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.
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.