Paleoanthropologists have found multiple cut marks on a 1.45-million-year-old (Early Pleistocene) hominin fossil found in the Koobi Fora Formation in the Turkana region of Kenya.
“The information we have tells us that hominins were likely eating other hominins at least 1.45 million years ago,” said National Museum of Natural History paleoanthropologist Briana Pobiner.
“There are numerous other examples of species from the human evolutionary tree consuming each other for nutrition, but this fossil suggests that our species’ relatives were eating each other to survive further into the past than we recognized.”
In July 2017, Dr. Pobiner undertook a pilot study of hominin fossils from the Turkana region of Kenya dated to 1.8 to 1.5 million years ago, with an expectation of potentially finding some carnivore damage on these fossils.
However, she unexpectedly observed potential butchery marks on a single fossil: a fossilized hominin tibia, or shin bone.
This observation was unexpected because while butchery marks left by hominins on animal fossils beginning by at least the Early Pleistocene point to increased meat and marrow acquisition during the evolution of the genus Homo and hundreds of cut marked fossils of other animals have been identified from the Koobi Fora Formation, no cut marks on hominin fossils from this temporal and geographic area have been reported.
Dr. Pobiner and colleagues compared the shape of the marks to a database of 898 individual tooth, butchery and trample marks created through controlled experiments.
The analysis positively identified nine of the 11 marks as clear matches for the type of damage inflicted by stone tools.
The other two marks were likely bite marks from a big cat, with a lion being the closest match.
“The bite marks could have come from one of the three different types of saber-tooth cats prowling the landscape at the time the owner of this shin bone was alive,” Dr. Pobiner said.
“By themselves, the cut marks do not prove that the human relative who inflicted them also made a meal out of the leg, but this seems to be the most likely scenario.”
The cut marks are located where a calf muscle would have attached to the bone — a good place to cut if the goal is to remove a chunk of flesh.
The cut marks are also all oriented the same way, such that a hand wielding a stone tool could have made them all in succession without changing grip or adjusting the angle of attack.
“These cut marks look very similar to what I’ve seen on animal fossils that were being processed for consumption,” Dr. Pobiner said.
“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.”
“While this case may appear to be cannibalism to a casual observer, there is not enough evidence to make that determination because cannibalism requires that the eater and the eaten hail from the same species.”
The fossil shin bone from the Koobi Fora Formation was initially identified as Australopithecus boisei and then in 1990 as Homo erectus, but today, experts agree that there is not enough information to assign the specimen to a particular species of hominin.
The use of stone tools also does not narrow down which species might have been doing the cutting.
Recent research further called into question the once-common assumption that only one genus, Homo, made and used stone tools.
So, this fossil could be a trace of prehistoric cannibalism, but it is also possible this was a case of one species chowing down on its evolutionary cousin.
None of the stone-tool cut marks overlap with the two bite marks, which makes it hard to infer anything about the order of events that took place.
For instance, a big cat may have scavenged the remains after hominins removed most of the meat from the leg bone.
It is equally possible that a big cat killed an unlucky hominin and then was chased off or scurried away before opportunistic hominins took over the kill.
“You can make some pretty amazing discoveries by going back into museum collections and taking a second look at fossils,” Dr. Pobiner said.
“Not everyone sees everything the first time around. It takes a community of scientists coming in with different questions and techniques to keep expanding our knowledge of the world.”
The results were published in the journal Scientific Reports.
B. Pobiner et al. 2023. Early Pleistocene cut marked hominin fossil from Koobi Fora, Kenya. Sci Rep 13, 9896; doi: 10.1038/s41598-023-35702-7