Butchery marks on a fossilized bone suggest human ancestors ate each other, shocking researchers

• A researcher found what appear to be cut marks on the bone of a human ancestor.
• The position of the marks suggests the flesh may have been removed for consumption.

Nine cut marks on the fossilized shin bone of a Homo sapien ancestor may indicate that early human relatives may have been cannibals who butchered and ate each other.

Researchers from the Smithsonian's National Museum of Natural History published a study in Scientific Reports describing the cuts on the 1.45-million-year-old bone.

"My first reaction was, 'What?!'" paleoanthropologist Briana Pobiner, who led the study, told Insider. "I was totally shocked. I was really not expecting to find these sorts of cut marks."

Pobiner was originally examining the fossilized tibia for bite marks from predators. The bone is part of the National Museums of Kenya's Nairobi National Museum collection.

While there were two bite marks from a big cat, potentially a saber-tooth cat, the other nine marks were more similar to butchery marks found on animal fossils that appeared to be hunted and eaten by humans and their ancestors.

Because the cut marks and bites don't overlap, it's not clear who got to the bone first, a hominin or the big cat.

Distinguishing between teeth, tools, and trampling

The cut marks are in a row and of a similar size and shape, which suggests they're not puncture marks from an animal bite, which would appear rounder and less uniform, Pobiner said.

Cut marks are also "usually deeper, and they have a v-shape on the bottom because the tools that make them have a sharp edge," Pobiner said.

To create the cutting marks, Stone Age hominids, aka human-related ancestors, could have used flint knives. They made these tools by using a rock to break a sharp shard off another rock.

Pobiner sent molds of the bone cuts to Michael Pante, a paleoanthropologist with Colorado State University. He used 3D scans of the molds to compare the cuts to a database of other marks, including various types of stone tools, crocodile and mammal bites, cow tramplings, and strike damage from anvils and hammerstones.

Almost all of the bone's marks could be classified as cut marks with a high degree of confidence, Pobiner said.

Not all cut marks mean cannibalism

Defleshing, disarticulation, and skinning are all means of removing flesh from bone and have different purposes, Pobiner said.

Skinning usually happens before further butchering, defleshing is usually for consuming the meat, and disarticulation is for transporting pieces of an animal.

"The way we distinguish between those types of marks is usually where the marks are," Pobiner said. Skinning marks are often at the ankles or wrists, and disarticulation cuts are at the joints.

The tibia's marks are located where a small muscle attaches under the back of the knee. "Because of that, our interpretation was that this was part of the action of cutting off big chunks of meat, like your big calf muscle," Pobiner said.

While she can't be sure the defleshing was done for eating purposes, Pobiner said it's a more likely explanation than for ritual or burial reasons. "We don't have any kind of evidence for symbolic behavior until maybe a million years later in the fossil record," she said.

Paleoanthropologist Mary Leakey found the tibia bone in Kenya in 1970. Because no other bones or a skull were found with it, it's not possible to determine the exact species of hominin the bone belonged to.

It's also not clear if it was a member of the same species who butchered and potentially ate the flesh from the bone, meaning it wasn't necessarily cannibalism. But there are instances of human cannibalism, such as the 15,000-year-old inhabitants of Gough's Cave in England.

Pobiner hopes the findings will inspire other researchers to return to existing collections to look for more cut marks. "Discoveries don't just happen in the field," she said. "They sometimes happen in museums."