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

Ambient Temperature During Gestation and Cold-Related Adult Mortality in a Swedish Cohort, 1915 to 2002

For all climatic regions, mortality due to cold exceeds mortality due to heat. We examine whether cold-related mortality in adulthood varies positively with unusually benign ambient temperature during gestation, using data on over 13,500 Swedes from the Uppsala Birth Cohort Study born in 1915-1929 and followed until 2003. We link daily thermometer temperatures in Uppsala (1914 to 2002) to subjects, from their estimated date of conception onwards. We estimate survival models with time-varying explanatory variables, focusing on the two leading causes of cold-related death in adulthood: ischaemic heart disease (IHD) and stroke. An increase in the prevalence of warm temperatures during gestation leads to a significantly higher rate of mortality due to cold-related IHD. However, we do not find such a relation for cold-related stroke mortality. Additional analyses show that birthweight percentile or gestational age do not mediate discovered findings. The IHD results indicate that ambient temperature during gestation independent of birth month modifies the relation between cold and adult mortality

Vanishing twins, spared cohorts, and the birthweight of periviable infants born to Black and white women in the United States.

Pregnancies ending before 26 weeks contribute 1% of births but 40% of infant deaths in the United States. The rate of these periviable births to non-Hispanic (NH) Black women exceeds four times that for NH whites. Small male periviable infants remain most likely to die. NH white periviable males weigh more than their NH Black counterparts. We argue that male infants born from twin gestations, in which one fetus died in utero (i.e., the vanishing twin syndrome), contribute to the disparity. We cannot directly test our argument because vanishing typically occurs before clinical recognition of pregnancy. We, however, describe and find associations that would emerge in vital statistics were our argument correct. Among male periviable singleton births from 288 monthly conception cohorts (January 1995 through December 2018), we found an average NH white advantage of 30 grams (759 grams versus 729 grams). Consistent with our argument, however, cohorts signaling relatively few survivors of the vanishing twin syndrome showed no disparity

Exposure to the early COVID‐19 pandemic and early, moderate and overall preterm births in the United States: A conception cohort approach

BackgroundThe United States (US) data suggest fewer-than-expected preterm births in 2020, but no study has examined the impact of exposure to the early COVID-19 pandemic at different points in gestation on preterm birth.ObjectiveOur objective was to determine-among cohorts exposed to the early COVID-19 pandemic-whether observed counts of overall, early and moderately preterm birth fell outside the expected range.MethodsWe used de-identified, cross-sectional, national birth certificate data from 2014 to 2020. We used month and year of birth and gestational age to estimate month of conception for birth. We calculated the count of overall (<37 weeks gestation), early (<33 weeks gestation) and moderately (33 to <37 weeks gestation) preterm birth by month of conception. We employed time series methods to estimate expected counts of preterm birth for exposed conception cohorts and identified cohorts for whom the observed counts of preterm birth fell outside the 95% detection interval of the expected value.ResultsAmong the 23,731,146 births in our study, the mean prevalence of preterm birth among monthly conception cohorts was 9.7 per 100 live births. Gestations conceived in July, August or December of 2019-that is exposed to the early COVID-19 pandemic in the first or third trimester-yielded approximately 3245 fewer moderately preterm and 3627 fewer overall preterm births than the expected values for moderate and overall preterm. Gestations conceived in August and October of 2019-that is exposed to the early COVID-19 pandemic in the late second to third trimester-produced approximately 498 fewer early preterm births than the expected count for early preterm.ConclusionsExposure to the early COVID-19 pandemic may have promoted longer gestation among close-to-term pregnancies, reduced risk of later preterm delivery among gestations exposed in the first trimester or induced selective loss of gestations

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