Sex Differences in Early-Age Mortality: The Preconception Origins Hypothesis.

The preconception origins hypothesis holds that some of the preconception and prenatal environmental factors that have been shown to determine the offspring sex ratio also explain sex differences in early-age mortality (Pongou 2013). It extends and complements the biological hypothesis, which affirms that the mortality sex gap originates in biological and genetic differences between the sexes. As such, it offers a broad framework for understanding changes in male–female differences in early-age mortality across space and over time. I argue that this hypothesis is consistent with the concurrent increase in the proportion of female births and in the relative mortality of female to male infants in the United States since World War II.