An Analysis of Variance in Reproductive Success: What Drives Sexual Selection in a Human Mating System?

Individual reproductive success varies within every population, and the greater the variation, the greater the opportunity for sexual selection. But “reproductive success” is a complex issue in human populations, and not easily quantifiable. Here, we apply a model originally designed to study sexual selection in birds (Webster et al. 1995), to help identify and quantify the components of mating success in human groups. The two main components are within-pair reproductive success and extra-pair reproductive success, and these can be divided into even more specific units: number of mates, mate quality (measured by fecundity), and mate fidelity (proportion of young produced per mate). By analyzing the variance in these individual components, and their contribution to total variance in reproductive success, we can begin to predict where sexual selection will be strongest within a mating system. Furthermore, studying these components across several populations, or over a period of time, would allow researchers to determine how mating systems—and species—are affected by particular ecological and cultural variables.