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Scientists Are Skeptical that Intelligence in Homo naledi “Erases Human Exceptionalism”

Photo credit: Lee Roger Berger research team, CC BY 4.0 , via Wikimedia Commons.

A major science news story is making the rounds right now about how the hominid species Homo naledi may have had high intelligence, buried its dead, used fire, and even carved markings into a cave wall. All this is unexpected since Homo naledi’s brain size is not much different from that of a chimp. 

Given the extensive media attention (e.g., Wall Street Journal, NewsweekABC News, Associated PressNew York Times, to name a few), you might think this is some completely new proposal that just got published in a major scientific journal. That inference would be wrong. At least when it comes to burial of the dead and use of fire, these are old claims about Homo naledi that have been controversial for years but are now being reinvigorated based upon new evidence presented in a series of three preprint papers (herehere, and here). The papers were uploaded at bioRxiv, which, of course, is a preprint server, not a scientific journal. Newsweek thus observes, “The papers are still in preprint, however, so they are yet to be published officially in a peer-reviewed journal.” The Associated Press notes, “The research has not been peer-reviewed yet and some outside scientists think more evidence is needed to challenge what we know about how humans evolved their complex thinking.” 

Someone must have a good PR team at work to generate such a large batch of news stories about mostly old claims based entirely upon preprints! is even running a story about the project’s lead scientist, Lee Berger, heralding “South Africa’s Lee Berger, palaeontology action hero”!

Scientists Are Skeptical

Peer-reviewed or not, and hyped or not, the data exists and it’s worth discussing. And apparently quite a few scientists are skeptical. The New York Times notes:

But a number of experts on ancient engravings and burials said that the evidence did not yet support these extraordinary conclusions about Homo naledi. The cave evidence found so far could have a range of other explanations, they said. The skeletons might have been merely left on the cave floor, for example. And the charcoal and engravings found in the cave might have been left by modern humans who entered long after Homo naledi became extinct.

“It seems that the narrative is more important than the facts,” said Maxime Aubert, an archaeologist at Griffith University in Australia.

An article at The Conversation authored by a quartet of four archaeologists, based in Australia, Kenya, Spain, and Germany, shows that some prominent scientists aren’t convinced. The article, titled “Major new research claims smaller-brained Homo naledi made rock art and buried the dead. But the evidence is lacking,” covers the three main claims: use of fire, burial of the dead, and the presence of cave art.

Let’s take a look at each of these.

Torching Fire Use by Homo naledi?

The skeptical quartet note that the investigators have not published any evidence that demonstrates Homo nalediused fire in the cave:

In public lectures and on social media they clarify they have found new evidence for hearths, including charcoal, ash, discoloured clay and burned animal bones. Yet none of the scientific research needed to confirm the use of fire has been carried out. Or if it has, it hasn’t been published.

Previously acquired radiocarbon dates obtained by the site investigators on the apparent hearth material provided very late dates that distanced the hearths from the remains of Homo naledi by several hundred thousand years.

These are pretty strong criticisms. The quartet says the investigators are making assertions that have simply not been backed up by evidence presented to the public. In that case, claims of Homo naledi’s fire use seem totally unestablished. 

Burying Claims of Burial of the Dead

As for burial of the dead, the skeptical quartet note that there are “rigorous criteria agreed upon by the scientific community for identifying intentional human burial.” But, they argue, the Homo naledi evidence does not meet this standard:

[I]s there actually evidence for funerary behaviour at Rising Star Cave? According to standards set by the palaeoanthropology community, the evidence presented so far indicates no.

They continue:

[N]ot one of the burials provides compelling evidence of a deliberately excavated pit. Indeed, the shallow cavities may not be dug pits at all, but natural depressions where the bodies accumulated and were later disturbed by trampling, or partial cave collapse.

The alleged burials also fail to meet another fundamental criteria for deliberate burials: anatomical alignment of the body and articulation of skeletal remains.

In a deliberate burial, the body is generally intact and any minimal displacement can be explained by decomposition. That’s because burial involves immediately covering the body with soil, which protects the anatomical integrity of the skeleton.

Rising Star Cave so far hasn’t produced evidence for anything other than the general spatial association of some skeletal elements. At most, it provides evidence for the in-situ decomposition of particular body parts, such as an ankle, and partial hand and foot articulations.

Moreover, confirming intentional burial in the past has required the presentation of human remains in an arrangement that can’t have been achieved by chance. However, the scattered distribution of the remains at Rising Star prevents reconstruction of their original positions.

Other claimed evidence for funerary behaviour is equally uncompelling. A stone artefact supposedly included in the burial as a “grave good” is said to have scratches and edge serrations from use. But this so-called artefact’s shape suggests it may be natural. It’s still encased in sediment and has only been studied through synchrotron X-ray.

But perhaps the biggest barrier to confirming the status of the findings is that so far none of the alleged burials have been fully excavated. It’s therefore impossible to assess the completeness of the bodies, their original position, and the limits of the purported pits.

The New York Times elaborates:

But María Martinón-Torres, the director of Spain’s National Research Center on Human Evolution, said that such speculations were premature based on the evidence presented so far. “Hypotheses need to be built on what we have, not what we guess,” she said.

Dr. Martinón-Torres considered funerary caching more likely than burials, pointing out that the oval depressions did not contain full skeletons in complete alignment. If Homo naledi brought the bodies into the cave and left them on the cave floor, the bones could have become separated as the bodies decomposed. “Still, I think the possibility of having funerary caching with this antiquity is already stunning,” she said.

“I’m highly optimistic that they have burials, but the jury is still out,” said Michael Petraglia, the director of the Australian Research Center for Human Evolution. Dr. Petraglia wanted to see more detailed analysis of the sediment and other kinds of evidence before judging whether the ovals were burials. “The problem is that they’re ahead of the science,” he said.

And Paul Pettitt, an archaeologist at Durham University in England, said it was possible that Homo naledi did not bring the bodies in, either for caching or burying. The bodies might have washed in. “I’m not convinced that the team have demonstrated that this was deliberate burial,” he said.

Likewise the UK’s Natural History Museum quotes a scientist who is not buying it:

Dr Silvia Bello is an expert on the evolution of human behaviour at the Museum, and was not involved in the study.

‘It sounds ridiculous because we’re used to burials, but they are not the easiest of things to define or recognise,’ explains Silvia. ‘If you have a body that is completely buried, when it decomposes the bone collapses in a certain way and in a certain order. So, this could give an indication that the body was buried whole, but it doesn’t necessarily tell you that it was a burial. The researchers call what they have found a “feature”, which I thought was very generic.’

‘There are two things at play. One is the burial, and one is the funerary behaviour: you can have a funerary behaviour without a burial.’

Science News also has a story quoting critics of claims that this new evidence establishes burial of the dead:

Some researchers consider the new evidence inadequate to confirm that H. naledi interred its own in cave graves. …

“I think that deliberate burial of the dead by Homo naledi is clear, although it is unlikely that the evidence so far presented will satisfy all scholars,” says archaeologist Michael Petraglia of Griffith University in Brisbane, Australia, who is not part of Berger’s team.

One objection comes from paleoanthropologist María Martinón-Torres, director of the Spanish National Research Center on Human Evolution in Burgos. She suspects that disconnected skeletal parts described in the new papers accumulated either after bodies of the dead that had been placed in cave shafts later fell through or had been left at the back of underground caves. Trampling or other H. naledi activities in caves could eventually have produced fragmentary sets of fossils uncovered by Berger’s group, says Martinón-Torres, who along with Petraglia studied the oldest known H. sapiens burial in Africa.

It’s possible that periodic water seepage into the underground caves helped to move partial or complete H. naledi corpses down sloping cave floors until they came to rest in natural depressions that Berger’s team suggests are intentional burial sites, says archaeologist Paul Pettitt of Durham University in England.

Presumably, if other hominids entered the cave later, then they could also be responsible for the markings on the cave wall.

Is the Writing on the Wall?

As for the markings on the cave wall, these are clearly artificial — that much seems obvious. But it’s quite another task to demonstrate that they were produced by the species Homo naledi. The problem is that the markings are at this point totally undated and thus it’s difficult to say whether they were made by Homo naledi or some later species — perhaps even by humans — who entered the cave and scraped up the wall. This point is reiterated by multiple stories:

  • Science News notes: “[T]here is no way to determine whether H. naledi or perhaps later H. sapiens visitors to the underground caves — part of South Africa’s Rising Star Cave System, about 40 kilometers west of Johannesburg — created the undated engravings found by Berger’s group. … But the underground cave engravings remain undated. There is no way to know whether people reached the cave chambers within the past few thousand years and carved those wall patterns, Pettitt says.” 
  • In an Associated Press story, Rick Potts of the Smithsonian makes a similar point: “Scientists haven’t yet been able to identify how old the engravings are. So Potts said the current evidence can’t say for sure whether H. naledi was truly the one to create the symbols, or if some other creature — maybe even H. sapiens — made its way down there at some point.”
  • The New York Times likewise states: “As for the engravings and the fires, experts said it wasn’t clear that Homo naledi was responsible for them. It was possible they were the work of modern humans who came into the cave thousands of years later. ‘The whole thing is unconvincing, to say the least,’ said João Zilhão, an archaeologist at the University of Barcelona.”
  • The quartet of skeptical archaeologists writing at The Conversation also note: “The problem with the rock art at Rising Star Cave is that it’s undated. To imply any link with Homo naledi requires firm dates. This could be achieved through using dating techniques on associated residues or natural deposits covering the art, or by studying materials from excavated and dated archaeological layers that can be linked to the art (for instance, if they contain engraving tools or engraved rock fall fragments). …In the absence of dating, it’s simply spurious to claim the engravings were made by Homo naledi, rather than by another species (and potentially at a much later date).”

Incidentally, the cave markings look very similar to markings made by Neanderthals — whom we already know were highly intelligent. As John Hawks told the Wall Street Journal:

Similar ancient hashtags have been documented at a Neanderthal site in Gibraltar that is just tens of thousands of years old. “They are uncannily similar, and they are 8,000 kilometers apart, you know, it is just crazy,” Hawks said.

Neanderthal fossils aren’t known from southern Africa, but any similarly smart hominid (like Homo sapiens) could have made these marks.

“Erases the Idea of Human Exceptionalism”

The possibility that some later species made the cave markings is not even considered by many news outlets, including ABC News, which is completely credulous about claims that these markings were made by the precise individuals who “laid to rest” the bones that are found in the cave:

The researchers began to hypothesize that Homo naledi buried its dead during continued excavations in 2018 and in July 2022, those hunches were not only proven but amplified once Berger and his team found skeletal remains of Homo naledi and then carvings on the wall above them to mark those laid to rest there.

The symbols included triangles, squares and a sort-of “hashtag” sign, as in two cross-hatching equal signs, Berger said. However, it is unclear what these carvings meant, and researchers will be delving into whether there is a “random chance” that Homo naledi used the same symbols as humans or if they were obtained from some sort of shared ancestry.

Why do so many folks seem so eager to accept unsubstantiated claims about Homo nalediABC News spells out what the investigators want to accomplish with this research:

The finding was “striking” and “shocking” and erases the idea of human exceptionalism — that humans are different than animals and special due to their big brains. Homo naledi had brains about the size of a chimpanzee, and yet practiced ritual burials, a behavior previously assumed was only done by humans, Berger said.

They get points for candor, at least. The purpose of these stretched and unverified claims of high intelligence in a small-brained hominid is apparently to “erase the idea” that human beings are “special” and “exceptional.”

Keep in mind that Berger et al.’s previous claims about Homo naledi’s intelligence have been highly disputed and their initial claims that the species lived 2-3 million years ago turned out to be exaggerated by a factor of 10. Time will tell if these latest Homo naledi claims from Berger’s team stand up. I’m skeptical, to say the least.