The human brain has undergone a threefold increase in size as well as changes in cytoarchitecture and neurochemical organization since the split with the last common ancestor with chimpanzees and bonobos. These changes have likely promoted increased cognitive flexibility but may also have come at the cost of increased vulnerability to neurodegenerative diseases like Alzheimer's disease (AD). Alzheimer's disease is the most common form of age-dependent dementia, and previous research suggests that humans may be uniquely vulnerable to AD. Primate comparative induced pluripotent stem cell models offer a unique opportunity to study the cellular and molecular mechanisms underlying this vulnerability. Plaques composed of amyloid-beta (aβ) are a hallmark pathology of AD, and while the exact role of aβ in disease pathogenesis remains incompletely understood, it is clear that aβ can have a neurotoxic effect and plays a role in the characteristic loss of neurons and synapses. Here we investigate susceptibility to aβ-induced toxicity in induced pluripotent stem cell-derived neurons from humans-both with and without AD, the two Pan species-a chimpanzee and a bonobo, and a rhesus macaque. To measure toxicity, we looked at cell death, along with other metrics of neuronal health and connectivity (neuritic beading and synaptic puncta density, respectively). We also employed transcriptomic approaches (RNA sequencing) to investigate molecular mechanisms underlying observed species differences. Our findings show that macaque neurons are less sensitive to aβ than human and ape neurons, and RNA sequencing points to molecular mechanisms that may underlie potentially protective responses in both macaque and ape neurons relative to humans. This work highlights the importance of studying AD from a comparative lens and provides insights into variation in susceptibility to AD among primates.
The Caijiagou-C (CJG-C) site is an early Middle Pleistocene site (0.59-0.75 Ma) that was discovered in the Nihewan Basin, North China. It was systematically excavated from 2020 to 2021. Hundreds of well-preserved mammalian fossils, dominated by large ungulates such as equids and bovids were unearthed. Notable cut marks and impact marks are frequently observed on these fossils. A taphonomic analysis of the site revealed that hominins rather than carnivores contributed mainly to the formation of the faunal assemblage at CJG-C. The anatomical distribution of bone surface modifications further indicated that hominins had primary access to the carcasses. Diverse butchery stages-such as skinning, disarticulation, evisceration, filleting, and marrow extraction-reflect a full-sequence carcass processing pattern, which is rarely observed in East Asia during the Early and early Middle Pleistocene. The clear anthropogenic pattern and multistage butchery sequence suggest that CJG-C can best be interpreted as a small-scale kill-butchery locality, where large ungulates were processed in situ, although we cannot rule out occasional contributions from other depositional processes. Overall, CJG-C provides one of the best-documented early Middle Pleistocene examples of systematic carcass processing in northern East Asia, holding important implications for understanding hominin subsistence strategies in this region.
The quadrupedal walking gait displayed by most primates differs from that of other mammals in several characteristics. To understand the functional implications of these characteristics, it is useful to explore known exceptions to these generalizations and to determine how widespread any such characteristic actually is. Lorises are one such exception in not exhibiting the typical primate pattern of higher peak vertical forces on their hind limbs than forelimbs. A distinctive pattern of scapulohumeral muscle recruitment is an example of a primate characteristic based only on anthropoids. This study uses electromyography (EMG) to 1) explore the activity patterns of limb retractors in the slow loris (Nycticebus coucang) to address questions related to their unusual weight support distribution and 2) determine if scapulohumeral muscle recruitment in prosimians is like that observed in anthropoids. The EMG results for the hind limb retractors in the slow loris were like those of other primates and did not match study predictions. While the forelimb retractor results did agree with predictions, their inferred contributions to locomotor mechanics were not what was expected. The recruitment patterns for the scapulohumeral muscles in the slow loris as well as four lemur species displayed a mix of similarities and differences to the EMG patterns observed in anthropoids and may relate to a shift in shoulder mechanics between prosimians and anthropoids. However, rather than explaining the higher forelimb than hind limb peak vertical forces, the limb retractor EMG results only raised additional questions about how this distribution of forces is brought about.
Bone surface modifications (BSMs) provide data for modeling predator-prey dynamics and trophic interactions in the fossil record. However, the utility of BSM data depends on our ability to correctly infer which unobservable actions or ecological agents produced these marks, and commonly used qualitative methods may be insufficient to discriminate among BSMs that exhibit substantial macromorphological overlap. Recently, quantitative BSM identification methods have been employed to overcome this taphonomic equifinality, which, despite their methodological rigor, remain underused because they require large databases of experimentally generated BSMs. In the present study, we introduce TaphoSource, an open-source database containing point cloud and measurement data for 942 experimentally generated BSMs, created by replicating five possible taphonomic and depositional actions, as well as 12 fossilized BSMs from the 1.7-million-year-old HWK EE site in Olduvai Gorge, Tanzania. To highlight the utility of this dataset, we used random forest models to distinguish among the five experimentally generated BSM categories based on measurement variability, achieving approximately 73% accuracy. These data were then used to train a random forest model to identify the actions responsible for the 12 fossilized BSMs in the TaphoSource database. We openly disseminate these data so that other researchers can conduct quantitative BSM modeling studies without the need to generate expensive and time-consuming experimental datasets. We anticipate that these data will have broader applications for reconstructing and modeling spatiotemporal trends in carnivory, providing deeper insights into the evolution of both hominin and non-hominin mammalian carnivory and behavior throughout the Plio-Pleistocene.
Mandibular ramus morphology is central to paleoanthropology, yet many quantitative workflows emphasize whole-shape summaries and do not explicitly report the intrinsic geometry of particular anatomical curves and surfaces. We present an automated pipeline that extracts key features of the notch-condyle complex from three-dimensional surface meshes, positions specimens in anatomically defined reference frames, and outputs standardized object-level measurements suitable for reproducible comparison and downstream statistics. We demonstrate the approach on a mixed sample of Pleistocene and Holocene hominin mandibles/rami. Correlation structure and principal component analysis are used to summarize covariation, and permutation-based tests evaluate whether predefined groups differ in multivariate space. Overall, the descriptors show limited redundancy, with only a small subset exhibiting moderate to strong coupling, indicating that the pipeline captures multiple, partly independent aspects of local ramus geometry. The principal component analysis indicates that variability is distributed across several dimensions rather than dominated by a single axis. In the first two components, Holocene specimens form a relatively compact cluster, whereas Pleistocene specimens are more broadly dispersed, with substantial overlap among fossil groups. Despite this overlap, permutation-based testing in reduced principal component space detects a significant effect of group membership, consistent with a conservative Holocene-Pleistocene shift combined with marked within-group dispersion in the fossil sample.
Humans are traditionally classified as diurnal primates, although field evidence from small-scale societies complicates a rigid behavioral reading of that designation. Here, I evaluate the Human Diel Flexibility hypothesis-the idea that Homo sapiens retains diurnal circadian physiology while expressing unusually flexible 24-hour activity for a large-bodied anthropoid. In study 1, I conducted actigraphy-based comparisons of diel (i.e., 24 hour) activity patterns across 10 primate species, including Hadza hunter-gatherers, gibbons (Hylobates), and seven lemur species. Functional linear modeling and Bayesian multivariate analysis revealed that Hadza individuals exhibit elevated night-time activity and a significantly lower day-to-night time ratio (DNTR) than gibbons, overlapping with some lemur genera in this dataset. In study 2, I compiled a comparative dataset of day-to-night activity ratios from 24 primate species and conducted phylogenetic generalized least squares analyses. I found that humans maintain a relatively high cathemerality index in this comparative framework by ecological and morphological variables and that endocranial volume is a significant positive predictor of diel flexibility. Evolutionary model comparisons are consistent with a two-regime Ornstein-Uhlenbeck model with distinct optima for humans and nonhuman primates, suggesting divergent selective pressures on human sleep-wake architecture. I propose the Social Sleep Theory to explain this pattern: through sociotechnological niche construction-group vigilance, fire, and shelter-humans evolved short, flexible, and high-quality sleep that enabled activity redistribution across the diel cycle. These findings challenge a rigid behavioral model of human diurnality while preserving the distinction between circadian physiology and activity expression and expand our understanding of how temporal niche plasticity has contributed to the ecological success of H. sapiens.
The evolution of human bipedalism has traditionally been reconstructed from the pelvis and lower limb, whereas the contribution of the vertebral motion segment has received far less attention. This study introduces the vertebral apophyseal ring (AR) as a novel proxy for reconstructing spinal biomechanics in fossil hominins. Several vertebrae with complete ARs from Australopithecus afarensis A.L. 288-1 were compared with vertebrae from 240 adult modern humans, a Neanderthal (Kebara), an Upper Paleolithic modern human (Ohalo II), 20 chimpanzees (Pan troglodytes), and 24 gorillas (Gorilla gorilla). Vertebral body and AR dimensions were measured from vertebrae T4-L5 (L4 in apes), and corresponding ratios were calculated. Statistical differences between modern humans and African apes were assessed using Welch's analysis of variance followed by Games-Howell post hoc tests. Relative AR size in A.L. 288-1 consistently falls within the range of chimpanzees and gorillas rather than modern humans, indicating that A. afarensis spinal motion segments differed functionally from those of modern humans. Because AR reduction is associated with enlargement of the nucleus pulposus, our findings suggest that spinal adaptations necessary for efficient load absorption, torsional flexibility, and endurance locomotion evolved later in human evolution. These results indicate that the evolution of humanlike bipedalism was a gradual and mosaic process. Although Australopithecus possessed the fundamental capacity for upright walking, it retained primitive spinal features indicative of a less optimized locomotor system. The emergence of a fully modern human gait, therefore, involved progressive reorganization of the vertebral motion segment rather than a single evolutionary transition.
Hominin lumbar vertebrae are characterized by adaptations for bipedal locomotion, which are mostly known from adults. However, vertebrae of Homo erectus are exclusively known from immature individuals. As such, understanding the ontogeny of lumbar vertebrae is warranted. Here, we use three-dimensional geometric morphometrics to quantify the morphology of three H. erectus upper lumbar vertebrae, D2672 from Dmanisi, Georgia; KNM-WT 15000 from Nariokotome, Kenya; and SK 853 from Swartkrans, South Africa, as well as those of two Australopithecus sediba U.W.88-92 and U.W.88-232 from Malapa, South Africa, in a comparative developmental context to assess the likely vertebral positions of D2672 and SK 853. The result suggests that the vertebral position of D2672 cannot be distinguished between the first and second lumbar vertebrae, while SK 853 most likely represents a first lumbar vertebra. We also quantified the ontogenetic variation in the first and second lumbar vertebrae of modern humans, from late infancy to full adulthood, and compared these with H. erectus. In modern humans, the lumbar vertebrae increase in size and undergo a series of shape changes across ontogeny. In particular, the vertebral canal relatively decreases in dorsoventral length but increases in mediolateral length with age, thus juveniles possess relatively narrower vertebral canals than adults. All H. erectus individuals fall within the range of modern humans at a comparable developmental stage in the morphospace, despite their smaller size, suggesting that the vertebral traits associated with humanlike bipedal locomotion were established relatively early in ontogeny and in the evolutionary process.
A comprehensive and accurate database of the human fossil record is a necessity for synthetic understanding of hominin biological and behavioral evolution, yet it has remained an elusive goal for decades. This paper presents a conceptual framework for an online database of the human fossil record, called Origins, and an implementation of that framework for the 1200+ hominin fossils of the Omo-Turkana Basin of northern Kenya and southern Ethiopia. The Omo-Turkana Basin is one of the largest and most significant hominin fossil assemblages in Africa and marks the first major milestone in developing a comprehensive database for the entire hominin fossil record globally. We discuss the theoretical foundation underlying the conceptual model used for Origins, the technical details for the establishment and utilization of Origins, and the roadmap for future and ongoing development of this resource.
This study presents an incised ochre artefact from the Yanling site in the Luonan Basin, the Qinling Mountains region, central China. The specimen, recovered from a well-stratified paleosol, bears deep incisions consistent with intentional scoring. The optical stimulated luminescence dating results indicate that the artefact dates to approximately 80 ka ago. Physicochemical analyses, including X-ray fluorescence, X-ray diffraction, and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, reveal that the sample consists primarily of iron oxides and clay minerals, which are some of the most frequent constituents in ochre materials and thus support the artefact's identification as an ochre piece. This finding represents the earliest known incised ochre artefact from East Asia and provides new evidence for ochre use and behavioral complexity in the region.
The upper middle Eocene Pondaung Formation of central Myanmar has yielded some of the earliest stem anthropoids outside Afro-Arabia. In contrast, strepsirrhine primates are rare and previously known only from the small-bodied sivaladapids Kyitchaungia takaii and Paukkaungia parva. Here we report a new large-bodied sivaladapid based on an isolated M3 from Pondaung, described as Guangxilemur rarissimus sp. nov. The tooth exhibits diagnostic features of Guangxilemur, including a subrectangular outline, a deep trigon basin, an incipient mesostyle, a well-developed buccal cingulum, and pronounced enamel wrinkling. Its dimensions indicate a body mass of approximately 4.1-4.8 kg, substantially larger than previously known Pondaung strepsirrhines and closely matching estimates for the controversial partial postcranial skeleton NMMP 20, previously attributed to the amphipithecine Pondaungia. Because NMMP 20 displays clear strepsirrhine affinities and corresponds in size to G. rarissimus, we reassign this specimen to the new taxon. This resolves the long-standing debate over the phylogenetic identity of NMMP 20 and eliminates a major source of conflict between craniodental and postcranial data, hampering previous interpretations of early anthropoid evolution in Asia. Additional material of Paukkaungia supports the recognition of greater ecological diversity among sivaladapids within the Pondaung primate community.
A growing body of archaeological data points towards distinct cultural innovations during Marine Isotopic Stage (MIS) 5 in Africa. At Bushman Rock Shelter in South Africa, we described previously a large corpus of end-scrapers that constitute a technological novelty in the context of MIS 5 developments. Here, we describe 25 bones with impressions collected from the same deposits. Middle Stone Age layers at the site represent a succession of distinct technological phases, but the bones with impressions are strictly associated with one of them only, characterised by the presence of end-scrapers. Our refined optically stimulated luminescence and U-series chronology, presented here, dates securely this technological association to 103 ± 3 ka. Amongst the bones with impressions, there is a marked preference for the diaphyses of large ungulate long bones. Scraping marks linked to periosteum removal and evidence of fresh breakage indicate the use of bones while still fresh. Macro- and microscopic characteristics of the used areas confirm that the bones were used during percussive activities. The orientation of the bone surface modifications indicates repeated, similar technological gestures. We propose that these bones with impressions are bone retouchers that were fully integrated into the production of the end-scrapers and that they document a clear technological imbrication between the processing of animal resources and the manufacture and use of stone tools. We argue that the use of bones in lithic retouching or resharpening activities represents a critical step in the technological process that led to the exploitation of bone as a versatile raw material by hunter-gatherers.
The functional role of the gluteus medius differs between extant humans and other primates. In nonhuman primates, the muscle rotates the pelvis in the horizontal plane and assists forelimb reach. By contrast, in humans, it pulls the pelvis upward in the frontal plane and contributes to mediolateral stability during bipedal gait. In the earliest evolutionary stage of bipedalism, however, a functional flexibility would have been required to cope with both bipedalism and locomotion using all four limbs. This study conducted a moment arm analysis based on a model-kinematics matching approach in Japanese macaques (Macaca fuscata), which lack any morphological adaptations for bipedalism. We hypothesized that it was postural change itself that triggered the functional transition of the gluteus medius. The primary action of the gluteus medius was found to shift from medial rotation to abduction with a change from quadrupedal to bipedal walking. This is likely to have been caused by a change in the geometric relationship between the muscular force vector and femoral orientation. This indicates that the gluteus medius has the faculties to change its action regardless of iliac morphology while also suggesting that the behavioral changes preceded morphological adaptations in the evolutionary process of the hip abductor apparatus. In the earliest evolutionary stage, a versatile gluteus medius likely facilitated mediolaterally stable bipedal gaits while ensuring the kinematic demands of quadrupedal locomotion, which led to a seamless locomotor transition to bipedalism.
We used traits from the Arizona State University Dental Anthropology System (ASUDAS) to investigate the Out-of-Africa II dispersal (∼70,000-50,000 BP) and biogeographic dynamics within the continent since the Late Pleistocene. Mean measure of divergence (MMD) distances from 32 recent global and five Early-Late Holocene African dental samples (n = 3167 individuals) were compared with FST distances from matched genetic samples (n = 566), serving as an independent line of validation. We then incorporated multidimensional scaling (MDS), Mantel correlations, linear regression, and novel minimum-slope geographic distances to reconstruct global population structure. Strong correlations (rm > 0.7) resulted between MMD and FST matrices and between the latter and their respective minimum-slope distances. The dental and genetic MDS plots revealed the patterning characteristic of seriated spatial or temporal data, indicating greater diversity within Africa than outside of it. Inclusion of the ancient samples revealed long-term phenetic continuity in East and South Africa and a south-north gradient in dental variation. Regressing MDS coordinates against minimum-slope distances yielded the highest R2 value for recent and ancient South African samples (≤0.86), mirroring genetic clines linked with deep Pleistocene structure and Holocene population movements. These findings are consistent with isolation by distance and compatible with serial founder processes associated with the Late Pleistocene dispersal from East Africa. They also suggest Sub-Saharan Africans had formed regionally structured but interconnected populations throughout the Holocene, with South African groups retaining high diversity and features reflecting deep ancestry. Overall, the ASUDAS traits broadly track population history and patterns observed in neutral genomic structure.
The development of hypotheses regarding the specific ways in which environmental change influenced hominin evolution is often hampered by time-averaged paleoenvironmental reconstructions. The rich and continuous fossil record of the Shungura Formation provides an excellent opportunity to reconstruct paleoenvironments in narrower temporal intervals to better elucidate the degree of variability in hominin habitats. Here, we reconstruct submember-scale habitat variation in Member G (2.26-1.92 Ma) by applying a novel three-dimensional (3D) geometric morphometric approach to bovid astragalus ecomorphology. Using canonical variates analyses and between-group principal components analysis with extant bovids (n = 136), we investigate how 3D astragalus shape can distinguish among four habitat categories with varying vegetation cover (forest, heavy cover, light cover, and open). When those models are applied to complete fossil astragali from Member G (n = 195), we find that astragali representing all four categories are present throughout, but varying proportions of each category suggest shifts in the relative abundance of wooded vs. open habitats. The base of Member G is inferred as more open, with a shift toward more wooded habitats from submember G-7 to G-12, followed by a return to more open habitats. This trend cannot be solely attributed to variable preservation among submembers as it occurs within a consistent depositional setting. This underscores that Member G is characterized by short-term fluctuations in paleoenvironmental conditions and demonstrates the utility of this 3D approach for reconstructing subtle environmental shifts.
Transformative technologies that alter raw material properties, rather than just raw material shape and size, are key proxies for the evolution of human cognition and social learning. Silcrete heat treatment in the southern African Middle Stone Age (MSA) is one such proxy. Yet debate now centers not on whether heat treatment occurred in the African MSA but on how it was organized across settings-from controlled insulated setups to embedded hearth-side practices-and how factors such as raw material properties and fire management conditioned those choices. In this study, we argue that archaeological heating-temperature distributions for silcretes provide a proxy for reconstructing fire-use contexts, which in turn allow inference of how heat treatment was organized within broader domestic and social practices. We apply a nondestructive near-infrared protocol-targeting changes in silanol (SiOH) and molecular water (H2O)-to estimate heating temperatures for Howiesons Poort artefacts from Diepkloof and Mertenhof Rock Shelters. As calibration, we use a dataset comprising 225 observations on silcrete flakes heated to prespecified temperatures, which underpins both categorical classification and continuous temperature prediction for the archaeological collection. Heating temperature estimates for the archaeological materials cluster at ∼400-450 °C-an established optimal range for improving silcrete knappability-with smaller numbers of lower and higher values forming expected tails, a pattern that implies intentional fire temperature management by humans. This distribution of temperature estimates is more consistent with lateralized heating adjacent to domestic hearths than with tightly controlled insulated systems. While such a pattern does not uniquely demonstrate embedded heat treatment, it is most parsimoniously explained by routine placement of silcrete within the thermal gradients of domestic fires rather than by the use of segregated, specialized heating systems. We suggest that later MSA groups possessed the capacity for tightly controlled heating but typically met technological goals with minimal organizational overhead, reflecting risk-sensitive choices about time, fuel, and raw material fracture. By showing how a transformative technology was integrated into routine domestic contexts, our results highlight cross-domain cognition and probably low-friction social transmission as key dimensions of later MSA technologies-traits that foreshadow later expansions of complexity in Homo sapiens.
Shualim Rockshelter is situated in the arid central highlands of the Negev in southern Israel and features three occupation layers, spanning from the Initial Upper Paleolithic to the Early Upper Paleolithic, with ages ranging from 47 to 36 ka cal. BP. Site chronology was established by radiocarbon dating of ostrich eggshell fragments and optically stimulated dating of sediments. Cultural variability was assessed through a technotypological analysis of each layer, employing the chaîne opératoire methodology. Layers I and II are attributed to the Ahmarian culture, dating roughly from 45 to 36 ka cal. BP, whereas Layer III is associated with the Initial Upper Paleolithic with an age between 46 and 43 ka cal. BP. Intra-site variability indicates technological shifts from unidirectional reduction sequences producing Levallois-like points in Layer III, to bidirectional sequences for the production of coarse el-Wad points in Layer II. Layer I differs from Layer II as it depicts a highly slender point production, based on narrow-fronted unidirectional cores and finely retouched el-Wad points. Layer I also yielded an ostrich eggshell fragment with etchings and an antler point. Two perforated Mediterranean mollusks were found, one in Layer I and the other in Layer II. The various technological modes documented at the site, including the presence of perforated and painted seashells and an antler point, all suggest a large mobility range and sustained intergroup interactions between hunter-gatherers from Mediterranean and arid regions.
De Nadale Cave is a Neanderthal site located in the Berici Hills of Northeast Italy that provides important insights into regional Middle Paleolithic occupational dynamics. This paper presents the results of the first combined uranium-series and electron spin resonance (U-S/ESR) dating study of herbivore teeth recovered from the site. Three bovid and cervid teeth yield U-S/ESR ages of 79 ± 9 ka, 72 ± 11 ka, and 55 ± 11 ka, with a calculated weighted mean age of 70.1 ± 5.9 ka. These age estimates align with, and further clarify, earlier biochronological findings at De Nadale Cave, as well as previous analyses of charcoal fragments and U/Th dating undertaken on a large herbivore tooth from the site. The new U-S/ESR ages are statistically indistinguishable from the previously published U/Th minimum age of 70.2 +1.0/-0.9 ka when considering their 2σ uncertainty ranges. The consistency of these results supports the reliability of the U-S/ESR chronological framework at De Nadale and indicates that Neanderthal occupation of the site potentially occurred close to the transition between late Marine Isotope Stage (MIS) 5 and early MIS 4, providing important insights into Neanderthal occupation patterns during the harsh stadial and transitional climate phases of the Late Pleistocene. More broadly, the improved chronological framework for De Nadale indicates that Middle Paleolithic Quina technology is likely associated with this MIS transition, in accordance with emerging chronological findings from similar archaeological sites across Western Europe.
