Handedness and season of birth: A gender-invariant relation

In an earlier study, Dellatolas, Curt and Lellouch (1991) concluded that ha ndedness is not related to season of birth. However, post-hoc exploration o f their and other sets of data has shown that there is an apparent tendency for left-handedness to be more prevalent in the period March-July than in the period August-February. The present work tested this seasonal hypothesi s prospectively among university students. It was found that the proportion of all left-handed participants who were born in the period March-July was indeed significantly greater than the proportion of all right-handed parti cipants who were born in the same period. Furthermore, the pattern of seaso nal influence upon handedness did not vary significantly between females an d males. The relation between handedness and season of birth may be linked to seasonal variation in other factors such as the incidence of infectious agents.