In a new review published [November 22] in PNAS, [evolutionary biologist Daniel] Lieberman and his Harvard co-authors grapple with the “active grandparent hypothesis,” using biomedical research and evolutionary studies to explain how humans evolved to need physical activity, particularly in and after middle age, to increase life span and reduce the risk of disease.
Lieberman spoke with STAT from Copenhagen, where he is pursuing further research, about health span vs. life span, why stress from exercise is good for us, and which animals are couch potatoes.
[STAT:] Do we know why physical activity keeps us healthy longer?
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[Lieberman:] There are some hypotheses. The first hypothesis is that in humans, physical activity evolved to help extend health span. Prior to medicine, health span equaled life span….Our general hypothesis is that we evolved all kinds of responses to physical activity that improve health span over the long term, not just when you’re young, but when you’re old. And that those responses are largely due to energy allocation.
Until recently, energy was limited, people couldn’t go to the 7-Eleven and grab 200 calories. People had to be very physically active, which takes energy.
