II 
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 back- 
wards 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 intelli- 
gence 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, fore- 
seeing 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 know- 
ledge of the factors in the evolution-process, especially by his analysis 
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