Dermatoglyphic analysis of total finger ridge count in female monozygotic twins discordant for sexual orientation

Abstract

This study was designed to test the hypothesis that prenatal environment contributes to the development of sexual orientation in females. The research involved a dermatoglyphic analysis of finger ridge count in two groups of female monozygotic twins: a study group which was discordant for sexual orientation, and a control group which was concordant for sexual orientation. The trait, total finger ridge count, was analyzed using the Wilcoxon matched pair statistic. In the female control group ridge counts were not significantly different. However, for the female twins discordant for sexual orientation, the null hypothesis was rejected (T = 0; p ≤ .01), with the lesbian twins showing a consistent trend for lower total finger ridge counts than their heterosexual cotwins. It is concluded that in females, prenatal environmental differences are correlated with differences in sexual orientation, and that second trimester prenatal environment is likely to be a contributing factor in the etiology of this trait.