Scientists Reject Claim that Homo Naledi Buried Their Dead in 250,000 BC

In 2023, a team of researchers led by renowned paleoanthropologist Lee Berger, a National Geographic Explorer in Residence, published a set of articles and produced a Netflix documentary that made some extraordinary claims. They said they’d found proof that an archaic human species known as Homo naledi, which Berger and his colleagues had only discovered a decade earlier, had deliberately buried their dead inside the Rising Star cave system in South Africa in approximately 250,000 BC. Furthermore, they said that markings found on the cave walls near the ancient hominin’s skeletal remains had been left by Homo naledi artists, and likely had some kind of symbolic meaning.

These claims created an immediate controversy, since in addition to living between 335,000 and 236,000 years ago Homo naledi had apparently been quite small and had brains that were only one-third the size of modern humans. So naturally, researchers set out to test these new ideas about the surprisingly advanced intelligence of this archaic human species, which represent a huge departure from the current consensus.

In an article just published in the journal PaleoAnthropology, a team of researchers led by George Mason University anthropology professor Kimberly Foecke report that they’ve found no meaningful evidence to suggest that Homo naledi actually buried their dead. They say that the research performed by Lee Berger and his colleagues was flawed, and that Berger jumped the gun by going public with his amazing hypothesis.

Kimberly Foecke. (George Mason University)

When Science Goes Wrong: The Anatomy of a Controversy

What originally sparked scrutiny of their colleagues in the anthropological community is the way Berger and his team chose to introduce their theories. Instead of submitting their work to a peer-reviewed journal, they chose to have their articles published without peer review in an open-access journal known as eLife.

The eLife model lets scholars and scientists publish research in what is known as preprint form, after which other researchers are invited to submit their opinions about the quality and conclusions of that work. The original researchers are supposed to use this feedback to refine, modify, or amend their study and its conclusions, and then later submit their edited and revised work to an actual peer-reviewed journal.

In this case, rather than waiting to go through such a process, the Berger team quickly followed up their preprint articles with a Netflix documentary called “Unknown: Cave of Bones,” which presented the team’s theory to the public as an established fact. They supplemented the documentary with an extensive publicity campaign, ensuring that their ideas would become much more widely known.

But in the newly published PaleoAnthropology article, Foecke and her colleagues present evidence to show that the methodologies the Berger team relied on to reach their stunning conclusions were flawed.

Dr Lee Berger with hashtag carving in Rising Star cave system. Insert; Possible Homo naledi burial pit. (© Berger et al., 2023)

To investigate whether or not some Homo naledi skeletons found in the Dinaldi chamber of the Rising Star cave system had been buried at some point, Berger and his group performed an extensive study of the cave floor sediments surrounding the fossilized bones.

One of the methods they used to complete this work is known as x-ray fluorescence (XRF), which requires the bombardment of soil samples with steams of x-rays that will reveal their chemical composition. If the composition of soil layers around skeletal remains is more diverse than the composition of soil layers farther away, it could mean the soil had been dug up and mixed by the burial process. The team also performed another type of testing known as particle size distribution (PSD) analysis, which looked for variations in grain size in the cave soil that would be consistent with it having been dug up and filled back in around dead bodies.

As their conclusion about Homo naledi burial practices suggests, Berger’s team claimed that their testing proved that the soil around some of the skeletons had indeed been dug up, as would be expected if the bodies were buried. But in their study, Foecke and her colleagues dispute this assertion.

Image of Homo naledi remains, in what is a possible burial pit in the cave system. (Berger et al., 2023)

The data that the Berger team supplied about their testing procedures in their eLife articles was incomplete, they said, and when Foecke and her team attempted to duplicate Berger’s XRF and PSD results using normal testing protocols, they were unable to do so. In fact, they found no evidence of soil mixing on the Rising Star cave floor at all, meaning there was no real proof to show that Homo naledi had buried anyone or anything there.

“I hope that this work is able to instill some skepticism in the public when it comes to archaeological research in the public eye,” Foecke stated in a George Mason University press release announcing her team’s findings. “We see so often flashy shows with charismatic archaeologists presenting huge claims about the past, but we must hold scientists who communicate with the public accountable to the science itself and ensure that we as a field are doing good work.”

What Was Homo Naledi Really Like? Will We Ever Know?

While Lee Berger has yet to comment on the new research calling his conclusions into doubt, one of his colleagues has.

Tebogo Makhubela, a geochemist from the University of Johannesburg who supervised the sedimentalogical testing undertaken by the Berger team, has acknowledged that some of his work should be dismissed from consideration.

“The decision to use XRF and PSD was, in hindsight, incorrect,” he admitted in an interview with Science. He noted that the latest testing shows that the soil on the cave floor in the Rising Star system has been extensively mixed through natural processes, and therefore lacks the variability between layers that is necessary to detect digging activity.

However, Makhubela also stated that he thinks the criticism from Foecke’s team and other skeptics is unfair.

 “Our team published a preprint, open for comments from colleagues and the public … Foecke et al. assumed that the current version of the preprint is the version of record, which is inaccurate,” he explained.

Makhubela told Science that he and his colleagues have read all the critiques of their work and are currently working on revisions of their eLife articles that will address the various concerns that have been raised. He stated that the revised work would include new and more substantial evidence to support his team’s claims of cave burials, including fresh sediment data that reveals the presence of unique trace elements near the skeletal remains that are consistent with a burial process.

It remains to be seen if the critics will be satisfied by the coming revisions. Whether they are or aren’t, there seems to be a consensus in the paleoanthropological community that the Berger team made a mistake by going public with their claims before any sort of peer-review process had been completed.

While this dispute plays itself out, the true mental abilities of Homo naledi will remain officially categorized as unknown. And they may stay that way, if no other evidence emerges that could shed light on this fascinating question.

Top image: Three-quarter and frontal views of Homo naledi skull from Lesedi Chamber, South Africa. Inset; Image Homo naledi remains in situ at Rising Star cave.  Source: Hawks, J et al/Elife Sciences, Inset; Berger et al., 2023

By Nathan Falde