page_title: Fluctuating asymmetry
section_title: Mate attraction
hierarchical_section_title: Fluctuating asymmetry / In sexual selection / Mate attraction
caption_attribution_description: Panorpa japonica
context_page_description: As a form of biological asymmetry, fluctuating asymmetry, along with anti-symmetry and direction asymmetry, refers to small, random deviations away from perfect bilateral symmetry. This deviation from perfection is thought to reflect the genetic and environmental pressures experienced throughout development, with greater pressures resulting in higher levels of asymmetry. Examples of FA in the human body include unequal sizes of bilateral features in the face and body, such as left and right eyes, ears, wrists, breasts, testicles, and thighs.
  Research has exposed multiple factors that are associated with FA. As measuring FA can indicate developmental stability, it can also suggest the genetic fitness of an individual. This can further have an effect on mate attraction and sexual selection, as less asymmetry reflects greater developmental stability and subsequent fitness. Human physical health is also associated with FA. For example, young men with greater FA report more medical conditions than those with lower levels of FA. Multiple other factors can be linked to FA, such as intelligence and personality traits.
context_section_description: Symmetry has been shown to affect physical attractiveness. Those with lower levels of fluctuating asymmetry (FA) are often rated as more attractive. Various studies have supported this. The relationship between FA and mate attraction has been studied in both males and females. As FA reflects developmental stability and quality, it has been suggested that we prefer those as more attractive/with low FA because it signals traits such as health and intelligence.
  Research has shown that the female partners of men with lower levels of FA experience a higher number of copulatory orgasms, compared to the female partners of males with higher levels of FA. Other studies have also found that the voices of men and women with low fluctuating asymmetry are rated as more attractive, suggesting that voice may be indicative of developmental stability. Research has shown attractiveness ratings of men's scent are negatively correlated with FA, but FA is unrelated to attractiveness ratings for women's scent, and women's preferences for the scent of more symmetric men appears limited to the most fertile phases of the menstrual cycle. However, research has failed to find changes in women's preferences for low FA across the menstrual cycle when assessing pictures of faces, as opposed to scents. Facial symmetry has been positively correlated with higher occurrences of mating. Also, one study used 3-D scans of male and female bodies, and showed videos of these scans to a group of individuals who rated the bodies on attractiveness. It was found that, for both males and females, lower levels of FA were associated with higher attractiveness ratings. It was also found that sex-typical joint configurations were rated as more attractive and linked to lower FA in men, but not women. Men with higher FA have been shown to have higher levels of oxidative stress and lower levels of attractiveness. Research has also provided evidence that FA is linked to extra-pair copulation, as women have been shown to prefer men with lower levels of FA as extra-pair partners. However, the literature is mixed regarding the relationship between attractiveness and FA. For example, in one study, altering images of faces to in a way that reduced asymmetry led to observers rating such faces as less, rather than more, attractive. Research by Van Dongen also found FA to be unrelated to attractiveness, physical strength and level of masculinity in both men and women.
caption: FA in Japanese scorpionflies (Panorpa japonica) is linked to fighting and mating success.
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