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 sexual selection models needn’t make use of sexes, that sexes lack explanatory significance in such models. I offer a framework of reproductive dimorphism and argue it’s better than that of sexes, because it (i) is more compatible with explanations of sexual selection and (ii) allows for their greater applicability.