proved, but only generally recognized as evident. A broader knowledge
has brought about the same state of opinion for greater groups of
relationships. Systematic affinities find their one possible explanation
by the aid of this principle; without it, all similarity is only
apparent and accidental. Geographic and paleontologic facts, brought
together by Darwin and others on a previously unequalled scale, point
clearly in the same direction. The vast amount of evidence of all [4]
comparative sciences compels us to accept the idea. To deny it, is to
give up all opportunity of conceiving Nature in her true form.

The general features of the theory of descent are now accepted as the
basis of all biological science. Half a century of discussion and
investigation has cleared up the minor points and brought out an
abundance of facts; but they have not changed the principle. Descent
with modification is now universally accepted as the chief law of nature
in the organic world. In honor of him, who with unsurpassed genius, and
by unlimited labor has made it the basis of modern thought, this law is
called the "Darwinian theory of descent."

Darwin's second contribution to this attainment was his proof of the
possibility of a physiological explanation of the process of descent
itself. Of this possibility he fully convinced his contemporaries, but
in indicating the particular means by which the change of species has
been brought about, he has not succeeded in securing universal
acceptation. Quite on the contrary, objections have been raised from the
very outset, and with such force as to compel Darwin himself to change
his views in his later writings. This however, was of no avail, and
objections and criticisms have since steadily accumulated. Physiologic
facts concerning the origin of [5] species in nature were unknown in the
time of Darwin. It was a happy idea to choose the experience of the