Objective: In recent years, studies regarding the biological etiology of homosexuality have focused on the sexually dimorphic development of the brain during fetal life. Prenatal testosterone may play an important role for the differentiation of the brain and sexual orientation (1). Based on this view, homosexuality may be caused by inadequate testosterone levels during the development of the brain. Moreover, prenatal testosterone levels are thought to masculinize 2nd to 4th finger length ratio (2D:4D) as well as other sexually dimorphic features. Women usually have a higher 2D:4D than men. Thus the aim of the present study was to evaluate 2nd to 4th finger length ratio (2D:4D) that is claimed to indirectly reşect the effects of prenatal testosterone levels on brain in homosexual male individuals.
Methods: The study included 40 men aged 18-35 years, who defined themselves as homosexual and 40 men aged 18-34 years, who defined themselves as heterosexual. A personal questionnaire, which is developed by our group and involved some sociodemographic data of subjects, and Bem Sexual Role Inventory (BSRI) (2) were applied in both groups. Both hands of all participants were copied by using a standard copier and an electronic digital caliper with a 0.01 mm precision were used for the measurements of the digits. Second and fourth finger lengths of each hand were measured from the baseline up to the tip of the finger on the copy. The ratios were obtained by dividing the length of 2nd finger to that of the 4th.
Results: When gay men were compared to heterosexual men, BSRI femininity and masculinity scores of gay men were significantly higher and lower than those of heterosexual men, respectively. The lengths of the 2nd and the 4th fingers at right and left hands of the homosexual men were found to be shorter than those measured in the heterosexual men. However, no significant difference was found in 2D: 4D ratios of both groups.
Conclusion: The lack of significant difference in 2D:4D ratios of the groups does not support the hypothesis in the literature suggesting that 2D:4D ratio reşects the effects of prenatal testosterone levels.