Fire, engravings, burial all bogus???
Let's talk about naledi.
I'm sorry this blog has become a broken record over these questions, but I have been interested and excited about these hominin remains for years now. I don't want to just ignore the current state of things.
Quick recap: The remarkable remains from the Dinaledi chamber were first published in 2015. Lee Berger's research team claimed they were members of genus Homo (our own genus) but that they were a species new to science. They called this newly discovered species Homo naledi, but the real excitement over these remains was their hypothesis that the bodies of these creatures had been intentionally placed there in the deep recesses of that cave. The evidence for that was basically lack of a credible alternative explanation. The chamber contained thousands of bones of the same species, all highly similar and placed over time. At the same time, other bones of African animals were generally lacking. The bones were also in partial articulation and astonishingly well preserved. They did not appear to be the result of predator accumulation or some catastrophic event. The chamber where they were found lacked any opening above, from which these creatures could have fallen and died. Put all that together, and it appears that the easiest explanation is intentional emplacement of the bodies. That doesn't mean burial of course, but it certainly is provocative.
Creationists have been famously divided. Some of us claim that Homo naledi is human and that the body disposal evidence would be understandable given that they're human. Others have denied that Homo naledi is human and have either downplayed the evidence of body disposal or tried to invoke other, less likely proposals for how this accumulation of bones occurred.
About a year ago, Lee Berger announced that his team had discovered copious evidence of fire throughout the cave, including the Dinaledi Chamber where the majority of the bones were found. I was excited by this. It seemed to confirm my suspicion that whoever placed these bodies down there must have had light to penetrate that deeply into the dark zone of the cave. This was all announced in a lecture with the promise of a scientific paper following shortly thereafter.
Six months later, still no fire paper. Not even a preprint. Then we got the announcement of engravings and intentional burial followed by a book and a documentary. And then I just got really suspicious of the whole thing. The movie basically told the story of the discovery of the fire evidence, the engravings, and the purported graves. The book was largely the novelization of the movie. It started to look like the announcements and these meager papers were attempts to get something on the scientific record before the movie and book appeared.
Did I mention that it's a year since the fire announcement and still no fire paper? Yeah.
When I first wrote about the purported burial and engraving evidence, I was cautious about both. I thought the burial evidence was pretty good at the time, even claiming that it's at least as good as the evidence for burial of Neandertals. I think that was a rash and regrettable assessment. The problem I have is one of posture. The text of the paper reconstructs the posture of the individuals in the purported graves, and it sounded plausible to me when I read it. But I just can't make sense of the diagrams. The published figures in the papers are figures 2 and 10. You'll note that the bones aren't labeled in any of them, even though they describe the layout of the skeleton in detail in the text. So if you want to verify the text description, it's very difficult with the poor diagram. In Figure 2, depicting Dinaledi Chamber Feature 1, I see a femur and what appears to be a tibia. And then a lot of little brown, indistinguishable blobs. The text says they recovered "eighty-three identifiable bone fragments and teeth," but all you can see in the diagram is a jumbled mess of fragments.
The Hill Antechamber feature is shown in figure 10. Here we have the same problem, the bones are just not labeled to any extent. The authors say they recovered ninety skeletal and 51 dental elements from this feature, which was excavated as a block of sediment that's evidently still sealed in the field jacket. From the diagram, you can make out a foot, the teeth, and maybe a hand, and the rest looks like a jumble of bones. Unlike Dinaledi Chamber Feature 1, this diagram includes a side view where you can clearly see that the bones are in two separate horizons. The authors tell us that the torso and upper limb elements are in the upper horizon and the lower limb elements are in the lower horizon, and they interpret this as a single body. But it looks more like two half bodies in two completely separate depositional horizons. Since this feature was excavated from the side of a slope, it seems plausible that there were originally two bodies, and the other halves of these bodies have eroded downslope. But I can't even tell that because the diagrams are so difficult to decipher.
The paper also indicates that scans of the "burial" features are available on Morphosource and other materials are available on FigShare. I can't find any of that, so I can't even look at the scans myself to see if I can make out the identity of the bones and the supposed posture of the "burials." So who knows what these are? I've tried looking at stills of these diagrams from the movie and from video lectures, and while they are slightly clearer, I'm still not sure about the posture of these alleged burials. So it's all very uncertain.
What about the compositional differences between the soil in the pits where the bodies are and the surrounding sediment? That could be nothing more than the presence of the bones. Soil with bones is compositionally different from soil without bones.
The evidence of burial is supposedly enhanced by the observation of a "tool-shaped rock," which the paper refers to as an "artifact." This tool-shaped rock is still encased in the field jacket that holds the Hill Antechamber Feature, so we can't actually verify that it is a tool and not just a rock. And that's my primary problem with interpreting this as a tool. We just don't know what it is, because it's still stuck in the field jacket.
Now with the engravings, I was convinced it was an engraving but that there was no evidence presented connecting it to Homo naledi. I read the whole paper expecting some report of the date in the title, but you know what? There wasn't any attempt to date the engravings. They just decided it was made by Homo naledi, and then they applied the dates of Homo naledi remains to the engravings. So the title is not a finding of the research in the paper. It's just speculation.
Still, I concluded my previous commentary optimistically by noting, "But to argue that someone else made the fires or carved those lines introduces ad hoc hypotheses of cave intruders for which we have no other evidence (yet reported). The simplest explanation is that the hominin buried under the engravings next to the hearths is the one who made them both."
Now that brings us up to date prior to a few weeks ago, when the Journal of Human Evolution published a comprehensive response to these papers, which not only rejected pretty much every conclusion of Berger's team but also took the publication model to task for allowing such things to get into the public domain before peer review. More about that below.
The new paper is No scientific evidence that Homo naledi buried their dead and produced rock art by Martinón-Torres and colleagues. They dissect every claim from the very beginning of the body disposal idea back in 2015, and their title I think is also inappropriate. It's not that there's no evidence. It's that the evidence is currently inconclusive. And after what I've read in this paper, I think it's even more inconclusive than I'd come to believe.
They point out a number of issues that I already pointed out here, and they add a few more that I wouldn't know (as an armchair observer). One thing they noted especially was uncertainty regarding the supposed "pit" in which these bodies were found. The sedimentation in these caves is very complex, and you can have whole blocks of sediment covered by other sediment, giving the appearance of a break in the sediment like you would see on the edge of a previously excavated and filled pit. So instead of seeing the differences in sediment as a hole that's been dug and filled in, the different might actually due to a block of sediment next to the bones. I'm not sure that explains everything about these features, but it's definitely something to keep in mind.
They think the tool-shaped rock fell off the side of the cave and may not be an artifact at all. And that's at least as plausible as the artifact speculation as long as the rock remains unexcavated and unexamined.
They hardly mention the fire evidence because of course there's no paper to talk about, but they do suggest it's very possible that Homo sapiens could be responsible for any fire evidence in the cave. Worse, they claim that fire would not be necessary for animals to navigate the cave. I find that impossible to accept. Maybe crickets, cave fish, salamanders, sure. OK, bats too. But I can't think of any other mammals that venture that far underground intentionally. Maybe I'll be corrected by some reader, but this notion of large animals going deep into the cave without light is not anything we need to worry about.
Most devastating in my mind is their treatment of the engravings. As it turns out, there are other exposures of Malmani dolomite from the region that show exactly the same sort of markings from plain erosion. Malmani dolomite is the rock that makes up the walls of the Dinaledi chamber and the other significant caves in the area. Martinón-Torres and colleagues show photographs of crosshatched erosional markings on Malmani dolomite from nearby Drimolen, and they look exactly like the marks called engravings by Berger's team. So are the markings in the Dinaledi Chamber engravings or erosion? Well, they sure do look like erosion.
They also raised the issue of the partial baboon skeleton reported in the papers that described the Letimela skull. These baboon remains were found in the narrow, labyrinthine passages beyond the Chaos Chamber which is even deeper in the cave than the Dinaledi Chamber. I've been thinking about this one myself. Martinón-Torres and colleagues think it's evidence that these remote passages were explored by more than just hominins and therefore there's nothing particularly special about the accumulation of hominin bones. I'm not so sure. On the one hand the partial baboon skeleton is very interesting, but I think the overwhelming presence of hominin bones still counts as something unusual when compared to the caves roundabout. So I'm suspicious of the significance of the baboon skeleton. I'm just not sure what it means. Thousands of naledi bones and a lone partial baboon skeleton. What does that mean???
Martinón-Torres and colleagues conclude that the most parsimonious explanation is that animals used this cave and that the accumulation of hominin bones is not that special. They cite some unpersuasive studies by Egeland et al. and by Nel et al. (both of which I commented on and found wanting) as alternative models of how the bones got there. I didn't find that compelling at all. I don't think the notion of body disposal is less parsimonious than some other explanation, because I think body disposal explains more of the data. It remains the inference to the best explanation, and it's therefore the most parsimonious explanation of the largest range of information we have. So I was bothered by the way Martinón-Torres and colleagues were very critical of Berger and company but were quite willing to overlook obvious shortcomings of other studies that were also critical of Berger and company (or to indulge in fantastic ideas like large mammals exploring deep into caves without sight). Everybody has a bias.
None of that, however, changes my reaction to the last year's announcements about the fire, the engravings, the graves, and the "tool-shaped rock." The fire is unpublished and can't be assessed. The engravings could very easily be natural erosion. Despite my previous positive assessment, the graves are wildly inconclusive. And the rock is a rock until we can actually test it for intentional modification. Martinón-Torres and colleagues really nailed the criticism of those points and meshed well with my own growing reservations.
I guess it's most frustrating to me because Berger has taken criticism for jumping to conclusions regarding body disposal and compromising his science for the sake publicity and sensationalism. In the past, I thought those were unfair criticisms, but this past year, I don't know what to say about all this. Berger knew the movie and book were coming out, and it looks like he tried to rush those papers into the literature before that happened. He didn't get the fire paper out, and the other papers were just unpersuasive, even to little old amateur me. It really does look like he's letting the publicity drive his scientific procedures and agenda, and the science seems to be suffering. Then there was the whole shooting-fossils-into-space debacle, which was entirely publicity driven. I'm disappointed.
Then again, Berger's collaborator John Hawks puts a different spin on the fire evidence. He sees this as part of their intention to do open science. They found evidence of fire, so they shared it. That does make some sense to me. And I find it ironic that the critics were complaining that Homo naledi couldn't navigate without fire, and then when the fire evidence is found, critics complain that animals don't need fire to navigate that far into the cave. Can't win. The question remains: How can we link these fire evidences to Homo naledi?
Shortcomings aside, does this make a compelling story aside from the latest deficiencies? Forget about the fire, engravings, and burials, and just think about the body disposal. That remains to me as persuasive as it was. I still find it very hard to imagine an alternative explanation that will satisfactorily explain the peculiar attributes of this cave of bones. The fire evidence would definitely add to this if they can definitively tie it to Homo naledi. The burial, tool, and engraving evidence looks like it has as long way to go before it's persuasive though. So we're kind of where we were a year ago, but with tantalizing new possibilities that still need to be explored. Body disposal remains the best explanation of the distribution of the Homo naledi fossils.
The other important thing to remember is that absence of evidence is not evidence of absence. The evidence of fire and graves linked to Homo naledi may be absent at present, but there could very well be surprises still awaiting us. At the very least, they could open that jacket on the Hill Antechamber Feature and start excavating. Let's see that rock in there. The evidence of fire that has been shown can be examined further. So there's plenty of work ahead, and I'm sure Berger's team is already on it.
Feedback? Email me at toddcharleswood [at] gmail [dot] com. If you enjoyed this article, please consider a contribution to Core Academy of Science. Thank you.
Have you read my book? You should check that out too!
