I’m kind of lazy. I admit it. I like to walk, ride a bike, and splash around in a pool, but I don’t indulge in a lot of exercise beyond that.
Now a Harvard professor named Daniel Lieberman says I can blame human evolution. In a recent paper, “Is Exercise Really Medicine? An Evolutionary Perspective,” he explains his ideas.
First, he says (and this is the sentence I really like), “It is natural and normal to be physically lazy.” Why? Because human evolution has led us to exercise only as much as we must to survive.
We all know that our ancestors lived as hunter-gatherers and that food was often scarce. Lieberman adds this idea: Resting was key to conserving energy for survival and reproduction. “In other words, humans were born to run—but as little as possible.”
As he points out, “No hunter-gatherer goes out for a jog, just for the sake of it….” Thus, we evolved “to require stimuli from physical activity.” For example, muscles become bigger and more powerful with use, and they atrophy when they’re not used. In the human circulatory system, “vigorous activity stimulates expansion of …circulation,” improves the heart’s ability to pump blood, and increases the elasticity of arteries. But with less exercise, arteries stiffen, the heart pumps less blood, and metabolism slows.
Lieberman emphasizes that this entire process evolved to conserve energy whenever possible. Muscles use a lot of calories, making them costly to maintain. Muscle wasting thus evolved as a way to lower energy consumption when physical activity wasn’t required.
What about now? Until recently, it was never possible in human history to lead an existence devoid of activity. The result: According to Lieberman, the mechanisms humans have always used to reduce energy expenditures in the absence of physical activity now manifest as diseases.
So maladies like heart disease, diabetes, and osteoporosis are now the consequences of adaptations that evolved to trim energy demand, and modern medicine is now stuck with treating the symptoms.
In the past, hunter-gatherers had to exercise because if they didn’t, they had nothing to eat. Securing food was an enormous incentive. But today, for most humans there are very few incentives to exercise.
How do we change that? Although there’s “no silver bullet,” Lieberman thinks we can try to make activity “more fun for more people.” Maybe making exercise more “social” would help. Community sports like soccer teams and fun-runs might encourage more people to get active.
Lieberman has another suggestion. At his own university, students are no longer required to take physical education as part of the curriculum. Harvard voted its physical-education requirement out of existence in the 1970s, and he thinks it’s time to reinstate it. He notes surveys that show that very few students who are not athletes on a team get sufficient exercise. A quarter of Harvard undergraduates have reported being sedentary.
Because “study after study shows that…people who get more physical activity have better concentration, their memories are better, they focus better,” Lieberman argues that the time spent exercising is “returned in spades…not only in the short term, but also in the long term. Shouldn’t we care about the long-term mental and physical health of our students?”
Lieberman makes a powerful argument for reinstating phys-ed in those colleges and universities that have dropped it. His argument also makes sense for those of us no longer in school.
Let’s foil what the millennia of evolution have done to our bodies and boost our own level of exercise as much as we can.
[Daniel Lieberman’s paper was the focus of an article in the September-October 2016 issue of Harvard Magazine. He’s the Lerner professor of biological sciences at Harvard.]