Natural selection may favor older mothers

older woman

Researchers at the University of Sheffield have applied an evolutionary ‘use it or lose it’ principle as they studied past marriage and reproduction patterns. They speculate that there will be a time in the future when the fertility range for women shifts from younger, perhaps 14-28 years old, to older, maybe 25-45, groups of women. In other words use your fertility when you have it or lose it altogether through evolutionary changes.

Researchers from the University’s Department of Animal and Plant Sciences, studied Finnish church records from the 18th and 19th centuries a time during which almost everyone married and divorce was forbidden, to trace the survival, marriage and reproductive histories of 1,591 women.

They found that women aged 30-35 were the most likely to be married. Those that married wealthy husbands were married at a younger age but to relatively older men. They appear to gain an edge for having large families because of their wealth and age, but also an increased risk of widowhood. The study seems to suggest that women did not have children at older ages because they were widowed with limited resources, or already had children but came from a lower economic class. Society did not support older mothers.

Today (and for the foreseeable future), society is radically different. Through the advent of birth control and women’s rights, women now control their reproduction and delay marriage and/or family. As a result, the natural selection maintaining young-age fertility might weaken and natural selection may favor the old-age fertility model. This could potentially lead to improvement in old-age fertility over many generations.

One of the researchers, Duncan Gillespie, said “In today’s society, family building appears to be increasingly postponed to older ages, when relatively few women in our evolutionary past would have had the opportunity to reproduce. As a result, this could lead to future evolutionary improvements in old age female fertility. . . Childbearing within a relationship is still the norm in modern society, but at ages where fewer women have the chance to reproduce, we should expect the evolution of fertility.”

Source: Shemina Davis, University of Sheffield, Medical News Today


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