Editor’s Note: This story was initially published with the title “Team including Princeton anthropologist makes groundbreaking discovery on early human burial practices.” This story has been significantly updated with new information from the peer reviews revealed publicly shortly before initial publication. The original text can be found here.
Eight years after discovering a new species in the human lineage, the Homo naledi, a team of scientists from National Geographic working in collaboration with Princeton anthropology professor Agustín Fuentes announced their findings in a newly-reviewed preprint: Homo naledi buried their dead. Until now, burying the dead and other cognitive-based behaviors such as using symbols have only been linked with larger-brained Homo sapiens and Neanderthals.
The team also announced the discovery of rock engravings, which they believe to be created by Homo naledi, in the Rising Star cave system in South Africa.
But announcement in popular media such as the National Geographic, CNN, the front page of the New York Times, and a new Netflix documentary entitled Unknown: Cave of Bones was of preprints, which are first-drafts of studies prior to peer review. The flashy rollout became a source of controversy when critical peer reviews were published on July 12 — only five days before Unknown: Cave of Bones was released.
Fuentes has pointed out that the core claim of the research: that the Homo naledi brought bodies to a specific underground cave has not been challenged.
“The Homo naledi brought their dead down into this really deep, hard-to-get-to cave space and then buried them down there. That’s really amazing for a couple of reasons,” Fuentes said, regarding the significance of the findings.
“One is that [it requires] a lot of coordination, cooperation, foresight, compassion, and care for the dead. Also, you need light to get down there, so there might have been some kind of fire involved. And three is that on a wall in the passageway, we see these engravings, mainly lines, carved onto the wall with a stone or something similar. So we have what looks like burials, and what look like engravings right beside them, with no evidence of any other living thing except for the Homo naledi being down there. This is truly remarkable,” Fuentes continued.
The Homo naledi is an extinct species of in the human lineage with a brain around one-third the size of that of a modern human, so these findings about the Homo naledi, alive over 150,000 years before humans, seemed to provide invaluable insights into their cultural and cognitive capabilities, challenging previous assumptions about our evolutionary ancestors.
The Homo naledi remains were first discovered in the Rising Star Cave system, and the site has continued to yield notable findings. The Homo naledi have a “mosaic” morphology in the sense that some of its features, including shoulder and pelvis, are more primitive while its hands and feet are more modern in the evolutionary sense.
“The Rising Star is an amazing cave system, and it is just terrifying and beautiful and wonderful at the same time,” said Fuentes.
The evidence for deliberate burial practices by the Homo naledi come from a cave chamber within The Rising Star known as the Dinaledi Chamber, where the original Homo naledi fossils were found.
Fuentes detailed the complex process of entering the cave and its greater significance as he along with the rest of the team on-site went further throughout the system.
“You suit up and climb down into the cave, angling and squeezing yourself in. And then you come out in these spaces and you look around and think, this is not just a rock, this is not just a cave. This place meant something to the Homo naledi,” Fuentes added.
Inside the chamber, researchers discovered what they propose are a series of burial chambers, or “ossuaries,” containing fossilized Homo naledi remains. These burial chambers were carefully arranged and contained multiple individuals, suggesting to the researchers that the bodies were intentionally placed there, rather than arriving there as the result of natural processes.
Figure 1: Image of two burial features discovered in the Dinaledi Chamber. A. Square area outlines position of burials relative to 2013 –2016 excavations. B. Photograph of main burial feature (Feature 1) containing the single body of an adult specimen of Homo naledi. Feature 2 shows the edge of a burial containing at least one juvenile body. C and D illustrate the bones as positioned within the graves.
Courtesy of Lee Berger et al. / National Geographic 2023
The researchers have uncovered numerous Homo naledi fossils, including those of both very young infants and elderly adults. As the team ventured further into the caves, it became evident to them that in fact the Homo naledi were very familiar with and actively utilizing various sections of the cave system.
Deep inside one of the chambers, they found rock engravings that they believed to have been made by the Homo naledi. These engravings, dating back approximately 241,000 to 335,000 years, depict geometric patterns such as squares, crosses and X’s.
Numerous engravings and etchings on a wall in the Rising Star Cave System. The panel shows repeated etchings likely done over a considerable period. The etchings include geometric figures such as squares, ladders, triangles, crosses, and X’s.
Courtesy of Lee Berger et al. / National Geographic 2023b
The engravings could represent some of the earliest evidence of symbolic behavior and artistic expression among early humans. The discovery of rock engravings by the Homo naledi suggests that these cognitive abilities were not limited to our own species but were present in other lineages as well.
‘In its current form the paper … does not meet the standards of our field’
The research was accepted by the journal eLife, which has a unique model: first the paper is accepted, then peer reviews are posted publicly. The attributions of markings to the Homo naledi and layout of the remains to intentional burial, however, was met with skepticism by peer reviewers.
On the markings, one reviewer wrote, “The evidential bar for [this claim] is necessarily high, and I don't believe that it has been cleared here … It should be considered possible that Homo naledi made the engravings in the Dinaledi cave system. The problem is that other explanations [namely, that they were left by post-Homo naledi human ancestors] are not precluded.”
Another reviewer added, “[The claims] made here seem entangled, premature and speculative. Whilst there is no evidence to refute [their conclusions], there isn't convincing evidence to confirm them.”
The reviews expressed dissatisfaction with aspects of the methodology and the robustness of the evidence.
The reviewers levied a variety of criticisms. Many pointed to insufficient evidence that the spatial displacement of the bones was a result of deliberate burial practices and not natural processes — with the analysis lacking consideration of joint disarticulation during decomposition, integration of geology and sedimentology into the interpretation of the finding, and rigorous elimination of other hypotheses for the bones’ arrangement such as erosion and sediment slumping.
The first reviewer wrote, “In its current form the paper … does not meet the standards of our field … The working hypothesis is that the features are intentional burials, and the authors seek to support this hypothesis throughout rather than test it.”
Another reviewer wrote, “There is a significant amount of missing information in the study presented here, which fails to convince me that the human remains described represent primary burials.”
Multiple reviewers said that they were unsatisfied with the quantity and quality of evidence supporting their claims, with some even saying that conclusions cannot be drawn until the entire cave has been excavated. According to Fuentes, however, digging further with the presently-available technology would damage potential artifacts. In around a decade, he predicted, technology will have progressed to a point where complete excavation without damage is possible.
In the authors’ official preliminary response to the peer reviews, they wrote, “We will examine what appear to be the key critical issues raised regarding the data and the analyses and how we propose to address these as we revise the papers. We will also address several philosophical and ethical issues raised by the reviews and our proposal for dealing with these.”
When these reviews that call into question the validity of the findings were released, many expressed their frustration with how the research was widely promoted before the review process.
Palaeoanthropologist Andy Herries tweeted, “I have no issue with the idea that non Homo sapiens species disposed of their dead, but I do have an expectation that there is robust scientific evidence to support such statements before scientists go on massive media campaigns regarding these ideas.”
At the same time, researchers responsible for the studies say that they think that the too-early press push may have caused peer reviewers to frame their typical, methods-based critiques of a study as a harsher denunciation.
Fuentes said, “I think that in retrospect, like [the publicity] messed up the review pool a little bit, I think people were much harsher than they normally would have been. Because so much of it was public.”
Fuentes felt that the discourse around the fiasco detracted from a simpler claim: that the Homo naledi buried their dead.
The reviews cast doubt on some of Fuentes and his team’s findings. What remains uncontested, however, is that Homo naledi made a difficult traverse into a case and to dispose of bodies in a specific location.
“My whole thing was like, dude, they brought the bodies down.” Fuentes said, “as science should, [the reviews are] focusing on the micro details, and forgetting the big picture.”
A new, unconventional method of publication
The reason that the press tour proceeded the final paper is a new way of publishing research. Through eLife’s model, instead of the standard process of scholars creating first drafts and sending them off for peer review which may or may not lead to a published, peer-reviewed paper, eLife accepts papers then publishes the preprints and peer reviews simultaneously.
Fuentes made the case that this public process simply makes transparent the standard process of science. “What you’re seeing,” he said “is that something was put out, a bunch of reviewers responding to it, and, now, you’re gonna see the revisions in response to the reviewers, but all of it is in real time and totally accessible to people. That system, it’s a weird system, it’s new, and I think it’s freaking people out.”
Making science more accessible, Fuentes said, is important to him and related to his new method. He said, “I think the academy is awesome. I love it. I’ve spent my life there. But you know what, it’s also inaccessible to the majority of people. And so translating, right, being in that space where you can get people super excited about science. That’s, you know, that’s magic.”
The significance of the discovery: ‘something shocking’
The basic discovery that the Homo naledi carried the bodies to a specific place shifts our understanding of human evolution.
“I think what we are suggesting is that we really have to take a step back. It used to be that we said, you need to have a certain brain size in order to be able to bury your dead,” said Marc Kissel, an assistant Anthropology professor at Appalachian State University and one of the authors of the study.
“We are now finding such behaviors in species that have a third of our brain size and I think this is something shocking,” he added.
The Rising Star Cave system continues to be a treasure trove of archaeological and paleoanthropological discoveries. As researchers delve deeper into its chambers, they anticipate uncovering even more clues about the rich history of our ancestors and the fascinating world they inhabited. Further research and exploration are underway to unravel the mysteries hidden within the Rising Star Cave system and to unlock the secrets of our shared evolutionary past.
Regarding the future work that can be done to expand the findings of the study, Kissel pointed out a broad range of questions that could be addressed.
“One aspect to further explore would be trying to figure out why we are only finding the Homo naledi in this one cave system. I think this is very surprising and strange,” said Kissel. “We should also take a step back and think about why in the first place, burials were associated with larger brain sizes and how can we reconcile that with the finding that the Homo naledi buried their dead too. I think there is a lot of potential there.”
For now, what we know, Fuentes said, is that “something that is like us, but not us, with a brain half the size, got their stuff together, got their community together, took their dead deep underground and they did this over generations. That's amazing.”
A reconstruction of Homo naledi’s head by paleoartist John Gurche based on skull remains from Rising Star cave highlights its unique blend of primitive and advanced traits.
Courtesy of Mark Thiessen / National Geographic
Mahya Fazel-Zarandi is a senior News contributor for the ‘Prince.’
Julian Hartman-Sigall is an assistant News editor for the ‘Prince.’
Please send corrections to corrections[at]dailyprincetonian.com.
Correction: This piece has been updated to clarify preprints and peer reviews are published simultaneously by eLife and that the peer reviews were published on July 12.
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