws and institutions and
customs and ideas on the basis of the Darwinian law rather than on that
of Lamarck.
Looking forward to the hope that the human race may become consciously
and increasingly master of itself and of its destiny, and recognizing
the Darwinian principle of the selection of the fittest as the _only_
means of preventing the moral and physical degeneracy which, like an
internal dry rot, has hitherto been the besetting danger of all
civilizations, I desire that the thinkers who mould the opinions of
mankind shall not be led astray from the true path of enduring progress
and happiness by reliance on fallacious beliefs which will not bear
examination. Such, at least, is the feeling or motive which has prompted
me to devote much time and thought to a difficult but important inquiry
in a debatable region of inference and conjecture, where (I am afraid)
evidence on either side can never be absolutely conclusive, and where,
especially, the absolute demonstration of a universal negative cannot
reasonably be expected.
CONTENTS.
PAGE
PREFACE v
IMPORTANCE AND BEARING OF THE INQUIRY 1
SPENCER'S EXAMPLES AND ARGUMENTS 6-44
DIMINUTION OF THE JAWS 6
DIMINISHED BITING MUSCLES OF LAP-DOGS 12
CROWDED TEETH 14
BLIND CAVE-CRABS 17
NO CONCOMITANT VARIATION FROM CONCOMITANT DISUSE 17
THE GIRAFFE, AND NECESSITY FOR CONCOMITANT VARIATION 18
ALLEGED RUINOUS EFFECTS OF NATURAL SELECTION 23
ADVERSE CASE OF NEUTER INSECTS 24
ÆSTHETIC FACULTIES 29
LACK OF EVIDENCE 34
INHERITED EPILEPSY IN GUINEA-PIGS 35
INHERITED INSANITY AND NERVOUS DISORDERS 36
INDIVIDUAL AND TRANSMISSIBLE TYPE NOT MODIFIED ALIKE 40
DARWIN'S EXAMPLES 45-100
REDUCED WINGS OF BIRDS OF OCEANIC ISLANDS 49
DROOPING EARS AND DETERIORATED INSTINCTS 53
WINGS AND LEGS OF DUCKS AND FOWLS 55
PIGEONS' WINGS 62
SHORTENED BREAST-BONE IN PIGEONS 64
SHORTENED FEET IN PIGEONS 70
SHORTENED LEGS OF RABBITS 70
BLIND CAVE-ANIMALS 72
INHERITED HABITS 73
TAMENESS OF RABBITS 76
MODIFICATIONS OBVIOUSLY ATTRIBUTABLE TO SELECTION 82
SIMILAR EFFECTS OF NATURAL SELECTION AND USE-INHERITANCE 83
INFERIORITY OF SENSES IN EUROPEANS 85
SHORT-SIGHT IN WATCHMAKERS AND ENGRAVERS 85
LARGER HANDS OF LABOURERS' INFANTS 87
THICKENED SOLE IN INFANTS 88
A SOURCE OF MENTAL CONFUSION 91
WEAKNESS OF USE-INHERITANCE 94
INHERITED INJURIES 101-118
INHERITED MUTILATIONS 101
THE MOTMOT'S TAIL 110
OTHER INHERITED INJURIES MENTIONED BY DARWIN 111
QUASI-INHERITANCE 116
MISCELLANEOUS CONSIDERATIONS 119-143
TRUE RELATION OF PARENTS AND OFFSPRING 119
INVERSE INHERITANCE 123
EARLY ORIGIN OF THE OVA 124
MARKED EFFECTS OF USE AND DISUSE ON THE INDIVIDUAL 126
WOULD NATURAL SELECTION FAVOUR USE-INHERITANCE? 127
USE-INHERITANCE AN EVIL 128
VARIED EFFECTS OF USE AND DISUSE 134
USE-INHERITANCE IMPLIES PANGENESIS 137
PANGENESIS IMPROBABLE 138
SPENCER'S EXPLANATION OF USE-INHERITANCE 141
CONCLUSIONS 144-156
USE-INHERITANCE DISCREDITED AS UNNECESSARY, UNPROVEN,
AND IMPROBABLE 144
MODERN RELIANCE ON USE-INHERITANCE MISPLACED 145
ARE THE EFFECTS OF USE AND DISUSE INHERITED?
IMPORTANCE AND BEARING OF THE INQUIRY.
The question whether the effects of use and disuse are inherited, or, in
other words, whether acquired characters are hereditary, is of
considerable interest to the general student of evolution; but it is, or
should be, a matter of far deeper interest to the thoughtful
philanthropist who desires to ensure the permanent welfare and happiness
of the human race. So profoundly important, in fact, are the moral,
social, and political conclusions that depend on the answer to this
inquiry, that, as Mr. Herbert Spencer rightly says, it "demands, beyond
all other questions whatsoever, the attention of scientific men."
It is obvious that we can produce important changes in the individual.
We can, for example, improve his muscles by athletics, and his brain by
education. The use of organs enlarges and strengthens them; the disuse
of parts or faculties weakens them. And so great is the power of habit
that it is proverbially spoken of as "second nature." It is thus certain
that we can modify the individual. We can strengthen (or weaken) his
body; we can improve (or deteriorate) his intellect, his habits, his
morals. But there remains the still more important question which we are
about to consider. Will such modifications be inherited by the offspring
of the modified individual? Does individual improvement transmit itself
to descendants independently of personal teaching and example? Have
artificially produced changes of structure or habit any inherent
tendency to become congenitally transmissible and to be converted in
time into fixed traits of constitution or character? Can the
philanthropist rely on such a tendency as a hopeful factor in the
evolution of mankind?--the only sound and stable basis of a higher and
happier state of things being, as he knows or ought to know, the innate
and constitutionally-fixed improvement of the race as a whole. If
acquired modifications are impressed on the offspring and on the race,
the systematic moral training of individuals will in time produce a
constitutionally moral race, and we may hope to improve mankind even in
defiance of the unnatural selection by which a spurious but highly
popular philanthropy would systematically favour the survival of the
unfittest and the rapid multiplication of the worst. But if acquired
modifications do not tend to be transmitted, if the use or disuse of
organs or faculties does not similarly affect posterity by inheritance,
then it is evident that no innate improvement in the race can take place
without the aid of natural or artificial selection.
Herbert Spencer maintains that the effects of use and disuse _are_
inherited in kind, and in his _Factors of Organic Evolution_[1] he has
supported his contention with a selection of facts and reasonings which
I shall have the temerity to examine and criticize. Darwin also held the
same view, though not so strongly. And here, to prevent
misunderstanding, I may say that the admiration and reverence and
gratitude due to Darwin ought not to be allowed to interfere in the
slightest degree with the freest criticism of his conclusions. To
perfect his work by the correction of really extraneous errors is as
much a sacred duty as to study and apply the great truths he has taught.
FOOTNOTES:
[1] Which originally appeared in the _Nineteenth Century_ for April and
May, 1886.
SPENCER'S EXAMPLES AND ARGUMENTS.
DIMINUTION OF THE JAWS IN CIVILIZED RACES.
Mr. Spencer verified this by comparing English jaws with Australian and
Negro jaws at the College of Surgeons.[2] He maintains that the
diminution of the jaw in civilized races can _only_ have been brought
about by inheritance of the effects of lessened use. But if English jaws
are lighter and thinner than those of Australians and Negroes, so too is
the rest of the skull. As the diminution in the weight and thickness of
the walls of the cranium cannot well be ascribed to disuse, it must be
attributed to some other cause; and this cause may have affected the jaw
also. Cessation of the process by which natural selection[3] favoured
strong thick bones during ages of brutal violence might bring about a
change in this direction. Lightness of structure, facilitating agility
and being economical of material, would also be favoured by natural
selection so far as strength was not too seriously diminished.
Sexual selection powerfully affects the human face, and so must affect
the jaws--as is shown by the differences between male and female jaws,
and by the relative lightness and smallness of the latter, especially in
the higher races. Human preference, both sexual and social, would tend
to eliminate huge jaws and ferocious teeth when these were no longer
needed as weapons of war or organs of prehension, &c. We can hardly
assume that the lower half of the face is specially exempt from the
influence of natural and sexual selection; and the effects of these
undoubted factors of evolution must be fully considered before we are
entitled to call in the aid of a factor whose existence is questioned.
After allowing for lost teeth and the consequent alveolar absorption,
and for a reduction proportional to that shown in the rest of the skull,
the difference in average weight in fifty European and fourteen
Australian male jaws at the College of Surgeons turned out to be less
than a fifth of an ounce, or about 5 per cent. This slight reduction may
be much more than accounted for by such causes as disuse in the
individual, human preference setting back the teeth, and partial
transference of the much more marked diminution seen in female jaws.
There is apparently no room for accumulated _inherited_ effects of
ancestral disuse. The number of jaws is small, indeed; but weighing them
is at least more decisive than Mr. Spencer's mere inspection.
The differences between Anglo-Saxon male jaws and Australian and
Tasmanian jaws are most easily explained as effects of human preference
and natural selection. We can hardly suppose that disuse would maintain
or develop the projecting chin, increase its perpendicular height till
the jaw is deepest and strongest at its extremity, evolve a side flange,
and enlarge the upper jaw-bone to form part of a more prominent nose,
while drawing back the savagely obtrusive teeth and lips to a more
pleasing and subdued position of retirement and of humanized beauty. If
human preference and natural selection caused some of these differences,
why are they incompetent to effect changes in the direction of a
diminution of the jaw or teeth? And if use and disuse are the sole
modifying agents in the case of the human jaw, why should men have any
more chin than a gorilla or a dog?
The excessive weight of the West African jaws at the College of Surgeons
is partly _against_ Mr. Spencer's contention, unless he assumes that
Guinea Negroes use their jaws far more than the Australians, a
supposition which seems extremely improbable. The heavier skull and
narrower molar teeth point however to other factors than increased use.
The striking variability of the human jaw is strongly opposed to the
idea of its being under the direct and dominant control of so uniform a
cause as ancestral use and disuse. Mr. Spencer regards a variation of 1
oz. as a large one, but I found that the English jaws in the College of
Surgeons varied from 1·9 oz. to 4·3 oz. (or 5 oz. if lost teeth were
allowed for); Australian jaws varied from 2 oz. to 4·5 oz. (with _no_
lost teeth to allow for); while in Negro jaws the maximum rose to over
5-1/2 oz.[4] In spite of disuse some European jaws were twice as heavy
as the lightest Australian jaw, either absolutely or (in some cases)
relatively to the cranium. The uniformity of change relied upon by Mr.
Spencer is scarcely borne out by the facts so far as male jaws are
concerned. The great reduction in the weight of _female_ jaws _and
skulls_ evidently points to sexual selection and to panmixia under male
protection.
I think, on the whole, we must conclude that the human jaws do not
afford satisfactory proof of the inheritance of the effects of use and
disuse, inasmuch as the differences in their weight and shape and size
can be more reasonably and consistently accounted for as the result of
less disputable causes.
DIMINISHED BITING MUSCLES OF LAP-DOGS.
The next example, the reduced biting muscles, &c., of lap-dogs is also
unsatisfactory as a proof of the inheritance of the effects of disuse;
for the change can readily be accounted for without the introduction of
such a factor. The previous natural selection of strong jaws and teeth
and muscles is reversed. The conscious or unconscious selection of
lap-dogs with the least tendency to bite would easily bring about a
general enfeeblement of the whole biting apparatus--weakness of the
parts concerned favouring harmlessness. Mr. Spencer maintains that the
dwindling of the parts concerned in clenching the jaw is certainly not
due to artificial selection because the modifications offer no
appreciable external signs. Surely hard biting is sufficiently
appreciable by the person bitten without any visual admeasurement of the
masseter muscles or the zygomatic arches. Disuse during lifetime would
also cause some amount of degeneracy; and I am not sure that Mr. Spencer
is right in _entirely_ excluding economy of nutrition from the problem.
Breeders would not over-feed these dogs; and the puppies that grew most
rapidly would usually be favoured.
CROWDED TEETH.
The too closely-packed teeth in the "decreasing" jaws of modern men (p.
13)[5] are also suggestive of other causes than use and disuse. Why is
there not simultaneous variation in teeth and jaws, if disuse is the
governing factor? Are we to suppose that the size of the human teeth is
maintained by use at the same time that the jaws are being diminished by
disuse? Mr. Spencer acknowledges that the crowding of bull-dogs' and
lap-dogs' teeth is caused by the artificial selection of shortened jaws.
If a similar change is really occurring in man, could it not be
similarly explained by some factor, such as sexual selection, which
might affect the outward appearance at the cost of less obvious defects
or inconveniences?
Mr. Spencer points to the decay of modern teeth as a sign or result of
their being overcrowded through the diminution of the jaw by disuse.[6]
But the teeth which are the most frequently overcrowded are the lower
incisors. The upper incisors are less overcrowded, being commonly
pressed outwards by the lower arc of teeth fitting inside them in
biting. The lower incisors are correspondingly pressed inwards and
closer together. Yet the upper incisors decay--or at least are
extracted--about twenty times as frequently as the closely packed lower
incisors.[7] Surely this must indicate that the cause of decay is not
overcrowding.
The lateness and irregularity of the wisdom teeth are sometimes
supposed to indicate their gradual disappearance through want of room in
a diminishing jaw. But a note on Tasmanian skulls in the _Catalogue of
the College of Surgeons_ (p. 199) shows that this lateness and
irregularity have been common among Tasmanians as well as among
civilized races, so that the change can hardly be attributed to the
effects of disuse under civilization.
BLIND CAVE-CRABS.
The cave-crabs which have lost their disused eyes but _not the disused
eye-stalks_ appear to illustrate the effects of natural selection rather
than of disuse. The loss of the exposed, sensitive, and
worse-than-useless eye, would be a decided gain, while the disused
eye-stalk, being no particular detriment to the crab, would be but
slightly affected by natural selection, though open to the cumulative
effects of disuse. The disused but better protected eyes of the blind
cave-rat are still "of large size" (_Origin of Species_, p. 110).
NO CONCOMITANT VARIATION FROM CONCOMITANT DISUSE.
It is but fair to add that these instances of the cave-crab's eye-stalk
and the closely-packed teeth are put forward by Mr. Spencer with the
more immediate object of proving that there is "no concomitant
variation in co-operative parts," even when "formed out of the same
tissue, like the crab's eye and its peduncle" (pp. 12-14, 23, 33). It
escapes his notice, however, that in two out of his three cases it is
_disuse_, or _diminished use_, which fails to cause concomitant
variation or proportionate variation.
THE GIRAFFE, AND NECESSITY FOR CONCOMITANT VARIATION.
Having unwittingly shown that lessened use of closely-connected and
co-operative parts does not cause concomitant variation in these parts,
Mr. Spencer concludes that the concomitant variation requisite for
evolution can only be caused by altered degrees of use or disuse. He
elaborately argues that the many co-ordinated modifications of parts
necessitated by each important alteration in an animal are so complex
that they cannot possibly be brought about except by the inherited
effect of the use and disuse of the various parts concerned. He holds,
for instance, that natural selection is inadequate to effect the
numerous concomitant changes necessitated by such developments as that
of the long neck of the giraffe. Darwin, however, on the contrary, holds
that natural selection alone "would have sufficed for the production of
this remarkable quadruped."[8] He is surprised at Mr. Spencer's view
that natural selection can do so little in modifying the higher animals.
Thus one of the chief arguments with which Mr. Spencer supports his
theory is so poorly founded as to be rejected by a far greater authority
on such subjects. All that is needed is that natural selection should
preserve the tallest giraffes through times of famine by their being
able to reach otherwise inaccessible stores of foliage. The continual
variability of all parts of the higher animals gives scope for
innumerable changes, and Nature is not in a hurry. Mr. Spencer, however,
says that "the chances against any adequate readjustments fortuitously
arising must be infinity to one." But he has also shown that altered
degree of use does not cause the needed concomitant variation of
co-operative parts. So the chances against a beneficial change in an
animal must be, at a liberal estimate, infinity to two. Mr. Spencer, if
he has proved anything, has proved that it is practically impossible
that the giraffe can have acquired a long neck, or the elk its huge
horns, or that any species has ever acquired any important modification.
Mr. Wallace, in his _Darwinism_, answers Mr. Spencer by a collection of
facts showing that "variation is the rule," that the range of variation
in wild animals and plants is much greater than was supposed, and that
"each part varies to a considerable extent independently" of other
parts, so that "the materials constantly ready for natural selection to
act upon are abundant in quantity and very varied in kind." While
co-operative parts would often be more or less correlated, so that they
would tend to vary together, coincident variation is not necessary. The
lengthened wing might be gained in one generation, and the strengthened
muscle at a subsequent period; the bird in the meanwhile drawing upon
its surplus energy, aided (as I would suggest) by the strengthening
effect of increased use in the individual. Seeing that artificial
selection of complicated variations has modified animals in many points
either simultaneously or by slow steps, as with otter-sheep, fancy
pigeons, &c. (many of the characters thus obtained being clearly
independent of use and disuse), natural selection must be credited with
similar powers, and Mr. Wallace concludes that Mr. Spencer's
insuperable difficulty is "wholly imaginary."
The extract concerning a somewhat similar "class of difficulties," which
Mr. Spencer quotes from his _Principles of Biology_, is faulty in its
reasoning,[9] though legitimate in its conclusion concerning the
increasing difficulty of evolution in proportion with the increasing
number and complexity of faculties to be evolved. But this increasing
difficulty of complex evolution is only overcome by _some_
favourably-varying individuals and species--not by all. And as the
difficulty increases we find neglect and decay of the less-needed
faculties--as with domesticated animals and civilized men, who lose in
one direction while they gain in another. The increasing difficulty of
complex evolution by natural selection is no proof whatever of
use-inheritance[10] except to those who confound difficulty with
impossibility.
ALLEGED RUINOUS EFFECTS OF NATURAL SELECTION.
Mr. Spencer further contends that natural selection, by unduly
developing specially advantageous modifications without the necessary
but complex secondary modifications, would render the constitution of a
variety "unworkable" (p. 23). But this seems hardly feasible, seeing
that natural selection must continually favour the most workable
constitutions, and will only preserve organisms in proportion as they
combine general workableness with the special modification. On the other
hand, according to Mr. Spencer himself, use-inheritance must often
disturb the balance of the constitution. Thus it tends to make the jaws
and teeth unworkable through the overcrowding and decay of the
teeth--there being, as his illustrations show, no simultaneous or
concomitant or proportional variation in relation to altered degree of
use or disuse.
ADVERSE CASE OF NEUTER INSECTS.
Mr. Spencer also holds that most mental phenomena, especially where
complex or social or moral, can only be explained as arising from
use-inheritance, which becomes more and more important as a factor of
evolution as we advance from the vegetable world and the lower grades of
animal life to the more complex activities, tastes, and habits of the
higher organizations (preface, and p. 74). But there happens to be a
tolerably clear proof that such changes as the evolution of complicated
structures and habits and social instincts _can_ take place
independently of use-inheritance. The wonderful instincts of the working
bees have apparently been evolved (at least in all their later social
complications and developments) without the aid of use-inheritance--nay,
in spite of its utmost opposition. Working bees, being infertile
"neuters," cannot as a rule transmit their own modifications and habits.
They are descended from countless generations of queen bees and drones,
whose habits have been widely different from those of the workers, and
whose structures are dissimilar in various respects. In many species of
ants there are two, and in the leaf-cutting ants of Brazil there are
_three_, kinds of neuters which differ from each other and from their
male and female ancestors "to an almost incredible degree."[11] The
soldier caste is distinguished from the workers by enormously large
heads, very powerful mandibles, and "extraordinarily different"
instincts. In the driver ant of West Africa one kind of neuter is three
times the size of the other, and has jaws nearly five times as long. In
another case "the workers of one caste alone carry a wonderful sort of
shield on their heads." One of the three neuter classes in the
leaf-cutting ants has a single eye in the midst of its forehead. In
certain Mexican and Australian ants some of the neuters have huge
spherical abdomens, which serve as living reservoirs of honey for the
use of the community. In the equally wonderful case of the termites, or
so-called "white ants" (which belong, however, to an entirely different
order of insect from the ants and bees) the neuters are blind and
wingless, and are divided into soldiers and workers, each class
possessing the requisite instincts and structures adapting it for its
tasks. Seeing that natural selection can form and maintain the various
structures and the exceedingly complicated instincts of ants and bees
and wasps and termites in direct defiance of the alleged tendency to
use-inheritance, surely we may believe that natural selection,
unopposed by use-inheritance, is equally competent for the work of
complex or social or mental evolution in the many cases where the strong
presumptive evidence cannot be rendered almost indisputable by the
exceptional exclusion of the modified animal from the work of
reproduction.
Ants and bees seem to be capable of altering their habits and methods of
action much as men do. Bees taken to Australia cease to store honey
after a few years' experience of the mild winters. Whole communities of
bees sometimes take to theft, and live by plundering hives, first
killing the queen to create dismay among the workers. Slave ants attend
devotedly to their captors, and fight against their own species. Forel
reared an artificial ant-colony made up of five different and more or
less hostile species. Why cannot a much more intelligent animal modify
his habits far more rapidly and comprehensively without the aid of a
factor which is clearly unnecessary in the case of the more intelligent
of the social insects?
ÆSTHETIC FACULTIES.
The modern development of music and harmony (p. 19) is undeniable, but
why could it only have been brought about by the help of the inheritance
of the effects of use? Why are we to suppose that "minor traits" such as
the "æsthetic perceptions" cannot have been evolved by natural selection
(p. 20) or by sexual selection? Darwin holds that our musical faculties
were developed by sexual preference long before the acquisition of
speech. He believes that the "rhythms and cadences of oratory are
derived from previously developed musical powers"--a conclusion "exactly
opposite" to that arrived at by Mr. Spencer.[12] The emotional
susceptibility to music, and the delicate perceptions needed for the
higher branches of art, were apparently the work of natural and sexual
selection in the long past. Civilization, with its leisure and wealth
and accumulated knowledge, perfects human faculties by artificial
cultivation, develops and combines means of enjoyment, and discovers
unsuspected sources of interest and pleasure. The sense of harmony,
modern as it seems to be, must have been a latent and indirect
consequence of the development of the sense of hearing and of melody.
Use, at least, could never have called it into existence. Nature favours
and develops enjoyments to a certain extent, for they subserve
self-preservation and sexual and social preference in innumerable ways.
But modern æsthetic advance seems to be almost entirely due to the
culture of latent abilities, the formation of complex associations, the
selection and encouragement of talent, and the wide diffusion and
imitation of the accumulated products of the well-cultivated genius of
favourably varying individuals. The fact that uneducated persons do not
enjoy the higher tastes, and the rapidity with which such tastes are
acquired or professed, ought to be sufficient proof that modern culture
is brought about by far swifter and more potent influences than
use-inheritance. Neither would this hypothetical factor of evolution
materially aid in explaining the many other rapid changes of habit
brought about by education, custom, and the changed conditions of
civilization generally. Powerful tastes--as is incontestably shown in
the cases of alcohol and tobacco--lie latent for ages, and suddenly
become manifest when suitable conditions arise. Every discovery, and
each step in social and moral evolution, produces its wide-spreading
train of consequences. I see no reason why use-inheritance need be
credited with any share in the cumulative results of the invention of
printing and the steam-engine and gunpowder, or of freedom and security
under representative government, or of science and art and the partial
emancipation of the mind of man from superstition, or of the innumerable
other improvements or changes that take place under modern civilization.
Mr. Spencer suggests an inquiry whether the greater powers possessed by
eminent musicians were not mainly due to the inherited effect of the
musical practice of their fathers (p. 19). But these great musicians
inherited far more than their parents possessed. The excess of their
powers beyond their parents' must surely be attributed to spontaneous
variation; and who shall say that the rest was in any way due to
use-inheritance? If, too, the superiority of geniuses proves
use-inheritance, why should not the inferiority of the sons of geniuses
prove the existence of a tendency which is the exact opposite of
use-inheritance? But nobody collects facts concerning the degenerate
branches of musical families. Only the favourably varying branches are
noticed, and a general impression of rapid evolution of talent is thus
produced. Such cases might be explained, too, by the facts that musical
faculty is strong in both sexes, that musical families associate
together, and that the more gifted members may intermarry. Great
musicians are often astonishingly precocious. Meyerbeer "played
brilliantly" at the age of six. Mozart played beautifully at four. Are
we to suppose that the effect of the _adult_ practice of parents was
inherited at this early age? If use-inheritance was not necessary in the
case of Handel, whose father was a surgeon, why is it needed to account
for Bach?
LACK OF EVIDENCE.
The "direct proofs" of use-inheritance are not as plentiful as might be
desired, it appears (pp. 24-28). This acknowledged "lack of recognized
evidence" is indeed the weakest feature in the case, though Mr. Spencer
would fain attribute this lack of direct proof to insufficient
investigation and to the inconspicuous nature of the inheritance of the
modification. But there is an almost endless abundance of conspicuous
examples of the effects of use and disuse in the individual. How is it
that the subsequent inheritance of these effects has not been more
satisfactorily observed and investigated? Horse-breeders and others
could profit by such a tendency, and one cannot help suspecting that the
reason they ignore it must be its practical inefficacy, arising probably
from its weakness, its obscurity and uncertainty or its non-existence.
INHERITED EPILEPSY IN GUINEA-PIGS.
Brown-Séquard's discovery that an epileptic tendency artificially
produced by mutilating the nervous system of a guinea-pig is
occasionally inherited may be a fact of "considerable weight," or on the
other hand it may be entirely irrelevant. Cases of this kind strike one
as peculiar exceptions rather than as examples of a general rule or law.
They seem to show that certain morbid conditions may occasionally affect
both the individual and the reproductive elements or transmissible type
in a similar manner; but then we also know that such prompt and complete
transmission of an artificial modification is widely different from the
usual rule. Exceptional cases require exceptional explanations, and are
scarcely good examples of the effect of a general tendency which in
almost all other cases is so inconspicuous in its immediate effects.
Further remarks on this inherited epilepsy can be most conveniently
introduced later on in connection with Darwin's explanation of the
inherited mutilation which it usually accompanies, but which Mr. Spencer
does not mention.
INHERITED INSANITY AND NERVOUS DISORDERS.
Mr. Spencer infers that, because insanity is usually hereditary, and
insanity can be artificially produced by various excesses, therefore
this artificially-produced insanity must also be hereditary (p. 28).
Direct evidence of this conclusion would be better than a mere inference
which may beg the very question at issue. That the liability to insanity
commonly runs in families is no proof that strictly non-inherited
insanity will subsequently become hereditary. I think that theories
should be based on facts rather than facts on theories, especially when
those facts are to be the basis or proof of a further theory.
Mr. Spencer also points out that he finds among physicians "the belief
that nervous disorders of a less severe kind are inheritable"--a general
belief which does not necessarily include the transmission of purely
artificially-produced disorders, and so misses the point which is really
at issue. He proceeds, however, to state more definitely that "men who
have prostrated their nervous systems by prolonged overwork or in some
other way, have children more or less prone to nervousness." The
following observations will, I think, warrant at least a suspension of
judgment concerning this particular form of use-inheritance.
(1) The nervousness is seen in the _children_ at an early age, although
the nervous prostration from which it is supposed to be derived
obviously occurs in the parent at a much later period of life. This
change in time is contrary to the rule of inheritance at corresponding
periods; and, together with the unusual promptness and comparative
completeness of the inheritance, it may indicate a special injury or
deterioration of the reproductive elements rather than true inheritance.
The healthy brain of early life has failed to transmit its robust
condition. Is use-inheritance, then, only effective for evil? Does it
only transfer the newly-acquired weakness, and not the previous
long-continued vigour?
(2) Members of nervous families would be liable to suffer from nervous
prostration, and by the ordinary law of heredity alone would transmit
nervousness to their children.
(3) The shattered nerves or insanity resulting from alcoholic and other
excesses, or from overwork or trouble, are evidently signs of a grave
constitutional injury which may react upon the reproductive elements
nourished and developed in that ruined constitution. The deterioration
in parent and child may often display itself in the same organs--those
probably which are hereditarily weakest. Acquired diseases or disorders
thus appear to be transmitted, when all that was conveyed to the
offspring was the exciting cause of a lowered vitality or disordered
action, together with the ancestral liability to such diseases under
such conditions.
(4) Francis Galton says that "it is hard to find evidence of the power
of the personal structure to react upon the sexual elements, that is not
open to serious objection." Some of the cases of apparent inheritance he
regards as coincidence of effect. Thus "the fact that a drunkard will
often have imbecile children, although his offspring previous to his
taking to drink were healthy," is an "instance of simultaneous action,"
and not of true inheritance. "The alcohol pervades his tissues, and, of
course, affects the germinal matter in the sexual elements as much as it
does that in his own structural cells, which have led to an alteration
in the quality of his own nerves. Exactly the same must occur in the
case of many constitutional diseases that have been acquired by
long-continued irregular habits."[13]
INDIVIDUAL AND TRANSMISSIBLE TYPE NOT MODIFIED ALIKE BY THE DIRECT
EFFECT OF CHANGED HABITS OR CONDITIONS.
Mr. Spencer finds it hard to believe that the modifications conveyed to
offspring are not identical in tendency with the changes effected in the
parent by altered use or habit (pp. 23-25, 34). But it is perfectly
certain that the two sets of effects do not necessarily correspond. The
effect of changed habits or conditions on the individual is often very
far from coinciding with the effects on the reproductive elements or
the transmissible type. The reproductive system is "extremely
sensitive" to very slight changes, and is often powerfully affected by
circumstances which otherwise have little effect on the individual
(_Origin of Species_, p. 7). Various animals and plants become sterile
when domesticated or supplied with too much nourishment. The native
Tasmanians have already become extinct from sterility caused by greatly
changed diet and habits. If, as Mr. Spencer teaches, continued culture
and brain-work will in time produce lessened fertility or comparative
sterility, we may yet have to be careful that intellectual development
does not become a species of suicide, and that the culture of the race
does not mean its extinction--or at least the extinction of those most
susceptible of culture.
The reproductive elements are also disturbed and modified in innumerable
minor ways. Changed conditions or habits tend to produce a general
"plasticity" of type, the "indefinite variability" thus caused being
apparently irrelevant to the change, if any, in the individual.[14] A
vast number of variations of structure have certainly arisen
independently of similar parental modification as the preliminary.
Whatever first caused these "spontaneous" congenital variations affected
the reproductive elements quite differently from the individual. "When a
new peculiarity first appears we can never predict whether it will be
inherited." Many varieties of plants only keep true from shoots, and not
from seed, which is by no means acted on in the same way as the
individual plant. Seeing that such plants have _two_ reproductive
types, both constant, it is evident that these cannot both be modified
in the same way as the parent is modified. Many parental modifications
of structure and habit are certainly not conveyed to neuter ants and
bees; other modifications, which are not seen in the parents, being
conveyed instead. Many other circumstances tend to show that the
individual and the transmissible type are independent of each other so
far as modifications of parts are concerned.
It may seem natural to expect the transmission of an enlarged muscle or
a cultivated brain, but, on the other hand, why should it be
unreasonable to expect that a modification which was non-congenital in
origin should still remain non-congenital? Why should the
non-transmission of that which was not transmitted be surprising?
Mr. Spencer thinks that the non-transmission of acquired modifications
is incongruous with the great fact of atavism. But the great law of the
inheritance of that which is a development of the transmissible type
does not necessarily imply the inheritance of modifications acquired by
the individual. Because English children may inherit blue eyes and
flaxen hair from their Anglo-Saxon ancestors, it by no means follows
that an Englishman must inherit his father's sunburnt complexion or
smooth-shaven face. Of course atavism ultimately adopts many instances
of revolt against its sway. But to assume that these changes of type
_follow_ the personal change rather than cause it, is to assume the
whole question at issue. That like begets like is true as a broad
principle, but it has many exceptions, and the non-heredity of acquired
characters may be one of them.
FOOTNOTES:
[2] _Principles of Biology_, § 166, footnote. The English jaws are
somewhat lighter than the Australian jaws, though I could not undertake
to affirm that they are really shorter and smaller. In the typical
skulls depicted on p. 68 of the official guide to the mammalian
galleries at South Kensington, the typical Caucasian jaw is very much
larger than the Tasmanian jaw, although the repulsively obtrusive teeth
of the latter convey the contrary idea to the imagination. Mr. Spencer's
assumption that the ancient Britons had large jaws appears to me
erroneous. (See Professor Rolleston's _Scientific Papers and Addresses_,
i. p. 250.)
[3] Romanes, Galton, and Weismann have made great use of this principle
in explaining the diminution of disused organs. Weismann has given it
the name of _Panmixia_,--_all_ individuals being equally free to survive
and commingle their variations, and not merely selected or favoured
individuals. See his _Essays on Heredity_, &c., p. 90 (Clarendon Press).
[4] Inclusive in each case of fixed strengthening wire weighing about a
sixteenth of an ounce or less.
[5] References of course are to _Factors of Organic Evolution_.
[6] P. 13; and _Nineteenth Century_, February, 1888, p. 211.
[7] Tomes's _Dental Surgery_, pp. 273-275. Tomes observes that it is as
yet uncertain in what way civilization predisposes to caries. But he
shows that caries is caused by the lime salts in the teeth being
attacked by _acids_ from decomposing food in crevices, from artificial
drink such as cyder, from sugar, from medicine, and from vitiated
secretions of the mouth. It is evident that in civilized races natural
selection cannot so rigorously insist on sound teeth, sound
constitutions, and _protective alkaline_ saliva. The reaction of the
civilized mouth is often acid, especially when the system is disordered
by dyspepsia or other diseases or forms of ill-health common under
civilization. The main supply of saliva, which is poured from the cheeks
opposite the upper molars, is often acid when in small quantities. But
the submaxillary and sub-lingual saliva poured out at the foot of the
lower incisors and held in the front part of the jaw as in a spoon,
"differs from parotid saliva in being more alkaline" (Foster's _Text
Book of Physiology_, p. 238; Tomes, pp. 284, 685). One observer says
that the reaction near the lower incisors is "never acid." Hence (I
conclude) the remarkable immunity of the lower incisors and canines from
decay, an immunity which extends backwards in a lessening degree to the
first and second bicuspids. The close packing of the lower incisors may
assist by preventing the retention of decaying fragments of food. Sexual
selection may promote caries by favouring white teeth, which are more
prone to decay than yellow ones. Acid vitiation of the mucus might
account both for caries and (possibly) for the strange infertility of
some inferior races under civilization.
[8] _Origin of Species_, pp. 198-9; _Variation of Animals and Plants
under Domestication_, vol. ii. p. 328 footnote, also p. 206.
[9] Mr. Spencer weakly argues that an advantageous attribute (such as
swiftness, keen sight, courage, sagacity, strength, &c.) cannot be
increased by natural selection unless it is "of greater importance, for
the time being, than most of the other attributes"; and that natural
selection cannot develop any one superiority when animals are equally
preserved by "other superiorities." But as natural selection will
simultaneously eliminate tendencies to slowness, blindness, deafness,
stupidity, &c., it _must_ favour and improve many points simultaneously,
although no one of them may be of greater importance than the rest. Of
course the more complicated the evolution the slower it will be; but
time is plentiful, and the amount of elimination is correspondingly
vast.
[10] I venture to coin this concise term to signify _the direct
inheritance of the effects of use and disuse in kind_. Having a name for
a thing is highly convenient; it facilitates clearness and accuracy in
reasoning, and in this particular inquiry it may save some confusion of
thought from double or incomplete meanings in the shortened phrases
which would otherwise have to be employed to indicate this great but
nameless factor of evolution.
[11] _Origin of Species_, pp. 230-232; Bates's _Naturalist on the
Amazons_. Darwin is "surprised that no one has hitherto advanced the
demonstrative case of neuter insects, against the well-known doctrine of
inherited habit, as advanced by Lamarck." As he justly observes, "it
proves that with animals, as with plants, any amount of modification may
be effected by the accumulation of numerous, slight, spontaneous
variations, which are in any way profitable, without exercise or habit
having been brought into play. For peculiar habits confined to the
workers or sterile females, however long they might be followed, could
not possibly affect the males and fertile females, which alone leave any
descendants." Some slight modification of these remarks, however, may
possibly be needed to meet the case of "factitious queens," who
(probably through eating particles of the royal food) become capable of
producing a few male eggs.
[12] _Descent of Man_, pp. 573, 572, and footnote.
[13] _Contemporary Review_, December, 1875, p. 92.
[14] See _Origin of Species_, pp. 5-8. "Changed conditions induce an
almost indefinite amount of fluctuating variability, by which the whole
organization is rendered in some degree plastic" (_Descent of Man_, p.
30). It also appears that "the nature of the conditions is of
subordinate importance in comparison with the nature of the organism in
determining each particular form of variation;--perhaps of not more
importance than the nature of the spark, by which a mass of combustible
matter is ignited, has in determining the nature of the flames" (_Origin
of Species_, p. 8).
DARWIN'S EXAMPLES.
The most formidable cases brought forward by Mr. Spencer are from
Darwin. I shall endeavour to show, however, that Darwin was probably
wrong in retaining the older explanation of these facts, and that the
remains of the Lamarckian theory of use-inheritance need not any longer
encumber the great explanation which has superseded that fallacious and
unproven theory and has rendered it totally unnecessary. Meanwhile I
think it is an excellent sign that Mr. Spencer has to complain that
"Nowadays most naturalists are more Darwinian than Mr. Darwin
himself"--inasmuch as they are inclined to say that there is "no proof"
that the effects of use and disuse are inherited. Other excellent signs
are the recent issue of a translation of Weismann's important essays on
this and kindred subjects,[15] the strong support given to his views by
Wallace in his _Darwinism_, and their adoption by Ray Lankester in his
article on Zoology in the latest edition of the _Encyclopædia
Britannica_. So sound and cautious an investigator as Francis Galton had
also in 1875 concluded that "acquired modifications are barely, if at
all, _inherited_, in the correct sense of that word."
Darwin's belief in the inheritance of acquired characters was more or
less hereditary in the family. His grandfather, Erasmus Darwin,
anticipated Lamarck's views in his _Zoonomia_, which Darwin at one time
"greatly admired." His father was "convinced" of the "inherited evil
effects of alcohol," and to this extent at least he strongly impressed
the belief in the inheritance of acquired characters upon his
children's minds.[16] Darwin must also have been imbued with Lamarckian
ideas from other sources, although Dr. Grant's enthusiastic advocacy
entirely failed to convert him to a belief in evolution.[17]
"Nevertheless," he says, "it is probable that the hearing rather early
in life such views maintained and praised may have favoured my upholding
them under a different form in my _Origin of Species_"--a remark which
refers to Lamarck's views on the general doctrine of evolution, but
might also prove equally true if applied to Darwin's partial retention
of the Lamarckian explanation of that evolution. Professor Huxley has
pointed out that in Darwin's earlier sketch of his theory of evolution
(1844) he attached more weight to the inheritance of acquired habits
than he does in his _Origin of Species_ published fifteen years
later.[18] He appears to have acquired the belief in early life without
first questioning and rigorously testing it as he would have done had it
originated with himself. In later life it appeared to assist his theory
of evolution in minor points, and in particular it appeared absolutely
indispensable to him as the _only_ explanation of the diminution of
disused parts in cases where, as in domestic animals, economy of growth
seemed to be practically powerless. He failed to adequately notice the
effect of panmixia, or the withdrawal of selection, in causing or
allowing degeneracy and dwindling under disuse; and he hardly attached
sufficient importance to the fact that rudimentary organs and other
supposed effects of use or disuse are quite as marked features in
neuter insects which cannot transmit the effects of use and disuse as
they are in the higher animals.
REDUCED WINGS OF BIRDS OF OCEANIC ISLANDS.
Darwin himself has pointed out that the rudimentary wings of island
beetles, at first thought to be due to disuse, are mainly brought about
by natural selection--the best-winged beetles being most liable to be
blown out to sea. But he says that in birds of the oceanic islands "not
persecuted by any enemies, the reduction of their wings has probably
been caused by disuse." This explanation may be as fallacious as it is
acknowledged to have been in the case of the island beetles. According
to Darwin's own views, natural selection _must_ at least have played an
important part in reducing the wings; for he holds that "natural
selection is continually trying to economize every part of the
organization." He says: "If under changed conditions of life a
structure, before useful, becomes less useful, its diminution will be
favoured, for it will profit the individual not to have its nutriment
wasted in building up an useless structure.... Thus, as I believe,
natural selection will tend in the long run to reduce any part of the
organization, as soon as it becomes, through changed habits,
superfluous."[19] If, as Darwin powerfully urges (and he here ignores
his usual explanation), ostriches' wings are insufficient for flight in
consequence of the economy enforced by natural selection,[20] why may
not the reduced wings of the dodo, or the penguin, or the apteryx, or of
the Cursores generally, be wholly attributed to natural selection in
favour of economy of material and adaptation of parts to changed
conditions? The great principle of economy is continually at work
shaping organisms, as sculptors shape statues, by removing the
superfluous parts; and a mere glance at the forms of animals in general
will show that it is well-nigh as dominant and universal a principle as
is that of the positive development of useful parts. Other causes,
moreover besides actual economy, would favour shorter and more
convenient wings on oceanic islands. In the first place, birds that were
somewhat weak on the wing would be most likely to settle on an island
and stay there. Shortened wings would then become advantageous because
they would restrain fatal migratory tendencies or useless and perilous
flights in which the birds that flew furthest would be most often
carried away by storms and adverse winds. Reduced wings would keep the
birds near the shelter and the food afforded by the island and its
neighbourhood, and in some cases would become adapted to act as fins or
flappers for swimming under water in pursuit of fish.
The reduced size of the wings of these island birds is paralleled by the
remarkable thinness, &c., of the shell of the "gigantic land-tortoise"
of the Galapagos Islands. The changes seen in the carapace can hardly
have been brought about by the inherited effects of special disuse. Why
then should not the reduction of equally useless, more wasteful, and
perhaps positively dangerous wings be also due to an economy which has
become advantageous to bird and reptile alike through the absence of the
mammalian rivals whose places they are evidently being modified to fill?
The _complete_ loss of the wings in neuter ants and termites can
scarcely be due to the inherited effects of disuse; and as natural
selection has abolished these wings in spite of the opposition of
use-inheritance, it must clearly be fully competent to reduce wings
without its aid. In considering the rudimentary wings of the apteryx,
or of the moa, emu, ostrich, &c., we must not forget the frequent or
occasional occurrence of hard seasons, and times of drought and famine,
when Nature eliminates redundant, wasteful, and ill-adapted organisms in
so severe and wholesale a fashion. Where enemies are absent there would
be unrestrained multiplication, and this would greatly increase the
severity of the competition for food, and so hasten the elimination of
disused and useless parts.
DROOPING EARS AND DETERIORATED INSTINCTS.
Mr. Galton has pointed out that existing races and existing organs are
only kept at their present high pitch of organic excellence by the
stringent and incessant action of natural or artificial selection; and
the simple relaxation or withdrawal of such selective influences will
almost necessarily result in a certain amount of deterioration,
independently even of the principle of economy.[21] I think that this
cessation of a previous selective process will account for the
drooping--but _not diminished_--ears of various domesticated animals
(human preference and increased weight evidently aiding), and also for
the inferior instincts seen in them and in artificially-fed caterpillars
of the silk-moth, which now "often commit the strange mistake of
devouring the base of the leaf on which they are feeding, and
consequently fall down." Anyhow, I fail to see that anything is proved
by this latter case, except that natural instinct may be perverted or
aborted under unnatural conditions and a changed method of selection
which abolishes the powerful corrective formerly supplied by natural
selection.
WINGS AND LEGS OF DUCKS AND FOWLS.
The reduced wings and enlarged legs of domesticated ducks and fowls are
attributed by Darwin and Spencer to the inheritance of the effects of
use and disuse. But the inference by no means follows. Natural selection
would usually favour these adaptive changes, and they would also have
been aided by an artificial selection which is often unconscious or
indirect. Birds with diminished power of flight would be less difficult
to keep and manage, and in preserving and multiplying such birds man
would be unconsciously bringing about structural changes which would
easily be regarded as effects of use and disuse. "About eighteen
centuries ago Columella and Varro speak of the necessity of keeping
ducks in netted enclosures like other wild fowl, so that at this period
there was danger of their flying away."[22] Is it not probable that the
best fliers would escape most frequently, or would pine most if kept
confined? On the other hand, birds with lessened powers of flight would
not be eliminated as under natural conditions, but would be favoured;
and natural selection, together with artificial selection of the most
flourishing birds, would thicken and strengthen the legs to meet
increased demands upon them.
The diminution of the duck's wing is not great even in the birds that
"never fly," and from this we must deduct the direct effect of disuse on
the individual during its lifetime. As Weismann suggests, the
_inherited_ portion of the change could only be ascertained by comparing
the bones, &c., of wild and tame ducks _similarly reared_. If individual
disuse diminished the weight of the duck's wing-bones by 9 per cent.
there would be nothing left to account for.
I suspect that investigation would reveal anomalies inconsistent with
the theory of use-inheritance. Thus according to Darwin's tables of
comparative weights and measurements[23] the leg-bones of the Penguin
duck have slightly diminished in length, although they have increased 39
per cent. in weight. Relatively to the weight of the skeleton, the
leg-bones have shortened in the tame breeds of ducks by over 5 per cent.
(and in two breeds by over 8 per cent.) although they have increased
more than 28 per cent. in proportional weight.[24] How can increased use
simultaneously shorten and thicken these bones? If the relative
shortening is attributed to a heavier skeleton, then the apparently
reduced weight of the wing-bones is fully accounted for by the same
circumstance, and disuse has had no inherited effect.
Another strange circumstance is that the wing-bones have diminished _in
length only_. The shortening is about 6 per cent. more than in the
shortened legs, and it amounts to 11 per cent. as compared with the
weight of the skeleton. Such a shortening should represent a reduction
of 29 per cent. in weight, whereas the actual reduction in the weight of
the wing-bones relatively to the weight of the skeleton is only 9 per
cent. even in the breeds that never fly. Independently of shortening,
the disused wing-bones have actually thickened or increased in weight.
In the Aylesbury duck the disproportion caused by these conflicting
changes is so great that the wing-bones are 47 per cent. heavier than
they should be if their weight had varied proportionally with their
length.[25] The reduction in weight on which Darwin relies seems to be
entirely due to the shortening, and this shortening appears to be
irrelevant to disuse, since the wings of the Call duck are similarly
shortened in their proportions by 12 per cent., although this bird
habitually flies to such an extent that Darwin partly attributes the
greatly increased weight of its wing-bones to increased use under
domestication.
We find that _all_ the changes are in the direction of shorter and
thicker bones--a tendency which must be largely dependent upon the
suspension of the rigorous elimination which keeps the bones of the
wild duck _long and light_. The used leg-bones and the disused
wing-bones have alike been shortened and thickened, though in different
proportions. Natural or artificial selection might easily thicken legs
without lengthening them, or shorten wings without eliminating strong
heavy bones, but it can hardly be contended that use-inheritance has
acted in such conflicting ways. The thickening of the wing-bones has
actually more than kept pace with any increase of weight in the
skeleton, in spite of the effect of individual disuse and of the alleged
cumulative effect of ancestral disuse for hundreds of generations. The
case of the duck deserves special attention as a crucial one, if only
from the fact that in this instance, and in this instance only, has
Darwin given the weights of the skeletons, thus furnishing the means for
a closer examination of his details than is usually possible.
If we ignore such factors as selection, panmixia, correlation, and the
effects of use and disuse during lifetime, and still regard the case of
the domestic duck as a valid proof of the inheritance of the effects of
use and disuse, we must also accept it as an equally valid proof that
the effects of use and disuse are _not_ inherited. Nay, we may even have
to admit that, in two points out of four, the _inherited_ effect of use
and disuse on successive generations is exactly opposite to the
immediate effect on the individual.
Among fowls the wing-bones have lost much in weight but little or
nothing in length--which is the reverse of what has occurred in ducks,
although disuse is alleged to be the common cause in both cases. Some of
the fowls which fly least have their wing-bones as long as ever. In the
case of the Silk and Frizzled fowls--ancient breeds which "cannot fly at
all"--and in that of the Cochins, which "can hardly fly up to a low
perch," Darwin observes "how truly the proportions of an organ may be
inherited although not fully exercised during many generations."[26] In
four out of twelve breeds the wing-bones had become slightly heavier
relatively to the leg-bones. Do not these facts tend to show that the
changes in fowls' wings are due to fluctuating variability and selective
influences rather than to a general law whereby the effects of disuse
are cumulatively inherited?
PIGEONS' WINGS.
Concerning pigeons' wings Darwin says: "As fancy pigeons are generally
confined in aviaries of moderate size, and as even when not confined
they do not search for their own food, they must during many generations
have used their wings incomparably less than the wild rock-pigeon ...
but when we turn to the wings we find what at first appears a wholly
different and unexpected result."[27] This unexpected increase in the
spread of the wings from tip to tip is due to the feathers, which have
lengthened in spite of disuse. Excluding the feathers, the wings were
shorter in seventeen instances, and longer in eight. But as artificial
selection has lengthened the wings in some instances, why may it not
have shortened them in others? Wings with shortened bones would fold up
more neatly than the long wings of the Carrier pigeon for instance, and
so might unconsciously be favoured by fanciers. The selection of elegant
birds with longer necks or bodies would cause a relative reduction in
the wings--as with the Pouter, where the wings have been greatly
lengthened but not so much as the body.[28] Slender bodies, too, and the
lessened divergence of the furculum,[29] would slightly diminish the
spread of the wings, and so would affect the measurements taken. As the
wing-bones, moreover, are to some extent correlated with the beak and
the feet, the artificial selection of shortened beaks might tend to
shorten the wing as well as the feet. Under these circumstances how can
we be sure of the actual efficacy of use-inheritance? Surely selection
is as fully competent to effect slight changes in the direction of
use-inheritance as it undoubtedly is to effect great changes in direct
opposition to that alleged factor of evolution.
SHORTENED BREAST-BONE IN PIGEONS.
The shortening of the sternum in pigeons is attributed to disuse of the
flight muscles attached to it. The bone is only shortened by a third of
an inch, but this represents a very remarkable reduction in proportional
length, which Darwin estimates at from one-seventh to one-eighth, or
over 13 per cent. This marked reduction, too, quite unlike the slight
reduction of the wing-bones to which the other ends of the muscles are
attached, was universal in the eleven specimens measured by Darwin; and
the bone, though acknowledged to have been modified by artificial
selection in some breeds, is not so open to observation as wings or
legs. Even, however, if this relative shortening of the sternum remained
otherwise inexplicable, it might still be as irrelevant to use and
disuse as is the fact that "many breeds" of fancy pigeons have lost a
rib, having only seven where the ancestral rock-pigeon has eight.[30]
But the excessive reduction in the sternum is far from being
inexplicable. In the first place Darwin has somewhat over-estimated it.
Instead of comparing the deficiency of length with the increased length
which _should_ have been acquired (since the pigeons have increased in
average size) he compares it with the length of the breast-bone in the
rock-pigeon.[31] By this method if a pigeon had doubled in dimensions
while its breast-bone remained unaltered, the reduction would be put
down as 100 per cent., whereas obviously the true reduction would be
one-half, or 50 per cent. of what the bone _should be_. Avoiding this
error and a minor fallacy besides, a sound estimate reduces the supposed
reduction of 13 or 14 per cent. to one of 11·7 per cent., which is still
of course a considerable diminution.
Part of this reduction must be due to the direct effect of disuse during
the lifetime of the individual. Another and perhaps very considerable
part of the relative change must be attributed to the lengthening of the
neck or body by artificial selection, or to other modifications of
shape and proportion effected directly or indirectly by the same
cause.[32] The reduction is greatest in the Pouter (18-1/2 per cent.)
and in the Pied Scanderoon (17-1/2 per cent.). In the former the body
has been greatly elongated by artificial selection and three or four
additional vertebræ have been acquired in the hinder part of the
body.[33] In the latter a long neck increases the length of the bird,
and so causes, or helps to cause, the relative shortening of the
breast-bone. In the English Carrier--which experiences the effects of
disuse, as it is too valuable to be flown--the relative reduction of 11
per cent. is apparently more than accounted for by the "elongated
neck." The Dragon also has a long neck. In the Pouter, although the
breast-bone has been shortened by 18-1/2 per cent. relatively to the
length of the body, it has _lengthened_ by 20 per cent. relatively to
the _bulk_ of the body.[34] Darwin forgot to ask whether allowance must
not be made for a frequent, or perhaps general, elongation of the neck
and the hinder part of the body, and the relative shortening or the
throwing forward of the central portion containing the ribs (frequently
one less in number) and the sternum. The whole body of the pigeon is so
much under the control of artificial selection, that every precaution
must be taken to guard against such possible sources of error.[35]
Under domestication there would be a suspension of the previous
elimination of reduced breast-bones by natural selection (Weismann's
panmixia), and a diminution of the parts concerned in flying might even
be favoured, as lessened powers of _continuous_ flight would prevent
pigeons from straying too far, and would fit them for domestication or
confinement. Such causes might reduce some of the less observed parts
affected by flying, while still leaving the wing of full size for
occasional flight, or to suit the requirements of the pigeon-fanciers. A
change might thus be commenced like that seen in the rudimentary keel of
the sternum in the owl-parrot of New Zealand, which has lost the power
of flight although still retaining fairly-developed wings.
SHORTENED FEET IN PIGEONS.
Darwin thinks it highly probable that the short feet of most breeds of
pigeons are due to lessened use, though he owns that the effects of
correlation with the shortened beak are more plainly shown than the
effects of disuse.[36] But why need the inherited effects of disuse be
called in to explain an average reduction of some 5 per cent., when
Darwin's measurements show that in the breeds where long beaks are
favoured the principle of correlation between these parts has lengthened
the foot by 13 per cent. in spite of disuse?
SHORTENED LEGS OF RABBITS.
In the case of the domestic rabbit Darwin notices that the bones of the
legs have (relatively) become shorter by an inch and a half. But as the
leg-bones have _not_ diminished in relative weight,[37] they must
clearly have grown _thicker_ or denser. If disuse has shortened them, as
Darwin supposes, why has it also thickened them? The ears and the tail
have been lengthened in spite of disuse. Why then may not the ungainly
hind-legs have been shortened by human preference independently of the
inherited effects of disuse? By relying on apparently favourable
instances and neglecting the others it would be easy to arrive at all
manner of unsound conclusions. We might thus become convinced that
vessels tend to sail northwards, or that a pendulum oscillates more
often in one direction than in the other. It must not be forgotten that
it would be easy to cite an enormous number of cases which are in direct
conflict with the supposed law of use-inheritance.
BLIND CAVE-ANIMALS.
Weak or defective eyesight is by no means rare as a spontaneous
variation in animals, "the great French veterinary Huzard going so far
as to say that a blind race [of horses] could soon be formed." Natural
selection evolves blind races whenever eyes are useless or
disadvantageous, as with parasites. This may apparently be done
independently of the effects of disuse, for certain neuter ants have
eyes which are reduced to a more or less rudimentary condition, and
neuter termites are blind as well as wingless. In one species of ant
(_Eciton vastator_) the sockets have disappeared as well as the eyes. In
deep caves not only would natural selection cease to maintain good
eyesight but it would persistently favour blindness--or the entire
removal of the eye when greatly exposed, as in the cave-crab--and as Dr.
Ray Lankester has indicated,[38] there would have been a previous
selection of animals which through spontaneous weakness, sensitiveness,
or other affection of the eye found refuge and preservation in the cave,
and a subsequent selection of the descendants whose fitness for relative
darkness led them deeper into the cave or prevented them from straying
back to the light with its various dangers and severer competition.
Panmixia, however, as Weismann has shown, would probably be the most
important factor in causing blindness.
INHERITED HABITS.
Darwin says: "A horse is trained to certain paces, and the colt inherits
similar consensual movements."[39] But selection of the constitutional
tendency to these paces, and imitation of the mother by the colt, may
have been the real causes. The evidence, to be satisfactory, should show
that such influences were excluded. Men acquire proficiency in swimming,
waltzing, walking, smoking, languages, handicrafts, religious beliefs,
&c., but the children only appear to inherit the innate abilities or
constitutional proclivities of their parents. Even the songs of birds,
including their call-notes, are no more inherited than is language by
man (_Descent of Man_, p. 86). They are learned from the parent.
Nestlings which acquire the song of a distinct species, "teach and
transmit their new song to their offspring." If use-inheritance has not
fixed the song of birds, why should we suppose that in a single
generation it has transmitted a newly-taught method of walking or
trotting?
It is alleged that dogs inherit the intelligence acquired by association
with man, and that retrievers inherit the effects of their
training.[40] But selection and imitation are so potent that the
additional hypothesis of use-inheritance seems perfectly superfluous.
Where intelligence is not highly valued and carefully promoted by
selection, the intelligence derivable from association with man does
_not_ appear to be inherited. Lap-dogs, for instance, are often
remarkably stupid.
Darwin also instances the inheritance of dexterity in seal-catching as a
case of use-inheritance.[41] But this is amply explained by the ordinary
law of heredity. All that is needed is that the son shall inherit the
suitable faculties which the father inherited before him.
TAMENESS OF RABBITS.
Darwin holds that in some cases selection alone has modified the
instincts and dispositions of domesticated animals, but that in most
cases selection and the inheritance of acquired habits have concurred in
effecting the change. "On the other hand," he says, "habit alone in some
cases has sufficed; hardly any animal is more difficult to tame than the
young of the wild rabbit; scarcely any animal is tamer than the young of
the tame rabbit; but I can hardly suppose that domestic rabbits have
often been selected for tameness alone; so that we must attribute at
least the greater part of the inherited change from extreme wildness to
extreme tameness to habit and long-continued close confinement."[42]
But there are strong, and to me irresistible, arguments to the contrary.
I think that the following considerations will show that the greater
part, if not the whole, of the change must be attributed to selection
rather than to the direct inheritance of acquired habit.
(1) For a period which may cover thousands of generations, there has
been an entire cessation of the natural selection which maintains the
wildness (or excessive fear, caution, activity, &c.) so indispensably
essential for preserving defenceless wild rabbits of all ages from the
many enemies that prey upon them.
(2) During this same extensive period of time man has usually killed off
the wildest and bred from the tamest and most manageable. To some extent
he has done this consciously. "It is very conducive to successful
breeding to keep only such as are quiet and tractable," says an
authority on rabbits,[43] and he enjoins the selection of the
handsomest and _best-tempered_ does to serve as breeders. To a still
greater extent man has favoured tameness unconsciously and indirectly.
He has systematically selected the largest and most prolific animals,
and has thus doubled the size and the fertility of the domestic rabbit.
In consciously selecting the largest and most flourishing individuals
and the best and most prolific mothers, he _must_ have unconsciously
selected those rabbits whose relative _tameness_ or placidity of
disposition rendered it possible for them to flourish and to produce and
rear large and thriving families, instead of fretting and pining as the
wilder captives would do. When we consider how exceedingly delicate and
easily disturbed yet all-important a function is that of maternity in
the continually breeding rabbit, we see that the tamest and the least
terrified would be the most successful mothers, and so would continually
be selected, although man cared nothing for the tameness in itself. The
tamest mothers would also be less liable to neglect or devour their
offspring, as rabbits commonly do when their young are handled too soon,
or even when merely frightened by mice, &c., or disturbed by changed
surroundings.
(3) We must remember the extraordinary fecundity of the rabbit and the
excessive amount of elimination that consequently takes place either
naturally or artificially. Where nature preserved only the wildest, man
has preserved the tamest. If there is any truth in the Darwinian theory,
this thorough and long-continued reversal of the selective process
_must_ have had a powerful effect. Why should it not be amply sufficient
to account for the tameness and mental degeneracy of the rabbit without
the aid of a factor which can readily be shown to be far weaker in its
normal action than either natural or artificial selection? Why may not
the tameness of the rabbit be transferred to the group of cases in
which Darwin holds that "habit has done nothing," and selection has done
all?
(4) If use-inheritance has tamed the rabbit, why are the bucks still so
mischievous and unruly? Why is the Angora breed the only one in which
the males show no desire to destroy the young? Why, too, should
use-inheritance be so much more powerful in the rabbit than with other
animals which are far more easily tamed in the first instance? Wild
young rabbits when domesticated "remain unconquerably wild," and,
although they may be kept alive, they pine and "rarely come to any
good." Yet the animal which _acquires_ least tameness--or apparently,
indeed, none at all--inherits most! It appears, in fact, to inherit that
which it cannot acquire--a circumstance which indicates the selection of
spontaneous variations rather than the inheritance of changed habits.
Such variations occasionally occur in animals in a marked degree. Of a
litter of wolf-cubs, all brought up in the same way, "one became tame
and gentle like a dog, while the others preserved their natural
savagery." Is it not probable that permanent domestication was rendered
possible by the inevitable selection of spontaneous variations in this
direction? The _excessive_ tameness, too, of the young rabbit, while
easily explicable as a result of unconscious selection, is not easily
explained as a result of acquired habit. No particular care is taken to
tame or teach or domesticate rabbits. They are bred for food, or for
profit or appearance, and they are left to themselves most of their
time. As Sir J. Sebright notices with some surprise, the domestic rabbit
"is not often visited, and seldom handled, and yet it is always tame."
MODIFICATIONS OBVIOUSLY ATTRIBUTABLE TO SELECTION.
Innumerable modifications in accordance with altered use or disuse, such
as the enlarged udders of cows and goats, and the diminished lungs and
livers in highly bred animals that take little exercise, can be readily
and fully explained as depending on selection. As the fittest for the
natural or artificial requirements will be favoured, natural or
artificial selection may easily enlarge organs that are increasingly
used and economize in those that are less needed. I therefore see no
necessity whatever for calling in the aid of use-inheritance as Darwin
does, to account for enlarged udders, or diminished lungs, or the thick
arms and thin legs of canoe Indians, or the enlarged chests of
mountaineers, or the diminished eyes of moles, or the lost feet of
certain beetles, or the reduced wings of logger-headed ducks, or the
prehensile tails of monkeys, or the displaced eyes of soles, or the
altered number of teeth in plaice, or the increased fertility of
domesticated animals, or the shortened legs and snouts of pigs, or the
shortened intestines of tame rabbits, or the lengthened intestines of
domestic cats, &c.[44] Changed habits and the requisite change of
structure will usually be favoured by natural selection; for habit, as
Darwin says, "almost implies that some benefit great or small is thus
derived."
SIMILAR EFFECTS OF NATURAL SELECTION AND USE-INHERITANCE.
Here we perceive a difficulty which will equally trouble those who
affirm use-inheritance and those who deny. Broadly speaking, the
adaptive effects ascribed to use-inheritance coincide with the effects
of natural selection. The individual adaptability (as shown in the
thickening of skin, fur, muscle, &c., under the stimulus of friction,
cold, use, &c.) is identical in kind and direction with the racial
adaptability under natural selection. Consequently the alleged
inheritance of the advantageous effects of use and disuse cannot readily
be distinguished from the similarly beneficial effects of natural
selection. The indisputable fact that natural selection imitates or
simulates the beneficial effects ascribed to use-inheritance may be the
chief source and explanation of a belief which may prove to be
thoroughly fallacious. A similar simulation of course occurs under
domestication, where natural selection is partly replaced by artificial
selection of the best adapted and therefore most flourishing animals,
while in disused parts panmixia or the comparative cessation of
selection will aid or replace "economy of growth" in causing
diminution.[45]
INFERIORITY OF SENSES IN EUROPEANS.
"The inferiority of Europeans, in comparison with savages, in eyesight
and in the other senses," is attributed to "the accumulated and
transmitted effect of lessened use during many generations."[46] But why
may we not attribute it to the slackened and diverted action of the
natural selection which keeps the senses so keen in some savage races?
SHORT-SIGHT IN WATCHMAKERS AND ENGRAVERS.
Darwin notices that watchmakers and engravers are liable to be
short-sighted, and that short-sight and long-sight certainly tend to be
inherited.[47] But we must be careful not to beg the question at issue
by assuming that the frequent heredity of short sight necessarily covers
the heredity of artificially-produced short-sight. Elsewhere, however,
Darwin states more decisively that "there is ground for believing that
it may often originate in causes acting on the individual affected, and
may thence-forward become transmissible."[48] This impression may arise
(1) from the facts of ordinary heredity--the ancestral liability being
excited in father and son by similar artificial habits, such as reading,
and viewing objects closely as among watchmakers and engravers--or by
constitutional deterioration from indoor life, &c., acting upon a
constitutional liability of the eye to the "something like inflammation
of the coats, under which they yield" and so cause shortness of sight
by altering the spherical shape of the eye-ball. (2) Panmixia, or the
suspension of natural selection, together with altered habits, will
account for an increase of short-sight among the population generally.
(3) Long-sighted people could not work at watchmaking and engraving so
comfortably and advantageously as at other occupations, and hence would
be less likely to take to such callings.
LARGER HANDS OF LABOURERS' INFANTS.[49]
These are best explained as the result of natural selection and of the
diminution of the hand by sexual selection in the gentry. If the larger
hands of labourers' infants are really due to the inherited effects of
ancestral use, why does the development occur so early in life, instead
of only at a corresponding period, as is the rule? During the first few
years of its life, at least, the labourer's infant does no more work
than the gentleman's child. Why are not the effects of this disuse
inherited by the labourer's infant? If the enlargement of the infant's
hand illustrates the transference of a character gained later in life,
it is evident that the transference must take place in spite of the
inherited effects of disuse.
THICKENED SOLE IN INFANTS.
Darwin also attributes the thickened sole in infants, "long before
birth," to "the inherited effects of pressure during a long series of
generations."[50] But disuse should make the infant's sole _thin_, and
it is this thinness that should be inherited. If we suppose the
inheritance of the thickened soles of later life to be transferred to an
earlier period, we have the anomaly of the inherited effects of disuse
at that earlier period being overpowered by the untimely inheritance of
the effects of use at another. On the other hand, it is clear that
natural selection would favour thickened soles for walking on, and might
also promote an early development which would ensure their being ready
in good time for actual use; for variations in the direction of delay
would be cut off, while variations in the other direction would be
preserved. Anyhow, the mere transference of a character to an earlier
period is no proof of use-inheritance. The real question is whether the
thickened sole was gained by natural selection or by the inherited
effects of pressure, and the mere transference or hastened appearance of
the thickening does not in any degree solve this question. It merely
excludes the effect of disuse during lifetime, and thus presents a
fallacious appearance of being decisive. The thickened sole of the
unborn infant, however, like the lanugo or hairy covering, is probably a
result of the direct inheritance of ancestral stages of evolution, of
which the embryo presents a condensed epitome. While the relative
thinness of the infant's sole might be pointed to as the effect of
_disuse_ during a long series of generations, its thickness is rather an
illustration of atavism still resisting the effects of long-continued
disuse. There is nothing to show that the inheritable portion of the
full original thickness was not gained by natural selection rather than
by the directly inherited effect of use; and the latter, being
cumulative and indiscriminative in its action, would apparently have
made the sole very much thicker and harder than it is. If natural
selection were not supreme in such cases, how could we account for the
effects of pressure resulting in hard hoofs in some cases and only soft
pads in others?
A SOURCE OF MENTAL CONFUSION.
Of course in a certain sense this thickening of the sole has resulted
from use. In one sense or other, most--or perhaps all--of the results of
natural selection are inherited effects of use or disuse. Natural
selection preserves that which is of use and which is used, while it
eliminates that which is useless and is not used. The most confident
assertions of the effects of use and disuse in modifying the heritable
type, appear to rest on this indefeasible basis. Darwin's statements
concerning the effects of use and disuse in evolution can frequently be
read in two senses. They often command assent as undeniable truisms as
they stand, but are of course written in another and more debatable
sense. Thus in the case of the shortened wings and thickened legs of the
domestic duck, I believe equally with Darwin and Spencer that "no one
will dispute that they have resulted from the lessened use of the wings
and the increased use of the legs." "Use" is at bottom the determining
circumstance in evolution generally. The trunk of the elephant, the fin
of the fish, the wing of the bird, the cunning hand of man and his
complicated brain--and, in short, all organs and faculties
whatsoever--can only have been moulded and developed by use--by
usefulness and by using--but not necessarily by use-inheritance, not
necessarily by directly inherited effects of use or disuse of parts in
the individual. So, too, reduced or rudimentary organs are due to
disuse, but it by no means follows that the diminution is caused by any
direct tendency to the inheritance of the effects of disuse in the
individual. The effects of natural selection are commonly expressible as
effects of use and disuse, just as adaptation in nature is expressible
in the language of teleology. But use-inheritance is no more proven by
one of these necessary coincidences than special design is by the
other. The inevitable simulation of use-inheritance may be entirely
deceptive.
Darwin thinks that "there can be no doubt that use in our domestic
animals has strengthened and enlarged certain parts, and disuse
diminished them; and that such modifications are inherited." Undoubtedly
"such" or _similar_ modifications have often been inherited, but how can
Darwin possibly tell that they are not due to the simulation of
use-inheritance by natural or artificial selection acting upon general
variability? Of the inevitability of selection and of its generally
adaptive tendencies "there can be no doubt," and panmixia would tend to
reduce disused parts; so that there _must always_ remain grave doubts of
the alleged inheritance of the similar effects of use and disuse, unless
we can accomplish the extremely difficult feat of excluding both natural
and artificial selection as causes of enlargement, and panmixia and
selection as causes of dwindling.
WEAKNESS OF USE-INHERITANCE.
Use-inheritance is normally so weak that it appears to be quite helpless
when opposed to any other factor of evolution. Natural selection evolves
and maintains the instincts of ants and termites in spite of
use-inheritance to a more wonderful degree than it evolves the instincts
of almost any other animal with the fullest help of use-inheritance. It
develops seldom-used horns or natural armour just as readily as
constantly-used hoofs or teeth. Sexual selection evolves elaborate
structures like the peacock's tail in spite of disuse and natural
selection combined. Artificial selection appears to enlarge or diminish
used parts or disused parts with equal facility. The assistance of
use-inheritance seems to be as unnecessary as its opposition is
ineffective.
The alleged inheritance of the effects of use and disuse in our domestic
animals must be very slow and slight.[51] Darwin tells us that "there
is no good evidence that this ever follows in the course of a single
generation." "Several generations must be subjected to changed habits
for any appreciable result."[52] What does this mean? One of two things.
Either the tendency is very weak, or it is non-existent. If it is so
weak that we cannot detect its alleged effects till several generations
have elapsed, during which time the more powerful agency of selection
has been at work, how are we to distinguish the effects of the minor
factor from that of the major? Are we to conclude that use-inheritance
_plus_ selection will modify races, just as Voltaire firmly held that
incantations, together with sufficient arsenic, would destroy flocks of
sheep? Is it not a significant fact that the alleged instances of
use-inheritance so often prove to be self-conflicting in their details?
For satisfactory proof of the prevalence of a law of use-inheritance we
require normal instances where selection is clearly inadequate to
produce the change, or where it is scarcely allowed time or opportunity
to act, as in the immediate offspring of the modified individual. Of the
first kind of cases there seems to be a plentiful lack. Of the latter
kind, according to Darwin, there appears to be none--a circumstance
which contrasts strangely and suspiciously with the many decisive cases
in which variation from unknown causes has been inherited most
strikingly in the immediate offspring. It must be expected, indeed, that
among these innumerable cases some will accidentally mimic the alleged
effects of use-inheritance.
If Darwin had felt certain that the effects of habit or use tended in
any marked degree to be conveyed directly and cumulatively to succeeding
generations, he could hardly have given us such cautious, half-hearted
encouragement of good habits as the following:--"It is not improbable
that after long practice virtuous tendencies may be inherited." "Habits,
moreover followed during many generations probably tend to be
inherited."[53] This is probable, independently of use-inheritance. The
"many generations" specified or implied, will allow time for the play of
selective as well as of cumulatively-educative influences. There must
apparently be a constitutional or inheritable predisposition or fitness
for the habits spoken of, which otherwise would scarcely be continued
for many generations, except by the favourably-varying branches of a
family: which again is selection rather than use-inheritance.
Where is the necessity for even the remains of the Lamarckian doctrine
of inherited habit? Seeing how powerful the general principle of
selection has shown itself in cases where use-inheritance could have
given no aid or must even have offered its most strenuous opposition,
why should it not equally be able to develop used organs or repress
disused organs or faculties without the assistance of a relatively weak
ally? Selection evolved the remarkable protective coverings of the
armadillo, turtle, crocodile, porcupine, hedgehog, &c.; it formed alike
the rose and its thorn, the nut and its shell; it developed the
peacock's tail and the deer's antlers, the protective mimicry of various
insects and butterflies, and the wonderful instincts of the white ants;
it gave the serpent its deadly poison and the violet its grateful odour;
it painted the gorgeous plumage of the Impeyan pheasant and the
beautiful colours and decorations of countless birds and insects and
flowers. These, and a thousand other achievements, it has evidently
accomplished without the help of use-inheritance. Why should it be
thought incapable of reducing a pigeon's wing or enlarging a duck's
leg? Why should it be credited with the help of an officious ally in
effecting comparatively slight changes, when great and striking
modifications are effected without any such aid?
FOOTNOTES:
[15] Weismann's _Essays on Heredity_, &c. Clarendon Press, 1889.
[16] _Life and Letters_, i. p. 16. Darwin's reverence for his father
"was boundless and most touching. He would have wished to judge
everything else in the world dispassionately, but anything his father
had said was received with almost implicit faith; ... he hoped none of
his sons would ever believe anything because he said it, unless they
were themselves convinced of its truth--a feeling in striking contrast
with his own manner of faith" (_Life and Letters_, i. pp. 10, 11).
[17] _Ibid._, i. p. 38.
[18] _Life and Letters_, ii. p. 14.
[19] _Origin of Species_, pp. 117, 118.
[20] _Ibid._, p. 180.
[21] _Contemporary Review_, December, 1875, pp. 89, 93.
[22] _Variation of Animals and Plants under Domestication_, i. 292.
[23] _Variation of Animals and Plants under Domestication_, i. 299-301.
[24] To keep pace with this lateral increase in weight, the leg-bones
should have lengthened considerably so that their total deficiency in
proportional length is 17 per cent.,--a changed proportion which being
_linear_ is more excessive than the increase of weight by 28 per cent.
So marked is the effect of the combined thickening and shortening that
in the Aylesbury breed--which is the most typically representative
one--the leg-bones have become 70 per cent. heavier than they should be
if their thickness had continued to be proportional to their length.
[25] This excessive thickening under disuse appears to be due partly to
a positive lateral enlargement or increase of proportional weight of
about 7-1/2 per cent., and partly to a shortening of about 15 per cent.
Carefully calculated, the reduction of the weight of the wing-bones in
this breed is only 8·3 per cent. relatively to the whole skeleton, or
only 5 per cent. relatively to the skeleton _minus_ legs and wings. The
latter method is the more correct, since the excessive weight of the
leg-bones increases the weight of the skeleton more than the diminished
weight of the wing-bones reduces it.
[26] _Variation of Animals and Plants under Domestication_, i. 284.
[27] _Variation of Animals and Plants under Domestication_, i. 184, 185.
[28] _Ibid._, i. 144, 145.
[29] _Ibid._, i. 185.
[30] _Variation of Animals and Plants under Domestication_, i. 175.
[31] _Variation of Animals and Plants under Domestication_, i. 184. I
suspect that Darwin was in poor health when he wrote this page. He nods
at least four times in it. Twice he speaks of "twelve" breeds where he
obviously should have said eleven.
[32] If a prominent breast is admired and selected by fanciers, the
sternum might shorten in assuming a more forward and vertical position.
If the shortening of the sternum is entirely due to disuse, it seems
strange that Darwin has not noticed any similar shortening in the
sternum of the duck. But selection has not tended to make the duck
elegant, or "pigeon-breasted"; it has enlarged the abdominal sack
instead, besides allowing the addition of an extra rib in various cases.
[33] _Variation of Animals and Plants under Domestication_, 144, 175.
[34] _Variation of Animals and Plants under Domestication_, i. 179.
[35] In the six largest breeds the shortening of the sternum is nearly
twice as great as in the three smaller breeds which remain nearest the
rock-pigeon in size. We can hardly suppose that use-inheritance
especially affects the eight breeds that have varied most in size. If we
exclude these, there is only a total shortening of 7 per cent. to be
accounted for.
[36] _Variation of Animals and Plants under Domestication_, i. 183, 186.
[37] _Variation of Animals and Plants under Domestication_, i. 130, 135;
ii. 288.
[38] _Encyclopædia Britannica_, article "Zoology."
[39] _Variation of Animals and Plants under Domestication_, ii. 367.
[40] _Variation of Animals and Plants under Domestication_, ii. 367. Why
then does the cheetah inherit ancestral habits so inadequately that it
is useless for the chase unless it has first learned to hunt for itself
before being captured? (ii. 133).
[41] _Descent of Man_, p. 33.
[42] _Origin of Species_, pp. 210, 211.
[43] E. S. Delamer on _Pigeons and Rabbits_, pp. 132, 103. For other
points referred to, see pages 133, 102, 100, 95, 131.
[44] _Origin of Species_, pp. 188, 110; _Descent of Man_, pp. 32-35;
_Variation of Animals and Plants under Domestication_, ii. 289, 293. Use
or disuse during lifetime of course co-operates, and in some cases, as
in that of the canoe Indians, may be the principal or even perhaps the
_sole_ cause of the change.
[45] For the importance of panmixia as invalidating Darwin's strongest
evidence for use-inheritance--namely, that drawn from the effects of
disuse in highly-fed domestic animals where there is supposed to be no
economy of growth--see Professor Romanes on Panmixia, _Nature_, April 3,
1890.
[46] _Descent of Man_, p. 33.
[47] _Descent of Man_, p. 33.
[48] _Variation of Animals and Plants under Domestication_, i., 453.
[49] _Descent of Man_, p. 33.
[50] _Descent of Man_, p. 33.
[51] Wallace shows that the changes in our domestic animals, if spread
over the thousands of years since the animals were first tamed, must be
extremely insignificant in each generation, and he concludes that such
infinitesimal effects of use and disuse would be swallowed up by the far
greater effects of variation and selection (_Darwinism_, p. 436).
Professor Romanes has replied to him in the _Contemporary Review_
(August 1889), showing that this is no disproof of the existence of the
minor factor, inasmuch as slight changes in each generation need not
necessarily be matters of life and death to the individual, although
their cumulative development by use-inheritance might eventually become
of much service. But selection would favour spontaneous variations of a
similarly serviceable character. The slightest tendency to eliminate the
extreme variations in either direction would proportionally modify the
average in a breed. Use-inheritance appears to be so relatively weak a
factor that probably neither proof nor disproof of its existence can
ever be given, owing to the practical impossibility of disentangling its
effects (if any) from the effects of admittedly far more powerful
factors which often act in unsuspected ways. Thus wild ducklings, which
can easily be reared by themselves, invariably "die off" if reared with
tame ones (_Variation_, &c., i. 292, ii. 219). They cannot get their
fair share in the competition for food, and are completely eliminated.
Professor Romanes fully acknowledges that there is the "gravest possible
doubt" as to the transmission of the effects of disuse (Letter on
Panmixia, _Nature_, March 13, 1890).
[52] _Variation of Animals and Plants under Domestication_, ii. 287-289.
[53] _Descent of Man_, pp. 612, 131.
INHERITED INJURIES.
INHERITED MUTILATIONS.
The almost universal _non-inheritance_ of mutilations seems to me a far
more valid argument _against_ a general law of modification-inheritance
than the few doubtful or abnormal cases of such inheritance can furnish
in its favour. No inherited effect has been produced by the docking of
horses' tails for many generations, or by a well-known mutilation which
has been practised by the Hebrew race from time immemorial. As lost or
mutilated parts are reproduced in offspring independently of the
existence of those parts in the parent, there is the less reason to
suppose that the particular condition of parental parts transmits
itself, or tends to transmit itself, to the offspring. So unsatisfactory
is the argument derivable from inherited mutilations that Mr. Spencer
does not mention them at all, and Darwin has to attribute them to a
special cause which is independent of any general theory of
use-inheritance.[54]
Darwin's most striking case--and to my mind the only case of any
importance--is that of Brown-Séquard's epileptic guinea-pigs, which
inherited the mutilated condition of parents who had gnawed off their
own gangrenous toes when anæsthetic through the sciatic nerve having
been divided.[55] Darwin also mentions a cow that lost a horn by
accident, followed by suppuration, and subsequently produced three
calves which had on the same side of the head, instead of a horn, a bony
lump attached merely to the skin. Such cases may seem to prove that
mutilation _associated with morbid action_ is occasionally inherited or
repeated with a promptitude and thoroughness that contrast most
strikingly with the imperceptible nature of the immediate inheritance of
the effects of use and disuse; but they by no means prove that
mutilation in general is inheritable, and they are absolutely no proof
whatever of a _normal_ and non-pathological tendency to the inheritance
of acquired characters. Those who accept Darwin's special explanation
of the supposed inheritance of mutilations, ought to notice that his
explanation applies equally well under a theory which is strongly
adverse to use-inheritance--namely, Galton's idea of the sterilization
and complete "using up" of otherwise reproductive matter in the growth
and maintenance of the personal structure.
Darwin's explanation of inherited mutilations--which, as he notes, occur
"especially or perhaps exclusively" when the injury has been followed by
disease[56]--is that all the representative gemmules which would develop
or repair or reproduce the injured part are attracted to the diseased
surface during the reparative process and are there destroyed by the
morbid action.[57] Hence they cannot reproduce the part in offspring.
This explanation by no means implies that mutilation would _usually_
affect the offspring. On the contrary, in all ordinary cases of
mutilation the purely atavistic elements or gemmules would be set free
from any modifying influence of the non-existent or mutilated part. The
gemmules--as in Galton's theory of heredity and with neuter
insects--might be perfectly independent of pangenesis and the normal
inheritance of acquired characters. Such self-multiplying gemmules
without pangenesis would enable us to understand both the excessive
weakness or non-existence of normal use-inheritance, and the excessive
strength and abruptness of the effect of their partial destruction under
special pathological conditions.
The series of epileptic phenomena that can be excited by tickling a
certain part of the cheek and neck of the adult guinea-pig during the
growth and rejoining of the ends of the severed nerve, are said to be
repeated with striking accuracy of detail in the young who inherit
mutilated toes; but as epilepsy is often due to some _one_ exciting
cause or morbid condition, the single transmission of a highly morbid
condition of the system might easily reproduce the whole chain of
consequences and might also have caused the loss of toes.
The particulars of the guinea-pig cases are very inadequately
recorded,[58] but the results are so anomalous[59] that Brown-Séquard's
own conclusion is that the epilepsy and the inherited injuries are
_not_ directly transmitted, but that "what is transmitted is the morbid
state of the nervous system." He thinks that the missing toes may
"possibly" be exceptions to this conclusion, "but the other facts only
imply the transmission of a morbid state of the sympathetic or sciatic
nerve or of a part of the medulla oblongata." Until we can tell what is
transmitted, we are not in a position to determine whether there is any
true inheritance or only an exaggerated simulation of it under peculiar
circumstances. When the actual observers believe that the mutilations
and epilepsy are not the cause of their own repetition, and when these
observers guard themselves by such phrases as, "if any conclusion can at
present be drawn from those facts," we who have only incomplete reports
to guide us may well be excused if we preserve an even more pronounced
attitude of caution and reserve.[60] The morbid state of the system may
be wholly due to general injury of the germs rather than to specific
inheritance.
Weismann suggests that the morbid condition of the nervous system may be
due to some infection such as might arise from microbes, which find a
home in the mutilated and disordered nervous system in the parent, and
subsequently transmit themselves to the offspring through the
reproductive elements, as the infections of various diseases appear to
do--the muscardine silkworm disease in particular being known to be
conveyed to offspring in this manner.
But whether we can discover the true explanation or not, inherited
mutilations can hardly be accounted for as the result of a general
tendency to inherit acquired modifications. How could a factor which
seems to be totally inoperative in cases of ordinary mutilation, and
only infinitesimally operative in transmitting the normal effects of use
and disuse, suddenly become so powerful as to completely overthrow
atavism, and its own tendency to transmit the non-mutilated type of one
of the parents and of the non-mutilated type presented by the injured
parent in earlier life? Does not so striking and abrupt an
intensification of its usually insignificant power demand an explanation
widely different from that which might account for the extremely slow
and slight inheritance of the normal effects of use and disuse? Surely
it would be better to suspend one's judgment as to the true explanation
of highly exceptional and purely pathological cases rather than resort
to an hypothesis that creates more difficulties than it solves.
THE MOTMOT'S TAIL.
The narrowing of the long central tail feathers of the motmot is
attributed to the inherited effects of habitual mutilation (_Descent of
Man_, pp. 384, 603). But in the specimens at South Kensington[61] the
narrowness extends upwards much beyond the habitually denuded part, and
the broadened end is the broadest part of the whole feather. If the
inherited effect of an inch or two of denudation extends from three to
six inches upwards, why has it not also extended two inches downwards so
as to narrow the broadened end? The narrowness seems to be a mainly
relative or negative effect produced by the broadening out of a long
tapering feather at its end under the influence of sexual selection.
Several other birds have similarly narrowed or spoon-shaped feathers and
do not bite them. Is it not more feasible to suppose that this
attractive peculiarity first suggested its artificial intensification,
than to suppose that the bird began nibbling without any definite cause?
Sexual selection would then encourage the habit. Anyhow, it is as
impossible to show that the mutilation preceded the narrowing as it is
to show that tonsure preceded baldness.
OTHER INHERITED INJURIES MENTIONED BY DARWIN.
Darwin quotes some cases from Dr. Prosper Lucas's "long" but weak and
unsatisfactory "list of inherited injuries."[62] But Lucas was somewhat
credulous. One of his cases is that many girls were born in London
without mammæ through the injurious effect of certain corsets on the
mothers. He also gives a long account of a Jew who could read through
the thick covers of a book, and whose son inherited this "hyperæsthesia"
of the sense of sight in a still more remarkable degree (i. 113-119).
Evidently Lucas's cases cannot be accepted without some amount of
reserve.
The cases of the three calves which inherited the one-horned condition
of the cow, the two sons who inherited a father's crooked finger, and
the two sons who were microphthalmic on the same side as their father
had lost an eye, may be due to mere coincidence; or an inherited
constitutional tendency or liability might lead to somewhat similar
results in parent and offspring[63]--just as the tendency to certain
fatal diseases or to suicide may produce similar results in father and
son, although the artificially-produced hanging or apoplexy obviously
cannot be directly transmitted. That more than one of the offspring was
affected does not render the chances against coincidence "almost
infinitely great," as Darwin mistakenly supposes. It "frequently occurs"
that a man's sons or daughters may _all_ exhibit either a latent or a
newly-developed congenital peculiarity previously unknown;[64] and the
coincidence may merely be that one of the parents accidentally suffered
a similar kind of injury--a kind of coincidence which must of course
occasionally occur, and which may have been partly caused by a latent
tendency. The chances against coincidence are indeed great, but the
cases appear to be correspondingly rare.
Darwin acknowledges that many supposed instances of inherited mutilation
may be due to coincidence; and there is apparently no more reason for
attributing inherited scars, &c., to any special form of heredity than
to the effect of the mother's imagination on the unborn babe--a popular
but fallacious belief in corroboration of which far more alleged
instances could be collected than of the inheritance of injuries.
As an instance of the coincidences that occur, I may mention that a
friend of mine has a daughter who was born with a small hole in one ear,
just as if it were already pierced for the earring which she has since
worn in it. I suppose, however, that no one will venture to claim this
as an instance of the inheritance of a mutilation practised by female
ancestors, especially as such holes are not altogether unknown or
inexplicable, though very rarely occurring low down in the lobe of the
ear.[65]
Many cases are known of the inheritance of mutilations or malformations
arising congenitally from some abrupt variation in the reproductive
elements. In such cases as the one-eared rabbits, the two-legged pigs,
the three-legged dogs, the one-horned stags, hornless bulls, earless
rabbits, lop-eared rabbits, tailless dogs, &c., if the father or the
mother or the embryo had suffered from some accident or disease which
might plausibly have been assigned as the cause of the original
malformation, these transmitted defects would readily be cited as
instances of the inheritance of an accidentally-produced modification.
The inheritance of exostoses on horses' legs may be the inheritance of a
constitutional tendency rather than of the effect of the parents' hard
travelling. Horses congenitally liable to such formations would transmit
the liability,[66] and this might readily be mistaken for inheritance of
the results of the liability. An apparent increase in this liability
might arise from greater attention being now paid to it, or from
increased use of harder roads; or a real increase might be due to
panmixia and some obscure forms of correlation.
QUASI-INHERITANCE.
Of course artificially-caused ill-health or weakness in parents will
tend in a general way to injure the offspring. But deterioration thus
caused is only a form of quasi-inheritance, as I should prefer to call
it. Semi-starvation in a new-born babe is _not_ truly inherited from its
half-starved mother, but is the direct result of insufficient
nourishment. The general welfare of germs--as of parasites--is
necessarily bound up with that of the organism which feeds and shelters
them, but this is not heredity, and is quite irrelevant to the question
whether particular modifications are transmitted or not.
Another form of quasi-inheritance is seen in the communication of
certain infections to offspring. Not being transmitted by the action of
the organism so much as in defiance of it, such diseases are not truly
hereditary, though for convenience' sake they are usually so described.
A perversion or prevention of true inheritance is also seen in the
action of alcohol, or excessive overwork, or any other cause which by
originating morbid conditions in individuals may also injure the
reproductive elements.
These forms of quasi-inheritance are, of course, highly important so far
as the improvement of the race is concerned. So, too, is the fact that
improved or deteriorated habits and thoughts are transmitted by personal
teaching and influence and are cumulative in their effect. But all this
must not be confounded with the inheritance of acquired characters.
Cases of quasi-inheritance may perhaps be most readily distinguished
from cases of true inheritance by the time test. When a modification
acquired in adult life is promptly communicated to the child in early
life or from birth, it may rightly be suspected that the inheritance,
like that of money or title, is not truly congenital, but is extraneous
or even anti-congenital in its nature. Judged by such a standard, the
inherited injuries in Brown-Séquard's guinea-pigs are only exceptional
cases of quasi-inheritance, and are not necessarily indicative of any
general rule affecting true inheritance.
FOOTNOTES:
[54] A very able anatomist of my acquaintance denies the inheritance of
mutilations and injuries, although he strongly believes in the
inheritance of the effects of use and disuse.
[55] _Variation of Animals and Plants under Domestication_, i. 467-469.
Lost toes were only seen by Dr. Dupuy in three young out of two hundred.
Obersteiner found that most of the offspring of his epileptic
guinea-pigs were injuriously affected, being weakly, small, paralysed in
one or more limbs, and so forth. Only two were epileptic, and both were
weakly and died early (Weismann's _Essays_, p. 311). A morbid condition
of the spinal cord might affect the hind limbs especially (as in
paraplegia) and might occasionally cause loss of toes in the embryo by
preventing development or by ulceration. Brown-Séquard does not say that
the defective feet were on the same side as in the parents (_Lancet_,
Jan., 1875, pp. 7, 8).
[56] _Variation of Animals and Plants under Domestication_, ii. 57.
[57] _Ibid._, ii. 392. Perhaps it might be better to suppose that the
_best_ gemmules were sacrificed in repairing the injured _nerve_, and
hence only inferior substitutes were left to take their place, and could
only imperfectly reproduce the injured part of the nervous system in
offspring.
[58] Hence perhaps Mr. Spencer's error in representing the epileptic
liability as permanent and as coming on _after_ healing (_Factors of
Organic Evolution_, p. 27).
[59] It is not claimed that the imperfect foot was on the same side of
the body as in the parent, and where parents had lost _all_ the toes of
a foot, or the whole foot, the few offspring affected usually had lost
only two toes out of the three, or only a part of one or two or three
toes. Sometimes the offspring had toes missing on _both_ hind feet,
although the parent was only affected in _one_. _One_ diseased ear and
eye in the parent was "generally" or "always" succeeded by _two_ equally
affected ears and eyes in the offspring (cf. _Pop. Science Monthly_, New
York, xi. 334). The important law of inheritance at corresponding
periods was also set aside. Gangrene or inflammation commenced in both
ears and both eyes soon after birth (pointing possibly to infection of
some kind); the epileptic period commenced "perhaps two months or more
after birth," while the loss of toes had occurred before birth. In no
case, as Weismann points out, is the original mutilation of the nervous
system ever transmitted. Even where an extirpated ganglion was never
regenerated in the parent, the offspring always regained the part in an
apparently perfect condition. On the whole the conflicting results ought
to be as puzzling to those who may attribute them to a universal
tendency to inherit the exact condition of parents as they are to those
who, like myself, are sceptical as to the existence of such a law or
tendency.
[60] The various results need to be fully and impartially recorded, and
they should also be well tested and confirmed in proportion as they
appear improbable and contrary to general experience. Professor Romanes
has been carrying out the necessary experiments for some time past.
[61] Natural History Museum, central hall, third recess on the left.
[62] _Traité de l'Hérédité_, ii. 489; _Variation of Animals and Plants
under Domestication_, i. 469. If injuries are inherited, why has the
repeated rupture of the hymen produced no inherited effect?
[63] Compare the three cases of crooked fingers given in _Variation of
Animals and Plants under Domestication_, ii. 55, 240.
[64] _Ibid._, i. 460. Thus, where two brothers married two sisters all
the seven children were perfect albinos, although none of the parents or
their relatives were albinos. In another case the nine children of two
sound parents were all born blind (ii. 322).
[65] See pp. 179-182, _Evolution and Disease_, by J. Bland Sutton, to
whom and to our mutual friend Dr. D. Thurston I am indebted for
information on various points.
[66] _Variation of Animals and Plants under Domestication_, ii. 290; i.
454.
MISCELLANEOUS CONSIDERATIONS.
TRUE RELATION OF PARENTS AND OFFSPRING.
It is difficult to entirely free ourselves from the flattering and
almost universal idea that parents are true originators or creators of
copies of themselves. But the main truth, if not the whole truth, is
that they are merely the transmitters of types of which they and their
offspring are alike more or less similarly moulded resultants. A parent
is a trustee. He transmits, not himself and his own modifications, but
the stock, the type, the representative elements, of which he is a
product and a custodian in one. It seems probable that he has no more
definite or "particulate" influence over the reproductive elements
within him than a mother over the embryo or a vessel over its cargo.
Parent and offspring are like successive copies of books printed from
the same "type." A battered letter in the "type" will display its
effects in both earlier and later copies alike, but a purely extraneous
or acquired flaw in the first copy is not necessarily repeated in
subsequent copies. Unlike printer's type, however, the material source
of heredity is of a fluctuating nature, consisting of competing elements
derived from two parents and from innumerable ancestors.
Galton compares parent and child to successive pendants on the same
chain. Weismann likens them to successive offshoots thrown up by a long
underground root or sucker. Such comparisons indicate the improbability
of acquired modifications being transmitted to offspring.
That parts are developed in offspring independently of those parts in
parents is clear. Mutilated parents transmit parts which they do not
possess. The offspring of young parents cannot inherit the later stages
of life from parents who have not passed through them. Cases of remote
reversion or atavism show that ancestral peculiarities can transmit
themselves in a latent or undeveloped condition for hundreds or
thousands of generations. Many obvious facts compelled Darwin to suppose
that vast numbers of the reproductive gemmules in an individual are not
thrown off by his own cells, but are the self-multiplying progeny of
ancestral gemmules. Galton restricts the production of gemmules by the
personal structure to a few exceptional cases, and would evidently like
to dispense with pangenesis altogether, if he could only be sure that
acquired characters are never inherited. Weismann entirely rejects
pangenesis and the inheritance of acquired characters. This enables him
to explain heredity by his theory of the "Continuity of the
Germ-plasm."[67] Parent and offspring are alike successive products or
offshoots of this persistent germ-substance, which obviously would not
be correspondingly affected by modifications of parts in parents, and so
would render the transmission of acquired characters impossible.
INVERSE INHERITANCE.
Mr. Galton contends that the reproductive elements become sterile when
used in forming and maintaining the individual, and that only a small
proportion of them are so used.[68] He holds that the next generation
will be formed entirely, or almost entirely, from the residue of
undeveloped germs, which, not having been employed in the structure and
work of the individual, have been free to multiply and form the
reproductive elements whence future individuals are derived. Hence the
singular inferiority not infrequently displayed by the children of men
of extraordinary genius, especially where the ancestry has been only of
a mediocre ability. The valuable germs have been used up in the
individual, and rendered sterile in the structure of his person. Hence,
too, the "strong tendency to deterioration in the transmission of every
exceptionally gifted race." Mr. Galton's hypothesis "explains the fact
of certain diseases skipping one or more generations," and it "agrees
singularly well with many classes of fact;" and it is strongly opposed
to the theory of use-inheritance. The elements which are used die almost
universally without germ progeny: the germs which are _not_ used are the
great source of posterity. Hence, when the germs or gemmules which
achieve development are either better or worse than the residue, the
qualities transmitted to offspring will be of an inverse character. If
brain-work attracts, develops _and sterilizes_ the best gemmules, the
ultimate effect of education on the intellect of posterity may differ
from its immediate effect.
EARLY ORIGIN OF THE OVA.
As the ova are formed at as early a period as the rest of the maternal
structure, Galton notices that it seems improbable that they would be
correspondingly affected by subsequent modifications of parental
structure. Of course it is not certain that this is a valid argument. We
know that the paternal half of the reproductive elements does not enter
the ovum till a comparatively late stage in its history, and it is quite
possible that maternal elements or gemmules may also enter the ovum from
without. If reproductive elements were confined to one special part or
organ, we should be unable to explain the reproduction of lost limbs in
salamanders, and the persistent effect of intercrossing on subsequent
issue by the same mother, and the propagation of plants from shoots, or
of the begonia from minute fragments of leaves, or the development of
small pieces of water-worms into complete animals.
MARKED EFFECTS OF USE AND DISUSE ON THE INDIVIDUAL.
These are, to some extent, an argument against the cumulative
inheritance of such effects. When a nerve atrophies from disuse, or a
duct shrivels, or bone is absorbed, or a muscle becomes small or flabby,
it proves, so far, that the average effect of use through enormous ages
is _not_ transmitted. When the fibula of a dog's leg thickens by 400 per
cent. to a size "equal to or greater than" that of the removed tibia
which previously did the work,[69] it shows that in spite of disuse for
countless generations, the "almost filiform" bone has retained a
potentiality of development which is fully equal to that possessed by
the larger one which has been constantly used. When, after being reared
on the ailanthus, the caterpillars of the _Bombyx hesperus_ die of
hunger rather than return to their natural food, the inherited effect of
ancestral habit does not seem to be particularly strong. Neither is
there any strongly-inherited effect of long-continued ancestral wildness
in many animals which are easily tamed.
WOULD NATURAL SELECTION FAVOUR USE-INHERITANCE?
If use-inheritance is really one of the factors of evolution, it is
certainly a subordinate one, and an utterly helpless one, whenever it
comes into conflict with the great ruling principle of Selection. Would
this dominant cause of evolution have favoured a tendency to
use-inheritance if such had appeared, or would it have discouraged and
destroyed it? We have already seen that use-inheritance is unnecessary,
since natural selection will be far more effective in bringing about
advantageous modifications; and if it can be shown that use-inheritance
would often be an evil, it then becomes probable that on the whole
natural selection would more strongly discourage and eliminate it as a
hostile factor than it might occasionally favour such a tendency as a
totally unnecessary aid.
USE-INHERITANCE AN EVIL.
Use-inheritance would crudely and indiscriminately proportion parts to
actual work done--or rather to the varying _nourishment and growth_
resulting from a multiplicity of causes--and this in its various details
would often conflict most seriously with the real necessities of the
case, such as occasional passive strength, or appropriate shape,
lightness and general adaptation. If its accumulated effects were not
corrected by natural or sexual selection, horns and antlers would
disappear in favour of enlarged hoofs. The elephant's tusks would become
smaller than its teeth. Men would have callosities for sitting on, like
certain monkeys, and huge corns or hoofs for walking on. Bones would
often be modified disastrously. Thus the condyle of the human jaw would
become larger than the body of the jaw, because as the fulcrum of the
lever it receives more pressure. Some organs (like the heart, which is
always at work) would become inconveniently or unnecessarily large.
Other absolutely indispensable organs, which are comparatively passive
or are very seldom used, would dwindle until their weakness caused the
ruin of the individual or the extinction of the species. In eliminating
various evil results of use-inheritance, natural selection would be
eliminating use-inheritance itself. The displacement of Lamarck's theory
by Darwin's shows that the effects of use-inheritance often differ from
those required by natural selection; and it is clear that the latter
factor must at least have reduced use-inheritance to the very minor
position of comparative feebleness and harmlessness assigned to it by
Darwin.
Use-inheritance would be ruinous through causing unequal variation in
co-operative parts--of which Mr. Spencer may accept his own instances of
the jaws and teeth, and the cave-crab's lost eyes and persistent
eye-stalks, as typical examples. That the variation would be unequal
seems almost self-evident from the varying rapidity and extent of the
effects of use and disuse on different tissues and on different parts of
the general structure. The optic nerve may atrophy in a few months from
disuse consequent on the loss of the eye. Some of the bones of the
rudimentary hind legs of the whale are still in existence after disuse
for an enormous period. Evidently use-inheritance could not equally
modify the turtle and its shell, or the brain and its skull; and in
minor matters there would be the same incongruity of effect. Thus, if
the molar teeth lengthened from extra use the incisors could not meet.
Unequal and indiscriminate variation would throw the machinery of the
organism out of gear in innumerable ways.
Use-inheritance would perpetuate various evils. We are taught, for
instance, that it perpetuates short-sight, inferior senses, epilepsy,
insanity, nervous disorders, and so forth. It would apparently transmit
the evil effects of over-exertion, disuse, hardship, exposure, disease
and accident, as well as the defects of age or immaturity.
Would it not be better on the whole if each individual took a fresh
start as far as possible on the advantageous typical lines laid down by
natural selection? Through the long stages of evolution from primæval
protoplasm upwards, such species as were least affected by
use-inheritance would be most free to develop necessary but seldom-used
organs, protective coverings such as shells or skulls, and natural
weapons, defences, ornaments, special adaptations, and so forth; and
this would be an advantage--for survival would obviously depend on the
_importance_ of a structure or faculty in deciding the struggle for
existence and reproduction, and not on the total amount of its using or
nourishment. If natural selection had on the whole favoured this
officious ally and frequent enemy, surely we should find better evidence
of its existence.
Without laying undue stress upon the evil effects of use-inheritance, a
careful examination of them in detail may at least serve to
counter-balance the optimistic _a priori_ arguments for belief in that
plausible but unproven factor of evolution.
The benefits derivable from use-inheritance are largely illusory. The
effects of _use_, indeed, are generally beneficial up to a certain
point; for natural selection has sanctioned or evolved organs which
possess the property or potentiality of developing to the right extent
under the stimulus of use or nourishment. But use-_inheritance_ would
cumulatively alter this individual adaptability, and would tend to fix
the size of organs by the average amount of ancestral use or disuse
rather than by the actual requirements of the individual. Of course
under changed conditions involving increased or lessened use of parts it
might become advantageous; but even here it may prove a decided
hindrance to adaptive evolution in some respects as well as an
unnecessary aid in others. Thus in the case of animals becoming heavier,
or walking more, it would _lengthen_ the legs although natural selection
might require them to be shortened. In the Aylesbury duck and the Call
duck, if use-inheritance has increased the dimensions of the bones and
tendons of the leg, natural selection has had to counteract this
increase so far as length is concerned, and to effect 8 per cent. of
shortening besides. If use-inheritance thickens bones without
proportionally lengthening them, it would hinder rather than help the
evolution of such structures as the long light wings of birds, or the
long legs and neck of the giraffe or crane.
VARIED EFFECTS OF USE AND DISUSE.
The changes which we somewhat roughly and empirically group together as
the effects of "use and disuse" are of widely diverse character. Thus
bone, as the physiological fact, thickens under _alternations_ of
pressure (and the consequent increased flow of nourishment), but
atrophies under a steadily continued pressure; so that if the use of a
bone involved continuous pressure, the effect of such use would be a
partial or total absorption of that bone. Darwin shows that bone
lengthens as well as thickens from carrying a greater weight, while
tension (as seen in sailors' arms, which are used in pulling) appears to
have an equally marked effect in shortening bones (_Descent of Man_, p.
32). Thus different kinds of use may produce opposite results. The
cumulative inheritance of such effects would often be mischievous. The
limbs of the sloth and the prehensile tail of the spider monkey would
continually grow shorter, while the legs of the evolving elephant or
rhinoceros might lengthen to an undesirable extent. Such cumulative
tendencies of use-inheritance, if they exist, are obviously well kept
under by natural selection.
Although the ultimate effect of use is generally growth or enlargement
through increased flow of blood, the first effect usually is a loss of
substance, and a consequent diminution of size and strength. When the
loss exceeds the growth, use will diminish or deteriorate the part used,
while disuse would enlarge or perfect it. Teeth, claws, nails, skin,
hair, hoofs, feathers, &c., may thus be worn away faster than they can
renew themselves. But this wearing away usually stimulates the repairing
process, and so increases the rate of growth; that is, it will increase
the size produced, if not the size retained. Which effect of use does
use-inheritance transmit in such cases--the increased rate of growth, or
the dilapidation of the worn-out parts? We can hardly suppose that both
these effects of use will be inherited. Would shaving destroy the beard
in time or strengthen it? Will the continued shearing of sheep increase
or lessen the growth of wool? What will be the ultimate effect of
plucking geese's quills, and of the eider duck's abstraction of the down
from her breast? If the mutilated parts grow stronger or more
abundantly, why were the motmot's feathers alleged to be narrowed by the
inherited effects of ancestral nibbling?
The "use" or "work" or "function" of muscles, nerves, bones, teeth,
skin, tendon, glands, ducts, eyes, blood corpuscles, cilia, and the
other constituents of the organism, is as widely different as the
various parts are from each other, and the effects of their use or
disuse are equally varied and complicated.
USE-INHERITANCE IMPLIES PANGENESIS.
How could the transmission of these varied effects to offspring be
accounted for? Is it possible to believe, with Mr. Spencer, that the
effects of use and disuse on the parts of the personal structure are
simultaneously registered in corresponding impressions on the seminal
germs? Must we not feel, with Darwin apparently,[70] that the _only_
intelligible explanation of use-inheritance is the hypothesis of
Pangenesis, according to which each modified cell, or physiological
unit, throws off similarly-modified gemmules or parts of itself, which
ultimately reproduce the change in offspring? If we reject pangenesis,
it becomes difficult to see how use-inheritance can be possible.
PANGENESIS IMPROBABLE.
The more important and best-known phenomena of heredity do not require
any such hypothesis, and leading facts (such as atavism, transmission of
lost parts, and the general non-transmission of acquired characters) are
so adverse to it that Darwin has to concede that many of the
reproductive gemmules are atavistic, and that by continuous
self-multiplication they may preserve a practical "continuity of
germ-substance," as Weismann would term it. The idea that the
relationship of offspring to parent is one of direct descent is, as
Galton tells us, "wholly untenable"; and the only reason he admits some
supplementary traces of pangenesis into his "Theory of Heredity,"[71] is
that he may thus account for the more or less questionable cases of the
transmission of acquired characters. But there appears to be no
necessity even for this concession. We ought therefore to dispense with
the useless and gratuitous hypothesis that cells multiply by throwing
off minute self-multiplying gemmules, as well as by the well-known
method of self-division. If pangenesis occurs, the transmission of
acquired characters ought to be a prominent fact. The size, strength,
health and other good or evil qualities of the cells could hardly fail
to exercise a marked and corresponding effect upon the size and quality
of the reproductive gemmules thrown off by those cells. The direct
evidence tends to show that these free gemmules do not exist.
Transfusion of blood has failed to affect inheritance in the slightest
degree. Pangenesis, with its attraction of gemmules from all parts of
the body into the germ-cells, and the free circulation of gemmules in
the offspring till they hit upon or are attracted by the particular cell
or cells, with which alone they can readily unite, seems a less feasible
theory and less in conformity with the whole of the facts than an
hypothesis of germ-continuity which supposes that the development of the
germ-plasm and of the successive self-dividing cells of the body
proceeds from within. Darwin's keen analogy of the fertilization of
plants by pollen renders development from without conceivable, but as
there are no insects to convey gemmules to their destination, each kind
of gemmule would have to be exceedingly numerous and easily attracted
from amongst an inconceivable number of other gemmules. Arguments
against pangenesis can also be drawn from the case of neuter insects--a
fact which seems to have escaped Darwin's notice, although he had seen
how strongly that case was opposed to the doctrine which is the
essential basis of the theory of pangenesis.
SPENCER'S EXPLANATION OF USE-INHERITANCE.
Mr. Spencer's explanation of the inheritance of the effects of use and
disuse (p. 36) is that "while generating a modified _consensus_ of
functions and of structures, the activities are at the same time
impressing this modified _consensus_ on the sperm-cells and germ-cells
whence future individuals are to be produced"--a proposition which reads
more like metaphysics than science. Difficult to understand or believe
in ordinary instances, such _consensus_-inheritance seems impossible in
cases like that of the hive-bee. Can we suppose that the _consensus_ of
the activities of the working bee impresses itself on the sperm-cells
of the drones and on the germ-cells of the carefully secluded queen?
Büchner thinks so, for he says: "Although the queens and drones do not
now work, yet the capacities inherited from earlier times still remain
to them, especially to the former, and are kept alive and fresh by the
impressions constantly made upon them during life, and they are thus in
a position to transmit them to posterity." Surely it is better to
abandon a cherished theory than to be compelled to defend it by
explanations which are as inconsistent as they are inadequate. New
capacities are developed as well as old ones kept fresh. The massacre or
expulsion of the drones would have to impress itself on the germ-cells
of an onlooking queen, and the imprisonment of the queen on the
sperm-cells of the drones--and in such a way, moreover, as to be
afterwards developed into action in the neuters only. And
use-inheritance all the while is being thoroughly overpowered by
impression-inheritance--by the full transmission of that which is merely
seen in others! If such a law prevails, one may feel cold because an
ancestor thought of the frosty Caucasus. None of this absurdity would
arise if it were clearly seen that a parent is only a trustee--that
transmission and development are perfectly distinct--that parental
modifications are irrelevant to those transmitted to offspring.
FOOTNOTES:
[67] _Essays on Heredity_, p. 104. Weismann's theory is clear, simple
and convenient, but incomplete; for, unlike Darwin's theory of
pangenesis, it scarcely attempts any real explanation of the extremely
complex potentialities possessed by the reproductive elements. Perhaps
we might retain Darwin's self-multiplying gemmules without supposing
them to be thrown off by the cells, which will no longer be credited
with _two_ modes of multiplication. These minute germs or gemmules may
have been evolved by natural selection playing upon the sample germs
that achieve development; and they may exist either separately, or
(preferably but perhaps not invariably) in aggregates to form Weismann's
germ-plasm.
[68] _Contemporary Review_, Dec., 1875, p. 88.
[69] _Variation of Animals and Plants under Domestication_, ii. 286.
[70] _Variation of Animals and Plants under Domestication_, ii. 388,
398, 367; _Life and Letters_, iii. 44.
[71] _Contemporary Review_, Dec., 1875, pp. 94, 95.
CONCLUSIONS.
USE-INHERITANCE DISCREDITED AS UNNECESSARY, UNPROVEN, AND IMPROBABLE.
General experience teaches that acquired characters are not usually
inherited; and investigation shows that the apparent exceptions to this
great rule are probably fallacious. Even the alleged instances of
use-inheritance culled by such great and judicious selectors as Darwin
and Spencer break down upon examination; for they can be better
explained without use-inheritance than with it. On the other hand, the
adverse facts and considerations are almost strong enough to prove the
actual non-existence of such a law or tendency. There is no need to
undertake the apparently impossible task of demonstrating an absolute
negative. It will be enough to ask that the Lamarckian factor of
use-inheritance shall be removed from the category of accredited factors
of evolution to that of unnecessary and improbable hypotheses. The main
explanation or source of the fallacy may be found in the fact that
natural selection frequently imitates some of the more obvious effects
of use and disuse.
MODERN RELIANCE ON USE-INHERITANCE MISPLACED.
Modern philanthropy--so far at least as it ever studies ultimate
results--constantly relies on this ill-founded belief as its
justification for ignoring the warnings of those who point out the
ultimately disastrous results of a systematic defiance or reversal of
the great law of natural selection. This reliance finds strong support
in Mr. Spencer's latest teachings, for he holds that the inheritance of
the effects of use and disuse takes place universally, and that it is
now "the chief factor" in the evolution of civilized man (pp. 35, 74,
iv)--natural selection being quite inadequate for the work of
progressive modification. Practically he abandons the hope of evolution
by natural selection, and substitutes the ideal of a nation being
"modified _en masse_ by transmission of the effects" of its institutions
and habits. Use-inheritance will "mould its members far more rapidly and
comprehensively" than can be effected by the survival of the fittest
alone.
But could we rely upon the aid of use-inheritance if it really were a
universal law and not a mere simulation of one? Let us consider some of
the features of this alleged factor of evolution, seeing that it is
henceforth to be our principal means of securing the improvement of our
species and our continued adaptation to the changing conditions of a
progressive civilization.
It is curiously uncertain and irregular in its action. It diminishes or
abolishes some structures (such as jaws or eyes) without correspondingly
diminishing or abolishing other equally disused and closely related
parts (such as teeth, or eye-stalks). It thickens ducks' leg-bones while
allowing them to shorten. It shortens the disused wing-bones of ducks
and the leg-bones of rabbits while allowing them to thicken; and yet in
other cases it greatly reduces the thickness of bones without shortening
them. It transmits tameness most powerfully in an animal which usually
cannot acquire it. It aids in webbing the feet of water-dogs, but fails
to web the feet of the water-hen or to remove the web in the feet of
upland geese.[72] It allows the disused fibula to retain a potentiality
of development fully equal to that possessed by the long-used tibia. It
lengthens legs because they are used in supporting the body, and
shortens arms because they are used in pulling. Whether it enlarges
brain if used in one way and diminishes it if used in another, we cannot
tell; but it must obviously deaden nervous sensibilities in some cases
and intensify them in others. It enlarges hands long before they are
used, and thickens soles long before the time for walking on them. At
the same time, as if by an oversight, it so delays its transmission of
the habit of walking on these thickened soles, that the gradual and
tedious acquisition of the non-transmitted habit costs the infant much
time and trouble and often some pain and danger. Yet where aided by
natural selection, as with chickens and foals, it transmits the habit in
wonderful perfection and at a remarkably early date. It transmits new
paces in horses in a single generation, but fails to perpetuate the
songs of birds. It modifies offspring like parents, and yet allows the
formation of two reproductive types in plants, and of two or more types
widely different from the parents in some of the higher insects. It is
said to be indispensable for the co-ordinated development of man and the
giraffe and the elk, but appears to be unnecessary for the evolution and
the maintenance of wonderful structures and habits and instincts in a
thousand species of ants and bees and termites. It is the only possible
means of complex evolution and adaptation of co-operative parts, and yet
in Mr. Spencer's most representative case it renders such important
parts as teeth and jaws unsuited for each other, and is said to ruin the
teeth by the consequent overcrowding and decay. It survives amidst a
general "lack of recognised evidence," and only seems to act usefully
and healthily and regularly in quarters where it can least easily be
distinguished from other more powerful and demonstrable factors of
evolution. So little does it care to display its powers where they would
be easily verifiable as well as useful that practical breeders ignore
it. So slight is its independent power that it seems to allow natural
selection or sexual selection or artificial selection to modify
organisms in sheer defiance of its utmost opposition, just as readily as
they modify organisms in other directions with its utmost help. If it
partially perpetuates and extends the pecked-out indentations in the
motmot's tail feathers, it on the other hand fails to transmit the
slightest trace of mutilation in an almost infinite number of ordinary
cases, and even where the mutilation is repeated for a hundred
generations; and it apparently repairs rather than transmits the
ordinary and oft-repeated losses caused by plucking hair, down and
feathers, and the wear and tear of claws, teeth, hoofs and skin.
It is often mischievous as well as anomalous in its action. Under
civilization with its division of labour, the various functions of mind
and body are very unequally exercised. There is overwork or misuse of
one part and disuse and neglect of others, leading to the partial
breakdown or degeneration of various organs and to general deterioration
of health through disturbed balance of the constitution. The brain, or
rather particular parts of it, are often over-stimulated, while the body
is neglected. In many ways education and civilization foster nervousness
and weakness, and undermine the rude natural health and spirits of the
human animal. Alcohol, tobacco, tea, coffee, extra brain work, late
hours, dissipation, overwork, indoor life, division of labour,
preservation of the weak, and many other causes, all help to injure the
modern constitution; so that the prospect of cumulative intensification
of these evils by the additional influence of use-inheritance is not an
encouraging one. It is true that modern progress and prosperity are
improving the people in various respects by their direct action; but if
use-inheritance has any share in effecting this improvement it must also
transmit increased wants and more luxurious habits, together with such
evils as have already been referred to. As depicted by its defenders,
use-inheritance transmits evils far more powerfully and promptly than
benefits. It transmits insanity and shattered nerves rather than the
healthy brain which preceded the breakdown. It perpetuates, and
cumulatively intensifies, a deterioration in the senses of civilized
men, but it fails to perpetuate the rank vigour of various plants when
too well nourished, or the flourishing condition of various animals when
too fat or when tamed. It already transmits the short-sight caused by so
modern an art as watchmaking, but so fails to transmit the
long-practised art of seeing (as it does of walking and talking) that
vision is worse than useless to a man until he gradually acquires the
necessary but non-transmitted associations of sensation and idea by his
own experience. In a well-known case, a blind man on gaining his sight
by an operation said that "all objects seemed to touch his eyes, as what
he felt did his skin"--so little had the universal experience of
countless ages impressed itself on his faculties. Under normal healthy
conditions use-inheritance is so slow in its action that "several
generations" must elapse before it produces any appreciable effect, and
then that effect is only precisely what selection might be expected to
bring about without its aid. Strong for evil and slow for good, it can
convey epilepsy promptly in guinea pigs, but transmits the acquirements
of genius so poorly that our best student of the heredity of genius has
to account for the frequent and remarkable deterioration of the
offspring by a theory which is strongly hostile to use-inheritance. It
would tend to make organisms unworkable by the excessive differences in
its rate and manner of action on co-operative parts, and by adapting
these parts to the total amount of nourishment received rather than to
occasional necessity or actual usefulness. It would tend to stereotype
habits and convert reason into instinct.
How then can we rely upon use-inheritance for the improvement of the
race? Even if it is not a sheer delusion, it may be more detrimental as
a positive evil than it is advantageous as an unnecessary benefit; and
as a normal modifying agent it is miserably weak and untrustworthy in
comparison with the powerful selective influences by which nature and
society continually and inevitably affect the species for good or for
evil. The effects of use and disuse--rightly directed by education in
its widest sense--must of course be called in to secure the highly
essential but nevertheless _superficial, limited, and partly deceptive_
improvement of individuals and of social manners and methods; but as
this artificial development of already existing potentialities does not
directly or readily tend to become congenital, it is evident that some
considerable amount of natural or artificial selection of the more
favourably varying individuals will still be the only means of securing
the race against the constant tendency to degeneration which would
ultimately swallow up all the advantages of civilization. The selective
influences by which our present high level has been reached and
maintained may well be modified, but they must not be abandoned or
reversed in the rash expectation that State education, or State feeding
of children, or State housing of the poor, or any amount of State
socialism or public or private philanthropy, will prove permanently
satisfactory substitutes. If ruinous deterioration and other more
immediate evils, are to be avoided, the race must still be to the swift
and the battle to the strong. The healthy Individualism so earnestly
championed by Mr. Spencer must be allowed free play. Open competition,
as Darwin teaches, with its survival and multiplication of the fittest,
must be allowed to decide the battle of life independently of a foolish
benevolence that prefers the elaborate cultivation and multiplication of
weeds to the growth of corn and roses. We are trustees for the countless
generations of the future. If we are wise we shall trust to the great
ruling truths that we assuredly know, rather than to the seductive
claims of an alleged factor of evolution for which no satisfactory
evidence can be produced.
THE END.
RICHARD CLAY AND SONS, LIMITED, LONDON AND BUNGAY.
FOOTNOTES:
[72] Professor Romanes had casts made of the feet of upland geese, and
could not detect any diminution as compared with the web of other geese
in relation to the toes.
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