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.
Contents
Darwin’s Theory
Charles Darwin introduced the concept in The Descent of Man, and Selection in Relation to Sex (1871). He observed that some traits:
- Do not directly aid survival (e.g., bright colors could attract predators).
- Increase mating opportunities, either by:
- Competing with rivals (intrasexual selection).
- Attracting the opposite sex (intersexual selection).
Mechanisms
Intrasexual Selection
Refers to competition within a sex.
Definition: Members of one sex (usually males) compete for access to the other sex.
Traits favored:
- Weapons (e.g., antlers, horns, large body size).
- Aggressive behaviors (e.g., fighting, territorial displays).
Examples:
- Male elephant seals fighting for dominance.
- Stag beetles using mandibles in combat.
Intersexual Selection
Refers to mate choice.
Definition: One sex (often females) chooses mates based on desirable traits.
Traits favored:
- Ornaments (e.g., bright feathers, elaborate dances).
- Indicators of good genes (e.g., symmetry, health).
Examples:
- Peahens selecting peacocks with the most elaborate tails.
- Bowerbirds building intricate nests to impress females.
Why does sexual selection lead to exaggerated traits?
- Some traits (like a peacock’s tail) are costly to maintain, signaling genetic fitness. Only the strongest individuals can afford these "handicaps," proving their quality.
- If females prefer a trait (e.g., long tails), males with longer tails get more mates. Over generations, the trait becomes more extreme (runaway selection).
- Certain traits (e.g., bright colors) indicate health and parasite resistance. Females choose these males to pass on superior genes to offspring.
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
