Maternal inheritance and familial fecundity factors in male homosexuality.

This study, following Camperio-Ciani, Corna, and Capiluppi [(2004), Proceedings of the Royal Society of London, Series B, Biological Sciences, 271, 2217-2221] aimed to examine the familial history of male homosexuality, and test the so-called "fertile female" hypothesis for this trait in a contemporary British sample. Using a comparative survey design, we found that white (comprising those of Anglo-European descent) and non-white (comprising ethnic "Blacks, "South Asians," "East Asians," "Hispanics," and "Others") homosexual men (n = 147) had a significant excess of maternal but not paternal line male homosexual relatives compared to heterosexual men (n = 155). We also found significantly elevated fecundity of maternal aunts of white homosexual men compared to white heterosexual men, whereas non-white heterosexual men showed elevated fecundities of almost every class of relative compared to non-white homosexual men. No significant excess of older brothers was found in homosexual compared to heterosexual men, irrespective of ethnic grouping. These data were discussed in relation to possible population-related factors in evolutionary explanations for human male homosexuality.