Women can now blame men for hot flushes, mood swings and other symptoms of menopause they suffer from! (Agencies)
Men's preference for younger women in selecting mates may have led to menopause in older females, a new study led by an Indian-origin researcher has claimed.
Human males have shown a preference for younger women in selecting mates, stacking the Darwinian deck against continued fertility in older women, found researchers from McMaster University in Canada.
While conventional thinking has held that menopause prevents older women from continuing to reproduce, in fact, the researchers' new theory said it is the lack of reproduction that has given rise to menopause.
Menopause is actually an unintended outcome of natural selection – the result of its effects having become relaxed in older women, said the team led by biologist Rama Singh.
"In a sense it is like ageing, but it is different because it is an all-or-nothing process that has been accelerated because of preferential mating," said Singh.
Menopause is believed to be unique to humans, but no one had yet been able to offer a satisfactory explanation for why it occurs, Singh said. The prevailing "grandmother theory" holds that women have evolved to become infertile after a certain age to allow them to assist with rearing grandchildren, thus improving the survival of kin. Singh said that does not add up from an evolutionary perspective.
"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.
The new theory holds that, over time, competition among men of all ages for younger mates has left older females with much less chance of reproducing. The forces of natural selection, Singh said, are concerned only with the survival of the species through individual fitness, so they protect fertility in women while they are most likely to reproduce.
After that period, natural selection ceases to quell the genetic mutations that ultimately bring on menopause, leaving women not only infertile, but also vulnerable to a host of health problems.
"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," Singh said.
The development of menopause, then, was not a change that improved the survival of the species, but one that merely recognized that fertility did not serve any ongoing purpose beyond a certain age.
Singh pointed out that if women had historically been the ones to select younger mates, the situation would have been reversed, with men losing fertility. The study was published in the journal PLOS Computational Biology.
Women can now blame men for hot flushes, mood swings and other symptoms of menopause they suffer from!