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Comment by Retric | Hacker News Reader

Aging is more than just accumulated dammage, menopause is a clear counter example to this idea. However, dammage does accumulate so like most complex systems there are no simple answers.

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Menopause is an oddity and a puzzle. It isn't easily used to support any of the various points of view in aging research, partially because it is a human peculiarity that doesn't seem to be present in anything like a similar form in other primates or mammals. Theorizing has it linked with the grandmother hypothesis viewpoint on why humans are so much longer lived than other primates, and the evolutionary track by which we got here. You might look at these papers:

http://www.impactaging.com/papers/v6/n2/full/100640.html

http://www.pnas.org/content/110/33/13440

What ? This is not true at all. Menopause is present in all mammals. The reason you don't see it in most mammals is simple : the normal maximum age for most mammals is less than half of humans. Most animals grow to about 30-35 "dog-years", and die. Dogs and cats in captivity, some long-lived races, do experience menopause. If humans died at 30-35, which is about the expected age for humans in the natural habitat, it would be a very rare woman indeed that experience menopause. (Keep in mind that 35 is the average age of death for humans in nature. But at that age most deaths are still accidental, meaning there is a large deviation. A lot of kids would "naturally" die 5 years or younger (like 30-50%, depending on environment), then there is a certain chance of dying every year. IF a human can avoid nature, infection, fights (or you know, win them all), poisoning, famine, ... a male human would age to about 40-45 years in nature, a woman a little older. But no more than 2% or so will ever see their 45th birthday in a natural human population)

Here's the key, when a female baby takes her first breath (oxygen in the lungs), a mechanism is set off that causes the ovi to cut off all connections to the mother body. To put it simple: before a baby girl takes her first sip of mother's milk, all the baby's children have become independent lifeforms, no longer connected to the mother's body. The baby's DNA will sabotage and boobytrap it's own ability to create new ovi at that point. This of course means, among other things, that their numbers are 100% fixed at this point. This means that at that point the number of fertility cycles her body will go through is a constant from that point forward. There is a similar, but more complex, process set off in men (in men, too, the cells that form the reproductive cells are very isolated from the rest of the body).

When a human is disconnected from the umbilical, a number of changes happen as a result of that in order to switch to what you might call internal power if it were a robot. The immune system wakes up. The lungs inflate. The heart starts actually pumping blood around (yes it beats in babies, but a baby would survive without a beating heart as diffusion will actually happen fast enough. This is really sad when it happens since the baby is alive at that point, but growing will kill it). Cell reproduction rates are massively cut, and are moving towards replacement-only (a 2 year old is -almost- no longer making extra tissue. An adult is simply a 2 year old with "stretched" cells, not more cells)

Essentially nature is trying to protect the next generation from DNA alterations by external influences. Menopause is just a side-effect that evolution doesn't care about because women are unlikely to have viable children at that age.

Isn't menopoause caused by running out of eggs? Actually this is the same mechanism as reported in this story - a lack of stem cells. The interesting thing about this is the stem cells can be reactivated.

That's an oversimplification - menopause results from decreased levels of hormones that would normally be secreted during the process of egg maturation, among other potential causes [see ref 1].

Further, all the eggs a woman will ever have are created while she is developing in her own mother. This is totally distinct from stem cells, many of which are able to generate new stem cells throughout our lives, albeit at an ever-decreasing rate.

[1] http://www.mayoclinic.org/diseases-conditions/menopause/basi...

http://www.webmd.com/infertility-and-reproduction/news/20040...

I dug into this a bit. A good metric by which to measure exciting (and very controversial) papers like the one referenced by that link is to see whether the papers have been replicated by others in well-regarded journals.

While the principal author of that article published an equally-controversial paper in 2005, follow-up studies suggest that there are no newly-generated egg cells in mammals [1]. I think it's fair to say, again, that stem cells don't play a role in maturation of adult egg cells.

http://www.ncbi.nlm.nih.gov/pubmed/23630252

Everything when it comes to reproduction is an oversimplification, but the basic problem is the same a lack of active stem cells (there are still stem cells present). Once all the eggs are used up then the ovary stops producing oestrogen and the other hormones.

Menopause is not a clear counter example. For all intents and purposes it is a symptom of biological aging and thus the result of "accumulated damage" (assuming that is indeed the overarching mechanism).

Menopause usually starts around 51 but there is a lot of variability and around 1 percent of women experience menopause before age 40. So it's not a direct result of cell damage. Now, if your suggesting that it's an evolutionary response to cell damage that's possible however as fixing the damage would not remove that response the difference is somewhat meaningless.

Changes in brain chemistry are another thing that's probably not directly damage related as the declines start around mid 20's.

PS: Biology has a lot of odd edge cases, youngest mother is 5 oldest 74. http://en.wikipedia.org/wiki/List_of_youngest_birth_mothers

http://en.wikipedia.org/wiki/Pregnancy_over_age_50

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