Popular culture often shows cavemen as aggressive, club-wielding hunters. But what if most early humans were actually scavengers? The notion, first proposed by scholars in the second half of the 20th century, has since challenged the dated presumption that prehistoric men hunted food and women gathered it. It’s also changed how we understand the historical shift toward meat-eating—a dietary move that scholars think played an important role in human evolution.

While hunting is the act of killing animals for food, scavenging involves locating the remains of an animal that is already dead. Early 20th-century archaeologists who uncovered the remains of animal bones with early human tools assumed that prehistoric people—or more specifically, prehistoric men—must have hunted these animals for food. But later scholars noted that many of these tools seem more appropriate for cutting up bone and meat than for actually killing an animal. Given this, early humans may have been eating scraps left over from another animal’s kill.

Some interesting evidence for this emerged in a recent study of Kanjera South, a 2 million-year-old archaeological site in Kenya. Noticing that there were several isolated heads of “wildebeest-sized” animals at the site, researchers theorized that larger predators had trouble getting these large skulls open, making the heads available for early human scavengers to transport, crack open and gobble up the brains inside.

“[Kanjera South] hominins not only scavenged these head remains, they also transported them some distance to the archaeological site before breaking them open and consuming the brains,” anthropologist Joseph Ferraro, the study’s lead author, told Phys.org. “This is important because it provides the earliest archaeological evidence of this type of resource transport behavior in the human lineage.”

Ferraro and his team said the early humans who lived at Kanjera South showed signs of scavenging and hunting, meaning that picking apart an already-dead animal was not their only source of meat.

Still, it’s possible that scavenging alone could’ve provided enough nutrition for early humans. After observing that lions in Kenya’s Ol Pejeta Conservancy leave a large amount of their kill intact, paleoanthropologist Briana Pobiner hypothesized in a 2015 paper in the Journal of Human Evolution that saber-toothed cats living there 1.8 million years ago may have killed and consumed their prey in a similar way, leaving plenty left over for hungry hominids.

“An entire zebra carcass could yield almost 15 kilograms of meat in scraps of various sizes,” Pobiner wrote in American Scientist in 2016. “[T]his would provide more than 60,000 calories from a zebra carcass. That’s almost 107 Big Macs—enough for the entire daily caloric requirements of about 27 male Homo erectus.”

The way that early humans obtained meat matters because access to it likely played a big role in the story of human evolution. We know that over 6 million years, human brain size increased by 300 percent. Over the same period, human intestines got smaller, meaning that it took less energy to digest food. Early humans could obtain more calories and protein from meat using less digestive energy than they could from fruits, plants and seeds, so scholars assume that the switch in diet occurred along with these evolutionary changes.

Animals’ bone marrow may have been an important food source for scavengers, too—perhaps even more important than meat. That’s because it’s fattier than flesh and may have thus provided more energy, says anthropologist Jessica Thompson, the paper’s lead author of a 2019 research paper published in Current Anthropology.

“We’re used to thinking of meat as a fatty product,” Thompson told Discover magazine. “But wild game is not very fatty at all. If you eat a lot of lean meat it doesn’t actually provide you with the sustenance you need to function well… Bone marrow is actually a nicely accessible package of fat in an otherwise fat-poor landscape.” And since many carnivores leave an animal’s bones behind after a kill, these could’ve been a good source of food for scavengers.

Switching from a plant-based diet to an animal-based one didn’t necessarily cause the evolutionary changes in our brain and intestine sizes, but it may have made them possible. It also may have led early humans out of Africa as they followed the large carnivores whose prey they fed on. Archaeologists from an older era speculated that the development of hunting was what made early humans, well, human. But new research about the role scavenging played in our history complicates that picture.