Sexual Selection

Sexual selection is the evolutionary mechanism by which traits evolve because they improve mating success rather than survival. Proposed by Darwin as a complement to natural selection, it explains the existence of costly, conspicuous traits — peacock tails, elk antlers, elaborate bird song — that would be eliminated by purely survival-based selection. The mechanism is not merely about who survives; it is about who reproduces, and the criteria for reproductive success are often set by the choosing sex, creating a feedback loop that can drive traits to spectacular extremes.

Sexual selection operates through two channels: intrasexual selection (competition among members of one sex for access to the other) and intersexual selection (mate choice, where one sex selects partners based on specific traits). Both channels generate runaway dynamics that can produce sexual dimorphism — systematic differences between males and females of a species that exceed what functional divergence alone would predict.