We evolved to exercise

02/07/2019

The January issue of Scientific American has a great story by Herman Pontzer about how we humans are similar and profoundly different from our cousins—chimpanzees, bonobos, orangutans and gorillas—with whom we share over 97 percent of our DNA. Ponzer is a professor of evolutionary anthropology at Duke University who has studied hunter-gathering humans and apes for many years. Apes remain healthy at low activity levels, often spending eight to 10 hours a day resting, grooming and eating before going to sleep for nine to 10 hours. They remain remarkably healthy and lean at these low levels of physical activity, with very little heart disease or diabetes, even in captivity.  

For us humans, however, it’s a different story. We split from chimpanzees and bonobos about 6 to 7 million years ago. Recent findings indicate that we gradually became fully upright, walking creatures who could still get up into the trees. About 1.8 million years ago, we began to develop stone tools for butchering animals, indicating that we probably ran them down. At the same time we expanded out of Africa into Eurasia and as far as Indonesia; the ability to hunt as well as gather was the key. Relying on meat requires cooperation and sharing. It is thought that these early humans got roughly half their calories from plants and half from meat. Hunter-gatherers typically walked 12,000 to 18,000 steps a day. 

Our physiology has changed and adapted to this active life. The brain has evolved to need less sleep—about seven hours, far less than the apes. Our brain has also evolved to reward prolonged exercise by producing endocannabinoids. Exercise enables the expansion of the brain in childhood and adulthood, and is known to improve memory. Our leg muscles are 50 percent bigger than those in other apes, and we have more red blood cells to carry oxygen to our working muscles. 

You can understand that our bodies have evolved to require daily physical activity. Exercising muscles release hundreds of signaling molecules that reduce chronic inflammation and lower levels of testosterone, estrogen and progesterone. This may account for the reduced rate of reproductive cancers among those who exercise regularly. The morning rise of cortisol is blunted, which may mitigate stress. Exercise reduces insulin insensitivity and helps to put glucose into muscle glycogen instead of fat. Diabetes is thus prevented. Exercise improves the ability of the immune system to stave off infection. Even light activity, such as standing instead of sitting, is helpful.  

Another article in the January Scientific American concerns a genetic mutation that may have occurred in our species 2 to 3 million years ago, enabling humans to run long distances, sweat to cool off and hunt their prey to exhaustion. Biologist Ajit Varki at the University of California, San Diego is studying this hypothesis. 

The take-home message from these studies is that we have evolved to move—a lot more than most of us are accustomed to. To stay healthy as we grow from childhood into old age, we need to stay active. This will take social planning: to make more sidewalks, playgrounds and parks in many towns and cities, and to keep them safe. Children of all ages need places to get outside and play. They may also do sports, skateboard, bicycle, run with a dog, swim or dance. And it will take individual planning to bring activity into our adult lives despite sedentary desk jobs and the pull of screen time. We have evolved to move.

 

Sadja Greenwood, a longtime Bolinas resident now in Portland, is a retired physician.