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Opposite-Sex Twins and Adolescent Same-Sex Attraction 

We consider social, genetic, evolutionary, and hormonal transfer hypotheses for same-sex romantic preferences of adolescent (N=5,552) sibling pairs drawn from a nationally representative sample. We show that male but not female opposite-sex twins disproportionately report same-sex attraction; and that the pattern of concordance of same-sex preference among siblings is inconsistent with a simple genetic influence model. Our results provide substantial support for the role of social influences, reject the hormone transfer model, reject a speculative evolutionary theory, and are consistent with a general model that allows for genetic expression of same-sex attraction under specific, highly circumscribed, social conditions. Read More.