\[ **up: [[Sex (Biology)]]** ] --- # Examples of systems with more than two sexes (Biology) [[2025-0313. 'Fisher’s observation that ‘the sexes are, in fact always two’ might have been premature.'|'Fisher’s observation that ‘the sexes are, in fact always two’ might have been premature.']][^1] --- ## Theoretical Modelling [[2025-0313. For systems with more than two sexes, 'the genetic dynamics then depend on a rule, called mating kinetics, which determines the proportion of matings between each pair of sexes for given proportions of cells of the three sexes.'|For systems with more than two sexes, 'the genetic dynamics then depend on a rule, called mating kinetics, which determines the proportion of matings between each pair of sexes for given proportions of cells of the three sexes.']][^2] [[2025-0313. 'Of the four mating kinetics examined, two give a large advantage to rare sexes whose cells quickly find heterosexual partners, which implies an evolutionary increase in the number of sexes.'|'Of the four mating kinetics examined, two give a large advantage to rare sexes whose cells quickly find heterosexual partners, which implies an evolutionary increase in the number of sexes.']][^3] [[2025-0313. 'In contrast, the other two mating kinetics, in which gametes wait for suitable mates without being eliminated from the gamete pool during this waiting period, produce neutrally stable dynamics with curves or a surface of equilibria.'|'In contrast, the other two mating kinetics, in which gametes wait for suitable mates without being eliminated from the gamete pool during this waiting period, produce neutrally stable dynamics with curves or a surface of equilibria.']][^4] [[2025-0313. '... the number of sexes should increase when conjugal cells must find mates during a limited period of time, otherwise a two‐sex system should evolve.'|'... the number of sexes should increase when conjugal cells must find mates during a limited period of time, otherwise a two‐sex system should evolve.']][^5] [[2025-0313. '... the number of sexes should increase when conjugal cells must find mates during a limited period of time, otherwise a two‐sex system should evolve.'|'... there may be more isogamous species with three or more sexes than are currently known.']][^6] --- ## Pecking-order dominance system [[2025-0313. 'The WXY system in platyfish (Bull, 1983) is a three-sex pecking-order dominance system in which mating between the first and the third sex is not allowed.'|'Many non-XY systems observed in higher animals can also be regarded as a modification of the pecking-order dominance system.']][^7] [[2025-0313. 'The WXY system in platyfish (Bull, 1983) is a three-sex pecking-order dominance system in which mating between the first and the third sex is not allowed.'|'For example, the WXY system in platyfish (Bull, 1983) is a three-sex pecking-order dominance system in which mating between the first and the third sex is not allowed.']][^8] --- ## XY systems ### Examples #### African Pygmy Mouse: Male (XY) + Female (XX, XX* & X\*Y) See: [[African pygmy mouse#Four sexes (or naturally occurring sex reversal)|African pygmy mouse: four sexes (or, naturally occurring sex reversal)]] --- ## Non-XY systems ### Examples #### WXY System [[2025-0313. 'The WXY system in platyfish (Bull, 1983) is a three-sex pecking-order dominance system in which mating between the first and the third sex is not allowed.'|'For example, the WXY system in platyfish (Bull, 1983) is a three-sex pecking-order dominance system in which mating between the first and the third sex is not allowed.']][^9] [^1]: J. D. Parker, ’[[Parker. ‘A major evolutionary transition to more than two sexes’, 2004.|A major evolutionary transition to more than two sexes?]]’, *Trends in Ecology & Evolution*, vol. 19, issue 2 (2004), p. 83. [^2]: Yoh Iwasa and Akira Sasaki, ‘[[Iwasa & Sasaki. ‘Evolution of the number of sexes’, 1987.|Evolution of the number of sexes]]’, *Evolution* 41, Issue 1, 1 January 1987, p. 49. [^3]: Yoh Iwasa and Akira Sasaki, ‘[[Iwasa & Sasaki. ‘Evolution of the number of sexes’, 1987.|Evolution of the number of sexes]]’, *Evolution* 41, Issue 1, 1 January 1987, p. 49. [^4]: Yoh Iwasa and Akira Sasaki, ‘[[Iwasa & Sasaki. ‘Evolution of the number of sexes’, 1987.|Evolution of the number of sexes]]’, *Evolution* 41, Issue 1, 1 January 1987, p. 49. [^5]: Yoh Iwasa and Akira Sasaki, ‘[[Iwasa & Sasaki. ‘Evolution of the number of sexes’, 1987.|Evolution of the number of sexes]]’, *Evolution* 41, Issue 1, 1 January 1987, p. 49. [^6]: Yoh Iwasa and Akira Sasaki, ‘[[Iwasa & Sasaki. ‘Evolution of the number of sexes’, 1987.|Evolution of the number of sexes]]’, *Evolution* 41, Issue 1, 1 January 1987, p. 49. [^7]: Yoh Iwasa and Akira Sasaki, ‘[[Iwasa & Sasaki. ‘Evolution of the number of sexes’, 1987.|Evolution of the number of sexes]]’, *Evolution* 41, Issue 1, 1 January 1987, p. 59. [^8]: Yoh Iwasa and Akira Sasaki, ‘[[Iwasa & Sasaki. ‘Evolution of the number of sexes’, 1987.|Evolution of the number of sexes]]’, *Evolution* 41, Issue 1, 1 January 1987, p. 59. [^9]: Yoh Iwasa and Akira Sasaki, ‘[[Iwasa & Sasaki. ‘Evolution of the number of sexes’, 1987.|Evolution of the number of sexes]]’, *Evolution* 41, Issue 1, 1 January 1987, p. 59.