Archives of Sexual Behavior

, Volume 22, Issue 3, pp 187-206

First online:

Homosexual orientation in twins: A report on 61 pairs and three triplet sets

  • Frederick L. WhitamAffiliated withDepartment of Sociology, Arizona State University
  • , Milton DiamondAffiliated withDepartment of Anatomy and Reproductive Biology, John A. Burns School of Medicine, University of Hawaii
  • , James MartinAffiliated withDepartment of Sociology, Arizona State University

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Twin pairs in which at least one twin is homosexual were solicited through announcements in the gay press and personal referrals from 1980 to the present. An 18-page questionnaire on the “sexuality of twins” was filled out by one or both twins. Thirty-eight pairs of monozygotic twins (34 male pairs and 4 female pairs) were found to have a concordance rate of 65.8% for homosexual orientation. Twenty-three pairs of dizygotic twins were found to have a concordance rate of 30.4% for homosexual orientation. In addition, three sets of triplets were obtained. Two sets contained a pair of monozygotic twins concordant for sexual orientation with the third triplet dizygotic and discordant for homosexual orientation. A third triplet set was monozygotic with all three concordant for homosexual orientation. These findings are interpreted as supporting the argument for a biological basis in sexual orientation.

Key words

homosexuality twins triplets sexual orientation genetics