Eating meat may not have 'made us human,' contrary to popular theory

Humans have been around for about 2.5 million years. For at least 2.4 million years, people have been eating animals. This fact is evidenced by cut traces on fossil animal bones, surviving stone tools and analyses of our ancestors' teeth. While Homo habilisand Homo rudolfensis probably only ate a lizard here and there or the meaty remains left behind by other predators, Homo erectus was a hunter. Today, by some counts, the average American eats around 7,000 animals in a lifetime — including 4,500 fish, 2,400 chickens, 80 turkeys, 30 sheep, 27 pigs and 11 cows. This number not only sounds absurdly high; it raises a question: Is this really necessary?

According to one well-known theory meat consumption made us human. As early as the mid-1950s, paleoanthropologist Raymond Dart coined the idea that our early ancestors hunted animals to survive on the barren African savannah. Finally, in the 1990s, Leslie Aiello and Peter Wheeler posed the expensive-tissue hypothesis, according to which other tissues had to regress as the human brain evolved. They wanted to answer the question of where early hominins got the energy for their ever-growing organ of thought. While the brain volume of Homo rudolfensis was still about 750 cubic centimeters, Homo erectus already had up to 1,250 cubic centimeters. Today, Homo sapiens even has a brain volume of 1,100 to 1,800 cubic centimeters.

The human brain is an enormously expensive organ. Although it accounts for only a few percent of total body mass, it consumes a good fifth of total energy. Compared to roots, leaves and many other plant parts, meat (especially offal such as liver, heart or tongue) has a fairly high nutrient density with many proteins and, above all, fats. If it is also chopped up, it saves a lot of chewing, which means that the energy-rich food can be ingested with little energy consumption. Any surplus can then go to the development and operation of the brain — or so the argument goes.

Many people today justify their excessive meat consumption to themselves and others with these arguments. Modern man is a born meat eater, they reason, as a glance at human history shows. What's more, the mastery of fire, the development of language, the origin of the division of labor, the beginning of social hierarchies and even the emergence of culture could be related to hunting and eating meat. Accordingly, the consumption of meat is a natural need of humankind whereas vegetarianism is unnatural and possibly even harmful to health. But experts from such diverse fields as paleoanthropology and nutrition are questioning these ideas.

We are constantly evolving

Human evolution is not locked but instead constantly developing. What was true for our ancestors is not necessarily still true today. For example, food's availability, composition and preparation have changed enormously since early humans acquired a taste for meat. We no longer have to spend half a day stalking an animal. Modern breeding methods have significantly increased the nutrient content in plant foods. And over time, we have learned to cook our food so that it is easier to digest and nutrients are more accessible.

Today, meat is no longer a luxury product. On the contrary, a cutlet is sometimes cheaper than a sack of potatoes. However, its production consumes many times more resources. Some 77% of the world's arable land is used for meat and milk production, even though animal products provide only about 18% of the world's calorie needs. Even if there were an evolutionary link between meat consumption and becoming human, we should be able to emancipate ourselves from it today.

Moreover, numerous paleoanthropological studies cast doubt on, or refute, the "meat made us human" theory. For example, a team led by Ana Navarrete of the University of Zurich found no further evidence in the animal kingdom for the expensive-tissue hypothesis in extensive analyses. To be sure, "this highly intuitive idea has gained wide acceptance in paleoanthropology and many other fields, and is fueling public discussions about the optimal human diet," the group wrote in the journal Nature in 2011. However: "Contrary to the predictions of the expensive-tissue hypothesis, we found no negative correlations between the relative size of the brain and the digestive tract, other expensive organs or their combined sum among mammals or within [nonhuman] primates." It would be most surprising if the principle applied solely to human evolution.

In a 2022 study, a research group led by paleoanthropologists W. Andrew Barr of George Washington University and Briana Pobiner of the Smithsonian National Museum of Natural History took another systematic look at the purported archaeological evidence for the "meat made us human" theory. The scientists compiled data from 59 sites from nine major research areas in East Africa, ranging in age from 2.6 to 1.2 million years old. Then the team put all previous bone finds into chronological perspective. Archaeological evidence of meat consumption does increase sharply when looking at specimens linked to the emergence of the Homo erectusspecies, the researchers reported in the journal PNAS. However, they found, this trend reflects the scientific focus on that period of evolutionary development; that is, there is simply more material collected from sites linked to early Homo erectus. As a result, the picture is distorted and the connection between eating meat and the evolution of the genus Homo is falsely underscored, they said. "Our study undermines the idea that eating large quantities of meat drove evolutionary changes in our early ancestors," Barr said in a press release.

Harvard primatologist Richard Wrangham goes even further. He argues that the greatest revolution in human nutrition occurred not when we started eating meat, but when we learned to cook. By pounding and heating foods, he says, they are "predigested" so that our bodies have to expend less energy breaking them down. Cooked food would thus allow humans to absorb more energy than raw food, ultimately providing more fuel for the brain in less time.

Wrangham tested his theory by offering raw and cooked food to rats and mice. The result: mice raised on cooked food gained 15% to 40%t more weight than mice fed only raw food. Whether cooked food was really the key driver behind human evolution, however, is difficult to prove in detail. Fireplaces leave much more perishable traces than stone tools and bones. They are therefore more difficult to trace and date. It is possible that humans began cooking their food until it was soft much earlier than we think.

Victims of our own success

The flip side of Wrangham's hypothesis is that we now have become so good at processing food that — for the first time in human evolution — many people eat more calories than they can burn in a day. "After millennia of food scarcity, we've been living in food abundance for almost 70 years. Our bodies can't handle that," says Hans Hauner, professor of nutritional medicine at the Technical University of Munich. "We see today that high meat consumption shortens the lives of many people and can contribute to numerous diseases such as diabetes, cancer and cardiovascular ailments." It would therefore do us good to significantly reduce our meat consumption.

In the course of human history, meat never displaced other dietary components; it supplemented them. It's a bit like equipping a city with a subway system: it doesn't replace anything; it just increases efficiency. "In the course of their evolution, humans have always consumed what was available to them," Hauner explains. Thus, it is not meat consumption that makes us human, but rather our enormous metabolic adaptability. "Humans, unlike many other animals, are able to extract from different food sources in their environment what ensures their survival." Our muscles can burn carbohydrates, but likewise metabolize fatty acids. In the same way, our brains can also switch from a sugar-based diet, at least in part, to a ketogenic diet.

Lutz Kindler of the Leibniz Center for Archaeology agrees from a paleoanthropological perspective. "Animals, unlike plants, are independent of the season and available even in the most inhospitable regions of this earth," he says. "So when humans started moving northward from Africa, there were many advantages to accessing additional, non-plant food sources." There were also the social aspects of hunting and eating meat. "People had to organize themselves to be able to kill and cut up large animals despite their physical inferiority." That probably brought them together. Meat and its exploitation, he said, therefore had an influence on our behavioral evolution more than anything else. "From my point of view, however, meat was and is not necessarily nutritionally relevant. Proteins alone do not have a particularly high calorific value," Kindler adds.

The question remains whether we still need animal proteins and the micronutrients contained in meat today. As nutritionist Hauner points out, "Today there are quite competitive sportsmen who nourish themselves through a purely vegetarian or vegan diet. So you can also optimally supply your muscles and brain with vegetable proteins."

While studies worldwide have shown the value of a balanced, healthy diet with some amount of meat, dairy and other animal products, he says, "the only one that is really challenging is a vegan lifestyle. And even there, in this day and age, there are numerous ways to replace the missing substances."

Paleoanthropologist Kindler, meanwhile, believes that tastes and food sources are "handed down and more of a social issue than one of physiological evolution or instinct." So if people were to return more to the diet of their ancestors, eat more local fruits and vegetables, and eat significantly less meat, it would be good news for their health — and for our planet. After all, humans' enormous adaptability and insatiable appetite for meat today is one thing above all: an ecological disaster.

This article originally appeared in Spektrum der Wissenschaft and was reproduced with permission.

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