Did eating meat really make us human?

Twenty-four years ago, Briana Pobiner reached into the north Kenyan soil and put her hands on bones that had not been touched in 1.5 million years. Pobiner was digging up ancient animal bones and looking for signs that they had been butchered by our early ancestors to get at the fat, calories-rich bone marrow hidden within. It's really exciting.

Pobiner's interest in how the diet of our ancestors shaped their evolution and eventually the emergence of Homo sapiens was sparked by that moment. It seems that meat has played a crucial role. Our ancestors had short legs and small brains, similar to a Chimpanzees, and mostly ate plants. A new species emerged around 2 million years ago. Homo erectus had a larger brain, smaller gut, and limbs like modern humans. The fossils excavated by Pobiner show that someone was butchering animals to separate the lean meat from the bone. Paleontologists theorize that the evolution of humanlike features and meat eating are related.

“The explanation has been that meat-eating allowed this: we got a lot more nutrition, and these concentrated sources facilitated these changes,” Pobiner says. Large brains are phenomenal energy hogs—even at rest, a human brain consumes about 20 percent of the body’s energy. But a switch to a diet full of calorie-rich meat meant an excess of energy that could be directed to supporting larger, more complex brains. And if prehumans hunted their food, that would explain a shift toward longer limbs that were more efficient for stalking prey over great distances. Meat made us human, the conventional wisdom said. And Pobiner agreed.

In April 2020, Pobiner got a call that made her rethink her hypothesis. Andrew Barr, a paleontologist at George Washington University in Washington, DC, wasn't completely convinced about the link between meat-eating and Homo erectus. He wanted to use the fossil record to see if there was any evidence that humans were eating more meat around the time Homo erectus evolved. Pobiner liked the idea of questioning conventional wisdom, even if it's conventional wisdom that I buy into.

The researchers were unable to travel to Kenya for fieldwork because of the Pandemic, so they analyzed data from nine major research areas in Eastern Africa that cover millions of years of human evolution. They used different metrics to assess how well-researched each time period was, and how many bones with butchery marks were found in each site. In a new paper, Barr and Pobiner argue that the link between meat-eating and human evolution might be less certain than previously thought. The increase in butchered bones after the appearance of Homo erectus is actually a sampling bias. More bones were found when paleontologists went to look for them at dig sites from this era.

It doesn't rule out a link between meat-eating and evolutionary change, but it does suggest that the story might be a little more complicated. Paleontologists often sample the sites with well-preserved animal bones over and over again. The era during which Homo erectus evolved has been relatively under- studied. Barr says we keep going back to the same places.