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Sexual selection is a mode of natural selection where typically members of one gender choose mates of the other gender to mate with, called intersexual selection, and where females normally do the choosing, and competition between members of the same gender to sexually reproduce with members of the opposite sex, called intrasexual selection. These two forms of selection mean that some individuals have better reproductive success than others within a population either from being sexier or preferring sexier partners to produce offspring. For instance in the breeding season sexual selection in frogs occurs with the males first gathering at the water's edge and make their mating calls: croaking. The females then arrive and choose the males with the deepest croaks and best territories. Generalizing, males benefit from frequent mating and monopolizing access to a group of fertile females. Females have a limited number of offspring they can have and they maximize the return on the energy they invest in reproduction. First articulated by Charles Darwin who described it as driving speciation and that many organisms had evolved features whose function was deleterious to their individual survival, and then developed by Ronald Fisher in the early 20th century. Sexual selection can lead typically males to extreme efforts to demonstrate their fitness to be chosen by females, producing secondary sexual characteristics, such as ornate bird tails like the peacock plumage, or the antlers of deer, or the manes of lions, 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 sons, Fisher's principle explains why the sex ratio is 1:1 almost without exception. Sexual selection is also found in plants and fungi. The maintenance of sexual reproduction in a highly competitive world has long been one of the major mysteries of biology given that asexual reproduction can reproduce much more quickly as 50% of offspring are not males, unable to produce offspring themselves. However, research published in 2015 indicates that sexual selection can explain the persistence of sexual reproduction.〔(Population benefits of sexual selection explain the existence of males phys.org May 18, 2015 Report on a study by the University of East Anglia )〕 ==In organisms== * Sexual selection in birds - mammals - humans -scaled reptiles - amphibians - insects - spiders - major histocompatibility complex Sexual selection has been observed to occur in plants, animals and fungi.〔(Sexual selection in fugni Published by Journal of Evolutionary Biology )〕 In certain hermaphroditic snail and slug species of molluscs the throwing of love darts is a form of sexual selection.〔(Tales of two snails: sexual selection and sexual conflict in Lymnaea stagnalis and Helix aspersa Oxford Journals )〕 Certain male insects of the lepidoptera order of insects cement the vaginal pores of their females. Today, biologists say that certain evolutionary traits can be explained by intraspecific competition - competition between members of the same species - distinguishing between competition ''before'' or ''after'' sexual intercourse. *Before copulation, ''intrasexual selection'' - usually between males - may take the form of ''male-to-male combat''. Also, ''intersexual selection'', or ''mate choice'', occurs when females choose between male mates. Traits selected by male combat are called secondary sexual characteristics (including horns, antlers, etc.), which Darwin described as "weapons", while traits selected by mate (usually female) choice are called "ornaments". Due to their sometimes greatly exaggerated nature, secondary sexual characteristics can prove to be a hindrance to an animal, thereby lowering its chances of survival. For example, the large antlers of a moose are bulky and heavy and slow the creature's flight from predators; they also can become entangled in low-hanging tree branches and shrubs, and undoubtedly have led to the demise of many individuals. Bright colourations and showy ornamenations, such as those seen in many male birds, in addition to capturing the eyes of females, also attract the attention of predators. Some of these traits also represent energetically costly investments for the animals that bear them. Because traits held to be due to sexual selection often conflict with the survival fitness of the individual, the question then arises as to why, in nature, in which survival of the fittest is considered the rule of thumb, such apparent liabilities are allowed to persist. However, one must also consider that intersexual selection can occur with an emphasis on resources that one sex possesses rather than morphological and physiological differences. For example, males of ''Euglossa imperialis'', a non-social bee species, form aggregations of territories considered to be leks, to defend fragrant-rich primary territories. The purpose of these aggregations is only facultative, since the more suitable fragrant-rich sites there are, the more habitable territories there are to inhabit, giving females of this species a large selection of males with whom to potentially mate.〔Kimsey, Lynn Siri. "The behaviour of male orchid bees (Apidae, Hymenoptera, Insecta) and the question of leks." Animal Behaviour 28.4 (1980): 996-1004.〕 *After copulation, male–male competition distinct from conventional aggression may take the form of sperm competition, as described by Parker in 1970. More recently, interest has arisen in ''cryptic'' female choice,〔Eberhard, WG. (1996) ''Female control: Sexual selection by cryptic female choice.'' Princeton, Princeton University Press.〕 a phenomenon of internally fertilised animals such as mammals and birds, where a female will get rid of a male's sperm without his knowledge. Finally, sexual conflict is said to occur between breeding partners,〔Locke Rowe, Göran Arnvist. (2005) ''Sexual conflict'', Princeton Univ Press〕 sometimes leading to an evolutionary arms race between males and females. Sexual selection can also occur as a product of pheromone release, such as with the Stingless Bee, Trigona corvina. Female mating preferences are widely recognized as being responsible for the rapid and divergent evolution of male secondary sexual traits.〔Andersson M (1994). Sexual Selection. Princeton Univ Press, Princeton, NJ.〕 Females of many animal species prefer to mate with males with external ornaments - exaggerated features of morphology such as elaborate sex organs. These preferences may arise when an arbitrary female preference for some aspect of male morphology — initially, perhaps, a result of genetic drift — creates, in due course, selection for males with the appropriate ornament. One interpretation of this is known as the sexy son hypothesis. Alternatively, genes that enable males to develop impressive ornaments or fighting ability may simply show off greater disease resistance or a more efficient metabolism, features that also benefit females. This idea is known as the good genes hypothesis. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「sexual selection」の詳細全文を読む スポンサード リンク
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