In September I reported that a team of Homo naledi researchers, led by paleoanthropologist Lee Berger, had claimed in a Netflix documentary that the species buried its dead, used fire, used tools, and made rock art. Because Homo naledi had a brain only a bit larger than a chimp’s, this evidence was used to bolster attacks on human exceptionalism. Or as the punchline of the Netflix documentary put it, “We’re not that special.”

But claims of highly intelligent activity in Homo naledi turned out to be radically premature: they were made before the evidence was peer-reviewed, and when the peer reviews came out, the reviewers were highly skeptical. Now a paper in the Journal of Human Evolution has found “No scientific evidence that Homo naledi buried their dead and produced rock art.” It goes further, even critiquing the “strong media campaign” and “media hype” promoted by the H. naledi team. These are very unusual accusations coming from a scientific paper, which tells the story of what happened: 

In June of 2023, the journal eLife hosted three reviewed pre-prints by the Rising Star research team claiming that the Dinaledi and Hill Antechamber skeletal remains indicate deliberate burial practices and the production of associated rock art. Both the reviewed and previously unreviewed pre-prints were accompanied by a strong media campaign that quickly spread the revolutionary idea that the small-brained (~450–600 cc) hominins found deep in the Rising Star Cave system were capable of complex funerary behaviors equivalent to those attributed to larger-brained (~1400 cc) hominin species, Homo sapiens and Homo neanderthalensis. The media hype that accompanied both the unreviewed and reviewed, though currently unmodified, pre-prints at the time of this writing, triggered strong public controversy and an immediate debate about ‘modern human behavior’ but also about the way in which scientific work is communicated and perceived by the public. Here we will examine the evidence for the alleged burials and the purported rock art presented in the three reviewed pre-prints together with a consideration of the open reviews published alongside them. The peer reviews were unanimous in considering the evidence inadequate in its present form. Despite this, these versions remain available and communicated to the press and social media without yet integrating any of the referee’s comments.

The authors of the paper in Journal of Human Evolution are skeptical, however. They “argue that the evidence presented so far is not compelling enough to support the deliberate burial of the dead by H. naledi nor that they made the purported engravings.” They address each of these claims in more detail. 

Burial of the Dead?

The paper argues against intentional burial of the dead on the basis that burials usually involve articulated skeletons, but in this case “the hominin bones are not articulated but scattered.” They note that there is some limited articulation of some body parts but this can also occur in a natural death scenario. The “almost vertical position” of some of the skeletal remains is also very unlike what would be expected if someone was digging a grave for a body. 

Rejecting a Design Inference for Stone Tools

Berger and his team had claimed that a stone tool was encased in rock near a skeleton, showing Homo naledi used tools. The paper argues that “it is not possible to rule out the strong likelihood that this stone object is a geofact” — that is, a natural rock feature (as opposed to an artifact, which is a stone carved by an intelligent agent). They point out that it’s made of “the same material as the cave walls,” and the faces would represent “natural fractures” or “erosion.” Because the rock remains encased in sediment, they argue no one can presently perform the kind of study needed to make a proper determination, and thus the Homo naledi team’s claims can’t be verified. 

“No Scientific Evidence” of Fire

The authors point out that claims of fire were based upon inferences which assumed that Homo naledi individuals went into the cave for the purpose of burying the dead, and would have needed fire to find their way in the cave. But if they weren’t there burying the dead, then the need for fire is extinguished (pardon the pun). But what does the empirical data say? They make clear that the evidence for fire use isn’t there: 

More importantly, no scientific evidence (e.g., Fourier-transform infrared spectroscopy, micromorphology, archaeomagnetism) has been presented to indicate the occurrence of in situ burnt material, let alone hearths. Previously acquired radiocarbon dates obtained by the site investigators on one of the apparent hearths resulted in very young dates (Lee Berger, unpublished data), questioning its association to H. naledi. Moreover, the occurrence of charcoal is also common in caves, including in South African landscapes, where there are frequent wildfires, so finding burned material in a cave setting does not automatically indicate anthropogenic activity.

Are the Wall Markings Even Artificial? 

Many critics acknowledged that wall markings in the cave look like art, but they were uncertain about evidence linking the scrawls to Homo naledi. That is because the marks have not been dated. The markings might have been made much more recently, perhaps even by a human in very recent historic times. This paper affirms the criticism, but it also expresses a deeper skepticism about whether the markings are artificial at all. They write:

[N]umerous examples of shallow cross hatched and patterned natural erosional lines can be found throughout the Malmani dolomite, the geological formation that hosts Rising Star Cave and all the other Plio-Pleistocene hominin fossils in the region.

I can personally attest that what they are saying is true. I’ve spent a LOT of time walking around on dolomite in South Africa, in particular carbonates from the Transvaal Supergroup of which the Malmani Dolomite is a part. Linear patterns are extremely common in these rocks, in what is called “elephant skin” weathering. So while I would be willing to believe that the markings are artificial, in this type of rock a natural origin seems to be possible, too.

Commentators Taking the Side of the Critics

The scientific paper offers a very strong conclusion: 

There is no convincing scientific evidence to indicate that H. naledi buried their dead and produced rock art in the Rising Star Cave system based on the information thus far presented. As explained here, the investigators have not employed the wide range of scientific methods (e.g., chronology, taphonomy, sedimentology, micromorphology, geochemistry) designed to answer the questions posed nor applied the basic principles of archeothanatology to identify a deliberate burial.

These points have not gone unnoticed by scientific commentators. IFL Science has an article titled “Homo Naledi Probably Didn’t Bury Their Dead Or Make Rock Art After All” which essentially takes the side of the critics of high intelligence in H. naledi:

Unsurprisingly, not everyone was convinced, and a new study has poured a healthy dose of cold water on the recent surge in Homo naledi-mania. Not that that will do much to change the popular narrative, given that the team behind the spectacular claims have already released a Netflix documentary to hype up their research.

Part of the controversy stems from the fact that the evidence is concealed within the inaccessible Rising Star cave in South Africa. To fit through a crevasse leading to the supposed burial chamber, professor Lee Berger from the University of Witwatersrand first had to lose a huge amount of weight, yet still injured himself during his exploration.

The unreachability of the Homo naledi bones has prevented other researchers from entering the site and verifying Berger’s findings, and the Rising Star team have not invited any external experts to analyze their evidence. To make matters worse, the researchers’ findings were widely reported before they were even peer-reviewed.

However, according to the authors of a new critique, “the peer reviews were unanimous in considering the evidence [for Homo naledi burials and rock art] inadequate in its present form.”

IFL science is a heavily pro-evolution outlet, so when they accuse Homo naledi’s promoters and the Netflix documentary of pushing “hype” and “Homo naledi-mania,” that is really saying something.