On a warm Wednesday morning in October, Herman Pontzer puts on a wrinkled lab coat, adjusts his mask, and heads into his lab at Duke University, hoping to stress out a student. An undergraduate named Christina is resting on a lab table with her head in a clear plastic hood. Pontzer greets her formally and launches into a time-honored method to boost her blood pressure: He gives her an oral math test.

“Start off with number 1022 and subtract 13 until you get to zero,” he says, speaking at full volume to be heard over a clanking air conditioner. “If you make a mistake, we’ll start over again. You ready to go?”

“1009, 997,” Christina says.

“Start over,” Pontzer barks.

Christina, who has signed up for a “stress test,” laughs nervously. She tries again and gets to 889, only to have Pontzer stop her. This happens again and again. Then Pontzer asks her to multiply 505 by 117, out loud. By this point, she is clenching her sock-clad toes.

Postdoc Zane Swanson and undergrad Gabrielle Butler monitor her heart rate and how much carbon dioxide (CO₂) she exhales into the hood. Then Pontzer asks a set of questions designed to boost a student’s stress levels: What’s her dream job, and what exactly is she going to do after graduation?

It’s another day in the Pontzer lab, where he and his students measure how much energy people expend when they are stressed, exercising, or mounting an immune response to a vaccine, among other states. By measuring the CO₂ in Christina’s breath, he is finding out how much energy she has burned while coping with math anxiety.

At 44, Pontzer’s life’s work as a biological anthropologist is counting calories. It’s not to lose weight—at 1.85 meters tall and about 75 kilograms (6 feet 1 inch and 165 pounds), with a passion for running and rock climbing, he is “a skinny to normal size dude,” in the words of an online reviewer of Pontzer’s 2021 book Burn: New Research Blows the Lid Off How We Really Burn Calories, Lose Weight, and Stay Healthy.

Pontzer is happy to expound on weight loss on The Dr. Oz Show and NPR, but his real mission is to understand how, alone among great apes, humans manage to have it all, energetically speaking: We have big brains, lengthy childhoods, many children, and long lives. The energy budget needed to support those traits involves trade-offs he’s trying to unravel, between energy spent on exercise, reproduction, stress, illness, and vital functions.

By borrowing a method developed by physiologists studying obesity, Pontzer and colleagues systematically measure the total energy used per day by animals and people in various walks of life. The answers coming from their data are often surprising: Exercise doesn’t help you burn more energy on average; active hunter-gatherers in Africa don’t expend more energy daily than sedentary office workers in Illinois; pregnant women don’t burn more calories per day than other adults, after adjusting for body mass.

Pontzer’s skill as a popularizer can rankle some of his colleagues. His message that exercise won’t help you lose weight “lacks nuance,” says exercise physiologist John Thyfault of the University of Kansas Medical Center, who says it may nudge dieters into less healthy habits.

But others say besides busting myths about human energy expenditure, Pontzer’s work offers a new lens for understanding human physiology and evolution. As he wrote in Burn, “In the economics of life, calories are the currency.”

“His work is revolutionary,” says paleoanthropologist Leslie Aiello, past president of the Wenner-Gren Foundation, which has funded Pontzer’s work. “We now have data … that has given us a completely new framework for how we think about how humans adapted to energetic limits.”

The son of two high school English teachers, Pontzer grew up on 40 hectares of woods in the Appalachian hills near the small town of Kersey, Pennsylvania. His dad, who helped build their house, taught Pontzer to be curious about how things worked and to fix them. “No one ever called plumbers or electricians,” Pontzer recalls.

Those lessons in self-sufficiency and an outgoing nature helped him cope when his dad died when Pontzer was just 15. An older cousin also took him climbing, which taught him to be both brave and organized—skills he says later helped him take intellectual risks and challenge established ideas. “When you have a bad experience and life plucks you off your track, it’s scary,” Pontzer says. “You have to move forward, though, and that teaches you not to be scared of new things.”

Pontzer applied to a single college—Pennsylvania State University, whose football games were a highlight of his childhood. “I assumed I’d be my dad—go to Penn State, get my teaching degree, and stay in Kersey,” he says. But once at Penn State, he worked with the late, renowned paleoanthropologist Alan Walker and found himself considering grad school in biological anthropology.

After learning his promising student was choosing schools based on their proximity to mountains, Walker was blunt: He told Pontzer he was an idiot if he didn’t apply to Harvard University—and, once Pontzer was accepted, he’d be an idiot if he didn’t go.

Pontzer went. In the early 2000s, scientists knew little about humans’ total energy expenditure (TEE)—the number of kilocalories (the “calories” on food labels) a person’s 37 trillion cells burn in 24 hours. Researchers had measured the rate at which our bodies burn