Sexual selection
Sexual selection is evolutionary change driven by differences in mating and fertilization success. It helps explain ornaments, weapons, displays, mate choice, competition, and sexual dimorphism.
What sexual selection is
Sexual selection is a form of selection in which reproductive success differs because of access to mates or fertilizations. A trait can spread if it helps an individual win contests, attract partners, secure matings, or have gametes that succeed, even when the trait is costly in other ways.
Why it is different
Natural selection is often described in terms of survival and reproduction in an environment. Sexual selection focuses on the reproductive part more directly: who mates, how often, with whom, and with what fertilization success. The two processes can reinforce each other or pull in different directions.
Mate choice
Mate choice occurs when individuals prefer partners with certain signals, behaviors, or conditions. Songs, colors, dances, scents, ornaments, territories, gifts, and displays can all become targets of choice. Preferences may track health, species identity, compatibility, sensory bias, or inherited preferences.
Competition for mates
Competition can involve direct fights, threat displays, territory defense, sperm competition, mate guarding, or social dominance. Antlers, horns, larger body size, strong jaws, and other weapons often reflect contests among individuals competing for reproductive access.
Sexual dimorphism
Sexual dimorphism means that males and females of a species differ in traits beyond the reproductive organs themselves. Size, color, ornamentation, behavior, and weaponry may differ because the sexes face different reproductive pressures. The pattern is not always male-biased; some species show reversed or more complex roles.
Costs and tradeoffs
Sexually selected traits can be expensive. A bright color may attract predators, a display may consume energy, and a weapon may be costly to grow. These costs matter because selection acts on total reproductive success, not on beauty or strength alone. Traits persist only when benefits outweigh costs in a given context.
Runaway and conflict
In some cases, a preference and a display trait can reinforce each other across generations, producing exaggerated ornaments. Sexual selection can also create conflict when the reproductive interests of mates differ. These dynamics can influence behavior, anatomy, physiology, and sometimes speciation.
Why it matters
Sexual selection matters because it explains traits that survival-focused stories miss. It links behavior, ecology, genetics, development, and reproduction, and it helps scientists understand biodiversity, mating systems, sex differences, animal signals, and how populations can diverge over time.