My oldest son, now 18 years old, has a severely disabling genetic disorder; since infancy he’s been painstakingly cared for by a team of clinicians at Columbia University Medical Center in Manhattan. His geneticist, one of the most formidable intellects I’ve ever encountered, had worked on the Human Genome Project in the 1990s, sequencing the LEP gene, which codes for leptin, a hormone that helps to inhibit hunger pangs. She yearned to distill her research into a eureka pill for those of us susceptible to midnight refrigerator raids, that extra slice of chocolate cake — a Holy Grail of treatments. In the end, though, she and her colleagues fell short. “It’s all about diet and exercise,” she once told me, “just like your mother begged when you were a child.”
“Exercised,” a sweeping, vigorous new work from Daniel Lieberman, the Edwin M. Lerner II professor of Biological Sciences at Harvard, probes how and why exercise is so good for us when as a species we evolved as loafers in order to conserve calories for the lean seasons. Lieberman opens the book with a pun: the title refers not only to physical exertion in the pursuit of good health but also to the adjective exercised, “to be vexed, anxious, worried, harassed.” As he knows, most of us feel conflicted about exercise; the thought of 30 minutes on a NordicTrack elliptical or dead lifts at the gym can spike our blood pressure.
But is there an evolutionary underpinning to our collective dread? Lieberman argues that even our rail-thin ancestors were slackers. When we analyze a range of cultures around the globe, or even our close primate relatives, such as chimpanzees, we detect a clear pattern: our species is adept at spending much of our time just hanging out, in order to conserve calories. Throughout the book Lieberman refers to the Hadza, a foraging people clustered in Tanzania; despite profound differences between their routines and ours, between their diets and ours, the common biology is not that dissimilar. They sit around camps at about the same rates as those of us stuck in desk jobs.
He considers the act of sitting and whether it’s as bad for us as smoking cigarettes (it’s not)[HC1] [k2]. And he mulls the commercialization of fitness. “To me, the apotheosis of what’s good and bad about contemporary exercise is the treadmill. Treadmills are incredibly useful, but they are also loud, expensive, and occasionally treacherous . . . The only way I endure the tedium and discomfort of a treadmill workout is by listening to music or a podcast. What would my distant hunter-gather ancestors have thought of paying lots of money to suffer through needless physical activity on an annoying machine that gets us nowhere and accomplishes nothing?”
There’s a dry, didactic quality to “Exercised”; Lieberman’s a top-flight scientist and cogent writer, but the book lacks the stylistic spark of a Robert Sapolsky or David Eagleman. And yet Lieberman’s clarity never wavers. When the book shifts to prescriptive sections — should I focus on cardio rather than dumbbells? Are gym workouts still beneficial as we age? — he readily acknowledges the data is more suggestive than certain. (A runner, he tilts toward cardio as the preferred exercise.) He’s particularly good at busting myths, organizing chapters around debunking assumptions about what constitutes fitness and health. Eight hours of sleep may not be the most efficacious way to rest. Charles Atlas to the contrary, we evolved, as one chapter title describes it, “from brawny to scrawny,” leveraging our more gracile forms over, say, the bulk of the Neanderthals. His answers to physiological questions — “Is running bad for your knees?” “Should my 90-year-old grandmother bench-press each week?” — dispel lazy platitudes.
They also inspire. He presses his case on preventive care, often waved away by Americans as a violation of their freedom to be couch potatoes. “I am aware that people like me often sound like broken records. . . . Please don’t react that way for cancer, however, because the cancer-fighting potential of exercise is underappreciated and inefficiently explored. . . . Just as natural selection favors humans who acquire and then spend as many calories as possible on reproduction, the selection that drives cancer favors malignant cells that acquire as many calories as possible and then use them to create more copies of themselves.” He underscores the leading culprits — reproductive hormones, sugar, inflammation, and antioxidants — and illuminates why exercise may be our most potent weapon to stave off the emperor of all maladies.
To circle back to the Columbia geneticist’s point: If “Exercised” occasionally reads with the tone of your stern-voiced mother, wagging her finger and imploring you to eat your vegetables and jog around the block, then all to the good. Lieberman has accomplished his mission. But the science beneath his arguments is revelatory, with thrilling implications for evolutionary biology. Written in a brisk prose, with ample graphs, “Exercised” is an excellent compendium on the broad medical advantages of exercise and a roadmap out of our pandemic to better health.
Hamilton Cain is the author of “This Boy’s Faith: Notes from a Southern Baptist Upbringing” and a member of the National Book Critics Circle. He lives with his family in Brooklyn, N.Y.
Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding
Pantheon, 464 pages, $29.95