What do brain endocasts tell us? A comparative analysis of the accuracy of sulcal identification by experts and perspectives in palaeoanthropology

Palaeoneurology is a complex field as the object of study, the brain, does not fossilize. Studies rely therefore on the (brain) endocranial cast (often named endocast), the only available and reliable proxy for brain shape, size and details of surface. However, researchers debate whether or not specific marks found on endocasts correspond reliably to particular sulci and/or gyri of the brain that were imprinted in the braincase. The aim of this study is to measure the accuracy of sulcal identification through an experiment that reproduces the conditions that palaeoneurologists face when working with hominin endocasts. We asked 14 experts to manually identify well-known foldings in a proxy endocast that was obtained from an MRI of an actual in vivo Homo sapiens head. We observe clear differences in the results when comparing the non-corrected labels (the original labels proposed by each expert) with the corrected labels. This result illustrates that trying to reconstruct a sulcus following the very general known shape/position in the literature or from a mean specimen may induce a bias when looking at an endocast and trying to follow the marks observed there. We also observe that the identification of sulci appears to be better in the lower part of the endocast compared to the upper part. The results concerning specific anatomical traits have implications for highly debated topics in palaeoanthropology. Endocranial description of fossil specimens should in the future consider the variation in position and shape of sulci in addition to using models of mean brain shape. Moreover, it is clear from this study that researchers can perceive sulcal imprints with reasonably high accuracy, but their correct identification and labelling remains a challenge, particularly when dealing with extinct species for which we lack direct knowledge of the brain

Frontal sinuses and human evolution

The frontal sinuses are cavities inside the frontal bone located at the junction between the face and the cranial vault and close to the brain. Despite a long history of study, understanding of their origin and variation through evolution is limited. This work compares most hominin species’ holotypes and other key individuals with extant hominids. It provides a unique and valuable perspective of the variation in sinuses position, shape, and dimensions based on a simple and reproducible methodology. We also observed a covariation between the size and shape of the sinuses and the underlying frontal lobes in hominin species from at least the appearance of Homo erectus. Our results additionally undermine hypotheses stating that hominin frontal sinuses were directly affected by biomechanical constraints resulting from either chewing or adaptation to climate. Last, we demonstrate their substantial potential for discussions of the evolutionary relationships between hominin species

Of Tongues and Men: A Review of Morphological Evidence for the Evolution of Language

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Trends in cerebral organisation in Upper Palaeolithic and recent humans.

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The development of bite force resistance in modern humans and Neanderthals

Modern human and Neanderthal faces present clear morphological differences at all ontogenetic stages. Their post-natal ontogenetic allometric trajectories diverge [1] and in both species, as the various components of the mid-face develop and grow, bone facial remodelling is thought to play a key role in adapting them to their final adult form. In modern humans, maxillary growth is characterised by bone resorption on the anterior surface, whereas in Neanderthals extensive bone deposition is the common finding [2]. This morphogenetic difference is present by approximately 5 years of age [2]. During development, crania are loaded by forces applied to the masticatory system in feeding and manipulation. These change over time, as diet (e.g. weaning) and paramasticatory behaviour change. Differences are known to exist in adults between Homo sapiens and Neanderthals, with Homo sapiens relatively more efficient at generating bite forces but less able to support the strains and deformations produced by such forces [3,4]. Differences in mid-facial form between these species might be expected to be influenced and to influence the distribution and magnitude of strains experienced during masticatory system loading. Since bone adapts to loads, such differences might underlie and contribute to the distinctive distributions of facial remodelling fields in both species and so, to differences in craniofacial growth. The present study explores the ontogeny of modern human and Neanderthal biting resistance as a preliminary to assessing potential associations between the distributions of facial strains arising from biting and facial remodelling among hominins. Our aim is to see if any differences in strains exist during post-natal ontogeny. We test the null hypothesis that modes and magnitudes of cranial deformation do not differ between modern humans and Neanderthals at each age stage when exposed to similar constraints. We used ontogenetic series of Neanderthals and modern humans ranging from newborn to adult. Using 44 landmarks and 201 sliding semilandmarks multivariate regressions of cranial shape on size were used to create three surfaces representing the mean infant, juvenile, and adult stages. These surfaces were converted into finite element models and constrained and loaded in a standardised way to simulate right first incisor and P4/dm2 biting. Applied forces and material properties were identical among models to control all variables except craniofacial form. We compared the resulting deformations, maps of von Mises strains and tensile and compressive strains in the maxilla. The resulting deformations differ in both mode and magnitude between modern humans and Neanderthals. In both incisor and P4/dm2 biting simulations, modelled strains decrease between infants and adults, as is to be expected given differences in size. The infant modern human presents higher strains than the infant Neanderthal over the anterior and inferior maxilla in both biting simulations. This is reversed in the juvenile models and the strains are more similar in adults. Finally, for both biting simulations, modern humans and Neanderthals deform differently, reflecting the differences in developed strains at each age stage. These findings reflect differences in the dynamics of facial growth between modern humans and Neanderthals. Moreover, the differences in strains in the infant, juvenile maxillae in modern humans and Neanderthals model may to some extent underlie and explain the differences in maxillary surface remodelling in these two species. Further work on a wider range of models and loading scenarios is needed to explore this issue further. Acknowledgments: We would like to thanks D. Shapiro, Joan T. Richtsmeier, G. Holoborow, S. Black and L. Scheuer for the information and access to Bosma and Dundee-Scheuer human skeletal collections. For the access and permission to their fossil materials, we would like to thanks the different institutes and their collaborators: Musée national d’Histoire naturelle, Musée de l’Homme (Paris, France), Musée national de la Préhistoire and his director J.J. Cleyet Merle, Museum of Natural History (London, UK), Patrick Semal and the Institut Royal des Sciences naturelles de Belgique (Bruxelle, Belgique), Jean Jacques Hublin and Philipp Gunz from Max Planck Institute for Evolutionary Anthropology (Leizpig, Germany), Luca Bondioli and the Pigorini Museum (Università di Padova, Italy).We would also like to thank the Dan David Center of Human Evolution and Biohistory Research, Shmunis family anthropological institute, Sackler Faculty of Medicine, Tel Aviv University (Tel Aviv, Israel) for granting access to Amud 1. Finally, we thank the NESPOS platform for access to modern and fossil material. References: [1] Krovitz, G. E., 2003. Shape and growth differences between Neandertals and modern humans: grounds for a species-level distinction?. Cambridge Studies in Biological and Evolutionary Anthropology, 320-342. [2] Lacruz, R.S., Bromage, T.G., O’Higgins, P., Arsuaga, J.L., Stringer, C., Godinho, R.M., Warshaw, J., Martínez, I., Gracia-Tellez, A., De Castro, J.M.B. and Carbonell, E., 2015. Ontogeny of the maxilla in Neanderthals and their ancestors. Nature communications, 6(1), 1-6. [3] Godinho, R. M.,Fitton, L. C., Toro-Ibacache, V., Stringer, C. B., Lacruz, R. S., Bromage, T. G., O'Higgins, P., 2018. The biting performance of Homo sapiens and Homo heidelbergensis. Journal of Human Evolution, 118, 56-71. [4] O'Connor, C. F., Franciscus, R. G., Holton, N. E., 2005. Bite force production capability and efficiency in Neandertals and modern humans. American Journal of Physical Anthropology: The Official Publication of the American Association of Physical Anthropologists, 127(2), 129-151

Étude comparative de l’identification manuelle des plis cérébraux sur un cerveau humain, en utilisant un proxy-endocast obtenu par IRM

International audienceThe use of virtual endocasts allows investigation of the folding configurations of the cerebral cortex of extinct species. However, is that really possible? Our goal is to help answer this question by qualifying and quantifying the subjective identifications of the foldings on endocasts compared to their real configurations on the brain. We invited 14 paleoneurologists to manually reconstruct the foldings they could recognize in a proxy-endocast obtained from an in-vivo MRI. MRI data were obtained on a volunteer (female, 33 y/o) during a unique session with complementary sequences. The brain structures segmentation and the folding labelling were obtained with Morphologist with the T1. The MRI UTE sequence was used to segment the bone and create the proxy-endocast with the BrainVisa software. Paleoneurologists were asked to label the endocast. Their manual reconstructions were compared with the real sulci using the Dice index in conjunction with a similarity measure based on position and shape of the foldings. Results show that foldings located closer to the base of the skull are more accurately identified in location and shape than those located in the superior region of the brain, such as the Central Sulcus that was largely misidentified and positioned closer to the precentral region. Traces that appear to be foldings but are not were also identified. The nature of some of these traces remains unknown while in particular one misidentified trace corresponds to another type of structure: the parieto-occipital suture. We hope that the information presented in this work will help the palaeoanthropology community to be more careful with the identification of foldings that might be false or largely misidentified and to validate those that are generally well reconstructed, providing support and confidence in the subsequent studies that derive from them

A Middle Pleistocene Homo from Nesher Ramla, Israel

Our understanding of the origin, distribution, and evolution of early humans and their close relatives has been greatly refined by recent new information. Adding to this trend, Hershkovitz et al. have uncovered evidence of a previously unknown archaic Homo population, the “Nesher Ramla Homo” (see the Perspective by Mirazon Lahr). The authors present comprehensive qualitative and quantitative analyses of fossilized remains from a site in Israel dated to 140,000 to 120,000 years ago indicating the presence of a previously unrecognized group of hominins representing the last surviving populations of Middle Pleistocene Homo in Europe, southwest Asia, and Africa. In a companion paper, Zaidner et al. present the radiometric ages, stone tool assemblages, faunal assemblages, and other behavioral and environmental data associated with these fossils. This evidence shows that these hominins had fully mastered technology that until only recently was linked to either Homo sapiens or Neanderthals. Nesher Ramla Homo was an efficient hunter of large and small game, used wood for fuel, cooked or roasted meat, and maintained fires. These findings provide archaeological support for cultural interactions between different human lineages during the Middle Paleolithic, suggesting that admixture between Middle Pleistocene Homo and H. sapiens had already occurred by this tim

A Middle Pleistocene Homo from Nesher Ramla, Israel

It has long been believed that Neanderthals originated and flourished on the European continent. However, recent morphological and genetic studies have suggested that they may have received a genetic contribution from a yet unknown non-European group. Here we report on the recent discovery of archaic Homo fossils from the site of Nesher Ramla, Israel, which we dated to 140,000 to 120,000 years ago. Comprehensive qualitative and quantitative analyses of the parietal bones, mandible, and lower second molar revealed that this Homo group presents a distinctive combination of Neanderthal and archaic features. We suggest that these specimens represent the late survivors of a Levantine Middle Pleistocene paleodeme that was most likely involved in the evolution of the Middle Pleistocene Homo in Europe and East Asia

Les sinus frontaux au cours de l’évolution humaine

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Frontal sinuses and human evolution

The frontal sinuses are cavities inside the frontal bone located at the junction between the face and the cranial vault and close to the brain. Despite a long history of study, understanding of their origin and variation through evolution is limited. This work compares most hominin species' holotypes and other key individuals with extant hominids. It provides a unique and valuable perspective of the variation in sinuses position, shape, and dimensions based on a simple and reproducible methodology. We also observed a covariation between the size and shape of the sinuses and the underlying frontal lobes in hominin species from at least the appearance of Homo erectus. Our results additionally undermine hypotheses stating that hominin frontal sinuses were directly affected by biomechanical constraints resulting from either chewing or adaptation to climate. Last, we demonstrate their substantial potential for discussions of the evolutionary relationships between hominin species