Estimating the sex-specific effects of genes on facial attractiveness and sexual dimorphism

Abstract

Human facial attractiveness and facial sexual dimorphism (masculinity-femininity) are important facets of mate choice and are hypothesized to honestly advertise genetic quality. However, it is unclear whether genes influencing facial attractiveness and masculinity-femininity have similar, opposing, or independent effects across sex, and the heritability of these phenotypes is poorly characterized. To investigate these issues, we assessed facial attractiveness and facial masculinity-femininity in the largest genetically informative sample (n = 1,580 same- and opposite-sex twin pairs and siblings) to assess these questions to date. The heritability was ~0.50-0.70 for attractiveness and ~0.40-0.50 for facial masculinity-femininity, indicating that, despite ostensible selection on genes influencing these traits, substantial genetic variation persists in both. Importantly, we found evidence for intralocus sexual conflict, whereby alleles that increase masculinity in males have the same effect in females. Additionally, genetic influences on attractiveness were shared across the sexes, suggesting that attractive fathers tend to have attractive daughters and attractive mothers tend to have attractive sons.

Fig. 1

Competing evolutionary models of cross-sex genetic correlations in Attractiveness and Masculinity–femininity. a Intralocus sexual conflict model: signs (+/−) of genetic correlations indicate that genes increasing sexual attractiveness in one sex decrease it in the other. b Sex-limited model: only the genetic effects on Attractiveness are shared between the sexes; all other genetic correlations are 0. c Sex reversal model: signs of all cross-sex genetic correlations indicate that genes increasing sexual attractiveness in one sex also increase it in the other. Subscript F indicates female phenotypes and additive genetic factors, subscript M those for males

Fig. 1

Competing evolutionary models of cross-sex genetic correlations in Attractiveness and Masculinity–femininity. a Intralocus sexual conflict model: signs (+/−) of genetic correlations indicate that genes increasing sexual attractiveness in one sex decrease it in the other. b Sex-limited model: only the genetic effects on Attractiveness are shared between the sexes; all other genetic correlations are 0. c Sex reversal model: signs of all cross-sex genetic correlations indicate that genes increasing sexual attractiveness in one sex also increase it in the other. Subscript F indicates female phenotypes and additive genetic factors, subscript M those for males

Fig. 2

Results of the bivariate model of Attractiveness and Masculinity–femininity. A₁ and A₂ are additive genetic factors of Masculinity–femininity and Attractiveness, respectively; E₁ and E₂ are non-shared environmental factors. Path coefficients on the straight arrows are the factor loadings [95 % CI] and are equivalent to the square root of the additive genetic variances (heritabilities) and environmental variances reported in the text. Genetic and environmental correlations [95 % CI] are on the curved arrows connecting two different A or E factors. Note: Cross-sex genetic correlations (labeled R) do not include adjustment for 50 % genetic identity by descent between DZOS twins. a Results using Attractiveness and Masculinity–femininity ratings not controlled for Grooming, Acne, Smiling, or BMI. b Results using Attractiveness and Masculinity–femininity ratings controlled for Grooming, Acne, Smiling, and BMI

Fig. 2

Results of the bivariate model of Attractiveness and Masculinity–femininity. A₁ and A₂ are additive genetic factors of Masculinity–femininity and Attractiveness, respectively; E₁ and E₂ are non-shared environmental factors. Path coefficients on the straight arrows are the factor loadings [95 % CI] and are equivalent to the square root of the additive genetic variances (heritabilities) and environmental variances reported in the text. Genetic and environmental correlations [95 % CI] are on the curved arrows connecting two different A or E factors. Note: Cross-sex genetic correlations (labeled R) do not include adjustment for 50 % genetic identity by descent between DZOS twins. a Results using Attractiveness and Masculinity–femininity ratings not controlled for Grooming, Acne, Smiling, or BMI. b Results using Attractiveness and Masculinity–femininity ratings controlled for Grooming, Acne, Smiling, and BMI