When is a cannibal not a cannibal?

Everyone quickly sees a cannibal. The Romans thought the ancient Britons feasted on human flesh, and the Britons thought the same about the Irish. Not a few prehistoric finds have been suggestively, if not accurately, attributed to the work of ancient cannibals. In 1871, Mark Twain commented on the discovery of the bones of a primeval man of whom his colleagues are said to have made a meal: “I ask the candid reader, does this not seem like taking advantage of a gentleman who has been dead for two years?” million years?”

In the world of scholarly and scholarly paleoanthropology, claims of cannibalism are held to strict standards of evidence. That’s why more than a few eyebrows were raised about one earlier this week study in Scientific Reports claiming that a 1.45 million year old shin bone fragment – ​​found 53 years ago in Northern Kenya and sparsely documented – was an indication that our human ancestors not only butchered their own kind, but likely accompanying press release said it, also “chowing down”.

The press release described the finding as the “oldest conclusive evidence” of such behavior. “The information we have tells us that hominids probably ate other hominids at least 1.45 million years ago,” Briana Pobiner, a paleoanthropologist at the Smithsonian’s National Museum of Natural History and first author of the paper, said in the press release. “There are plenty of other examples of species from the human evolutionary tree consuming each other for nutrition, but this fossil suggests that our species’ relatives ate each other to survive further into the past than we thought.”

The discovery of part of the presumed victim raised one of the questions that keeps paleoanthropologists awake at night: When does markings on a bone indicate cannibalism? Or put another way, how much pre-modern evidence is needed to prove a modern theory?

Dr. Pobiner, an authority on cuts, had discovered the semi-shin bones fossil six summers ago when he was examining hominin bones found in a museum vault in Nairobi. She was inspecting the fossil for bite marks when she noticed 11 thin slashes, all pointing in the same direction and clustered around a spot where a calf muscle would have attached to the bone — the meatiest part of the lower leg, said Dr. Pobiner in an interview.

She sent molds of the scars to Michael Pante, a paleoanthropologist at Colorado State University and an author on the study, who made 3D scans and compared the shape of the incisions against a database of 898 teeth, trampling and slaughter marks. The analysis indicated that nine of the marks were consistent with the type of damage caused by stone tools. Dr. Pobiner said the placement and orientation of the cuts implied the meat had been stripped from the bone. From those observations, she extrapolated her thesis on cannibalism.

“As far as we can tell, this humanoid leg bone is treated like other animals, which we assume are eaten based on the many butcher marks on it,” said Dr. Pobiner. “It makes the most sense to assume that this butchery was also done for eating.”

In the study, Dr. Pobiner that cannibalism was a possible explanation for the defleshed bone. But her quotes in the press release sounded more definitive and, to the chagrin of colleagues, inspired headlines like “YABBA DABBA CHEW! Cavemen slaughtered and ate each other 1.45 million years ago, scientists say.”

Some experts praised the findings. “Thoughtful and perfectly pitched,” said James Cole, an archaeologist at the University of Brighton. Others called Dr. Pobiner’s advocacy of prehistoric cannibalism is exaggerated, if only because she offered no evidence that the meat had been eaten. “If they are butcher marks, we can’t be sure of cannibalism,” said Raphaël Hanon, a zooarchaeologist at the University of Witwatersrand, Johannesburg.

“Clickbait,” says Tim D. White, a paleoanthropologist at the University of California, Berkeley, best known for leading the team that discovered Ardipithecus ramidus, a probable human ancestor dated 4.4 million years ago. “Even if they are eventually shown to be both ancient and genuine, the simple presence of ambiguous scratches on an isolated fossil bone is not sufficient evidence of cannibalism.”

More often than not, verification of the practice is questionable. “Archaeologists and physical anthropologists do their best to make their field ‘real’ hard science, but the further back you go, the fuzzier the data gets,” said Peter Bullock, a retired chief archaeologist for the U.S. Army Corps of Engineers. “Cannibalism is usually the sexy interpretation, and I put a lot of effort into it. Why not a murder victim or the result of an autistic humanoid self-harming? Prove that you can’t.”

Controversy over ancient anthropophagy, or cannibalism, has raged in academia for more than a century. In 1925, Raymond Dart, an anatomist at the University of Witwatersrand, announced the discovery of a partial skull of an ape-like juvenile excavated in a quarry in the town of Taung. He named the prehuman species Australopithecus africanus – the southern monkey of Africa.

Largely from the appearance of the skull, Dr. Dart deduced that the child had died from a severe blow to the head, concluding that at least some australopithecines were “confirmed killers: carnivorous creatures, forcibly seizing living quarries, beating them to death, tearing apart their broken bodies , cut them to pieces, quenching their voracious thirst with the hot blood of victims and greedily devouring deathly pale writhing flesh.” Scientists now suspect that the so-called Taung child, who died 2.8 million years ago, was killed by an eagle or other large bird of prey.

Scholars have long debated whether to accept routine, common cannibalism in human prehistory, or deny that it ever occurred in the human family tree. “If you were fighting for survival, which is what our ancestors did every day, any source of nutrition would have been beneficial,” said Dr. Pante. The controversy intensified in 1979, when William Arens, a social anthropologist, argued in his book “The Man-Eating Myth: Anthropology and Anthropophagy” that there was almost no reliable historical and ethnographic evidence for the practice of cannibalism, except in isolated, terrible emergencies.

“Cannibalism revives sporadically when there are no anthropologists to observe it,” Dr. Arens. He claimed that virtually all accounts of cannibalism are hearsay, a propaganda tool by British Empire scholars to help tame the ignoble savage.

“Not much of Arens’s book survives today,” said Dr. White, the paleoanthropologist, “but it proved to be a useful heuristic tool for its time and a challenge to those interested in the nature and extent of cannibalism in recent and distant past.” Perhaps the book’s most lasting influence, he added, was to force academics to raise the standards of their evidence and scholarship.

Since then, clear evidence of systematic cannibalism among hominids has emerged in the fossil record. The earliest confirmation was discovered in 1994 in the Gran Dolina Cave in Spain’s Atapuerca Mountains. The remains of 11 individuals who lived some 800,000 years ago showed distinctive signs of being eaten, with bones showing lacerations, fractures where they had broken open to expose the marrow and human teeth marks.

Among our other evolutionary cousins ​​now confirmed to have practiced cannibalism are Neanderthals, with whom humans overlapped and mated for thousands of years. A study published in 2016 reported that Neanderthal bones found in a cave in Goyet, Belgium, and dated to about 40,000 BC. Showing signs of being butchered, split and used to sharpen the edges of stone tools. Bone fracture patterns in Homo antecessor, considered the last common ancestor of Neanderthals and Homo sapiens, suggest cannibalism dates back half a million years or more.

The bone fragment of Dr. Pobiner was recovered by Mary Leakey, a British paleoanthropologist, in the remote wasteland just east of Lake Turkana, then called Lake Rudolf, without an archaeological context of the fauna observed at the time of discovery. “Were there any other cut bones?” said Dr. White. “Were there any stone tools? Did the researchers try to return to the site to find the other end of the tibia?” He claimed those details are critical to drawing accurate conclusions about past events.

So, when do marks on a bone indicate prehistoric cannibalism? “On a single bone, never,” said Dr. White. “Showing that the scratches were made by a hominid using a stone tool is a methodological challenge. The bigger challenge is to show that such evidence has anything to do with cannibalism.”