Men to Blame for Menopause: Younger Women Preferred in Human Evolutionary History

First Posted: Jun 14, 2013 03:11 PM EDT

Are men to blame for menopause? They might be, according to a new study. In our evolutionary past, men's preference for younger mates made fertility pointless for older women. This, in turn, may have eventually led to menopause.

Menopause usually occurs in a woman's midlife, during her late 40s or early 50s. The condition signals the end of the fertile phase of her life as the primary workings of her ovaries cease to function. There are several symptoms associated with this transition, including hot flashes, night sweats and mood swings.

Yet these symptoms could all be explained through our unique history. Humans are actually the only species where females cannot reproduce throughout their lives, and previous studies have suggested that there may be a "grandmother effect." This suggests that women lose their fertility at an age where they may not live to care for another child. Instead, they're available to care for younger women's children.

Yet some scientists weren't satisfied with this theory. "How do you evolve infertility? It is contrary to the whole notion of natural selection," said Rama Singh, one of the researchers, in a news release. "Natural selection selects for fertility, for reproduction--not for stopping it."

Using computer models, the researchers developed a new theory which may explain why women undergo menopause. Over time, competition among men of all ages for younger mates has left older females with much less chance of reproducing. The forces of natural selection are concerned only with the survival of the species through individual fitness, so they protect fertility in women while they are most likely to reproduce.

After this period where women are most likely to reproduce, natural selection ceases to quell the genetic mutations that ultimately bring on menopause. This leaves women not only infertile, but also vulnerable to health problems

"This theory says that natural selection doesn't have to do anything," said Singh. "If women were reproducing all along, and there were no preference against older women, women would be reproducing like men are for their whole lives."

Essentially, the very fact that men selected younger women means that older women lost the ability to reproduce.  If women had selected younger men for reproduction, the outcome would have been reversed. Men would have lost their fertility while women would have stayed productive.

If you're a woman who's experienced menopause, you now officially have only men to blame.

The findings are published in the journal PLOS Computational Biology.

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