Researchers conclude that what causes menopause is—wait for it—men

Jun 13, 2013

After decades of laboring under other theories that never seemed to add up, a team led by biologist Rama Singh has concluded that what causes menopause in women is men.

Singh, an evolutionary , backed by computer models developed by colleagues Jonathan Stone and Richard Morton, has determined that menopause is actually an unintended outcome of natural selection – the result of its effects having become relaxed in .

Over time, human males have shown a preference for in selecting mates, stacking the Darwinian deck against continued fertility in older , the researchers have found.

"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," says Singh, a professor in McMaster's Department of Biology whose research specialties include the evolution of human diversity.

Stone is an associate professor in the Department of Biology and associate director of McMaster's Origins Institute, whose themes include the origins of humanity, while Morton is a professor emeritus in Biology.

While conventional thinking has held that menopause prevents older women from continuing to reproduce, in fact, the researchers' new theory says it is the lack of reproduction that has given rise to menopause.

Their work appears in the online, open-access journal PLOS Computational Biology.

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 says.

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 says that does not add up from an .

"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 says.

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 says, 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 doesn't have to do anything," Singh 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."

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.

For the vast majority of other animals, fertility continues until death, Singh explains, but women continue to live past their fertility because men remain fertile throughout their lives, and longevity is not inherited by gender.

Singh points out that if women had historically been the ones to select younger mates, the situation would have been reversed, with men losing fertility.

The consequence of menopause, however, is not only lost fertility for women, but an increased risk of illness and death that arises with hormonal changes that occur with menopause. Singh says a benefit of the new research could be to suggest that if developed over time, that ultimately it could also be reversed.

Explore further: Bodies at sea: Ocean oxygen levels may impact scavenger response

More information: Morton RA, Stone JR, Singh RS (2013) Mate Choice and the Origin of Menopause. PLoS Comput Biol 9(6): e1003092. doi:10.1371/journal.pcbi.1003092 http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003092.

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peter09
3.5 / 5 (6) Jun 13, 2013
Sort of confused here - surely once you stop breeding then evolution no longer applies - only by prolonging breeding will evolution have an effect. The only other mechanism for those not breeding is to help related offspring and I'm not sure that this would be relevant in this case.

Stopping breeding to prolog life is not relevant to the species.

Perhaps someone with more knowledge than me could clarify this.

El_Nose
2.7 / 5 (7) Jun 13, 2013
there is no driving force here -- no environmental imperative that that puts stress on females that can still bear children at an older age.... and since the bearing of children at a young age would seem to not effect the whether or not they can reproduce later in life how did this segment of the female population die out and never reproduce.

Unless it can be shown that the ability to reproduce throughout life also causes human females to consciously or heck unconsciously delay becoming pregnant or it significantly decrease sex drive til later in life -- thus establishing and introducing a survival factor into the mix - where it was harder to stay alive and thus large numbers of women with the ability to have children late in life died out -- i do not see the evolutionary pressure to discourage this trait in human females.
El_Nose
3.6 / 5 (5) Jun 13, 2013
The statements here seems to indicate that their is a consciousness to evolution that it chose this path because men preferred younger women -- that makes no sense... its not clean enough. --- Since we know that older people still regularly have sex -- and that there are enough young men that would have sex with anything with a pulse ( i assume the majority of us men have never been too picky ) this just doesn't hold water. In a low population area with few females - the male then did not attempt relations with older women at all... biological imperatives tend to fall apart when dealing with sentient beings.

The one thing a human is capable of that 90% of the animal kingdom will not do is chose to experience pain. Humans will kill themselves -- animals do not -- humans will do something again that they already know is painful like letting some one kick them ( tv show jacka$$) -- granted maybe the people on those shows are evolutionary deadends but they still exist
El_Nose
4.1 / 5 (7) Jun 13, 2013
the biggest problem I have with this - this -- assumption is that it was made by a male. Near the end of the article it is suggested that men pick their mates, giving women little to no choice in the matter.

This characteristic is prevalent in all the great apes (and whales fyi) -- and i do not think they have found the right answer. And another glaring issue is that many women that are starting to go through menopause have a sudden increase in libido and are attracted to younger men.
SuicideSamurai
1.9 / 5 (9) Jun 13, 2013
To put it most simply what actually evolved here was a tendency for a mutation in women that allowed for later in life infertility. That tendency did not affect human survivability because these women were already not breeding... Thus it was passed on.

If The preference had been for older women then later life infertility would have prevented certain women from breeding. Those women would then NOT pass on their infertility mutation. The trait would have been bred out.

Myno
4.4 / 5 (7) Jun 13, 2013
There is no natural selection against traits that show up after you die. For most of modern man's existence, the life span has been far less than the time to the onset of menopause.
SuicideSamurai
1.2 / 5 (6) Jun 13, 2013
the biggest problem I have with this - this -- assumption is that it was made by a male. Near the end of the article it is suggested that men pick their mates, giving women little to no choice in the matter.

This characteristic is prevalent in all the great apes (and whales fyi) -- and i do not think they have found the right answer. And another glaring issue is that many women that are starting to go through menopause have a sudden increase in libido and are attracted to younger men.


An increase in libido just prior to menopause would in any case increase the chance that a person mates successfully.

If the women in question successfully mates, because of that increase in libido, and produces offspring, those offspring are more likely to also carry the trait of increased libido just prior to menopause.

SuicideSamurai
2.5 / 5 (11) Jun 13, 2013
There is no natural selection against traits that show up after you die. For most of modern man's existence, the life span has been far less than the time to the onset of menopause.


Menopause occurs now around age 51. From About 1500 to 1850 it occurred around 45. 2300 years ago it occurred around 40. Im sure it occurred even earlier prior to the rise of civilization.
komone
4.5 / 5 (4) Jun 13, 2013
I find this unconvincing, since there is a different selective explanation. Humans are highly socialized and thus human women who live long enough would have a far higher chance of dying in childbirth. If the grandmother dies she is unable to assist with the protection of the viability of her second generation of genes (grandchildren), especially when the mother may have died through later childbirth or for many other reasons. Menopause viewed in that context could make selective sense.
pauljpease
5 / 5 (2) Jun 13, 2013
This sounds like the research that showed you can increase a species life expectancy simply by making them wait until they are very old before allowing them to mate. Individuals with "bad" genes die off before they can reproduce. In this situation, with human menopause, there is no positive selection for traits after 30-40 years of age, which was, until the last century, the normal human life expectancy. Same thing with cancer. Since people would traditionally die of other causes before they lived long enough to die of cancer, we generally have high probabilities of getting cancer when we're old (over 60). I would also add that menopause could have been a positive adaptation because it prevents competition for mating between mother and daughter, or granddaughter. There could be more social strife if all women were fertile their entire lives. Very interesting problem, regardless.
gwrede
1 / 5 (8) Jun 13, 2013
what causes menopause in women is men
Duh. So, even this is men's fault.

Rhymes well with the article about Sweden that I read today. Any sex there, except for gay sex, and (for the time being) heterosexual sex, is going to become criminal. I suspect even hetero sex had become criminal, if it werent for "historical reasons", for now.

I am seriously starting to wonder if it was a good idea to give women the right to vote. (Where Sweden actually was one of the first countries.)
Well
gwrede
2.8 / 5 (11) Jun 13, 2013
Oh, and by the way, if menopause is caused by men not doing old women, then by the same logic, girls today should reach maturity much later than before, because by the current rules, girls have to spend some 4 to 8 years of their first fertile years without a partner.

That should then cause the onset of periods to approach 18 years of age. Right??!!

SuicideSamurai
1 / 5 (6) Jun 13, 2013
This article has a terrible title and is written pretty poorly.

First off The actual cause of menopause is a series of genetic mutations leading to infertility for human women later in life.

Second men AND women are better off from an evolutionary standpoint to choose young mates as they are more likely to be healthy and thus bear viable offspring for a longer time period.

So what you have is those two factors leading to the reality that older women, who had this mutation were still breeding as younger women. That mutation because of how humans select mates, did not negatively affect human survival and was not bred out.

If humans, or just males, chose older mates, for some reason, then the mutation for infertility would have been highly maladaptive and the women with that mutation would not have bred, and would not have passed on the trait. However these women, carrying that particular set of mutations, and due to how humans select males did breed and did pass on that trait.
Code_Warrior
3.4 / 5 (5) Jun 14, 2013
Most people who have raised children don't want to do it again because they are 20-30 years older, don't have the energy they did 20-30 years ago, and don't want to sacrifice another 20-30 years of their life to raise a new batch of kids. It was well worth it to raise the kids and I wouldn't have done it any other way, but now that I'm almost done, it's time to relax, not make more babies. Sometimes I wonder if any of these theorists have actually raised any children.
thatsitalright
1.8 / 5 (5) Jun 14, 2013
The problem I have with this article, is that it presumes human males just go gallivanting off to mate with some fresh young women who are obviously not being contested by other males, especially from their own peer group. These fresh young women are just waiting around for an older male to club them over the head and drag them back to their caves.

The kind of society that would allow for these promiscuous old buggers, to completely detach sexually from their current mate (I doubt contraceptives are part of the equation), and reproduce successfully with younger women... Well damn. I think I will build a time machine.
El_Nose
5 / 5 (1) Jun 14, 2013
@thatsitalright

today that scecerio is played out daily in places like Palm beach, FL - Naples, FL and i am sure in other very affluent areas of the country. You can walk by tables with 80 yr old men with 20ish girls and hear conversations -- 'so what do you like' -- 'well i like diamonds and jewelry and ...'

Money allows elderly men to mate with a lot of younger women "driven by the biological imperative to be with a man that provides safety and food" -- HA,
Sean_W
1.8 / 5 (5) Jun 14, 2013
PATRIARCHY!!! Worse than Zionism and lizard people in the great pyramid of villainous forces.
nonknown101
2.1 / 5 (7) Jun 14, 2013
This has got to be the STUPIDIST conclusion they could come up with ! and the premise that fertility is non ending in most species is complete crapola.

ALL mammals lose fertility, an that is ALL, this clown is comparing insects and fish to Mammals which is as stupid as you can get !

Who has seen an old cat or dog go into heat? no heat , no fertility!

Now there may be some deer like critters that don't lose fertility before they get EATEN by some other critter or starve to death because their teeth are mostly gone !

the fact that a geneticist did this study with NO Biologists involved should have sent up the Flares and red flags at the university he works at !
arq
not rated yet Jun 16, 2013
So many studies on women in their 50s and 60s, but too few on men in their 50s and 60s. I humbly request phys org to publish those studies too.
TheGhostofOtto1923
1.8 / 5 (5) Jun 16, 2013
The researchers fail to acknowledge a key factor which changes the whole complexion of their conclusion.

Bearing human babies is dangerous and painful because of our huge heads. No other animal suffers like women do. And the danger only increases with age.

Men may prefer younger women because 1) there is less chance they are already carrying another mans baby, and 2) their offspring have a greater chance of surviving birth, and of having mothers who survive long enough to raise them.

Older women will avoid getting pregnant as it endangers their health. Menopause is a defense mechanism, and it has little to do with what men WANT.

A curious related issue - the hymen is rare among primates, occurring in only one species of lemur and one of gorilla. Did tribes unnaturally select for women born with this feature, as it was the only way to ensure that their champions were reproducing?

Islamists will kill their sisters who are not virgins. Hymen repair is a popular procedure in India.