Editing Sexual selection (section)

{{Short description|Mode of natural selection involving the choosing of and competition for mates}}
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{{Use British English|date=June 2015}}
[[File:Paradesia decora Keulemans.jpg|thumb|250px|Sexual selection creates colourful [[sexual dimorphism|differences between sexes]] in [[Goldie's bird-of-paradise]]. Male above; female below. Painting by [[John Gerrard Keulemans]].|alt=painting of male and female birds of paradise]]

'''Sexual selection''' is a mechanism of [[evolution]] in which members of one [[sex]] [[mate choice|choose mates]] of the other sex to [[mating|mate]] with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex (intrasexual selection). These two forms of selection mean that some individuals have greater [[reproductive success]] than others within a [[population]], for example because they are more [[Animal sexual behaviour|attractive]] or prefer more attractive partners to produce [[offspring]]. Successful males benefit from frequent mating and monopolizing access to one or more fertile females. Females can maximise the return on the energy they invest in reproduction by selecting and mating with the best males.

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The concept was first articulated by [[Charles Darwin]] who wrote of a "second agency" other than [[natural selection]], in which competition between mate candidates could lead to speciation. The theory was given a mathematical basis by [[Ronald Fisher]] in the early 20th century. Sexual selection can lead males to extreme efforts to demonstrate their [[fitness (biology)|fitness]] to be chosen by females, producing [[sexual dimorphism]] in [[secondary sexual characteristic]]s, such as the ornate [[plumage]] of [[birds-of-paradise]] and [[peafowl]], or the antlers of [[deer]]. Depending on the species, these rules can be reversed. This is caused by a [[positive feedback]] mechanism known as a [[Fisherian runaway]], where the passing-on of the desire for a trait in one sex is as important as having the trait in the other sex in producing the runaway effect. Although the [[sexy son hypothesis]] indicates that females would prefer male offspring, [[Fisher's principle]] explains why the [[sex ratio]] is most often 1:1. 
Sexual selection is widely distributed in the animal kingdom, and is also found in [[Sexual selection in flowering plants|plants]] and [[Sexual selection in fungi|fungi]].