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A gym user exercises on a treadmill at Kensington Leisure Centre in London on Dec. 2, 2020.BEN STANSALL/AFP/Getty Images

Here’s one small way in which this highly unusual year is not so different from its predecessors: In the waning weeks of January, gyms are empty.

Every year, we resolve to mend our sedentary ways and exercise more. We know it’s good for us. We were born to leap and thrust and ramble across the savannah. So why do we abandon those resolutions so quickly and predictably?

That’s the question at the heart of a new book by Harvard University evolutionary anthropologist Daniel Lieberman. Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding is, in some ways, a book full of excuses. Our aversion to wasting energy is hard-wired into our genes, he tells us: “Exhorting us to ‘Just Do It,’ ” he writes, “is about as helpful as telling a drug addict to ‘Just Say No.’ ”

Don’t celebrate yet, though. Lieberman sets out to puncture myths about what we were born to do and how we’re supposed to feel about it, but he’s not cancelling exercise, and he’s not promising to make it easy. Instead, he’s hoping that a more nuanced understanding of our evolutionary heritage can help us break away from the endless cycle of big goals and broken resolutions.

There’s an irony here. Lieberman’s most famous paper, co-written with University of Utah biologist Dennis Bramble and published in Nature in 2004, argued that humans were uniquely adapted to run long distances. This so-called “Born to Run” hypothesis later provided a title for Christopher McDougall’s 2009 bestseller about barefoot running, in which Lieberman figured prominently.

In Born to Run’s aftermath, Lieberman became associated – in the public mind, at least – with the idea that barefoot running, and running in general, was a natural activity that humans were “meant” to do. Around the same time, the paleo diet was exploding in popularity, as were fitness programs such as CrossFit that aimed to replicate the movement patterns of our pre-agrarian ancestors.

It’s clear that our bodies were shaped by the generations we spent as hunter-gatherers. Calories were scarce and survival was always on a razor’s edge, so we evolved to hoard energy.

Conversely, necessity also forced us to be physically active, and the resulting wear-and-tear to tissues and cells served as a crucial stimulus for the body’s self-repair mechanisms. Without exercise, the internal self-repair processes that keep us healthy grind to a halt.

Lieberman’s “active grandparent” hypothesis goes a step further, suggesting that genes that keep the body’s self-repair systems operating into old age, long after the reproductive years that evolution usually focuses on, allow grandparents to help their younger relatives survive and thrive. These genes are passed on and exercise is still the cue that triggers our cells to fight aging and extend life.

Despite all this, Lieberman himself was never a proponent of the idea that there’s an ideal “primal fitness” regimen that we should all seek to replicate. Sure, evolution shaped us to be capable of running long distances – but we did it only to survive. In the new book, he dismisses modern “born-to-runners” as “another irritating extreme [who] have read about how we evolved to run (this is partly my fault) and preach that running is the key to health and happiness, especially if you run barefoot.” And traditional hunter-gatherers, he points out, would see no reason to pack on energetically expensive muscle like a CrossFit devotee.

He is similarly dismissive of the romanticization of Indigenous groups such as the Tarahumara in Mexico, whose long-distance running exploits also featured in Born to Run. The idea that running is natural and easy for people uncorrupted by modern civilization is what Lieberman dubs “the myth of the athletic savage.”

Lieberman’s own work among the Tarahumara has convinced him that they are just as allergic to exercise – ”voluntary physical activity that is planned, structured, repetitive and undertaken to sustain or improve health and fitness” – as the rest of us. The difference is that their daily life as subsistence farmers necessitates an active life, and games that involve prolonged running are deeply embedded in their culture.

In that observation lies the seed of Lieberman’s prescription for how to overcome our aversion to wasted energy: We have to make it fun, sociable and easy to integrate into our lives. And when those tactics fail to prevent you from falling off the wagon, you should be kind to yourself: It’s what you were born to do.

Alex Hutchinson is the author of Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance. Follow him on Twitter @sweatscience.

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