A fossilized tibia spent years, decades, lost among the collections of the National Museum of Nairobi (Kenya). It was the shin bone of a hominid, a relative of Homo Sapiens, which lived around 1.45 million years ago and which had as many as nine cut marks.
No one paid much attention to it until paleoanthropologist Briana Pobiner of the Smithsonian Institution examined it with her magnifying glass. The researcher was looking for clues as to which prehistoric predators might have been hunting and eating our ancient relatives.
Pobiner was poring over the tibia for bite marks from extinct beasts when he suddenly noticed what clearly seemed to him to be evidence of carnage. Not only that. Results from subsequent analyzes indicate that this bone is the oldest evidence of close evolutionary relatives of humans killing and probably eating each other.
The left shin from 1.45 million years ago was found in northern Kenya, experts explain in an article published this Monday, June 26, in the journal Scientific Reports. 3D scanning of the fossil's surface revealed that the marks were from cuts inflicted by stone tools.
"The information we have tells us that hominins were probably eating other hominins," explains Pobiner. "There are many other examples of human species consuming each other for nourishment, but this fossil suggests that some relatives of our species ate each other for survival longer than we previously recognised," she adds.
To find out if what he was seeing on the surface of the bone were really cut marks, Pobiner sent molds made of the same material dentists use to create impressions of teeth to Michael Pante of Colorado State University and co-author of the study. .
Without any extra details about what was in front of him, Pante scanned the casts and compared the shape of the marks against a database of 898 individual tooth, butcher and stomp marks created through controlled experiments. The analysis identified nine of the 11 cuts as clear matches to the type of damage inflicted by the stone tools.
The other two marks were likely big cat bite marks, with the lion as the first choice. According to Pobiner, the bite marks could come from one of three different types of Sabretooth that roamed the area 1.45 million years ago.
By themselves, the cut marks do not prove that the human relative who inflicted them also practiced cannibalism. But the Smithsonian Institute paleoanthropologist says this is the most likely scenario because the marks are where the calf muscle attached to the bone, a good place to cut if the goal is to remove a piece of meat.
“These signals closely resemble what I have seen in animal fossils that were being processed for consumption,” Briana Pobiner said in a statement. "It seems more likely that the meat from this leg was eaten, and that it was eaten as food rather than as part of a ritual," she says.
Although the case can initially be classified as cannibalism, the researcher considers that this point is difficult to determine, since cannibalism requires that the eater and the eaten come from the same species. The fossil bone was initially identified as Australopithecus boisei and, in 1990, determined to be Homo erectus. Today, however, experts agree that there is not enough information to assign the tibia to a particular hominin species.
The use of stone tools does not limit the range of possibilities either. According to specialists, this fossil could be a trace of prehistoric cannibalism at the same time as it is also possible that it was a case of a species devouring its evolutionary cousin.
“You can make some pretty amazing discoveries by going back to museum collections and taking a second look at the fossils,” Pobiner says. “Not everyone sees everything the first time. It takes a community of scientists coming up with different questions and techniques to keep expanding our knowledge of the world”, he concludes.
