What Do Sexes Have to Do with (Models of) Sexual Selection?

Sexes are normally taken to be fundamental categories in biology-many sexually reproducing organisms fall under the categories of female/male. Much research aims at explaining differences between sexes. Sexual selection forms a central framework for explaining "typical" distributions of traits among sexes and explicating circumstances leading to "reversal." I claim that sexual selection models need not make use of sexes and that sexes lack explanatory significance in such models. I offer a framework of reproductive dimorphism and argue that it is better than that of sexes because it (1) is more compatible with explanations of sexual selection and (2) allows for their greater applicability.