HARVARD MAGAZINE (SEPT – OCT 2020): From the book EXERCISED: Why Something We Never Evolved to Do Is Healthy and Rewarding by Daniel E. Lieberman, to be published on September 8, 2020 by Pantheon Books:
‘….many of the mechanisms that slow aging and extend life are turned on by physical activity, especially as we get older. Human health and longevity are thus extended both by and for physical activity.’
Exercise is like scrubbing the kitchen floor so well after a spill that the whole floor ends up being cleaner. The modest stresses caused by exercise trigger a reparative response yielding a general benefit.
In order to elucidate the links between exercise and aging, I propose a corollary to the Grandmother Hypothesis, which I call the Active Grandparent Hypothesis. According to this idea, human longevity was not only selected for but was also made possible by having to work hard during old age to help as many children, grandchildren, and other younger relatives as possible survive and thrive. That is, while there may have been selection for genes (as yet unidentified) that help humans live past the age of 50, there was also selection for genes that repair and maintain our bodies when we are physically active.
Daniel E. Lieberman is a paleoanthropologist at Harvard University, where he is the Edwin M Lerner II Professor of Biological Sciences, and Professor in the Department of Human Evolutionary Biology. He is best known for his research on the evolution of the human head and the evolution of the human body.
From a HarvardMagazine.com online archive article:
Six factors measured by age 50 were excellent predictors of those who would be in the “happy-well” group–the top quartile of the Harvard men–at age 80: a stable marriage, a mature adaptive style, no smoking, little use of alcohol, regular exercise, and maintenance of normal weight. At age 50, 106 of the men had five or six of these factors going for them, and at 80, half of this group were among the happy-well. Only eight fell into the “sad-sick” category, the bottom quarter of life outcomes. In contrast, of 66 men who had only one to three factors at age 50, not a single one was rated happy-well at 80. In addition, men with three or fewer factors, though still in good physical health at 50, were three times as likely to be dead 30 years later as those with four or more.
The book examines the lives of a group of Harvard men who have been studied from their college years all the way to retirement and, in some cases, death. Its cornerstone is the Grant Study, a longitudinal investigation conceived in 1937 and launched at Harvard in 1939. With funding from dime-store magnate W. T. Grant, researchers signed up 268 members of the classes of 1941 through 1944, in their sophomore years, for an in-depth, lifelong study of “normal” adult development.