The 2nd : 4th digit ratio and asymmetry of hand performance in Jamaican children

Testosterone, particularly prenatal testosterone, has been implicated in th e aetiology of many extragenital sexually dimorphic traits. It is difficult to test directly for the effect of prenatal testosterone in humans. Howeve r, 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 n egatively 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 de termined sexually dirnorphic traits. We tested this for one case by examini ng the relationship between lateralised hand performance (LI-IP), as measur ed by an Annett peg board, and 2D:4D ratio in rural Jamaican children. 2D:4 D ratio was measured from photocopies and X rays of hands. A low 2D:4D rati o in the right hand of buys and girls (photocopies) and the right hand of b oys 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 L HP i.e. high ratio in the left and low in the right correlated with a tende ncy towards a fast performance with the left hand. II is suggested that the 2D:4D ratio may be associated with the expression of other sexually dirnor phic behavioural traits.