inite facts. Modern science began
by demanding--with Kepler and Newton--evidence of _varae causae_; this
demand Darwin industriously set himself to satisfy--hence the wealth
of material which he collected by his observations and his
experiments. He not only revived an old hypothesis, but he saw the
necessity of verifying it by facts. Whether the special cause on which
he founded the explanation of the origin of species--Natural
Selection--is sufficient, is now a subject of discussion. He himself
had some doubt in regard to this question, and the criticisms which
are directed against his hypothesis hit Darwinism rather than Darwin.
In his indefatigable search for empirical evidence he is a model even
for his antagonists: he has compelled them to approach the problems of
life along other lines than those which were formerly followed.

Whether the special cause to which Darwin appealed is sufficient or not, at
least to it is probably due the greater part of the influence which he has
exerted on the general trend of thought. "Struggle for existence" and
"natural selection" are principles which have been applied, more or less,
in every department of thought. Recent research, it is true, has discovered
greater empirical discontinuity--leaps, "mutations"--whereas Darwin
believed in the importance of small variations slowly accumulated. It has
also been shown by the experimental method, which in recent biological work
has succeeded Darwin's more historical method, that types once constituted
possess great permanence, the fluctuations being restricted within clearly
defined boundaries. The problem has become more precise, both as to
variation and as to heredity. The inner conditions of life have in both
respects shown a greater independence than Darwin had supposed in his
theory, though he always admitted that the cause of variation was to him a
great enigma, "a most perplexing problem," and that the struggle for life
could only occur where variation existed. But, at any rate, it was of the
greatest importance that Darwin gave a living impression of the struggle
for life which is everywhere going on, and to which even the highest forms
of existence must be amenable. The philosophical importance of these ideas
does not stand or fall with the answer to the question, whether natural
selection is a sufficient explanation of the origin of species or not it
has an independent, positive value for everyone who will observe life and
reali