Posted on 06/13/2013 5:44:55 PM PDT by rickmichaels
TORONTO – Theories abound as to why women go into menopause, but the latest hypothesis being put forward suggests it may be men — or specifically their preference for younger mates —that has led to women’s loss of fertility at a certain age.
Researchers at McMaster University believe that over tens of thousands of years, a lack of reproduction among older women has given rise to menopause as an unintended result of evolutionary natural selection.
Using computer modelling, the researchers found that over time, competition among men of all ages for younger mates left older females with much less chance of reproducing.
“We are saying somewhere along the line, men began to change their preference in mating,” said evolutionary biologist Rama Singh, co-author of the study published in this week’s issue of the journal PLOS Computational Biology.
“What we’re saying is that menopause will occur if there is a preferential mating with younger women and older women are not reproducing,” he said Thursday from Hamilton.
Singh said women would have had children when they were younger — from 15 to 30, based on the computer model.
Any genetic mutations that caused an end to fertility later in life would be passed down from generation to generation, he said.
And over time, an accumulation of such mutations harmful to female fertility ended up producing a menopausal period that became part of the overall human female genome, the hypothesis suggests.
“It’s a very simple theory. What it does is it demystifies menopause. … It becomes a simple age-related disease, if you can call it that,” said Singh.
“That’s just like all the mutations that affect our aging — white hair, weak muscles, this and that. These are mutations which affect fertility.”
The researchers’ hypothesis runs counter to prevailing theories about menopause, including the widely held “grandmother theory.”
That theory suggests that women evolved to become infertile after a certain age to allow them to assist with rearing grandchildren, thus helping to promote survival of their children’s offspring.
Kristen Hawkes, an anthropologist at the University of Utah in Salt Lake City, is among the leading proponents of the grandmother theory.
Other primates, such as chimpanzees, do not live as long as humans, but females of the species have a loss of fertility, or parturition, at similar ages to their human counterparts, she said. Female chimps rarely live beyond their child-bearing years, usually dying in their 30s or sometimes their 40s.
“The preference men have for young partners is a striking contrast with other primates,” Hawkes said by email, noting that it’s been well-documented that male chimpanzees prefer older females as mates.
“My guess about that has been it’s a consequence of our life history — something selection would favour after — not before — our grandmothering life history evolved … when women continue to be healthy and competent beyond their fertility.”
Singh, however, doesn’t believe the grandmother theory holds 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.
“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.”
Besides ending reproduction, menopause also affects a woman’s health as hormonal changes increase the risk for such conditions as cardiovascular disease and osteoporosis, said Singh.
He hopes the new theory might spawn research into ways to prevent menopause, which would lengthen a woman’s reproductive life while also helping to maintain better health as she ages.
“Until now, it has been something that you could not do anything about except (deal with) the symptoms.”
There’s also a tendency for more birth defects as parents - especially female - get older. So all else being equal, younger mates are better...not to mention softer pelvic bones for the birthing process.
... whose research is funded by? Government grant, no doubt.
Political science.
“Prior to the development of good stockades the normal human lifespan rarely exceeded 30 to 35 years.”
Makes one wonder how they came to know a maximum age of six score under those conditions.
HELLO, a huge percentage of women used to die early, in childbirth, which meant an older man, like my great grandpa, had to marry a younger woman to bear more children and raise the ones from the first wife, like my Great grandpa’s second wife did. She (the second wife) was probably 15 or so, and he in his 30s, when they married, and it was considered a good thing for a young girl to marry an established, financially secure man.
BTW, my grandma’s Mom died when Granny was 3 years old, so her Stepmom became her Mom.
HELLO, a huge percentage of women used to die early, in childbirth, which meant an older man, like my great grandpa, had to marry a younger woman to bear more children and raise the ones from the first wife, like my Great grandpa’s second wife did. She (the second wife) was probably 15 or so, and he in his 30s, when they married, and it was considered a good thing for a young girl to marry an established, financially secure man.
BTW, my grandma’s Mom died when Granny was 3 years old, so her Stepmom became her Mom.
hey the word menopause is sexist! time to change it to womenopause! /s
time to kill the greek root of that word.
“this is why you can’t placate any liberal. they are fighting and love the fighting, they don’t want the struggle to end, it never ends, nothing is ever enough, they just want to use the dialectic to get more and more extreme.”
That about sums it up. By definition, the Democratic party needs its base to believe that they’re forever victims in need of the government to be their savior.
Now I am totally lost. I thought it was because of Global Warming.
Just like the researcher suggesting that fellatio will help with a woman’s morning sickness. Even I wouldn’t try selling that one.
How about a more straightforward mechanism... older women have much less constitution to maintain a pregnancy, so there is no reproductive advantage to continuing fertility. On the negative side pregnancy can be dangerous to the older woman’s health, weakening or possibly killing her so that she cannot contribute to her children and grandchildren’s survival.
The natural preference of men for younger women is driven by the same calculus... the younger woman is more likely to carry to term and survive to help the offspring.
The fools get caught up in silly inversions of causation and can’t see the forest for the trees. Aging isn’t a product of evolution, it is a product of entropy. We are very complex organisms and damages and errors in our biological machinery build up and are not always 100% repairable. Repair of these damages requires energy inputs that impose costs on reproduction. The average lifespan of individuals within the species is a function of how reproductive strategies are optimized, but in the end entropy wins and all organisms breakdown and die.
Looks like the old adage still applies.
“If you can’t dazzle them with brilliance, baffle them with bullshit.”
WTH????? Oh never mind.p
I just thought it was all in the eggs.
Agreed. Why continue making babies when their odds of survival and yours are declining? The woman who is unable to have children at 40 can’t die of prenatal diabetes or labor complications. And she’ll be around to see her children born over the past 15 years to adulthood, improving their odds of survival.
Evolution favors successful propagation of the genome. Investment into a few offspring can be better than having many and most of them dying. And when a woman’s risk of dying from pregnancy complications or a simple inability to carry a child and provide for herself is too high, infertility is a survival trait. Because her continued survival increases the odds of her children growing up and having kids.
Now we’re back to the grandmother hypothesis. If Mom can’t die of childbirth because she can’t have another child, she pressures children to take mates and have kids, and she helps to raise them.
EXACTLY!
OMG!!!!
Stoopit as all get out.
I remember seeing something about this “grandmother” theory before—that grandmothers played an important role in helping the mothers raise the child. It ignored the fact that with the short life expectancy, there weren’t that many grandmothers around, and the main thing they were trying to divert attention from—the role of fathers in helping to raise children. In most mammals the mother does all the care of the children—after mating the father is gone until the female is in heat again. For most species that works fine. With human beings it would have led to extinction given the dangers from predators, difficulties of nursing mothers to get enough food if the men weren’t bringing in meat they had killed, and the extended years of childhood (so that women needed to be taking care of several children at once if the population wasn’t going to go into a terminal tailspin).
Here is another theory. If women were able to produce babies their whole lives, they would be dying while they still had young children, or even babies, leaving them orphans. Perhaps God’s plan was that women have their kids while they are young, then menopause hits so they stop reproducing, but they still have healthy years when they can finish raising heir family, and assist with the next generation too.
Menopause certainly isn’t fun, but neither is having a period.
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