Common Genetic Factors among Sexual Orientation, Gender Nonconformity, and Number of Sex Partners in Female Twins: Implications for the Evolution of Homosexuality. (25th February 2015)

• Record Type: Journal Article
• Authors: Burri, Andrea; Spector, Tim; Rahman, Qazi
• Is Part Of: Journal of sexual medicine. Volume 12:Number 4(2015:Apr.)
• Page Start: 1004
• Page End: 1011
• Publication Date: 2015-02-25
• Subjects: Sexual disorders -- Periodicals; Sex -- Periodicals; Sexual health -- Periodicals; 616.69005
• DOI: 10.1111/jsm.12847
• Languages: English
• ISSNs: 1743-6095

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <sec id="jsm12847-sec-0001" sec-type="section"> <title>Introduction</title> <p>Homosexuality is a stable population‐level trait in humans that lowers direct fitness and yet is substantially heritable, resulting in a so‐called Darwinian "paradox." Evolutionary models have proposed that polymorphic genes influencing homosexuality confer a reproductive benefit to heterosexual carriers, thus offsetting the fitness costs associated with persistent homosexuality. 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.</p> </sec> <sec id="jsm12847-sec-0002" sec-type="section"> <title>Aim</title> <p>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.</p> </sec> <sec id="jsm12847-sec-0003" sec-type="section"> <title>Methods</title> <p>Here, we used data from 996 female twins (498 twin pairs) comprising 242 full dizygotic pairs and 256 full monozygotic pairs (mean age 56.8) and 1, 555 individuals whose co‐twin did not participate. Measures of sexual orientation, sex typicality (recalled childhood gender nonconformity), and mating success (number of lifetime sexual partners) were completed.</p> </sec> <sec id="jsm12847-sec-0004" sec-type="section"> <title>Main Outcome Measure</title> <p>Variables were subject to multivariate variance component analysis.</p> </sec> <sec id="jsm12847-sec-0005" sec-type="section"> <title>Results</title> <p>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.</p> </sec> <sec id="jsm12847-sec-0006" sec-type="section"> <title>Conclusions</title> <p>Our findings suggest that genetic factors responsible for nonheterosexuality are shared with genetic factors responsible for the number of lifetime sexual partners via a latent sex typicality phenotype in human females. These results may have implications for evolutionary models of homosexuality but are limited by potential mediating variables (such as personality traits) and measurement issues. <bold>Burri A, Spector T, and Rahman Q. Common Genetic Factors among Sexual Orientation, Gender Nonconformity, and Number of Sex Partners in Female Twins: Implications for the Evolution of Homosexuality. J Sex Med 2015;12:1004–1011.</bold></p> </sec> </abstract>