Humans were already the dominant predatory species on Earth 2 million years ago – Study Finds

TEL AVIV, Israel Two million years ago, were humans already the king of the hill on planet Earth? Researchers at Tel Aviv University say evidence points to early humans being apex predators, meaning they sat atop the food chain as the most formidable hunters around.

The study of prehistoric diets finds large mammals going extinct in many regions of the globe, along with the depletion of animal food supplies at the close of the Stone Age, forced humans to progressively expand plants into their diet, until they had no option but to tame both animals and plants and become farmers.

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 in a media release. This comparison is futile, however, because two million years ago hunter-gatherer societies could hunt and consume elephants and other large animals while todays 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.

Dr. Ben-Dor and collaborators compiled roughly 25 examples from over 400 scholarly works addressing whether Stone Age people were specialist predators or generalized opportunistic feeders. Most of the teams evidence comes from studies of genomics, metabolic processes, physiology, and morphology of early humans.

One prominent example is the acidity of the human stomach, Dr. Ben-Dor adds. The acidity in our stomach is high when compared to omnivores and even to other predators. Producing and maintaining strong acidity require large amounts of energy, and its existence is evidence for consuming animal products. Strong acidity provides protection from harmful bacteria found in meat, and prehistoric humans, hunting large animals whose meat sufficed for days or even weeks, often consumed old meat containing large quantities of bacteria, and thus needed to maintain a high level of acidity.

Another indication of being predators is the structure of the fat cells in our bodies. In the bodies of omnivores, fat is stored in a relatively small number of large fat cells, while in predators, including humans, its the other way around: we have a much larger number of smaller fat cells, explained Dr. Ben-Dor. Significant evidence for the evolution of humans as predators has also been found in our genome. For example, geneticists have concluded that areas of the human genome were closed off to enable a fat-rich diet, while in chimpanzees, areas of the genome were opened to enable a sugar-rich diet.

The team used archaeological findings to enhance the data gathered from human biology. As an example, studies of stable isotopes found in the remains of ancient people, together with evidence of human-specific hunting behaviors, reveal that humans were expert hunters of big and mid-sized animals with a higher percentage of body fat. With this comparison, it became clear that humans were not only hypercarnivores but that they killed huge animals and obtained over 70 percent of their calories from meat as well.

Hunting large animals is not an afternoon hobby. 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, Dr. Ben-Dor explains.

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 collaborative model that scientists at Tel Aviv University (TAU) have been working on for over a decade offers a dramatic shift in the way we think about evolutionary history. Unlike the widely held belief that humans attribute their survivability to their nutritional adaptability, which enabled them to mix the killing of animals with the use of fruits and vegetables, the vision that is developing here shows that humans evolved primarily as carnivores of big animals.

Archaeological evidence does not overlook the fact that stone-age humans also consumed plants, the study author adds. But according to the findings of this study plants only became a major component of the human diet toward the end of the era.

Following the discovery of genetic variations and the style of unusual primitive tools for preparing plant foods, the investigators came to the conclusion that beginning approximately 85,000 years ago in Africa and approximately 40,000 years ago in Europe and Asia, progressive growth in plant food intake and dietary diversification occurred in line with changing ecological circumstances.

Additionally, the regional distinctiveness of the stone tool way of life grew, which is comparable to the variety of hunting tools in 20th century communities in terms of its origins and development. Throughout the two-million-year time frame in which humans were the most dominant species, scientists found extensive spans of uniformity and consistency in primitive tools, no matter how different the surrounding environment was.

Our study addresses a very great current controversy both scientific and non-scientific, says Prof. Ran Barkai. For many people today, the Paleolithic diet is a critical issue, not only with regard to the past but also concerning the present and future. 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.

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 into the biological and cultural evolution of humans.

This study is published in the American Journal of Physical Anthropology.

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Humans were already the dominant predatory species on Earth 2 million years ago - Study Finds