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A simple rule governs the evolution and development of hominin tooth size. Evans Alistair R,Daly E Susanne,Catlett Kierstin K,Paul Kathleen S,King Stephen J,Skinner Matthew M,Nesse Hans P,Hublin Jean-Jacques,Townsend Grant C,Schwartz Gary T,Jernvall Jukka Nature The variation in molar tooth size in humans and our closest relatives (hominins) has strongly influenced our view of human evolution. The reduction in overall size and disproportionate decrease in third molar size have been noted for over a century, and have been attributed to reduced selection for large dentitions owing to changes in diet or the acquisition of cooking. The systematic pattern of size variation along the tooth row has been described as a 'morphogenetic gradient' in mammal, and more specifically hominin, teeth since Butler and Dahlberg. However, the underlying controls of tooth size have not been well understood, with hypotheses ranging from morphogenetic fields to the clone theory. In this study we address the following question: are there rules that govern how hominin tooth size evolves? Here we propose that the inhibitory cascade, an activator-inhibitor mechanism that affects relative tooth size in mammals, produces the default pattern of tooth sizes for all lower primary postcanine teeth (deciduous premolars and permanent molars) in hominins. This configuration is also equivalent to a morphogenetic gradient, finally pointing to a mechanism that can generate this gradient. The pattern of tooth size remains constant with absolute size in australopiths (including Ardipithecus, Australopithecus and Paranthropus). However, in species of Homo, including modern humans, there is a tight link between tooth proportions and absolute size such that a single developmental parameter can explain both the relative and absolute sizes of primary postcanine teeth. On the basis of the relationship of inhibitory cascade patterning with size, we can use the size at one tooth position to predict the sizes of the remaining four primary postcanine teeth in the row for hominins. Our study provides a development-based expectation to examine the evolution of the unique proportions of human teeth. 10.1038/nature16972
The evolutionary history of the human face. Lacruz Rodrigo S,Stringer Chris B,Kimbel William H,Wood Bernard,Harvati Katerina,O'Higgins Paul,Bromage Timothy G,Arsuaga Juan-Luis Nature ecology & evolution The face is the most distinctive feature used to identify others. Modern humans have a short, retracted face beneath a large globular braincase that is distinctively different from that of our closest living relatives. The face is a skeletal complex formed by 14 individual bones that houses parts of the digestive, respiratory, visual and olfactory systems. A key to understanding the origin and evolution of the human face is analysis of the faces of extinct taxa in the hominin clade over the last 6 million years. Yet, as new fossils are recovered and the number of hominin species grows, the question of how and when the modern human face originated remains unclear. By examining key features of the facial skeleton, here we evaluate the evolutionary history of the modern human face in the context of its development, morphology and function, and suggest that its appearance is the result of a combination of biomechanical, physiological and social influences. 10.1038/s41559-019-0865-7
Neutral evolution of human enamel-dentine junction morphology. Monson Tesla A,Fecker Diego,Scherrer Marc Proceedings of the National Academy of Sciences of the United States of America Teeth have been studied for decades and continue to reveal information relevant to human evolution. Studies have shown that many traits of the outer enamel surface evolve neutrally and can be used to infer human population structure. However, many of these traits are unavailable in archaeological and fossil individuals due to processes of wear and taphonomy. Enamel-dentine junction (EDJ) morphology, the shape of the junction between the enamel and the dentine within a tooth, captures important information about tooth development and vertebrate evolution and is informative because it is subject to less wear and thus preserves more anatomy in worn or damaged specimens, particularly in mammals with relatively thick enamel like hominids. This study looks at the molar EDJ across a large sample of human populations. We assessed EDJ morphological variation in a sample of late Holocene modern humans ( = 161) from archaeological populations using μ-CT biomedical imaging and geometric morphometric analyses. Global variation in human EDJ morphology was compared to the statistical expectations of neutral evolution and "Out of Africa" dispersal modeling of trait evolution. Significant correlations between phenetic variation and neutral genetic variation indicate that EDJ morphology has evolved neutrally in humans. While EDJ morphology reflects population history, its global distribution does not follow expectations of the Out of Africa dispersal model. This study increases our knowledge of human dental variation and contributes to our understanding of dental development more broadly, with important applications to the investigation of population history and human genetic structure. 10.1073/pnas.2008037117
Reconstructing human population history from dental phenotypes. Scientific reports Dental phenotypic data are often used to reconstruct biological relatedness among past human groups. Teeth are an important data source because they are generally well preserved in the archaeological and fossil record, even when associated skeletal and DNA preservation is poor. Furthermore, tooth form is considered to be highly heritable and selectively neutral; thus, teeth are assumed to be an excellent proxy for neutral genetic data when none are available. However, to our knowledge, no study to date has systematically tested the assumption of genetic neutrality of dental morphological features on a global scale. Therefore, for the first time, this study quantifies the correlation of biological affinities between worldwide modern human populations, derived independently from dental phenotypes and neutral genetic markers. We show that population relationship measures based on dental morphology are significantly correlated with those based on neutral genetic data (on average r = 0.574, p < 0.001). This relatively strong correlation validates tooth form as a proxy for neutral genomic markers. Nonetheless, we suggest caution in reconstructions of population affinities based on dental data alone because only part of the dental morphological variation among populations can be explained in terms of neutral genetic differences. 10.1038/s41598-017-12621-y
Buccal dental-microwear and feeding ecology of Early Pleistocene Theropithecus oswaldi from Cueva Victoria (Spain). Martínez L M,Estebaranz-Sánchez F,Ferràndez-Cañadell C,Romero A,Ribot F,Galbany J,Gibert L,Pérez-Pérez A Journal of human evolution Despite the scarcity of fossil specimens of Theropithecus oswaldi in Eurasia, its presence out of Africa attests to the great dispersal of this Papionini genus during the Early Pleistocene. In the present study, we analyze the buccal dental microwear of T. oswaldi (T. o. leakeyi) fossil specimens from Cueva Victoria (Southeastern Spain). This analysis is the first characterization of the feeding ecology of T. oswaldi in Europe. The buccal microwear pattern of the molar and premolar teeth of T. oswaldi from Cueva Victoria shows great similarities to that observed for the extant frugivorous forest-dwelling Mandrillus sphinx and mangabeys (Cercocebus sp.)-both species adapted to durophagous dietary habits-while significantly different from that observed for the gramnivorous Theropithecus gelada. These results suggest that T. oswaldi from Cueva Victoria could have exploited both hard-shelled fruits or seeds and succulent fruits from open and forested Mediterranean ecosystems. 10.1016/j.jhevol.2019.102736
Dentine morphology of Atapuerca-Sima de los Huesos lower molars: Evolutionary implications through three-dimensional geometric morphometric analysis. Hanegraef Hester,Martinón-Torres María,Martínez de Pinillos Marina,Martín-Francés Laura,Vialet Amélie,Arsuaga Juan Luis,Bermúdez de Castro José María American journal of physical anthropology OBJECTIVES:This study aims to explore the affinities of the Sima de los Huesos (SH) population in relation to Homo neanderthalensis, Arago, and early and contemporary Homo sapiens. By characterizing SH intra-population variation, we test current models to explain the Neanderthal origins. MATERIALS AND METHODS:Three-dimensional reconstructions of dentine surfaces of lower first and second molars were produced by micro-computed tomography. Landmarks and sliding semilandmarks were subjected to generalized Procrustes analysis and principal components analysis. RESULTS:SH is often similar in shape to Neanderthals, and both groups are generally discernible from Homo sapiens. For example, the crown height of SH and Neanderthals is lower than for modern humans. Differences in the presence of a mid-trigonid crest are also observed, with contemporary Homo sapiens usually lacking this feature. Although SH and Neanderthals show strong affinities, they can be discriminated based on certain traits. SH individuals are characterized by a lower intra-population variability, and show a derived dental reduction in lower second molars compared to Neanderthals. SH also differs in morphological features from specimens that are often classified as Homo heidelbergensis, such as a lower crown height and less pronounced mid-trigonid crest in the Arago fossils. DISCUSSION:Our results are compatible with the idea that multiple evolutionary lineages or populations coexisted in Europe during the Middle Pleistocene, with the SH paradigm phylogenetically closer to Homo neanderthalensis. Further research could support the possibility of SH as a separate taxon. Alternatively, SH could be a subspecies of Neanderthals, with the variability of this clade being remarkably higher than previously thought. 10.1002/ajpa.23428