A new study concludes men could be the cause of menopause.
The research published in this week's PLoS Computational Biology reports menopause is the unintended result of natural selection stemming from a male preference for younger female mates.
That natural selection in effect lowered reproductive rates in older women, and eventually rendered fertility useless.
Evolutionary geneticists had previously thought that menopause prevents older women from continuing to reproduce but this research says the opposite: that a lack of reproduction gave rise to menopause.
The new study provides new clues as to what causes human menopause, which has thus far remained an unsolved evolutionary puzzle.
Study author Dr. Rama Singh of McMaster University in Ontario, Canada said in a press release, "Menopause is believed to be unique to humans, but no one had yet been able to offer a satisfactory explanation for why it occurs."
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The research refuted previous theories on the "grandmother effect" -- the idea that women lost their ability to bear children because "they might not live to see a child grow" or from an evolutionary perspective were needed to help assist with rearing grandchildren.
Singh stressed the research represents patterns from thousands of years ago, not current cultural norms.
He said that as females live longer and choose to give birth later, this could potentially alter when menopause occurs.
Today, the average age a woman enters menopause is 51.