Effects of season of birth on reproduction in contemporary humans: brief communication.

BACKGROUND At high latitudes the external environment varies with season, and therefore the season of birth may contribute to the developmental processes during the perinatal period. METHODS We investigated the association between birth season and measures of reproductive performance (offspring count, percentage childless individuals) in a contemporary sample of women and men. RESULTS In the male sample (n = 2342), men born in autumn had fewer offspring (mean 1.4 versus 1.62; P < 0.01) and a higher probability of remaining childless (32.6% versus 25.6%; P = 0.01) than men born in spring. The photoperiod at a male's birth was significantly positively correlated with his subsequent offspring count (P = 0.023). In the female sample, an association between birth season and reproduction was not found. CONCLUSIONS We assume that in men, among other seasonal factors, pre- or perinatal photoperiod might be involved in the underlying physiological mechanism.