Scientists at the University of Padova offer a resolution to the parodox of heritable homosexuality: homosexuality, in males at least, is [obviously] not an adaptation that ensures the survival of genes, but the side effect of one.

Andrea Camperio-Ciani and colleagues argue genetic factors favouring homosexual male offspring could make women more fertile. "Our data resolve this paradox by showing that there might be, hitherto unsuspected, reproductive advantages associated with male homosexuality," they said.

They looked at 98 homosexual and 100 heterosexual men and their relatives, which included more than 4,600 people overall.

The female relatives on the mother's side of the homosexual men tended to have more offspring than the female relatives on the father's side.

This suggests that these women who, in theory, pass on the gay trait to their male offspring are also more fertile.

In comparison, the female relatives on both the mother's and the father's side of the heterosexual men did not appear to be as fertile, having fewer offspring.