Sex ratios in the two Germanies: a test of the economic stress hypothesis.

BACKGROUND Literature describing temporal variation in the secondary sex ratio among humans reports an association between population stressors and declines in the odds of male birth. Explanations of this phenomenon draw on reports that stressed females spontaneously abort male more than female fetuses, and that stressed males exhibit reduced sperm motility. This work has led to the argument that population stress induced by a declining economy reduces the human sex ratio. No direct test of this hypothesis appears in the literature. Here, a test is offered based on a comparison of the sex ratio in East and West Germany for the years 1946 to 1999. The theory suggests that the East German sex ratio should be lower in 1991, when East Germany's economy collapsed, than expected from its own history and from the sex ratio in West Germany. METHODS The hypothesis is tested using time-series modelling methods. RESULTS The data support the hypothesis. The sex ratio in East Germany was at its lowest in 1991. CONCLUSION This first direct test supports the hypothesis that economic decline reduces the human sex ratio.