The evolutionary origins of menopause
I began reading up on this subject some years ago. I'm not an evolutionary biologist, but find the subject fascinating. Appologies to anyone here who is, as this is may be dated and incomplete info (if so please enlighten me), but it will make you believe in the value of older women.
At first glance, menopause would seem to be counter to evolutionary theory (the more offspring the better chance of leaving your genes to future generations, right?). Most mammals do not undergo menopause. Humans and (one other mammal** whose identity will be revealed below and which is not at all closely related to humans) were the only mammals known until recently to do so. I discovered three different theories on the origin of menopause:
(1) humans simply live too long. If other mammals lived as long as we do (based on heartbeats per lifetime or some other criterion) they might have menopause too.
(2) by nurturing grandchildren rather then children after a certain point in life, a woman may do more to ensure that her genes survive. It becomes a numbers argument: the survival of 2 grandchildren is the same as the survival of one child. But it has to play out over many generations with many other variables going on at the same time.
(3) groups, tribes, villages are more likely to survive periods of hardship (drought, flood, etc) if the group includes older women who have lived through similar hardship before. Without menopause, women wouldn't live as long. Remember Old Flo in Jane Goodall's first and 2nd chimp books? Pregnancy, childbirth, and lactation take a huge toll on a woman's body, particularly as she gets older. In most aboriginal (pre-literary) cultures, women were the storehouses of knowledge on local flora and nutrition. This theory was published around 1990 by a researcher who spent time with aboriginal cultures (in the Carribbean?) studying local flora and fauna. If he asked about the edibility of a certain plant that wasn't a normal part of the people's diet, he would be taken to see an old blind toothless crone who would remember what the people ate during the last drought 50 or 60 years ago. During the next drought, it was the knowledge possessed by this old woman which would ensure the group's survival. So evolutionary survival is based on social groups, but the result is the spread of genes that produce menopause. And older women were essential (until recent times) to survival. Doesn't that make you all feel good?
** The other mammal which has been known for decades to undergo menopause is the pilot whale. It's known because they were harvested commercially. Probably the orca too, but it wasn't commercially whaled.