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Human Reproduction Imposes Evolutionary Fitness Costs

Study of 19th century Mormons shows increased family size takes toll on parents and children

FRIDAY, Dec. 29 (HealthDay News) -- Having large families increases rates of parental mortality and reduces children's survival and reproduction, suggesting that reproduction imposes evolutionary fitness costs in humans, according to a report published online Dec. 27 in the Proceedings of the National Academy of Sciences Early Edition.

Dustin J. Penn, Ph.D., of the Austrian Academy of Sciences in Vienna, and a colleague studied records on 21,684 predominantly Mormon couples who were married between 1860 and 1895.

The researchers found that the couples bore an average 8.04 children and had 15.35 grandchildren. But they found that increasing family size was associated with decreased parental survivorship, especially for mothers even when accounting for childbirth mortality, and was also associated with lower offspring survival, especially for later-born children. They found that mothers who died prematurely had 3.22 fewer grandchildren compared with mothers who did not, while the comparable decline among deceased fathers was 1.71 fewer grandchildren.

"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)," the authors conclude.

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