gonochorism

n. [ Gr. &unr_; offspring + &unr_; to separate. ] (a) Separation of the sexes in different individuals; -- opposed to hermaphroditism. (b) In ontogony, differentiation of male and female individuals from embryos having the same rudimentary sexual organs. (c) In phylogeny, the evolution of distinct sexes in species previously hermaphrodite or sexless. [ 1913 Webster ]