Early humankind was hypercarnivorous, strongly preferring meat for about two million years before the development of agriculture, according to new research.
The paper, published in the American Journal of Physical Anthropology, is a dense and dizzyingly multidisciplinary work, drawing on biological, archaeological, and paleontological evidence to argue that homo has almost always been a highly specialized meat-eater. It was only in comparatively recent times that humankind shifted towards an omnivorous existence—possibly precipitated by the large-scale extinction of the megafauna that had been the foundation of the human diet.
Miki Ben-Dor, PhD, a co-author of the paper and an archaeologist with Israel’s Tel Aviv University, has been a longtime advocate for paleo and low-carbohydrate diets. Ben-Dor researched and wrote the study with his colleague Professor Ran Barkai and molecular biologist Rafael Sirtoli, a previous contributor to ASweetLife.
I was lucky enough to speak to Ben-Dor, who shared with me some of the highlights of his research and what practical conclusions he has drawn about nutrition for modern humans.
Hunting and Gathering
It’s not exactly controversial to portray the caveman as a hunter of large animals, but Ben-Dor believes that experts have nevertheless dramatically underestimated the degree to which early humankind relied on meat.
“The general opinion is that humans are very flexible and very smart, so that they could get any type of food, from either plant or animal sources, whenever they felt like it. That’s more or less the greatness of humans, and that flexibility allowed us to disperse and to survive.”
“This general opinion is largely based on present day hunter-gatherers. Most paleoanthropologists who try to reconstruct the diet of early humans end up relying on hunter-gatherers of today.”
Ben-Dor argues that this sort of logic is deeply flawed. Modern hunter-gatherers, who are often boxed into ecologically marginal areas by the spread of civilization, don’t necessarily tell us much about life for humans of the Pleistocene era. The earth has changed in the meantime, ecosystems have shifted, and perhaps most importantly, there is no longer a glut of very large animals to hunt and feed on.
Early humans—beginning with homo habilis, which emerged about two million years ago—were certainly omnivores, as we are today.
“I want to emphasize that humans did eat plants. We ate plants – there’s archaeological proof, and we came from a species that ate plants.”
But the word “omnivore” may not mean exactly what you think it means. The more precise, academic definition of “omnivore” indicates merely that an animal has the physiological capability of obtaining energy from both plant and animal sources. “But there is no specification regarding the ratio of plant to animal foods. So, if your diet includes 1% plants and the rest is animals, you’re still, technically speaking, omnivorous. Flexibility is not embedded in the term omnivore.”
“Humans were technically omnivores, nobody’s arguing about it. The question is, were they so flexible in their ability to obtain energy from plants and animals as to be omnivores in the way that normal people would define it? My answer is no.”
A good analogy for early humankind might be the wolf. Wolves get the overwhelming majority of their calories from meat, whether hunted and scavenged. But like their cousin the domesticated dog, wolves are indeed capable of eating plant matter, and are known to feast on berries. There’s no reason to think that early humans wouldn’t avail themselves of fruit or honey or edible plant matter if it were available—but was it a significant part of their diets?
Stable Isotope Analysis
Ben-Dor told me that there is only one definitive way to assess the trophic level of fossilized human remains: stable isotope analysis. The food we eat leaves a chemical fingerprint in our bones and collagen. Different ratios of carbon and nitrogen isotopes allow scientists to estimate the ratio of meat to plant matter consumed with some precision.
“In these studies, almost 100% of them, humans come out as carnivores. In some of them, they come out specifically as large prey carnivores. Only toward the end of the stone age – say about 20,000 years ago – do we start to see reduction in the trophic level.”
“If we rely on that method alone, we have to conclude that humans were carnivores.”
Unfortunately, stable isotope analysis cannot reach very far back into early human history. “The problem with this method is that it’s only reliable within the last 50,000 years. The genus homo has existed for more than 2 million years. And it’s only reliable in areas where collagen can be preserved in sufficient quantity,” typically colder regions.
To better assess the diet of earlier humans, Ben-Dor and his colleagues knew they had to piece together evidence from as many other angles as possible.
The Form of Our Body
“The form of our body—genetics, metabolism, morphology—tells us what we are meant to eat.”
If humankind enjoyed a mostly carnivorous diet for upwards of two million years, we would expect our bodies to be optimized for meat. And that’s exactly what we do see, according to Ben-Dor, once we compare our bodies to those of other primates and mammals.
The argument considers more than a dozen biological factors to argue that we are designed by evolution to prioritize meat. I’ll only briefly relay some of the most compelling pieces:
- The gut. “Generally speaking, we have the same type of gut as you find in carnivores – a short colon, and a long small intestine.” Humans have a colon 77% shorter, and a small intestine 64% longer, than those of our closest relative, the chimpanzee (after adjusting for body size). A longer colon allows the chimpanzee to metabolize fibrous plants that we humans simply cannot get energy from; our longer small intestine, on the other hand, is better able to extract energy from protein and fat.
- Teeth and jaws. Starting with homo erectus, the size of the human masticatory apparatus has steadily declined in size over time. Translation: we don’t need to chew as much as we used to. Chewing is another adaptation to deal with the fibrous plants found mostly in nature, a way of mashing and tenderizing tough foods to speed their digestion. Chimpanzees spend nearly half their waking day chewing.
- Stomach acidity. The more meat an animal eats, the more acidic its stomach tends to be, because the most dangerous foodborne pathogens are found on animal foods. The most acidic stomachs of all belong to scavengers, such as hyenas, feeding largely on carrion on which bacteria have already multiplied. Humans? Our stomachs are almost as acidic as those of scavengers.
The biological evidence is bolstered, Ben-Dor contends, by archaeological evidence. For example, why would humans require stomach acidity of a scavenger? The archaeological record has an answer.
“Archaeologists find both butchering sites and central consuming sites. Humans would take the prey, butcher it, take it to a central place, and could consume it for days or even weeks. Humans are very special carnivore scavengers, scavenging on their own prey.”
Other evidence abounds. The mass extinctions of large animals in the Americas, Europe and elsewhere coincided with the spread of humanity, an indication that our stone age forefathers strongly preferred such prey. And it was not until about 40,000 years ago that stone tools unambiguously associated with plant food preparation appear in the record. Perhaps the growing scarcity of large prey had inspired humans to look for food sources that they had previously ignored.
It wasn’t until the late stone age, within the last 50,000 years, that the preponderance of evidence suggests that humans had made the transition from carnivores to generalists. Agriculture boomed with the Neolithic Revolution, 11-12,000 years ago. But was that late change enough to change our biology fundamentally?
I asked Ben-Dor if he wouldn’t mind speculating on the meaning of his research for us modern eaters. While any such conclusions are outside of the scope of his academic inquiry, he was happy to share them with me nonetheless.
“I’m not looking for an ideal diet, I’m looking for a safe diet.”
“And in my opinion, the safest food that humans can consume is meat. Meat and fat. Because they are not different, in any real sense, from the meats that humans consumed for 2.5 million years.”
For years, Ben-Dor favored a “paleo” diet, eschewing modern processed foods and favoring not only meats and fats but also minimally handled fruits and vegetables. But his recent research has given him some doubt about the plant-based foods that we have access to:
“None of the plants that humans used to eat are available today in the supermarket, and we don’t know exactly how they prepared those plants.”
“I try to avoid plants. I eat meat, and I eat fat.”