Literature describing environmental influences on human conception and gestation implies that the ratio of male to female live births should vary positively over time with the population's ability to produce and distribute goods and services. No direct test of this hypothesis appears in the literature despite its apparent importance in understanding the biological implications of collective choices. We offer a test based on Swedish data for the years 1862 through 1991. The results support the hypothesis. We argue that the findings have implications for basic science as well as for the debate over the biological effects of social policy.