Global Patterns of Seasonal Variation in Human Birth Rates - Influence of Climate and Economic and Social Factors

The frequency of live births exhibit seasonal variation in almost all human populations, but the causes of this variation are not fully understood. Currently, data on the pattern of births is not available for all regions. At least in highly developed countries, a decrease in seasonal variation has been observed. The present investigation examined the effect of fertility and seasonality in 38 countries in the Northern and Southern hemispheres. A marked differentiation was discovered in the seasonality of births between the hemispheric regions, as well as variations at dissimilar latitudes. The seasonality in the Southern hemisphere is the opposite of that in the Northern hemisphere, and the further south a region in the Northern hemisphere is, the later in the year the birth peak occurs. Although the variation in birth rates is greater in less developed countries than in highly developed ones and greater in Islamic than in Christian nations, the pattern of birth seasonality is braodly comparable. The present study suggests that the main influences on fertility seasonality are related to climatic conditions. The impacts of the economic situation and religion were rather small, but indicate that the correlation between the number of births and the season of the year decreases as the standard of living increases. To establish causality between births and seasons, more data on the living conditions of the population in each region are needed than were available for the current study.