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.

Facial averageness and genetic quality: testing heritability, genetic correlation with attractiveness, and the paternal age effect

“…In previous papers, we computed objective scores of facial sexual dimorphism from the facial photographs and also had them rated for subjective facial masculinity/femininity (for further detail, see Lee et al, 2014; Mitchem et al, 2013). When comparing these scores with facial averageness scores calculated here, we found no significant association with either objective sexual dimorphism ( r = -.05, CI = -.13, .03, and r = .02, CI = -.06, .12 for males and females respectively) nor rated facial masculinity/femininity ( r = .03, CI = -.04, .10, and r = -.01, CI = -.08, .05 for males and females respectively).…”

“…Participants were 1698 twin individuals (304 monozygotic (MZ) twin pairs, 479 dyzygotic (DZ) twin pairs) and 125 of their siblings from 913 families who took part in either the Brisbane Adolescent Twin Studies (BATS, N = 1321) located in Queensland, Australia (Wright & Martin, 2004) or from the Longitudinal Twin Study (LTS, N = 502) located in Colorado, USA (Mitchem et al, 2013; Rhea, Gross, Haberstick, & Corley, 2013). For participants who were part of BATS, twins were tested (and photographs taken) as close as possible to their 16 th birthday ( M = 16.03 years, SD = .46 years) and their siblings as close as possible to their 18 th birthday ( M = 17.67 years, SD = .1.22).…”

“…Facial attractiveness ratings computed from only male and only female raters correlated very highly with facial attractiveness computed from all raters (r = .94 for male raters and r = .93 for females); given the high concordance, and that the facial attractiveness scores from all raters contained substantially less measurement error, we used this score for all analyses. For more detail on the rating process and further analyses of observer ratings, see Mitchem et al (2013).…”

Genetic Factors That Increase Male Facial Masculinity Decrease Facial Attractiveness of Female Relatives

“…(See the Supplemental Material available online for details of the analysis.) For more detail on the rating process and genetic analyses of observer ratings, see Mitchem et al (2013).…”

“…However, no objective measures of masculinity were used, and heritability could not be estimated because members of a standard nuclear family equally share both genes and family environment, which are therefore completely confounded. In another study, Mitchem et al (2013) used facial photos of monozygotic (identical) and dizygotic (nonidentical) twins to distinguish the influence of genes and family environment on facial masculinity and attractiveness; again, however, no objective measures were used. It has been shown previously that subjective ratings of masculinity are based on additional factors other than morphological masculinity, which changes the association with traits such as attractiveness (Scott, Pound, Stephen, Clark, & Penton-Voak, 2010).…”