A TWIN REGISTRY STUDY OF MALE AND FEMALE SEXUAL ORIENTATION

Monozygotic (MZ), same-sex dizygotic (DZ) and opposite-sex (OS) twins from the Twin Minnesota Twin Registry responded to a sexual orientatio n survey. Using the relative frequencies of heterosexuals, bisexuals, and homosexuals responding to the survey and generalizing these freque ncies to the entire Registry, the prevalence of bisexuality among wome n was estimated as 1.58% and among men, 2.08%. For homosexuality, prev alence rates for women and men were 1.68% and 2.49%, respectively. Hom osexual and heterosexual attraction, behavior, and self-identification were significantly more heritable in women than men. For men, no sign ificant genetic effects were found for number of opposite- and same-se x sexual encounters, nor for sexual orientation. No evidence was found for different genes influencing the sexual orientation of men and wom en.