doctrine. It is quite true that persons as diverse in their general
views as Milton the Protestant and the celebrated Jesuit Father Suarez,
each put upon the first chapter of Genesis the interpretation embodied
in Milton's poem. It is quite true that this interpretation is that
which has been instilled into every one of us in our childhood; but I do
not for one moment venture to say that it can properly be called the
Biblical doctrine. It is not my business, and does not lie within my
competency, to say what the Hebrew text does, and what it does not
signify; moreover, were I to affirm that this is the Biblical doctrine,
I should be met by the authority of many eminent scholars, to say
nothing of men of science, who, at various times, have absolutely denied
that any such doctrine is to be found in Genesis. If we are to listen to
many expositors of no mean authority, we must believe that what seems so
clearly defined in Genesis--as if very great pains had been taken that
there should be no possibility of mistake--is not the meaning of the
text at all. The account is divided into periods that we may make just
as long or as short as convenience requires. We are also to understand
that it is consistent with the original text to believe that the most
complex plants and animals may have been evolved by natural processes,
lasting for millions of years, out of structureless rudiments. A person
who is not a Hebrew scholar can only stand aside and admire the
marvellous flexibility of a language which admits of such diverse
interpretations. But assuredly, in the face of such contradictions of
authority upon matters respecting which he is incompetent to form any
judgment, he will abstain, as I do, from giving any opinion.
In the third place, I have carefully abstained from speaking of this as
the Mosaic doctrine, because we are now assured upon the authority of
the highest critics, and even of dignitaries of the Church, that there
is no evidence that Moses wrote the Book of Genesis, or knew anything
about it. You will understand that I give no judgment--it would be an
impertinence upon my part to volunteer even a suggestion--upon such a
subject. But, that being the state of opinion among the scholars and the
clergy, it is well for the unlearned in Hebrew lore, and for the laity,
to avoid entangling themselves in such a vexed question. Happily, Milton
leaves us no excuse for doubting what he means, and I shall therefore be
safe in speaking of the opinion in question as the Miltonic hypothesis.
Now we have to test that hypothesis. For my part, I have no prejudice
one way or the other. If there is evidence in favour of this view, I am
burdened by no theoretical difficulties in the way of accepting it; but
there must be evidence. Scientific men get an awkward habit--no, I won't
call it that, for it is a valuable habit--of believing nothing unless
there is evidence for it; and they have a way of looking upon belief
which is not based upon evidence, not only as illogical, but as immoral.
We will, if you please, test this view by the circumstantial evidence
alone; for, from what I have said, you will understand that I do not
propose to discuss the question of what testimonial evidence is to be
adduced in favour of it. If those whose business it is to judge are not
at one as to the authenticity of the only evidence of that kind which is
offered, nor as to the facts to which it bears witness, the discussion
of such evidence is superfluous.
But I may be permitted to regret this necessity of rejecting the
testimonial evidence the less, because the examination of the
circumstantial evidence leads to the conclusion, not only that it is
incompetent to justify the hypothesis, but that, so far as it goes, it
is contrary to the hypothesis.
The considerations upon which I base this conclusion are of the simplest
possible character. The Miltonic hypothesis contains assertions of a
very definite character relating to the succession of living forms. It
is stated that plants, for example, made their appearance upon the third
day, and not before. And you will understand that what the poet means
by plants are such plants as now live, the ancestors, in the ordinary
way of propagation of like by like, of the trees and shrubs which
flourish in the present world. It must needs be so; for, if they were
different, either the existing plants have been the result of a separate
origination since that described by Milton, of which we have no record,
nor any ground for supposition that such an occurrence has taken place;
or else they have arisen by a process of evolution from the original
stocks.
In the second place, it is clear that there was no animal life before
the fifth day, and that, on the fifth day, aquatic animals and birds
appeared. And it is further clear that terrestrial living things, other
than birds, made their appearance upon the sixth day and not before.
Hence, it follows that, if, in the large mass of circumstantial evidence
as to what really has happened in the past history of the globe we find
indications of the existence of terrestrial animals, other than birds,
at a certain period, it is perfectly certain that all that has taken
place, since that time, must be referred to the sixth day.
In the great Carboniferous formation, whence America derives so vast a
proportion of her actual and potential wealth, in the beds of coal which
have been formed from the vegetation of that period, we find abundant
evidence of the existence of terrestrial animals. They have been
described, not only by European but by your own naturalists. There are
to be found numerous insects allied to our cockroaches. There are to be
found spiders and scorpions of large size, the latter so similar to
existing scorpions that it requires the practised eye of the naturalist
to distinguish them. Inasmuch as these animals can be proved to have
been alive in the Carboniferous epoch, it is perfectly clear that, if
the Miltonic account is to be accepted, the huge mass of rocks extending
from the middle of the Palæozoic formations to the uppermost members of
the series, must belong to the day which is termed by Milton the sixth.
But, further, it is expressly stated that aquatic animals took their
origin on the fifth day, and not before; hence, all formations in which
remains of aquatic animals can be proved to exist, and which therefore
testify that such animals lived at the time when these formations were
in course of deposition, must have been deposited during or since the
period which Milton speaks of as the fifth day. But there is absolutely
no fossiliferous formation in which the remains of aquatic animals are
absent. The oldest fossils in the Silurian rocks are exuviæ of marine
animals; and if the view which is entertained by Principal Dawson and
Dr. Carpenter respecting the nature of the _Eozoön_ be well-founded,
aquatic animals existed at a period as far antecedent to the deposition
of the coal as the coal is from us; inasmuch as the _Eozoön_ is met with
in those Laurentian strata which lie at the bottom of the series of
stratified rocks. Hence it follows, plainly enough, that the whole
series of stratified rocks, if they are to be brought into harmony with
Milton, must be referred to the fifth and sixth days, and that we cannot
hope to find the slightest trace of the products of the earlier days in
the geological record. When we consider these simple facts, we see how
absolutely futile are the attempts that have been made to draw a
parallel between the story told by so much of the crust of the earth as
is known to us and the story which Milton tells. The whole series of
fossiliferous stratified rocks must be referred to the last two days;
and neither the Carboniferous, nor any other, formation can afford
evidence of the work of the third day.
Not only is there this objection to any attempt to establish a harmony
between the Miltonic account and the facts recorded in the fossiliferous
rocks, but there is a further difficulty. According to the Miltonic
account, the order in which animals should have made their appearance in
the stratified rocks would be this: Fishes, including the great whales,
and birds; after them, all varieties of terrestrial animals except
birds. Nothing could be further from the facts as we find them; we know
of not the slightest evidence of the existence of birds before the
Jurassic, or perhaps the Triassic, formation; while terrestrial animals,
as we have just seen, occur in the Carboniferous rocks.
If there were any harmony between the Miltonic account and the
circumstantial evidence, we ought to have abundant evidence of the
existence of birds in the Carboniferous, the Devonian, and the Silurian
rocks. I need hardly say that this is not the case, and that not a trace
of birds makes its appearance until the far later period which I have
mentioned.
And again, if it be true that all varieties of fishes and the great
whales, and the like, made their appearance on the fifth day, we ought
to find the remains of these animals in the older rocks--in those which
were deposited before the Carboniferous epoch. Fishes we do find, in
considerable number and variety; but the great whales are absent, and
the fishes are not such as now live. Not one solitary species of fish
now in existence is to be found in the Devonian or Silurian formations.
Hence we are introduced afresh to the dilemma which I have already
placed before you: either the animals which came into existence on the
fifth day were not such as those which are found at present, are not the
direct and immediate ancestors of those which now exist; in which case,
either fresh creations of which nothing is said, or a process of
evolution, must have occurred; or else the whole story must be given up,
as not only devoid of any circumstantial evidence, but contrary to such
evidence as exists.
I placed before you in a few words, some little time ago, a statement of
the sum and substance of Milton's hypothesis. Let me now try to state,
as briefly, the effect of the circumstantial evidence bearing upon the
past history of the earth which is furnished, without the possibility of
mistake, with no chance of error as to its chief features, by the
stratified rocks. What we find is, that the great series of formations
represents a period of time of which our human chronologies hardly
afford us a unit of measure. I will not pretend to say how we ought to
estimate this time, in millions or in billions of years. For my purpose,
the determination of its absolute duration is wholly unessential. But
that the time was enormous there can be no question.
It results from the simplest methods of interpretation, that leaving out
of view certain patches of metamorphosed rocks, and certain volcanic
products, all that is now dry land has once been at the bottom of the
waters. It is perfectly certain that, at a comparatively recent period
of the world's history--the Cretaceous epoch--none of the great physical
features which at present mark the surface of the globe existed. It is
certain that the Rocky Mountains were not. It is certain that the
Himalaya Mountains were not. It is certain that the Alps and the
Pyrenees had no existence. The evidence is of the plainest possible
character, and is simply this:--We find raised up on the flanks of these
mountains, elevated by the forces of upheaval which have given rise to
them, masses of Cretaceous rock which formed the bottom of the sea
before those mountains existed. It is therefore clear that the elevatory
forces which gave rise to the mountains operated subsequently to the
Cretaceous epoch; and that the mountains themselves are largely made up
of the materials deposited in the sea which once occupied their place.
As we go back in time, we meet with constant alternations of sea and
land, of estuary and open ocean; and, in correspondence with these
alternations, we observe the changes in the fauna and flora to which I
have referred.
But the inspection of these changes give us no right to believe that
there has been any discontinuity in natural processes. There is no
trace of general cataclysms, of universal deluges, or sudden
destructions of a whole fauna or flora. The appearances which were
formerly interpreted in that way have all been shown to be delusive, as
our knowledge has increased and as the blanks which formerly appeared to
exist between the different formations have been filled up. That there
is no absolute break between formation and formation, that there has
been no sudden disappearance of all the forms of life and replacement of
them by others, but that changes have gone on slowly and gradually, that
one type has died out and another has taken its place, and that thus, by
insensible degrees, one fauna has been replaced by another, are
conclusions strengthened by constantly increasing evidence. So that
within the whole of the immense period indicated by the fossiliferous
stratified rocks, there is assuredly not the slightest proof of any
break in the uniformity of Nature's operations, no indication that
events have followed other than a clear and orderly sequence.
That, I say, is the natural and obvious teaching of the circumstantial
evidence contained in the stratified rocks. I leave you to consider how
far, by any ingenuity of interpretation, by any stretching of the
meaning of language, it can be brought into harmony with the Miltonic
hypothesis.
There remains the third hypothesis, that of which I have spoken as the
hypothesis of evolution; and I purpose that, in lectures to come, we
should discuss it as carefully as we have considered the other two
hypotheses. I need not say that it is quite hopeless to look for
testimonial evidence of evolution. The very nature of the case precludes
the possibility of such evidence, for the human race can no more be
expected to testify to its own origin, than a child can be tendered as a
witness of its own birth. Our sole inquiry is, what foundation
circumstantial evidence lends to the hypothesis, or whether it lends
none, or whether it controverts the hypothesis. I shall deal with the
matter entirely as a question of history. I shall not indulge in the
discussion of any speculative probabilities. I shall not attempt to show
that Nature is unintelligible unless we adopt some such hypothesis. For
anything I know about the matter, it may be the way of Nature to be
unintelligible; she is often puzzling, and I have no reason to suppose
that she is bound to fit herself to our notions.
I shall place before you three kinds of evidence entirely based upon
what is known of the forms of animal life which are contained in the
series of stratified rocks. I shall endeavour to show you that there is
one kind of evidence which is neutral, which neither helps evolution nor
is inconsistent with it. I shall then bring forward a second kind of
evidence which indicates a strong probability in favour of evolution,
but does not prove it; and, lastly, I shall adduce a third kind of
evidence which, being as complete as any evidence which we can hope to
obtain upon such a subject, and being wholly and strikingly in favour of
evolution, may fairly be called demonstrative evidence of its
occurrence.
II
THE HYPOTHESIS OF EVOLUTION. THE NEUTRAL AND THE FAVOURABLE EVIDENCE
In the preceding lecture I pointed out that there are three hypotheses
which may be entertained, and which have been entertained, respecting
the past history of life upon the globe. According to the first of these
hypotheses, living beings, such as now exist, have existed from all
eternity upon this earth. We tested that hypothesis by the
circumstantial evidence, as I called it, which is furnished by the
fossil remains contained in the earth's crust, and we found that it was
obviously untenable. I then proceeded to consider the second
hypothesis, which I termed the Miltonic hypothesis, not because it is of
any particular consequence whether John Milton seriously entertained it
or not, but because it is stated in a clear and unmistakable manner in
his great poem. I pointed out to you that the evidence at our command as
completely and fully negatives that hypothesis as it did the preceding
one. And I confess that I had too much respect for your intelligence to
think it necessary to add that the negation was equally clear and
equally valid, whatever the source from which that hypothesis might be
derived, or whatever the authority by which it might be supported. I
further stated that, according to the third hypothesis, or that of
evolution, the existing state of things is the last term of a long
series of states, which, when traced back, would be found to show no
interruption and no breach in the continuity of natural causation. I
propose, in the present and the following lecture, to test this
hypothesis rigorously by the evidence at command, and to inquire how far
that evidence can be said to be indifferent to it, how far it can be
said to be favourable to it, and, finally, how far it can be said to be
demonstrative.
From almost the origin of the discussions about the existing condition
of the animal and vegetable worlds and the causes which have determined
that condition, an argument has been put forward as an objection to
evolution, which we shall have to consider very seriously. It is an
argument which was first clearly stated by Cuvier in his criticism of
the doctrines propounded by his great contemporary, Lamarck. The French
expedition to Egypt had called the attention of learned men to the
wonderful store of antiquities in that country, and there had been
brought back to France numerous mummified corpses of the animals which
the ancient Egyptians revered and preserved, and which, at a reasonable
computation, must have lived not less than three or four thousand years
before the time at which they were thus brought to light. Cuvier
endeavoured to test the hypothesis that animals have undergone gradual
and progressive modifications of structure, by comparing the skeletons
and such other parts of the mummies as were in a fitting state of
preservation, with the corresponding parts of the representatives of the
same species now living in Egypt. He arrived at the conviction that no
appreciable change had taken place in these animals in the course of
this considerable lapse of time, and the justice of his conclusion is
not disputed.
It is obvious that, if it can be proved that animals have endured,
without undergoing any demonstrable change of structure, for so long a
period as four thousand years, no form of the hypothesis of evolution
which assumes that animals undergo a constant and necessary progressive
change can be tenable; unless, indeed, it be further assumed that four
thousand years is too short a time for the production of a change
sufficiently great to be detected.
But it is no less plain that if the process of evolution of animals is
not independent of surrounding conditions; if it may be indefinitely
hastened or retarded by variations in these conditions; or if evolution
is simply a process of accommodation to varying conditions; the argument
against the hypothesis of evolution based on the unchanged character of
the Egyptian fauna is worthless. For the monuments which are coeval with
the mummies testify as strongly to the absence of change in the physical
geography and the general conditions of the land of Egypt, for the time
in question, as the mummies do to the unvarying characters of its living
population.
The progress of research since Cuvier's time has supplied far more
striking examples of the long duration of specific forms of life than
those which are furnished by the mummified Ibises and Crocodiles of
Egypt. A remarkable case is to be found in your own country, in the
neighbourhood of the falls of Niagara. In the immediate vicinity of the
whirlpool, and again upon Goat Island, in the superficial deposits
which cover the surface of the rocky subsoil in those regions, there are
found remains of animals in perfect preservation, and among them, shells
belonging to exactly the same species as those which at present inhabit
the still waters of Lake Erie. It is evident, from the structure of the
country, that these animal remains were deposited in the beds in which
they occur at a time when the lake extended over the region in which
they are found. This involves the conclusion that they lived and died
before the falls had cut their way back through the gorge of Niagara;
and, indeed, it has been determined that, when these animals lived, the
falls of Niagara must have been at least six miles further down the
river than they are at present. Many computations have been made of the
rate at which the falls are thus cutting their way back. Those
computations have varied greatly, but I believe I am speaking within the
bounds of prudence, if I assume that the falls of Niagara have not
retreated at a greater pace than about a foot a year. Six miles,
speaking roughly, are 30,000 feet; 30,000 feet, at a foot a year, gives
30,000 years; and thus we are fairly justified in concluding that no
less a period than this has passed since the shell-fish, whose remains
are left in the beds to which I have referred, were living creatures.
But there is still stronger evidence of the long duration of certain
types. I have already stated that, as we work our way through the great
series of the Tertiary formations, we find many species of animals
identical with those which live at the present day, diminishing in
numbers, it is true, but still existing, in a certain proportion, in the
oldest of the Tertiary rocks. Furthermore, when we examine the rocks of
the Cretaceous epoch, we find the remains of some animals which the
closest scrutiny cannot show to be, in any important respect, different
from those which live at the present time. That is the case with one of
the cretaceous lamp-shells (_Terebratula_) which has continued to exist
unchanged, or with insignificant variations, down to the present day.
Such is the case with the _Globigerinæ_, the skeletons of which,
aggregated together, form a large proportion of our English chalk. Those
_Globigerinæ_ can be traced down to the _Globigerinæ_ which live at the
surface of the present great oceans, and the remains of which, falling
to the bottom of the sea give rise to a chalky mud. Hence it must be
admitted that certain existing species of animals show no distinct sign
of modification, or transformation, in the course of a lapse of time as
great as that which carries us back to the Cretaceous period; and which,
whatever its absolute measure, is certainly vastly greater than thirty
thousand years.
There are groups of species so closely allied together, that it needs
the eye of a naturalist to distinguish them one from another. If we
disregard the small differences which separate these forms, and consider
all the species of such groups as modifications of one type, we shall
find that, even among the higher animals, some types have had a
marvellous duration. In the chalk, for example, there is found a fish
belonging to the highest and the most differentiated group of osseous
fishes, which goes by the name of _Beryx_. The remains of that fish are
among the most beautiful and well-preserved of the fossils found in our
English chalk. It can be studied anatomically, so far as the hard parts
are concerned, almost as well as if it were a recent fish. But the genus
_Beryx_ is represented, at the present day, by very closely allied
species which are living in the Pacific and Atlantic Oceans. We may go
still farther back. I have already referred to the fact, that the
Carboniferous formations, in Europe and in America, contain the remains
of scorpions in an admirable state of preservation and, that those
scorpions are hardly distinguishable from such as now live. I do not
mean to say that they are not different, but close scrutiny is needed in
order to distinguish them from modern scorpions.
More than this. At the very bottom Of the Silurian series, in beds which
are by some authorities referred to the Cambrian formation, where the
signs of life begin to fail us--even there, among the few and scanty
animal remains which are discoverable, we find species of molluscous
animals which are so closely allied to existing forms that, at one time,
they were grouped under the same generic name. I refer to the well known
_Lingula_ of the _Lingula_ flags, lately, in consequence of some slight
differences, placed in the new genus _Lingulella_. Practically, it
belongs to the same great generic group as the _Lingula_, which is to be
found at the present day upon your own shores and those of many other
parts of the world.
The same truth is exemplified if we turn to certain great periods of the
earth's history--as, for example, the Mesozoic epoch. There are groups
of reptiles, such as the _Ichthyosauria_ and the _Plesiosauria_, which
appear shortly after the commencement of this epoch, and they occur in
vast numbers. They disappear with the chalk and, throughout the whole of
the great series of Mesozoic rocks, they present no such modifications
as can safely be considered evidence of progressive modification.
Facts of this kind are undoubtedly fatal to any form of the doctrine of
evolution which postulates the supposition that there is an intrinsic
necessity, on the part of animal forms which have once come into
existence, to undergo continual modification; and they are as distinctly
opposed to any view which involves the belief, that such modification as
may occur, must take place, at the same rate, in all the different types
of animal or vegetable life. The facts, as I have placed them before you
obviously directly contradict any form of the hypothesis of evolution
which stands in need of these two postulates.