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Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #2: Partly

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2. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #1: I Don't Know

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Reviewer recommendation for manuscript number PONE-D-25-36789: “Earliest geometries. A cognitive investigation of Howiesons Poort engraved ostrich eggshells”

General remarks – the manuscript presents in intriguing idea, and interpretive framework for the early geometric patterns of EOES. Yet the large theoretical background described in the abstract and introduction do not seem to be validated, at least not as described in the conclusions. It is possibly not well explained, but the conclusions seem to be more “down to earth” compared to what is presented in the introduction. Thus, there seems to be a disconnect between the introduction and the discussion, which should be readjusted to focus more on the cognitive operations, and the transmission and transformation of the geometric forms.

In general, there is tendency for over-complication in terms of language, I would recommend careful read through of the manuscript to simplify words and restructure complicated sentences.

Overall, this could be a very interesting paper, after major revisions, simplifying the language and ideas, clarifying the methodology, and tying the theoretical background to the practical work.

Abstract

• The abstract is too general and theoretical and doesn’t really describe the essentials of the research. It should include the research question, the analytical tools used to tackle the question, as well a succinct description of the results and conclusions.

Method –

• There are several problems in the methodology, or points that could use clarification. It is understood that the data derives from published photographs, but this means that the authors have no control over positioning of the fragments. A non-uniform way of positioning will alter the lines, spatial relations between lines (parallelness etc.), the measurement of the angles, curvature, as well as distances between points. The authors acknowledge only the possible distortion in discussing metric measurements, but do not explicitly explain why they are measured anyway. If the measurements are skewed, can the information collected from them be crucial? The bias should be acknowledged for all parameters.

• What does tracing “both manually and digitally” mean? (Line 122) It seems like manual tracing in a digital format (QGIS)

• “Visual normalization” is unclear, does this mean that the normalization is particular to each etched line, as opposed to normalizing the assemblage? Line 125 - Citation of Biederman 1987 – a short sentence explaining the idea and the relevance of the theory to the present research. It seems a crucial reference to understand the method but a reference alone is not enough.

• In the methods section there is a list of numbered points (from line 129), which are not entirely clear. Do they refer to the tolerance thresholds? Or are they steps in the methodology? If so, it should be differentiated in the text as a sub-title within the methodology. The points could include references to figures or possibly replace by a figure illustrating and outlining the analytical steps; alongside an illustration of the differentiation between lines and segments (and their “directionality”) and examples of why and how they are segmented.

Reviewer #2: This paper addresses an interesting question in the field of cognitive archaeology, that of what cognitive mechanisms underlie graphic symbolism in our species. The authors attempt to contribute to answering that question by analysing a corpus of early visual sign manifestations: the engraved ostrich eggshells (OES) found at the South African sites of Diepkloof and Klipdrft Shelter, and Apollo 11 in Namibia, all dating back some 60-65,000 years to an archaeological complex known as Howiesons Poort.

The present study carries out the first quantitative analyses of the OES with the aim to identify the cognitive processes that supported the creation of the engravings. Whereas the methods seem meticulous and raise important questions about the materials and their creators, I also found several shortcomings, detailed below.

1. General.

One of the main claims of the study seems to be that the engraved OES show intentionality, awareness, and precise execution. This is backed by the precise quantitative analyses presented by the authors. However, the intentionality of the engravings has never been in question. Since they were first published, several papers have argued that the motifs were made purposefully and originally constituted complex geometric patterns (e.g., Henshilwood et al., 2014; Nel and Haaland, 2023; Texier et al., 2010; 2013; Tylén et al., 2020 Vogelsang et al., 2010). Also, the earlies Blombos engraving has already been identified as following geometric primitives. In this sense, I wonder what this paper contributes to the already ongoing discussion about early symbolism, other than another method of analysing the geometric patterns.

2. Introduction

The introduction goes into an interesting discussion on the cognitive fundaments of geometry and spatial cognition, but I feel this is not followed up in the discussion with sufficient depth. After having shown that the OES patterns were conceived following geometric ‘rules’, it would have been interesting to read why this is relevant to human cognition during the MSA.

3. Materials and Methods

a) Regarding the materials and methods, it is understandable that the authors worked from published materials, and this practice is common in archaeology. However, I miss a limitations section where it is explicitly acknowledged that working from second hand sources has constraints, along with issues of working with fragmentary material, and the chronological span between samples, which I feel is much underplayed throughout the paper (despite all materials belonging to the HP, there are potentially five millennia between some of them).

b) The dataset section should include the sample size with exclusions (these are mentioned in the results section but should be described in the materials and methods section).

4. Results and discussion.

a) In my opinion, there are several statements that should be elaborated. For example, line 205 reads: “EOES were engraved with perceptually grounded basic geometric affordances, that is straight/curved lines, parallel/ secant segments, and right/non-right angles, and cognitively salient strategies”. I don’t fully grasp what is meant with ‘cognitively salient strategies’. Are the authors referring to visual saliency of low-level features, or to processing fluency? In general, the terminology should be better explained for readers who are not too familiar with cognitive science lingo.

b) Line 291 claims that the patters exhibit a “cognitively traceable ‘grammar’”. This is an interesting conclusion but sadly it leads nowhere. For this to be supported, the authors should demonstrate if and how the production process follows a recurrent series of steps across the sample (e.g., certain types of lines often follow from others in a sequence), as it has been shown to be the case for stone-tool technologies (Stout et al., 2021). The mere repetition of segments and angles may show intentionality but does not constitute an action grammar. If I misunderstood, and this is actually what they found, it should be explained better and discussed in the framework of relevant literature.

c) I miss a discussion on the internal variability of the sample. I mean, it would have been interesting to see whether and to what extent the fragments of each site differed from each other, perhaps alluding to different production strategies or local pattern preferences.

d) Line 349 starts discussing pattern variations and their possible causes (different tools, skill levels, etc.). Again, this is an interesting discussion that falls short. Elaborating how different tools and skills could have led to different patterns (supported ideally by experimental work) would offer a novel approach to these materials, in the way this has been done for figurative engravings (Rivero, 2016).

5. Conclusion

The conclusion that this study offers a new way of understanding “the mechanisms by which geometric strategies were organized, transmitted, transformed, and stabilized within early human communities” (Line 369) seems to me an overstatement, given the gaps mentioned above. The following lines suggest that some of the questions raised in this review might be addressed in future work, so perhaps this analysis was premature and the authors should have waited until they could offer an more robust paper.

Cited references:

Henshilwood, C. S., van Niekerk, K. L., Wurz, S., Delagnes, A., Armitage, S. J., Rifkin, R. F., ... & Mienies, S. S. (2014). Klipdrift shelter, southern Cape, South Africa: preliminary report on the Howiesons Poort layers. Journal of Archaeological Science, 45, 284-303.

Nel, T. H., & Haaland, M. M. (2023). Klipdrift Shelter, South Africa. In Handbook of Pleistocene Archaeology of Africa: Hominin behavior, geography, and chronology (pp. 1549-1561). Cham: Springer International Publishing.

Rivero, O. (2016). Master and apprentice: evidence for learning in Palaeolithic portable art. Journal of Archaeological Science, 75, 89-100.

Stout, D., & Chaminade, T. (2012). Stone tools, language and the brain in human evolution. Philosophical Transactions of the Royal Society B: Biological Sciences, 367(1585), 75-87.

Texier, P. J., Porraz, G., Parkington, J., Rigaud, J. P., Poggenpoel, C., & Tribolo, C. (2013). The context, form and significance of the MSA engraved ostrich eggshell collection from Diepkloof Rock Shelter, Western Cape, South Africa. Journal of Archaeological Science, 40(9), 3412-3431.

Texier, P. J., Porraz, G., Parkington, J., Rigaud, J. P., Poggenpoel, C., Miller, C., ... & Verna, C. (2010). A Howiesons Poort tradition of engraving ostrich eggshell containers dated to 60,000 years ago at Diepkloof Rock Shelter, South Africa. Proceedings of the National Academy of Sciences, 107(14), 6180-6185.

Tylén, K., Fusaroli, R., Rojo, S., Heimann, K., Fay, N., Johannsen, N. N., ... & Lombard, M. (2020). The evolution of early symbolic behavior in Homo sapiens. Proceedings of the National Academy of Sciences, 117(9), 4578-4584.

Vogelsang, R., Richter, J., Jacobs, Z., Eichhorn, B., Linseele, V., & Roberts, R. G. (2010). New excavations of Middle Stone Age deposits at Apollo 11 Rockshelter, Namibia: stratigraphy, archaeology, chronology and past environments. Journal of African Archaeology, 8(2), 185-218.

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Earliest geometries. A cognitive investigation of Howiesons Poort engraved ostrich eggshells

PONE-D-25-36789R1

Dear Dr. Ferrara,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Iris Groman-Yaroslavski, Ph.D

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions??>

Reviewer #1: Yes

Reviewer #2: Yes

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3. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #1: I Don't Know

Reviewer #2: Yes

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4. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #1: Yes

Reviewer #2: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: (No Response)

Reviewer #2: Thank you for addressing all of the reviewers' queries. The paper is much mor streamlined and clear. My only additional comment is: in line 63 of the revised ms the authors mention with certainty that the ostrich eggs have been used to store water since the MSA, however I suggest a bit more nuance, as this is an assumption but it has not been tested (e.g., no analyses of the shells have been done to determine whether they were used for water or some other liquid, or maybe they were not used as containers). So I suggest simply adding that 'it is assumed'.

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Reviewer #1: No

Reviewer #2: No

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