Twenty-four years ago, Brianna Poebiner arrived in northern Kenya and touched bones that were last touched 1.5 million years ago. Pobiner, a longtime anthropologist, was digging up the bones of ancient animals and searching for cuts and bruises. These traces show that the animals were butchered by our early ancestors in an attempt to obtain fatty, high-calorie bone marrow.
“The creature that butchered this animal does not look exactly like you, but you are discovering direct evidence of its behavior,” said Pobiner, who now works at the Smithsonian Institution in Washington. “It’s really exciting.” At that moment, Pobiner became interested in how the diet of our ancestors shaped our evolution, and eventually led to the emergence of our species, the wise man.
Meat seems to have played an important role in human evolution. Our distant ancestors ate mostly plants and had short legs and small brains the size of chimpanzees. But about two million years ago, a new species appeared that had characteristics that were clearly similar to those of humans.
Humans had larger brain positions, smaller intestines, and limbs that bore a striking resemblance to modern humans. Fossils from the same time, such as those excavated by Pobiner in Kenya, show that a man was butchering animals to separate meat from bone and extract bone marrow.
For decades, paleontologists have theorized that the evolution of human traits and the eating of meat are closely related. “The explanation was that eating meat made us eat a lot more food, and these dense resources facilitated these changes,” says Pobiner.
Large brains consume a lot of energy. The human brain consumes about 20% of the body’s energy, even at rest. But switching to a high-meat, high-calorie diet meant extra energy that could be used to support larger, more complex brains. If the ancestors of humans hunted their food, this explains the evolution of taller limbs that were more efficient at pursuing prey at long distances. It has been widely believed that meat made us human. Pobiner agreed.
But in April 2020, Pobiner received a call that prompted him to reconsider the hypothesis. The call came from Andrew Barr, a paleontologist at George Washington University who was unconvinced about the connection between upright humans and carnivores. He wanted to use the fossil record to find out if there was any evidence that human ancestors ate more meat when humans evolved upright, or it seems so because we were not looking for it enough. To Pobiner, this project seemed appealing because it challenged public belief.
Researchers were unable to travel to Kenya to conduct field work due to globalization. Instead, they analyzed data from four research areas in East Africa that span millions of years of human evolution. They used different criteria to assess how well each period was examined and how many bones were found with butcher-related artifacts in each area.
In a new article in PNAS, Barr and Popiner argue that the link between carnivore and human evolution may be less certain than previously thought. They concluded that the apparent increase in butchered bones after the advent of upright humans was in fact a slant of sampling: more paleontologists were looking for bones in archaeological sites from this period, and as a result found more.
The new study does not rule out a link between eating meat and evolutionary change, but suggests that the story may be a little more complex. Bar says:
If we want to say how common a behavior has been, we need a way to take into account the fact that in some periods of time and in some places we have sought it more than others.
Because well-preserved sites of animal bones are relatively rare, paleontologists often sample them frequently. But the study of Bar and Pobiner showed that other sites from 1.9 to 2.6 million years ago (the period when humans evolved upright) were not studied much. “We are drawn to places that preserve fossils, because they are the raw materials of our science,” says Barr. “So we always go back to the same places.” For once, the results of a new study indicate a gap in paleontological records that needs to be filled.
There may have been other factors responsible for the evolution of human traits, or there may have been a significant increase in meat consumption in earlier periods that we have not yet been able to see.
“Sometimes there is no evidence of a butcher, and sometimes there is a lot of evidence,” said Jessica Thompson, an anthropologist at Yale University. “Something must have happened in the meantime.”
Thomson is not entirely convinced that the new article calls into question the hypothesis that meat made us human. His skepticism has to do with how the authors of the article published in PNAS assess the extent to which different time periods have been examined.
The authors examined how many mammal species have been found in fossil records from a particular time period. They argued that if paleontologists had spent much time exploring the sites of a particular period, we would have more mammal species in the fossil record of that period. They then used this criterion to assess whether sites with evidence of butchered bones came from well-studied periods.
But Thomson points out that the criterion of “species richness” may not be the best way to measure whether paleontologists have looked far enough for butchered bone fragments. Not all archeological sites are explored in the same way, he says.
Paleontologists (who study the life of ancient humans) may look carefully for pieces of butchered bone in a particular place, even if this period of time has not been well studied by paleontologists looking for other types of fossils.
Thomson points out that the general belief may be true: If researchers have not been able to find much evidence of butchery on bones before the advent of man, it is not necessarily because they did not look for it enough. This may be due to the fact that there are not many examples of butchers in that period.
Finally, Thomson agrees that the only sure way to find out is to look more closely at time periods from which we have relatively little data. He says:
What these results show me is that we have a serious problem with sampling. We have to enter the sedimentary layers, which are related to 2.6 to 1.9 million years ago. We need to know what is going on.
Even if the new findings do not completely disprove the meat hypothesis, the story of human evolution in this period may be more than that. Stephen Merritt, an anthropologist studying the evolution of carnivore at the University of Alabama, says there is a lot of ignorance about how upright people behave. Did they eat carnivores or hunt themselves? How did humans learn to butcher animals? When they killed a mountain goat, did they share its meat with other members of their species (like other copies) or did they keep most of the food for themselves?
Although it is more difficult to find evidence for these behaviors, they may have played an important role in evolution. Another theory that explains the emergence of some human traits is the “grandmother hypothesis”: since climate change reduced our ancestors’ access to plant foods such as fruits, older females became especially important because of the knowledge of breaking plant brains and They had to pull plant tubers out of the ground. They could then share the food with the children and help the babies wean faster and leave their mothers to give birth to their next child sooner.
This may explain why humans evolved to live relatively long after menopause. But like any evolutionary theory, this case is based on a few glimpses of an image that has long since faded.
Human evolution may have been the result of many more factors than what the upright man ate for dinner, but there is still a great deal of focus on ancestral diets in society.
Proponents of the Paleolithic diet avoid processed foods and support the consumption of raw meat and plants. They argue that it is healthier for us to eat the diets that early humans ate. (Some people avoid cooked meat altogether, even though the evidence for the use of fire in cooking dates back hundreds of thousands of years). Jordan Peterson (Canadian psychologist and author) and his daughter chose a diet that included only beef, salt and water, which valley nutritionists warn about.
High-fat, low-carb ketogenic diets are often seen as a return to our ancestors’ diets, but studies show that ancient human diets may have contained much less meat than what modern diets suggest.
For some, the story of the origin of man, which is deeply rooted in carnivore, suggests that humans owe their existence to their desire for blood and flesh.
In fact, emerging evidence is a little more complex. Carnivore may have evolved alongside other behaviors that have unleashed the power of our larger brains and put us on the path to creating complex languages and communities. Merit says:
Perhaps meat made us human, not only because we ate it, but also because of the social work we did in connection with it. Instead of asking if meat made us human, I want to know how meat made us human.
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