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 a priori
considerations. The question is a question of historical fact.