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Information regarding age, sex, birth stress, and handedness was obtained form 762 university faculty members and 1869 undergraduate and medical students, who also provided age, sex, and handedness information for their first-degree relatives. In addition, students reported the occupations and educational levels of their parents. Analyses of the effects of birth order, reported birth stress, and maternal, paternal, and joint parental age showed that an increased incidence of sinistrality was only rarely associated with high birth risk; in all cases, the effects were confined to male subjects, most frequently male faculty members. Sinistrality was not associated with low socioeconomic status; on the contrary, there were significantly more sinistrals among parents of high than of low educational and occupational levels. The pathogenic hypothesis has other implications which fail to find support in the current literature, thus casting further doubt on the proposition that all sinistrality is pathological in origin.