The Evolution of Diet

It’s suppertime in the Amazon of lowland Bolivia, and Ana Cuata Maito is stirring a porridge of plantains and sweet manioc over a fire smoldering on the dirt floor of her thatched hut, listening for the voice of her husband as he returns from the forest with his scrawny hunting dog.

With an infant girl nursing at her breast and a seven-year-old boy tugging at her sleeve, she looks spent when she tells me that she hopes her husband, Deonicio Nate, will bring home meat tonight. “The children are sad when there is no meat,” Maito says through an interpreter, as she swats away mosquitoes.

Nate left before dawn on this day in January with his rifle and machete to get an early start on the two-hour trek to the old-growth forest. There he silently scanned the canopy for brown capuchin monkeys and raccoonlike coatis, while his dog sniffed the ground for the scent of piglike peccaries or reddish brown capybaras. If he was lucky, Nate would spot one of the biggest packets of meat in the forest—tapirs, with long, prehensile snouts that rummage for buds and shoots among the damp ferns.

This evening, however, Nate emerges from the forest with no meat. At 39, he’s an energetic guy who doesn’t seem easily defeated—when he isn’t hunting or fishing or weaving palm fronds into roof panels, he’s in the woods carving a new canoe from a log. But when he finally sits down to eat his porridge from a metal bowl, he complains that it’s hard to get enough meat for his family: two wives (not uncommon in the tribe) and 12 children. Loggers are scaring away the animals. He can’t fish on the river because a storm washed away his canoe.

The story is similar for each of the families I visit in Anachere, a community of about 90 members of the ancient Tsimane Indian tribe. It’s the rainy season, when it’s hardest to hunt or fish. More than 15,000 Tsimane live in about a hundred villages along two rivers in the Amazon Basin near the main market town of San Borja, 225 miles from La Paz. But Anachere is a two-day trip from San Borja by motorized dugout canoe, so the Tsimane living there still get most of their food from the forest, the river, or their gardens.

I’m traveling with Asher Rosinger, a doctoral candidate who’s part of a team, co-led by biological anthropologist William Leonard of Northwestern University, studying the Tsimane to document what a rain forest diet looks like. They’re particularly interested in how the Indians’ health changes as they move away from their traditional diet and active lifestyle and begin trading forest goods for sugar, salt, rice, oil, and increasingly, dried meat and canned sardines. This is not a purely academic inquiry. What anthropologists are learning about the diets of indigenous peoples like the Tsimane could inform what the rest of us should eat.

Rosinger introduces me to a villager named José Mayer Cunay, 78, who, with his son Felipe Mayer Lero, 39, has planted a lush garden by the river over the past 30 years. José leads us down a trail past trees laden with golden papayas and mangoes, clusters of green plantains, and orbs of grapefruit that dangle from branches like earrings. Vibrant red “lobster claw” heliconia flowers and wild ginger grow like weeds among stalks of corn and sugarcane. “José’s family has more fruit than anyone,” says Rosinger.

Yet in the family’s open-air shelter Felipe’s wife, Catalina, is preparing the same bland porridge as other households. When I ask if the food in the garden can tide them over when there’s little meat, Felipe shakes his head. “It’s not enough to live on,” he says. “I need to hunt and fish. My body doesn’t want to eat just these plants.”

As we look to 2050, when we’ll need to feed two billion more people, the question of which diet is best has taken on new urgency. The foods we choose to eat in the coming decades will have dramatic ramifications for the planet. Simply put, a diet that revolves around meat and dairy, a way of eating that’s on the rise throughout the developing world, will take a greater toll on the world’s resources than one that revolves around unrefined grains, nuts, fruits, and vegetables.

Until agriculture was developed around 10,000 years ago, all humans got their food by hunting, gathering, and fishing. As farming emerged, nomadic hunter-gatherers gradually were pushed off prime farmland, and eventually they became limited to the forests of the Amazon, the arid grasslands of Africa, the remote islands of Southeast Asia, and the tundra of the Arctic. Today only a few scattered tribes of hunter-gatherers remain on the planet.

That’s why scientists are intensifying efforts to learn what they can about an ancient diet and way of life before they disappear. “Hunter-gatherers are not living fossils,” says Alyssa Crittenden, a nutritional anthropologist at the University of Nevada, Las Vegas, who studies the diet of Tanzania’s Hadza people, some of the last true hunter-gatherers. “That being said, we have a small handful of foraging populations that remain on the planet. We are running out of time. If we want to glean any information on what a nomadic, foraging lifestyle looks like, we need to capture their diet now.”

So far studies of foragers like the Tsimane, Arctic Inuit, and Hadza have found that these peoples traditionally didn’t develop high blood pressure, atherosclerosis, or cardiovascular disease. “A lot of people believe there is a discordance between what we eat today and what our ancestors evolved to eat,” says paleoanthropologist Peter Ungar of the University of Arkansas. The notion that we’re trapped in Stone Age bodies in a fast-food world is driving the current craze for Paleolithic diets. The popularity of these so-called caveman or Stone Age diets is based on the idea that modern humans evolved to eat the way hunter-gatherers did during the Paleolithic—the period from about 2.6 million years ago to the start of the agricultural revolution—and that our genes haven’t had enough time to adapt to farmed foods.

A Stone Age diet “is the one and only diet that ideally fits our genetic makeup,” writes Loren Cordain, an evolutionary nutritionist at Colorado State University, in his book The Paleo Diet: Lose Weight and Get Healthy by Eating the Foods You Were Designed to Eat. After studying the diets of living hunter-gatherers and concluding that 73 percent of these societies derived more than half their calories from meat, Cordain came up with his own Paleo prescription: Eat plenty of lean meat and fish but not dairy products, beans, or cereal grains—foods introduced into our diet after the invention of cooking and agriculture. Paleo-diet advocates like Cordain say that if we stick to the foods our hunter-gatherer ancestors once ate, we can avoid the diseases of civilization, such as heart disease, high blood pressure, diabetes, cancer, even acne.

That sounds appealing. But is it true that we all evolved to eat a meat-centric diet? Both paleontologists studying the fossils of our ancestors and anthropologists documenting the diets of indigenous people today say the picture is a bit more complicated. The popular embrace of a Paleo diet, Ungar and others point out, is based on a stew of misconceptions.

Meat has played a starring role in the evolution of the human diet. Raymond Dart, who in 1924 discovered the first fossil of a human ancestor in Africa, popularized the image of our early ancestors hunting meat to survive on the African savanna. Writing in the 1950s, he described those humans as “carnivorous creatures, that seized living quarries by violence, battered them to death … slaking their ravenous thirst with the hot blood of victims and greedily devouring livid writhing flesh.”

Eating meat is thought by some scientists to have been crucial to the evolution of our ancestors’ larger brains about two million years ago. By starting to eat calorie-dense meat and marrow instead of the low-quality plant diet of apes, our direct ancestor, Homo erectus, took in enough extra energy at each meal to help fuel a bigger brain. Digesting a higher quality diet and less bulky plant fiber would have allowed these humans to have much smaller guts. The energy freed up as a result of smaller guts could be used by the greedy brain, according to Leslie Aiello, who first proposed the idea with paleoanthropologist Peter Wheeler. The brain requires 20 percent of a human’s energy when resting; by comparison, an ape’s brain requires only 8 percent. This means that from the time of H. erectus, the human body has depended on a diet of energy-dense food—especially meat.

Fast-forward a couple of million years to when the human diet took another major turn with the invention of agriculture. The domestication of grains such as sorghum, barley, wheat, corn, and rice created a plentiful and predictable food supply, allowing farmers’ wives to bear babies in rapid succession—one every 2.5 years instead of one every 3.5 years for hunter-gatherers. A population explosion followed; before long, farmers outnumbered foragers.

Over the past decade anthropologists have struggled to answer key questions about this transition. Was agriculture a clear step forward for human health? Or in leaving behind our hunter-gatherer ways to grow crops and raise livestock, did we give up a healthier diet and stronger bodies in exchange for food security?

When biological anthropologist Clark Spencer Larsen of Ohio State University describes the dawn of agriculture, it’s a grim picture. As the earliest farmers became dependent on crops, their diets became far less nutritionally diverse than hunter-gatherers’ diets. Eating the same domesticated grain every day gave early farmers cavities and periodontal disease rarely found in hunter-gatherers, says Larsen. When farmers began domesticating animals, those cattle, sheep, and goats became sources of milk and meat but also of parasites and new infectious diseases. Farmers suffered from iron deficiency and developmental delays, and they shrank in stature.

Despite boosting population numbers, the lifestyle and diet of farmers were clearly not as healthy as the lifestyle and diet of hunter-gatherers. That farmers produced more babies, Larsen says, is simply evidence that “you don’t have to be disease free to have children.”

The real Paleolithic diet, though, wasn’t all meat and marrow. It’s true that hunter-gatherers around the world crave meat more than any other food and usually get around 30 percent of their annual calories from animals. But most also endure lean times when they eat less than a handful of meat each week. New studies suggest that more than a reliance on meat in ancient human diets fueled the brain’s expansion.

Year-round observations confirm that hunter-gatherers often have dismal success as hunters. The Hadza and Kung bushmen of Africa, for example, fail to get meat more than half the time when they venture forth with bows and arrows. This suggests it was even harder for our ancestors who didn’t have these weapons. “Everybody thinks you wander out into the savanna and there are antelopes everywhere, just waiting for you to bonk them on the head,” says paleoanthropologist Alison Brooks of George Washington University, an expert on the Dobe Kung of Botswana. No one eats meat all that often, except in the Arctic, where Inuit and other groups traditionally got as much as 99 percent of their calories from seals, narwhals, and fish.

So how do hunter-gatherers get energy when there’s no meat? It turns out that “man the hunter” is backed up by “woman the forager,” who, with some help from children, provides more calories during difficult times. When meat, fruit, or honey is scarce, foragers depend on “fallback foods,” says Brooks. The Hadza get almost 70 percent of their calories from plants. The Kung traditionally rely on tubers and mongongo nuts, the Aka and Baka Pygmies of the Congo River Basin on yams, the Tsimane and Yanomami Indians of the Amazon on plantains and manioc, the Australian Aboriginals on nut grass and water chestnuts.

“There’s been a consistent story about hunting defining us and that meat made us human,” says Amanda Henry, a paleobiologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig. “Frankly, I think that misses half of the story. They want meat, sure. But what they actually live on is plant foods.” What’s more, she found starch granules from plants on fossil teeth and stone tools, which suggests humans may have been eating grains, as well as tubers, for at least 100,000 years—long enough to have evolved the ability to tolerate them.

The notion that we stopped evolving in the Paleolithic period simply isn’t true. Our teeth, jaws, and faces have gotten smaller, and our DNA has changed since the invention of agriculture. “Are humans still evolving? Yes!” says geneticist Sarah Tishkoff of the University of Pennsylvania.

One striking piece of evidence is lactose tolerance. All humans digest mother’s milk as infants, but until cattle began being domesticated 10,000 years ago, weaned children no longer needed to digest milk. As a result, they stopped making the enzyme lactase, which breaks down the lactose into simple sugars. After humans began herding cattle, it became tremendously advantageous to digest milk, and lactose tolerance evolved independently among cattle herders in Europe, the Middle East, and Africa. Groups not dependent on cattle, such as the Chinese and Thai, the Pima Indians of the American Southwest, and the Bantu of West Africa, remain lactose intolerant.

Humans also vary in their ability to extract sugars from starchy foods as they chew them, depending on how many copies of a certain gene they inherit. Populations that traditionally ate more starchy foods, such as the Hadza, have more copies of the gene than the Yakut meat-eaters of Siberia, and their saliva helps break down starches before the food reaches their stomachs.

These examples suggest a twist on “You are what you eat.” More accurately, you are what your ancestors ate. There is tremendous variation in what foods humans can thrive on, depending on genetic inheritance. Traditional diets today include the vegetarian regimen of India’s Jains, the meat-intensive fare of Inuit, and the fish-heavy diet of Malaysia’s Bajau people. The Nochmani of the Nicobar Islands off the coast of India get by on protein from insects. “What makes us human is our ability to find a meal in virtually any environment,” says the Tsimane study co-leader Leonard.

Studies suggest that indigenous groups get into trouble when they abandon their traditional diets and active lifestyles for Western living. Diabetes was virtually unknown, for instance, among the Maya of Central America until the 1950s. As they’ve switched to a Western diet high in sugars, the rate of diabetes has skyrocketed. Siberian nomads such as the Evenk reindeer herders and the Yakut ate diets heavy in meat, yet they had almost no heart disease until after the fall of the Soviet Union, when many settled in towns and began eating market foods. Today about half the Yakut living in villages are overweight, and almost a third have hypertension, says Leonard. And Tsimane people who eat market foods are more prone to diabetes than those who still rely on hunting and gathering.

For those of us whose ancestors were adapted to plant-based diets—and who have desk jobs—it might be best not to eat as much meat as the Yakut. Recent studies confirm older findings that although humans have eaten red meat for two million years, heavy consumption increases atherosclerosis and cancer in most populations—and the culprit isn’t just saturated fat or cholesterol. Our gut bacteria digest a nutrient in meat called L-carnitine. In one mouse study, digestion of L-carnitine boosted artery-clogging plaque. Research also has shown that the human immune system attacks a sugar in red meat that’s called Neu5Gc, causing inflammation that’s low level in the young but that eventually could cause cancer. “Red meat is great, if you want to live to 45,” says Ajit Varki of the University of California, San Diego, lead author of the Neu5Gc study.

Many paleoanthropologists say that although advocates of the modern Paleolithic diet urge us to stay away from unhealthy processed foods, the diet’s heavy focus on meat doesn’t replicate the diversity of foods that our ancestors ate—or take into account the active lifestyles that protected them from heart disease and diabetes. “What bothers a lot of paleoanthropologists is that we actually didn’t have just one caveman diet,” says Leslie Aiello, president of the Wenner-Gren Foundation for Anthropological Research in New York City. “The human diet goes back at least two million years. We had a lot of cavemen out there.”

In other words, there is no one ideal human diet. Aiello and Leonard say the real hallmark of being human isn’t our taste for meat but our ability to adapt to many habitats—and to be able to combine many different foods to create many healthy diets. Unfortunately the modern Western diet does not appear to be one of them.

The latest clue as to why our modern diet may be making us sick comes from Harvard primatologist Richard Wrangham, who argues that the biggest revolution in the human diet came not when we started to eat meat but when we learned to cook. Our human ancestors who began cooking sometime between 1.8 million and 400,000 years ago probably had more children who thrived, Wrangham says. Pounding and heating food “predigests” it, so our guts spend less energy breaking it down, absorb more than if the food were raw, and thus extract more fuel for our brains. “Cooking produces soft, energy-rich foods,” says Wrangham. Today we can’t survive on raw, unprocessed food alone, he says. We have evolved to depend upon cooked food.

To test his ideas, Wrangham and his students fed raw and cooked food to rats and mice. When I visited Wrangham’s lab at Harvard, his then graduate student, Rachel Carmody, opened the door of a small refrigerator to show me plastic bags filled with meat and sweet potatoes, some raw and some cooked. Mice raised on cooked foods gained 15 to 40 percent more weight than mice raised only on raw food.

If Wrangham is right, cooking not only gave early humans the energy they needed to build bigger brains but also helped them get more calories from food so that they could gain weight. In the modern context the flip side of his hypothesis is that we may be victims of our own success. We have gotten so good at processing foods that for the first time in human evolution, many humans are getting more calories than they burn in a day. “Rough breads have given way to Twinkies, apples to apple juice,” he writes. “We need to become more aware of the calorie-raising consequences of a highly processed diet.”

It’s this shift to processed foods, taking place all over the world, that’s contributing to a rising epidemic of obesity and related diseases. If most of the world ate more local fruits and vegetables, a little meat, fish, and some whole grains (as in the highly touted Mediterranean diet), and exercised an hour a day, that would be good news for our health—and for the planet.

On my last afternoon visiting the Tsimane in Anachere, one of Deonicio Nate’s daughters, Albania, 13, tells us that her father and half-brother Alberto, 16, are back from hunting and that they’ve got something. We follow her to the cooking hut and smell the animals before we see them—three raccoonlike coatis have been laid across the fire, fur and all. As the fire singes the coatis’ striped pelts, Albania and her sister, Emiliana, 12, scrape off fur until the animals’ flesh is bare. Then they take the carcasses to a stream to clean and prepare them for roasting.

Nate’s wives are cleaning two armadillos as well, preparing to cook them in a stew with shredded plantains. Nate sits by the fire, describing a good day’s hunt. First he shot the armadillos as they napped by a stream. Then his dog spotted a pack of coatis and chased them, killing two as the rest darted up a tree. Alberto fired his shotgun but missed. He fired again and hit a coati. Three coatis and two armadillos were enough, so father and son packed up and headed home.

As family members enjoy the feast, I watch their little boy, Alfonso, who had been sick all week. He is dancing around the fire, happily chewing on a cooked piece of coati tail. Nate looks pleased. Tonight in Anachere, far from the diet debates, there is meat, and that is good.

Ann Gibbons is the author of The First Human: The Race to Discover Our Earliest Ancestors. Matthieu Paley photographed Afghanistan’s Kyrgyz for our February 2013 issue.

The magazine thanks The Rockefeller Foundation and members of the National Geographic Society for their generous support of this series of articles.