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Title:  Lectures on Evolution
Title:  This is Essay #3 from "Science and Hebrew Tradition"

Author:  Thomas Henry Huxley

May, 2001  [Etext #2629]


The Project Gutenberg Etext of Lectures on Evolution, by Huxley
 
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Lectures on Evolution
This is Essay #3 from "Science and Hebrew Tradition"
by Thomas Henry Huxley




I
THE THREE HYPOTHESES RESPECTING THE HISTORY OF NATURE

We live in and form part of a system of things of immense
diversity and perplexity, which we call Nature; and it is a
matter of the deepest interest to all of us that we should form
just conceptions of the constitution of that system and of its
past history. With relation to this universe, man is, in extent,
little more than a mathematical point; in duration but a
fleeting shadow; he is a mere reed shaken in the winds of force.
But as Pascal long ago remarked, although a mere reed, he is a
thinking reed; and in virtue of that wonderful capacity of
thought, he has the power of framing for himself a symbolic
conception of the universe, which, although doubtless highly
imperfect and inadequate as a picture of the great whole, is yet
sufficient to serve him as a chart for the guidance of his
practical affairs. It has taken long ages of toilsome and often
fruitless labour to enable man to look steadily at the shifting
scenes of the phantasmagoria of Nature, to notice what is fixed
among her fluctuations, and what is regular among her apparent
irregularities; and it is only comparatively lately, within the
last few centuries, that the conception of a universal order and
of a definite course of things, which we term the course of
Nature, has emerged.

But, once originated, the conception of the constancy of the
order of Nature has become the dominant idea of modern thought.
To any person who is familiar with the facts upon which that
conception is based, and is competent to estimate their
significance, it has ceased to be conceivable that chance should
have any place in the universe, or that events should depend
upon any but the natural sequence of cause and effect. We have
come to look upon the present as the child of the past and as
the parent of the future; and, as we have excluded chance from a
place in the universe, so we ignore, even as a possibility, the
notion of any interference with the order of Nature.
Whatever may be men's speculative doctrines, it is quite certain
that every intelligent person guides his life and risks his
fortune upon the belief that the orderof Nature is constant, and
that the chain of natural causation is never broken.

In fact, no belief which we entertain has so complete a logical
basis as that to which I have just referred. It tacitly
underlies every process of reasoning; it is the foundation of
every act of the will. It is based upon the broadest induction,
and it is verified by the most constant, regular, and universal
of deductive processes. But we must recollect that any human
belief, however broad its basis, however defensible it may seem,
is, after all, only a probable belief, and that our widest and
safest generalisations are simply statements of the highest
degree of probability. Though we are quite clear about the
constancy of the order of Nature, at the present time, and in
the present state of things, it by no means necessarily follows
that we are justified in expanding this generalisation into the
infinite past, and in denying, absolutely, that there may have
been a time when Nature did not follow a fixed order, when the
relations of cause and effect were not definite, and when extra-
natural agencies interfered with the general course of Nature.
Cautious men will allow that a universe so different from that
which we know may have existed; just as a very candid thinker
may admit that a world in which two and two do not make four,
and in which two straight lines do inclose a space, may exist.
But the same caution which forces the admission of such
possibilities demands a great deal of evidence before it
recognises them to be anything more substantial. And when it is
asserted that, so many thousand years ago, events occurred in a
manner utterly foreign to and inconsistent with the existing
laws of Nature, men, who without being particularly cautious,
are simply honest thinkers, unwilling to deceive themselves or
delude others, ask for trustworthy evidence of the fact.

Did things so happen or did they not? This is a historical
question, and one the answer to which must be sought in the same
way as the solution of any other historical problem.

So far as I know, there are only three hypotheses which ever
have been entertained, or which well can be entertained,
respecting the past history of Nature. I will, in the first
place, state the hypotheses, and then I will consider what
evidence bearing upon them is in our possession, and by what
light of criticism that evidence is to be interpreted.

Upon the first hypothesis, the assumption is, that phenomena of
Nature similar to those exhibited by the present world have
always existed; in other words, that the universe has existed,
from all eternity, in what may be broadly termed its
present condition.

The second hypothesis is that the present state of things has
had only a limited duration; and that, at some period in the
past, a condition of the world, essentially similar to that
which we now know, came into existence, without any precedent
condition from which it could have naturally proceeded.
The assumption that successive states of Nature have arisen,
each without any relation of natural causation to an antecedent
state, is a mere modification of this second hypothesis.

The third hypothesis also assumes that the present state of
things has had but a limited duration; but it supposes that this
state has been evolved by a natural process from an antecedent
state, and that from another, and so on; and, on this
hypothesis, the attempt to assign any limit to the series of
past changes is, usually, given up.

It is so needful to form clear and distinct notions of what is
really meant by each of these hypotheses that I will ask you to
imagine what, according to each, would have been visible to a
spectator of the events which constitute the history of the
earth. On the first hypothesis, however far back in time that
spectator might be placed, he would see a world essentially,
though perhaps not in all its details, similar to that which now
exists. The animals which existed would be the ancestors of
those which now live, and similar to them; the plants, in like
manner, would be such as we know; and the mountains, plains, and
waters would foreshadow the salient features of our present land
and water. This view was held more or less distinctly, sometimes
combined with the notion of recurrent cycles of change, in
ancient times; and its influence has been felt down to the
present day. It is worthy of remark that it is a hypothesis
which is not inconsistent with the doctrine of
Uniformitarianism, with which geologists are familiar.
That doctrine was held by Hutton, and in his earlier days by
Lyell. Hutton was struck by the demonstration of astronomers
that the perturbations of the planetary bodies, however great
they may be, yet sooner or later right themselves; and that the
solar system possesses a self-adjusting power by which these
aberrations are all brought back to a mean condition.
Hutton imagined that the like might be true of terrestrial
changes; although no one recognised more clearly than he the
fact that the dry land is being constantly washed down by rain
and rivers and deposited in the sea; and that thus, in a longer
or shorter time, the inequalities of the earth's surface must be
levelled, and its high lands brought down to the ocean.
But, taking into account the internal forces of the earth,
which, upheaving the sea-bottom give rise to new land, he
thought that these operations of degradation and elevation might
compensate each other; and that thus, for any assignable time,
the general features of our planet might remain what they are.
And inasmuch as, under these circumstances, there need be no
limit to the propagation of animals and plants, it is clear that
the consistent working out of the uniformitarian idea might lead
to the conception of the eternity of the world. Not that I mean
to say that either Hutton or Lyell held this conception--
assuredly not; they would have been the first to repudiate it.
Nevertheless, the logical development of some of their arguments
tends directly towards this hypothesis.

The second hypothesis supposes that the present order of things,
at some no very remote time, had a sudden origin, and that the
world, such as it now is, had chaos for its phenomenal
antecedent. That is the doctrine which you will find stated most
fully and clearly in the immortal poem of John Milton--the
English <i>Divina Commedia--</i> "Paradise Lost." I believe it
is largely to the influence of that remarkable work, combined
with the daily teachings to which we have all listened in our
childhood, that this hypothesis owes its general wide diffusion
as one of the current beliefs of English-speaking people. If you
turn to the seventh book of "Paradise Lost," you will find there
stated the hypothesis to which I refer, which is briefly this:
That this visible universe of ours came into existence at no
great distance of time from the present; and that the parts of
which it is composed made their appearance, in a certain
definite order, in the space of six natural days, in such a
manner that, on the first of these days, light appeared; that,
on the second, the firmament, or sky, separated the waters
above, from the waters beneath the firmament; that, on the third
day, the waters drew away from the dry land, and upon it a
varied vegetable life, similar to that which now exists, made
its appearance; that the fourth day was signalised by the
apparition of the sun, the stars, the moon, and the planets;
that, on the fifth day, aquatic animals originated within the
waters; that, on the sixth day, the earth gave rise to our four-
footed terrestrial creatures, and to all varieties of
terrestrial animals except birds, which had appeared on the
preceding day; and, finally, that man appeared upon the earth,
and the emergence of the universe from chaos was finished.
Milton tells us, without the least ambiguity, what a spectator
of these marvellous occurrences would have witnessed. I doubt
not that his poem is familiar to all of you, but I should like
to recall one passage to your minds, in order that I may be
justified in what I have said regarding the perfectly concrete,
definite, picture of the origin of the animal world which Milton
draws. He says:--

"The sixth, and of creation last, arose
With evening harp and matin, when God said,
'Let the earth bring forth soul living in her kind,
Cattle and creeping things, and beast of the earth.
Each in their kind!' The earth obeyed, and, straight
Opening her fertile womb, teemed at a birth
Innumerous living creatures, perfect forms,
Limbed and full-grown. Out of the ground uprose,
As from his lair, the wild beast, where he wons
In forest wild, in thicket, brake, or den;
Among the trees in pairs they rose, they walked;
The cattle in the fields and meadows green;
Those rare and solitary; these in flocks
Pasturing at once, and in broad herds upsprung.
The grassy clods now calved; now half appears
The tawny lion, pawing to get free
His hinder parts--then springs, as broke from bonds,
And rampant shakes his brinded mane; the ounce,
The libbard, and the tiger, as the mole
Rising, the crumbled earth above them threw
In hillocks; the swift stag from underground
Bore up his branching head; scarce from his mould
Behemoth, biggest born of earth, upheaved
His vastness; fleeced the flocks and bleating rose
As plants; ambiguous between sea and land,
The river-horse and scaly crocodile.
At once came forth whatever creeps the ground,
Insect or worm."

There is no doubt as to the meaning of this statement, nor as to
what a man of Milton's genius expected would have been actually
visible to an eye-witness of this mode of origination of
living things.

The third hypothesis, or the hypothesis of evolution, supposes
that, at any comparatively late period of past time, our
imaginary spectator would meet with a state of things very
similar to that which now obtains; but that the likeness of the
past to the present would gradually become less and less, in
proportion to the remoteness of his period of observation from
the present day; that the existing distribution of mountains and
plains, of rivers and seas, would show itself to be the product
of a slow process of natural change operating upon more and more
widely different antecedent conditions of the mineral frame-work
of the earth; until, at length, in place of that frame-work, he
would behold only a vast nebulous mass, representing the
constituents of the sun and of the planetary bodies. Preceding
the forms of life which now exist, our observer would see
animals and plants, not identical with them, but like them,
increasing their differences with their antiquity and, at the
same time, becoming simpler and simpler; until, finally, the
world of life would present nothing but that undifferentiated
protoplasmic matter which, so far as our present knowledge goes,
is the common foundation of all vital activity.

The hypothesis of evolution supposes that in all this vast
progression there would be no breach of continuity, no point at
which we could say "This is a natural process," and "This is not
a natural process;" but that the whole might be compared to that
wonderful operation of development which may be seen going on
every day under our eyes, in virtue of which there arises, out
of the semi-fluid comparatively homogeneous substance which we
call an egg, the complicated organisation of one of the higher
animals. That, in a few words, is what is meant by the
hypothesis of evolution.

I have already suggested that, in dealing with these three
hypotheses, in endeavouring to form a judgment as to which of
them is the more worthy of belief, or whether none is worthy of
belief--in which case our condition of mind should be that
suspension of judgment which is so difficult to all but trained
intellects--we should be indifferent to all <i>a priori</i>
considerations. The question is a question of historical fact.
The universe has come into existence somehow or other, and the
problem is, whether it came into existence in one fashion, or
whether it came into existence in another; and, as an essential
preliminary to further discussion, permit me to say two or three
words as to the nature and the kinds of historical evidence.

The evidence as to the occurrence of any event in past time may
be ranged under two heads which, for convenience' sake, I will
speak of as testimonial evidence and as circumstantial evidence.
By testimonial evidence I mean human testimony; and by
circumstantial evidence I mean evidence which is not human
testimony. Let me illustrate by a familiar example what I
understand by these two kinds of evidence, and what is to be
said respecting their value.

Suppose that a man tells you that he saw a person strike another
and kill him; that is testimonial evidence of the fact of
murder. But it is possible to have circumstantial evidence of
the fact of murder; that is to say, you may find a man dying
with a wound upon his head having exactly the form and character
of the wound which is made by an axe, and, with due care in
taking surrounding circumstances into account, you may conclude
with the utmost certainty that the man has been murdered;
that his death is the consequence of a blow inflicted by another
man with that implement. We are very much in the habit of
considering circumstantial evidence as of less value than
testimonial evidence, and it may be that, where the
circumstances are not perfectly clear and intelligible, it is a
dangerous and unsafe kind of evidence; but it must not be
forgotten that, in many cases, circumstantial is quite as
conclusive as testimonial evidence, and that, not unfrequently,
it is a great deal weightier than testimonial evidence.
For example, take the case to which I referred just now.
The circumstantial evidence may be better and more convincing
than the testimonial evidence; for it may be impossible, under
the conditions that I have defined, to suppose that the man met
his death from any cause but the violent blow of an axe wielded
by another man. The circumstantial evidence in favour of a
murder having been committed, in that case, is as complete and
as convincing as evidence can be. It is evidence which is open
to no doubt and to no falsification. But the testimony of a
witness is open to multitudinous doubts. He may have been
mistaken. He may have been actuated by malice. It has constantly
happened that even an accurate man has declared that a thing has
happened in this, that, or the other way, when a careful
analysis of the circumstantial evidence has shown that it did
not happen in that way, but in some other way.

We may now consider the evidence in favour of or against the
three hypotheses. Let me first direct your attention to what is
to be said about the hypothesis of the eternity of the state of
things in which we now live. What will first strike you is, that
it is a hypothesis which, whether true or false, is not capable
of verification by any evidence. For, in order to obtain either
circumstantial or testimonial evidence sufficient to prove the
eternity of duration of the present state of nature, you must
have an eternity of witnesses or an infinity of circumstances,
and neither of these is attainable. It is utterly impossible
that such evidence should be carried beyond a certain point of
time; and all that could be said, at most, would be, that so far
as the evidence could be traced, there was nothing to contradict
the hypothesis. But when you look, not to the testimonial
evidence--which, considering the relative insignificance of the
antiquity of human records, might not be good for much in this
case--but to the circumstantial evidence, then you find that
this hypothesis is absolutely incompatible with such evidence as
we have; which is of so plain and so simple a character that it
is impossible in any way to escape from the conclusions which it
forces upon us.

You are, doubtless, all aware that the outer substance of the
earth, which alone is accessible to direct observation, is not
of a homogeneous character, but that it is made up of a number
of layers or strata, the titles of the principal groups of which
are placed upon the accompanying diagram. Each of these groups
represents a number of beds of sand, of stone, of clay, of
slate, and of various other materials.

On careful examination, it is found that the materials of which
each of these layers of more or less hard rock are composed are,
for the most part, of the same nature as those which are at
present being formed under known conditions on the surface of
the earth. For example, the chalk, which constitutes a great
part of the Cretaceous formation in some parts of the world, is
practically identical in its physical and chemical characters
with a substance which is now being formed at the bottom of the
Atlantic Ocean, and covers an enormous area; other beds of rock
are comparable with the sands which are being formed upon sea-
shores, packed together, and so on. Thus, omitting rocks of
igneous origin, it is demonstrable that all these beds of stone,
of which a total of not less than seventy thousand feet is
known, have been formed by natural agencies, either out of the
waste and washing of the dry land, or else by the accumulation
of the exuviae of plants and animals. Many of these strata are
full of such exuviae--the so-called "fossils." Remains of
thousands of species of animals and plants, as perfectly
recognisable as those of existing forms of life which you meet
with in museums, or as the shells which you pick up upon the
sea-beach, have been imbedded in the ancient sands, or muds, or
limestones, just as they are being imbedded now, in sandy, or
clayey, or calcareous subaqueous deposits. They furnish us with
a record, the general nature of which cannot be misinterpreted,
of the kinds of things that have lived upon the surface of the
earth during the time that is registered by this great thickness
of stratified rocks. But even a superficial study of these
fossils shows us that the animals and plants which live at the
present time have had only a temporary duration; for the remains
of such modern forms of life are met with, for the most part,
only in the uppermost or latest tertiaries, and their number
rapidly diminishes in the lower deposits of that epoch. In the
older tertiaries, the places of existing animals and plants are
taken by other forms, as numerous and diversified as those which
live now in the same localities, but more or less different from
them; in the mesozoic rocks, these are replaced by others yet
more divergent from modern types; and, in the paleozoic
formations, the contrast is still more marked. Thus the
circumstantial evidence absolutely negatives the conception of
the eternity of the present condition of things. We can say,
with certainty, that the present condition of things has existed
for a comparatively short period; and that, so far as animal and
vegetable nature are concerned, it has been preceded by a
different condition. We can pursue this evidence until we reach
the lowest of the stratified rocks, in which we lose the
indications of life altogether. The hypothesis of the eternity
of the present state of nature may therefore be put out
of court.


Fig. 1.--Ideal Section of the Crust of the Earth.

 
We now come to what I will term Milton's hypothesis--the
hypothesis that the present condition of things has endured for
a comparatively short time; and, at the commencement of that
time, came into existence within the course of six days. I doubt
not that it may have excited some surprise in your minds that I
should have spoken of this as Milton's hypothesis, rather than
that I should have chosen the terms which are more customary,
such as "the doctrine of creation," or "the Biblical doctrine,"
or "the doctrine of Moses," all of which denominations, as
applied to the hypothesis to which I have just referred, are
certainly much more familiar to you than the title of the
Miltonic hypothesis. But I have had what I cannot but think are
very weighty reasons for taking the course which I have pursued.
In the first place, I have discarded the title of the "doctrine
of creation," because my present business is not with the
question why the objects which constitute Nature came into
existence, but when they came into existence, and in what order.
This is as strictly a historical question as the question when
the Angles and the Jutes invaded England, and whether they
preceded or followed the Romans. But the question about creation
is a philosophical problem, and one which cannot be solved, or
even approached, by the historical method. What we want to learn
is, whether the facts, so far as they are known, afford evidence
that things arose in the way described by Milton, or whether
they do not; and, when that question is settled it will be time
enough to inquire into the causes of their origination.

In the second place, I have not spoken of this doctrine as the
Biblical 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
Palaeozoic 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 exuviae
of marine animals; and if the view which is entertained by
Principal Dawson and Dr. Carpenter respecting the nature of the
<i>Eozoon</i> 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 <i>Eozoon</i> 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 thus: 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 gives 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.
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