[Illustration: HEX CURASSOW FEEDING YOUNG BIRD, WITH PLUMAGE OF THE
GLOBOSE CURASSOW]
THE MAKING
OF SPECIES
BY DOUGLAS DEWAR, B.A. (Cantab), I.C.S., F.Z.S.
AND FRANK FINN, B.A. (Oxon), F.Z.S., M.B.O.U.
WITH FIFTEEN ILLUSTRATIONS
LONDON: JOHN LANE THE BODLEY HEAD
NEW YORK: JOHN LANE COMPANY MCMIX
_Turnbull & Spears, Printers, Edinburgh_
PREFACE
Post-Darwinian books on evolution fall naturally into four classes. I.
Those which preach Wallaceism, as, for example, Wallace’s _Darwinism_,
Poulton’s _Essays on Evolution_, and the voluminous works of Weismann.
II. Those advocating Lamarckism. Cope’s _Factors of Evolution_ and the
writings of Haeckel belong to this class. III. The writings of De Vries,
forming a group by themselves. They advocate the theory that species
spring suddenly into being; that new species arise by mutations from
pre-existing species. IV. The large number of books of a more judicial
nature, books written by men who decline to subscribe to any of the above
three creeds. Excellent examples of such works are Kellog’s _Darwinism
To-Day_, Lock’s _Recent Progress in the Study of Variation, Heredity, and
Evolution_, and T. H. Morgan’s _Evolution and Adaptation_.
All four classes are characterised by defects.
Books of the two first classes exhibit the faults of ardent partisanship.
They formulate creeds, and, as Huxley truly remarked, “Science commits
suicide when it adopts a creed.” The books which come under the third
category have the defects of extreme youth. De Vries has discovered a new
principle, and it is but natural that he should exaggerate its
importance, and see in it more than it contains. But, as time wears on,
these faults will disappear, and the theory of mutations will assume its
true form and fall into its proper place, which is somewhere between the
dustbin, to which Wallaceians would relegate it, and the exalted pinnacle
on to which De Vries would elevate it.
In the present state of our knowledge, books of Class IV. are the most
useful to the student, since they are unbiassed, and contain a judicial
summing-up of the evidence for and against the various evolutionary
theories which now occupy the field. Their chief defect is that they are
almost entirely destructive. They shatter the faith of the reader, but
offer nothing in place of that which they have destroyed. T. H. Morgan’s
_Evolution and Adaptation_, however, contains much constructive matter,
and so is the most valuable work of this class in existence.
Zoological science stands in urgent need of constructive books on
evolution—books with leanings towards neither Wallaceism, nor Lamarckism,
nor De Vriesism; books which shall set forth facts of all kinds,
concealing none, not even those which do not admit of explanation in the
present state of our knowledge.—It has been our aim to produce a book of
this description.
We have endeavoured to demonstrate that neither pure Lamarckism nor pure
Wallaceism affords a satisfactory explanation of the various phenomena of
the organic world. We have further, while recognising the very great
value of the work of De Vries, tried to show that that eminent botanist
has allowed his enthusiasm to carry him a little too far into the realm
of speculation. We have followed up the exposure of the weak points of
the theories, which at present occupy the field, with certain
suggestions, which, we believe, throw new light on many biological
problems.
Our aim in writing this book has been twofold. In the first place we have
attempted to place before the general public in simple language a true
statement of the present position of biological science. In the second
place, we have endeavoured to furnish the scientific men of the day with
food for reflection.
Even as the British nation seems to be slowly but surely losing, through
its conservatism, the commercial supremacy it had the good fortune to
gain last century, so is it losing, through the unwillingness of many of
our scientific men to keep abreast of the times, that scientific
supremacy which we gained in the middle of last century by the labours of
Charles Darwin and Alfred Russell Wallace. To-day it is not among
Englishmen, but among Americans and Continentals, that we have to look
for advanced scientific ideas.
Even as the Ultra-Cobdenites believe that Free Trade is a panacea for all
economic ills, so do most English men of science believe that natural
selection offers the key to every zoological problem. Both are living in
a fool’s paradise. Another reason why Great Britain is losing her
scientific supremacy is that too little attention is paid to bionomics,
or the study of live animals. Morphology, or the science of dead
organisms, receives more than its due share of attention. It is in the
open, not in the museum or the dissecting-room, that nature can best be
studied. Far be it from us to deprecate the study of morphology. We wish
merely to insist upon the fact, that the leaders of biological science
must of necessity be those naturalists who go to the tropics and other
parts of the earth where nature can be studied under the most favourable
conditions, and those who conduct scientific breeding experiments.
Natural selection—the idea which has revolutionised modern biological
science—came, not to professors, but to a couple of field-naturalists who
were pursuing their researches in tropical countries. It is absurd to
expect those who stay at home and gain most of their knowledge
second-hand to be the pioneers of biological science.
We fear that this book will come as a rude shock to many scientific men.
By way of consolation we may remind such that they will find themselves
in much the same position as that occupied by theologians immediately
after the appearance of the _Origin of Species_.
At that time theological thought was cramped by dogma. But the clergy
have since reconsidered their position, they have modified their views,
and thus kept abreast of the times. Meanwhile scientific men have lagged
behind. The blight of dogma has seized hold of them. They have adopted a
creed to which all must subscribe or be condemned as heretics. Huxley
said that the adoption of a creed was tantamount to suicide. We are
endeavouring to save biology in England from committing suicide, to save
it from the hands of those into which it has fallen.
We would emphasise that it is not Darwinism we are attacking, but that
which is erroneously called Neo-Darwinism. Neo-Darwinism is a
pathological growth on Darwinism, which, we fear, can be removed only by
a surgical operation.
Darwin, himself, protested in vain against the length to which some of
his followers were pushing his theory. On p. 657 of the new edition of
the _Origin of Species_ he wrote: “As my conclusions have lately been
much misrepresented, and as it has been stated that I attribute the
modification of species exclusively to natural selection, I may be
permitted to remark that in the first edition of this work, and
subsequently, I placed in a most conspicuous position—namely, at the
close of the Introduction—the following words: ‘I am convinced that
natural selection has been the main but not the exclusive means of
modification.’ This has been of no avail. Great is the power of steady
misrepresentation; but the history of science shows that this power does
not long endure.”
Notwithstanding this protest the Wallaceians continue on their course,
and give to the world a spurious Darwinism. It is our belief that were
Darwin alive to-day his sympathies would be with us, and not with those
who call themselves his followers. It was one of Darwin’s strong points
that he never avoided facts. If new facts came to light which were
incompatible with a theory of his, he promptly modified his theory. Since
his death a number of new facts have come to light which, in our opinion,
plainly indicate that the theory of natural selection as enunciated by
Darwin needs considerable modification.
We have in this book set forth certain of these facts and indicated the
directions in which the Darwinian theory seems to require modification.
This volume originated as the result of several conversations we, the
joint authors, had last summer. We discovered that we had a great many
ideas in common on the subject of evolution. This seemed strange, seeing
that our education had not been on the same lines. One of us took a
degree in natural science at Cambridge, and subsequently entered His
Majesty’s Indian Civil Service, but continued his zoological studies in
India as a hobby. The other, a naturalist from childhood, nevertheless
took a classical degree at Oxford, then received a technical zoological
training, adopted zoology as a profession, and held for some years a
position in the Natural History Museum at Calcutta.
Our conversations revealed that we were both of opinion that biology is
in an unhealthy condition, especially in England, and that the science
sorely needs some fresh impetus. Neither of us had the time to attempt,
single-handed, to give the required impetus, but as one of us happened to
be home on eighteen months’ leave, we thought we might undertake the task
in collaboration.
We felt that we might collaborate the more successfully because the large
number of facts collected by the one of us form the necessary complement
to the philosophical studies of the other.
We have endeavoured, so far as possible, to avoid technical terms, and
have made a special point of quoting, wherever practicable, familiar
animals as examples, in order that the work may make its appeal not only
to the zoologist but to the general reader.
It may, perhaps, be urged against us that we have quoted too freely from
popular writings, including those of which we are the authors. Our reply
to this is that the study of bionomics, the science of living animals,
occupies so small a place in English scientific literature that we have
been compelled to have recourse to popular works for many of our facts;
and we would, moreover, point out that a popular work is not necessarily
inaccurate in its information.
In conclusion, we would warn the reader against the danger of confounding
Inference with Fact. The failure to distinguish between the two has
vitiated much of the work of the Wallaceian school of biologists.
Facts are always to be accepted. Inferences should be scrutinised with
the utmost care.
In making our deductions, we have endeavoured to act without bias. We
shall, therefore, welcome any new facts, be they consistent with, or
opposed to, our inferences.
D. D.
F. F.
CONTENTS
PAGE
CHAPTER I 1
Rise of the Theory of Natural Selection and its Subsequent Development
Pre-Darwinian Evolutionists—Causes which led to the speedy triumph
of the theory of Natural Selection—Nature of the opposition which
Darwin had to overcome—Post-Darwinian biology—Usually accepted
classification of present-day biologists as Neo-Lamarckians and
Neo-Darwinians is faulty—Biologists fall into three classes rather
than two—Neo-Lamarckism: its defects—Wallaceism: its
defects—Neo-Darwinism distinguished from Neo-Lamarckism and
Wallaceism—Neo-Darwinism realises the strength and weakness of the
theory of Natural Selection, recognises the complexity of the
problems which biologists are endeavouring to solve.
CHAPTER II 30
Some of the more Important Objections to the Theory of Natural Selection
Brief statement of Theory—Objections to the Theory fall into two
classes—Those which strike at the root of the Theory—Those which
deny the all-sufficiency of Natural Selection—Objections which
strike at root of Theory are based on misconception—Objections to
Wallaceism—The Theory fails to explain the origin of
Variations—Natural Selection called on to explain too much—Unable
to explain beginnings of new organs—The Theory of change of
function—The co-ordination of variations—The fertility of races of
domesticated animals—Missing links—Swamping effects of
intercrossing—Small variations cannot have a survival value—Races
inhabiting same area—Excessive specialisation—Chance and Natural
Selection—Struggle for existence most severe among young
animals—Natural Selection fails to explain mimicry and other
phenomena of colour—Conclusion, that scarcely an organism exists
which does not possess some feature inexplicable on the theory of
Natural Selection as held by Wallace and his followers.
CHAPTER III 52
Variation
The assumption of Darwin and Wallace that variations are haphazard
in origin and indefinite in direction—If these assumptions be not
correct Natural Selection ceases to be the fundamental factor in
evolution—Darwin’s views regarding variation underwent
modification—He eventually recognised the distinction between
definite and indefinite variations, and between continuous and
discontinuous variations—Darwin attached but little importance to
either definite or discontinuous variations—Darwin’s views on the
causes of variations—Criticism of Darwin’s views—Variations appear
to occur along certain definite lines—There seems to be a limit to
the extent to which fluctuating variations can be accumulated—De
Vries’ experiments—Bateson on “discontinuous variation”—Views held
by De Vries—Distinction between continuous and discontinuous
variations—The work of De Vries—Advantages enjoyed by the botanist
in experimenting on the making of species—Difficulties encountered
by the animal breeder—Mutations among animals—The distinction
between germinal and somatic variations—The latter, though not
transmitted to offspring, are often of considerable value to their
possessor in the struggle for existence.
CHAPTER IV 111
Hybridism
The alleged sterility of hybrids a stumbling-block to
evolutionists—Huxley’s views—Wallace on the sterility of
hybrids—Darwin on the same—Wallace’s theory that the infertility of
hybrids has been caused by Natural Selection so as to prevent the
evils of intercrossing—Crosses between distinct species not
necessarily infertile—Fertile crosses between species of
plants—Sterile plant hybrids—Fertile mammalian hybrids—Fertile bird
hybrids—Fertile hybrids among amphibia—Limits of
hybridisation—Multiple hybrids—Characters of hybrids—Hybridism does
not appear to have exercised much effect on the origin of new
species.
CHAPTER V 133
Inheritance
Phenomena which a complete theory of inheritance must explain—In
the present state of our knowledge it is not possible to formulate
a complete theory of inheritance—Different kinds of
inheritance—Mendel’s experiments and theory—The value and
importance of Mendelism has been exaggerated—Dominance sometimes
imperfect—Behaviour of the nucleus of the sexual
cell—Chromosomes—Experiments of Delage and Loeb—Those of Cuénot on
mice and Castle on guinea pigs—Suggested modification of the
generally-accepted Mendelian formulæ—Unit characters—Biological
isomerism—Biological molecules—Interpretation of the phenomena of
variation and heredity on the conception of biological
molecules—Correlation—Summary of the conception of biological
molecules.
CHAPTER VI 170
The Colouration of Organisms
The theory of protective colouration has been carried to absurd
lengths—It will not bear close scrutiny—Cryptic colouring—Sematic
colours—Pseudo-sematic colours—Batesian and Müllerian
mimicry—Conditions necessary for mimicry—Examples—Recognition
markings—The theory of obliterative colouration—Criticism of the
theory—Objections to the theory of cryptic colouring—Whiteness of
the Arctic fauna is exaggerated—Illustrative tables—Pelagic
organisms—Objectors to the Neo-Darwinian theories of colouration
are to be found among field naturalists—G. A. B. Dewar, Gadow,
Robinson, F. C. Selous quoted—Colours of birds’ eggs—Warning
colouration—Objections to the theory—Eisig’s theory—So-called
intimidating attitudes of animals—Mimicry—The case for the
theory—The case against the theory—“False mimicry”—Theory of
recognition colours—The theory refuted—Colours of flowers and
fruits—Neo-Darwinian explanations—Objections—Kay Robinson’s
theory—Conclusion that Neo-Darwinian theories are untenable—Some
suggestions regarding the colouration of animals—Through the
diversity of colouring of organisms something like order runs—The
connection between biological molecules and colour—Tylor on colour
patterns in animals—Bonhote’s theory of pœcilomeres—Summary of
conclusions arrived at.
CHAPTER VII 297
Sexual Dimorphism
Meaning of the term—Fatal to Wallaceism—Sexual Selection—The law of
battle—Female preference—Mutual Selection—Finn’s
experiments—Objections to the theory of Sexual Selection—Wallace’s
explanation of sexual dimorphism stated and shown to be
unsatisfactory—The explanation of Thomson and Geddes shown to be
inadequate—Stolzmann’s theory stated and criticised—Neo-Lamarckian
explanation of sexual dimorphism stated and criticised—Some
features of sexual dimorphism—Dissimilarity of the sexes probably
arises as a sudden mutation—The four kinds of mutations—Sexual
dimorphism having shown itself, Natural Selection determines
whether or not the organisms which display it shall survive.
CHAPTER VIII 345
The Factors of Evolution
Variation along definite lines and Natural Selection are undoubtedly
important factors of evolution—Whether or not sexual selection is a
factor we are not yet in a position to decide—_Modus operandi_ of
Natural Selection—Correlation an important factor—Examples of
correlation—Correlation is a subject that requires close
study—Isolation a factor in evolution—Discriminate
isolation—Indiscriminate isolation—Is the latter a factor?—Romanes’
views—Criticism of these—Indiscriminate isolation shown to be a
factor—Summary of the methods in which new species arise—Natural
Selection does not make species—It merely decides which of certain
ready-made forms shall survive—Natural Selection compared to a
competitive examination and to a medical board—We are yet in
darkness as to the fundamental causes of the Origin of Species—In
experiment and observation rather than speculation lies the hope of
discovering the nature of these causes.
Footnotes 389
Index 389
LIST OF ILLUSTRATIONS
FACING PAGE
Heck’s Curassow feeding Young Bird, which has the Plumage of the Hens
of the Globose Curassow, its Father’s Species _Frontispiece_
_By permission of the Avicultural Society._
A Turbit belonging to Mr H. P. Scatliff 92
_From “The Modern Turbit,” published by “The Feathered World,” London._
Yellow-Rumped and Chestnut-Breasted Finches, with Specimens in
Transitional State 98
On the left, the yellow-rumped finch; on the right, the
chestnut-breasted; birds in state of change in the middle.
_By permission of the Avicultural Society._
Male Amherst Pheasant 122
The chief colours of this species (_Chrysolophus amherstiæ_) are
white and metallic green, so that it is very different in
appearance from its near ally the gold pheasant.
Harlequin Quail (_Coturnix delegorguei_) 124
_By permission of the Avicultural Society._
Rain Quail (_Coturnix coromandelica_) 124
The markings on the throats of these quails are of the type usually
put down as “recognition marks,” but as the Harlequin Quail is
African and the Rain Quail Indian, the two species cannot possibly
interbreed. The pattern, then, can have no “recognition”
significance.
_By permission of the Avicultural Society._
Bouru Friar-Bird 222
Like most of the group to which it belongs, this honey-eater
(_Tropidorhynchus bouruensis_) is a soberly coloured bird, but is
noisy, active, and aggressive.
_By permission of Messrs Hutchinson & Co._
Bouru Oriole 222
This “mimicking” oriole (_Oriolus bouruensis_) is of the same tone
of colour as its supposed model the Friar-bird of the same island.
_By permission of Messrs Hutchinson & Co._
King-Crow or Drongo 232
This very conspicuous black bird (_Dicrurus ater_), ranging from
Africa to China, is a striking feature of the landscape wherever it
occurs.
_By permission of Messrs Hutchinson & Co._
Drongo-Cuckoo 232
The fork of the tail in this bird is unique among cuckoos, but is
nevertheless much less developed than in the supposed model, and
may be an adaptation for evolutions in flight, as such tails
usually appear to be.
_By permission of Messrs Hutchinson & Co._
Shikra Hawk 236
The upper surface of the tail, not shown in this drawing, exactly
corresponds with that of the cuckoo “mimic.”
_By permission of Messrs Hutchinson & Co._
Hawk-Cuckoo 236
This species (_Hierococcyx varius_) is commonly known in India as
the “Brain-fever bird.”
_By permission of Messrs Hutchinson & Co._
Brazilian Troupial 284
This species (_Icterus vulgaris_) is that most frequently seen in
captivity; the pattern of colour is found in several other allied
forms.
_By permission of Messrs Hutchinson & Co._
Indian Black-Headed Oriole 284
Several other orioles besides this (_O. melanocephalus_) have the
black head.
_By permission of Messrs Hutchinson & Co._
Queen Whydah 298
This species (_Tetraenura regia_) is a typical example of seasonal
sexual dimorphism, the male being long-tailed and conspicuously
coloured only during the breeding season, and at other times
resembling the sparrow-like female.
_By permission of the Foreign Bird Club._
Courtship of Skylark 314
Illustrating display by a species with no decorative colouring or
sex difference.
THE MAKING OF SPECIES
CHAPTER I
RISE OF THE THEORY OF NATURAL SELECTION AND ITS SUBSEQUENT DEVELOPMENT
Pre-Darwinian Evolutionists—Causes which led to the speedy triumph of
the theory of Natural Selection—Nature of the opposition which Darwin
had to overcome—Post-Darwinian biology—Usually accepted classification
of present-day biologists as Neo-Lamarckians and Neo-Darwinians is
faulty—Biologists fall into three classes rather than
two—Neo-Lamarckism: its defects—Wallaceism: its defects—Neo-Darwinism
distinguished from Neo-Lamarckism and Wallaceism—Neo-Darwinism realises
the strength and weakness of the theory of Natural Selection,
recognises the complexity of the problems which biologists are
endeavouring to solve.
Darwinism and evolution are not interchangeable terms. On this fact it is
impossible to lay too much emphasis. Charles Darwin was not the
originator of the theory of evolution, nor even the first to advocate it
in modern times. The idea that all existing things have been produced by
natural causes from some primordial material is as old as Aristotle. It
was lost sight of in the mental stagnation of the Middle Ages. In that
dark period zoological science was completely submerged. It was not until
men shook off the mental lethargy that had held them for many generations
that serious attention was paid to biology. From the moment when men
began to apply scientific methods to that branch of knowledge the idea of
evolution found supporters.
Buffon suggested that species are not fixed, but may be gradually changed
by natural causes into different species.
Goethe was a thorough-going evolutionist; he asserted that all animals
were probably descended from a common original type.
Lamarck was the first evolutionist who sought to show the means whereby
evolution has been effected. He tried to prove that the efforts of
animals are the causes of variation; that these efforts originate changes
in form during the life of the individual which are transmitted to its
offspring.
St Hilaire was another evolutionist who endeavoured to explain how
evolution had occurred. He believed that the transformations of animals
are effected by changes in their environment. These hypotheses were
considered, and rightly considered, insufficient to explain anything like
general evolution, so that the idea failed for a time to make headway.
Strength of Darwin’s Position
As knowledge grew, as facts accumulated, the belief in evolution became
more widespread. Hutton, Lyell, Spencer, and Huxley were all convinced
that evolution had occurred, but they could not explain how it had
occurred.
Thus, by the middle of last century, all that was needed to make
evolution an article of scientific belief was the discovery of a method
whereby it could be effected. This Darwin and Wallace were able to
furnish in the shape of the theory of natural selection. The discovery
was made independently, but Darwin being the older man, the more
influential, and the one who had gone the more deeply and carefully into
the matter, gained the lion’s share of the credit of the discovery. The
theory of natural selection is universally known as the Darwinian theory,
notwithstanding the fact that Darwin, unlike Wallace, always recognised
that natural selection is not the sole determining factor in organic
evolution.
From the moment of the enunciation of his great hypothesis, Darwin’s
position was an exceedingly strong one. Everything was in his favour.
As we have seen, the theory was enunciated at the psychological moment,
at the time when zoological science was ripe for it. Most of the leading
zoologists were evolutionists at heart, and were only too ready to accept
any theory which afforded a plausible explanation of what they believed
to have occurred.
Hence the rapturous welcome accorded to the theory of natural selection
by the more progressive biologists.
Another point in Darwin’s favour was the delightful simplicity of his
hypothesis. Nothing could be more enticingly probable. It is based on the
unassailable facts of variation, heredity, and the tendency of animals to
multiply in numbers. Everybody knows that the breeder can fix varieties
by careful breeding. Darwin had simply to show that there is in nature
something to take the part played among domesticated animals by the human
breeder. This he was able to do. As the numbers of species remain
stationary, it is evident that only a small portion of the animals that
are born can reach maturity. A child can see that the individuals most
likely to survive are those best adapted to the circumstances of their
life. Even as the breeder weeds out of his stock the creatures not suited
to his purpose, so in nature do the unfit perish in the everlasting
struggle for existence.
In nature there is a selection corresponding to that of the breeder.
It is useless to deny the existence of this selection in nature, this
natural selection. The only disputable point is whether such selection
can do all that Darwin demanded of it.
The man in the street, then, was able to comprehend the theory of natural
selection. This was greatly in its favour. Men are usually well disposed
towards doctrines which they can readily understand.
The nineteenth century was a superficial age. It liked simplicity in all
things. If Darwin could show that natural selection was capable of
producing one species, men were not only ready but eager to believe that
it could explain the whole of organic evolution.
The simplicity of the Darwinian theory has its evil side. It has
undoubtedly tended to make modern biologists superficial in their
methods. It has, indeed, stimulated the imagination of men of science;
but the stimulation has not in all cases been a healthy one.
So far from adhering to the sound rule laid down by Pasteur, “never
advance anything that cannot be proved in a simple and decisive manner,”
many modern naturalists allow their imagination to run riot, and so
formulate ill-considered theories, and build up hypotheses on the most
insecure foundations. “A tiny islet of truth,” writes Archdale Reid, “is
discovered, on which are built tremendous and totally illegitimate
hypotheses.”
Another source of Darwin’s strength was the vast store of knowledge he
had accumulated. For twenty years he had been steadily amassing facts in
support of his hypothesis. He enunciated no crude theory, he indulged in
no wild speculations. He was content to marshal a great array of facts,
and to draw logical conclusions therefrom. He was as cautious in his
deductions as he was careful of his facts. He thus stood head and
shoulders above the biologists of his day. He was a giant among pigmies.
So well equipped was he that those who attempted to oppose him found
themselves in the position of men, armed with bows and arrows, who seek
to storm a fortress defended by maxim guns.
Nor was this all. The majority of the best biologists of his time did not
attempt to oppose him. They were, as we have seen, ready to receive with
open arms any hypothesis which seemed to explain how evolution had
occurred. Some of them perceived that there were weak points in the
Darwinian theory, but they preferred not to expose these; they were
rather disposed to make the best of the hypothesis. It had so many merits
that it seemed to them but reasonable to suppose that subsequent
investigation would prove that the defects were apparent rather than
real.
Opponents of Darwin
We hear much of the “magnitude of the prejudices” which Darwin had to
overcome, and of the mighty battle which Darwin and his lieutenant Huxley
had to fight before the theory of the origin of species by natural
selection obtained acceptance. We venture to say that statements such as
these are misleading. We think we may safely assert that scarcely ever
has a theory which fundamentally changed the prevailing scientific
beliefs met with less opposition. It would have been a good thing for
zoology had Darwin not obtained so easy a victory.
Sir Richard Owen, a distinguished anatomist, certainly attacked the
doctrine in no unmeasured terms, but his attack was anonymous and so
cannot be considered very formidable. Far more important was the
opposition of Dr St George Mivart, whose worth as a biologist has never
been properly appreciated. His most important work, entitled the _Genesis
of Species_, might be read with profit even now by many of our modern
Darwinians.
For some time after the publication of the _Origin of Species_ Mivart
appears to be almost the only man of science fully alive to the weak
points of the Darwinian theory. The great majority seem to have been
dazzled by its brilliancy.
The main attack on Darwinism was conducted by the theologians and their
allies, who considered it to be subversive of the Mosaic account of the
Creation. Now, when one whose scientific knowledge is, to say the best of
it, not extensive, attacks a man who has studied his subject
dispassionately for years, and invariably expresses himself with extreme
caution, the onslaught can have but one result—the attacker will be
repulsed with heavy loss, and the onlookers will have a higher opinion of
his valour than of his common sense.
The theologians were in the unfortunate position of warriors who do not
know what it is against which they are fighting; they confounded natural
selection with evolution, and directed the main force of their attack
against the latter, under the impression that they were fighting the
Darwinian theory.
It was the misfortune of those theologians that it is possible to prove
that evolution, or, at any rate, some evolution has occurred; they thus
kicked against the pricks with disastrous results to themselves. When
this attack had been repulsed men believed that the theory of natural
selection had been demonstrated, that it was as much a law of nature as
that of gravitation. What had really happened was that the fact of
evolution had been proved, and the theory of natural selection obtained
the credit. Men thought that Darwinism was evolution. Had the theologians
admitted evolution but denied the ability of natural selection to explain
it, the Darwinian theory, in all probability, would not have gained the
ascendency which it now enjoys.
Evolution and Natural Selection
To us who are able to look back dispassionately upon the biological
warfare of the last century, Darwin’s opponents—or the majority of
them—appear very foolish. We must, however, bear in mind that at the time
of the publication of the _Origin of Species_ both natural selection and
evolution were comparatively unknown ideas. Darwin had to fight for both.
He had to prove evolution as well as natural selection. Many of the facts
adduced by him supported both. It is, therefore, not altogether
surprising that many of his opponents failed to distinguish between them.
A glance at the _Origin of Species_ will suffice to show how considerable
is the portion of the book that deals with the evidence in favour of
evolution rather than of natural selection.
Of the fourteen chapters which make up the book no fewer than nine are
devoted to proving that evolution has occurred. It has been truly said,
that for every one fact biologists have found in support of the special
theory of natural selection they have found ten facts supporting the
doctrine of evolution. Darwin, then, was in the position of a skilled
barrister who has a plausible case and who knows the ins and outs of his
brief, while his opponents stood in the shoes of inexperienced counsel
who had but recently received their brief, and who had not had the time
to master the details thereof. In such circumstances it is not difficult
to predict which way the verdict of the jury will go.
Darwin, moreover, had a charming personality. Never was a man with a
theory less dogmatic. Never was the holder of a theory more careful of
the expressions he used. Never was a scientific man more ready to give
ear to his opponents, to meet them half way, and, where necessary, to
compromise. Darwin was not afraid of facts, and was always ready to alter
his views when they appeared to be opposed to facts. The average
scientific man of to-day makes facts fit his theory; if they refuse to
fit it he ignores or denies them.
Darwin continually modified his views; when he found himself in a tight
place he did not hesitate to resort to Lamarckian factors, such as the
inheritance of the effects of use and disuse and of the effects of
environment. He conceded that natural selection was insufficient to
account for all the phenomena of organic evolution, and advanced the
theory of sexual selection in order to account for facts which the major
hypothesis seemed to him incapable of explaining.
Darwin, moreover, having ample private means, was not obliged to work for
a living, and was therefore able to devote the whole of his time to
research. The advantages of such a position cannot be over-estimated,
and, perhaps, have not been sufficiently taken into account in
apportioning the praise between Darwin and Wallace for their great
discovery.
Huxley
To all these factors in Darwin’s favour we must add his good fortune in
possessing so able a lieutenant as Huxley.
Huxley was an ardent evolutionist, an able writer, and a brilliant
debater. A man of his mental calibre was able, like a clever barrister,
to make out a plausible case for any theory which he chose to take up.
While nominally a strong supporter of the Darwinian theory, he was in
reality fighting for the doctrine of descent. Had _any_ plausible theory
of evolution been enunciated, Huxley would undoubtedly have fought for it
equally earnestly.
A firm believer in evolution, Huxley was, as Professor Poulton says,
confronted by two difficulties,—first, the insufficiency of the evidence
of evolution, and, secondly, the absence of any explanation of how the
phenomenon had occurred. The _Origin of Species_ solved both these
difficulties. It adduced much weighty evidence in favour of evolution,
and suggested a _modus operandi_. Small wonder, then, that Huxley became
a champion of Darwinism. But, as Poulton writes, on page 202 of _Essays
on Evolution_, “while natural selection thus enabled Huxley freely to
accept evolution, he was by no means fully satisfied with it.” “He never
committed himself to a full belief in natural selection, and even
contemplated the possibility of its ultimate disappearance.” To use
Huxley’s own words: “Whether the particular shape which the doctrine of
evolution, as applied to the organic world, took in Darwin’s hands, would
prove to be final or not, was, to me, a matter of indifference.”
The result of the fortuitous combination of the circumstances which we
have set forth was that in a surprisingly short time the theory of
natural selection came to be regarded as a law of nature on a par with
the laws of gravitation. Thus, paradoxical though it seems, practical
certainty was given to a hitherto uncertain doctrine by the addition of a
still more uncertain theory.
“At once,” writes Waggett, “the theory of development leapt from the
position of an obscure guess to that of a fully-equipped theory and
almost a certainty.”
Darwin thus became a dictator whose authority none durst question. A
crowd of slavish adherents gathered round him, a herd of men to whom he
seemed an absolutely unquestionable authority. Darwinism became a creed
to which all must subscribe. It still retains this position in the
popular mind.
Growing Opposition to Darwinism
The ease with which the theory of natural selection gained supremacy was,
as we have already said, a misfortune to biological science. It produced
for a time a considerable mental stagnation among zoologists. Since
Darwin’s day the science has not made the progress that might reasonably
have been expected, because the theory has so captivated the minds of the
majority of biologists that they see everything through Darwinian
spectacles. The wish has been in many cases the father to the
observation. Zoologists are ever on the lookout for the action of natural
selection, and in consequence frequently imagine they see it where it
does not exist. Many naturalists, consciously or unconsciously, stretch
facts to make them fit the Darwinian theory. Those facts which refuse to
be so distorted are, if not actively ignored or suppressed, overlooked as
throwing no light upon the doctrine. This is no exaggeration. A perusal
of almost any popular book dealing with zoological theory leaves the
impression that there is nothing left to be explained in the living
world, that there is no door leading to the secret chambers of nature to
which natural selection is not an “open sesame.”
But the triumph of natural selection has not been so complete as its more
enthusiastic supporters would have us believe. Some there are who have
never admitted the all-sufficiency of natural selection. In the British
Isles these have never been numerous. In the United States of America and
on the Continent they are more abundant. The tendency seems to be for
them to increase in numbers. Hence the recent lamentations of Dr Wallace
and Sir E. Ray Lankester. Modern biologists are commonly supposed to fall
into two schools of thought—the Neo-Darwinian and the Neo-Lamarckian.
The former are the larger body, and pin their faith absolutely to natural
selection. They deny the inheritance of acquired characters, and preach
the all-sufficiency of natural selection to explain the varied phenomena
of nature. The Neo-Lamarckians do not admit the omnipotency of natural
selection. Some of them allow it no virtue. Others regard it as a force
which keeps variation within fixed limits, which says to each organism,
“thus far shalt thou vary and no farther.” This school lays great stress
on the inheritance of acquired characters, especially on the inheritance
of the effects of use and disuse.
The above statement of the recent developments of Darwinism is
incomplete, for it fails to include those who occupy a middle position.
If it be possible to classify a large number of men of which scarcely any
two hold identical views, it is into three, rather than two, classes that
they must be divided.
Speaking broadly, evolutionists of to-day may be said to represent three
distinct lines of thought. For the sake of classification we may speak of
them as falling into three schools, which we may term the Neo-Lamarckian,
the Wallaceian, and the Neo-Darwinian, according as their views incline
towards those held by Lamarck, Wallace, or Darwin.
The Neo-Lamarckian School
As adherents of the Neo-Lamarckian school, we cite Cope, Spencer, Orr,
Eimer, Naegeli, Henslow, Cunningham, Haeckel, Korchinsky, and a number of
others. It may almost be said of these Neo-Lamarckians that each holds a
totally distinct theory of evolution. So heterogeneous are their views
that it is difficult to find a single article common to the evolutionary
belief of all. It is commonly asserted that all Neo-Lamarckians are
agreed, firstly, that acquired characters are transmissible; and,
secondly, that such transmission is an important factor in the production
of new species. This assertion is certainly true of the great bulk of
Neo-Lamarckians, but it does not appear to hold in the case of those who
believe that evolution is the result of some unknown inner force. So far
as we can see, a belief in the inheritance of acquired characters is not
necessary to the theories of orthogenesis held by Naegeli and Korchinsky.
For that reason it would possibly be more correct to place those who hold
such views in a fourth school. Since, however, a number of undoubted
Neo-Lamarckians, as, for example, Cope, believe in an inner growth-force,
it is convenient to regard Naegeli as a Neo-Lamarckian. His views need
not detain us long. Those who wish to study them in detail will find them
in his _Mechanisch-physiologische Theorie der Abstammungslehre_.
Naegeli believes that there is inherent in protoplasm a growth-force,
which makes each organism in itself a force making towards progressive
evolution. He holds that animals and plants would have become much as
they are now even if no struggle for existence had taken place. “To the
believers in this kind of . . . orthogenesis,” writes Kellog (_Darwinism
To-day_, p. 278), “organic evolution has been, and is now, ruled by
unknown inner forces inherent in organisms, and has been independent of
the influence of the outer world. The lines of evolution are immanent,
unchangeable, and ever slowly stretch toward some ideal goal.” It is easy
to enunciate such a theory, impossible to prove it, and difficult to
disprove it.
It seems to us that the fact that, so soon as organisms are removed from
the struggle for existence, they tend to degenerate, is a sufficient
reason for refusing to accept theories of the description put forth by
Naegeli. More truly Lamarckian is Eimer’s theory of orthogenesis,
according to which it is the environment which determines the direction
which variation takes; and the variations which are induced by the
environment are transmitted to the offspring.
Orr’s Views
Spencer and Orr preach nearly pure Lamarckism. The former, while fully
recognising the importance of natural selection, considered that
sufficient weight has not been given to the effects of use and disuse, or
to the direct action of the environment in determining or modifying
organisms.
The similarity of the views of Orr and Lamarck is best seen by comparing
their respective explanations of the long neck of the giraffe. Lamarck
thought that this was the direct result of continual stretching. The
animal continually strains its neck in the search for food, hence it
grows longer as the individual grows older, and this elongated neck has
been transmitted to the offspring. Orr writes, on page 164 of his
_Development and Heredity_: “The giraffe seems to present the most
remarkable illustration of the lengthening of the bones as the result of
the frequent repetition of such shocks. As is well known, this animal
feeds on the foliage of trees. From the earliest youth of the species,
and the earliest youth of each individual, it must have been stretching
upwards for food, and, as is the custom of such quadrupeds, it must have
constantly raised itself off its forefeet, and, as it dropped, must have
received a shock that made itself felt from the hoofs through the legs
and vertical neck to the head. In the hind legs the shock would not be
felt. It is impossible to imagine that an animal which, during the
greater part of every day of its life (both its individual and racial
life), performed motions so uniform and constant, would not be peculiarly
specialised as a result. The forces acting upon such an animal are widely
different from the forces acting upon an animal which eats the grass at
its feet like an ox, or one which must run and climb like a goat or a
deer, and the resultant modifications of growth in the several cases must
also be different. The principle of increased growth in the direction of
the shock, resulting from superabundant repair of the momentary
compression, explains how the giraffe acquired the phenomenal length of
the bones of its forelegs and neck; and the absence of the shock in the
hind-quarters shows why they remained undeveloped and absurdly
disproportionate to the rest of the body.”
Inheritance of Acquired Characters
It seems to us that a fatal objection to all these Neo-Lamarckian
theories of evolution is that they are based on the assumption that
acquired characters are inherited, whereas all the evidence goes to show
that such characters are not inherited. In these days, when scientific
knowledge is so widely diffused, it is scarcely necessary to say that all
the characteristics which an organism displays are either congenital or
inborn, or acquired by the organism during its lifetime. Thus a man may
have naturally a large biceps muscle, and this is a congenital character;
or he may by constant exercise develop or greatly increase the size of
the biceps. The large biceps, in so far as it has been increased by
exercise, is said to be an acquired character, for it was not inherited
by its possessor, but acquired by him in his lifetime. We must bear in
mind that the period in the life history of an organism at which a
character appears, is not necessarily a test as to whether it is
congenital or acquired, for a great many congenital characters, such as a
man’s beard, do not appear until some years after birth. As we have seen,
the Neo-Lamarckians believe that it is possible for an organism to
transmit to its offspring characters which it has acquired during the
course of its existence. But, as we have already said, the evidence goes
to show that such characters are not inherited. For example, the tail of
the young fox-terrier is not shorter than that of other breeds of dogs,
notwithstanding the fact that its ancestors have for generations had the
greater portion of their caudal appendage removed shortly after birth.
We do not propose to discuss at any great length the vexed question of
the inheritance of acquired characters, for the simple reason that the
Neo-Lamarckians have not brought forward a single instance which
indubitably proves that such characters are inherited.
Mr J. T. Cunningham, in a paper of great value and interest, entitled
“The Heredity of Secondary Sexual Characters in relation to Hormones: a
Theory of the Heredity of Somatogenic Characters,” which appeared in vol.
xxvi., No. 3, of the _Archiv für Entwicklungsmechanik des Organismen_,
states: “The dogma that acquired characters cannot be inherited . . . is
founded not so much on evidence, or the absence of evidence, as on _a
priori_ reasoning, on the supposed difficulty or impossibility of
conceiving a means by which such inheritance could be effected.” Such
appears certainly to be true of some zoologists, but we trust that Mr
Cunningham will do us the justice to believe that our opinion that the
inheritance of acquired characters does not play an important part in the
evolution of, at any rate, the higher animals, is based, not on the
ground of _a priori_ reasoning, but on facts. All the evidence seems to
show that such characteristics are not inherited. If, as Mr Cunningham
thinks, all secondary sexual characters are due to the inheritance of the
effects of use, etc., how is it that no Neo-Lamarckian is able to bring
forward a clear case of the inheritance of a well-defined acquired
character? If such characteristics are habitually inherited, countless
examples should be forthcoming. Fanciers in their endeavours are
constantly “doctoring” the animals they keep for show purposes; and it
seems to us certain that if acquired characters are inherited, breeders
would long ago have discovered this and acted upon the discovery. If
Neo-Darwinians are charged with refusing to believe that acquired
characters are inherited because they “cannot conceive the means by which
it could be effected,” may it not be said with equal justice that many
Neo-Lamarckians believe that acquired characters are inherited, not on
evidence thereof, but because if such characters are not inherited it is
very difficult to account for many of the phenomena presented by the
organic world?
In many of the lower animals, as, for example, the hydra, the germinal
material is diffused through the organism, so that a complete individual
can be developed from a small portion of the creature. In such
circumstances it seems not improbable that the external environment may
act directly on the germinal substance, and induce changes in it which
may perhaps be transmitted to the offspring. If this be so, it would seem
that some acquired characters may be inherited in such organisms. Very
many plants can be propagated from cuttings, buds, etc., so that we might
reasonably expect some acquired characters to be hereditary in them. The
majority of botanists appear to hold Lamarckian views; but on the
evidence at present available, it is doubtful whether such views are the
correct ones.
Plants are so plastic, so protean, so sensitive to their environment that
their external structure appears to be determined by the external
conditions in which they find themselves quite as much as by their
inherited tendencies. In this respect they differ very considerably from
the higher animals. The peacock, for example, presents the same outward
appearance[1] whether bred and reared in Asia or Europe, in a hot or
cold, a damp or a dry climate. The same plant, on the other hand, differs
greatly in outward appearance according as it is grown in a dry or a damp
soil, a hot or a cold country. In his recent book _The Heredity of
Acquired Characters in Plants_, the Rev. G. Henslow cites several
examples of the celerity with which plants react to their environment. On
page 32 he writes: “The following is an experiment I made with the common
rest-harrow (_Ononis spinosa, L._) growing wild in a very dry situation
by a roadside. I collected some seeds, and also took cuttings. These I
planted in a garden border, keeping this well moist with a hand-light
over it, and a saucer of water, so that the air should be thoroughly
moist as well. Its natural conditions were thus completely reversed. They
all grew vigorously. The new branches of the first year’s growth bore
spines, proving their hereditary character, but instead of their being
long and stout, they were not an inch long, and like needles. This proved
the spines to be a hereditary feature. In the second year there were none
at all; moreover, the plants blossomed, and, taken altogether, there was
no appreciable difference from _O. repens, L._”
From this experiment Professor Henslow draws the inference that acquired
characters tend to be inherited in plants. In our opinion the experiment
affords strong evidence against the Lamarckian doctrine. Here we have a
plant which has, perhaps, for thousands of generations developed spines
owing to its dry environment. If acquired characters are inherited we
should have expected this spiny character to have become fixed and
persisted under changed conditions, for some generations at any rate. But
what do we find? By the second year the thorns have entirely disappeared.
All the years during which the plant was exposed to a dry environment
have left no stamp upon it. The fact that the new branches of the first
year’s growth bore small spines is not, as Professor Henslow asserts,
proof of their hereditary character. It merely shows that the initial
stimulus to their development occurred while the plant was still in its
dry surroundings.
In the same way all other so-called proofs of the heredity of acquired
characters break down when critically examined.
In our opinion “not proven” is the proper verdict on the question of the
possibility of the inheritance of acquired characters in the higher
animals. One thing is certain, and that is that acquired characters are
not commonly inherited in those organisms in which there is a sharp
distinction between the germinal and the somatic cells.
It is nothing short of a misfortune that Haeckel’s _History of Creation_,
which seems to be so widely read in England, should be built on a
fallacious foundation. It seems to us that this work is calculated to
mislead rather than to teach.
Our attitude is not quite that of the Wallaceian school, which denies the
possibility of the inheritance of acquired characters. In practice,
however, the attitude we adopt is as fatal to Lamarckism in all its forms
as the dogmatic assertions of the Wallaceians. It matters not whether
acquired characters are very rarely or never inherited. In either case
their inheritance cannot have played an important part in evolution. All
those theories which rely on use-inheritance as a factor in evolution are
therefore in our opinion worthless, being opposed to facts. Our attitude,
then, is that the inheritance of acquired characteristics, if it does
occur, is so rare as to be a negligible quantity in organic evolution.
We may add that the position which we occupy will not be affected even if
the Lamarckians do succeed eventually in proving that some acquired
characters are really inherited. Such proof would merely help to
elucidate some of the problems which confront the biologist. Thus the
question of the inheritance of acquired characters, while full of
interest, has no very important bearing on the question of the making of
species.
The Wallaceian School
The Wallaceians hold the doctrines which have been set forth above as
those of the Neo-Darwinian school. It is incorrect to call those who pin
their faith to the all-sufficiency of natural selection Neo-Darwinians,
because Darwin at no time believed that natural selection explained
everything. Darwin moreover was a Lamarckian to the extent that he was
inclined to think that acquired characteristics could be inherited. His
theory of inheritance by gemmules involved the assumption that such
characters are inherited. It is Wallace who out-Darwins Darwin, who
preaches the all-sufficiency of natural selection. For this reason we dub
the school which holds this article of belief, and to which Weismann,
Poulton, and apparently Ray Lankester belong, the Wallaceian school.
Weismann has put forth a theory of inheritance, that of the continuity of
the germ plasm, which makes this inheritance a physical impossibility. We
believe that the Wallaceians have erred as far from the truth as the
Lamarckians have, because, as we shall show hereafter, a great many of
the organs and structures displayed by organisms cannot be explained on
the natural selection hypothesis. Those who pin their faith to this,
needlessly increase the difficulty of the problem which they have to
face.
There remains the third school, to which we belong, and of which Bateson,
De Vries, Kellog and T. H. Morgan appear to be adherents. This school
steers a course between the Scylla of use-inheritance and the Charybdis
of the all-sufficiency of natural selection. It may seem surprising to
some that we should class De Vries as a Neo-Darwinian, seeing that he is
the originator of the theory of evolution by means of mutations, which we
shall discuss in Chapter III. of this work. As a matter of fact the
theory of mutations should be regarded, not as opposed to the theory of
Darwin, but as a theory engrafted upon it. De Vries himself writes:—“My
work claims to be in full accord with the principles laid down by
Darwin.” Similarly Hubrecht writes in the _Contemporary Review_ for
November 1908: “Paradoxical as it may sound, I am willing to show that my
colleague, Hugo de Vries, of Amsterdam, who a few years ago grafted his
_Mutations Theorie_ on the thriving and very healthy plant of Darwinism,
is a much more staunch Darwinian than either Dr Wallace himself, or the
two great authorities in biological science whom he mentions, Sir William
Thistleton Dyer and Professor Poulton.”
Complexity of the Problem
Having classified ourselves, it remains for us (the authors of the
present work) to define our position more precisely. Like Darwin we
welcome all factors which appear to be capable of effecting evolution. We
have no axe to grind in the shape of a pet hypothesis, and consequently
our passions are not roused when men come forward with new ideas
seemingly opposed to some which already occupy the field. We recognise
the extreme complexity of the problems that confront us. We look facts in
the face and decline to ignore any, no matter how ill they fit in with
existing theories. We recognise the strength and the weakness of the
Darwinian theory. We see plainly that it has the defect of the period in
which it was enunciated. The eighteenth century was the age of
cocksureness, the age in which all phenomena were thought to be capable
of simple explanation.
This is well exemplified by the doctrines of the Manchester school as
regards political and economic science. The whole art of legislation was
thought to be summed up in the words _laissez faire_. The whole sphere of
legitimate government was asserted to be the keeping of order and the
enforcing of contracts. Experience has demonstrated that a State guided
solely by these principles is wretchedly governed. A large proportion of
recent Acts of Parliament limits the freedom of contract. Such
limitations are necessary in the case of contracts between the weak and
the strong. Similarly the earlier economists considered political economy
a very simple affair. They asserted that men are actuated by but one
motive—the love of money. All their men were economic men, men devoid of
all attributes save an intense love of gold. Experience has shown that
these premises are not correct. Love of family, pride of race, caste
prejudices are more or less deeply implanted in men, so that they are
rarely actuated solely by the love of money.
The Aim of the Biologist
Thus it is that the political economy of to-day as set forth by Marshall
is far more complex and less dogmatic than that of Ricardo or Adam Smith.
Similarly the political philosophy of Sidgwick is very different to that
of Herbert Spencer. So is it with the theory of organic evolution. The
theory of natural selection is no more able to explain all the varied
phenomena of nature than is Ricardo’s assumption that all men are
actuated solely by the love of money capable of accounting for the
multifarious existing economic phenomena. Even as the love of wealth is
an important motive of human actions, so is natural selection an
important factor in evolution. But even as the majority of human actions
are the resultant of a variety of motives, so are the majority of
existing organisms the resultant of a complex system of forces. Even as
it is the duty of the economist to discover the various motives which
lead to human actions, so is it the duty of the biologist to bring to
light the factors which are operative in the making of species.