Seasonality of births in human populations.

ABSTRACT

PIP: Reviewing leading hypotheses on the seasonality of births in human populations, the authors find no 1 explanation to be supported by existing data. Births are highly seasonal in all human populations, with great variation in the timing of seasonal patterns across populations. Available literature estimates birth seasonality for many countries and time periods, but differing methodologies and the frequent use of small populations pose obstacles to comparing patterns across populations. This paper's estimates of seasonal patterns document major regularities and unify existing estimates to come to the above conclusions about the ubiquity of birth seasonality. This conclusion and basic facts about births seasonality are presented in the paper. No simple rule exists to describe and/or predict which seasonal patterns of births particular populations will exhibit. Dramatic and puzzling differences exist between countries and time periods in the pattern of seasonal variation, making much of the determinants of birth seasonality an unresolved mystery of empirical demography. Questions abound for both the biological and behavioral research of fertility. 2 effects noted as most consistent with seasonal patterns, however, are weather and leisure time due to holidays. To better understand the determinants of birth seasonality, the authors advise the use of variables other than births, employing more disaggregated data sets, and explicitly accounting for multivariate explanations.