Left-handedness as a function of sex, maternal versus paternal inheritance, and report bias.
The right-shift (RS) theory suggests that sex differences for handedness are due to the displacement of a chance distribution of asymmetry farther to the right in females than males by about 20%. An analysis of studies in the literature shows that when handedness is assessed by self-report, paired samples of males and females differ for incidence of left-handedness as predicted, but for parents assessed by indirect-report, there are fewer left-handed mothers than expected. When handedness is assessed by self-report in both generations, the RS genetic model successfully predicts the distribution in families. It is also successful at different levels of criterion from left-writing to non-right-handedness. The RS predictions are not always consistent with the findings of studies that depended on indirect report of parental handedness. When parental incidences are low the proportion of left-handed children in the families of left-handed mothers is higher than expected. When parental incidences are high, predictions for the families of left-handed mothers are excellent, but the percentage of left-handed children in the families of left-handed fathers is lower than expected. Data for all indirect-report studies are combined to test the idea that the chief cause of poor fit is underreporting of left-handed mothers by right-handed children. Transfer of right-handed children from R x R to R x L families, thereby raising the percentage of left-handed mothers by about 1%, is sufficient to give good fits to RS predictions for both sexes.
Department of Psychology, University of Leicester, UK. "M.Annett">doc@le.ac.uk
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Annett
D000328:Adult; D015982:Bias; D002648:Child; D004292:Dominance, Cerebral / Q000235:genetics*; D005260:Female; D007839:Functional Laterality / Q000235:genetics*; D006801:Humans; D008297:Male; D008957:Models, Genetic; D010641:Phenotype; D014960:X Chromosome; D014998:Y Chromosome