The ratio of 2nd to 4th digit length and male homosexuality

• Published in: Ethology and Sociobiology 2000-09, Vol.21 (5), p.333-345
• Main Authors: Robinson, S.J, Manning, J.T
• Format: Article
• Language: English
• Subjects: 2nd:4th digit ratio; Birth order; Correlation; Edinburgh; Ethology; Homosexuality; Hormones; Human genetics; Liverpool; London; Male homosexuality; Men; Sociobiology; United Kingdom; Whites
• ISSN: 1090-5138; 0162-3095; 1879-0607
• DOI: 10.1016/S1090-5138(00)00052-0

Sexual orientation may be influenced by prenatal levels of testosterone and oestrogen. There is evidence that the ratio of the length of 2nd and 4th digits (2D:4D) is negatively related to prenatal testosterone and positively to oestrogen. We report that (a) 2D:4D was lower in a sample of 88 homosexual men than in 88 sex- and age-matched controls recruited without regard to sexual orientation, (b) within the homosexual sample, there was a significant positive relationship between mean 2D:4D ratio and exclusive homosexuality, (c) overall, there was a decrease in 2D:4D from controls to homosexual men to bisexual men and (d) fraternal birth order, a positive predictor of male homosexuality, was not associated with 2D:4D in a sample of 240 Caucasian men recruited without regard to sexual orientation and 45 homosexual men. Further work is needed to confirm the relationships between 2D:4D and sexual orientation. However, these and other recent data tend to support an association between male homosexuality and high fetal testosterone. Very high testosterone levels may be associated with a sexual preference for both men and women.