Sexual dimorphism in the ontogeny of second (2D) and fourth (4D) digit lengths, and digit ratio (2D:4D)

ObjectiveSex differences are often reported in digit lengths and digit ratio (2D:4D). However, the ontogeny of these sex differences and their interrelationships are less well known. MethodsWe considered sex differences in the lengths of the 2nd (2D) and 4th (4D) digit and 2D:4D in children aged 2 to 18 years (Sample I, n=680) and adults aged 18 to 30 years (Sample II, n=89,246). Digit length was determined by direct experimenter-measurement (Sample I) and direct self-measurement (Sample II). The data were tested with two-factor ANOVA's (sex and year-group). ResultsIn both samples, there were significant main effects of sex and year-group, and a significant interaction effect on digit length. Digit length was positively related to age in both samples. Boys had longer digits than girls but only after 13 years. Men had longer digits than women and the dimorphism increased from 18 to 30 years. There were significant sex differences in 2D:4D (males