Sexual Selection and Human Geographic Variation

Among early modern humans, a woman would face stronger competition for a mate the further away she was from the equator. Men were less available because they 1) hunted over longer distances that increased male mortality proportionately and 2) were less able to offset the resulting man shortage through polygyny. The longer the winter, the costlier it became to provision a second wife and her children, since women could not gather food in winter. Women competed the most for mates in the 'continental Arctic,' where wandering herds were the main food source. Conversely, men competed the most for mates in the Tropics, particularly after year-round agriculture emerged. This means of subsistence allowed women to become primary food producers, thereby freeing men to take more wives. Because mate competition has varied in intensity among human populations, sexual selection has correspondingly varied in intensity for certain traits, often highly visible and colorful ones. Intense female-female competition may explain an unusual convergence of color traits in northern and eastern Europeans. Intense male-male competition may explain increased masculinization of body build in highly polygynous agricultural populations of sub-Saharan Africa.