[1880]
Many of you will be familiar with the aspect of this small green-covered
book. It is a copy of the first edition of the "Origin of Species," and
bears the date of its production--the 1st of October 1859. Only a few
months, therefore, are needed to complete the full tale of twenty-one years
since its birthday.
Those whose memories carry them back to this time will remember that the
infant was remarkably lively, and that a great number of excellent persons
mistook its manifestations of a vigorous individuality for mere
naughtiness; in fact there was a very pretty turmoil about its cradle. My
recollections of the period are particularly vivid, for, having conceived a
tender affection for a child of what appeared to me to be such remarkable
promise, I acted for some time in the capacity of a sort of under-nurse,
and thus came in for my share of the storms which threatened the very life
of the young creature. For some years it was undoubtedly warm work; but
considering how exceedingly unpleasant the apparition of the newcomer must
have been to those who did not fall in love with him at first sight, I
think it is to the credit of our age that the war was not fiercer, and that
the more bitter and unscrupulous forms of opposition died away as soon as
they did.
I speak of this period as of something past and gone, possessing merely an
historical, I had almost said an antiquarian interest. For, during the
second decade of the existence of the "Origin of Species," opposition,
though by no means dead, assumed a different aspect. On the part of all
those who had any reason to respect themselves, it assumed a thoroughly
respectful character. By this time, the dullest began to perceive that the
child was not likely to perish of any congenital weakness or infantile
disorder, but was growing into a stalwart personage, upon whom mere goody
scoldings and threatenings with the birch-rod were quite thrown away.
In fact, those who have watched the progress of science within the last ten
years will bear me out to the full, when I assert that there is no field of
biological inquiry in which the influence of the "Origin of Species" is not
traceable; the foremost men of science in every country are either avowed
champions of its leading doctrines, or at any rate abstain from opposing
them; a host of young and ardent investigators seek for and find
inspiration and guidance in Mr. Darwin's great work; and the general
doctrine of evolution, to one side of which it gives expression, obtains,
in the phenomena of biology, a firm base of operations whence it may
conduct its conquest of the whole realm of Nature.
History warns us, however, that it is the customary fate of new truths to
begin as heresies and to end as superstitions; and, as matters now stand,
it is hardly rash to anticipate that, in another twenty years, the new
generation, educated under the influences of the present day, will be in
danger of accepting the main doctrines of the "Origin of Species," with as
little reflection, and it may be with as little justification, as so many
of our contemporaries, twenty years ago, rejected them.
Against any such a consummation let us all devoutly pray; for the
scientific spirit is of more value than its products, and irrationally held
truths may be more harmful than reasoned errors. Now the essence of the
scientific spirit is criticism. It tells us that whenever a doctrine claims
our assent we should reply, Take it if you can compel it. The struggle for
existence holds as much in the intellectual as in the physical world. A
theory is a species of thinking, and its right to exist is coextensive with
its power of resisting extinction by its rivals.
From this point of view, it appears to me that it would be but a poor way
of celebrating the Coming of Age of the "Origin of Species," were I merely
to dwell upon the facts, undoubted and remarkable as they are, of its
far-reaching influence and of the great following of ardent disciples who
are occupied in spreading and developing its doctrines. Mere insanities and
inanities have before now swollen to portentous size in the course of
twenty years. Let us rather ask this prodigious change in opinion to
justify itself: let us inquire whether anything has happened since 1859,
which will explain, on rational grounds, why so many are worshipping that
which they burned, and burning that which they worshipped. It is only in
this way that we shall acquire the means of judging whether the movement we
have witnessed is a mere eddy of fashion, or truly one with the
irreversible current of intellectual progress, and, like it, safe from
retrogressive reaction.
Every belief is the product of two factors: the first is the state of the
mind to which the evidence in favour of that belief is presented; and the
second is the logical cogency of the evidence itself. In both these
respects, the history of biological science during the last twenty years
appears to me to afford an ample explanation of the change which has taken
place; and a brief consideration of the salient events of that history will
enable us to understand why, if the "Origin of Species" appeared now, it
would meet with a very different reception from that which greeted it in
1859.
One-and-twenty years ago, in spite of the work commenced by Hutton and
continued with rare skill and patience by Lyell, the dominant view of the
past history of the earth was catastrophic. Great and sudden physical
revolutions, wholesale creations and extinctions of living beings, were the
ordinary machinery of the geological epic brought into fashion by the
misapplied genius of Cuvier. It was gravely maintained and taught that the
end of every geological epoch was signalised by a cataclysm, by which every
living being on the globe was swept away, to be replaced by a brand-new
creation when the world returned to quiescence. A scheme of nature which
appeared to be modelled on the likeness of a succession of rubbers of
whist, at the end of each of which the players upset the table and called
for a new pack, did not seem to shock anybody.
I may be wrong, but I doubt if, at the present time, there is a single
responsible representative of these opinions left. The progress of
scientific geology has elevated the fundamental principle of
uniformitarianism, that the explanation of the past is to be sought in the
study of the present, into the position of an axiom; and the wild
speculations of the catastrophists, to which we all listened with respect a
quarter of a century ago, would hardly find a single patient hearer at the
present day. No physical geologist now dreams of seeking, outside the range
of known natural causes, for the explanation of anything that happened
millions of years ago, any more than he would be guilty of the like
absurdity in regard to current events.
The effect of this change of opinion upon biological speculation is
obvious. For, if there have been no periodical general physical
catastrophes, what brought about the assumed general extinctions and
re-creations of life which are the corresponding biological catastrophes?
And, if no such interruptions of the ordinary course of nature have taken
place in the organic, any more than in the inorganic, world, what
alternative is there to the admission of evolution?
The doctrine of evolution in biology is the necessary result of the logical
application of the principles of uniformitarianism to the phenomena of
life. Darwin is the natural successor of Hutton and Lyell, and the "Origin
of Species" the logical sequence of the "Principles of Geology."
The fundamental doctrine of the "Origin of Species," as of all forms of the
theory of evolution applied to biology, is "that the innumerable species,
genera, and families of organic beings with which the world is peopled have
all descended, each within its own class or group, from common parents, and
have all been modified in the course of descent." [Footnote: _Origin of
Species_, ed. I, p. 457.]
And, in view of the facts of geology, it follows that all living animals
and plants "are the lineal descendants of those which lived long before the
Silurian epoch." [Footnote: _Origin of Species_, p. 458.]
It is an obvious consequence of this theory of descent with modification,
as it is sometimes called, that all plants and animals, however different
they may now be, must, at one time or other, have been connected by direct
or indirect intermediate gradations, and that the appearance of isolation
presented by various groups of organic beings must be unreal.
No part of Mr. Darwin's work ran more directly counter to the
prepossessions of naturalists twenty years ago than this. And such
prepossessions were very excusable, for there was undoubtedly a great deal
to be said, at that time, in favour of the fixity of species and of the
existence of great breaks, which there was no obvious or probable means of
filling up, between various groups of organic beings.
For various reasons, scientific and unscientific, much had been made of the
hiatus between man and the rest of the higher mammalia, and it is no wonder
that issue was first joined on this part of the controversy. I have no wish
to revive past and happily forgotten controversies; but I must state the
simple fact that the distinctions in the cerebral and other characters,
which were so hotly affirmed to separate man from all other animals in
1860, have all been demonstrated to be non-existent, and that the contrary
doctrine is now universally accepted and taught.
But there were other cases in which the wide structural gaps asserted to
exist between one group of animals and another were by no means fictitious;
and, when such structural breaks were real, Mr. Darwin could account for
them only by supposing that the intermediate forms which once existed had
become extinct. In a remarkable passage he says--
"We may thus account even for the distinctness of whole classes from each
other--for instance, of birds from all other vertebrate animals--by the
belief that many animal forms of life have been utterly lost, through which
the early progenitors of birds were formerly connected with the early
progenitors of the other vertebrate classes." [Footnote: _Origin of
Species_, p. 431.] Adverse criticism made merry over such suggestions as
these. Of course it was easy to get out of the difficulty by supposing
extinction; but where was the slightest evidence that such intermediate
forms between birds and reptiles as the hypothesis required ever existed?
And then probably followed a tirade upon this terrible forsaking of the
paths of "Baconian induction."
But the progress of knowledge has justified Mr. Darwin to an extent which
could hardly have been anticipated. In 1862, the specimen of
_Archæopteryx_, which, until the last two or three years, has remained
unique, was discovered; and it is an animal which, in its feathers and the
greater part of its organisation, is a veritable bird, while, in other
parts, it is as distinctly reptilian.
In 1868, I had the honour of bringing under your notice, in this theatre,
the results of investigations made, up to that time, into the anatomical
characters of certain ancient reptiles, which showed the nature of the
modifications in virtue of which the type of the quadrupedal reptile passed
into that of a bipedal bird; and abundant confirmatory evidence of the
justice of the conclusions which I then laid before you has since come to
light.
In 1875, the discovery of the toothed birds of the cretaceous formation in
North America by Professor Marsh completed the series of transitional forms
between birds and reptiles, and removed Mr. Darwin's proposition that "many
animal forms of life have been utterly lost, through which the early
progenitors of birds were formerly connected with the early progenitors of
the other vertebrate classes," from the region of hypothesis to that of
demonstrable fact.
In 1859, there appeared to be a very sharp and clear hiatus between
vertebrated and invertebrated animals, not only in their structure, but,
what was more important, in their development. I do not think that we even
yet know the precise links of connection between the two; but the
investigations of Kowalewsky and others upon the development of
_Amphioxus_ and of the _Tunicata_ prove, beyond a doubt, that the
differences which were supposed to constitute a barrier between the two are
non-existent. There is no longer any difficulty in understanding how the
vertebrate type may have arisen from the invertebrate, though the full
proof of the manner in which the transition was actually effected may still
be lacking.
Again, in 1859, there appeared to be a no less sharp separation between the
two great groups of flowering and flowerless plants. It is only
subsequently that the series of remarkable investigations inaugurated by
Hofmeister has brought to light the extraordinary and altogether unexpected
modifications of the reproductive apparatus in the _Lycopodiaceæ_, the
_Rhizocarpeæ_, and the _Gymnospermeæ_, by which the ferns and the
mosses are gradually connected with the Phanerogamic division of the
vegetable world.
So, again, it is only since 1859 that we have acquired that wealth of
knowledge of the lowest forms of life which demonstrates the futility of
any attempt to separate the lowest plants from the lowest animals, and
shows that the two kingdoms of living nature have a common borderland which
belongs to both, or to neither.
Thus it will be observed that the whole tendency of biological
investigation, since 1859, has been in the direction of removing the
difficulties which the apparent breaks in the series created at that time;
and the recognition of gradation is the first step towards the acceptance
of evolution.
As another great factor in bringing about the change of opinion which has
taken place among naturalists, I count the astonishing progress which has
been made in the study of embryology. Twenty years ago, not only were we
devoid of any accurate knowledge of the mode of development of many groups
of animals and plants, but the methods of investigation were rude and
imperfect. At the present time, there is no important group of organic
beings the development of which has not been carefully studied; and the
modern methods of hardening and section-making enable the embryologist to
determine the nature of the process, in each case, with a degree of
minuteness and accuracy which is truly astonishing to those whose memories
carry them back to the beginnings of modern histology. And the results of
these embryological investigations are in complete harmony with the
requirements of the doctrine of evolution. The first beginnings of all the
higher forms of animal life are similar, and however diverse their adult
conditions, they start from a common foundation. Moreover, the process of
development of the animal or the plant from its primary egg, or germ, is a
true process of evolution--a progress from almost formless to more or less
highly organised matter, in virtue of the properties inherent in that
matter.
To those who are familiar with the process of development, all _a
priori_ objections to the doctrine of biological evolution appear
childish. Any one who has watched the gradual formation of a complicated
animal from the protoplasmic mass, which constitutes the essential element
of a frog's or a hen's egg, has had under his eyes sufficient evidence that
a similar evolution of the whole animal world from the like foundation is,
at any rate, possible.
Yet another product of investigation has largely contributed to the removal
of the objections to the doctrine of evolution current in 1859. It is the
proof afforded by successive discoveries that Mr. Darwin did not
over-estimate the imperfection of the geological record. No more striking
illustration of this is needed than a comparison of our knowledge of the
mammalian fauna of the Tertiary epoch in 1859 with its present condition.
M. Gaudry's researches on the fossils of Pikermi were published in 1868,
those of Messrs. Leidy, Marsh, and Cope, on the fossils of the Western
Territories of America, have appeared almost wholly since 1870, those of M.
Filhol on the phosphorites of Quercy in 1878. The general effect of these
investigations has been to introduce to us a multitude of extinct animals,
the existence of which was previously hardly suspected; just as if
zoologists were to become acquainted with a country, hitherto unknown, as
rich in novel forms of life as Brazil or South Africa once were to
Europeans. Indeed, the fossil fauna of the Western Territories of America
bid fair to exceed in interest and importance all other known Tertiary
deposits put together; and yet, with the exception of the case of the
American tertiaries, these investigations have extended over very limited
areas; and, at Pikermi, were confined to an extremely small space.
Such appear to me to be the chief events in the history of the progress of
knowledge during the last twenty years, which account for the changed
feeling with which the doctrine of evolution is at present regarded by
those who have followed the advance of biological science, in respect of
those problems which bear indirectly upon that doctrine.
But all this remains mere secondary evidence. It may remove dissent, but it
does not compel assent. Primary and direct evidence in favour of evolution
can be furnished only by palæontology. The geological record, so soon as it
approaches completeness, must, when properly questioned, yield either an
affirmative or a negative answer: if evolution has taken place, there will
its mark be left; if it has not taken place, there will lie its refutation.
What was the state of matters in 1859? Let us hear Mr. Darwin, who may be
trusted always to state the case against himself as strongly as possible.
"On this doctrine of the extermination of an infinitude of connecting links
between the living and extinct inhabitants of the world, and at each
successive period between the extinct and still older species, why is not
every geological formation charged with such links? Why does not every
collection of fossil remains afford plain evidence of the gradation and
mutation of the forms of life? We meet with no such evidence, and this is
the most obvious and plausible of the many objections which may be urged
against my theory." [Footnote: _Origin of Species_, ed. 1, p. 463.]
Nothing could have been more useful to the opposition than this
characteristically candid avowal, twisted as it immediately was into an
admission that the writer's views were contradicted by the facts of
palæontology. But, in fact, Mr. Darwin made no such admission. What he says
in effect is, not that palæontological evidence is against him, but that it
is not distinctly in his favour; and, without attempting to attenuate the
fact, he accounts for it by the scantiness and the imperfection of that
evidence.
What is the state of the case now, when, as we have seen, the amount of our
knowledge respecting the mammalia of the Tertiary epoch is increased
fifty-fold, and in some directions even approaches completeness?
Simply this, that, if the doctrine of evolution had not existed,
palaeontologists must have invented it, so irresistibly is it forced upon
the mind by the study of the remains of the Tertiary mammalia which have
been brought to light since 1859.
Among the fossils of Pikermi, Gaudry found the successive stages by which
the ancient civets passed into the more modern hyænas; through the Tertiary
deposits of Western America, Marsh tracked the successive forms by which
the ancient stock of the horse has passed into its present form; and
innumerable less complete indications of the mode of evolution of other
groups of the higher mammalia have been obtained. In the remarkable memoir
on the phosphorites of Quercy, to which I have referred, M. Filhol
describes no fewer than seventeen varieties of the genus _Cynodictis_,
which fill up all the interval between the viverine animals and the
bear-like dog _Amphicyon_; nor do I know any solid ground of objection
to the supposition that, in this _Cynodictis-Amphicyon_ group, we have
the stock whence all the Viveridæ, Felidæ, Hyænidæ, Canidæ, and perhaps the
Procyonidæ and Ursidæ, of the present fauna have been evolved. On the
contrary, there is a great deal to be said in favour.