Modelling conflicts of interest in reproductive decision-making

It is a common assumption that men desire more children than women do in high fertility countries. Evolutionary demographers have tried to explain females’ relatively lower desired fertility by invoking the larger costs faced by women, a woman’s desire to invest more in each child, and a woman’s certainty that her children are genetically related to her. There are known trade-offs between the quantity and quality of children, but no clear reason why women and men should experience these differently. Furthermore, in the simplest scenario, in the case of strict (i.e. life-long) monogamy, since a man’s lifetime reproductive success is tied to that of his reproductive partner, both individuals should have the same optimal family size. In this paper we develop a theoretical framework for examining the circumstances under which we expect conflicts of interest between partnered men and women in their fitness-maximizing optimal number of offspring. Using evolutionary simulations and dynamic programming to model behaviour, we examine the effects of paternity uncertainty, reproductive senescence, and the ability to switch or acquire more partners on the extent to which women and men will have different optima regarding the numbers of offspring and the pace of reproduction.