Sexual selection facts for kids
Sexual selection is a special kind of natural selection. It is a theory of Charles Darwin that certain traits can be explained by competition within a species.
Darwin defined sexual selection as the effects of the "struggle between the individuals of one sex, generally the males, for the possession of the other sex". It is usually males who fight each other. Traits selected by male combat are called secondary sexual characteristics (including horns, antlers, etc.) and sometimes referred to as 'weapons'. Traits selected by mate choice are called 'ornaments'.
Females often prefer to mate with males with external ornaments—exaggerated features of morphology. 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. Sexual selection is still being researched and discussed today.
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Modern views
Ernst Mayr said:
- "Since Darwin’s days it has become clear that this kind of selection includes a far wider realm of phenomena, and instead of sexual selection it is better referred to as selection for reproductive success... genuine selection, not elimination, is involved, unlike survival selection. Considering how many new kinds of selection for reproductive success are discovered year after year, I am beginning to wonder whether it is not even more important than survival selection, at least in certain higher organisms".
Competition between members of the same species
Today, biologists would say that certain evolutionary traits can be explained by competition between members of the same species. Competition can be before or after mating.
Competition between males and females
- Before mating, 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".
- After mating, male–male competition may take the form of sperm competition, the competition between the sperm of two different males to fertilize an ovum. in 1970. More recently, interest has arisen in cryptic female choice, where a female will get rid of a male's sperm without his knowledge. This occurs in a wide range of species.
Related pages
Images for kids
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Sexual selection creates colourful differences between sexes (sexual dimorphism) in Goldie's bird-of-paradise. Male above; female below. Painting by John Gerrard Keulemans
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Sexual selection protected flour beetles from extinction in a ten-year experiment.
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The peacock tail in flight, the proposed classic example of a Fisherian runaway
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Male mountain gorilla, a species with very large males
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Protarchaeopteryx was flightless, but had feathers, perhaps used in courtship, that pre-adapted it for flight.
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Among mammals, the male gorilla is much larger than female.
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Males of many spiders, such as this Phidippus putnami, have elaborate courtship displays.
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A male Abedus indentatus belostomatid bug carries eggs on its back.
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Each firefly species attracts mates with its own flash pattern.
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Male Dendropsophus microcephalus calling
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Territorial fight in the Indian rat snake, Ptyas mucosa
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Male Victoria's riflebird displaying to a female
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A male satin bowerbird guards its bower from rival males in the hope of attracting females with its decorations.
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Male southern elephant seals fighting on Macquarie Island for the right to mate
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Citronella flower's symmetry may have been subject to sexual selection by its pollinators.
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See also
In Spanish: Selección sexual para niños
