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Thank you very much for your revised manuscript. I hope you agree that the review process resulted in an improved paper. It is now accepted.
I have sought the opinion of the one reviewer who suggested major revisions and he feels the paper is ready to be accepted. I essentially agree and thank you for your revisions and responding to the reviews' concerns. I have marked this as Minor Revisions because I noted a few minor typos in the submitted manuscript that I marked in the annotated pdf. I am giving you the chance to go over the manuscript one last time, as when I accept the manuscript it goes straight to production. Double check the references too as there is no copy editing provided during the production process. Congratulations on your nice work.
The authors have done an excellent job of addressing the concerns of all three reviewers, and I am satisfied with the response to my own comments. The manuscript reads much better after these edits.
No further concerns, the authors have adequately justified the choice of methods, and the incorporation of multiple estimates of body mass for KNM-ER 1808 is appreciated.
No further concerns
Thank you for addressing these comments thoroughly, and for the opportunity to review this manuscript.
I have received three reviews of your manuscript. While all see the merits of this manuscript, two suggest minor revisions, but the third feels major revisions are required. I am sympathetic to the concerns of Reviewer 3, particularly with respect to tightening up the manuscript and the potential implications of variation in mass estimates for the results and interpretation. Accordingly, I have marked the manuscript as requiring major revisions. If you can address the comments in the review and attached annotated manuscript, I am more than happy to consider a revised version. The other reviewers also provide important comments. Reviewer 1 has a number of useful grammatical corrections and asks for greater clarity on a couple of methodological issues. You should be able to address these while still tightening the manuscript to accommodate Reviewer 3. I will leave it to you to decide whether to follow Reviewer 1’s specific suggestion on word choice. Reviewer 2 has a specific question regarding potential pathology of specimens in the comparative H. erectus sample. If you feel you can suitably address these concerns, I look forward to receiving your revised manuscript.
The following numbers refer to line number, followed by my comments. All are minor corrections.
55-58: I don’t think the catalogue of citations is necessary to support this point. Please pick the few (five at most) most relevant citations out of this list.
68-74: Very long sentence.
76: Grammar: Missing word – “broaden [the] current understanding”
78: Grammar: “humeri” not “humerus”
108: “seminal”—please replace with “initial” or some synonymous word. “Seminal” is gendered and archaic language.
121: Grammar: “modern-human like”, correct to “modern human-like”
134-136: A citation to support this statement would be appropriate.
276: Referencing format error: “…mobility)(Shang et al.,…)” ”…mobility; Shang et al.,…”
346: Referencing format error: (Weidenreich, 1941) not italicised
361: Referencing format error: (Weidenreich, 1941) not italicised
396: Missing word—“5% [of] length”
418: Missing terms: “identify AP and ML” “identify anteroposterior (AP) and mediolateral (ML)”. As a matter of form, these should always be defined before they are abbreviated, despite being common terminology.
499: Syntax: the opening sentence alludes to the %CA of Humerus II being similar to something else, other than KNM-ER 1808. Is something else being compared to Humerus II, or should the sentence read: “The midshaft of Humerus II exhibits a high estimate of %CA, similar to the %CA of the KNM-ER 1808 cross section…”?
674: Language accuracy—Change “inferiorly-rotated and human-like scapula” to “human-like laterally-oriented scapular glenoid”
Figs 3 & 4: Labels for the axes required, as well as a legend for the abbreviations in Fig. 3.
Tables 1 & 2 should be swapped. The results for Humerus II are discussed before the results for Humerus III, but Table 1 refers to Humerus III. Please make Table 1 the results for Humerus II and Table 2 the results for Humerus III.
Figure S4: Grammar—“proximalmost” “proximal-most”. Please also label the unit of measurement, either in the figure itself or in the caption.
Figure S5: Please include a legend for the abbreviations used in the figure.
With regard to the methodology and experimental design, I have few criticisms; they are, for the most part, appropriate to the objectives of the study. I do, however, have a few comments on the comparative samples and would like some clarification on other points.
The African Homo erectus sensu lato sample quite understandably consists only of KNM-ER 1808 which shows evidence of pathological apposition of bone on the long bones, though significantly without entheseal involvement. Initial assessments by Walker et al. (1982)attributed the pathology to hypervitiminosis A by way of the consumption of bee brood. Hypervitiminosis A, however, affects the entheses. Noting the lack of entheseal involvement, the pathology has more recently been attributed by Rothschild et al. (1995) to treponematosis in the form of yaws, which does not affect muscle attachment sites and causes extensive bone destruction. While Ruff (2008) used Leakey and Walker’s “corrected” cast of KNM-ER 1808 in his analyses and his values are used in the present paper, a justification of the use of this specimen would be appropriate at this juncture. If not a justification, then at least a discussion of the limitations and possible effects the pathology of the specimen may have on the results, especially as they could be profound.
278-280: “we report separate right and left humeral properties of Tianyuan 1 and emphasise same-side comparisons when possible” – why were left humeri not sampled for the recent modern Chinese samples, especially as you emphasise same-side comparisons?
339-356: This section is somewhat convoluted to read, so perhaps some time could be spent clarifying it. Did you create an artificial volume rending of Humerus II by rescaling a volume rendering of Humerus III? These two humeri differ quite notably in cortical thickness it seems, so was some warping/morphing conducted to match the published measurements or the radiograph? If so, this needs to be made more explicit. I understood all the steps independently, but the reasoning for doing it was not clear.
The results appear to be of interest to the field and the findings have the potential to add much-needed information about temporal and geographic variations in humeral strength and rigidity properties in H. erectus sensu lato. I do have concerns that the pathological status of KNM-ER 1808 may be confounding the results, and the authors will need to address this.
In lines 636—665, the authors’ discuss observed humeral robusticity, rigidity, and strength differences between African and East Asia hominin populations. The African H. erectus material, including KNM-ER 1808, has previously been attributed to a different species, Homo ergaster. They do not touch on it in the text, but it would be worth discussing the implications of a separate species attribution for the African material in relation to their findings.
Xing et al. have conducted much-needed humeral diaphyseal robusticity and strength comparisons of material attributed to H. erectus sensu lato from Africa and East Asia. The article is well-written, barring the occasional grammatical error. The results, while interesting, must be tempered by acknowledgement of the pathological status of KNM-ER 1808 and the unclear impact this might have on the interpretation of their results. Greater clarity is also required in the methods section when explaining how the Humerus II medullary cavity estimates were arrived at considering the fossil itself was lost and only Weidenreich’s documentation exists. These and other concerns will need to be addressed before publication.
This study comprises largely of direct comparison of values for populations without any statistical analysis. This is understandable due to the small sample sizes; however, Humerus II has been associated with a femur from Locality 1 and KNM-ER 1808 has associated femora. It would have been interesting to perform reduced major axis regressions (a la Ruff, 2009) with the African and East Asian samples to add some statistical power to the evaluations of relative strength proportions in the present study.
The manuscript if very clearly written, in professional English, and easy to follow and understand. The background and context is adequate, and the tables and figures are professional.
The research hypothesis is very clear. Due to the nature of the fossil samples, multiple levels of estimation were necessary in order to complete the analysis. The authors are quite clear about the process involved in these estimation, and provide details on exactly how the estimation was undertaken. Their commitment to total transparency in this is notable. While estimations were necessary, they explain them well, and I feel they are justified within the scope of the analysis.
Conclusions are clear and robust, and based on the evidence.
In general, this is a clear, well-written manuscript about an interesting and important topic. Little has been published explicitly quantifying levels of long bone robusticity prior to Neandertals, and this paper will expand this slowly growing body of literature. I recommend this manuscript for publication with only one small revision:
Please mention somewhere how the KNM-ER 1808 cross-sections were corrected for the periosteal pathology on the long bones of this specimen. I realize this data was borrowed from Ruff, 2008, but I had to go look up that article to figure out whether or not this current analysis could possibly be affected by the documented pathology on this specimen. Just a sentence or two in the methods section would spare readers from having to look this up in the original publication.
In this manuscript, Xing et al provide an assessment of cortical robusticity (using uCT) from the East Asian humeri of H.erectus (HE) to compare with their African counterparts, and to provide the first anatomical description and cortical data on humerus III from Zhoukoudian Locality 1. They conclude that the humeri of East Asian HE are more robust than African HE, but tend to fall within the lower end of the range of standardized robusticity for more recent hominin samples from the same geographical area.
The paper is well written, detailed, and technically competent. However, I found it to be overly long and descriptive, and had lost interest by the time I had begun reading the results. The material and conclusions could have been delivered in about 1/2 the space, without compromising the scientific integrity or relevant details. I would suggest severely reducing the length of the manuscript, even if there are no page limits in this journal, it is the readers that should be kept in mind.
As an example of places that could be cut, the methods of dating are not germane to the study, only the dates. Readers can move onto the original material on this, on the environmental reconstructions, etc. if they choose to. The anatomical description of Humerus III was also overly detailed for this reviewer - perhaps some of this duplicates Woo and Chia (1954) as well. I would like to see them summarized in graphical format, with labels pointing out the most salient features on the excellent digital photographs in Figure 1. This would also benefit future users of the material for presentations, etc.
I think it is also important for the authors to provide a clearer rationale for the study. Specifically, what new information is gained that was not available before in Weidenreich (1941) + Woo and Chia (1954)? It seems we might have arrived at the same conclusion from reading those two papers without the additional benefit of the uCT cortical data.
Inasmuch as this is mostly an anatomical description of Humerus III and other East Asian HE humeri, the data reporting and experimental design are sound.
I do have two comments, however:
1) I am unclear on why there is a section that reports on standardization by length only (L478-494), and one (more correct) on standardizing by the product of length and estimated body mass? It was not clear why the former was included, since body masses were estimated for the latter anyway? Perhaps I am missing something, but I could not determine the point of the length-only standardization, as all cortical variables were reported in the L*BM standardization as well in the relevant tables.
2) I would like to know why the standardization for length included up to three possible values (even though these varied only by 5.3%), while the mean body mass values were taken as a single value, for the standardization. The BM data, for example on KNM-ER 1808 varies by as much as 40kg. Using Grabowski et al's estimate of 39.5, rather than 60kg mean, would dramatically increase the robusticity of the African HE, putting it much closer to the East Asian hominins. Since much of the results depend on this estimate, it seems more prudent to include a range of values for BM as well as for HL.
The findings are valid, to the extent that one agrees with the chosen body mass estimates of Tianyuan and KNM-ER 1808.
For the former, I have a hard time seeing that this individual would be 85 kg with an inferred humeral length of 327mm. By my admittedly quick calculations, this individual would have had a stature around 170cm (Trotter and Gleser 1952, though there may be better ones out there now). This would give this individual a BMI of 29.4, very close to what would be considered obese by modern standards. This is not to say that such large individuals couldn't exist around 40kya, but I personally find this to be a stretch. While on this topic, can the authors speculate on the more than 25% difference in total cortical area between the left and right humeri of this individual? Seems extreme as a R-L asymmetry.
For the latter, see my comments in point 2. I would like to see ranges of body mass estimates here to provide a proper comparison with the other samples.
I have attached an annotated manuscript with some minor editorial suggestions in addition to the above.
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