Selection in utero : An evolutionary connection between the political environment and male twin infant mortality

Abstract Background and Objectives Evolutionary theory and research suggest that spontaneous abortion of male twins varies over time with adversity in the population. This “selection in utero” has attracted little attention from clinical researchers. We attribute this to failure of basic literature to connect selection in utero to clinically important problems. We hypothesize a connection to racial disparities in infant mortality. Invoking relaxed selection in utero, prior research reports that Non-Hispanic Black women pregnant at the election of Barrack Obama as President, birthed more male twins than expected. We reason that if relaxed selection in utero accounted for the “excess” male twins, a disproportionate fraction would be frail and die in infancy. Methodology We test our reasoning with time-series methods that control confounders affecting infant mortality among female twins born to non-Hispanic Black women and among male twins born to non-Hispanic white women. Results As hypothesized, the ratio of Black to white infant mortality rates among twin males born from the “Obama cohorts” appears 40% greater than statistically expected. Conclusion and Implications The National Academy of Medicine has characterized racial disparities in health as “inexcusable” and ranked them 3rd among targets for biomedical research in the United States. We show that evolutionary theory provides an explanation of why an event desired by a majority of American voters appeared followed by an increase in an undesired disparity in infant mortality. Our findings, combined with the National Academy’s ranking, therefore suggest that biomedical researchers should pay greater attention to evolutionary explanations of health disparities.