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Sexual dimorphism in the ontogeny of second (2D) and fourth (4D) digit lengths, and digit ratio (2D:4D)
Author(s) -
Manning John T.,
Fink Bernhard
Publication year - 2018
Publication title -
american journal of human biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.559
H-Index - 81
eISSN - 1520-6300
pISSN - 1042-0533
DOI - 10.1002/ajhb.23138
Subject(s) - numerical digit , digit ratio , ontogeny , sexual dimorphism , biology , evolutionary biology , arithmetic , mathematics , zoology , genetics , testosterone (patch)
Objective Sex 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. Methods We 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). Results In 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 < females), but no significant effect of age and no interaction effect of age and sex on 2D:4D in children or adults. Conclusions Between 2 and 30 years, the lengths and the sexual dimorphisms of 2D and 4D are dependent on age. In contrast, 2D:4D is not age‐dependent. We discuss our findings in the context of the ontogeny of digits and in the light of recent claims on the presence of static allometry in 2D and 4D lengths.