Here's an article on The Grandmother Hypothesis. Personally, I didn't take the idea seriously until a biological anthropologist told me that menopause was a tightly integrated proactive cascade of biochemical changes which shuts down female procreative capacity. In contrast, human males exhibit declining fertility in a gradual fashion due to a generalized breakdown of bodily function. I am generally suspicious of some sort of adaptation when something so precise in our physiology seems on the surface to reduce fitness. Update: Here is an article from the originator of The Grandmother Hypothesis:
This article assesses effects of the modern world on hunter-gatherer adult mortality, with special reference to the Hadza. Evidence suggests that such effects are not sufficient to deny the existence of substantial life expectancy at the end of the childbearing career. Data from contemporary hunter-gatherers(Ache, !Kung, Hadza) match longevity extrapolated from regressions of lifespan on body and brain weight. Twenty or so vigorous years between the end of reproduction and the onset of significant senescence does require an explanation.
Note: I expect readers of this weblog to comprehend that small (e.g., less than 1%) selection coefficients over long periods of time are evolutionarily significant.