Old men mate with young women as an explanation for long human lifespan

I meant to get into this PLoS One paper, but never got around to it. Here's a quick and dirty Yahoo! News story on it.

some data from the paper in the news story:

In all six groups, women stopped having children on average by their 50s, while some men continued to reproduce. The age after which men showed no reproduction varied among the groups and included:
Canada—Men showed fertility until 55 years old.
!Kung—55 years old
Gambia—75 years old
Yanomamo—70 years old
Ache—65 years old
Tsimane—60 years old

I think this complements the grandmother hypothesis as an explanation for long lifespans in humans. The take home message is that productivity in later age humans is highly valued due to a big productivity deficit in early life due to the importance of acquiring embodied capital due to our evolved feeding and social niche. (that was not well written, but hopefully kinda clear) - basically humans are altricial and require a lot of investment due to our ecological niche, therefore increasing payoffs to longevity and long-term productivity.... so that's why females prefer older guys who can provide such important child-rearing resources, since they have built up a lot of embodied capital, and also why older aged females can be vital (as grandparents).