Behavior Genetics

, Volume 21, Issue 1, pp 75–96 | Cite as

Sexual orientation, sexual identity, and sex-dimorphic behaviors in male twins

  • Neil Buhrich
  • J. Michael Bailey
  • Nicholas G. Martin


Sexual orientation, sexual identity, and sex-dimorphic behaviors were assessed concurrently and retrospectively, for childhood, in 95 pairs of male monozygotic (MZ) twins and 63 pairs of dizygotic (DZ) twins. There was a significantly higher rate of adult homosexuality among the MZ than among DZ twins. We employed a model-fitting approach using LISREL to test for genetic and environmental influences on variation for each trait singly and on the covariation among all six traits (three for childhood and three for adulthood). Univariate analyses confirmed the presence of familial factors for five of the six variables but were generally unable to distinguish shared environmental from genetic influences. Hierarchial tests of multivariate models supported the existence of an additive genetic factor contributing to the covariance among the variables. More restrictive multivariate models yielded a significant genetic influence on sexual orientation. Because of the different rates of orientation by zygosity and because of the restrictive nature of some of the multivariate models, our results are best considered tentative but do suggest that further biometrically oriented studies of sexual orientation and its correlates would be worthwhile.

Key Words

sexual orientation twins heritability 


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Copyright information

© Plenum Publishing Corporation 1991

Authors and Affiliations

  • Neil Buhrich
    • 1
  • J. Michael Bailey
    • 2
  • Nicholas G. Martin
    • 3
  1. 1.Department of PsychiatrySt. Vincent's Hospital and University of New South WalesSydneyAustralia
  2. 2.Department of PsychologyNorthwestern UniversityEvanston
  3. 3.Queensland Institute of Medical ResearchBrisbaneAustralia

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