“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 Helvetius 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 aquire 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? I do not see how he is to resist an argument in favour of Votes for Oysters. An adherent of evolution should maintain that not only the doctrine of the equality of all men, but also that of the rights of man, must be condemned as unbiological, since it makes too emphatic a distinction between men and other animals.”
–from A History of Western Philosophy, by Bertrand Russell