∞ generated and posted on 2016.09.10 ∞
Biased reproductive success that results from variation in access to potential mates.
For sexual organisms, sexual access to mates is essential for fitness and access often can require what is essentially permission from a potential mate before mating can commence. Alternatively, such access can require that one first fight or otherwise compete with members of one's own gender.
Permission often can involve judgment of the attractiveness of a potential mate and, as a consequence, natural selection tends to favor those organisms which are most attractive to potential mates. Which gender is affected often depends on how much energy and effort the choosing gender has to put into the raising of offspring, with greater discrimination tending to be associated with greater costs stemming from choosing poorly. See intersexual selection.
Fighting can require large body size or various weapons, often resulting in the evolution of sexual dimorphism. See intrasexual selection. See also prezygotic barriers such as those associated with behavioral isolation.
Sexual selection is most notable (and noticeable) when the results are adaptations that seemingly run counter to the carrier's survival, such as the peacock's tail. That counter intuitiveness, however, can actually be the point, where certain genders essentially are handicapped so that those with less than ideal genes are less able to survive than the otherwise might be.
That is, the selecting gender is not necessarily selecting for arbitrary features so much as aspects that can be good indicators of overall Darwinian fitness. Similarly, attractiveness often is dependent on traits that tend to degrade given poor nutrition or excessive parasite loads, again providing not so much arbitrary features as robust indicators of healthfulness as well as the potential to survive.