Hand preference and skill in 115 children of two left-handed parents.

Abstract

A second sample of children of L × L parents resembled a first sample (Annett, 1974) in the distribution of hand preferences and of hand skill. The mean difference between the hands in skill (L—R) was slightly but not significantly biased in favour of the right hand and 31 per cent were sinistral writers. Three tests were made on the combined samples of the hypotheses, derived from the right shift (RS) theory of handedness (Annett, 1972), that the L — R skills of the majority are not biased to either side, but that some are biased to the right hand like controls, in spite of being reared by two left‐handed parents. Children with a possibly pathologically sinistral parent, and children in families where neither left‐handed parent had a close sinistral relative, resembled controls more closely than the remaining children. The L — R distribution was compatible with expectations for three genotypes, as expected if the RS depends on a single gene (Annett, 19786).Analyses for sex differences found sons and daughters alike for hand, eye and foot preferences and for L—R skill. Analyses of reports of developmental problems of speech, reading, writing or spelling found an excess of affected males over females smaller than expected in the general population. The incidences of such reports in the sons and daughters of L × L families were almost identical, with incidences reported for the fathers and mothers, respectively, of dyslexics (Annett & Kilshaw, 19826). The findings were consistent with the view that sex differences in hand preferences, L — R skill and the risk of developmental language problems in the general population are all due to the more effective expression of the rs + gene in females than males, and that the gene is more often absent in the children of L × L families than in the general population.