Scientists formerly believed that men were more interested in young females because of their fertility. A new study challenges that theory and suggests the reason women go through menopause at middle age is because men have historically been more interested in sleeping with younger women.
Professor Rama Singh of McMaster University in Canada calls man’s instinctual preference for younger females “preferential mating.” Because men are interested in younger women, evolution saw fit to take away the ability for older women to have children, Singh said.
Singh, the study’s co-author, claimed if it weren’t for preferential mating, then women might be able to produce children until they died. This also means that if women shunned older men and preferred males in their age group, then evolution probably would have left middle-aged men infertile, too.
Menopause usually occurs in women between the age of 45 and 55. However, fertility drops significantly in females as early as age 35, at which time it can become difficult to conceive.
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Most other species do not go through menopause. Even chimpanzees continues making babies into old age, but then male chimps prefer older females.
"Our first assumption is that mating in humans is not random with respect to age, which means men of all ages prefer to mate with younger women," Singh said. "If mating is with younger women, any deleterious mutations which affect women's reproduction later in life will accumulate because they are not being acted on by natural selection."
Researchers believe it took 50,000 to 100,000 years for gene mutations to make female menopause universal. It would take a similar amount of time to push menopause back via evolution. Singh said technological advances in fertility are more likely to extend fertility in women.
The study was published in the June 13 issue of “PLOS Computational Biology.”