Decision letter | Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa

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Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa

Decision letter

Affiliation details

James Cook University, Australia; University of the Witwatersrand, South Africa; University of Johannesburg, South Africa; University of Wisconsin-Madison, United States; Simon Fraser University, Canada; University of Colorado Denver, United States; Duke University, United States; Texas A&M University, United States; University of Zurich, Switzerland; American University, United States
Nicholas J Conard, Reviewing editor, University of Tübingen, Germany
Johannes Krause, Reviewing editor, University of Tübingen, Germany

eLife posts the editorial decision letter and author response on a selection of the published articles (subject to the approval of the authors). An edited version of the letter sent to the authors after peer review is shown, indicating the substantive concerns or comments; minor concerns are not usually shown. Reviewers have the opportunity to discuss the decision before the letter is sent (see review process). Similarly, the author response typically shows only responses to the major concerns raised by the reviewers.

Thank you for submitting your work entitled “Geological and taphonomic evidence for deliberate body disposal by the primitive hominin species Homo naledi from the Dinaledi Chamber, South Africa” for peer review at eLife. Your submission has been evaluated by a Senior Editor (Ian Baldwin), two guest Reviewing Editors (Nicholas Conard and Johannes Krause), and two peer reviewers. One of the two peer reviewers, Palmira Saladié, has agreed to share her identity.

The reviewers have discussed the reviews with one another, and Nicholas Conard has drafted this decision to help you prepare a revised submission.

The Dinaledi Chamber site is potentially very interesting because of the amount of hominin fossils that have been recovered there. This paper describes the geological and taphonomic study of a cave site where more than 1500 hominin fossils have been recovered in two excavation campaigns. The fossils were found on the surface of the cave floor and in one excavation pit of 0.8x0.8m and 50 cm of maximum depth.

I share the reviewers' opinion on the great importance of the paper you have submitted to eLife. One said: “I believe that the description of the site is relevant for publication by itself since it is a new and very important site.” The other commented:

“The methods used in the investigation were correct, and their arguments are based on good evidence. The paper is clear and the set of fossils from the Dinaledi Chamber is obviously an exceptional assemblage in the world. It will certainly increase our understanding of human evolution, but also the knowledge about the evolution of human behavior many times so difficult to infer. The authors have inferred through taphonomic and geological studies that is an intentional accumulation of remains of hominins, located at a very early age. This hypothesis will not be free of possible controversy; however, empirical data that are available appear to suggest that one cannot point to any other optional hypothesis, in my view.”

I also share their opinion that we should view this paper as an initial report. The issues of hominin intentionality are controversial, and these along with other taphonomic questions will need a more detailed and critical assessment in the future.

For example, one reviewer said: “I believe that the conclusions provided in the manuscript submitted by the authors go too far in interpreting the data provided […]. Based on [the] limited evidence about the stratigraphy and its relationship to the fossils, it is premature to make detailed interpretations about the site formation processes. In fact, the stratigraphic section of the site presented in the article consists of an unscaled schematic diagram. At the same time, the main unit – where the fossils have been recovered – clearly consists of reworked sediments and no direct (geo-chronological) or indirect (bio-chronological) age has been provided for the deposits. Finally, the taphonomic assertions in the main text of the article [would] need to be supported by corresponding quantitative data (e.g. number and frequencies of each fracture attribute, comparison with other modern or archaeological assemblages, statistical analysis, etc).”

In this context, I recommend that you follow the constructive criticism of the reviewers and present the multiple possible interpretations as competing hypotheses that need to undergo more testing in the future. I have no problem with you stating your preference and your reasons for preferring this interpretation, but do focus on this as one of multiple explanations and give fair treatment to multiple points of view. I think this will defuse some of the controversy about the site while still allowing you to state your preferred interpretation.

Revisions required:

1) We strongly recommend that you revise the current manuscript into a descriptive article about the architecture of the cave, the preliminary geological analysis (stratigraphy, mineralogy…), the description of the fossiliferous deposit, and so on, leaving the interpretations about the origin of the fossil accumulation for forthcoming and more detailed papers. The authors have provided much relevant data regarding the description of the karst system, which is important to their interpretation.

On the other hand, if the authors wish to maintain the current title and interpretations of the paper, they must provide all the necessary data to support the taphonomic conclusions: e.g., fracture patterns of cranial and postcranial remains, bone surface modifications (at least frequencies), statistical comparisons of taphonomic features with modern and/or archaeological assemblages, elaboration of detailed stratigraphic cross-sections, etc. If the authors provide detailed data about the fracture patterns, the results should be compared with other assemblages, see for example Villa, P., Mahieu, E., 1991. J Hum. Evol. 21, 27–48. Hominin bone accumulations in karst systems are often very complex to study and interpret, and the Dinaledi Chamber is particularly interesting in this regard.

2) There are several examples of hominin fossils being found in cave systems (e.g. Atapuerca-Sima de los Huesos, Krapina, Peștera cu Oase). Some comparison with these other cases is warranted (or at the very least mentioned). How is the accumulation in the Dinaledi Chamber similar or different taphonomically from the accumulations at these other sites? The authors might choose a different set of sites, but some kind of comparison with the geological context and/or taphonomic aspects of other sites in the fossil record should be mentioned or discussed.

Other points to consider:

1) It would be interesting to know in greater detail the age of the individuals recorded. The authors indicate that there are individuals of all ages, from neonates to senile. However, this age profile may correspond with a case of catastrophic death. A better exposure of the age profile may help reject a single event of death.

2) Are many remains absent in the assemblage? I understand that this is a fragmentary and not fully excavated set, but it would be interesting to know the relationship between bone mineral density present to better appreciate the conservation of the remains (and the absence of the activity of different taphonomic processes and agents as carnivores or the weathering).

3) A better description of the bone breakage and their characteristics is desirable. In fact, if the bodies were thrown into the chamber, some bones could eventually present some perimortem fracturing.