Prenatal testosterone exposure and sexual dimorphism; the relationship between second to fourth digit ratio, sexual-orientation and spatial abilities.

Background: second (2D) to fourth (4D) digit ratio is a crude anthropometric index of prenatal testosterone exposure and is a sexually dimorphic trait with men tending to have a lower digit ratio than females. Similarly, the difference between right-hand and left-hand 2D:4D ratios (Dr-l) is sexually dimorphic with males tending to have negative values. Numerous studies have investigated the association between 2D:4D ratios and a range of testosterone balance influenced traits and conditions including spatial ability and sexual-orientation although discrepancies exist within the literature. Objectives: To measure and calculate 2D:4D ratios and (Dr-l) values. Establish whether correlations exist between ratios and sexual orientation and spatial abilities. Methods: 65 volunteers participated in this project. Digit measurements were taken using digital vernier callipers. Ethnicity, hand-dominance and sexual-orientation were established through questionnaires. The Santa Barbra solids test assessed spatial ability. Participants were separated according to gender (males n=26, females n=39) and further sub-grouped with regards to ethnicity, hand-dominance and sexual-orientation. Results: Digit ratios were significantly lower in male right hand ratios and Dr-l values compared to females. Although consistent with regards to gender, ethnicity appeared to be a significant covariate. 2D:4D ratios do not appear to be an index of sexual-orientation or spatial abilities. Conclusion: Right hand 2D:4D ratios and Dr-l values are sexually dimorphic. Demographic limitations may be accountable for the lack of correlation between digit ratios and sexual orientation. There are no correlations between digit ratios and spatial abilities. Key Words: 2D:4D, Dr-l, prenatal testosterone, sexual-orientation, spatial abilities, sexual dimorphismbsc_humunpub2152_ethesesunpu