Intrasexual competition largely refers to evolved behavior that is targeted at outperforming same-sex conspecifics in competition for reproductive opportunities. E.g. people generally avoid making a fool out of themselves to avoid being outcompeted on grounds of having the reputation of a moron. One study showed winning wrestling fights increases reproductive success even when the wrestling fights are staged, and even the losers attain more reproductive success on average than non wrestlers. To avoid constant engagement in competition, many species have evolved a behavior in which the less dominant individual eventually surrenders and accepts his lower status, giving rise to dominance hierarchies.
Intrasexual competition can occur as direct competition, e.g. by physical violence and intimidation, gossip or bullying, or by indirectly by courtship which consists in the advertisement of the quality of one's genes to the opposite sex, especially genes that are under runaway sexual selection and involves impressing the opposite sex, e.g. by eliciting super stimuli in their brains. Male courtship additionally consists in signaling their willingness and ability to provide resources as women heavily depend on them, whereas female courtship consists only in displaying sexually selected dimorphic traits, beauty and adornment.
Presumably, adaptations for intrasexual competition drive much of human conflict. People go great lengths to save face, e.g. declare wars, which is presumably primarily an adaptation to evade intrasexually competitive gossip and maintain status. Such adaptations can explain accusations of gayness and other paraphilias and related forms of reputation denigration, which may even be a contributing factor in e.g. contemporary rape hysteria.
- Adolescent Bullying, Dating, and Mating: Testing an Evolutionary Hypothesis, Researchgate