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runaway hypothesis

runaway hypothesis A hypothesis proposed by R. A.Fisher in 1930 to explain the consequences of female selection of a particular male trait (e.g. the length of the tail in a bird). Over successive generations such selection would favour increasingly extreme development of the trait (i.e. the tails of males would become longer) until the fitness of the male was reduced. (This tendency has been demonstrated experimentally by shortening or lengthening the tails of male birds.) Eventually, males would be so overspecialized as to bring the species to extinction, were it not for the restraining influence of natural selection, which halts the development before that stage can be reached. See also handicap principle.

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