Male lifespan and the secondary sex ratio.

Literature speculating on the fetal origins of later life morbidity often invokes the "damaged cohort" theory, i.e., that maternal responses to exogenous shocks induce "stress reactivity" in fetuses and thereby shorten the lifespan of males in utero during stressful times. A rival, or "culled cohort," theory posits that exogenous shocks to gravid females induce spontaneous abortions of frail male fetuses, leaving relatively hardy survivors who enjoy, on average, lifespans longer than males in less stressed birth cohorts. A recent test based on archival data from Sweden supported the culled cohort theory. Several characteristics of the Swedish data, however, raise questions regarding the external validity of the findings. We repeat the test with data from Denmark, Iceland, and England and Wales. We use time-series methods that control for trends, seasonal cycles, and other forms of autocorrelation that could confound the test. None of the results supports the "damaged cohort" theory. Consistent with the Swedish findings and with evolutionary theory, we find support in Iceland and England and Wales for the "culled cohort" theory. We discuss the implications of our findings for basic research as well as for public health.