New Material of the Earliest Hominid from the Upper Miocene of Chad

Anthropolog

Human shoulder development is adapted to obstetrical constraints

ヒトは小さく生まれて大きく育つ --その秘密は鎖骨にあり--. 京都大学プレスリリース. 2022-04-13.In humans, obstetrical difficulties arise from the large head and broad shoulders of the neonate relative to the maternal birth canal. Various characteristics of human cranial development, such as the relatively small head of neonates compared with adults and the delayed fusion of the metopic suture, have been suggested to reflect developmental adaptations to obstetrical constraints. On the other hand, it remains unknown whether the shoulders of humans also exhibit developmental features reflecting obstetrical adaptation. Here we address this question by tracking the development of shoulder width from fetal to adult stages in humans, chimpanzees, and Japanese macaques. Compared with nonhuman primates, shoulder development in humans follows a different trajectory, exhibiting reduced growth relative to trunk length before birth and enhanced growth after birth. This indicates that the perinatal developmental characteristics of the shoulders likely evolved to ease obstetrical difficulties such as shoulder dystocia in humans

The ancestry and affiliations of Kennewick Man

Kennewick Man, referred to as the Ancient One by Native Americans, is a male human skeleton discovered in Washington state (USA) in 1996 and initially radiocarbon dated to 8,340-9,200 calibrated years before present (BP). His population affinities have been the subject of scientific debate and legal controversy. Based on an initial study of cranial morphology it was asserted that Kennewick Man was neither Native American nor closely related to the claimant Plateau tribes of the Pacific Northwest, who claimed ancestral relationship and requested repatriation under the Native American Graves Protection and Repatriation Act (NAGPRA). The morphological analysis was important to judicial decisions that Kennewick Man was not Native American and that therefore NAGPRA did not apply. Instead of repatriation, additional studies of the remains were permitted. Subsequent craniometric analysis affirmed Kennewick Man to be more closely related to circumpacific groups such as the Ainu and Polynesians than he is to modern Native Americans. In order to resolve Kennewick Man's ancestry and affiliations, we have sequenced his genome to ∼1× coverage and compared it to worldwide genomic data including for the Ainu and Polynesians. We find that Kennewick Man is closer to modern Native Americans than to any other population worldwide. Among the Native American groups for whom genome-wide data are available for comparison, several seem to be descended from a population closely related to that of Kennewick Man, including the Confederated Tribes of the Colville Reservation (Colville), one of the five tribes claiming Kennewick Man. We revisit the cranial analyses and find that, as opposed to genome-wide comparisons, it is not possible on that basis to affiliate Kennewick Man to specific contemporary groups. We therefore conclude based on genetic comparisons that Kennewick Man shows continuity with Native North Americans over at least the last eight millennia

Femoral ontogeny in humans and great apes and its implications for their last common ancestor

Inferring the morphology of the last common ancestor of humans, chimpanzees and gorillas is a matter of ongoing debate. Recent findings and reassessment of fossil hominins leads to the hypothesis that the last common ancestor was not extant African ape-like. However, an African great-ape-like ancestor with knuckle walking features still remains plausible and the most parsimonious scenario. Here we address this question via an evolutionary developmental approach, comparing taxon-specific patterns of shape change of the femoral diaphysis from birth to adulthood in great apes, humans, and macaques. While chimpanzees and gorillas exhibit similar locomotor behaviors, our data provide evidence for distinct ontogenetic trajectories, indicating independent evolutionary histories of femoral ontogeny. Our data further indicate that anthropoid primates share a basic pattern of femoral diaphyseal ontogeny that reflects shared developmental constraints. Humans escaped from these constraints via differential elongation of femur

Individual-based modelling of population growth and diffusion in discrete time

Individual-based models (IBMs) of human populations capture spatio-temporal dynamics using rules that govern the birth, behavior, and death of individuals. We explore a stochastic IBM of logistic growth-diffusion with constant time steps and independent, simultaneous actions of birth, death, and movement that approaches the Fisher-Kolmogorov model in the continuum limit. This model is well-suited to parallelization on high-performance computers. We explore its emergent properties with analytical approximations and numerical simulations in parameter ranges relevant to human population dynamics and ecology, and reproduce continuous-time results in the limit of small transition probabilities. Our model prediction indicates that the population density and dispersal speed are affected by fluctuations in the number of individuals. The discrete-time model displays novel properties owing to the binomial character of the fluctuations: in certain regimes of the growth model, a decrease in time step size drives the system away from the continuum limit. These effects are especially important at local population sizes of <50 individuals, which largely correspond to group sizes of hunter-gatherers. As an application scenario, we model the late Pleistocene dispersal of Homo sapiens into the Americas, and discuss the agreement of model-based estimates of first-arrival dates with archaeological dates in dependence of IBM model parameter settings

Virtual reconstruction and geometric morphometrics as tools for paleopathology: A new approach to study rare developmental disorders of the skeleton

Survey studies of osteoarchaeological collections occasionally yield specimens exhibiting rare skeletal developmental disorders. Beyond paleopathological diagnosis, however, it is often difficult to gain insight into the processes, mechanisms, and consequences of the pathology, notably because archaeological specimens are often fragmentary. Here, we propose a combination of virtual reconstruction (VR) and geometric morphometrics (GM) to address these issues. As an example, we use VR to reconstruct the only known archaeological specimen exhibiting persistence of the pelvic triradiate cartilage and compare it via GM with a set of healthy pelvises representing both sexes and different ontogenetic stages. Our results evidence (i) a marked deviation of the pathological pelvis from the adult mean shape, (ii) the retention of typical male features, and (iii) the retention of a paedomorphic ratio between iliac and ischiopubic size. Altogether, such data offer new insights into the modularity and integration of pelvic ontogeny, while at the same time demonstrating the usefulness of a combined VR/GM approach as complement to classical methods of paleopathology

Effects of cranial integration on hominid endocranial shape

Because brains do not fossilize, the internal surface of the braincase (endocast) serves as an important source of information about brain growth, development, and evolution. Recent studies of endocranial morphology and development in great apes, fossil hominins, and modern humans have revealed taxon‐specific differences. However, it remains to be investigated to which extent differences in endocranial morphology reflect differences in actual brain morphology and development, and to which extent they reflect different interactions of the brain and its case with the cranial base and face. Here we address this question by analyzing the effects of cranial integration on endocranial morphology. We test the ‘spatial packing’ and ‘facial orientation’ hypotheses, which propose that size and orientation of the neurocranium relative to the viscerocranium influence endocranial shape. Results show that a substantial proportion of endocranial shape variation along and across ontogenetic trajectories is due to cranial integration. Specifically, the uniquely globular shape of the human endocast mainly results from the combination of an exceptionally large brain with a comparatively small face. Overall, thus, cranial integration has pervasive effects on endocranial morphology, and only a comparatively small proportion of inter‐ and intra‐taxon variation can directly be associated with variation in brain morphology