Right- and left-hand skill I: Effects of age, sex and hand preference showing superior skill in left-handers.

Hand preference and hand skill were examined in relation to sex and age from 3 1/2 to 50+ years. The data were drawn from several samples which avoided volunteer bias, either by selecting children according to birth-date or by taking complete class groups. The distribution of hand preference and of asymmetry of skill gave no evidence of systematic changes with age. Younger children were more variable and showed larger absolute differences in favour of the right hand than older children but L-R times were similar over most of the age range. Time for peg moving decreased with increasing age to a minimum in the late teens, remained stable for the next three decades and increased slightly in the 50+ age group. Males were faster than females with the left hand in almost all age groups. Females tended to be faster than males with the right hand up to 10 years of age but males then equalled and surpassed females, to be faster in most older groups. Correlations between hands did not vary systematically with age or sex. Left-handers were faster than right-handers and right mixed-handers were intermediate for peg-moving time by the non-preferred hand, in both sexes and both sets of samples. Differences for the preferred hand were less clear but still favoured left-handers in several comparisons. The findings raise the possibility that left hemisphere specialization for language is achieved through a right hemisphere handicap and that left-handers escape this risk to cerebral efficiency.