Background: It has been suggested that both adult sexual orientation and the 2nd to 4th finger length ratio (2D:4D) are influenced by prenatal testosterone levels. Bearing this in mind, 2D:4D has been tested as a proxy measure of the putative prenatal testosterone impact on adult human homosexuality, but the results are inconsistent. To date, most studies in this field of research comprise categorical group comparison of heterosexuals and homosexuals with respect to their 2D:4D.
Aims: The purpose of our study was to evaluate 2D:4D and the dimensional perspective of sexual orientation in addition to categorical results.
Methods: We examined a community-based sample of 409 subjects and calculated correlations of 2D:4D and sexual orientation as a continuum ranging from homosexual to heterosexual.
Results: We found a significant negative correlation of 2D:4D with homosexual orientation (fantasy, attraction, activity and general score) in women, but not in men.
Conclusions: Our results indicate that with higher prenatal testosterone levels in women, the likelihood of homosexual orientation might increase. We hypothesize a continuous neurohormonal sexual differentiation of the brain, most notably for women, that overrides categories and results in varying dimensions of sexual orientation. This hypothesis contrasts with the predominant suggestion of fixed organizational effects of androgens in the brain and a categorical sexual orientation.