Another look at the "deliberate body disposal" hypothesis in Rising Star Cave

The recovery of over a thousand human fossils from Rising Star Cave in South Africa has ignited debate among paleoanthropologists over the origins of human mortuary behavior. The fossils were deposited some 300,000 years ago and occur deep within the recesses of the cave system. Today, it is extraordinarily difficult to access the bone chambers--so difficult, in fact, that some believe the bones represent the corpses of people who were deliberately placed in the cave by other humans.  As I wrote in a previous post, my colleagues and I are skeptical of this "deliberate body disposal" hypothesis for a variety of reasons.

Late last year, researchers from the Rising Star team announced in a series of papers in the journal PaleoAnthropology the recovery of still more skeletal material in the cave. They again claim that the most likely explanation for the fossils is intentional disposal by humans. I was invited by the editor-in-chief of the South African Journal of Science to write a short commentary on the issue. Let me first emphasize how difficult it is to work in the cave system: it is dark and damp, the passages are tight, and the stratigraphy is extremely complex. Kudos to the Rising Star team not only for taking on the challenge, but for their open approach to the science. Many of the publications and accompanying data appear in open access journals and the public can follow the research via live streams and other venues. Having said that, I remain suspicious of the "deliberate body disposal" claim, and the commentary lays out why:

• There is good reason to believe that the cave system looked different 300,000 years ago than it does today. Importantly, the fossil-bearing chambers that appear to be largely cut off from the surface may not have been so in the past. It is therefore possible that water could have infiltrated the deepest recesses of the cave. What would have arrived with the water? A bunch of debris like sediments, leaves, branches, and, yes, bones.
• The human bones are poorly preserved, so any marks that might indicate their arrival via non-human means--tooth marks from carnivores, abrasion marks from bouncing around in water--will be difficult to detect.
• Baboon bones have also been found in at least one chamber. This shows us that the bones of a large-bodied primate can arrive within a seemingly inaccessible section of the cave system without deliberate disposal. (Unless, of course, baboons or perhaps humans were intentionally dragging baboons corpses into the cave.) 
• Many of the human fossils show cracks that mimic the weathering damage seen on bones that lay out in the open. This suggests that the fossils may have been exposed to the surface before their final interment in the cave.
• The frequencies of bones in the chamber do not represent complete corpses. This means that complete corpses did not enter the chamber in the first place or, if they did, then something disturbed them afterwards.

Paul Pettitt offers a very thoughtful commentary on the Rising Star data as well. He makes what I think is a critical distinction: namely the intentional deposition of corpses in a specific place (what Pettitt calls "funerary caching") versus the complex, symbolic ideas that accompany such behavior among modern humans. He points out that a variety of organisms, including non-human primates, interact with the corpses of their conspecifics, and many organisms also exhibit behaviors in the presence of the dead that we might interpret as grieving. He argues, then, that the deposition of bodies in deep caves can occur "without any sophisticated cognitive rationale behind the behaviour." In other words, there is no reason to automatically dismiss deliberate disposal just because these hominins were not modern humans. I agree completely. Pettitt also raises the important issue of whether or not alternative entrances to the cave existed in the past--other entrances that, if open to the surface at some point, could have served as conduits for stuff, including bones.

Is deliberate disposal a viable explanation for the fossil remains? Sure. But it still seems to me that other explanations--that the remains were washed in from somewhere else, for example--are sufficient and at least as parsimonious. Apparently an announcement from the Rising Star team is on the horizon that may produce new evidence that confirms, or at least strengthens, the deliberate disposal hypothesis (fire, maybe?).   

References:

Egeland, CP, Pickering, TR, Fadem, CM, Domínguez-Rodrigo, M. (2022). "Back from the Dead": another response to the contextual bases of the Rising Star 'deliberate disposal' hypothesis. South African Journal of Science. doi.org/10.17159/sajs.2022/13873

Pettitt, P. (2022). Did Homo naledi dispose of their dead in the Rising Star Cave system? South African Journal of Science. doi.org/10.17159/sajs.2022/15140