Sexual selection

Sexual selection is the theory that competition for mates between individuals of the same sex (typically males) drives the evolution of certain traits. Within a species, one sex (typically females) acts as a limiting resource for the other (typically males). Competition over the limiting sex results in sexual selection. It is distinct from ecological selection which is the competition for other limiting resources within the species' ecological niche.

Intrasexual and intersexual selection

Sexual selection takes two major forms: intrasexual selection (aka Male-male competition) in which members of the less limiting sex (typically males) compete aggressively between themselves for access to the more limiting sex, and intersexual selection (aka female choice) in which males compete with each other to be chosen by females.

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:The sexual struggle is of two kinds: in the one it is between the individuals of the same sex, generally the males, in order to drive away or kill their rivals, the females remaining passive; while in the other, the struggle is likewise between the individuals of the same sex, in order to excite or charm those of the opposite sex, generally the females, which no longer remain passive, but select the more agreeable partners. --Charles Darwin, 1871.

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In addition to direct aggression, male-male competition may take the form of sperm competition.

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Typically however, sexual selection refers to the process of female choice.

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