Sexual selection

Sexual selection is the mode of natural selection in which individuals compete for mates and in which mate choice by one sex drives the evolution of traits in the other. First proposed by Charles Darwin in 1871 to explain extravagant and seemingly maladaptive traits like the peacock's tail, sexual selection operates through two mechanisms: intrasexual selection (competition among members of one sex for access to the other) and intersexual selection (choice of mates by one sex based on preferred traits). The process can produce runaway dynamics where a preference and the trait it selects for become mutually reinforcing, potentially leading to extreme elaboration that reduces survival fitness.

The concept has been formalized mathematically through models of evolutionary game theory and has been extended to human behavior through evolutionary psychology, where it is invoked to explain sex differences in risk-taking, ornamentation, and status competition. Critics argue that human sexual behavior is too culturally variable to be explained primarily by sexual selection, and that the theory risks conflating biological predisposition with social convention. The productive middle ground is to treat sexual selection as one selective pressure among many, interacting with cultural evolution, economic structure, and institutional design to produce the observed diversity of human mating systems.