Temperature oscillations may shorten male lifespan via natural selection in utero
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Much literature argues that natural selection has conserved mechanisms that spontaneously abort fetuses, particularly males, least likely to survive in prevailing environmental conditions including cold ambient temperature. These reports imply the hypothesis that males in gestation during relatively warm periods who confront relatively cold climates in early life live, on average, shorter lives than other males. We estimate the effect of warm-to-cold temperature shifts on the observed lifespan at age one of males born in Sweden from 1850 through 1915. We test this hypothesis using annual cohort lifespan at age 1 year for Swedish males from 1850 to 1915. For our independent variable, we score a series “1” for birth cohorts that experienced relatively warm temperatures in utero but relatively cold temperatures from age 1 through 4 years, and “0” for other cohorts. We use time-series methods, which adjust the data to remove autocorrelation, to estimate the association between these variables. Consistent with theory, males in gestation during relatively warm times who encounter relatively cold temperatures in early life have a shorter lifespan than other males. The association survives adjustment for the longevity of females as well as the main effect of temperatures during gestation and early life. Our findings imply that the increased frequency and amplitude of temperature shifts expected from climate change could influence which humans survive gestation and how long they live.
KeywordsBirth Cohort Cold Temperature Spontaneous Abortion Temperature Shift Test Equation
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