Menopause, with its dreaded hot flashes, sleep problems and more, now comes with at least one conciliation for women: It's all men's fault, according to new research.
Human male preference for younger women has actually stacked the Darwinian deck against continued fertility in older women, concludes the study, published in the latest issue of PLoS Computational Biology.
"I think male-driven sexual selection, the male sex drive, has been a major factor driving sexual selection in humans," co-author Rama Singh told Discovery News, adding that if "there were no preference against older women, women would be reproducing like men are for their whole lives."
Singh, an evolutionary geneticist at McMaster University, conducted the research with colleagues Richard Morton and Jonathan Stone. They used computer simulation to mathematically model how genes change over time among mating pairs and others in a given population.
"Mating preference in males for younger females relaxed selection on older females," co-author J.R. Stone, associate director of McMaster's Origins Institute, told Discovery News.
In short, these older gals tend to be dumped or ignored in favor of younger women, who in theory have better genes and can, because of their age and energy, possibly reproduce more, keeping the male's lineage going.
Women, of course, don't just drop dead after menopause. The forces of natural selection seek only the survival of the species through individual fitness. They protect fertility in women while they are most likely to reproduce, but after that period, they cease to quell the genetic mutations that ultimately bring on menopause and a possible host of other potential health problems, such as increased risk for heart attack and stroke.
Human, and killer whale, females, who also go through menopause, often live long lives after their baby-producing days are done. They even continue to increase the propagation of their genes during later life.
"They do this by helping to increase the survival of their older sons, which in turn increases the number of grandchildren fathered by their sons," Darren Croft, a senior lecturer in animal behavior at the University of Exeter, told Discovery News. "Through this process, evolution favors females that live longer after their menopause. This explains why female killer whales have evolved the longest lifespan after menopause of all non-human animals."
Menopause is, however, extremely rare in the animal kingdom, with only a handful of non-human animal females also going through this "change of life." Stone said "prolonged life spans probably are a major factor." The other animals may simply not live long enough to evolve menopause.
Regarding so-called "male menopause," Singh said, "I think menopause in men is not a real menopause but kind of a joke and it refers to lack of interest in sex!"
Interested or not in sex, the majority of men do remain fertile throughout the rest of their adult lives.
The good news for women is that such research might, in future, allow doctors to reverse menopause.
"The new theory opens up the possibility that menopause could be delayed by hormonal treatment," Singh explained. "This would be a good thing for career women starting a family late in life."
Younger men pairing with older women -- so-called cougars -- could also work wonders too.
Over time, if the cougar trend continues, it could affect how menopause evolves, perhaps prolonging when it happens, "provided these younger men/older women couples reproduce," Singh said.