In 2017, Briana Pobiner, a paleoanthropologist at the Smithsonian National Museum, pointed a magnifying lens at a 1.45 million-year-old tibia and saw a series of neat slashes. The bone belonged to the National Museums of Kenya in Nairobi, where Pobiner had gone to look for animal tooth marks on ancient hominin bones. While researchers generally assume that animals killed and ate our ancient ancestors, relatively little evidence has ever come to light.

But this was a different kind of evidence, as the nine slashes resembled butchery marks, meaning another human had inflicted them with a stone tool.

“These cut marks look very similar to what I’ve seen on animal fossils that were being processed for consumption,” Pobiner says in a press release. “It seems most likely that the meat from this leg was eaten and that it was eaten for nutrition as opposed to for a ritual.”

Cannibalism in Question

If Pobiner is right about the tibia, its marks present the oldest conclusive evidence to date of a hominin butchering another hominin. Whether this constituted cannibalism is unknown as that requires two parties (an eater and an eaten) of the same species, while neither in this case are known for sure. After Mary Leakey discovered the bone in 1970, Richard Leakey classified it as an Australopithecus boisei. But later sources proposed Homo erectus and other species.

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Pobiner was less interested in resolving this decades-long dispute than in confirming that the slashes came from a stone tool. Doing so meant making use of a special database of bone marks and injuries, so she made impressions of the slashes along with two others that likely came from animal teeth. She sent the molds to Michael Pante, a paleoanthropologist at Colorado State University, along with no information as to their origins or her suspicions.

Pante scanned in the molds and compared them against a database of about 900 other examples of bones injured by tools, trampling and carnivores. The database confirmed Pobiner’s early conclusions and further proposed that a large cat, maybe even a saber tooth tiger, had made the two teeth marks. Whether the animal left the two marks before or after the hominin died, the researchers couldn’t say.

Reasons for Eating the Hominin

Examination of the slashes yielded yet more evidence, from their V-shape reminiscent of a cutting tool to their unremarkable coloring. Since that matched the rest of the bone, the paper says, the marks likely occurred before fossilization.

Scientists have documented cannibalism in more than 1,300 species, including several primates, the paper says, for reasons that were nutritional, aggressive, affectionate, psychotic, ritualistic, funerary, spiritual, magical or for purposes of war. Counted among those species are Neanderthals and early Homo sapiens, who practiced cannibalism at early sites.

In this case, the wielder of the stone tool appeared to have removed a leg muscle next to the calf, for purposes of eating.

“You can make some pretty amazing discoveries by going back into museum collections and taking a second look at fossils,” Pobiner says in a press release. “It takes a community of scientists coming in with different questions and techniques to keep expanding our knowledge of the world.”

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