Sex and ethnic differences in 2nd to 4th digit ratio of children

Background: The ratio between the length of the 2nd or index finger and the 4th or ring finger (2D:4D) differs between the sexes, such that males have lower 2D:4D than females, and shows considerable ethnic differences, with low values found in Black populations. It has been suggested that the sex difference in 2D:4D arises early in development and that finger ratio is a correlate of prenatal testosterone and oestrogen. In children, 2D:4D has been reported to be associated with measures of-fetal growth, congenital adrenal hyperplasia, developmental psychopathology, autism and Asperger's syndrome. However, little is known of the patterns of sex and ethnic differences in the 2D:4D ratio of children. Aim: To investigate sex and ethnic differences in 2D:4D in Caucasian, Oriental and Black children. Study design: Population survey. Method: The 2D:4D ratio was measured from photocopies of the right hand of Berber children from Morocco, Uygur and Han children from the North-West province of China, and children from Jamaica. Results: There were 798 children in the total sample (90 Berbers, 438 Uygurs, 118 Han, and 152 Jamaicans). The 2D:AD ratio was lower in males than in females and this was significant for the overall sample and for the Uygur, Han and Jamaican samples. There were significant ethnic differences in 2D:4D. The Oriental Han had the highest mean 2D:4D, followed by the Caucasian Berbers and Uygurs, with the lowest mean ratios found in the Afro-CaribbeanJamaicans. The sex and ethnic differences were independent of one another with no significant interaction effect. In the overall sample there were no associations between 2D:4D and age and height. Conclusions: In common with adults, the 2D:4D ratio of children shows sex and ethnic differences with low values found in a Black group. There was no overall association between 2D:4D and age and height suggesting that the sex and ethnic differences in 2D:4D appear early and do not show appreciable change with growth. (C) 2004 Elsevier Ireland Ltd. All rights reserved.