Does Allen's rule rule? : a reanalysis of ecogeographic variation in modern human limb proportions

In the late 1970s Derek Roberts presented the first systematic analyses of the impact of climate on human morphological variability. One of his key findings was that humans follow Allen's Rule, which holds that there is a positive correlation between peripheral body part size and temperature in homeothermic species. Roberts' conclusions regarding the applicability of Allen's Rule to humans have been widely accepted. However, three features of his analyses are potentially problematic. First, he used a sample that is strongly biased towards warm climates. Second, he maximized sample size of each limb segment at the expense of among-segment comparability. Third, he ignored the confounding effects of phylogeny. In this study the reliability of Roberts' conclusions were evaluated in relation to the aforementioned problems. In the first set of analyses, Roberts' analyses were replicated to ensure the dataset is comparable to his. In the second, the impact of sampling was investigated by examining the range of variation present especially among the warm climate populations. In the third, the impact of over-representation of warm temperature populations was evaluated by stratifying random samples by temperature. In the fourth, stratified analyses were conducted using populations with data for all limb segments. In the last set of analyses, the influence of phylogeny was investigated through phylogenetically-controlled correlation analyses. The first set of analyses was consistent with Roberts' conclusions indicating that the dataset is appropriate. In the second, the slope of the regression line was variable such that both positive and negative correlations were obtained for many segments, which emphasizes the impact of sample selection. The third set supported the idea that overrepresentation of warm climates is problematic as only two segments yielded statistically significant correlations. In the fourth, the pattern of limb proportion variation did not support previous analyses, suggesting that Roberts' decision to maximize sample size at the expense of among-segment comparability is problematic. The fifth set of analyses indicated that phylogeny has a significant impact on the results of the correlation analyses. Together, the results of the analyses reported here cast doubt on the claim that humans follow Allen's Rule.Arts, Faculty ofAnthropology, Department ofGraduat

Exploring morphological phylogenetics of fossil hominins

A reliable phylogeny is critical for the study of hominin evolution, yet there remains considerable debate about the relationships among hominin species. Phylogenetic analyses conducted to date differ in various analytical aspects such as the fossil samples and characters used to infer their relationships. Given the importance of a phylogeny in the study of hominin evolution, these analytical issues must be explored further. The four studies were designed to address some key issues in the phylogenetic analysis in palaeoanthropology. The first study investigated the effects of using small samples in standard phylogenetic analyses. The second study used a new method—¬tip-dated Bayesian analysis—to test various phylogenetic hypotheses pertaining to three recent debates. The third study used the tip-dated Bayesian method to evaluate the phylogenetic and temporal placement of a newly discovered species, Homo naledi, in the hominin phylogeny. The fourth study explored the impact of cranial modularity on the choice of characters used to reconstruct the phylogeny of the hominins. Results suggest that small sample sizes can often be problematic when reconstructing phylogenetic relationships of extant hominoids. However, the choice of character coding methods may mitigate the effects of small samples. Bayesian phylogenetic analyses were conducted to evaluate various hypotheses from three recent debates and some hypotheses can be strongly refuted based on current evidence. The results of the analyses suggest that there is strong evidence that Homo naledi belongs to the clade of Homo and Australopithecus sediba, but its place within this clade is currently ambiguous. Preliminary work places the fossil at approximately 1 Ma. Different cranial regions contain conflicting phylogenetic signals, but none of the regions particularly stand out as having more homoplastic characters. The hominin phylogeny is necessary to study hominin evolution, and as such, it is important to improve the methods used to reconstruct the evolutionary relationships of hominins. The use of Bayesian phylogenetic methods is promising for palaeoanthropology as it can narrow the scope of debate surrounding phylogenetic hypotheses. It allows us to highlight where ambiguities in the data and the model exist and demonstrate the limit of the interpretation of the current fossil evidence

Data from: Bayesian analysis of a morphological supermatrix sheds light on controversial fossil hominin relationships

The phylogenetic relationships of several hominin species remain controversial. Two methodological issues contribute to the uncertainty—use of partial, inconsistent datasets and reliance on phylogenetic methods that are ill-suited to testing competing hypotheses. Here, we report a study designed to overcome these issues. We first compiled a supermatrix of craniodental characters for all widely accepted hominin species. We then took advantage of recently developed Bayesian methods for building trees of serially sampled tips to test among hypotheses that have been put forward in three of the most important current debates in hominin phylogenetics—the relationship between Australopithecus sediba and Homo, the taxonomic status of the Dmanisi hominins, and the place of the so-called hobbit fossils from Flores, Indonesia, in the hominin tree. Based on our results, several published hypotheses can be statistically rejected. For example, the data do not support the claim that Dmanisi hominins and all other early Homo specimens represent a single species, nor that the hobbit fossils are the remains of small-bodied modern humans, one of whom had Down syndrome. More broadly, our study provides a new baseline dataset for future work on hominin phylogeny and illustrates the promise of Bayesian approaches for understanding hominin phylogenetic relationships

Data from: Bayesian analysis of a morphological supermatrix sheds light on controversial fossil hominin relationships

The phylogenetic relationships of several hominin species remain controversial. Two methodological issues contribute to the uncertainty—use of partial, inconsistent datasets and reliance on phylogenetic methods that are ill-suited to testing competing hypotheses. Here, we report a study designed to overcome these issues. We first compiled a supermatrix of craniodental characters for all widely accepted hominin species. We then took advantage of recently developed Bayesian methods for building trees of serially sampled tips to test among hypotheses that have been put forward in three of the most important current debates in hominin phylogenetics—the relationship between Australopithecus sediba and Homo, the taxonomic status of the Dmanisi hominins, and the place of the so-called hobbit fossils from Flores, Indonesia, in the hominin tree. Based on our results, several published hypotheses can be statistically rejected. For example, the data do not support the claim that Dmanisi hominins and all other early Homo specimens represent a single species, nor that the hobbit fossils are the remains of small-bodied modern humans, one of whom had Down syndrome. More broadly, our study provides a new baseline dataset for future work on hominin phylogeny and illustrates the promise of Bayesian approaches for understanding hominin phylogenetic relationships

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Data from: The evolutionary relationships and age of Homo naledi: an assessment using dated Bayesian phylogenetic methods

Homo naledi is a recently discovered species of fossil hominin from South Africa. A considerable amount is already known about H. naledi but some important questions remain unanswered. Here we report a study that addressed two of them: “Where does H. naledi fit in the hominin evolutionary tree?” and “How old is it?” We used a large supermatrix of craniodental characters for both early and late hominin species and Bayesian phylogenetic techniques to carry out three analyses. First, we performed a dated Bayesian analysis to generate estimates of the evolutionary relationships of fossil hominins including H. naledi. Then we employed Bayes factor tests to compare the strength of support for hypotheses about the relationships of H. naledi suggested by the best-estimate trees. Lastly, we carried out a resampling analysis to assess the accuracy of the age estimate for H. naledi yielded by the dated Bayesian analysis. The analyses strongly supported the hypothesis that H. naledi forms a clade with the other Homo species and Australopithecus sediba. The analyses were more ambiguous regarding the position of H. naledi within the (Homo, Au. sediba) clade. A number of hypotheses were rejected, but several others were not. Based on the available craniodental data, Homo antecessor, Asian Homo erectus, Homo habilis, Homo floresiensis, Homo sapiens, and Au. sediba could all be the sister taxon of H. naledi. According to the dated Bayesian analysis, the most likely age for H. naledi is 912 ka. This age estimate was supported by the resampling analysis. Our findings have a number of implications. Most notably, they support the assignment of the new specimens to Homo, cast doubt on the claim that H. naledi is simply a variant of H. erectus, and suggest H. naledi is younger than has been previously proposed

The evolutionary relationships and age of Homo naledi : an assessment using dated Bayesian phylogenetic methods

Acknowledgements We wish to express our gratitude to the National Geographic Society and the National Research Foundation of South Africa for funding the discovery, recovery, and analysis of the H. naledi material. The study reported here was also made possible by grants from the Social Sciences and Humanities Research Council of Canada, the Canada Foundation for Innovation, the British Columbia Knowledge Development Fund, the Canada Research Chairs Program, Simon Fraser University, the DST/NRF Centre of Excellence in Palaeosciences (COE-Pal), as well as by a Discovery Grant from the Natural Sciences and Engineering Research Council of Canada, a Young Scientist Development Grant from the Paleontological Scientific Trust (PAST), a Baldwin Fellowship from the L.S.B. Leakey Foundation, and a Seed Grant and a Cornerstone Faculty Fellowship from the Texas A&M University College of Liberal Arts. We would like to thank the South African Heritage Resource Agency for the permits necessary to work on the Rising Star site; the Jacobs family for granting access; Wilma Lawrence, Bonita De Klerk, Merrill Van der Walt, and Justin Mukanku for their assistance during all phases of the project; Lucas Delezene for valuable discussion on the dental characters of H. naledi. We would also like to thank Peter Schmid for the preparation of the Dinaledi fossil material; Yoel Rak for explaining in detail some of the characters used in previous studies; William Kimbel for drawing our attention to the possibility that there might be a problem with Dembo et al.’s (2015) codes for the two characters related to the articular eminence; Will Stein for helpful discussion about the Bayesian analyses; Mike Lee for his comments on this manuscript; John Hawks for his support in organizing the Rising Star workshop; and the associate editor and three anonymous reviewers for their valuable comments. We are grateful to S. Potze and the Ditsong Museum, B. Billings and the School of Anatomical Sciences at the University of the Witwatersrand, and B. Zipfel and the Evolutionary Studies Institute at the University of the Witwatersrand for providing access to the specimens in their care; the University of the Witwatersrand, the Evolutionary Studies Institute, and the South African National Centre of Excellence in PalaeoSciences for hosting a number of the authors while studying the material; and the Western Canada Research Grid for providing access to the high-performance computing facilities for the Bayesian analyses. Last but definitely not least, we thank the head of the Rising Star project, Lee Berger, for his leadership and support, and for encouraging us to pursue the study reported here.Peer reviewedPostprintPostprin