Stone age humans used to dine mainly on meat, a new study reports. It was only as megafauna (the huge animals of yore, like mammoths) died off that vegetables were increasingly making their way on the menu.

A new paper offers a fresh and interesting interpretation of how humanity made the trek from hunting to agriculture. According to the findings, ancient humans were primarily carnivores, with game meat making up an important part of their diet. But as the species they hunted died out, vegetables and plant matter made up a growing part of their diets. These extinctions likely also led to the domestication of plants and animals, as our ancestors needed to secure sources of food.

Traditional cuisine

“So far, attempts to reconstruct the diet of stone-age humans were mostly based on comparisons to 20th-century hunter-gatherer societies,” explains Dr. Miki Ben-Dor of the Jacob M. Alkov Department of Archaeology at Tel Aviv University, first author of the paper.

“This comparison is futile, however, because two million years ago hunter-gatherer societies could hunt and consume elephants and other large animals — while today’s hunter-gatherers do not have access to such bounty. The entire ecosystem has changed, and conditions cannot be compared. We decided to use other methods to reconstruct the diet of stone-age humans: to examine the memory preserved in our own bodies, our metabolism, genetics, and physical build. Human behavior changes rapidly, but evolution is slow. The body remembers.”

The team trawled through almost 400 scientific papers from various disciplines, trying to determine whether stone-age humans were carnivores or omnivores. They collected around 25 lines of evidence, mostly from papers dealing with genetics, metabolism, physiology, and morphology, that can help us determine this.

One of the tidbits cited by the team includes the acidity of the human stomach. This is “high when compared to omnivores and even to other predators”, they explain, which means our bodies have to spend extra energy to keep them so. But it also provides some protection from bacteria often found in meat, suggesting that this was an adaptation meant to help our ancestors eat meat. Ancient peoples hunted large animals whose meat would feed the group for days or weeks, meaning they often ate old meat laden with bacteria.

Another clue they list is the way our bodies store fat. Omnivores, they explain, tend to store fat in a relatively small number of large cells. Predators do it the other way around — humans also share this latter approach of using a large number of relatively small cells. A comparison with chimpanzees also shows that areas of our genetic code are inactivated to specialize us for a fat-rich diet (in chimps, these changes support a sugar-rich diet).

Archeological evidence also supports the meat-eating hypothesis. Isotope ratio studies on the bones of ancient humans, alongside evidence of how they hunted, suggests our ancestors specialized in hunting large or medium-sized animals that had a lot of fat. Large social predators today also hunt large animals and get over 70% of their energy from animal sources, the team writes, and this parallel suggests that early human groups acted a lot like hypercarnivores.

“Hunting large animals is not an afternoon hobby,” says Dr. Ben-Dor. “It requires a great deal of knowledge, and lions and hyenas attain these abilities after long years of learning. Clearly, the remains of large animals found in countless archaeological sites are the result of humans’ high expertise as hunters of large animals.”

“Many researchers who study the extinction of the large animals agree that hunting by humans played a major role in this extinction — and there is no better proof of humans’ specialization in hunting large animals. Most probably, like in current-day predators, hunting itself was a focal human activity throughout most of human evolution. Other archaeological evidence — like the fact that specialized tools for obtaining and processing vegetable foods only appeared in the later stages of human evolution — also supports the centrality of large animals in the human diet, throughout most of human history.”

The findings go against the grain of our previous hypotheses on how humans evolved. Previously, it was assumed that humans’ dietary flexibility allowed them to adapt to a wide range of situations and environments, giving them an evolutionary edge; but the current findings suggest that we evolved largely as predators instead. That’s not to mean that they ate only meat — there is well-documented evidence of plant-eating during this time — but plants only gained a central part in their diets in the latter days of the stone age.

Stone tools specialized for processing plants started appearing around 85,000 years ago in Africa and about 40,000 years ago in Europe and Asia, the team adds, suggesting plants were increasingly being eaten. The researchers also explain that such tools show an increase in local uniqueness over time, a process similar to that seen in 20th-century hunter-gatherer societies. In contrast, during the time when the team believes humans acted more like apex predators, stone tools maintained very high degrees of similarity and continuity regardless of local ecological conditions.

“Our study addresses a very great current controversy — both scientific and non-scientific. It is hard to convince a devout vegetarian that his/her ancestors were not vegetarians, and people tend to confuse personal beliefs with scientific reality,” adds Prof. Ran Barkai, also of the Jacob M. Alkov Department of Archaeology at Tel Aviv University, and a co-author of the paper.

“Our study is both multidisciplinary and interdisciplinary. We propose a picture that is unprecedented in its inclusiveness and breadth, which clearly shows that humans were initially apex predators, who specialized in hunting large animals. As Darwin discovered, the adaptation of species to obtaining and digesting their food is the main source of evolutionary changes, and thus the claim that humans were apex predators throughout most of their development may provide a broad basis for fundamental insights on the biological and cultural evolution of humans.”

The paper “The evolution of the human trophic level during the Pleistocene” has been published in the American Journal of Physical Anthropology.