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Computer model shows men to blame for menopause
June 14, 2013 2:07 PM   Subscribe

Men to Blame for Menopause: Younger Women Preferred in Human Evolutionary History. Humans are actually the only species where females cannot reproduce throughout their lives, and previous studies have suggested that there may be a "grandmother effect." This suggests that women lose their fertility at an age where they may not live to care for another child. Instead, they're available to care for younger women's children. Yet some scientists weren't satisfied with this theory. "How do you evolve infertility? It is contrary to the whole notion of natural selection" ... Original paper published in PLOS Computational Biology - Mate Choice and the Origin of Menopause

Abstract:

Human menopause is an unsolved evolutionary puzzle, and relationships among the factors that produced it remain understood poorly. Classic theory, involving a one-sex (female) model of human demography, suggests that genes imparting deleterious effects on post-reproductive survival will accumulate. Thus, a ‘death barrier’ should emerge beyond the maximum age for female reproduction. Under this scenario, few women would experience menopause (decreased fertility with continued survival) because few would survive much longer than they reproduced. However, no death barrier is observed in human populations. Subsequent theoretical research has shown that two-sex models, including male fertility at older ages, avoid the death barrier. Here we use a stochastic, two-sex computational model implemented by computer simulation to show how male mating preference for younger females could lead to the accumulation of mutations deleterious to female fertility and thus produce a menopausal period. Our model requires neither the initial assumption of a decline in older female fertility nor the effects of inclusive fitness through which older, non-reproducing women assist in the reproductive efforts of younger women. Our model helps to explain why such effects, observed in many societies, may be insufficient factors in elucidating the origin of menopause.


Author Summary:

The origin and evolution of menopause is understood poorly and explanations remain contentious. Virtually ignored among explanations is the effect that mate choice can exert on an evolving population. We designed and used a computational model and computer simulation to show that male mating preference for younger females in humans could have led to the accumulation of mutations deleterious to female fertility and thereby produced menopause. Our model demonstrates for the first time that neither an assumption of pre-existing diminished fertility in older women nor a requirement of benefits derived from older, non-reproducing women assisting younger women in rearing children is necessary to explain the origin of menopause.
posted by Golden Eternity (68 comments total) 14 users marked this as a favorite

 
Humans are actually the only species where females cannot reproduce throughout their lives

Apparently not

Also, "blame" is perhaps an unnecessarily loaded term for reporting on a biology paper.
posted by East Manitoba Regional Junior Kabaddi Champion '94 at 2:14 PM on June 14, 2013 [36 favorites]


seconding "blame" here as a terrible word. Designed here to make people angry and to click on the link.
posted by Ironmouth at 2:15 PM on June 14, 2013 [9 favorites]


Why would it make you angry? No one is responsible for "human nature". Blame is one of the words we use to indicate a causal relationship.
posted by esprit de l'escalier at 2:22 PM on June 14, 2013 [1 favorite]


How do you evolve infertility? It is contrary to the whole notion of natural selection"

By that measure, so is homosexuality.
posted by zabuni at 2:23 PM on June 14, 2013 [6 favorites]


Yep.
posted by General Tonic at 2:25 PM on June 14, 2013 [1 favorite]


Humans also have to squeeze their big-headed infants through their weight-bearing pelvises, making them more likely to die in childbirth.

I guess the idea that this could be the reason human females eventually become infertile (to give them a chance of living into old age as a opposed to virtually guarenteeing that they eventually die in childbirth, in the absense of birth control, as their bodies deteriorate) is what they're calling the "grandmother effect" hypthosis. Since they say it could also be called the "mother" effect (maximizing the chances that they will live to raise all their children, as opposed to not being around for the one they eventually die giving birth to...)

They're saying that they can account for the effect purely by mate selection without that "grandmother effect"... But to me it seems like, wouldn't all species have some mate selection pressure toward young mates? Surely that's not something that's special about humans in the same way that "being more likely to die while giving birth" is? That makes the latter sound like a more likely theory to me, even if they can come up with a mathematical model under which it's not "necessary."
posted by OnceUponATime at 2:27 PM on June 14, 2013 [7 favorites]


How do you evolve infertility? It is contrary to the whole notion of natural selection

How do you evolve death? Wouldn't it be better for the well-adapted members of prior generations to carry forward into later ones, until they're displaced by better-adapted children?
posted by cosmic.osmo at 2:27 PM on June 14, 2013 [3 favorites]


A less inflammatory headline might be something like "Mate Selection May Play Role in Menopause," but that's not click-bait, so I guess it's just crazy to wish for.
posted by rtha at 2:28 PM on June 14, 2013 [12 favorites]


As a man: sorry.
posted by infinitywaltz at 2:29 PM on June 14, 2013 [4 favorites]


How do you evolve infertility?

How do you evolve death?


How do you mend a broken heart?
posted by HuronBob at 2:31 PM on June 14, 2013 [31 favorites]


Using computer models, the researchers developed a new theory which may explain why women undergo menopause. 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 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 this period where women are most likely to reproduce, natural selection ceases to quell the genetic mutations that ultimately bring on menopause. This leaves women not only infertile, but also vulnerable to health problems


This sounds likely, except for the part about males and competition - that sounds like evolutionary psychology bullshit.

Didn't we just now start living long enough for menopause relatively recently? That seems a more likely explanation.
posted by bleep at 2:32 PM on June 14, 2013 [6 favorites]


How do you evolve infertility? It is contrary to the whole notion of natural selection

It's fairly useless to keep quoting this question out of context; the researcher is asking a relatively naive question rhetorically as a setup for explaining the research. It helps a little to read the press release linked in the article to put this in context.
posted by George_Spiggott at 2:33 PM on June 14, 2013


How do you evolve infertility? It is contrary to the whole notion of natural selection"

By that measure, so is homosexuality.


That's just silly. Selection works for groups too. The analysis of benefits may be different at a group vs individual level.

Think about insects. Why would it be advantageous for a bee not to be fertile? But it may be very advantageous for a group of bees to have tons of members not be fertile, so that specialization can develop for particular tasks which confers overall benefits to the group.

Now, for example - not asserting this to be the case, just giving an example - if for instance having some members of the group be non-reproducing (f.ex. through homosexuality), might lessen sexual competition while at the same time free those members to perform valuable services, that group might have better overall survival compared to a group of all males and all females be fertile. Which might account for the persistence of homosexuality across species for such a lengthy period of time - it might provide an edge, which is why it has not been eliminated.
posted by VikingSword at 2:33 PM on June 14, 2013 [7 favorites]


(maximizing the chances that they will live to raise all their children, as opposed to not being around for the one they eventually die giving birth to...)

Not to mention any previous children who are still minors when the mother dies.
posted by stopgap at 2:34 PM on June 14, 2013 [1 favorite]


Also, "blame" is perhaps an unnecessarily loaded term for reporting on a biology paper.

Dog ate the hypothesis.
posted by Blazecock Pileon at 2:35 PM on June 14, 2013 [1 favorite]


So it was men, eh?
I've been wondering who to blame menopause on for a long time..
SOMEONE. MUST. PAY.
posted by jeisme at 2:37 PM on June 14, 2013 [4 favorites]


It seems there is a presupposition here that animals don't have any particular preference for younger mates. I don't think its true or animal planet has been lying to me about some things.

And this seems to contradict
Menopause in Nonhuman Primates?

"Menopause is a naturally occurring process in which the permanent cessation of ovulation is associated with a variety of physiological and structural changes in aging female primates. One obstacle to the acceptance of nonhuman primates as models of human menopause has been the tendency to focus on differences rather than commonalities. For example, it is apparent that the onset of reproductive decline occurs relatively later in the life span of nonhuman primates than of humans, resulting in a more protracted postreproductive period in humans Although postreproductive survival is important from an evolutionary standpoint, menopause is fundamentally a physiological process, and a gradual decline and eventual cessation of female reproductive capacity, based on a host of criteria, appears to be a consistent feature of aging in every primate species that has been examined."
posted by logonym at 2:39 PM on June 14, 2013 [4 favorites]


I mean, this just bothers me greatly:

Essentially, the very fact that men selected younger women means that older women lost the ability to reproduce. If women had selected younger men for reproduction, the outcome would have been reversed. Men would have lost their fertility while women would have stayed productive.

Really? So during all the time that humans were evolving, it was always men picking younger women to the extent that it had such a huge effect on women? It just seems like a stretch to say human behavior across cultures can have such a focused effect given what we know about how variable human behavior is.
posted by bleep at 2:45 PM on June 14, 2013 [8 favorites]


Blame is one of the words we use to indicate a causal relationship.

In that case, there should be no reason not to replace it with the word "praise".
posted by DU at 2:49 PM on June 14, 2013 [7 favorites]


If y'all will change that "blame" to "credit", I'll own up to it.
posted by HuronBob at 2:53 PM on June 14, 2013 [1 favorite]


Um, doesn't the likelihood of impotence increase with age?
posted by Peevish at 2:54 PM on June 14, 2013 [2 favorites]


But this one elicits a few interesting questions: We are told that men are the more selective sex. That goes straight against the usual evolutionary-psychology argument that women are the more selective sex. It also goes against the usual evolutionary-psychology argument that men can mate with thousands of women, no trouble.

So why would men not mate with older women, too?

Another problem with the study is that the researchers seem to assume nothing bad happens to sperm quality as men age. Research suggests that this is not correct. The number of mutations in the sperm grows with age, the motility of the sperm decreases as well. Ignoring all that may not matter for the arguments in this piece, but it shows a lack of knowledge of the relevant area.

Finally, chimpanzees appear to prefer older females for mating purposes. Given that we are so often told to look at our closest relatives for guidance about our biology and behavior, that difference might be worth pondering about.

posted by jaguar at 2:54 PM on June 14, 2013 [8 favorites]


On the face this seems like a correlation≠causation problem. I'm willing to accept that menopause is an outcome statistically consistent with men choosing younger women as mates over time, but it seems like a stretch to say that's the only conceivable (see what I did there?) explanation, and seems like the authors might be applying what they see in the world around them today to our earliest ancestors.
posted by adamrice at 2:56 PM on June 14, 2013 [1 favorite]


"Academics striving for Nature cover story to blame for latest metafilter flame war."
posted by Coventry at 2:57 PM on June 14, 2013 [6 favorites]


Not every trait exists because it has been selected for an advantage it confers. Sometimes it's a mistake that just doesn't gum up the works badly enough to be worth fixing.
posted by localroger at 2:57 PM on June 14, 2013 [18 favorites]


Male homosexuality may have evolved due to sexually antagonistic selection.
posted by ogooglebar at 2:59 PM on June 14, 2013 [10 favorites]


Gotta side with "this smacks of evolutionary psychology" - especially the "because men dig hot chicks, amirite?" aspect.

Thanks, East Manitoba Regional Junior Kabaddi Champion '94, and later logonym, for that article reference. Every damned "Only humans ..." seems to get overturned.

At this point, our uniqueness appears to be based solely on being the only species to have developed both baseball cards and electrically heated mattress covers.
posted by IAmBroom at 3:00 PM on June 14, 2013 [9 favorites]


How do you evolve death?

Death By Design does a good job explaining why and how cellular death came to be the norm.
posted by nathancaswell at 3:00 PM on June 14, 2013 [4 favorites]


(it's on instant Netflix)
posted by nathancaswell at 3:01 PM on June 14, 2013


ogooglebar, that was a more interesting article than the FPP article by a long way, I think.
posted by OnceUponATime at 3:11 PM on June 14, 2013 [1 favorite]


> Designed here to make people angry and to click on the link.

See my forthcoming PLOS article, Everything bad is caused by clickbait.
posted by jfuller at 3:21 PM on June 14, 2013 [1 favorite]


Seems reasonable. "Men" is right there in the name, after all.
posted by feloniousmonk at 3:22 PM on June 14, 2013 [1 favorite]


Essentially, the very fact that men selected younger women means that older women lost the ability to reproduce. If women had selected younger men for reproduction, the outcome would have been reversed. Men would have lost their fertility while women would have stayed productive.

Really? So during all the time that humans were evolving, it was always men picking younger women to the extent that it had such a huge effect on women? It just seems like a stretch to say human behavior across cultures can have such a focused effect given what we know about how variable human behavior is.


It's kind of silly to focus on menopause, since everything that makes us mammals, primates and human is the result of thousands of generations of men and women making mate choices.

But honestly, I think it would be pretty hard to get ANY 70 year old mammal to successfully reproduce. I think longevity is just not a first order effect of natural selection. I would expect that if there were any reproductive advantage to the grandparent generation, it would be second order at best- I would expect that older people in a tribe that care for the young and give them an advantage would be spread across the whole tribe, not just their own descendents.
posted by gjc at 3:25 PM on June 14, 2013 [1 favorite]


Another thing to consider- perhaps, if there ever were a tendency for humans to be fertile for their whole lives, the downside outweighed the upside. It could be as simple as the mental decline that begins around middle age. Their offspring didn't survive as well, so the trait just sort of fell by the wayside. Not so much that it was disfavored by mates, but that it wasn't as advantageous as other traits that weren't as evolutionarily expensive.
posted by gjc at 3:32 PM on June 14, 2013


Oh geez, a human evolution paper that takes as its premise some random shitty thing about contemporary American society (contempt for older women and disqualification of them as sexual persons) and finds a way to frame it as an essential component of our evolutionary history, and in the process grab a few headlines.

That's never been done before.

Bonus points for the whole thing being a completely armchair exercise in "computational biology" that didn't involve even one actual living creature.

It's like they're playing with a Japanese dating sim game and calling it science.
posted by edheil at 3:40 PM on June 14, 2013 [13 favorites]


Humans are actually the only species where females cannot reproduce throughout their lives

cough cough wrong cough

Here we use a stochastic, two-sex computational model implemented by computer simulation to show how male mating preference for younger females could lead to the accumulation of mutations deleterious to female fertility

I bet I could show you models where the same thing could lead to older women developing heat vision with which they could burn younger women to a fine ash useful for the creation of makeup.

I mean, seriously. If you're saying this could lead to mutations in one direction, it could also lead to mutations in another direction, namely increased fertility in older women to offset the other negatives of the aging process.
posted by Cool Papa Bell at 3:42 PM on June 14, 2013 [8 favorites]


I bet I could show you models where the same thing could lead to older women developing heat vision with which they could burn younger women to a fine ash

So...menopause, then?
posted by yoink at 3:53 PM on June 14, 2013 [9 favorites]


Why would it make you angry? No one is responsible for "human nature". Blame is one of the words we use to indicate a causal relationship.

Blame is assigning responsibility for a fault or wrong, which implies moral guilt. That is not the same as causation.

It is designed, I think, to make women angry and click on the link.
posted by Ironmouth at 3:56 PM on June 14, 2013 [6 favorites]


As a man who has never had a partner more than four years away from my age and who has had two partners older than myself, I refuse to take any part of the blame for this.
posted by Decani at 4:00 PM on June 14, 2013 [1 favorite]


How do you evolve infertility? It is contrary to the whole notion of natural selection"

All of Hymenoptera would like a word with you.
posted by sourwookie at 4:02 PM on June 14, 2013 [5 favorites]


"How do you evolve infertility? It is contrary to the whole notion of natural selection"

Like using the word blame, this is an overly simplistic and misleading view of this issue. Just off the top of my head, I would blame increasing likelihood of deleterious mutations or other cell-level issues in the egg for evolved infertility with age. (Stop with the buzzing - I'm talking about mammals.)
posted by sneebler at 4:07 PM on June 14, 2013 [1 favorite]


Gosh, terrible article.

The forces of natural selection 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.

No, the forces of natural selection are concerned only with the survival of genes through individuals, so they optimise fertility in men and women when this is most likely to result in more individuals with these genes. For example, fertility is not developed ("protected") in humans under ten years, although many other organisms are fertile earlier (e.g. bacteria, from twenty minutes after birth) Women may choose older mates, but only older mates with more resources.
posted by alasdair at 4:36 PM on June 14, 2013 [2 favorites]


My personal theory is that the purpose of menopause is to get ladies of a certain age out of the fray of hormones and childbearing so that we can prepare ourselves for our natural role as Rulers of the Universe. It makes about as much sense.
posted by jokeefe at 4:41 PM on June 14, 2013 [8 favorites]


Male sexual selection isn't necessary for the grandmother hypothesis. Imagine two populations, one with a mutation that turns off ovulation at age 40, one without. In the population with the mutation, there is an 80 year old women. (Average life expectancy in hunter-gatherer cultures is low, but old people can and do live just as old as in modern society). In the population without the mutation, no woman has survived past sixty because of the strain and risks of childbirth.

Along comes a ferocious drought, the like no one has seen in 70 years. The Old Woman remembers where the tribe found water, and food, 70 years ago. Her tribe lives. The other tribe dies. The mutation is passed along.

Five generations later, there's a ferocious cold winter, the like no one has seen in 65 years...
posted by musofire at 4:43 PM on June 14, 2013 [5 favorites]


some random shitty thing about contemporary American society (contempt for older women and disqualification of them as sexual persons)

If you can point at a group of humans somewhere where the women are having children while they are very old, your comment may have more validity. As it is, it makes sense to try to understand this. Which might lead to better health care regimes for aging women.

Bonus points for the whole thing being a completely armchair exercise in "computational biology" that didn't involve even one actual living creature.


They're looking at human evolution over a greater-than-human lifetime timescale - a real-world study would involve locking a thousand psych undergrads in a box for a few thousand years. If they'd looked at some actual living non-human creature, you could point out that 'humans are nothing like zebrafish/naked mole rats so why does this study have any validity?'.
posted by sebastienbailard at 4:44 PM on June 14, 2013 [1 favorite]


So it was men, eh?
I've been wondering who to blame menopause on for a long time..
SOMEONE. MUST. PAY.


Every man who has lived with a menopausal woman knows deep in his heart that the male of the species is to blame. FOR EVERYTHING.

At this point, our uniqueness appears to be based solely on being the only species to have developed both baseball cards and electrically heated mattress covers.

Monkeys with car keys. ...or easily bypassed electronics.

Seriously, shaky premise. Seriously shaky premise.
posted by BlueHorse at 4:49 PM on June 14, 2013 [1 favorite]


The idea that natural selection (i.e. mere survival differentials) doesn't carry enough signal to account for every possible variation simultaneously doesn't even occur to these guys. It's hilarious to watch.
posted by effugas at 4:50 PM on June 14, 2013 [5 favorites]


Also, how common was menopause in antiquity?
posted by effugas at 4:51 PM on June 14, 2013


yes

i knew it

men are ruiners
posted by elizardbits at 5:16 PM on June 14, 2013 [3 favorites]


they ruin things
posted by elizardbits at 5:16 PM on June 14, 2013 [3 favorites]


I'm ruining your things right now in the manliest way possible.
posted by davejay at 5:21 PM on June 14, 2013 [4 favorites]


Yes but have you summoned a motorcycle with your moustache because that is the most manly thing possible.
posted by elizardbits at 5:25 PM on June 14, 2013 [6 favorites]


Well, duh - of course menopause confers an evolutionary advantage. Any social group benefits greatly from a population of tough, knowledgeable, highly-experienced women who give exactly zero fucks about what the men think.
posted by Mary Ellen Carter at 5:34 PM on June 14, 2013 [10 favorites]


This just in:

Women to Blame for Impotence: Younger Men Preferred in Human Evolutionary History. Humans are actually the only species where males cannot reliably achieve erection throughout their lives, and previous studies have suggested that there may be a "grandfather effect." This suggests that men lose erectile function at an age where they may not live to care for another child. Instead, they're available to care for younger men's children. Yet some scientists weren't satisfied with this theory. "How do you evolve impotence? It is contrary to the whole notion of natural selection".

posted by mariokrat at 6:22 PM on June 14, 2013 [11 favorites]


Re: Mary Ellen Carter's comment. There's a quote attributed to Margaret Mead:

"The most creative force in the world is the menopausal woman with zest."
posted by mariokrat at 6:23 PM on June 14, 2013


So why would men not mate with older women, too?

Because older women are less likely to fall for men's crap?
posted by srboisvert at 6:29 PM on June 14, 2013 [6 favorites]


So how does this explain the fact that Immigrants Are More Fertile?
posted by homunculus at 7:12 PM on June 14, 2013


I'm ruining your things right now in the manliest way possible.

ill be in my bunk
posted by nathancaswell at 7:35 PM on June 14, 2013 [2 favorites]


I always thought that since we removed ourselves from the much rougher and shorter lifespans of animals in the wild, we just live longer than our natural expiry date and things just run out or start running wonky.
posted by L'Estrange Fruit at 8:01 PM on June 14, 2013 [2 favorites]


I knew it.

Its all YOUR fault I sweat like a pig. *shakes fist at "men of metafilter"*

at an age where they may not live to care for another child

I HATE this thread already.

*implodes in a shower of hormones*
posted by infini at 9:00 PM on June 14, 2013 [3 favorites]


my bad
posted by echocollate at 11:37 PM on June 14, 2013 [1 favorite]


I always thought Doris Lessing's The Marriages Between Zones Three, Four and Five was a very helpful discussion about the meaning of maturity in a society that leaves behind - or outlives - its investment in sexuality. (Plus a whole bunch of other stuff - here's a link to the unusually comprehensive Wikipedia article.)
posted by sneebler at 7:43 AM on June 15, 2013 [2 favorites]


Isn't the preference for young females more likely caused by infertility amongst older females rather than conversely? A priori, I'd imagine fertility should be the first priority for biological influences on mate selection? And surviving to raise your children and grand children sounds like an awful good biological reason to become infertile.
posted by jeffburdges at 7:47 AM on June 15, 2013


"How do you evolve infertility? It is contrary to the whole notion of natural selection"

I hate this. It comes up all the time, and it stems from people thinking about the individual, whereas almost nothing in nature acts at the level of the individual. Natural Selection more usually operates on groups of individuals; such as colonies / species / populations / ecologies etc.

There are masses of examples of infertility being a successful adaptation. Ant colonies get along just fine without most of the population having to get involved in the pesky act of reproduction.
posted by samworm at 3:12 PM on June 15, 2013 [2 favorites]


Another explanation from an anthropology blog I find much more satisfactory than men's preference for younger mates causes menopause:

"So, increasing the gap between menopause and death increases the chances of success for offspring (because their mother lives longer to support them into adulthood). As childbirth becomes ever more dangerous (because of normal aging process) it "pays more" to stay alive and raise the kids already born than to gain more kids, at the risk of losing the ones you already have."
posted by logonym at 4:18 AM on June 16, 2013 [1 favorite]


"Humans are actually the only species where females cannot reproduce throughout their lives"

What? No, that's totally wrong. Like, ridiculously wrong.

I have a four year-old hen who stopped producing eggs about a year ago. At the same time she developed several physical and behavioral traits which are the secondary sex characteristics of roosters. (Spurs, long pointed hackle feathers, and the occasional attempt to crow.)

At about this age, chickens go through this big hormonal change. It's totally normal.

And we're talking about an animal so primitive that the males don't have a penis, and the females just have one all-purpose hole for everything (called a cloaca).

Obviously menopause is more than just a strange rare quirk of human biology.

(P.S. I notice that the authors of the paper are all dudes. Figures, right?!)
posted by ErikaB at 8:52 AM on June 17, 2013 [2 favorites]


Spurs, long pointed hackle feathers, and the occasional attempt to crow.

Check.
posted by infini at 8:56 AM on June 17, 2013 [2 favorites]


Male homosexuality may have evolved due to sexually antagonistic selection.

...or maybe not: Previously.
posted by ogooglebar at 12:19 PM on June 17, 2013


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