Why We Both Enjoy Exercise and Avoid It

In geology, a clast is a fragment of an older rock, now broken up and embedded in a younger one. In religion and philosophy, an icon is a revered symbol of long-accepted wisdom. Put the two together and you get iconoclast: a person who breaks cherished beliefs into fragments.

This is the role Daniel E. Lieberman, a professor of evolutionary biology at Harvard University, has adopted in his new book, Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding (Pantheon 2021, $29.95 hb.)

It’s not a “running” book and doesn’t claim to be one. But it is chock-full of fascinating information for runners — much of which might also make us better comrades to our non-running friends and family. Not that Lieberman is an outsider to the sport. He’s one of “us”: a multi-time Boston Marathon finisher who could run a 3:20:16 marathon at age 51 (he’s now 56).

Lieberman is best known as the scientist behind Christopher McDougall’s sensational book Born to Run. In fact, the title of that book was borrowed from a blurb on the cover of a 2004 issue of Nature, which featured Lieberman’s study of our distance-running heritage, officially titled “Endurance running and the evolution of Homo.” In it, Lieberman argued that among the animal kingdom, humans are supremely adapted distance runners — something that was not, at the time, the accepted wisdom.

In the new book, he again takes the role of iconoclast — or, more specifically, myth buster — structuring the book around a dozen myths, many of them promoted by runners, such as we evolved to exercise, and laziness is a modern aberration.

His thesis is something diehard “born to run” advocates may resist. We aren’t, he says, born to exercise. In fact, the concept we know as “exercise” would have been totally alien to our ancient ancestors.

To determine what our ancestors would have viewed as normal, Lieberman has devoted much of his career to researching remote regions in Kenya, Tanzania, Ethiopia, Namibia, the Amazon — and, of course, the Copper Canyon of Mexico, made famous in McDougall’s book — in search of cultures that retain roots of our ancient past.

He has instrumented hunter-gatherers with FitBits (or the research-laboratory equivalent thereof) and laboriously trucked a treadmill and generator to power it over terrible roads into remote regions, in an effort to do exercise physiology tests on subsistence farmers. The latter didn’t work well; running or walking on a treadmill is a skill that takes practice, and his results were skewed by his subjects’ worries about falling off this unfamiliar device.

But in another test — more of a dare than a true experiment — one of his graduate students attempted to carry a 10-gallon bucket of water on his head, up a big hill from a stream to a village. It was something the petite Kenyan women did daily, with relative ease. The graduate student managed it, but only with difficulty. And not all of the water made it with him.

This is the gist of the first part of Lieberman’s thesis — which is as simple and straightforward as is, in retrospect, the realization that if you put someone who’s never seen one before on a treadmill, they might not walk or run normally. Our ancestors didn’t evolve to “exercise.” They evolved to hunt, forage, and do chores.

In fact, he says — leading to the second point of his thesis — we are also adapted to not do unnecessary exercise.

People in the hunter/gatherer cultures he studied don’t go on runs just for the sake of doing them. They do what they need to do, then, for the most part, sit around, chat, work on projects, and pretty much act like couch potatoes (albeit without the couch) whenever possible. His studies of Hadza hunter-gatherers in Tanzania, for example, found that on an average day they walked or jogged about 11.5 kilometers a day, or 50 miles a week. The rest of the time — about 85 percent of their waking hours — they didn’t do anything more than light activities, if that.

“For generation after generation,” he writes, “our ancestors…woke up each morning thankful to be alive and with no choice but to spend several hours walking, digging, and doing other physical activities to survive to the next day. Sometimes they also played or danced for enjoyment and social reasons. Otherwise, they generally steered clear of nonessential physical activities that divert energy from the only thing evolution really cares about: reproduction.”

Then comes the kicker: “The resulting paradox is that our bodies never evolved to function optimally without lifelong physical activity but our minds never evolved to get us moving unless it is necessary, pleasurable, or otherwise rewarding.”

So, what does this mean to us as runners?

First, it means that running as sport/exercise isn’t what we are built to do. We evolved to be active, but not to train for a marathon…or even a 5K. We didn’t evolve to “train” for anything other than survival.

That said, it’s intriguing that Lieberman’s studies may have found a “sweet spot” at about 40 to 50 miles a week. He doesn’t address that directly in his book, but that does seem to be a level many people can build to in training, even with only average biomechanics. Beyond that, some can, some can’t. We’ve always known that most runners’ bodies can’t tolerate 100-mile weeks, even if the elites can. Now, maybe we know why.

But most importantly, he found that the difficulty we sometimes find in getting out the door isn’t a character flaw. It’s literally in our genes. Which means there’s no point lambasting our non-running friends too hard in an effort to get them moving. They are doing what comes naturally.

The problem, Lieberman argues, is a “mismatch” between our genes and our rapidly changing modern environment, which has shifted far more quickly than our bodies can adapt. I.e., his findings don’t mean that our sedentary neighbors wouldn’t benefit from becoming more active — quite the contrary — but do mean that their difficulty in doing so isn’t some kind of moral failure. It’s a trap that those of us who have been fortunate enough to be active all our lives have managed to avoid.

The book also addresses a number of other issues, such as the effect of age on performance, which, Lieberman says, leads to yet another myth that we are doomed to become substantially less active as we age (though we might have to adjust how we train for that activity, a topic he doesn’t address).

Bottom line: this is a really interesting book. If you want to know why running feels so good and so natural, there’s even a section on that.

But mostly, it’s a reassurance that being active is an important part of being human. Running isn’t necessary for that…but it certainly is fun, and there’s even a section on why evolution has given us that particular joy.