Evolutionary Perspectives on Male-Male Competition, Violence, and Homicide

Aggression and violence are common elements of male mating competition across animal species. The level of violence across species, across human populations, and across individuals within societies corresponds with the intensity of male mating competition. In humans, peak rates of violence and homicide occur as males reach reproductive maturity and contest directly for mates, as well as for the social status and resources that facilitate attraction of prospective partners. In modern societies, levels of mortality from violence decrease considerably as males marry, start families, and undergo a life history shift from mating effort to paternal investment. In other societies, especially those with extended male fertility from additional sequential and/or simultaneous mating partners, risky behaviors including violence persist at higher levels throughout adulthood. Across species, those with higher degrees of male reproductive inequality (polygyny) have higher rates of violence and male mortality. There is a parallel pattern for the degree of polygyny across human populations, as well as for the degree of inequality in social status and resource holdings that are historically tied to male reproductive success. Temporal fluctuations in social stressors such as higher extrinsic mortality and higher socioeconomic inequality also elevate rates of violent behavior and mortality from homicide within societies. Androgen production mirrors the pattern of risky and violent male behavior across the life span, indicating a physiological basis in the mechanisms underlying male sexuality.