On the evolution of male competitiveness

Why are some societies monogamous and others polygynous? Most theories of polygyny invoke male heterogeneity as an explanation. Arguing that such heterogeneity depends on men’s willingness to compete against each other in the first place, I propose an evolutionary game to model the evolution of this trait. Lack of competitiveness (and the associated monogamous unions) is shown to be compatible with evolution if male reproductive success decreases with the number of wives. In a model where the man and his spouse(s) make fertility and child care choices that aim at maximizing reproductive success, I show that, due to men’s involvement in child care and female agency over her fertility, male reproductive success is decreasing in the number of wives under certain conditions and increasing in others. The model thus sheds light on the variation in polygyny rates across space and time in human societies