title: Heritable factors influence sexual orientation in women.
abstract: Homosexual female probands with monozygotic cotwins, dizygotic cotwins, or adoptive sisters were recruited using homophile publications. Sexual orientation of relatives was assessed either by asking relatives directly, or, when this was impossible, by asking the probands. Of the relatives whose sexual orientation could be confidently rated, 34 (48%) of 71 monozygotic cotwins, six (16%) of 37 dizygotic cotwins, and two (6%) of 35 adoptive sisters were homosexual. Probands also reported 10 (14%) nontwin biologic sisters to be homosexual, although those sisters were not contacted to confirm their orientations. Heritabilities were significant using a wide range of assumptions about both the base rate of homosexuality in the population and ascertainment bias. The likelihood that a monozygotic cotwin would also be homosexual was unrelated to measured characteristics of the proband such as self-reported history of childhood gender nonconformity. Concordant monozygotic twins reported similar levels of childhood gender nonconformity.
authors.affiliation: Department of Psychology, Northwestern University, Evanston, Ill 60208.
authors.forename: J M
authors.initials: JM
authors.lastname: Bailey
authors.forename: R C
authors.initials: RC
authors.lastname: Pillard
authors.forename: M C
authors.initials: MC
authors.lastname: Neale
authors.forename: Y
authors.initials: Y
authors.lastname: Agyei
mesh_terms: D000300:Adoption; D000328:Adult; D001727:Bisexuality / Q000706:statistics & numerical data; D005260:Female; D005824:Genetics, Behavioral; D006716:Homosexuality / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D008875:Middle Aged; D008957:Models, Genetic; D012737:Sex Factors; D012725:Sexual Behavior / Q000502:physiology / Q000706:statistics & numerical data; D014429:Twins, Dizygotic / Q000706:statistics & numerical data; D014430:Twins, Monozygotic / Q000706:statistics & numerical data