Polymorphism and Natural Selection

Abstract

The general grounds, originally put forward by Darwin, for considering that natural selection will in a great variety of circumstances favor diversity within a species, seem to have been taken over uncritically in application to cases of balanced polymorphism, in which stability is often assured by some degree of physiological deficiency in some of the genotypes. Recent notes by Cain and Sheppard have gone far to distinguish these cases. The present note suggests that, on quite different grounds, polymorphism may play a part in specific evolution in somewhat the same way that a randomized strategy may be advantageous in the Theory of Games; the opponents being "natural enemies," or competitors evolving in a common ecology, and the "game" extending over evolutionary periods involving the progressive modification of the participants. Selection by physiological incapacity is not the governing factor here.