Etiology of male sexual orientation in an Australian twin sample

Abstract

Previous studies investigating the etiology of male homosexuality have found evidence for familial aggregation of male homosexuality. However, most of these have used highly selected samples, leading to the possibility that the results obtained are due to volunteer biases. The data analysed here consist of anonymous responses to a questionnaire on sexual behaviour and attitudes obtained from a large community-based sample of Australian male twins aged 18-52. Significant heritabilities were observed for a range of psychological and behavioural measures (orientation of present sexual feelings and fantasies, ever having been sexually attracted to a man, attitude to homosexual sex, number of male and female sexual partners), with approximately 42 to 60 per cent of observed variance estimated to be due to genetic influences in these variables. Familial aggregation was also observed in other measures (sexual behaviour in the past twelve months, attitude to heterosexual sex) but it was not possible to determine ...