Did Men's Yen for Younger Women Cause Menopause?
Study found bias may have sidelined older women sexually, prompted changes that led to infertility
WebMD News Archive
By Barbara Bronson Gray
THURSDAY, June 13 (HealthDay News) -- Can women blame men for menopause?
They may have a case, according to new research that suggests it was men's interest in mating with younger females that gave evolutionary rise to menopause by sidelining older women from reproduction.
Menopause -- when a woman stops getting menstrual periods and can't become pregnant -- is unique to humans and its cause is still unknown, explained study author and evolutionary biologist Rama Singh. "We accept as a given the idea that older women tend to be unable to reproduce," but Singh said this is actually an "evolutionary puzzle."
It has long been thought that menopause is what causes women, primarily in their early 50s, to stop being able to get pregnant, but the researchers found evidence that things could actually have occurred the other way around. In other words, infertility may have been the cause, not the effect, of menopause in early humans.
There are at least 10 theories of why menopause occurs, according to the researchers, including ideas based on the fact that women are living longer and depleting the number of eggs in their ovaries, to what is called the "grandmother hypothesis." That idea holds that menopause allows older women to provide childcare that contributes to the survival of their grandchildren, making them more fit or valuable to the human tribe.
But Singh's research, published online June 13 in the journal PLOS Computational Biology, suggests something altogether new.
"This paper is saying that men have played the major or dominant part in choosing mates," said Singh, who is a professor of population genetics and evolution at McMaster University, in Canada. "Somewhere along the line in our evolutionary history, males did not mate randomly but preferred young women because they are more attractive."
Going way back in human history, people reproduced all their lives, explained Singh. While it's possible that some women may have experienced menopause 30,000 years ago, now 100 percent of women experience it. "Menopause is an evolutionary phenomenon," he said.
The scientists found that the development of menopause seems to have done nothing to improve the chances of human survival over time, but rather occurred because women of a certain age weren't finding mates, and thus reproductive ability was unnecessary for them.
Yet Singh pointed out that if women long ago had been the ones choosing younger mates, older men would have been the ones losing their fertility, not women.
The process of natural selection favors the most fit, so women who are most likely to reproduce are protected, explained Singh. Natural selection is the gradual, non-random process through which biological traits become either more or less common, due to the way reproduction occurs, Singh explained.