Differential fitness costs of reproduction between the sexes.
Natural selection does not necessarily favor maximal reproduction because reproduction imposes fitness costs, reducing parental survival, and offspring quality. Here, we show that parents in a preindustrial population in North America incurred fitness costs from reproduction, and women incurred greater costs than men. We examined the survivorship and reproductive success (Darwinian fitness) of 21,684 couples married between 1860 and 1895 identified in the Utah Population Database. We found that increasing number of offspring (parity) and rates of reproduction were associated with reduced parental survivorship, and significantly more for mothers than fathers. Parental mortality resulted in reduced survival and reproduction of offspring, and the mothers' mortality was more detrimental to offspring than the fathers'. Increasing family size was associated with lower offspring survival, primarily for later-born children, indicating a tradeoff between offspring quantity versus quality. Also, we found that the costs of reproduction increased with age more for women than men. Our findings help to explain some puzzling aspects of human reproductive physiology and behavior, including the evolution of menopause and fertility declines associated with improvements in women's status (demographic transitions).
Penn
Dustin J
DJ
Konrad Lorenz Institute for Ethology, Austrian Academy of Sciences, Savoyenstrasse 1a, A-1160 Vienna, Austria. d.penn@klivv.oeaw.ac.at
Smith
Ken R
KR
D000293:Adolescent; D000328:Adult; D000883:Anthropology; D005075:Biological Evolution; D002648:Child; D002675:Child, Preschool; D005220:Fathers; D005260:Female; D005298:Fertility; D005789:Genealogy and Heraldry; D049672:History, 19th Century; D049673:History, 20th Century; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008593:Menopause; D008875:Middle Aged; D009035:Mothers; D010298:Parity; D010809:Physical Fitness / Q000502:physiology; D011247:Pregnancy; D012098:Reproduction / Q000502:physiology*; D012727:Sex Characteristics; D015996:Survival Rate; D014589:Utah / Q000453:epidemiology