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Fisherian runaway: Difference between revisions
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[[File:Peacock courting peahen.jpg|alt=|thumb|"The females may be dull looking, but they're very picky." A peacock courting a peahen]] | [[File:Peacock courting peahen.jpg|alt=|thumb|"The females may be dull looking, but they're very picky." A peacock courting a peahen]] | ||
Fisherian runaway is a feedback loop occurring over many generations, in which the one sex (either male or female) becomes more choosy about a heritable trait for the simple reason that it will make the offspring more attractive. As the the choosiness for the trait increases, the selective pressure to prefer the trait increases too, forming a [https://en.wikipedia.org/wiki/Positive_feedback_loop positive feedback loop]. In response to the increased choosiness, the other sex evolves to enlarge, overcomplicate or beautify that trait in efforts of becoming more attractive. The exponential nature of positive feedback loops exerts a strong selection pressure that can, in theory, even overcome the selective pressure for survival itself and hence lead to extinction. For example, exaggerated traits may reduce mobility and increase vulnerability to predators and to sudden environmental changes. | Fisherian runaway is a feedback loop occurring over many generations, in which the one sex (either male or female) becomes more choosy about a heritable trait for the simple reason that it will make the offspring more attractive. As the the choosiness for the trait increases, the selective pressure to prefer the trait increases too, forming a [https://en.wikipedia.org/wiki/Positive_feedback_loop positive feedback loop]. In response to the increased choosiness, the other sex evolves to enlarge, overcomplicate or beautify that trait in efforts of becoming more attractive. The exponential nature of positive feedback loops exerts a strong selection pressure that can, in theory, even overcome the selective pressure for survival itself and hence lead to extinction. For example, exaggerated traits may reduce mobility and increase vulnerability to predators and to sudden environmental changes. | ||
=== Initiation === | |||
Such feedback loops can be initiated by arbitrary aesthetic selection, but also when a trait is slightly otherwise correlated with fitness (e.g. health), or when a trait is similar in appearance to attractive or otherwise valuable objects or body parts.<ref>Fuller, R. C., Houle, D., & Travis, J. 2005. ''Sensory Bias as an Explanation for the Evolution of Mate Preferences.'' [[https://www.jstor.org/stable/10.1086/444443 Abstract]], p. 444</ref> For example, women's breasts may have evolved to mimic their buttocks because the latter was already a sexually attractive body part before humans developed upright posture, and then Fisherian runaway may have lead to breasts becoming increasingly larger and increasingly attractive to men. | Such feedback loops can be initiated by arbitrary aesthetic selection, but also when a trait is slightly otherwise correlated with fitness (e.g. health), or when a trait is similar in appearance to attractive or otherwise valuable objects or body parts.<ref>Fuller, R. C., Houle, D., & Travis, J. 2005. ''Sensory Bias as an Explanation for the Evolution of Mate Preferences.'' [[https://www.jstor.org/stable/10.1086/444443 Abstract]], p. 444</ref> For example, women's breasts may have evolved to mimic their buttocks because the latter was already a sexually attractive body part before humans developed upright posture, and then Fisherian runaway may have lead to breasts becoming increasingly larger and increasingly attractive to men. | ||
=== Alternative explanation for ornament === | |||
Another mechanism that could explain exaggerated ornament and the immense sexual attraction to it, is [https://en.wikipedia.org/wiki/Handicap_principle Zahavi's handicap principle], also called the ''good genes hypothesis'' which claims that exaggerated ornament is a costly and hence reliable signal of other desirable traits. For example, a peacock with a very large tail would be easy prey (which is costly), and thus would most likely have other good traits that make up for this handicap (good genes). There is, however, little supporting scientific evidence. In humans in particular, beauty is not strongly correlated with health at all (only weakly), and even less with cognitive ability.<ref>https://incels.wiki/w/Scientific_Blackpill#Attractive_people_are_perceived_much_more_positively_than_they_really_are</ref> | |||
=== Summary === | |||
In summary, beauty could have evolved simply by sexual selection, i.e. mate selection favoring objective [[beauty]] (simplicity). But feedback loops as mentioned above may have exaggerated aspects of it, leading to increased sexual dimorphism and amplified and narrowed the attraction to specific kinds of beautiful phenotypes. This also stabilizes the phenotype, making it harder to adapt to environmental changes. Any sort of sexual dimorphism, whether behavioral or ornamental likely tends to get reinforced by such feedback loops because sexual dimorphism is inherently attractive.<ref>https://incels.wiki/w/Scientific_Blackpill#Even_chickens_prefer_sexually_dimorphic_human_faces.2C_to_the_same_extent_as_humans</ref> | In summary, beauty could have evolved simply by sexual selection, i.e. mate selection favoring objective [[beauty]] (simplicity). But feedback loops as mentioned above may have exaggerated aspects of it, leading to increased sexual dimorphism and amplified and narrowed the attraction to specific kinds of beautiful phenotypes. This also stabilizes the phenotype, making it harder to adapt to environmental changes. Any sort of sexual dimorphism, whether behavioral or ornamental likely tends to get reinforced by such feedback loops because sexual dimorphism is inherently attractive.<ref>https://incels.wiki/w/Scientific_Blackpill#Even_chickens_prefer_sexually_dimorphic_human_faces.2C_to_the_same_extent_as_humans</ref> | ||
Since females are [[Bateman's principle|more choosy]] in many species throughout the animal kingdom (including humans), the males tend to be more ornamented. | Since females are [[Bateman's principle|more choosy]] in many species throughout the animal kingdom (including humans), the males tend to be more ornamented. | ||
== Animal examples == | == Animal examples == | ||