to distinguish the various services which he rendered to the theory of
organic evolution.

(I) As everyone knows, the general idea of the Doctrine of Descent is that
the plants and animals of the present-day are the lineal descendants of
ancestors on the whole somewhat simpler, that these again are descended
from yet simpler forms, and so on backwards towards the literal "Protozoa"
and "Protophyta" about which we unfortunately know nothing. Now no one
supposes that Darwin originated this idea, which in rudiment at least is as
old as Aristotle. What Darwin did was to make it current intellectual
coin. He gave it a form that commended itself to the scientific and public
intelligence of the day, and he won wide-spread conviction by showing with
consummate skill that it was an effective formula to work with, a key which
no lock refused. In a scholarly, critical, and pre-eminently fair-minded
way, admitting difficulties and removing them, foreseeing objections and
forestalling them, he showed that the doctrine of descent supplied a modal
interpretation of how our present-day fauna and flora have come to be.

(II) In the second place, Darwin applied the evolution-idea to particular
problems, such as the descent of man, and showed what a powerful organon it
is, introducing order into masses of uncorrelated facts, interpreting
enigmas both of structure and function, both bodily and mental, and, best
of all, stimulating and guiding further investigation. But here again it
cannot be claimed that Darwin was original. The problem of the descent or
ascent of man, and other particular cases of evolution, had attracted not a
few naturalists before Darwin's day, though no one (except Herbert Spencer
in the psychological domain (1855)) had come near him in precision and
thoroughness of inquiry.

(III) In the third place, Darwin contributed largely to a knowledge of the