Lectures on Evolution | Page 4

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