each generation. Thus from age to age deer run more swiftly, cats stalk their prey more silently,
and giraffes' necks become longer. Given enough time, this mechanism, so Darwin contended,
could account for the whole long development from the protozoa to homo sapiens.
This part of Darwin's theory has been much disputed, and is regarded by most biologists as subject
to many important qualifications. That, however, is not what most concerns the historian of
nineteenth-century ideas. From the historical point of view, what is interesting is Darwin's
extension to the whole of life of the economics that characterized the philosophical radicals. The
motive force of evolution, according to him, is a kind of biological economics in a world of free
competition. It was Malthus's doctrine of population, extended to the world of animals and plants,
that suggested to Darwin the struggle for existence and the survival of the fittest as the source of
evolution.
Darwin himself was a liberal, but his theories had consequences in some degree inimical to
traditional liberalism. The doctrine that all men are born equal, and that the differences between
adults are due wholly to education, was incompatible with his emphasis on congenital differences
between members of the same species. If, as Lamarck held, and as Darwin himself was willing to
concede up to a point, acquired characteristics were inherited, this opposition to such views as
those of Helvétius could have been somewhat softened; but it has appeared that only congenital
characteristics are inherited, apart from certain not very important exceptions. Thus the congenital
differences between men acquire fundamental importance.
There is a further consequence of the theory of evolution, which is independent of the particular
mechanism suggested by Darwin. If men and animals have a common ancestry, and if men
developed by such slow stages that there were creatures which we should not know whether to
classify as human or not, the question arises: at what stage in evolution did men, or their semi-
human ancestors, begin to be all equal? Would Pithecanthropus erectus, if he had been properly
educated, have done work as good as Newton's? Would the Piltdown Man have written
Shakespeare's poetry if there had been anybody to convict him of poaching? A resolute egalitarian
who answers these questions in the affirmative will find himself forced to regard apes as the
equals of human beings. And why stop with apes?