Life History Strategy Predicts Individual Differences in Sexually Selected Traits

Abstract

Humans, like all other organisms, have succeeded over evolutionary time by tackling only two basic problems: survival and reproduction. Organisms that reproduce sexually utilize specially-evolved mechanisms of sexual selection when addressing the latter problem. These mechanisms, intrasexual competition and intersexual selection, often occur differently between males and females. While these differences between men and women of our own species are well-researched, little is known about the sources of variation in these behaviors within each sex. The current study tested a novel hypothesis that utilizes life history theory to explain individual differences in sexually selected traits and behaviors. The relationship between life history strategy and both intrasexual competitiveness and intersexual choosiness was investigated, along with the effects of fertility across the menstrual cycle as a potential moderating variable in these relationships for women. It was predicted that both men and women with slower life history strategies would be less intrasexually competitive and more intersexually choosy, while those with faster strategies would be more competitive and less choosy, but that sex would moderate these relationships, as men were predicted to be more competitive and less choosy than women. Fertility across the menstrual cycle was also predicted to moderate these relationships for women, as they were predicted to be more competitive and choosy while in the fertile phase of the menstrual cycle. As predicted, there was a significant correlation between life history strategy and both competitiveness and choosiness. Increasingly faster strategies correlated with increased competitiveness and decreased choosiness. However, sex did not significantly moderate the relationships, and nor did fertility across the menstrual cycle for women. Thus, life history strategy appears to influence individual differences in intersexual and intrasexual selection for both men and women.