Sexually dimorphic 2D:4D ratio, height, weight, and their relation to number of sexual partners

The 2nd–4th finger length ratio (2D:4D) shows robust sexual dimorphism, with lower ratios evident in men compared to women. Several lines of evidence suggest that this sex difference is due to variable exposure to prenatal sex steroids in utero. Although not tested sufficiently, it has been suggested that 2D:4D may relate to sexual behaviour indices, in particular the number of sexual partners. However, this study did not find any significant relations between 2D:4D and number lifetime opposite-sex and same-sex partners in 159 men and 66 women. There were some associations between height, weight and number of sexual partners, but these appeared to be population-specific. There were also links between directional asymmetry and number of same-sex partners among ‘white’ men. Individual differences in developmental timing may uncouple 2D:4D from the sexual differentiation of other traits.