IN MODERN THOUGHT

I

DARWIN'S PREDECESSORS

BY J. ARTHUR THOMSON

_Professor of Natural History in the University of Aberdeen_

In seeking to discover Darwin's relation to his predecessors it is
useful 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 widespread 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 factors in the evolution-process, especially by his analysis of
what occurs in the case of domestic animals and cultivated plants, and
by his elaboration of the theory of Natural Selection which Alfred
Russel Wallace independently stated at the same time, and of which
there had been a few previous suggestions of a more or less vague
description. It was here