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Australopithecus afarensis lived between3.85 and 2.95 million years ago.


New evidence suggests hominins firstdeveloped outsized brains by scavenging fatty animal marrow, rather thanactively hunting for meat.


NORTHERN ETHIOPIA WAS once home to a vast,ancient lake. Saber-toothed cats prowled around it, giant crocodiles swamwithin. The streams and rivers that fed it — over 3 million years ago, duringthe Pliocene — left behind trails of sediment that have now hardened intosandstone.


Deposited within these layers are fossils:some of early hominins, along with the bones of hippos, antelope, andelephants. Anthropologist Jessica Thompson encountered two of these specimens,from an area named Dikika, in 2010.


Humans are the only primate to regularlyconsume animals larger than themselves. This nutritional exploitation,something Thompson and her colleagues call the “human predatory pattern,” haslong been synonymous with the flesh-eating, man-the-hunter view of humanorigins.


Because large animals such as antelope packa serious micro-and-macro-nutrient punch, scientists have thought their meatcontributed to humanity’s outsized brains. A consensus arose in the 1950s thatour ancestors first hunted small animals before moving on to larger beastsaround 2.6 million years ago. Flaked tool use and meat eating became definingcharacteristics of the Homo genus.


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


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


The new paper goes further: Harvestingouter-bone meat would have come at significant costs, the authors argue. Thechance of encountering predators is high when scraping raw flesh from acarcass. Chewing raw meat without specialized teeth doesn’t give much energeticbenefit, studies have shown. In addition, meat exposed to the elements willquickly rot.


Marrow and brains, meanwhile, are lockedinside bones and stay fresh longer. These highly nutritional parts are also aprecursor to the fatty acids involved with brain and eye development. And moreeasily than flesh-meat, bones could be carried away from carcass sites, safefrom predators.



Conventional thinking has been that thebehavioral 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, “Thisteam has shown that marrow may have in fact been more important. It’s a nuance,but an important nuance.”


As to who wielded these percussiveinstruments, the timeline presents a puzzle. The earliest Homo specimen is nowdated to 2.8 million years. The Dikika fossils suggest butchery behaviors at3.4 million years ago. Homo may have emerged earlier than scientists suspected— a theory that would need more fossil evidence to support it — or anotherhominin, such as Australopithecus, may have created tools before Homo.


Some scholars aren’t convinced by thestudy’s arguments, however. For example, Craig Stanford, an anthropologist atthe University of Southern California, questions the emphasis on homininscavenging behavior appearing before hunting. “We have no examples today ofanimals that scavenge but don’t hunt,” he adds.


To test the new theory, the review authorssuggest seeking out further evidence of percussive tools that predate flakedtools. Researchers could, they note, broaden the search for the signatures ofsuch instruments within both the existing fossil record and at dig sites.Thompson’s graduate students, for example, are using 3D scanning and artificialintelligence techniques to improve the identification of marks on fossils —whether they were created by early hominins, saber-toothed cats, hyenas, orother types of creatures.


What they uncover could deal a blow totheir theory, but it will also, undoubtedly, enrich our understanding of howour ancestors evolved.