Did hunter-gatherers really spend more energy than modern humans?

“A six-foot wall of fire was coming through our camp,” says Herman Pontzer. “Everything that you have is basically flammable: your diesel-soaked Land Rover, your tent, your test samples and all your food. So what the hell do you do?”

Luckily for Pontzer and his research team, this is a common occurrence for the Hadza people of Tanzania, one of the last hunter-gatherer populations in the world. ”We pulled all of our stuff into some part of their camp that was more or less grass-free and drove the Land Rovers through the fire where it had already burned,” says Ponzter. “Then we grabbed some tree branches and joined the Hadza to beat back the fire that was encroaching on the camp. They’re all singing and having a good time!”

It’s a snippet of the unique and exciting things Pontzer, an anthropologist at Hunter College in Manhattan, has seen during his years of research. Pontzer, 36, has traveled far beyond the ambience of his rural Pennsylvania hometown to investigate how primates and humans get and spend energy. “Energy is the common currency of biology,” he says. “If you want to talk about ecology, anatomy, behavior, reproduction, aging, all of it, the whole shooting match is plugged into metabolic energy. It’s the power source.” Some of his recent findings have challenged the long-held assumption that energy expenditure is tied to physical activity, generating a great deal of discussion among biologists, anthropologists and health experts alike.

As an undergraduate at Pennsylvania State University, Pontzer got hooked on evolutionary science, especially the evolution of humans. He went on to earn his Ph.D. at Harvard University, where he began researching primate energetics. At Harvard, he met Brian Wood and David Raichlen, anthropologists at Yale University and the University of Arizona, respectively. Both remember Pontzer as being very intelligent and pretty hilarious.

“He’s able to see problems and projects from very different perspectives than most people do,” says Raichlen. He and Wood would later become two of Pontzer’s most frequent research collaborators. “Working in the field with Herman has always been a blast,” says Wood.

After a few years as an assistant professor of anthropology at Washington University in St. Louis, Pontzer came to Hunter College. Around this time, he began to feel that he had hit a wall in his research. There were practically no data on energy use in hunter-gatherer humans, which made it difficult to study the evolution of metabolism and energy expenditure. Pontzer knew he had to remedy this problem if he was going to make any new progress.

The 300–400 Hadza in Tanzania make up one of the last hunter-gatherer populations in the world left to study. Thankfully, they are generous in allowing researchers to study them. “They know they’re the only ones who practice this lifestyle,“ says Pontzer, “and they’re happy to share.”

A day in the life of a Hadza man or woman starts at sunrise in a small tent, without electricity or running water. After a short breakfast, the women make plans to go foraging together for plant foods like berries and root vegetables, while the men muse about what game they will be hunting that day, usually individually. Women are back at mid-day to run other errands and tend to the children, while the men come back in the evening with meat and honey.

“The Hadza experience life in one of its most vibrant, vivid forms imaginable,” says Wood, who has spent a total of 30 months with the Hadza since 2004. “They seem to live in fast-motion, becoming independent sooner, marrying younger, having kids younger, and they are all much more familiar with the great trials and tribulations of life and death.”

While lacking amenities like the Internet or daily paper, the Hadza interact with outsiders more than many people think, regularly walking out to the local town or village to trade for things, or for social outings.

“There’s a common assumption that these populations are trapped in amber,” says Pontzer, “that they are socially and technologically isolated from the rest of the world. And pretty much all of that is not true. It’s more accurate to see them as living this traditional lifestyle because they prefer it.”

“Herman is very meticulous and very respectful of people participating in research projects,” says Raichlen. “He knows it’s very special opportunity to be out there and work with a group of people who are living an extraordinary life.”

Pontzer’s study with the Hadza, detailed in a 2012 paper published in PLoS ONE, was carried out in the summer of 2010. He and his research team, including Raichlen and Wood, asked a group of 30 Hadza men and women to drink a small amount of water with heavier isotopes of both hydrogen and oxygen. These isotopes were tracked over the course of two weeks through urine samples, giving the team a measure of energy expenditures.

Like most scientists, Pontzer and his colleagues assumed that because modern humans are typically more sedentary, they use less energy. However, they instead found the Hadza don’t spend any more energy than other, non hunter-gatherer populations typically do. “We were shocked by that,” he says.

The study has huge implications on how to approach the obesity epidemic plaguing the developed world, suggesting that increased activity will not have much of an impact on weight loss, Pontzer says. “It’s not how many calories you spend a day, but what you spend them on. So if you spend them on physical activity, maybe you spend them less on reproductive function, or less on immune function.”

But Pontzer stresses that exercise is still crucial to good health. “Activity may not necessarily keep you thin — in fact it won’t in the long term. But it might keep you from dying of chronic disease longer than you should.”

The unexpected results emphasize just how little is known about hunter-gatherer energetics. “People were just really surprised when the results came out,” Pontzer remembers. There was a lot of positive feedback from the scientific community, as well as a fair bit of skepticism, which he embraces. “It’s great to have the debate.”

Pontzer notes that many researchers are still trying to figure out how to use these new data, and says he is eager to follow up with more research on the Hadza with “a whole new set of research questions.” As one of the lucky few who will ever get to know the Hadza so intimately, it’s going to be very exciting to see what Pontzer discovers next.