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When Was the Last Time You Exercised?

If you're anything like the average American, it was probably a while ago. A new book says it's because humans evolved not to.

With Daniel Lieberman PhD

Evolution and exerciseJust because regular exercise is healthy doesn't mean that it's natural.

More than 80 percent of American adults don't get enough aerobic or muscle-strengthening exercise, and just five percent work out for the recommended 30 minutes per day for optimal health, according to the US Department of Health and Human Services.

Hearing this, you might be tempted to guilt yourself and pledge to exercise more. But a new book from Daniel Lieberman, a professor of Human Evolutionary Biology at Harvard University, claims it's normal and adaptive to feel resistant to exercise. Why? From an evolutionary perspective, human beings never evolved to exercise in the first place – at least not in the ways we think about obligatory exercise for health today. 

In Exercised: Why Something We Never Evolved To Do Is Healthy, Lieberman explores the behavior of our earliest ancestors, which he says can help us shed light on our own actions today. We talked to him about how the knowledge that exercise is inherently unnatural can help you find your own solution to get yourself off the couch. 

What inspired you to write Exercised?

I wanted to write a natural history of physical activity. In our current world, what we've done with exercise is that we've industrialized it, commercialized it, and medicalized it. And we haven't done a very good job at it, either. People are confused, anxious, and ambivalent about exercise – but I'm hoping that this alternative approach can help change that.

You explain in your book that human beings didn't evolve to exercise, and that it's unnatural. What do you mean by that exactly?

Humans, like every species, evolved to move. We have to do stuff – every time you move your body, your arm, your leg, that's physical activity. But exercise is a different, particular kind of physical activity. It's discretionary, it's voluntary for the sake of health and fitness. Until recently, nobody did that – ever. We all evolved with an instinct to avoid unnecessary exertion, like all animals, except when it's useful to us. Spending an hour on a treadmill when we don't have to run away from a predator or to find food, that's unnatural to us – it's bizarre.

What are other health myths your book explores about humans and how we evolved?

One myth is that we didn't evolve to sleep eight hours a night. Another myth is that sitting is abnormal – it's not “the new smoking,” as people have started to say. We've also never evolved to “take it easy” as we age – we actually evolved to be more physically active as we get older.

What did you find in your research on exercise and evolution that surprised you?

I'm a scientist – our job is to challenge ourselves, and so there was a lot I learned in the process of my research that surprised me. For example, I always thought that slouching caused back pain – but there's actually no evidence for that. People who slouch are no more likely to have back pain than people who don't, and it turns out that hunter-gatherers slouched a lot. The best predictor of back pain is how much endurance your back has. People who have less strength and endurance are more likely to slouch, so we've become confused about the cause and effect.

If exercising isn't normal for humans but still has such significant health benefits, particularly if you have an endocrine condition such as diabetes or a thyroid disorder, how can we motivate ourselves to actually do it regularly?

The last part of the book is about how we can apply the story of exercise to the modern world. I argue that we should treat exercise like education, which is also modern and strange. How do we make it both necessary and rewarding? School is necessary, but we can also make it enjoyable by having recess and art, and we can do the same for exercise. Making it social and having some kind of commitment contract I think is key.

How were you able to determine what ancient hunter-gatherers did millions of years ago, such as slouching?

The people I study are contemporary human beings, but we can learn a lot from how our ancestors behaved through them. The majority of the information we have about health has come from studying Americans, Europeans, and Australians. They're WEIRD – in other words, Western, Educated, Industrialized, Rich, and Democratic. Most of the world isn't like that. A large part of the book is how if you leave America and look at the rest of humanity you get a sense of what people were like up until the industrial revolution. Most of my work has been in Kenya, and I've also worked in Mexico with rural farmers.


What's the most important takeaway about the relationship between exercise and evolution from Exercised?

Understanding that we've commodified a really abnormal behavior. It works for a small percentage of people, but not for all of us. Telling people to exercise as medicine doesn't work and it isn't fun. Trudging on a treadmill for half an hour every day so you don't die of a heart attack doesn't motivate most people. We can help each other and be much more compassionate about physical activity – which really is good for us – by broadening our approach. Let's make it fun and enjoyable and stop telling myths. 

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