Humans are the only primates to regularly consume animals larger than themselves. This nutritional exploitation, something Thompson and her colleagues call the “human predatory pattern,” has long been synonymous with the flesh-eating, man-the-hunter view of human origins.

Because large animals such as antelope pack serious micro- and macro-nutrient punches, scientists have thought their meat contributed to the development of humanity’s outsize brains. A consensus arose in the 1950s that our ancestors first hunted small animals before moving on to larger beasts about 2.6 million years ago. Flaked-tool use and meat eating became defining characteristics of the Homo genus.

Read: A new genetic clue to how humans got such big brains

“It’s a very appealing story,” says Thompson. “Right around that time, there appeared to be the first stone tools and butchery marks. You have the origins of our Homo genus. A lot of people like to associate that with what it means to be human.”

Then, starting in the mid-1980s, an opposing theory arose in which Homo’s emergence wasn’t so tightly coupled with the origins of hunting and predatory dominance. Rather, early hominins first accessed brain-feeding nutrients through scavenging large-animal carcasses. The debate has rolled on through the decades, with evidence for the scavenging theory gradually building.

The new paper goes further: Harvesting outer-bone meat would have come at significant costs, the authors argue. The chance of encountering predators is high when scraping raw flesh from a carcass. Chewing raw meat without specialized teeth doesn’t give much energetic benefit, studies have shown. In addition, meat exposed to the elements will quickly rot.

Marrow and brains, meanwhile, are locked inside bones and stay fresh longer. These highly nutritional parts are also a precursor to the fatty acids involved in brain and eye development. And more easily than flesh meat, bones could be carried away from carcass sites, safe from predators.

Conventional thinking has been that the behavioral package of early hominins was to go after meat and marrow together, explains Briana Pobiner, a paleoanthropologist at the Smithsonian Institution, who did not contribute to the new paper. But in the new paper, she says, “this team has shown that marrow may have in fact been more important. It’s a nuance, but an important nuance.”

The Pliocene—between 5.3 million and 2.6 million years ago—was an era of dramatic change. An intensely variable and cooling climate transformed vast swaths of rain forest into mosaics of grassland and savanna. Large clearings spawned ecological niches for opportunistic and versatile hominins like Australopithecus—a likely contender for the Homo ancestor—and Kenyanthropus to fill in. Larger predators may well have left carcasses for them to scavenge.