A team of scientists at McMaster University have discovered that men are responsible for menopause in women.
Rama S. Singh, a professor in McMaster’s Department of Biology, along with colleagues Jonathan Stone and Richard Morton, have found that menopause is the result of natural selection.
The researchers identified that men have always had a preference for younger women when it comes to mating, which means that older women didn’t have the need to continue to be fertile – as men avoided mating with them.
Singh, whose research specialties include the evolution of human diversity, said that “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.”
Experts previously believed that menopause was a way of preventing older women from reproducing, however, this new finding, published in the journal PLOS Computational Biology, suggests that it is the lack of reproduction that caused menopause.
Singh said that nobody had been able to explain why menopause is so unique to humans, only two other animals stop breeding relatively early in their lifespan – killer whales and pilot whales.
The “grandmother theory” suggests that women are unable to have children after a certain age so that they can assist with the upbringing of their grandchildren.
A study conducted at the Universities of Exeter and Cambridge, both in England, found that females become increasingly genetically related to those they live with as they get older. Because of this, there is a motivation for older females to do what is best for the survival of those around them, creating a ‘grandmother role’.
However, Singh said that the theory doesn’t add up:
“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.”
This new theory says that older females had much less chance of reproducing, as men of all ages looked for younger mates.
Following this, genetic mutations occurred that brought on menopause among women when they reached a certain age, leaving them infertile.
Singh said:
“This theory says that natural selection doesn’t have to do anything. 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.”
Therefore, the development of menopause didn’t occur to improve survival, it only recognized that beyond a certain age fertility didn’t serve any purpose.
If the situation would have been reversed and women had historically only selected young males, men would be the one’s losing fertility at a certain age, Singh pointed out.
The researchers concluded that if the theory is true, menopause could potentially be reversed one day.
Written by Joseph Nordqvist