In this case, the discussion was on the evolutionary value of menopause, a phenomenon (nearly) unique to humans. Diamond raises and dismisses some typical arguments that don't make much sense, then advances the one widely-heard argument he (and FWIW I) find sensible: by skipping the last child or two, old women can help raise their grandchildren, and do more to ultimately increase their genes' survival than would a risky pregnancy. Grandmothers help not just with childcare: in some traditional societies such as the Hadza of Tanzania, grandmothers are the most economically productive people.
But then Diamond raises an argument of his own, a very interesting argument at the heart of Heather and my discussion: in traditional societies, old people are the library people turn to in times of crisis.
Any human societies that included individuals old enough to remember the last event like a [hurricane] had a better chance of surviving than did societies without such old people.... At times of crisis... prior death of such an older woman also tended to eliminate all of her surviving relatives from the gene pool.... The importance to society of the memories of old women is what I see as a major driving force behind the evolution of human female menopause.
The book is about a good deal more than menopause. And, like sex, the book is also fun. Thanks for loaning it to me, Heather. I'll have it back to you real soon now.