Daniel J. Kruger

University of Michigan

 

The relative proportions of potentially reproductive males and females in a population influence behavioral dynamics related to reproduction. Patterns following from the Operational Sex Ratio in other species are reflected in human populations. Because the reproductive strategies of men and women are somewhat divergent, market influences of supply and demand on the intensity of mating competition and selectivity for partners produce different outcomes in female biased and male biased populations. Scarce females are more effectively able to secure commitment from partners as well as demand higher levels of resource investment. Male mating opportunities are enhanced by scarcity and incentives for long-term commitment are diminished. This project documents the impact of the sex ratio on multiple aspects of human life history related to social and health outcomes, including youth violence, reproductive and marital dynamics, and birth outcomes. Results demonstrate the power of evolutionary Life History Theory as framework for understanding persistent social and health issues in modern populations and indicate that imbalance sex ratios are an important risk factor for adverse health outcomes.