|
Fisher's principle is an evolutionary model that explains why the sex ratio of most species which produce offspring through sexual reproduction is approximately 1:1 between males and females. It was famously outlined by Ronald Fisher in his 1930 book ''The Genetical Theory of Natural Selection''〔 (but incorrectly attributed to Fisher as original〔). Nevertheless, A. W. F. Edwards has remarked that it is "probably the most celebrated argument in evolutionary biology". Specifically, Fisher couched his argument in terms of parental expenditure, and predicted that parental expenditure on both sexes should be equal. Sex ratios that are 1:1 are hence known as "Fisherian", and those that are not 1:1 are "non-Fisherian" or "extraordinary" and occur because they break the assumptions made in Fisher's model.〔 Many eusocial wasps, such as the ''Polistes fuscatus'' and the ''Polistes exclamans'' seem to exhibit such a ratio at times. == Basic explanation == W.D. Hamilton gave the following basic explanation in his 1967 paper on "Extraordinary sex ratios", given the condition that males and females cost equal amounts to produce: :# Suppose male births are less common than female. :# A newborn male then has better mating prospects than a newborn female, and therefore can expect to have more offspring. :# Therefore parents genetically disposed to produce males tend to have more than average numbers of grandchildren born to them. :# Therefore the genes for male-producing tendencies spread, and male births become more common. :# As the 1:1 sex ratio is approached, the advantage associated with producing males dies away. :# The same reasoning holds if females are substituted for males throughout. Therefore 1:1 is the equilibrium ratio. In modern language, the 1:1 ratio is the evolutionarily stable strategy (ESS). In a population of individuals playing the ESS (i.e. producing equal numbers of sons and daughters), any other strategy (e.g. 51% sons and 49% daughters) would have lower fitness, and hence would be selected against. 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「Fisher's principle」の詳細全文を読む スポンサード リンク
|