Evolution of Menopause

Women dealing with the discomfort of hot flashes and night sweats now have a new reason to scowl at the nearest man.

New research into the biological function of menopause claims that men’s affinity for May-December relationships played a large role in women’s reproductive development.

Researchers at McMaster University in Ontario, Canada, published a study in the journal PLOS Computational Biology that says menopause is an unintended consequence of human evolution caused by natural selection and by men’s preference for younger romantic partners.   

“In a sense it is like aging, but it is different because it is an all-or-nothing process that has been accelerated because of preferential mating,” Rama Singh, a biology professor at McMaster, 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.”

Are Men the Bad Guys?

The latest theory is that older women stop producing estrogen and become infertile because men prefer to mate with younger women capable of giving birth to healthier children.

While this doesn’t mean that a man in a midlife crisis and his 20-year-old girlfriend are affecting women’s health today, it does offer one possible explanation for why women become less fertile as they age.

However, some experts are skeptical of this argument. 

“I know we like to blame men for a lot of things, but I don’t think this can be one of them,” Dr. Rebecca Brightman, a clinical instructor of Obstetrics, Gynecology and Reproductive Science at the Icahn School of Medicine at Mount Sinai Hospital, who wasn’t involved in the study, said in an interview with Healthline. 

Brightman said there are some Darwinian aspects of menopause, especially the high risks involved for both mother and child when older women become pregnant. 

“Pregnancy takes a toll on a woman’s body,” she said. “There’s an evolutionary advantage to being incapable of having children later in life. Mothers want to be around to care for their children.”

Natural Selection, Menopause, and Men

As an animal species competing with others for survival, menopause makes no sense; it prevents humans from reproducing as much as they would otherwise be able to. Whales and chimpanzees in captivity are the only other animals known to live beyond their ability to bear children. 

The new theory of menopause says the human species was able to thrive because men of all ages competed for younger mates. With all the focus on younger women, older females had a lesser chance of reproducing, so after long enough, their bodies learned to concentrate their fertility during the period when they were most likely to reproduce, the researchers wrote.

The scientists reached this conclusion using computational models and computer simulations. Testing different theories, they discovered that a male mating preference for younger females would explain the genetic mutations that produced menopause in older women. 

Based on this, the researchers theorized that menopause wasn’t an effort to protect the survival of the human species, but rather the body’s realization that fertility after a certain age was unnecessary. 

“This theory says 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,” Singh said.

Life After Menopause

Today, unlike thousands of years ago when living to age 30 meant you were an elder, more women than ever are living into their postmenopausal years. But beyond losing the ability to have children, postmenopausal women have an increased risk of serious illnesses like heart disease and osteoporosis.

With a better understanding of the biological function of menopause, Singh said that menopause could perhaps one day be reversed because it developed over time and isn’t an innate part of a woman’s reproductive cycle.

Other theories about the biological purpose of menopause include the “mother hypothesis” and “grandmother hypothesis,” which state that menopause allowed women to better care for their children and grandchildren by not risking a late pregnancy, but Singh said that those theories violate the nature of survival. 

“How do you evolve infertility? It is contrary to the whole notion of natural selection. Natural selection selects for fertility, for reproduction—not for stopping it,” he said.

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