Common genetic factors among sexual orientation, gender nonconformity, and number of sex partners in female twins: implications for the evolution of homosexuality. Journal of Sexual Medicine, 12 4 This benefit may consist of a "sex typicality" intermediate phenotype.
However, there are few empirical tests of this hypothesis using genetically informative data in humans. AIM: This study aimed to test the hypothesis that common genetic factors can explain the association between measures of sex typicality, mating success, and homosexuality in a Western British sample of female twins.
METHODS: Here, we used data from female twins twin pairs comprising full dizygotic pairs and full monozygotic pairs mean age Measures of sexual orientation, sex typicality recalled childhood gender nonconformity , and mating success number of lifetime sexual partners were completed.
RESULTS: We found that masculine women are more likely to be nonheterosexual, report more sexual partners, and, when heterosexual, also report more sexual partners.
Multivariate twin modeling showed that common genetic factors explained the relationship between sexual orientation, sex typicality, and mating success through a shared latent factor. These results may have implications for evolutionary models of homosexuality but are limited by potential mediating variables such as personality traits and measurement issues.
