The evolution of parental investment: re-examining the anisogamy argument.

In most animals with internal fertilization, the early costs of parenting by necessity falls on the female, whereas male and female investments are closer substitutes later on. After Dawkins and Carlisle's (1976) critique of Trivers' (1972) anisogamy argument, the conventional wisdom has been that early investment costs as such are irrelevant for the allocation of subsequent parental investment. However, in a stylized evolutionary model with recurrent mutations, we show that if only one parent bears early costs, then the other parent should bear a substantial fraction of later costs. The result implies that the conventional wisdom has shaky logical foundations and that we have yet to understand the interaction between anisogamy and non-gamete parental investment.