a large twin registry, Bailey, Dunne and Martin (2000)—pioneers in the research on causal factors of homosexuality—refuted their earlier findings of fairly large concordance rates, stating that they failed to find a significant genetic influence on homosexual orientation (Jones & Kwee, 2005). This does not mean that genetics do not play some role in sexual orientation; it means that the exact role is inconclusive, is most likely small, is ill defined in terms of “underlying mechanisms,” and is one