Abstract
Birth seasonality is a phenomenon that characterizes almost all the populations of the world. In spite of this, the causes underlying these seasonal fluctuations represent an as yet unsolved puzzle. Two main theoretical approaches have been proposed to explain birth seasonality. The first encompasses a social explanation and emphasizes the role of social, economic and cultural factors in determining the optimal moment (from a social perspective) for conception (e.g., according to the cycle of agricultural workload, religious festivity, marriage seasonality, etc.). The second theoretical approach encompasses an environmental explanation and focuses on the role that climatic factors (e.g., temperature, rainfall, light intensity, etc.) play in determining the optimal moment of conception from a biological perspective. Our paper may be collocated in the latter strand of the literature. The aim is to investigate the effects of temperature on conceptions, and subsequently on the seasonality of livebirths, while controlling for a possible social confounding effect, i.e. the seasonal pattern of marriage. To achieve this end, we empirically investigate the role of temperature as well as that of marriage seasonality in Italian regions for the period stretching from the Italian unification to the eve of World War II. We find that extreme temperatures (both cold and hot) negatively affect the number of births. At the same time, marriage seasonality also seems to be an important explicative factor of the seasonal fluctuation of live births.
Highlights
Birth seasonality characterizes almost all the populations of the world (Lam and Myron 1991, 1994; Doblhammer et al 1999)
Regarding the nine-months lagged monthly indicator of marriages, we find that a one percentage point increase in marriage seasonality leads to an approximate 0.05% increase in the seasonal indicators of live births
This means that extreme temperatures negatively affect the number of births
Summary
Birth seasonality characterizes almost all the populations of the world (Lam and Myron 1991, 1994; Doblhammer et al 1999). Following Roenneberg and Aschoff (1990), one may argue that the decline in seasonality observed in the US by Lam and Myron (1994) could be, at least in part, explained by the capillary diffusion of artificial light or by heating and air conditioning system which have equalized the number of hours of exposure to light across the year and reduced the influence of temperature (cf Condon 1991).1 This explanation is based on the idea that there exists an optimal period for reproduction for humans. When the body senses that day-length is decreasing after 23 September the process is aborted, whereas it is allowed to proceed after 21 March”
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