Handedness trends across age groups in a Japanese sample of 2316

Hand-preference data of 2316 Japanese were analyzed by age groups, sex, and familial sinistrality. Right-hand preference increased across age groups at least up to 30 years for men, while women showed relatively stable and stronger preference for right-hand use. Unlike some Western studies, no linear trends across age groups were found for both sexes. Declining cultural censorship against left-handedness would not be responsible for the trends, since there was no evidence indicating such a decline in Japan. Hypotheses of reduced longevity and life-long adaptation to the right-handed world are not satisfactory either, since both hypotheses assume a linear trend spanning the entire life span. Thus, it seems that a single-factor hypothesis which explains all the results by resorting to a single cause does not account for the complex results found in this and other studies.