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Lectures on Evolution
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 Miltonthe
English Divina Commedia 〃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