Differences in the Quality of Semen in Outdoor Workers during Summer and Winter

To the Editor: The article by Levine et al. (July 5 issue)¹ on differences in the quality of semen during the summer and winter misstates the demographic evidence on the seasonality of births and conceptions. Contrary to the authors' assertions, demographers have not “repeatedly noted reductions in the birth rate during spring in nonequatorial regions with warm climates.” In fact, two major seasonal patterns have been identified: a North American pattern, in which there is a decline in the rate of conception in the summer (and hence a drop in the spring birth rate), and a European pattern, in which.