Fisher's principle

Fisher's principle is an evolutionary model that explains why the sex ratio of most species that produce offspring through sexual reproduction is approximately 1:1 between males and females. A. W. F. Edwards has remarked that it is "probably the most celebrated argument in evolutionary biology".^[1]

Fisher's principle was outlined by Ronald Fisher in his 1930 book The Genetical Theory of Natural Selection^[2] (but has been incorrectly attributed as original to Fisher^[1]). 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.^[3]^[4]

^ ^a ^b Cite error: The named reference Edwards98 was invoked but never defined (see the help page).
^ Cite error: The named reference Fisher30 was invoked but never defined (see the help page).
^ Cite error: The named reference Hamilton67 was invoked but never defined (see the help page).
^ Charnov, E., and Bull, J. (1989). "Non-fisherian sex ratios with sex change and environmental sex determination", Nature 338, pp. 148–150. https://doi.org/10.1038/338148a0 Retrieved 29 March 2022.

[Edwards98-1] Cite error: The named reference Edwards98 was invoked but never defined (see the help page).

[Fisher30-2] Cite error: The named reference Fisher30 was invoked but never defined (see the help page).

[Hamilton67-3] Cite error: The named reference Hamilton67 was invoked but never defined (see the help page).

[4] Charnov, E., and Bull, J. (1989). "Non-fisherian sex ratios with sex change and environmental sex determination", Nature 338, pp. 148–150. https://doi.org/10.1038/338148a0 Retrieved 29 March 2022.

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