Birth order, birth stress and handedness.

Left-handed and right-handed parents in personally visited families were asked about the perinatal history of themselves, and their children. Reported birth stress (RBS) was as frequent for right-handers as for left-handers. The children of left-handed mothers were not more likely to have RBS than the children of right-handed mothers. The incidence of RBS was greater for first borns than children of later birth rank. A weak trend to a higher proportion of birth ranks 1st and 4th + among left- than right-handers was found for daughters, but not for fathers, mothers or sons. Empirical and theoretical objections to the hypothesis that pathology of the left hemisphere is a major determinant of left-handedness are reviewed.