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BACKGROUND: Digit ratio (2D:4D) from soft-tissue measurements of fingers from children and adults from Black and White ethnic groups show sex differences (males

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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:4D 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-Caribbean Jamaicans. 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.

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There is evidence that the ratio of the length of the 2nd and 4th digit (2D:4D) is negatively related to prenatal and adult concentrations of testosterone. It has also been reported that high levels of testosterone at conception in both fathers and mothers are associated with an increased sex ratio (proportion of males at birth). It follows from these observations that low values of 2D:4D may be related to high sex ratio. We present evidence from three populations (English, Spanish and Jamaican) that 2D:4D is negatively related to sex ratio, independent of the sex and ethnicity of the parents.

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Testosterone, particularly prenatal testosterone, has been implicated in the aetiology of many extragenital sexually dimorphic traits. It is difficult to test directly for the effect of prenatal testosterone in humans. However, Manning, Scutt, Wilson, and Lewis-Jones (1998b) have recently shown that the ratio of the length of the 2nd and 4th digits (2D:4D) in right hands negatively predicts testosterone levels in men. As digit ratios are fixed in utero it may be that the 2D:4D ratio is associated with many prenatally determined sexually dimorphic traits. We tested this for one case by examining the relationship between lateralised hand performance (LHP), as measured by an Annett peg board, and 2D:4D ratio in rural Jamaican children. 2D:4D ratio was measured from photocopies and X rays of hands. A low 2D:4D ratio in the right hand of boys and girls (photocopies) and the right hand of boys only (X rays) was associated with a reduction in rightward performance asymmetry. In both samples the difference in 2D:4D ratio between the hands (2D:4D left hand-2D:4D right hand) showed the strongest relationship with LHP i.e. high ratio in the left and low in the right correlated with a tendency towards a fast performance with the left hand. It is suggested that the 2D:4D ratio may be associated with the expression of other sexually dimorphic behavioural traits.

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Fluctuating asymmetry, small deviations from perfect bilateral symmetry, is negatively correlated with health and positively correlated with sexual selection in human adults, but the accumulation, persistence, and fitness implications of asymmetries during childhood are largely unknown. Here, we introduce the Jamaican Symmetry Project, a long-term study of fluctuating asymmetry and its physical and behavioral correlates in rural Jamaican children. The project is based on an initial sample of 285 children (156 boys and 129 girls), aged 5 to 11 years. We describe the design of the project and the methodology of measuring 10 paired morphometric traits. All traits except hand width showed fluctuating asymmetry. Fluctuating asymmetries of the legs tended to be related and were less than half as great as fluctuating asymmetries of the arms and ears. Therefore the legs may show high developmental stability resulting from selection for mechanical efficiency. A fluctuating asymmetry composite score revealed that boys have significantly lower fluctuating asymmetry than girls and that this effect resides mainly in the elbows. There were significant positive relationships between composite fluctuating asymmetry and age, height, and weight, but multiple regression analyses showed that age was negatively related to fluctuating asymmetry, whereas body size was positively correlated. These findings are compared with results from recent English studies.

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Fluctuating asymmetry, small deviations from perfect bilateral symmetry, is negatively correlated with health and positively correlated with sexual selection in human adults, but the accumulation, persistence, and fitness implications of asymmetries during childhood are largely unknown. Here, we introduce the Jamaican Symmetry Project, a long-term study of fluctuating asymmetry and its physical and behavioral correlates in rural Jamaican children. The project is based on an initial sample of 285 children (156 boys and 129 girls), aged 5 to 11 years. We describe the design of the project and the methodology of measuring 10 paired morphometric traits. All traits except hand width showed fluctuating asymmetry. Fluctuating asymmetries of the legs tended to be related and were less than half as great as fluctuating asymmetries of the arms and ears. Therefore the legs may show high developmental stability resulting from selection for mechanical efficiency. A fluctuating asymmetry composite score revealed that boys have significantly lower fluctuating asymmetry than girls and that this effect resides mainly in the elbows. There were significant positive relationships between composite fluctuating asymmetry and age, height, and weight, but multiple regression analyses showed that age was negatively related to fluctuating asymmetry, whereas body size was positively correlated. These findings are compared with results from recent English studies (Au)

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