Homo naledi Skeleton
© Berger et al. eLife 2015;4:e09560. DOI: 10.7554/eLife.09560, Creative CommonsResearchers unearthed fossils from at least 15 individuals belonging to the newfound species, Homo naledi, in the Rising Star cave system in South Africa.
In June I wrote about three new preprint papers posted at bioRxiv from the paleoanthropology team that discovered Homo naledi. They claim that the small-brained species had high intelligence — burying its dead, using fire, and even scrawling on a cave wall. At that time the papers had not yet been published in a peer-reviewed journal, yet the team promoted these claims to the media with the punchline that this evidence, as ABC News interpreted it, "erases the idea of human exceptionalism." Now the papers have been published as reviewed preprints in the journal eLife (see here, here, and here) — alongside peer review. These reviews are extremely doubtful about the papers' claims, and multiple voices in the scientific community have been harshly critical.

"Incomplete and Inadequate"

Nature covered the debate in an article titled "Sharp criticism of controversial ancient-human claims tests eLife's revamped peer-review model." According to the subtitle, "High-profile researchers say the small-brained Homo naledi exhibited advanced behaviours such as burials, but peer reviewers say there's no evidence." The article quotes a paleoarchaeologist who reviewed one of the eLife papers, stating: "there just wasn't any science in the paper ultimately." The Nature article further states:
Many scientists were deeply sceptical of the evidence presented. The scattered bones bore little resemblance to those of more completely articulated skeletons from other archaeological sites in which intentional burial is clear, critics said. And the researchers did not make a convincing case that the wall scratchings were made by a hominin, and presented no evidence that they date to a period when H. naledi occupied the cave.

"I don't see an anatomical connection, I don't see a hole or a pit that has been intentionally dug," says María Martinón-Torres, a palaeoanthropologistat the Spanish National Research Center for Human Evolution in Burgos, who co-authored an essay critiquing the H. naledi findings the day after their announcement. "These hypotheses have been sold with a very strong media campaign before the evidence was ready to support it."

A Unique Model

The journal eLife has a unique peer-review publishing model. They post papers alongside public reports from reviewers, and the authors of a paper apparently are not obligated to modify the paper in response to the reviewers' critiques. Nature explains the implications of this model:
The papers' peer reviews, posted on 12 July, come to much the same conclusion about the scientific evidence. After citing a litany of missing evidence, one reviewer wrote: "The manuscript in its current condition is deemed incomplete and inadequate, and should not be viewed as finalized scholarship."

[...]

Sven Ouzman, an archaeologist and rock-art specialist at the University of Western Australia in Perth, who reviewed the engravings paper for eLife, says that "the possibility has been raised but the proof really isn't there". He worries that eLife's publishing model has created a loophole that allows unsupported studies to stand. "It's essentially up there and published, and they can say, 'we have reviewed the reviewer's comments, and we thank them for it. But we stand by our arguments," he says. "That's sort of cheeky."

Reviewing the Reviews

I could not find a single reviewer who accepted the claims of the papers. To give some examples of general comments they made:
  • "Unfortunately, the evidence presented in the two related submissions that the current paper entirely relies on is Incomplete at this stage."
  • "Given the inadequate analyses in the accompanying papers and the lack of evidence for stone tools in the naledi sites, the present claims for the expression of culturally and symbolically mediated behaviors by this small-brained hominin must be adequately established. The importance of the paper thus rests on the validity of the claimed evidence — including contextual aspects — for rock engraving, mortuary practices, and the use of fire presented in the associated two papers. The claims in both associated papers are inadequate, incomplete, and largely assumption- (rather than evidence) based. As responsible and ethical researchers, the team must return to the sites, conduct the required standard chronomoetric and taphonomic studies and weigh the strength of the evidence before proceeding with the current claims."
They were harshly critical of claims of intentional burial of the skeletons:
  • "The main point of the paper is to describe three possible burial features. The working hypothesis is that the features are intentional burials, and the authors seek to support this hypothesis throughout rather than test it."
  • "I feel that 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, i.e. singular events where the bodies are placed in their final resting places. Insufficient evidence is provided to differentiate between natural processes and intentional funerary practices."
  • "That H. naledi buried their dead here can't be excluded based on the data, but neither is it supported here. My view is that this paper is premature and that more excavation and the use of geoarchaeological techniques (especially micromorphology) are required to sort this out (or go a long way towards sorting it out)."
As for the markings on the cave wall, the reviewers generally agreed they were of artificial origin but said insufficient work had been done to show that the markings were made by Homo naledi and not some later fully human individuals:
  • Regarding the claimed drawings on the cave wall: "the scratches could as easily have been made by a modern-day farmer 50 years ago, as Homo naledi ~335 kya."
  • "To assume that no other individual entered the cave system from the time of Homo naledi until 40 years ago is an unrealistic and faulty assumption. This reviewer does not discount that the engravings could have been made by Homo naledi, but the evidence must be sufficient to support this statement or provide other alternatives as working hypotheses."
  • "Based on the evidence presently available, however, I feel that we have no robust grounds for asserting when these engravings were made, by whom they were made, or for what reason they were made."
  • "The claims relating to artificiality, age and authorship made here seem entangled, premature and speculative. Whilst there is no evidence to refute them, there isn't convincing evidence to confirm them."
In defense of the authors of the studies, it should be noted that they have pledged to modify some of their conclusions in future papers in response to the reviewers' comments. But it seems clear that the claims presented thus far are highly disputed.

Promoting Claims on Netlfix

Even the mainstream media have been covering these disagreements. The Guardian ran a story titled "Were small-brained early humans intelligent? Row erupts over scientists' claim." Says the subtitle, "Homo naledi was claimed to be artistic, make tools and bury its dead, but warring experts now ask, where's the evidence?" The article explains the claims that were made by Homo naledi's promoters and the implications of the debate:
"We now face the prospect that a creature before humans was contemplating an afterlife. It completely changes how we have to think about human evolution," said anthropologist Lee Berger, who has led the Rising Star investigations.

The claim certainly raised key questions about human nature. If small-brained creatures like H. naledi could already make fire, art, tools and graves, what was the function of all the extra grey matter modern humans evolved? The question raised prospects of an intriguing scientific debate.
But then came the peer reviews:
Then the tide turned. Peer reviews of the H. naledi study appeared. These papers are "imprudent and incomplete", announced one last week. "These claims are inadequate, incomplete and are largely assumption-based — rather than evidence-based," warned another, while a third dismissed the papers because they "do not present convincing evidence".

As a result, Berger's team has found itself at the centre of a scientific storm. "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," said palaeoanthropologist Andy Herries of La Trobe University in Melbourne, Australia.

This point was backed by Paige Madison, a researcher at Arizona State University. "To push a notion that is so unsubstantiated that it has met with rejection by the scientific community is irresponsible," she said.
How exactly were these claims "pushed"? Well, not just with press releases sent out to the media but also with a Netflix documentary.

"We're Not That Special"

This Netflix documentary (which I've just watched) says there is "clear" evidence of the use of fire by Homo naledi, that they had a "culture" of "human-level complexity," that they intentionally buried bodies in the cave — in one case burying an individual with a "tool" which the documentary calls a "pen." They claim there are "pictographs" on the wall of the cave — and even at one point say "Homo naledi made art in that cave" and did it "with a utensil designed for the purpose."

Furthermore, Homo naledi "may have been contemplating an afterlife," including "an image that death is a transition," with H. naledi "enacting a passage to another place in order to deposit the dead." The documentary claims there was "full commitment and belief," with "all of this meaning something" pertaining to "belief and belief systems" and even "spirituality." There are lengthy animated scenes showing individuals grieving over dead members of their clan and then burying them in the cave. The documentary even shows scenes of Homo naledi raising their hands in the cave in some apparent form of worship juxtaposed with modern footage of people of various religious traditions raising their hands in worship. According to the documentary, Homo naledi provides "hard evidence for this incredible capacity for religiousness and eventually religion" which "flourishes and grows for better and for worse in contemporary humans."

And then there's the punchline again: Homo naledi is "redefining what it is that makes us complex humans. And apparently we're not as complex and special as we seem to be. ... We're not that special."

The Experts Are Not Impressed

The claims made in the Netflix documentary did not go over well with scientific commentators:
Exaggerating the intellectual prowess of H. naledi, as featured in a recent Netflix documentary, could detract from study of the site in future, added Prof Chris Stringer of the Natural History Museum, London. "Rising Star is such a great site and the naledi material is so wonderful that there was really no need to over-egg the pudding," he said. "It's going to cause problems of credibility in future, which may even affect funding for more work."
The article in The Guardian continues:
None of these claims impress reviewers of the papers written by Berger and his team, however. Other interpretations of these findings have not been adequately explored, detractors argue. "The consequences of rushing publication with such a significant unsubstantiated find will likely result in perilous ramifications," said one reviewer.

[...]

Not every scientist is convinced by this stance, however. "Rather than engaging with concerns, the team appears to be denying problems with their methods and analysis and are attacking peer reviewers' motives in an attempt to undermine their criticism," said Madison.
Despite all this criticism, you have to give credit where credit is due: In the Netflix documentary, lead naledi researcher Lee Berger managed to get in good enough shape to climb down into Dinaledi Chamber — an impressive feat given how small the passageway is. But it seems that if his team's claims about Homo naledi's intelligence and culture are to be accepted, they're going to have to get their scientific arguments into better shape as well.