June 14, 2013 9:00 am
Menopause is a pretty weird thing, if you think about it. Suddenly, at a certain age, your body shuts down the ability to reproduce, resulting in symptoms like hot flashes, difficulty sleeping, reduced interest in sex and increased vaginal infections. The whole process seems like a pretty strange thing, especially if reproduction is a cornerstone of evolution. So why do we have it? Well, one recent study suggests that men may be to blame.
Research in the journal PLOS Computational Biology turned to some computer simulations to figure out why any species would set up a system to shut down reproduction long before death. After all, it’s hard to see how a genetic predisposition to sterility would be helpful.
The most common hypothesis out there about menopause is called the “grandmother hypothesis.” The premise here is that when we started living together in groups it became useful for the older females to stop having their own babies, and start helping the younger females raise theirs. But there’s a problem with that hypothesis, says Rama Singh, the lead author of the new study. The Los Angeles Times explains:
But the problem with the grandmother hypothesis, Singh added, is that it doesn’t explain how the mutation causing sterility in older women came to be so common in the first place. Genes that suppress reproduction shouldn’t be able to thrive — if an individual can’t pass them to offspring, they should die out.
So Singh’s work suggested a different hypothesis. Men tend to prefer younger females as mates. They have for thousands of years. When Singh and his colleagues added that factor into their computer models they suddenly saw an increase of mutations that harmed the fertility of older women. After a while, these accumulating mutations stuck. The women still shared the longevity genes that their male counterparts had, so they were living just as long, but they no longer reproduced.
Of course, this whole thing is really hard to prove. The Los Angeles Times spoke with Cedric Puleston, who has also researched menopause but wasn’t involved in this study. While he said the work was “really compelling” he also noted that it wasn’t conclusive:
“[T]hat’s as far as you can go with this … although the paper provides a powerful argument in favor, it’s not proof that male mate choice caused menopause. Showing that an explanation is compatible with reality is sometimes the best we can do.”
Now, humans aren’t the only species that has menopause. Some primates like rhesus monkeys and chimpanzees get it. And some other species further removed from our own might get it, like elephants and some whales, but no one is certain. For the most part, menopause is, as the authors put it “almost uniquely human” and we might have men to blame. But we might not. As the LA Times puts it, “thanks a lot, guys.” Maybe.
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