Yonatan Sahle

George Perry

eLife assessment
The discovery of Homo naledi-associated evidence for intentional burial and engravings would undoubtedly have important implications for our understanding of the evolution of complex cognition and behavior. Based on claims made in two related preprints by Berger et al., this study discusses the potential implications of the purported mortuary practice and symbolic behaviors claimed to be associated with the small-brained H. naledi remains. Unfortunately, the evidence presented in the two related submissions that the current paper entirely relies on is incomplete at this stage.

anonymous

Reviewer #1 (Public Review):
As this experience as a reviewer has been unusual, it may be helpful to outline some relevant parameters of the task at the outset. While I was invited to review the Fuentes et al. study only, two additional papers concerning the claimed engravings and burials associated with Homo naledi by Berger and colleagues were also provided as components of the reviewer package. The two manuscripts presenting the archaeological evidence are accessible as preprints in bioRxiv, by Lee Berger and colleagues ('2023a, 2023b').
Unfortunately, the arguments in the Fuentes et al manuscript hinge entirely on the strength of archaeological evidence for engravings and intentional burial by Homo naledi (presented in the abovementioned two preprints). All inferences regarding hominin behaviour and biology of Homo naledi, discussed by Fuentes and colleagues, are wholly dependent on the evidence presented in the archaeology preprints being true.
Yet both of the archaeological manuscripts are unfortunately weak. In short, the claims for engravings depend on the demonstration of several elements of association that are rather standard for linking material traces found in the archaeological record with particular hominin behaviours. For the particular arguments by Berger and colleagues to be demonstrated, the traces on the rock surface need to be linked causally with hominin agency, in other words, their anthropogenic nature need to be established. The author of the engravings needs to be demonstrated as a particular hominin species (Homo naledi in this case), and the activity of engraving needs to have taken place ~241-335 kya. After reading the manuscript on the engravings, however, what is clear is that the scratches could as easily have been made by a modern-day farmer 50 years ago, as Homo naledi ~335 kya. Berger and colleagues do not present any evidence to the contrary, they simply describe their narrative as the most parsimonious scenario. A particularly curious piece of information presented as evidence is a list of individuals known to have entered the Dinaledi system in recent times (and known not to have scratched the walls, one presumes, though this is not stated).
The question of intentional burial is more complex. What we know from other widely accepted early burials is that documenting the geoarchaeological context of the hominin remains is critical to assess the likelihood of an intentional burial - this needs to be established at the outset through high quality fieldwork. Yet even the boundaries of the excavation presented in the burial manuscript appear so angled or skew relative to one another (Fig. 2a) that the individual squares look to be aligned with different XY grids, which does not instill confidence in the quality of field documentation. One can make out very little from the sediment section images - which are key to identifying intrusive features associated with burials - and the multivariate geochemical analysis of sediments is unconvincing: a scatterplot (not a biplot) should have been provided showing the geochemistry of the burial sediment samples relative to the immediately surrounding sediment characteristics. While one remains excited about the potential for a spectacular archaeological discovery within the Dinaledi cave system, unfortunately, the three manuscripts provided do not present convincing evidence to that effect.

Reviewer #2 (Public Review):
Fuentes et al. provide a detailed and thoughtful commentary on the evolutionary and behavioral implications of complex behaviors associated with a small-brained hominin, Homo naledi. Within the Rising Star Cave of South Africa, Berger et al. 2023a,b proposed evidence that Homo naledi intentionally buried their dead through complex mortuary practices and engaged in symbolic expression by engraving the cave walls in cross-hatching motifs. Two burials were identified in the Rising Star cave subsystems: Feature 1 in the Dinaledi Chamber and a feature in the Hill Antechamber. The engravings are located in the Hill Antechamber near the passageway leading into the Dinaledi chamber. The authors aimed to provide evidence for burials by (1) testing sediment samples for mineral composition from within and outside the burial feature; (2) demonstrating an interruption in the stratigraphy indicative of a "bowl-shaped" feature; (3) evaluating the anatomical coherence of the skeletal remains; (4) demonstrate matrix-supported positioning of skeletal elements; and (5) determine the compatibility of non-articulated material with decomposition and subsequent collapse. Berger et al. 2023b evaluated the engravings through high resolution photography, cross-polarization, and 3D photogrammetry. Neither article involved radiometric dating of materials. While the review by Fuentes et al. highlights important assumptions about the relationship between hominin brain size, cognition, and complex behaviors, the evidence presented by Berger et al. 2023a,b does not support the claim that Homo naledi engaged in burial practices or symbolic expression through wall engravings.
The major weaknesses for Berger et al. 2023a are as follows:
<ol>
<li>The mineral composition from sediment sampled from within Dinaledi Feature 1 is not different compared to the surrounding sediment, which is one rationale proposed by the authors that would lead to the conclusion of a burial pit. An effort to replicate the multivariate statistical analysis using the data provided in SI Table 1 by this reviewer failed, and thus, the results are not replicable.</li>
<li>The authors failed to provide clear visualizations or analysis that showed an unambiguous interruption in the stratigraphy surrounding the Dinaledi Feature 1.</li>
<li>Attempts 1 and 2 were applied solely to Dinaledi Feature 1, not the Hill Antechamber Feature.</li>
<li>Skeletal cohesion does suggest that the bodies were likely covered or protected by external environment. However, given the geological context, there is minimal opportunity for scavengers or other agents to scatter the skeletal remains within such an isolated location. Thus, this alone cannot solely support intentional burials as this line of evidence is subject to equifinality.</li>
<li>Similar to the preceding statement, evidence for matrix-supported elements was inconclusive at best. There was no mention of sedimentary rate or expectations for how quickly sediments would naturally bury the remains of whole bodies in the chamber compared with the rate of decomposition of buried remains.</li>
</ol>
The major weaknesses for Berger et al. 2023b are as follows:
<ol>
<li>While this is incredibly difficult to accomplish, dating rock art or other cave wall engravings is the only method to ensure that the etchings were created during the time of Homo naledi. Unfortunately, this was not attempted. Instead, the authors state that "This description is intended to document the discovery and provide spatial and contextual information prior to any further analyses that may require invasive sampling." Yet, the authors assign a date to the engravings in the title of the paper. Here, the authors are generating interpretations before analyses are attempted.</li>
<li>The engravings are indeed very interesting and are likely anthropogenic in origin. However, the argument that these engravings were created by Homo naledi is based on the bold assumption that "No physical or cultural evidence of any other hominin population occurs within this part of the cave system, and there is no evidence that recent humans or earlier hominins ever entered any adjacent area of the cave until surveys by human cave explorers during the last 40 years." (page 6). 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.</li>
</ol>
As a discipline, paleoanthropology aims to understand the evolutionary history of the hominin clade through fossil remains, material culture, and, most recently, ancient DNA. The methods and approaches that we as paleoanthropologists use to understand the past often bridge both the humanities and the hard sciences to create a unique understanding of our shared history. We are only limited by the conditions in which time and attrition has erased pieces of our collective story from the earth. Thus, it is our responsibility to ensure that our interpretations of the past are supported by measurable and testable means, to the best of our ability, and that hypotheses are not presented as conclusions.
Unfortunately, this is not the case for Berger et al. 2023a,b. The work presented by the authors is imprudent and incomplete and does not meet the requirements set forth by our discipline. While it is important that scholars publish their work in a dutiful timeline, it is arguably more critical for scholars to take the necessary time to ensure the integrity and resolution of the work. The consequences for rushing publications with such a significant unsubstantiated find will likely result in perilous ramifications, as it is more difficult to correct an idea than to introduce one.

Reviewer #3 (Public Review):
This paper presents the cognitive implications of claims made in two accompanying papers (Berger et al. 2023a, 2023b) about the creation of rock engravings, the intentional disposal of the dead, and fire use by Homo naledi. The importance of the paper, therefore, relies on the validity of the claims for the presence of socio-culturally complex and cognitively demanding behaviors that are presented in the associated papers. Given the archaeological, hominin, and taphonomic analyses in the associated papers are not adequate to enable the exceptional claims for naledi-associated complex behaviors, the inferences made in this paper are currently inadequate and incomplete.
The claimed behaviors are widely recognized as complex and even quintessential to Homo sapiens. The implications of their unequivocal association with such a small-brained Middle Pleistocene hominin are thus far reaching. Accordingly, the main thrust of the paper is to highlight that greater cognition and complex socio-cultural behaviors were not necessarily associated with a positively encephalized brain. This argument begs the obvious question of whether absolute brain size and/or encephalization quotient (i.e., the actual brain volume of a given species relative the expected brain size for a species of the same average body size) can measure cognitive capacity and the complexity of socio-cultural behaviors among late Middle Pleistocene hominins.
Claims for a positive correlation between absolute and/or relative brain size and cognitive ability are not common in discussions surrounding the evolution of Middle- and Late Pleistocene hominin behavior. Currently, the bulk of the evidence for early complex technological and social behaviors derives from multiple sites across South Africa and postdates the emergence of H. sapiens by more than 100,000 years. Such lag in the expression of complex technologies and behaviors within our species renders the brain size-implies-cognitive capacity argument moot. Instead, a rich body of research over the past several decades has focused on aspects related to socio-cultural, environmental, and even the wiring of the brain in order to understand factors underlying the expression of the capacity for greater behavioral variability. In this regard, even if the claimed evidence for complex behaviors among the small-brained naledi populations proves valid, the exploration of the specific/potential socio-cultural, neuro-structural, ecological and other factors will be more informative than the emphasis on absolute/relative brain size.
The paper presents as supporting evidence previous claims for the appearance of similar complex behaviors predating the emergence of our species, H. sapiens, although it does acknowledge their controversial nature. It then uses the current claims for the association of such behaviors with H. naledi as decisive. 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.

Burials and engravings in a small-brained hominin, Homo naledi, from the late Pleistocene: contexts and evolutionary implications

Figures and data

Archaeological evidence of culturally-mediated, meaning-making, behaviors.

Endocranial volume estimates for hominin cranium.

Table of evidence of potential mortuary behavior in hominins.

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