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.

The use and detection of quantum dots as nanotracers in environmental fate studies of engineered nanoparticles.

Investigations of the behavior and effects of engineered nanoparticles (ENPs) on human health and the environment need detailed knowledge of their fate and transport in environmental compartments. Such studies are highly challenging due to low environmental concentrations, varying size distribution of the particles and the interference with the natural background. A strategy to overcome these limits is to use mimics of ENPs with unique detectable properties that match the properties of the ENPs as nanotracers. A special class of ENPs that can be tracked are quantum dots (QDs). QDs are composed of different metals, metalloids, or more recently also carbon (e.g., graphene), that result in unique optical properties. This allows the tracking of such particles by fluorescence microscopic and photometric techniques. Many types of QDs consist of heavy elements, allowing to track and visualize these particles also by electron microscopy and to quantitate the particles indirectly based on these elements. QDs can also be surface modified in various ways which enable them to be used as a label or as traceable mimics for ENPs. This review reflects a broad range of methods to synthesize and modify QDs based on metals, metalloids, and graphene for studying the environmental fate of nanoparticles and discusses and compares analytical methods that can be used for tracking and quantifying QDs. In addition, we review applications of QDs as ENP mimics in environmental studies of surface waters, soils, microorganisms, and plants with respect to the applied analytical techniques.

Disentangling cortical functional connectivity strength and topography reveals divergent roles of genes and environment.

The human brain varies across individuals in its morphology, function, and cognitive capacities. Variability is particularly high in phylogenetically modern regions associated with higher order cognitive abilities, but its relationship to the layout and strength of functional networks is poorly understood. In this study we disentangled the variability of two key aspects of functional connectivity: strength and topography. We then compared the genetic and environmental influences on these two features. Genetic contribution is heterogeneously distributed across the cortex and differs for strength and topography. In heteromodal areas genes predominantly affect the topography of networks, while their connectivity strength is shaped primarily by random environmental influence such as learning. We identified peak areas of genetic control of topography overlapping with parts of the processing stream from primary areas to network hubs in the default mode network, suggesting the coordination of spatial configurations across those processing pathways. These findings provide a detailed map of the diverse contribution of heritability and individual experience to the strength and topography of functional brain architecture.

Assessing the status of the KNM-ER 42700 fossil using Homo erectus neurocranial development.

Based on ontogenetic data of endocranial shape, it has been proposed that a younger than previously assumed developmental status of the 1.5-Myr-old KNM-ER 42700 calvaria could explain why the calvaria of this fossil does not conform to the shape of other Homo erectus individuals. Here, we investigate (ecto)neurocranial ontogeny in H. erectus and assess the proposed juvenile status of this fossil using recent Homo sapiens, chimpanzees (Pan troglodytes), and Neanderthals (Homo neanderthalensis) to model and discuss changes in neurocranial shape from the juvenile to adult stages. We show that all four species share common patterns of developmental shape change resulting in a relatively lower cranial vault and expanded supraorbital torus at later developmental stages. This finding suggests that ectoneurocranial data from extant hominids can be used to model the ontogenetic trajectory for H. erectus, for which only one well-preserved very young individual is known. However, our study also reveals differences in the magnitudes and, to a lesser extent, directions of the species-specific trajectories that add to the overall shared pattern of neurocranial shape changes. We demonstrate that the very young H. erectus juvenile from Mojokerto together with subadult and adult H. erectus individuals cannot be accommodated within the pattern of the postnatal neurocranial trajectory for humans. Instead, the chimpanzee pattern might be a better 'fit' for H. erectus despite their more distant phylogenetic relatedness. The data are also compatible with an ontogenetic shape trajectory that is in some regards intermediate between that of recent H. sapiens and chimpanzees, implying a unique trajectory for H. erectus that combines elements of both extant species. Based on this new knowledge, neurocranial shape supports the assessment that KNM-ER 42700 is a young juvenile H. erectus if H. erectus followed an ontogenetic shape trajectory that was more similar to chimpanzees than humans.

Drimolen cranium DNH 155 documents microevolution in an early hominin species.

Paranthropus robustus is a small-brained extinct hominin from South Africa characterized by derived, robust craniodental morphology. The most complete known skull of this species is DNH 7 from Drimolen Main Quarry, which differs from P. robustus specimens recovered elsewhere in ways attributed to sexual dimorphism. Here, we describe a new fossil specimen from Drimolen Main Quarry, dated from approximately 2.04-1.95 million years ago, that challenges this view. DNH 155 is a well-preserved adult male cranium that shares with DNH 7 a suite of primitive and derived features unlike those seen in adult P. robustus specimens from other chronologically younger deposits. This refutes existing hypotheses linking sexual dimorphism, ontogeny and social behaviour within this taxon, and clarifies hypotheses concerning hominin phylogeny. We document small-scale morphological changes in P. robustus associated with ecological change within a short time frame and restricted geography. This represents the most highly resolved evidence yet of microevolutionary change within an early hominin species.

Ontogenetic changes of diploic channels in modern humans.

OBJECTIVES: The diploic channels are bony passages of veins, running within frontal, parietal, and occipital bones. In this study, we investigate ontogenetic changes of these channels in a sample of nonadult and adult modern humans. MATERIALS AND METHODS: Using computed tomography scans of dried crania, we provide quantitative comparisons of lumen size, branch length, volume, and vascular asymmetries, and correlations with age, cranial size, and bone thickness. RESULTS: The vascular system displays progressive but nonlinear changes throughout ontogeny, becoming even more complex with adulthood. Vascular variables are significantly different in frontal, parietal, and occipital bones for most of the postnatal ontogeny. Diploic channels of the left and right sides are developed similarly. Vascular variables display a nonlinear association with age and cranial size in modern humans. Cranial bone thickness is shown to be a major determinant of lumen size, branch length, and volume. CONCLUSIONS: A previous radiographic survey suggested that diploic channels are more developed in adult modern humans than in nonadults. Recent advances in digital anatomy have been used in this study to investigate this craniovascular structure. The complexity of the channels increases during development, with a noticeable boost in adults. Taking into account the potential metabolic differences and constraints associated with modern human brain size and shape, the vascular differences found might be related to endocranial thermoregulation.

Australopithecus afarensis endocasts suggest ape-like brain organization and prolonged brain growth.

Human brains are three times larger, are organized differently, and mature for a longer period of time than those of our closest living relatives, the chimpanzees. Together, these characteristics are important for human cognition and social behavior, but their evolutionary origins remain unclear. To study brain growth and organization in the hominin species Australopithecus afarensis more than 3 million years ago, we scanned eight fossil crania using conventional and synchrotron computed tomography. We inferred key features of brain organization from endocranial imprints and explored the pattern of brain growth by combining new endocranial volume estimates with narrow age at death estimates for two infants. Contrary to previous claims, sulcal imprints reveal an ape-like brain organization and no features derived toward humans. A comparison of infant to adult endocranial volumes indicates protracted brain growth in A. afarensis, likely critical for the evolution of a long period of childhood learning in hominins.

A morphometric comparison of the parietal lobe in modern humans and Neanderthals.

The modern human brain and braincase have a characteristic globular shape including parietal and cerebellar bulging. In contrast, Neanderthals, although having similar endocranial volume, displayed more elongated endocrania with flatter parietal and cerebellar regions. Based on endocranial imprints, we compare the parietal lobe morphology of modern humans and Neanderthals, as this brain region is central to several cognitive functions including tool use and visual imaging. In paleoneurology, shape analyses of endocasts are based either on anatomical landmarks that represent endocranial surface features homologous to cortical convolutions (impressions of brain gyri and sulci) or on dense meshes of semilandmarks that capture overall endocranial shape. Previous analyses using the former suggested that modern humans have relatively longer and taller parietal lobes than extinct human species, while the latter emphasized parietal bulging without a significant size difference of parietal regions. In the present study, we combine both anatomical landmarks and surface semilandmarks to investigate the morphological differences of the parietal lobes between modern humans and Neanderthals. Despite limitations by landmark uncertainty, our analyses were able to detect and confirm average different parietal shapes, with modern humans displaying taller and anteroposteriorly extended parietal lobes. We also show mean size differences, with modern humans displaying slightly larger surface areas on the dorsal posterior parietal region, and on a lateral region comprising the supramarginal gyrus, angular gyrus, and intraparietal sulcus. While we observed average differences in the parietal form between the two species, their ranges of distribution overlap, indicating the differences could be a matter of degree. Thus, further analyses on intraspecific variation in parietal lobe morphology within modern human brains should help understand the differences between globular and elongated endocrania. This is crucial because changes to the parietal cortex might affect associative and integrative functions between somatic and visual primary inputs.

Contemporaneity of Australopithecus, Paranthropus, and early Homo erectus in South Africa.

Understanding the extinction of Australopithecus and origins of Paranthropus and Homo in South Africa has been hampered by the perceived complex geological context of hominin fossils, poor chronological resolution, and a lack of well-preserved early Homo specimens. We describe, date, and contextualize the discovery of two hominin crania from Drimolen Main Quarry in South Africa. At ~2.04 million to 1.95 million years old, DNH 152 represents the earliest definitive occurrence of Paranthropus robustus, and DNH 134 represents the earliest occurrence of a cranium with clear affinities to Homo erectus These crania also show that Homo, Paranthropus, and Australopithecus were contemporaneous at ~2 million years ago. This high taxonomic diversity is also reflected in non-hominin species and provides evidence of endemic evolution and dispersal during a period of climatic variability.

Evolution of brain lateralization: A shared hominid pattern of endocranial asymmetry is much more variable in humans than in great apes.

Brain lateralization is commonly interpreted as crucial for human brain function and cognition. However, as comparative studies among primates are rare, it is not known which aspects of lateralization are really uniquely human. Here, we quantify both pattern and magnitude of brain shape asymmetry based on endocranial imprints of the braincase in humans, chimpanzees, gorillas, and orangutans. Like previous studies, we found that humans were more asymmetric than chimpanzees, however so were gorillas and orangutans, highlighting the need to broaden the comparative framework for interpretation. We found that the average spatial asymmetry pattern, previously considered to be uniquely human, was shared among humans and apes. In humans, however, it was less directed, and different local asymmetries were less correlated. We, thus, found human asymmetry to be much more variable compared with that of apes. These findings likely reflect increased functional and developmental modularization of the human brain.

Skull reconstruction of the late Miocene ape Rudapithecus hungaricus from Rudabánya, Hungary.

We report on a computer-based reconstruction of a well-preserved ape skull from late Miocene deposits in Rudabánya, Hungary. Based on micro-computed tomographic scans of the original Rudapithecus hungaricus partial cranium RUD 200 and the associated mandible RUD 212 we realign displaced bone fragments, and reconstruct the shape of the upper and lower jaws guided by occlusal fingerprint analysis of dental wear patterns. We apply geometric morphometric methods based on several hundred landmarks and sliding semilandmarks to estimate missing data, and create multiple reconstructions of the specimen. We then compare the reconstructed overall cranial shape, as well as the volume and shape of the endocast, with extant primates. Multiple reconstructions of RUD 200 yield an average endocranial volume of 234 cc (S.D.: 9 cc; range: 221-247 cc). RUD 200 is most similar to African apes in overall cranial shape, but in a statistical analysis of endocranial shape the specimen falls closest to extant hylobatids. Our data suggest that R. hungaricus from the late Miocene in Europe displays aspects of the overall cranial geometry typical of extant African great apes, but it does not show an evolutionary reorganization of the brain evident in Pan, Gorilla, and Pongo.

Medical diagnoses showed low relatedness in an explorative mutual information analysis of 190,837 inpatient cases.

OBJECTIVES: We aimed to quantify the shared information between medical diagnoses of an adult inpatient population to explore both multimorbidity patterns and vice versa the unrelatedness of medical diagnoses. STUDY DESIGN AND SETTING: This was a cross-sectional study, performed at a tertiary care center in Switzerland. Diagnoses were routinely coded using the International Classification of Diseases, 10th revision. RESULTS: Among 190,837 inpatient cases, 7,994 unique diagnoses were coded. There were 31.9 million possible diagnosis pairs; the respective mutual information scores in diagnosis pairs were low (range, 10-7 to 0.237). There were 148 pairs of diagnoses with a mutual information score higher than 0.01, which formed several clinically plausible disease clusters; 27.2% of cases did not have a diagnosis that belonged to one of the morbidity clusters. CONCLUSION: In an explorative analysis, we observed a high unrelatedness of diagnoses in a tertiary-care inpatient population. This finding indicates that although multimorbidity patterns can be observed, inpatient cases frequently have further, unrelated diagnoses, which share little information with specific other diagnoses. Therefore, management of multimorbid patients should be individualized and may not be generalized based on a few multimorbidity patterns or clusters.

Morphological trends in arcade shape and size in Middle Pleistocene Homo.

OBJECTIVES: Middle Pleistocene fossil hominins, often summarized as Homo heidelbergensis sensu lato, are difficult to interpret due to a fragmentary fossil record and ambiguous combinations of primitive and derived characters. Here, we focus on one aspect of facial shape and analyze shape variation of the dental arcades of these fossils together with other Homo individuals. MATERIALS AND METHODS: Three-dimensional landmark data were collected on computed tomographic scans and surface scans of Middle Pleistocene fossil hominins (n = 8), Homo erectus s.l. (n = 4), Homo antecessor (n = 1), Homo neanderthalensis (n = 13), recent (n = 52) and fossil (n = 19) Homo sapiens. To increase sample size, we used multiple multivariate regression to reconstruct complementary arches for isolated mandibles, and explored size and shape differences among maxillary arcades. RESULTS: The shape of the dental arcade in H. erectus s.l. and H. antecessor differs markedly from both Neanderthals and H. sapiens. The latter two show subtle but consistent differences in arcade length and width. Shape variation among Middle Pleistocene fossil hominins does not exceed the amount of variation of other species, but includes individuals with more primitive and more derived morphology, all more similar to Neanderthals and H. sapiens than to H. erectus s.l. DISCUSSION: Although our results cannot reject the hypothesis that the Middle Pleistocene fossil hominins belong to a single species, their shape variation comprises a more primitive morph that represents a likely candidate for the shape of the last common ancestor of Neanderthals and H. sapiens, and a more derived morph resembling Neanderthals. The arcade shape difference between Neanderthals and H. sapiens might be related to different ways to withstand mechanical stress.

Neandertal Introgression Sheds Light on Modern Human Endocranial Globularity.

One of the features that distinguishes modern humans from our extinct relatives and ancestors is a globular shape of the braincase [1-4]. As the endocranium closely mirrors the outer shape of the brain, these differences might reflect altered neural architecture [4, 5]. However, in the absence of fossil brain tissue, the underlying neuroanatomical changes as well as their genetic bases remain elusive. To better understand the biological foundations of modern human endocranial shape, we turn to our closest extinct relatives: the Neandertals. Interbreeding between modern humans and Neandertals has resulted in introgressed fragments of Neandertal DNA in the genomes of present-day non-Africans [6, 7]. Based on shape analyses of fossil skull endocasts, we derive a measure of endocranial globularity from structural MRI scans of thousands of modern humans and study the effects of introgressed fragments of Neandertal DNA on this phenotype. We find that Neandertal alleles on chromosomes 1 and 18 are associated with reduced endocranial globularity. These alleles influence expression of two nearby genes, UBR4 and PHLPP1, which are involved in neurogenesis and myelination, respectively. Our findings show how integration of fossil skull data with archaic genomics and neuroimaging can suggest developmental mechanisms that may contribute to the unique modern human endocranial shape.

Covariation of the endocranium and splanchnocranium during great ape ontogeny.

That great ape endocranial shape development persists into adolescence indicates that the splanchnocranium succeeds brain growth in driving endocranial development. However, the extent of this splanchnocranial influence is unknown. We applied two-block partial least squares analyses of Procrustes shape variables on an ontogenetic series of great ape crania to explore the covariation of the endocranium (the internal braincase) and splanchnocranium (face, or viscerocranium). We hypothesized that a transition between brain growth and splanchnocranial development in the establishment of final endocranial form would be manifest as a change in the pattern of shape covariation between early and adolescent ontogeny. Our results revealed a strong pattern of covariation between endocranium and splanchnocranium, indicating that chimpanzees, gorillas, and orangutans share a common tempo and mode of morphological integration from the eruption of the deciduous dentition onwards to adulthood: a reflection of elongating endocranial shape and continuing splanchnocranial prognathism. Within this overarching pattern, we noted that species variation exists in magnitude and direction, and that the covariation between the splanchnocranium and endocranium is somewhat weaker in early infancy compared to successive age groups. When correcting our covariation analyses for allometry, we found that an ontogenetic signal remains, signifying that allometric variation alone is insufficient to account for all endocranial-splanchnocranial developmental integration. Finally, we assessed the influence of the cranial base, which acts as the interface between the face and endocranium, on the shape of the vault using thin-plate spline warping. We found that not all splanchnocranial shape changes during development are tightly integrated with endocranial shape. This suggests that while the developmental expansion of the brain is the main driver of endocranial shape during early ontogeny, endocranial development from infancy onwards is moulded by the splanchnocranium in conjunction with the neurocranium.

Author Correction: New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens.

In the originally published version of this Letter, the x axis in Fig. 3a should have been: 'PC1: 26%' rather than 'PC1: 46%', and the y axis should have been: 'PC2: 16%' rather than 'PC2: 29%'. We also noticed an error in the numbering of the fossils from Qafzeh: Qafzeh 27 should be removed, and Qafzeh 26 is actually Qafzeh 25, following Tillier (2014)1 and Schuh et al. (2017)2 and personal communication with B. Vandermeersch and M. D. Garralda. The correct enumeration of Qafzeh samples in the 'Mandibular metric data' section of the Methods is therefore: 'Qafzeh (9, 25)' rather than 'Qafzeh (9, 26, 27)'. Owing to the removal of Qafzeh 27, the convex hull of early modern humans changes slightly in Extended Data Fig. 1c. The sample sizes in Extended Data Fig. 1c should have read: Middle Pleistocene archaic Homo n = 19 (instead of 11), Neanderthals n = 40 (instead of 41), early modern humans n = 12 (instead of 7), and recent modern humans n = 46 (instead of 48). In Extended Data Table 2, the mean and standard deviation of corpus height and breadth at mental foramen for early modern humans should have been: x̅ = 33.15, σ = 3.26 for height (rather than x̅ = 34.23, σ = 4.57); and x̅ = 16.25, σ = 1.28 for breadth (rather than x̅ = 16.04, σ = 1.75). Accordingly, n = 12 (rather than n = 13) for both breadth and height. These errors have been corrected in the Letter online (the original Extended Data Fig. 1 is shown in Supplementary Information to this Amendment). These changes do not alter any inferences drawn from the data.

Reconstruction, endocranial form and taxonomic affinity of the early Homo calvaria KNM-ER 42700.

When first described, the small calvaria KNM-ER 42700 from Ileret, Kenya, was considered a late juvenile or young adult and assigned to Homo erectus. However, this species attribution has subsequently been challenged because the specimen's neurocranial shape differs substantially from that of H. erectus adults. Here, (1) we describe the postmortem damage and deformation that could have influenced previous shape analyses, (2) present digital reconstructions based on computed tomographic scans correcting for these taphonomic defects, and (3) analyze the reconstructed endocranial shape and form, considering both static allometry among adults and ontogenetic allometry. To this end, we use geometric morphometrics to analyze the shape of digital endocasts based on landmarks and semilandmarks. Corroborating previous studies of the external surface, we find that the endocranial shape of KNM-ER 42700 falls outside the known adult variation of H. erectus. With an endocranial volume estimate between 721 and 744 ml, size cannot explain its atypical endocranial shape when static allometry within H. erectus is considered. However, the analysis of ontogenetic allometry suggests that it may be a H. erectus individual that is younger than previously thought and had not yet reached adult endocranial shape. Future work should therefore comprehensively review all cranial indicators of its developmental age, including closure of the spheno-occipital synchondrosis. An alternative hypothesis is that KNM-ER 42700 represents an as yet unidentified species of early Homo. Importantly, KNM-ER 42700 should not be included in the adult hypodigm of H. erectus.

Using the covariation of extant hominoid upper and lower jaws to predict dental arcades of extinct hominins.

Upper and lower jaws are well represented in the fossil record of mammals and are frequently used to diagnose species. Some hominin species are only known by either their maxillary or mandibular morphology, and in this study, we explore the possibility of predicting their complementary dental arcade shape to aid the recognition of conspecific specimens in the fossil record. To this end, we apply multiple multivariate regression to analyze 3D landmark coordinates collected on associated upper and lower dental arcades of extant Homo, Pan, Gorilla, Pongo, and Hylobates. We first study the extant patterns of variation in dental arcade shape and quantify how accurate predictions of complementary arcades are. Then we explore applications of this extant framework for interpreting the fossil record based on two fossil hominin specimens with associated upper and lower jaws, KNM-WT 15000 (Homo erectus sensu lato) and Sts 52 (Australopithecus africanus), as well as two non-associated specimens of Paranthropus boisei, the maxilla of OH 5 and the Peninj mandible. We find that the shape differences between the predictions and the original fossil specimens are in the range of variation within genera or species and therefore are consistent with their known affinity. Our approach can provide a reference against which intraspecific variation of extinct species can be assessed. We show that our method predicts arcade shapes reliably even if the target shape is not represented in the reference sample. We find that in extant hominoids, the amount of within-taxon variation in dental arcade shape often overlaps with the amount of between-taxon shape variation. This implies that whereas a large difference in dental arcade shape between two individuals typically suggests that they belong to different species or even genera, a small shape difference does not necessarily imply conspecificity.

The evolution of modern human brain shape.

Modern humans have large and globular brains that distinguish them from their extinct Homo relatives. The characteristic globularity develops during a prenatal and early postnatal period of rapid brain growth critical for neural wiring and cognitive development. However, it remains unknown when and how brain globularity evolved and how it relates to evolutionary brain size increase. On the basis of computed tomographic scans and geometric morphometric analyses, we analyzed endocranial casts of Homo sapiens fossils (N = 20) from different time periods. Our data show that, 300,000 years ago, brain size in early H. sapiens already fell within the range of present-day humans. Brain shape, however, evolved gradually within the H. sapiens lineage, reaching present-day human variation between about 100,000 and 35,000 years ago. This process started only after other key features of craniofacial morphology appeared modern and paralleled the emergence of behavioral modernity as seen from the archeological record. Our findings are consistent with important genetic changes affecting early brain development within the H. sapiens lineage since the origin of the species and before the transition to the Later Stone Age and the Upper Paleolithic that mark full behavioral modernity.