Evolution & Human Behavior
Volume 29, Issue 6 , Pages 424-433, November 2008

Genetic factors predisposing to homosexuality may increase mating success in heterosexuals

  • Brendan P. Zietsch

      Affiliations

    • Genetic Epidemiology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia
    • Corresponding Author InformationCorresponding author. Tel.: +61 7 33620169; fax: +61 7 66950101.
  • ,
  • Katherine I. Morley

      Affiliations

    • Genetic Epidemiology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia
  • ,
  • Sri N. Shekar

      Affiliations

    • Genetic Epidemiology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia
  • ,
  • Karin J.H. Verweij

      Affiliations

    • Genetic Epidemiology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia
  • ,
  • Matthew C. Keller

      Affiliations

    • Institute of Behavior Genetics, University of Colorado, Boulder, CO, USA
  • ,
  • Stuart Macgregor

      Affiliations

    • Genetic Epidemiology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia
  • ,
  • Margaret J. Wright

      Affiliations

    • Genetic Epidemiology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia
  • ,
  • J. Michael Bailey

      Affiliations

    • Department of Psychology, Northwestern University, Evanston, IL, USA
  • ,
  • Nicholas G. Martin

      Affiliations

    • Genetic Epidemiology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia

Received 21 April 2008; received in revised form 1 July 2008 published online 19 August 2008.

Abstract 

There is considerable evidence that human sexual orientation is genetically influenced, so it is not known how homosexuality, which tends to lower reproductive success, is maintained in the population at a relatively high frequency. One hypothesis proposes that while genes predisposing to homosexuality reduce homosexuals' reproductive success, they may confer some advantage in heterosexuals who carry them. However, it is not clear what such an advantage may be. To investigate this, we examine a data set where a large community-based twin sample (N=4904) anonymously completed a detailed questionnaire examining sexual behaviors and attitudes. We show that psychologically masculine females and feminine men are (a) more likely to be nonheterosexual but (b), when heterosexual, have more opposite-sex sexual partners. With statistical modelling of the twin data, we show that both these relationships are partly due to pleiotropic genetic influences common to each trait. We also find a trend for heterosexuals with a nonheterosexual twin to have more opposite-sex partners than do heterosexual twin pairs. Taken together, these results suggest that genes predisposing to homosexuality may confer a mating advantage in heterosexuals, which could help explain the evolution and maintenance of homosexuality in the population.

Keywords: Homosexuality, Sexual orientation, Genetic, Environmental, Mating success, Evolution, Antagonistic pleiotropy, Darwinian paradox, Heritability, Gender identity, Masculinity, Femininity

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 This research was funded by a small grant to J.M.B. from the US National Institute of Mental Health and a small Commonwealth AIDS Research Grant to N.G.M.

PII: S1090-5138(08)00068-8

doi:10.1016/j.evolhumbehav.2008.07.002

Evolution & Human Behavior
Volume 29, Issue 6 , Pages 424-433, November 2008