Menopause

[Night]

How did menopause become evolutionarily advantageous? Does anyone know? I can't figure it out for the life of me lol...

[Jack]

Not everything is advantageous. Some things are "left over" from a time when they served a purpose. I believe menopause signals the end of the menstrual cycle in women, the end of the natural child-bearing years of life. Perhaps women once died young enough that menopause wasn't an issue. Now that we live longer, all kinds of health issues have arisen that weren't problems before.

I'm not a doctor, have never played one on TV..so I could be totally out in left field here. But since you asked...

[Milton Bradley]

My thinking is right in line with Isherwoods here. Just seems logical.

[Jack]

On the other hand, Night, if you're asking about male menopause, I believe it has something to do with 18 year old girls and sports cars, but I'm not there yet so I can't say for sure.

[Carrie Spooner]

The purpose of menopause is to prevent women from conceiving when it would be of great risk to themselves and their unborn child. This prevents many maternal and fetal/neonatal deaths due to advanced maternal age. The evolutionary connection isn't as obvious but I suppose the psychological ramifications of these mothers and babies dying could have quite an effect on the reproduction of the next generation.

[Thanatos]

I always thought it was because of average lifespans. Do you ever wonder why things stop working after about 40? For most of human history the world was a rather dangerous and unforgiving place with estimated lifespans of about 35 (still is in some third world countries). Most people never lived to go bald or run out of eggs. Statistically a lion or smallpox or something is supposed to have gotten you already.

If nobody ever lives to run out of eggs or die of Alzheimer's, then theres no evolutionary pressure to come up with a solution. Like an appliance the week after its warranty expires things start sputtering and slowing and generally misbehaving. Now that humans come with a longer evolutionary warranty in most areas of the world this should start changing...but don't hold your breath.

[Night]

Quote by: Isherwood Not everything is advantageous. Some things are "left over" from a time when they served a purpose. I believe menopause signals the end of the menstrual cycle in women, the end of the natural child-bearing years of life. Perhaps women once died young enough that menopause wasn't an issue. Now that we live longer, all kinds of health issues have arisen that weren't problems before. I'm not a doctor, have never played one on TV..so I could be totally out in left field here. But since you asked...

That's what I was thinking, however something this big and complicated must certainly have an evolutionary advantage, otherwise some woman would not go through menopause.

I think there's a different answer

Quote by: Carrie Spooner The purpose of menopause is to prevent women from conceiving when it would be of great risk to themselves and their unborn child. This prevents many maternal and fetal/neonatal deaths due to advanced maternal age. The evolutionary connection isn't as obvious but I suppose the psychological ramifications of these mothers and babies dying could have quite an effect on the reproduction of the next generation.

To maintain evolutionary viability, it must make the woman better able to produce children, survival after child birth (and child raising) doesn't really matter.

As for psychologically affecting the generation afterwards...hmm...that's a very interesting answer, but most woman 40,000 years ago didn't reach menopause.

[Athena]

Quote by: Carrie Spooner The purpose of menopause is to prevent women from conceiving when it would be of great risk to themselves and their unborn child. This prevents many maternal and fetal/neonatal deaths due to advanced maternal age. The evolutionary connection isn't as obvious but I suppose the psychological ramifications of these mothers and babies dying could have quite an effect on the reproduction of the next generation.

May I add to what you said, that civilization seems the result of grandmothers, and that would have an evolutionary impact. These women need to be free of parental responsibility to function as grandmothers. Here is an evolutionary selection explanation given by someone who studies the subject.

Discover Magazine July 1996 As a result, human children in most societies do not become capable of economic independence until their teens or twenties. Before that, they remain dependent on their parents, especially on the mother, because mothers tend to provide more child care than do fathers. Parents not only bring food and teach toolmaking but also provide protection and status within the tribe. In traditional societies, early death of either parent endangers a child's life even if the surviving parent remarries, because of possible conflicts with the stepparent's genetic interests. A young orphan who is not adopted has even worse chances of surviving. Hence a hunter-gatherer mother who already has several children risks losing her genetic investment in them if she does not survive until the youngest is at least a teenager. That's one cruel fact underlying human female menopause. Another is that the birth of each successive child immediately jeopardizes a mother's previous children because the mother risks dying in childbirth. In most other animal species that risk is very low. For example, in one study of 401 rhesus monkey pregnancies, only three mothers died in childbirth. For humans in traditional societies, the risk is much higher and increases with age. Even in affluent twentieth-century Western societies, the risk of dying in childbirth is seven times higher for a mother over the age of 40 than for a 20-year-old. But each new child puts the mother's life at risk not only because of the immediate risk of death in childbirth but also because of the delayed risk of death related to exhaustion by lactation, carrying a young child, and working harder to feed more mouths. Infants of older mothers are themselves increasingly unlikely to survive or be healthy, because the risks of abortion, stillbirth, low birth weight, and genetic defects rise as the mother grows older. For instance, the risk of a fetus's carrying the genetic condition known as Down syndrome increases from one in 2,000 births for a mother under 30, one in 300 for a mother between the ages of 35 and 39, and one in 50 for a 43-year-old mother to the grim odds of one in 10 for a mother in her late forties.

[Night]

What I'm asking is, why would menopause happen in woman everywhere (meaning it had to be very important evolutionarily) when most woman never got old enough to go through menopause?

[Thanatos]

Quote by: Night What I'm asking is, why would menopause happen in woman everywhere (meaning it had to be very important evolutionarily) when most woman never got old enough to go through menopause?

It may not just be one thing. Preventing people from having children once they've accumulated too much genetic damage is valid too, and leaving women free to be grandmothers could have helped.

Or possibly those things might not have been very influential and it could be like asking why all batteries of a given type and brand fail after about the same amount of use. I wish I knew more about the biology of menopause; all the literature still says its because the woman runs out of eggs but I know that's wrong:

Myth of Limited Oocytes in Women - Associated Content

I wish I understood why the oocyte stem cells stop working after a while. Have they run out of telomeres or otherwise reached some physical limit and worn out? Or is it something preprogrammed? Understanding what's going on in there would go a long way to answering your question with more than speculation.

[Milton Bradley]

Quote by: Night What I'm asking is, why would menopause happen in woman everywhere (meaning it had to be very important evolutionarily) when most woman never got old enough to go through menopause?

Perhaps the evolutionary mechanism is lagging behind the huge advance peoples life spans advanced post industrial revolution.

[gallo]

Actually, any mammal will undergo menopause if it lives long enough. We had a white miniature poodle that had not been spayed (we thought she might be breed-able until we became aware that she had a congenital birth defect). When she was quite old, she formed an uterine abscess and became quite ill. After a course of antibiotics, she was spayed. Her white fur then turned a light tan, typical of white poodle puppies, that prompted her name, "Nutmeg", in the first place. After she has passed her induced menopause, she again became white.

So the answer is that menopause isn't evolutionarily advantageous. Menopause happens only when mammals have lived long enough to reproduce. In most species, menopause is rare because individual females don't live long enough. On the other hand, they have lived long enough to have reproduced. That is the point of natural selection and evolution - reproductive success.

Actually, now that I think about it, menopause does offer an evolutionary advantage to a species in that it removes older generations that may not be as well adapted to a changing environment from the reproductive pool.

[Suburbanite]

Quote by: Night To maintain evolutionary viability, it must make the woman better able to produce children, survival after child birth (and child raising) doesn't really matter.

Firstly, evolution is not about increased productivity, it is about increased survival chances. Secondly, how can a woman have two children if the first child killed her?

What I really don't get, evolutionarily, is why humans have such bad vision.

[Suburbanite]

Quote by: Night What I'm asking is, why would menopause happen in woman everywhere (meaning it had to be very important evolutionarily) when most woman never got old enough to go through menopause?

We don't know the life expectancy of early man. Just because the average lifespan was lower doesn't mean their weren't still plenty of outliers dieing older and younger. And maybe menopause happened earlier on in life for earlier cultures and has changed since.

[gallo]

Quote by: Suburbanite Firstly, evolution is not about increased productivity, it is about increased survival chances.

No, it's not. You seem to have terribly confused the mechanisms that cause the process of evolution with the process. Evolution is about change (or sometimes stasis) in the heritable makeup of populations of organisms over time. One mechanism of that change is natural selection, which may be what you think you are talking about. Natural selection is most simply stated as differential reproductive success. In other words, certain beneficial characters give an organism a reproductive advantage. While that may mean that such an organism has survived to reproduce, it also means that such an organism tends to be more successful in leaving offspring. A further point that is implied is that the offspring must also have increased reproductive success. A good example was given by Jonathan Weiner in his Pulitzer Prize winning book, The Beak of the Finch. Peter and Rosemary Grant spent 20 years studying Darwin finches on a small island in the Galapagos. They successfully trapped and tagged every bird on the island for those 20 years (and more). They were able to recognize each bird on sight. In those years, two male ground finches both survived much longer (by years) than any other finches on the island. They were also quite successful 'producers', as you state it. Their broods were, on average, larger and, of course, they produced more over the years. If evolution is all about survival, then you might think that these two birds might have been significant in the evolution of ground finches on the island. That's not the case. Actually, their effect was zero since not a single one of their offspring lived to reproduce.

@Night:

What I'm asking is, why would menopause happen in woman everywhere (meaning it had to be very important evolutionarily) when most woman never got old enough to go through menopause?

Actually, just because a characteristic is universal does not necessarily mean that it has an evolutionary advantage. Especially in the case of menopause. What is evolutionarily significant is whether the woman survived to reproduce. You don't know it, but you answered your own question when you mentioned that in early mankind, there were probably few women that lived long enough to go through menopause.

You are also looking at this from a very limited viewpoint. Some years ago, in the days of extended families, the elderly assisted in raising the offspring of their children. Thus, they assisted in passing on their genes to further generations. There are examples of such activity in many species, where non-reproductive females assist in the caring of the young born of other females, usually a close relative.

[Kuldeep]

I wonder, if menopause occurs even in egg bearing species/birds and fruit bearing trees !!!!

Aging seems to be only reason !! Since at older age it won't be possible to rare their (older specie's) young ones, nature has put an automatic check in reproduction!!!!

[Thanatos]

Quote by: Kuldeep I wonder, if menopause occurs even in egg bearing species/birds and fruit bearing trees !!!! Aging seems to be only reason !! Since at older age it won't be possible to rare their (older specie's) young ones, nature has put an automatic check in reproduction!!!!

Come to think of it, chickens can't lay once they're really old. I have no knowledge of trees.

[Kuldeep]

To my knowledge even fruit bearing trees stop fruit bearing after a particular time period ! A botanist can tell us better !

[Suburbanite]

Quote by: gallo No, it's not. You seem to have terribly confused the mechanisms that cause the process of evolution with the process. Evolution is about change (or sometimes stasis) in the heritable makeup of populations of organisms over time. One mechanism of that change is natural selection, which may be what you think you are talking about. Natural selection is most simply stated as differential reproductive success. In other words, certain beneficial characters give an organism a reproductive advantage. While that may mean that such an organism has survived to reproduce, it also means that such an organism tends to be more successful in leaving offspring. A further point that is implied is that the offspring must also have increased reproductive success. A good example was given by Jonathan Weiner in his Pulitzer Prize winning book, The Beak of the Finch. Peter and Rosemary Grant spent 20 years studying Darwin finches on a small island in the Galapagos. They successfully trapped and tagged every bird on the island for those 20 years (and more). They were able to recognize each bird on sight. In those years, two male ground finches both survived much longer (by years) than any other finches on the island. They were also quite successful 'producers', as you state it. Their broods were, on average, larger and, of course, they produced more over the years. If evolution is all about survival, then you might think that these two birds might have been significant in the evolution of ground finches on the island. That's not the case. Actually, their effect was zero since not a single one of their offspring lived to reproduce.

Again, I'm going to disagree. Evolution is not about increased productivity, it is about increased chances of survival, which can include a decrease in productivity to sustain a population on a shortened food supply for example. I'm not sure if your study disproves me either, you need to go into detail about the contradiction between "They were also quite successful 'producers', as you state it" and "Actually, their effect was zero since not a single one of their offspring lived to reproduce." The first two finches are proof that the result of evolution is better chances of survival. Their non-reproductive offspring could've been a victim to a number of contingencies you haven't gone into.

[Rainbow]

Quote by: Night What I'm asking is, why would menopause happen in woman everywhere (meaning it had to be very important evolutionarily) when most woman never got old enough to go through menopause?

There are variety of essential factors - already posted by others, within this thread.
I believe that DNA coding could supply us with some additional (and maybe the most crucial) answers.