Natural Selection _In Utero_ Contributes to the Male Longevity Deficit in Contemporary Human Populations

Much literature invokes natural selection to explain the pervasive deficit in the average lifespan of men compared to women.^1^ The explanation assumes that mothers, not fathers, provisioned children over much of human existence, and that women who lived long enough to help their children and grand children survive to reproductive age had more grandchildren and great-grandchildren than did shorter-lived women.^2^ Although this argument implies that natural selection would conserve mutations that conferred longevity on mothers but not fathers,^3,4^ it offers no explanation of the considerable changes over historic time in the male longevity deficit thereby implying that these arise solely from culture.^5^ I show, however, that natural selection _in utero_ empirically predicts variability over time in the deficit. This mechanism spontaneously aborts less fit fetuses during stressful times and reportedly selects more against males than females. My finding suggests that natural selection interacts with culture to predictably affect both the life span and sex ratio of contemporary human populations

Male fetal loss in the U.S. following the terrorist attacks of September 11, 2001

Background: The secondary sex ratio (i.e., the odds of a male birth) reportedly declines following natural disasters, pollution events, and economic collapse. It remains unclear whether this decline results from an excess of male fetal loss or reduced male conceptions. The literature also does not converge as to whether the terrorist attacks of September 11, 2001 induced "communal bereavement", or the widespread feeling of distress among persons who never met those directly involved in the attacks. We test the communal bereavement hypothesis among gravid women by examining whether male fetal deaths rose above expected levels in the US following September 11, 2001. Methods: We apply interrupted time-series methods to all fetal deaths at or greater than the 20(th) week of gestation in the US from 1996 to 2002. Time-series methods control for trends, seasonality, and other forms of autocorrelation that could induce spurious associations. Results: Results support the hypothesis in that the fetal death sex ratio (i.e., the odds of a male fetal death) increased above its expected value in September 2001. Additional analysis of the secondary sex ratio indirectly supports that the terrorist attacks may have threatened the gestation of male more than female fetuses. Conclusions: Societal responses to events such as September 11, 2001 do not appear confined only to persons who have ever met the deceased. The fetal death sex ratio in the US population may serve as a sentinel indicator of the degree to which pregnant women react to population stressors

Selection in utero contributes to the male longevity deficit

The literature offering evolutionary explanations of the male longevity deficit does not address temporal variation in the deficit. This circumstance appears attributable to the fact that natural selection intuitively explains the deficit's pervasive and persistent nature, while social processes more parsimoniously explain its temporal variability. I offer consilience of these perspectives by speculating that selection in utero, a mechanism both conserved by natural selection and affected by social processes, could induce deviations around trend in the male longevity deficit. I describe the mechanism and offer an empirical test of its possible effect among Swedes - a population with the longest continuous record of sex-specific longevity in annual birth cohorts. I replicate the test with data from England and Wales. Results support the hypothesis that selection in utero against less fit males may explain part of the difference in longevity between males and females in modern populations.Selection in utero Male longevity deficit Sweden UK Gender Mortality Natural selection