Examination of Fe and Cu Isotope Variation in Great Apes Using an Optimized Protocol

RATIONALE

Iron deficiency plagues reproductive-aged women across the world, and blood loss during menstruation is proposed as the driving force. To assess if other factors related to reproduction influence Fe and Cu isotope variation in females, we measured Fe and Cu isotope compositions in the bones of chimpanzees and bonobos.

METHODS

To do this, we optimize the protocol for isolating Fe and Cu (and Zn) from phosphate-rich skeletal materials for further analysis via MC-ICP-MS. Then, we address possible Fe and Cu variation sources in non-menstruating apes (n = 26, of which the sex of 10 was obtained by DNA analysis).

RESULTS

The optimized method reduced acid volume by ~14%, and sample preparation time by ~37.5%. We did not find significant sex differences in δ56Fe values (Δ56Fef-m = 0.13‰) or δ65Cu values (Δ65Cuf-m = 0.33‰).

CONCLUSION

Given the similar Δ56Fef-m values between non-menstruating apes and humans, reproductive investment, instead of menstruation alone, is a key factor that drives Fe deficiency in reproductive-aged women and is important to consider with proxies of iron status. Our optimized protocol provides an effective method for exploring iron status in other mammalian species.

Evidence for the Efficacy of Conflict-reducing Practices in Undergraduate Evolution Education in a Randomized Controlled Study

Conflict-reducing practices during evolution instruction have been recommended to increase students' perceived compatibility between evolution and religion, increase evolution acceptance, and decrease stereotypes about religious students in science. However, the efficacy of these practices has not been demonstrated in a randomized controlled design making it uncertain whether they are causing the effects reported in less controlled studies. Further, we do not know the extent to which the religious identities of instructors may impact their effectiveness. In this study, we randomly assigned 2623 undergraduate students in 19 biology courses across different states to receive an evolution video with 1) no conflict-reducing practices, 2) conflict-reducing practices implemented by a non-religious instructor, or 3) conflict-reducing practices implemented by a Christian instructor. We found that the evolution videos with conflict-reducing practices led to decreased conflict, increased compatibility, and increased acceptance of human evolution compared with the video without conflict-reducing practices. Further, the Christian and non-religious instructor conditions were equally effective at improving all student outcomes, except the non-religious instructor was more effective for increasing perceived compatibility between religion and evolution among atheist students. These results illustrate that conflict-reducing practices, implemented by either Christian or non-religious instructors, can be effective in a controlled study.

Phalangeal cortical bone distribution reveals different dexterous and climbing behaviors in Australopithecus sediba and Homo naledi

The evolution of the human hand is marked by a transition from a hand primarily used for locomotion to one primarily used for dexterous manipulation. The hand skeletons of Plio-Pleistocene hominins have different mosaics of human-like features associated with enhanced dexterity and ape-like features associated with locomotor hand use. However, the functional relevance of the ape-like features is debated, particularly due to a lack of complete and associated hand remains. Here, we investigate the internal phalangeal cortical structure of the nearly complete Australopithecus sediba MH2 hand and Homo naledi hand 1 to provide both insight into the manual behaviors of these fossil hominins and functional clarity regarding the mosaic features found within their hands. The phalangeal cortical structure demonstrates diversity in Plio-Pleistocene hand use, with A. sediba and H. naledi each indicating different dexterous abilities and different climbing strategies, supporting the functional importance of the ape-like features.

The locomotor ecology of wild western lowland gorillas: How does the largest ape exploit complex arboreal environments?

Western lowland gorillas are the largest and most sexually dimorphic ape that habitually exploits arboreal environments. Their size, robust musculature and specialised adaptations in the hands and feet, which are suited for terrestrial quadrupedal locomotion, make them interesting models for understanding how great apes are able to exploit complex arboreal habitats. We present a comprehensive analysis of the arboreal locomotor ecology of western lowland gorillas by studying their behaviour and ecology in the context of their morphology. A group of fully habituated wild western lowland gorillas was followed for 12 months in Loango National Park, Gabon. Statistical analysis applying regression modelling and Akaike's Information Criterion was used to identify the relationships between locomotor behaviours, height, contextual behaviour, support use, hand posture and body size. Our findings suggest that the gorillas were not restricted in their ability to access and move around in tree canopies because of their size or postcranial morphology. Instead, they exhibited considerable behavioural flexibility and engaged in locomotor behaviours that contradicted classic body size predictions for primates. To offset the risks of moving on small supports, the gorillas used hand-assisted bipedal locomotion on multiple small supports, rather than relying on suspensory locomotion. We suggest that this is linked to their hand dimensions, which have been selected to facilitate efficient quadrupedal walking on the ground. The silverback gorilla engaged in less horizontal locomotion in the canopy, spent less time at heights above 20 m, and used large supports more often than the adult females, blackback and adolescents, but the type and number of supports used did not vary between body size groups. We also found that the reproductive status of the females (presence or absence of small infants) may have shaped how they responded to risks when solving the problem of gap-crossing in the trees. Overall, our results highlight that the gorillas likely prioritised risk minimisation in the supports that they used in arboreal environments at the cost of increased energy expenditure.

A phylogenetic perspective on the evolution of early hominin foot morphology

Changes in foot morphology have played a crucial role in the evolution of bipedalism. Examining the evolution of pedal characters among hominins makes it possible to identify when and where key anatomical changes required for bipedalism evolved. This study uses ancestral character reconstruction to investigate foot morphology in the Homo + Pan last common ancestor and subsequent nodes in the hominin phylogeny. We explore the pattern of hominin foot evolution and examine the presence of terrestrial and arboreal adaptations at hominin ancestral nodes. In this study, we analyzed 62 discrete pedal characters hypothesized to be functionally significant. Our likelihood-based approach supports the hypothesis of a Pan-like last common ancestor of humans and chimpanzees. The earliest foot synapomorphies in hominins are related to foot and ankle eversion and midtarsal stability. These results are consistent with the hypothesis that lateral midfoot stability might have evolved before medial midfoot stability. Moreover, several homoplasies were inferred across different taxa, particularly related to features hypothesized to reflect joint mobility and the longitudinal arch. Finally, the Paranthropus and the Australopithecus africanus + Australopithecus sediba clades evolved arboreal characteristics, suggesting adaptations for arboreality. Overall, the results demonstrate how pedal characters evolved in hominins from an African ape-like ancestor.

Analyzing Instantaneous Energy in Bipedal Walking of Baboons: A Model for Exploring the Evolutionary Transition Toward Efficient Bipedalism in Hominins

OBJECTIVE

Non-human primates exhibit bipedal walking with a typical "bent-hip, bent-knee" posture, incurring additional energy costs as shown by studies using electromyography and mechanical analysis. During the evolution of habitual bipedalism in hominins, this mode underwent a gradual refinement, culminating in the genus Homo. To explore energy conservation mechanisms and the influence of kinematics during occasional bipedal walking, we investigated energy dynamics within different body segments in an ontogenetic sample of baboons.

MATERIALS AND METHODS

Kinematic and morphometric data from 17 baboons, including mature and immature individuals, were initially collected at the CNRS Primatology station (France). We calculated the potential and kinetic (rotational and translational) energies of various body segments over 40 strides, followed by a comparison with human data.

RESULTS

Age-related kinematic differences influence energy recovery percentages in baboons, particularly in the shank and trunk segments. While significant differences can be observed between baboons and humans, such as in the trunk, arm, and foot segments, similarities exist in the thigh and shank segments, with the thigh being the primary segment for substantial energy transfer. Unlike humans, baboons lack an optimal speed range for energy recovery.

DISCUSSION

We present a model for energy recovery in flexed bipedal walking. While baboon bipedalism is inefficient in energy recovery, minor trunk motion adjustments could greatly enhance efficiency. These subtle refinements have the potential to increase energy recovery rates, making bipedalism more practical for regular use. From an evolutionary perspective, such improvements would be particularly noteworthy considering other challenging activities like climbing and arboreal quadrupedalism.

Locomotor adaptation in the hominoid clavicle through ontogeny

Reconstructions of the locomotor behavior of early hominins have been hindered by our incomplete understanding of the form-function relationship in the extant hominoid shoulder. Although extensive research has highlighted the role of the highly mobile shoulder in supporting the locomotor diversity and versatility observed in hominoids, the contribution of the clavicle and its morphological diversity to shoulder function remains significantly underexplored. In this study, we analyzed the cross-sectional geometry of the ape clavicle using a large ontogenetic sample to identify new osteological signals related to locomotor adaptation in the shoulder. We assessed the interspecific and intraspecific differences in cortical bone distribution, with ratios of cortical properties describing the relative eccentricity of the cross section (the ratio of the second moments of area about the maximum [IMAX] and minimum [IMIN] principal axes [IMAX/IMIN]), the orientation of the anatomical plane that eccentricity is occurring in (the ratio of the second moments of area relative to the craniocaudal [IX] and dorsoventral [IY] axes [IX/IY]), and the relative proportion of cortical bone in each section. Our analyses demonstrate that the hominoid clavicle holds strong signals of locomotor adaptation that can be identified both across taxa and through ontogeny. Gibbons and orangutans have a relatively uniform clavicular cortical geometry throughout life, with gibbon clavicles built to best withstand habitual, unidirectional bending forces and orangutan clavicles remodeled to resist unpredictable, multidirectional loading. Furthermore, we find a clear signal of increased clavicular bending in the same portion of the diaphysis through ontogeny in the cortical geometry of chimpanzees and gorillas, likely reflecting both the shifts toward terrestriality through ontogeny and bending rigidity needed for continued arboreality at a larger body mass. Ultimately, these results are promising for the identification of locomotor adaptation in the shoulder of early hominins, especially Australopithecus, and highlight the key structural role of the clavicle in ape locomotion.

A three-dimensional geometric morphometric study of Miocene ape lumbar vertebrae, with implications for hominoid locomotor evolution

Miocene apes represent snapshots in time of key transitions in hominoid evolution. While all extant apes are adapted to orthograde posture and suspensory behavior, many Miocene apes demonstrate evidence for pronogrady and habitual arboreal quadrupedalism or present 'mosaic' morphologies suggestive of locomotion and posture unlike any extant catarrhine. Here, we use three-dimensional geometric morphometrics to study penultimate lumbar vertebrae of extant anthropoids and those of three well-preserved Miocene apes: Ekembo nyanzae (KNM-MW 13142), Morotopithecus bishopi (UMP 67-28), and Pierolapithecus catalaunicus (IPS 21350-64), which have been interpreted as a pronograde arboreal quadruped, an orthograde suspensory or vertical climbing ape, and an orthograde vertical climber that was not adapted to suspensory behavior, respectively. Our results show that E. nyanzae shares three-dimensional shape space with terrestrial papionins, whereas M. bishopi and P. catalaunicus fall within overlapping morphospace shared by Ateles and hylobatids. Morotopithecus bishopi and P. catalaunicus share with hylobatids and brachiating atelids (Ateles and Brachyteles) well-established features such as dorsal lumbar transverse (costal) processes and a newly identified feature in this study, the presence of a convex pillar along the pars interarticularis that forms the lateral borders of the laminae. The latter feature is also shared with E. nyanzae. Together with their large body size estimates, we interpret these results to indicate that E. nyanzae was primarily a pronograde quadruped that may have been semiterrestrial rather than strictly arboreal, while M. bishopi and P. catalaunicus were adapted to both orthogrady and forelimb-dominated climbing and suspension.

A Dryopithecine Talus From Abocador de Can Mata (Vallès-Penedès Basin, NE Iberian Peninsula): Morphometric Affinities and Evolutionary Implications for Hominoid Locomotion

OBJECTIVES

The functional interpretation of postcranial remains of Middle Miocene great apes from Europe (dryopithecines) suggests a combination of quadrupedalism and orthograde behaviors without modern analogs. We provide further insights based on an isolated dryopithecine talus (IPS85037) from the Middle Miocene (11.7 Ma) Abocador de Can Mata locality ACM/C8-B* (Vallès-Penedès Basin, NE Iberian Peninsula), which represents the most complete one known to date.

MATERIAL AND METHODS

We compare the specimen with an extant anthropoid sample (n = 68) and the stem hominoid Ekembo heseloni (KMN RU 2036, ~18 Ma, Kenya) using 3D geometric morphometrics. For the two fossil tali, we assess their phenetic affinities using a between-group principal components analysis (bgPCA), estimate body mass based on centroid size, and make locomotor inferences using a partial least-squares regression (PLSR) between talar shape and locomotor repertoire.

RESULTS

Its large inferred body mass (~38 kg) and the possession of several modern hominoid-like features (albeit combined with more plesiomorphic traits) support the attribution of IPS85037 to a male dryopithecine. The bgPCA indicates that IPS85037 falls close to the extant hominoid variation and is less cercopithecoid-like than that of Ekembo, whose inferred locomotor repertoire is vastly dominated by quadrupedalism (81%). In contrast, the locomotor repertoire inferred from IPS85037 combines important quadrupedal (32%) and vertical climbing/clambering (50%) components with only moderate suspension (10%).

DISCUSSION

Our results align with previous inferences derived from other postcranial elements of Middle Miocene dryopithecines and, given their classification as crown hominoids, support the hypothesis that certain suspensory adaptations shared by extant hylobatids and hominids likely evolved independently.

Reanalysis of Samburupithecus reveals similarities to nyanzapithecines

Samburupithecus kiptalami is an ape found in Late Miocene deposits (ca. 9.5 Ma) of northern Kenya. Initial assessments of the holotype specimen (KNM-SH 8531), a female-gorilla-sized maxillary fragment preserving the postcanine tooth row, noted similarities to gorillas or to African apes more broadly. More recently, primitive features of the maxilla and dentition have been used to propose a stem hominoid position for Samburupithecus. In particular, Samburupithecus shares some dental features with orepithecids (nyanzapithecines and Oreopithecus). To evaluate these competing hypotheses, and investigate possible affinities to oreopithecids, we reanalyzed the dentition of Samburupithecus quantitatively and assessed qualitative dental and maxillary features shared by oreopithecids and Samburupithecus. Based on the results of our analyses, we suggest that Samburupithecus is a late-occurring African oreopithecid, which we regard as a long-lived family of stem hominoids. The inclusion of Samburupithecus within Oreopithecidae highlights that stem hominoids and oreopithecids, in particular, spanned a large range of body sizes, similar to the range of size variation seen among all extant apes. Finally, the presence of oreopithecids in Africa on either side of a notable gap in the Late Miocene African fossil record of apes (from ∼13 to 10 Ma) demonstrates that the rarity of fossil African apes (i.e., nonhominin hominines) during this period is likely due to sampling biases rather than a recent immigration back into Africa from Eurasia.

Muscle synergy in several locomotor modes in chimpanzees and Japanese macaques, and its implications for the evolutionary origin of bipedalism through shared muscle synergies

Recent evidence indicates that human ancestors utilized a combination of quadrupedal walking, climbing, and bipedal walking. Therefore, the origin of bipedalism may be linked to underlying mechanisms supporting diverse locomotor modes. This study aimed to elucidate foundations of varied locomotor modes from the perspective of motor control by identifying muscle synergies and demonstrating similarities in synergy compositions across different locomotor modes in chimpanzees and Japanese macaques. Four muscle synergies were extracted for bipedal and quadrupedal walking in both the chimpanzees and macaques, as well as for vertical climbing in the chimpanzees. Bipedal walking synergies were generally analogous to those observed in quadrupedal walking and vertical climbing. Specifically, the bipedal walking synergies during the stance and swing phase in the chimpanzees were substitutable with those of vertical climbing and quadrupedal walking, respectively. For the macaque, not all bipedal walking synergies exhibited similarities to quadrupedal walking synergies, likely due to instability during the single support phase of bipedalism. These findings suggest that synergies from vertical climbing and quadrupedal walking might be transferred to bipedal walking, as seen in the chimpanzees, and that this sharing of synergies might form a foundation for a diverse range of locomotor capacities including bipedal walking.

Primate Phenotypes: A Multi-Institution Collection of 3D Morphological Data Housed in MorphoSource

The field of phenomics is experiencing unprecedented advances thanks to the rapid growth of morphological quantification based on three-dimensional (3D) imaging, online data repositories, team-oriented collaborations, and open data-sharing policies. In line with these progressions, we present an extensive primate phenotypic dataset comprising >6,000 3D scans (media) representing skeletal morphologies of 386 individual specimens covering all hominoid genera (except humans) and other selected primates. The digitized specimens are housed in physical collections at the American Museum of Natural History, the National Museum of Natural History, the Royal Museum for Central Africa (Belgium), the Cleveland Museum of Natural History, and Stony Brook University. Our technical validation indicates that despite the diverse digitizing devices used to produce the scans, the final 3D models (meshes) can be safely combined to collect comparable morphometric data. The entire dataset (and detailed associated metadata) is freely available through MorphoSource. Hence, these data contribute to empowering the future of primate phenomics and providing a roadmap for future digitization and archiving of digital data from other collections.

Orangutans and chimpanzees produce morphologically varied laugh facesin response to the age and sex of their social partners

Laugh faces of humans play a key role in everyday social interactions as a pervasive tool of communication across contexts. Humans often vary the degree of mouth opening and teeth exposure when producing these facial expressions, which may depend on who their social partner is (e.g., their gender and age as well as their social relationship), serving this way different functions. Although it was found that laugh faces show evolutionary continuity across humans and non-human great apes according to the Principle of Maximum Parsimony, little is known about the function of laugh face variations from an evolutionary perspective. Hence, the present work examined the morphology of laugh faces in orangutan and chimpanzee dyadic play to test if they are modified with dependence on the playmate's characteristics (sex, age and social relationship). In total, we analysed over 600 facial expressions of 14 orangutans and 17 chimpanzees by coding the specific muscle activations (Action Units, i.e. AUs) contributing to these expressions, using OrangFACS and ChimpFACS, respectively. Our results suggest that age difference and, to a lesser extent, playmate sex influence laugh face morphology in both taxa, but in opposite ways. While the orangutans of our study seem to expose their upper teeth (with AU10) and to pull the mouth corners (with AU12) more towards weaker partners (younger and female), possibly to communicate non-hostility, the chimpanzees showed both upper and lower teeth exposure (with AU10 and AU16) more often when interacting with the stronger partners (older individuals), possibly to communicate submissiveness. These findings suggest that the ability of humans to modify laugh faces with dependence on social partner characteristics has most likely evolved from pre-existing traits, going back at least to the last common ancestor of today's great apes, including humans.

Sex differences in positional behavior of chimpanzees (Pan troglodytes schweinfurthii) living in the dry and open habitat of Issa Valley, Tanzania

OBJECTIVES

Many early fossil hominins are associated with savanna-mosaic paleohabitats, and high sexual dimorphism that may reflect differences in positional behavior between sexes. However, reconstructions of hominin behavior and the selective pressures they faced in an open habitat are limited by a lack of studies of extant apes living in contemporary, analogous habitats. Here, we describe adult chimpanzee positional behavior in the savanna-mosaic habitat of the Issa Valley, Tanzania, to test whether Issa chimpanzees show larger sex-differences in positional behavior than their forest-dwelling counterparts.

MATERIALS AND METHODS

We quantified and compared adult locomotor and postural behavior across sexes (6 females, 7 males) in the riparian forest (closed) and miombo woodland (open) vegetation types at Issa Valley (13,743 focal observations). We then compared our results to published data of chimpanzee communities living in more forested habitats.

RESULTS

Issa females and males both spent less time arboreally in open vegetation and showed similar locomotor and postural behavior on the same substrates, notably using a high level of suspensory locomotion when arboreal. Females were, however, more arboreal than males during locomotor behavior, as well as compared with females from other communities. Issa males behaved similarly to males from other communities.

CONCLUSION

Results suggest that open habitats do not elicit less arboreal behaviors in either sex, and may even select for suspensory locomotion to effectively navigate an open canopy. An open habitat may, however, increase sex differences in positional behavior by driving female arboreality. We suggest this is because of higher energetic demands and predator pressures associated with open vegetation, which are likely exaggerated for reproducing females. These results have implications for the interpretation of how sexual dimorphism may influence reconstructions of hominin positional behavior.

First evolutionary insights into the human otolithic system

The human otolithic system (utricle and saccule), housed within the bony vestibule of the inner ear, establishes our sense of balance in conjunction with the semicircular canals. Yet, while the morphological evolution of the semicircular canals is actively explored, comparative morphological analyses of the otolithic system are lacking. This is regrettable because functional links with head orientation suggest the otolithic system could be used to track postural change throughout human evolution and across primates more broadly. In this context, we present the first analysis of the evolution of the human otolithic system within an anthropoid primate setting. Using the vestibule as a morphological proxy for the utricle and saccule, we compare humans to 13 other extant anthropoid species, and use phylogenetically-informed methods to find correlations with body size, endocranial flexion, and head-neck posture. Our results, obtained through micro-CT of 136 inner ears, reveal two major evolutionary transitions in hominoids, leading to distinctive vestibular morphology in humans, characterized by otolithic morphology resembling squirrel monkeys (possibly due to reversal), with a pronounced supraovalic fossa. Finally, we find a positional signal embedded in the anthropoid bony vestibule, providing the foundation to further explore the evolution of human head-neck posture using inner ear morphology.

Molar enamel-dentine junction shape of Pliobates cataloniae and other Iberian pliopithecoids

The phylogenetic relationships of the small-bodied catarrhine Pliobates cataloniae (∼11.6 Ma, NE Iberian Peninsula) have been controversial since its original description. However, the recent report of additional dentognathic remains has supported its crouzeliid pliopithecoid status. Based on the available hypodigm, the molar enamel-dentine junction (EDJ) shape of P. cataloniae is compared with that of other pliopithecoids from the same basin as well as both extinct and extant hominoids to further evaluate its pliopithecoid affinities. We also quantitatively compare the EDJ shape among these taxa by means of landmark-based three-dimensional geometric morphometrics using principal component analysis (PCA), canonical variate analysis, and between-group PCA. Permutation tests are performed to test whether Pliobates variation exceeds that of extant hominoid genera. Results indicate that Pliobates is similar in molar EDJ shape to other pliopithecoids, particularly crouzeliids. The variation displayed by Pliobates upper molars is less marked at the EDJ level than at the outer enamel surface, probably owing to differential enamel wear and intraspecific differences in enamel thickness. Multivariate analyses of EDJ shape show that all pliopithecoids (including Pliobates) cluster together in the PCAs, canonical variate analyses, and between-group PCAs and occupy a different portion of the morphospaces from extinct and extant hominoids. Posterior and typicality probabilities strongly support the classification of Pliobates as a pliopithecoid, wheras permutation tests fail to reject the single-genus hypothesis for the P. cataloniae hypodigm. We conclude that P. cataloniae is a crouzeliid pliopithecoid, as recently supported by cladistic analyses of craniodental characters, and that previous cladistic results that supported a stem hominoid status are attributable to postcranial convergences with crown hominoids. Our results further highlight the potential of three-dimensional geometric morphometrics analyses of the EDJ shape for better informing fossil primate alpha-taxonomy by means of quantitatively testing hypotheses about tooth shape variation.

Brain Evolution in the Times of the Pandemic and Multimedia

BACKGROUND

In this paper, we argue that recent unprecedented social changes arising from social media and the internet represent powerful behavioral and environmental forces that are driving human evolutionary adaptive responses in a way that might reshape our brain and the way it perceives reality and interacts with it. These forces include decreases in physical activity, decreases in exposure to light, and face-to-face social interactions, as well as diminished predictability in biological rhythms (i.e., the sleep cycle is no longer dictated by natural light exposure and season).

SUMMARY

We discuss the roles of stress and of creativity and adaptability in Homo sapiens evolution and propose mechanisms for human adaptation to the new forces including epigenetic mechanisms, gene-culture coevolution, and novel mechanisms of evolution of the nervous system.

KEY MESSAGES

We present the provocative idea that evolution under the strong selective pressures of today's society could ultimately enable H. sapiens to thrive despite social, physical, circadian, and cultural deprivation and possible neurological disease, and thus withstand the loss of factors that contribute to H. sapiens survival of today. The new H. sapiens would flourish under a lifestyle in which the current form would feel undervalued and replaceable.

And the stars look down: science beyond the finite : From prehistorical science to postscience

Modern science has brought undisputable welfare to mankind, but also harmful consequences, and it has to face great challenges to find a way out of the current global crisis.

Middle and Late Pleistocene Denisovan subsistence at Baishiya Karst Cave

Genetic and fragmented palaeoanthropological data suggest that Denisovans were once widely distributed across eastern Eurasia1-3. Despite limited archaeological evidence, this indicates that Denisovans were capable of adapting to a highly diverse range of environments. Here we integrate zooarchaeological and proteomic analyses of the late Middle to Late Pleistocene faunal assemblage from Baishiya Karst Cave on the Tibetan Plateau, where a Denisovan mandible and Denisovan sedimentary mitochondrial DNA were found3,4. Using zooarchaeology by mass spectrometry, we identify a new hominin rib specimen that dates to approximately 48-32 thousand years ago (layer 3). Shotgun proteomic analysis taxonomically assigns this specimen to the Denisovan lineage, extending their presence at Baishiya Karst Cave well into the Late Pleistocene. Throughout the stratigraphic sequence, the faunal assemblage is dominated by Caprinae, together with megaherbivores, carnivores, small mammals and birds. The high proportion of anthropogenic modifications on the bone surfaces suggests that Denisovans were the primary agent of faunal accumulation. The chaîne opératoire of carcass processing indicates that animal taxa were exploited for their meat, marrow and hides, while bone was also used as raw material for the production of tools. Our results shed light on the behaviour of Denisovans and their adaptations to the diverse and fluctuating environments of the late Middle and Late Pleistocene of eastern Eurasia.

The taxonomy of Sahelanthropus tchadensis from a craniometric perspective

Sahelanthropus tchadensis has raised much debate since its initial discovery in Chad in 2001, given its controversial classification as the earliest representative of the hominin lineage. This debate extends beyond the phylogenetic position of the species, and includes several aspects of its habitual behavior, especially in what regards its locomotion. The combination of ancestral and derived traits observed in the fossils associated with the species has been used to defend different hypotheses related to its relationship to hominins. Here, the cranial morphology of Sahelanthropus tchadensis was assessed through 16 linear craniometric measurements, and compared to great apes and hominins through Principal Component Analysis based on size and shape and shape information alone. The results show that S. tchadensis share stronger morphological affinities with hominins than with apes for both the analysis that include size information and the one that evaluates shape alone. Since TM 266-01-060-1 shows a strong morphological affinity with the remaining hominins represented in the analysis, our results support the initial interpretations that S. tchadensis represents an early specimen of our lineage or a stem basal lineage more closely related to hominins than to Panini.

Evolution of Glutamate Metabolism via GLUD2 Enhances Lactate-Dependent Synaptic Plasticity and Complex Cognition

Human evolution is characterized by rapid brain enlargement and the emergence of unique cognitive abilities. Besides its distinctive cytoarchitectural organization and extensive inter-neuronal connectivity, the human brain is also defined by high rates of synaptic, mainly glutamatergic, transmission, and energy utilization. While these adaptations' origins remain elusive, evolutionary changes occurred in synaptic glutamate metabolism in the common ancestor of humans and apes via the emergence of GLUD2, a gene encoding the human glutamate dehydrogenase 2 (hGDH2) isoenzyme. Driven by positive selection, hGDH2 became adapted to function upon intense excitatory firing, a process central to the long-term strengthening of synaptic connections. It also gained expression in brain astrocytes and cortical pyramidal neurons, including the CA1-CA3 hippocampal cells, neurons crucial to cognition. In mice transgenic for GLUD2, theta-burst-evoked long-term potentiation (LTP) is markedly enhanced in hippocampal CA3-CA1 synapses, with patch-clamp recordings from CA1 pyramidal neurons revealing increased sNMDA receptor currents. D-lactate blocked LTP enhancement, implying that glutamate metabolism via hGDH2 potentiates L-lactate-dependent glia-neuron interaction, a process essential to memory consolidation. The transgenic (Tg) mice exhibited increased dendritic spine density/synaptogenesis in the hippocampus and improved complex cognitive functions. Hence, enhancement of neuron-glia communication, via GLUD2 evolution, likely contributed to human cognitive advancement by potentiating synaptic plasticity and inter-neuronal connectivity.

Conserved patterns and locomotor-related evolutionary constraints in the hominoid vertebral column

The evolution of the hominoid lineage is characterized by pervasive homoplasy, notably in regions such as the vertebral column, which plays a central role in body support and locomotion. Few isolated and fewer associated vertebrae are known for most fossil hominoid taxa, but identified specimens indicate potentially high levels of convergence in terms of both form and number. Homoplasy thus complicates attempts to identify the anatomy of the last common ancestor of hominins and other taxa and stymies reconstructions of evolutionary scenarios. One way to clarify the role of homoplasy is by investigating constraints via phenotypic integration, which assesses covariation among traits, shapes evolutionary pathways, and itself evolves in response to selection. We assessed phenotypic integration and evolvability across the subaxial (cervical, thoracic, lumbar, sacral) vertebral column of macaques (n = 96), gibbons (n = 77), chimpanzees (n = 92), and modern humans (n = 151). We found a mid-cervical cluster that may have shifted cranially in hominoids, a persistent thoracic cluster that is most marked in chimpanzees, and an expanded lumbosacral cluster in hominoids that is most expanded in gibbons. Our results highlight the highly conserved nature of the vertebral column. Taxa appear to exploit existing patterns of integration and ontogenetic processes to shift, expand, or reduce cluster boundaries. Gibbons appear to be the most highly derived taxon in our sample, possibly in response to their highly specialized locomotion.

Ghosts of extinct apes: genomic insights into African hominid evolution

We are accustomed to regular announcements of new hominin fossils. There are now some 6000 hominin fossils, and up to 31 species. However, where are the announcements of African ape fossils? The answer is that there are almost none. Our knowledge of African ape evolution is based entirely on genomic analyses, which show that extant diversity is very young. This contrasts with the extensive and deep diversity of hominins known from fossils. Does this difference point to low and late diversification of ape lineages, or high rates of extinction? The comparative evolutionary dynamics of African hominids are central to interpreting living ape adaptations, as well as understanding the patterns of hominin evolution and the nature of the last common ancestor.

Behavioral and phylogenetic correlates of limb length proportions in extant apes and monkeys: Implications for interpreting hominin fossils

The body proportions of extant animals help inform inferences about the behaviors of their extinct relatives, but relationships between body proportions, behavior, and phylogeny in extant primates remain unclear. Advances in behavioral data, molecular phylogenies, and multivariate analytical tools make it an opportune time to perform comprehensive comparative analyses of primate traditional limb length proportions (e.g., intermembral, humerofemoral, brachial, and crural indices), body size-adjusted long bone proportions, and principal components. In this study we used a mix of newly-collected and published data to investigate whether and how the limb length proportions of a diverse sample of primates, including monkeys, apes, and modern humans, are influenced by behavior and phylogeny. We reconfirm that the intermembral index, followed by the first principal component of traditional limb length proportions, is the single most effective variable distinguishing hominoids and other anthropoids. Combined limb length proportions and positional behaviors are strongly correlated in extant anthropoid groups, but phylogeny is a better predictor of limb length proportion variation than of behavior. We confirm convergences between members of the Atelidae and extant apes (especially Pan), members of the Hylobatidae and Pongo, and a potential divergence of Presbytis limb proportions from some other cercopithecoids, which correlate with adaptations for forelimb-dominated behaviors in some colobines. Collectively, these results substantiate hypotheses indicating that extinct hominins and other hominoid taxa can be distinguished by analyzing combinations of their limb length proportions at different taxonomic levels. From these results, we hypothesize that fossil skeletons characterized by notably disparate limb length proportions are unlikely to have exhibited similar behavioral patterns.

Cardiac differentiation of chimpanzee induced pluripotent stem cell lines with different subspecies backgrounds

The comparative analysis between humans and non-human primates is an instrumental approach for elucidating the evolutional traits and disease propensity of humans. However, in primates, cross-species analyses of their developmental events have encountered constraints because of the ethical and technical limitations in available sample collection, sequential monitoring, and manipulations. In an endeavor to surmount these challenges, in recent years, induced pluripotent stem cells (iPSCs) have garnered escalating interest as an in vitro tool for cross-species analyses between humans and non-human primates. Meanwhile, compared to humans, there is less information on in vitro differentiation of non-human primate iPSCs, and their genetic diversity including subspecies may cause different eligibility to in vitro differentiation methods. Therefore, antecedent to embarking on a comparative analysis to humans, it is a prerequisite to develop the efficacious methodologies for in vitro differentiation regardless of the intraspecies genetic background in non-human primates. In this study, we executed the in vitro differentiation of cardiomyocytes from four chimpanzee iPSC lines with different subspecies and individual backgrounds. To induce cardiomyocytes from chimpanzee iPSCs, we evaluated our methodology for in vitro cardiac differentiation of human iPSCs. Eventually, with minor alterations, our cardiac differentiation method was applicable to all chimpanzee iPSC lines tested as assessed by the expression of cardiac marker genes and the beating ability. Hence, our in vitro differentiation method will advance iPSC-based research of chimpanzee cardiac development and also hold possible utility to cross-species analyses among primate species.

The Miocene primate Pliobates is a pliopithecoid

The systematic status of the small-bodied catarrhine primate Pliobates cataloniae, from the Miocene (11.6 Ma) of Spain, is controversial because it displays a mosaic of primitive and derived features compared with extant hominoids (apes and humans). Cladistic analyses have recovered Pliobates as either a stem hominoid or as a pliopithecoid stem catarrhine (i.e., preceding the cercopithecoid-hominoid divergence). Here, we describe additional dental remains of P. cataloniae from another locality that display unambiguous synapomorphies of crouzeliid pliopithecoids. Our cladistic analyses support a close phylogenetic link with poorly-known small crouzeliids from Europe based on (cranio)dental characters but recover pliopithecoids as stem hominoids when postcranial characters are included. We conclude that Pliobates is a derived stem catarrhine that shows postcranial convergences with modern apes in the elbow and wrist joints-thus clarifying pliopithecoid evolution and illustrating the plausibility of independent acquisition of postcranial similarities between hylobatids and hominids.

A comparative study of muscle activity and synergies during walking in baboons and humans

Bipedal locomotion was a major functional change during hominin evolution, yet, our understanding of this gradual and complex process remains strongly debated. Based on fossil discoveries, it is possible to address functional hypotheses related to bipedal anatomy, however, motor control remains intangible with this approach. Using comparative models which occasionally walk bipedally has proved to be relevant to shed light on the evolutionary transition toward habitual bipedalism. Here, we explored the organization of the neuromuscular control using surface electromyography (sEMG) for six extrinsic muscles in two baboon individuals when they walk quadrupedally and bipedally on the ground. We compared their muscular coordination to five human subjects walking bipedally. We extracted muscle synergies from the sEMG envelopes using the non-negative matrix factorization algorithm which allows decomposing the sEMG data in the linear combination of two non-negative matrixes (muscle weight vectors and activation coefficients). We calculated different parameters to estimate the complexity of the sEMG signals, the duration of the activation of the synergies, and the generalizability of the muscle synergy model across species and walking conditions. We found that the motor control strategy is less complex in baboons when they walk bipedally, with an increased muscular activity and muscle coactivation. When comparing the baboon bipedal and quadrupedal pattern of walking to human bipedalism, we observed that the baboon bipedal pattern of walking is closer to human bipedalism for both baboons, although substantial differences remain. Overall, our findings show that the muscle activity of a non-adapted biped effectively fulfills the basic mechanical requirements (propulsion and balance) for walking bipedally, but substantial refinements are possible to optimize the efficiency of bipedal locomotion. In the evolutionary context of an expanding reliance on bipedal behaviors, even minor morphological alterations, reducing muscle coactivation, could have faced strong selection pressure, ultimately driving bipedal evolution in hominins.

Lufengpithecus inner ear provides evidence of a common locomotor repertoire ancestral to human bipedalism

Various lines of evidence have been used to infer the origin of human bipedalism, but the paucity of hominoid postcranial fossils and the diversity of inferred locomotor modes have tended to confound the reconstruction of ancestral morphotypes. Examination of the bony labyrinth morphology of the inner ear of extinct and living hominoids provides independent evidence for inferring the evolution of hominoid locomotor patterns. New computed tomography data and morphometric analyses of the Late Miocene ape Lufengpithecus indicate that it and other stem great apes possess labyrinths similar to one another and show that hominoids initially evolved from a positional repertoire that included orthogrady, below-branch forelimb suspension and progression, above-branch bipedalism, climbing, clambering, and leaping (hylobatid-like) to one that comprised above-branch quadrupedalism, below-branch forelimb suspension, vertical climbing, limited leaping, terrestrial quadrupedal running and walking, possibly with knuckle walking, and short bouts of bipedalism (chimpanzee-like). The bony labyrinth morphology of Lufengpithecus indicates that it probably conforms more closely to the last common ancestors of crown hominoids and hominids in its locomotor behavior than do other Miocene hominoids. Human bipedalism evolved from this common archetypal Lufengpithecus-like locomotor repertoire. The low evolutionary rate of semicircular canal morphology suggests that Lufengpithecus experienced a relative stasis in locomotor behavior, probably due to the uplift of the Tibetan Plateau, which created a stable environment in the Miocene of southwestern China.

Biomechanical and taxonomic diversity in the Early Pleistocene in East Africa: Structural analysis of a recently discovered femur shaft from Olduvai Gorge (bed I)

Recent Plio-Pleistocene hominin findings have revealed the complexity of human evolutionary history and the difficulties involved in its interpretation. Moreover, the study of hominin long bone remains is particularly problematic, since it commonly depends on the analysis of fragmentary skeletal elements that in many cases are merely represented by small diaphyseal portions and appear in an isolated fashion in the fossil record. Nevertheless, the study of the postcranial skeleton is particularly important to ascertain locomotor patterns. Here we report on the discovery of a robust hominin femoral fragment (OH 84) at the site of Amin Mturi Korongo dated to 1.84 Ma (Olduvai Bed I). External anatomy and internal bone structure of OH 84 were analyzed and compared with previously published data for modern humans and chimpanzees, as well as for Australopithecus, Paranthropus and Homo specimens ranging from the Late Pliocene to Late Pleistocene. Biomechanical analyses based on transverse cross-sections and the comparison of OH 84 with another robust Olduvai specimen (OH 80) suggest that OH 84 might be tentatively allocated to Paranthropus boisei. More importantly, the identification of a unique combination of traits in OH 84 could indicate both terrestrial bipedalism and an arboreal component in the locomotor repertoire of this individual. If interpreted correctly, OH 84 could thus add to the already mounting evidence of substantial locomotor diversity among Early Pleistocene hominins. Likewise, our results also highlight the difficulties in accurately interpreting the link between form and function in the human fossil record based on fragmentary remains, and ultimately in distinguishing between coeval hominin groups due to the heterogeneous pattern of inter- and intraspecific morphological variability detected among fossil femora.

Covariation between the shape and mineralized tissues of the rib cross section in Homo sapiens, Pan troglodytes and Sts 14

OBJECTIVES

Studying rib torsion is crucial for understanding the evolution of the hominid ribcage. Interestingly, there are variables of the rib cross section that could be associated with rib torsion and, consequently, with the morphology of the thorax. The aim of this research is to conduct a comparative study of the shape and mineralized tissues of the rib cross section in different hominids to test for significant differences and, if possible, associate them to different thoracic morphotypes.

MATERIALS AND METHODS

The sample consists of the rib cross sections at the midshaft taken from 10 Homo sapiens and 10 Pan troglodytes adult individuals, as well as from A. africanus Sts 14. The shape of these rib cross sections was quantified using geometric morphometrics, while the mineralized tissues were evaluated using the compartmentalization index. Subsequently, covariation between both parameters was tested by a Spearman's ρ test, a permutation test and a linear regression.

RESULTS

Generally, P. troglodytes individuals exhibit rib cross sections that are rounder and more mineralized compared to those of H. sapiens. However, the covariation between both parameters was only observed in typical ribs (levels 3-10). Although covariation was not found in the rib cross sections of Sts 14, their parameters are closer to P. troglodytes.

DISCUSSION

On the one hand, the differences observed in the rib cross sections between H. sapiens and P. troglodytes might be related to different degrees of rib torsion and, consequently, to different thoracic 3D configurations. These findings can be functionally explained by considering their distinct modes of breathing and locomotion. On the other hand, although the rib cross sections belonging to Sts 14 are more similar to those of P. troglodytes, previous publications determined that their overall morphology is closer to modern humans. This discrepancy could reflect a diversity of post-cranial adaptations in Australopithecus.

The KIR repertoire of a West African chimpanzee population is characterized by limited gene, allele, and haplotype variation

Introduction

The killer cell immunoglobulin-like receptors (KIR) play a pivotal role in modulating the NK cell responses, for instance, through interaction with major histocompatibility complex (MHC) class I molecules. Both gene systems map to different chromosomes but co-evolved during evolution. The human KIR gene family is characterized by abundant allelic polymorphism and copy number variation. In contrast, our knowledge of the KIR repertoire in chimpanzees is limited to 39 reported alleles, with no available population data. Only three genomic KIR region configurations have been mapped, and seventeen additional ones were deduced by genotyping.

Methods

Previously, we documented that the chimpanzee MHC class I repertoire has been skewed due to an ancient selective sweep. To understand the depth of the sweep, we set out to determine the full-length KIR transcriptome - in our MHC characterized pedigreed West African chimpanzee cohort - using SMRT sequencing (PacBio). In addition, the genomic organization of 14 KIR haplotypes was characterized by applying a Cas9-mediated enrichment approach in concert with long-read sequencing by Oxford Nanopore Technologies.

Results

In the cohort, we discovered 35 undescribed and 15 already recorded Patr-KIR alleles, and a novel hybrid KIR gene. Some KIR transcripts are subject to evolutionary conserved alternative splicing events. A detailed insight on the KIR region dynamics (location and order of genes) was obtained, however, only five new KIR region configurations were detected. The population data allowed to investigate the distribution of the MHC-C1 and C2-epitope specificity of the inhibitory lineage III KIR repertoire, and appears to be skewed towards C2.

Discussion

Although the KIR region is known to evolve fast, as observed in other primate species, our overall conclusion is that the genomic architecture and repertoire in West African chimpanzees exhibit only limited to moderate levels of variation. Hence, the ancient selective sweep that affected the chimpanzee MHC class I region may also have impacted the KIR system.

Paleoenvironmental inferences on the Late Miocene hominoid-bearing site of Can Llobateres (NE Iberian Peninsula): An ecometric approach based on functional dental traits

Hispanopithecus laietanus from the Late Miocene (9.8 Ma) of Can Llobateres 1 (CLL1; Vallès-Penedès Basin, NE Iberian Peninsula) represents one of the latest occurrences of fossil apes in Western mainland Europe, where they are last recorded at ∼9.5 Ma. The paleoenvironment of CLL1 is thus relevant for understanding the extinction of European hominoids. To refine paleoenvironmental inferences for CLL1, we apply ecometric models based on functional crown type (FCT) variables-a scoring scheme devised to capture macroscopic functional traits of occlusal shape and wear surfaces of herbivorous large mammal molars. Paleotemperature and paleoprecipitation estimates for CLL1 are provided based on published regional regression models linking average FCT of large herbivorous mammal communities to climatic conditions. A mapping to Whittaker's present-day biome classification is also attempted based on these estimates, as well as a case-based reasoning via canonical variate analysis of FCT variables from five relevant biomes. Estimates of mean annual temperature (25 °C) and mean annual precipitation (881 mm) classify CLL1 as a tropical seasonal forest/savanna, only in partial agreement with the canonical variate analysis results, which classify CLL1 as a tropical rainforest with a higher probability. The former biome agrees better with previous inferences derived from fossil plants and mammals, as well as preliminary isotopic data. The misclassification of CLL1 as a tropical forest is attributed to the mixture of forest-adapted taxa with others adapted to more open environments, given that faunal and plant composition indicates the presence of a dense wetland/riparian forest with more open woodlands nearby. The tested FCT ecometric approaches do not provide unambiguous biome classification for CLL1. Nevertheless, our results are consistent with those from other approaches, thus suggesting that FCT variables are potentially useful to investigate paleoenvironmental changes through time and space-including those that led to the extinction of European Miocene apes.

Paleoenvironments of Late Devonian tetrapods in China

The major evolutionary transition from fish to amphibian included Late Devonian tetrapods that were neither fish nor amphibian. They had thick necks and small limbs with many digits on elongate flexuous bodies more suitable for water than land. Habitats of Devonian tetrapods are of interest in assessing selective pressures on their later evolution for land within three proposed habitats: 1, tidal flats, 2, desert ponds, and 3, woodland streams. Here we assess paleoenvironments of the Late Devonian tetrapod Sinostega from paleosols in Shixiagou Canyon near Zhongning, Ningxia, China. Fossil tetrapods, fish, molluscs, and plants of the Zhongning Formation are associated with different kinds of paleosols, representing early successional vegetation, seasonal wetlands, desert shrublands, and riparian woodlands, and paleoclimates ranging from semiarid moderately seasonal to monsoonal subhumid. The tetrapod Sinostega was found in a paleochannel of a meandering stream below a deep-calcic paleosol supporting well drained progymnosperm woodland in a monsoonal subhumid paleoclimate. This habitat is similar to that of the tetrapods Densignathus, Hynerpeton, and an indeterminate watcheeriid from Pennsylvania, USA. Chinese and Pennsylvanian Late Devonian tetrapods lived in productive woodland streams, choked with woody debris as a refuge from large predators. Habitats of other Devonian tetrapods have yet to be assessed from studies of associated paleosols as evidence for their ancient climate and vegetation.

Implications of outgroup selection in the phylogenetic inference of hominoids and fossil hominins

Understanding the phylogenetic relationships among hominins and other hominoid species is critical to the study of human origins. However, phylogenetic inferences are dependent on both the character data and taxon sampling used. Previous studies of hominin phylogenetics have used Papio and Colobus as outgroups in their analyses; however, these extant monkeys possess many derived traits that may confound the polarities of morphological changes among living apes and hominins. Here, we consider Victoriapithecus and Ekembo as more suitable outgroups. Both Victoriapithecus and Ekembo are anatomically well known and are widely accepted as morphologically primitive stem cercopithecoid and hominoid taxa, respectively, making them more appropriate for inferring polarity for later-occurring hominoid- and hominin-focused analyses. Craniodental characters for both taxa were scored and then added to a previously published matrix of fossil hominin and extant hominoid taxa, replacing outgroups Papio and Colobus over a series of iterative analyses using both parsimony and Bayesian inference methods. Neither the addition nor replacement of outgroup taxa changed tree topology in any analysis. Importantly, however, bootstrap support values and posterior probabilities for nodes supporting their relationships generally increased compared to previous analyses. These increases were the highest at extant hominoid and basal hominin nodes, recovering the molecular ape phylogeny with considerably higher support and strengthening the inferred relationships among basal hominins. Interestingly, however, the inclusion of both extant and fossil outgroups reduced support for the crown hominid node. Our findings suggest that, in addition to improving character polarity estimation, including fossil outgroups generally strengthens confidence in relationships among extant hominoid and basal hominins.

The reconstructed cranium of Pierolapithecus and the evolution of the great ape face

Pierolapithecus catalaunicus (~12 million years ago, northeastern Spain) is key to understanding the mosaic nature of hominid (great ape and human) evolution. Notably, its skeleton indicates that an orthograde (upright) body plan preceded suspensory adaptations in hominid evolution. However, there is ongoing debate about this species, partly because the sole known cranium, preserving a nearly complete face, suffers from taphonomic damage. We 1) carried out a micro computerized tomography (CT) based virtual reconstruction of the Pierolapithecus cranium, 2) assessed its morphological affinities using a series of two-dimensional (2D) and three-dimensional (3D) morphometric analyses, and 3) modeled the evolution of key aspects of ape face form. The reconstruction clarifies many aspects of the facial morphology of Pierolapithecus. Our results indicate that it is most similar to great apes (fossil and extant) in overall face shape and size and is morphologically distinct from other Middle Miocene apes. Crown great apes can be distinguished from other taxa in several facial metrics (e.g., low midfacial prognathism, relatively tall faces) and only some of these features are found in Pierolapithecus, which is most consistent with a stem (basal) hominid position. The inferred morphology at all ancestral nodes within the hominoid (ape and human) tree is closer to great apes than to hylobatids (gibbons and siamangs), which are convergent with other smaller anthropoids. Our analyses support a hominid ancestor that was distinct from all extant and fossil hominids in overall facial shape and shared many features with Pierolapithecus. This reconstructed ancestral morphotype represents a testable hypothesis that can be reevaluated as new fossils are discovered.

A comparative approach for characterizing the relationship among morphology, range-of-motion and locomotor behaviour in the primate shoulder

Shoulder shape directly impacts forelimb function by contributing to glenohumeral (GH) range-of-motion (ROM). However, identifying traits that contribute most to ROM and visualizing how they do so remains challenging, ultimately limiting our ability to reconstruct function and behaviour in fossil species. To address these limitations, we developed an in silico proximity-driven model to simulate and visualize three-dimensional (3D) GH rotations in living primate species with diverse locomotor profiles, identify those shapes that are most predictive of ROM using geometric morphometrics, and apply subsequent insights to interpret function and behaviour in the fossil hominin Australopithecus sediba. We found that ROM metrics that incorporated 3D rotations best discriminated locomotor groups, and the magnitude of ROM (mobility) was decoupled from the anatomical location of ROM (e.g. high abduction versus low abduction). Morphological traits that enhanced mobility were decoupled from those that enabled overhead positions, and all non-human apes possessed the latter but not necessarily the former. Model simulation in A. sediba predicted high mobility and a ROM centred at lower abduction levels than in living apes but higher than in modern humans. Together these results identify novel form-to-function relationships in the shoulder and enhance visualization tools to reconstruct past function and behaviour.

Are vipers prototypic fear-evoking snakes? A cross-cultural comparison of Somalis and Czechs

Snakes are known as highly fear-evoking animals, eliciting preferential attention and fast detection in humans. We examined the human fear response to snakes in the context of both current and evolutionary experiences, conducting our research in the cradle of humankind, the Horn of Africa. This region is characterized by the frequent occurrence of various snake species, including deadly venomous viperids (adders) and elapids (cobras and mambas). We conducted experiments in Somaliland and compared the results with data from Czech respondents to address the still unresolved questions: To which extent is human fear of snakes affected by evolutionary or current experience and local culture? Can people of both nationalities recognize venomous snakes as a category, or are they only afraid of certain species that are most dangerous in a given area? Are respondents of both nationalities equally afraid of deadly snakes from both families (Viperidae, Elapidae)? We employed a well-established picture-sorting approach, consisting of 48 snake species belonging to four distinct groups. Our results revealed significant agreement among Somali as well as Czech respondents. We found a highly significant effect of the stimulus on perceived fear in both populations. Vipers appeared to be the most salient stimuli in both populations, as they occupied the highest positions according to the reported level of subjectively perceived fear. The position of vipers strongly contrasts with the fear ranking of deadly venomous elapids, which were in lower positions. Fear scores of vipers were significantly higher in both populations, and their best predictor was the body width of the snake. The evolutionary, cultural, and cognitive aspects of this phenomenon are discussed.

The first Miocene fossils from coastal woodlands in the southern East African Rift

The Miocene was a key time in the evolution of African ecosystems witnessing the origin of the African apes and the isolation of eastern coastal forests through an expanding arid corridor. Until recently, however, Miocene sites from the southeastern regions of the continent were unknown. Here, we report the first Miocene fossil teeth from the shoulders of the Urema Rift in Gorongosa National Park, Mozambique. We provide the first 1) radiometric ages of the Mazamba Formation, 2) reconstructions of paleovegetation in the region based on pedogenic carbonates and fossil wood, and 3) descriptions of fossil teeth. Gorongosa is unique in the East African Rift in combining marine invertebrates, marine vertebrates, reptiles, terrestrial mammals, and fossil woods in coastal paleoenvironments. The Gorongosa fossil sites offer the first evidence of woodlands and forests on the coastal margins of southeastern Africa during the Miocene, and an exceptional assemblage of fossils including new species.

Downclimbing and the evolution of ape forelimb morphologies

The forelimbs of hominoid primates (apes) are decidedly more flexible than those of monkeys, especially at the shoulder, elbow and wrist joints. It is tempting to link the greater mobility of these joints to the functional demands of vertical climbing and below-branch suspension, but field-based kinematic studies have found few differences between chimpanzees and monkeys when comparing forelimb excursion angles during vertical ascent (upclimbing). There is, however, a strong theoretical argument for focusing instead on vertical descent (downclimbing), which motivated us to quantify the effects of climbing directionality on the forelimb kinematics of wild chimpanzees (Pan troglodytes) and sooty mangabeys (Cercocebus atys). We found that the shoulders and elbows of chimpanzees and sooty mangabeys subtended larger joint angles during bouts of downclimbing, and that the magnitude of this difference was greatest among chimpanzees. Our results cast new light on the functional importance of downclimbing, while also burnishing functional hypotheses that emphasize the role of vertical climbing during the evolution of apes, including the human lineage.

The evolution of hominoid locomotor versatility: Evidence from Moroto, a 21 Ma site in Uganda

Living hominoids are distinguished by upright torsos and versatile locomotion. It is hypothesized that these features evolved for feeding on fruit from terminal branches in forests. To investigate the evolutionary context of hominoid adaptive origins, we analyzed multiple paleoenvironmental proxies in conjunction with hominoid fossils from the Moroto II site in Uganda. The data indicate seasonally dry woodlands with the earliest evidence of abundant C₄ grasses in Africa based on a confirmed age of 21 million years ago (Ma). We demonstrate that the leaf-eating hominoid Morotopithecus consumed water-stressed vegetation, and postcrania from the site indicate ape-like locomotor adaptations. These findings suggest that the origin of hominoid locomotor versatility is associated with foraging on leaves in heterogeneous, open woodlands rather than forests.

Homo medicus: The transition to meat eating increased pathogen pressure and the use of pharmacological plants in Homo

The human lineage transitioned to a more carnivorous niche 2.6 mya and evolved a large body size and slower life history, which likely increased zoonotic pathogen pressure. Evidence for this increase includes increased zoonotic infections in modern hunter-gatherers and bushmeat hunters, exceptionally low stomach pH compared to other primates, and divergence in immune-related genes. These all point to change, and probably intensification, in the infectious disease environment of Homo compared to earlier hominins and other apes. At the same time, the brain, an organ in which immune responses are constrained, began to triple in size. We propose that the combination of increased zoonotic pathogen pressure and the challenges of defending a large brain and body from pathogens in a long-lived mammal, selected for intensification of the plant-based self-medication strategies already in place in apes and other primates. In support, there is evidence of medicinal plant use by hominins in the middle Paleolithic, and all cultures today have sophisticated, plant-based medical systems, add spices to food, and regularly consume psychoactive plant substances that are harmful to helminths and other pathogens. We propose that the computational challenges of discovering effective plant-based treatments, the consequent ability to consume more energy-rich animal foods, and the reduced reliance on energetically-costly immune responses helped select for increased cognitive abilities and unique exchange relationships in Homo. In the story of human evolution, which has long emphasized hunting skills, medical skills had an equal role to play.

A reassessment of the distinctiveness of dryopithecine genera from the Iberian Miocene based on enamel-dentine junction geometric morphometric analyses

A vast diversity of catarrhines primates has been uncovered in the Middle to Late Miocene (12.5-9.6 Ma) of the Vallès-Penedès Basin (northeastern Spain), including several hominid species (Pierolapithecus catalaunicus, Anoiapithecus brevirostris, Dryopithecus fontani, Hispanopithecus laietanus, and Hispanopithecus crusafonti) plus some remains attributed to 'Sivapithecus' occidentalis (of uncertain taxonomic validity). However, Pierolapithecus and Anoiapithecus have also been considered junior synonyms of Dryopithecus by some authors, which entail a lower generic diversity and an inflated intrageneric variation of the latter genus. Since the distinction of these taxa partly relies on dental features, the detailed and quantitative analysis of tooth shape might help disentangling the taxonomic diversity of these Miocene hominids. Using diffeomorphic surface matching and three-dimensional geometric morphometrics, we investigate the enamel-dentine junction shape (which is a reliable taxonomic proxy) of these Miocene hominids, with the aim of investigating their degree of intra- and intergeneric variation compared with that of extant great ape genera. We conducted statistical analyses, including between-group principal component analyses, canonical variate analyses, and permutation tests, to investigate whether the individual and combined (i.e., Dryopithecus s.l.) variation of the extinct genera exceeds that of the extant great apes. Our results indicate that Pierolapithecus, Anoiapithecus, Dryopithecus, and Hispanopithecus show morphological differences of enamel-dentine junction shape relative to the extant great apes that are consistent with their attribution to different genera. Specifically, the variation displayed by the Middle Miocene taxa combined exceeds that of extant great ape genera, thus undermining the single-genus hypothesis. 'Sivapithecus' occidentalis specimens fall close to Dryopithecus but in the absence of well-preserved comparable teeth for Pierolapithecus and Anoiapithecus, their taxonomic attribution remains uncertain. Among the Hispanopithecus sample, IPS1802 from Can Llobateres stands out and might either be an outlier in terms of morphology, or represent another dryopithecine taxon.

Palaeobotanical evidence reveals the living conditions of Miocene Lufengpithecus in East Asia

BACKGROUND

Understanding the relationship between human evolution and environmental changes is the key to lifting the veil on human origin. The hypothesis that environmental changes triggered the divergence of humans from apes (ca. 9.3-6.5 million years ago, Ma) has been poorly tested because of limited continuous environmental data from fossil localities. Lufengpithecus (12.5-6.0 Ma) found on the southeastern margin of the Tibetan Plateau (SEMTP) across the ape-human split provides a good chance for testing this hypothesis.

RESULTS

Here, we reconstructed the habitats of L. keiyuanensis (12.5-11.6 Ma) with comprehensive vegetation, climate, and potential food web data by palaeobotanical evidence, together with other multidisciplinary data and partly tested the environment-driven hypothesis by revealing the living conditions of Lufengpithecus.

CONCLUSION

A detailed comparison of hominoids on different continents reveals their behaviour and fate divergence across the ape-human split against the background of global climate change, i.e., the stable living conditions of SEMTP not only provided a so-called 'refuge' for arboreal Lufengpithecus but also acted as a 'double-edged sword', preventing their further evolution while vegetation shifts in East Africa probably stimulated the emergence of human bipedalism, and the intense climatic changes in Europe possibly prevented those hominoids from surviving that time interval. Our findings provide interesting insight into the environmental impacts on the behavioural evolution of hominoids.

Hominin locomotion and evolution in the Late Miocene to Late Pliocene

In this review, we present on the evolution of the locomotor adaptation of hominins in the Late Miocene to Late Pliocene, with emphasis on some of the prominent advances and debates that have occurred over the past fifty years. We start with the challenging issue of defining hominin locomotor grades that are currently used liberally and offer our own working definitions of facultative, habitual, and obligate bipedalism. We then discuss the nature of the Pan-Homo last common ancestor and characterize the locomotor adaptation of Sahelanthropus, Orrorin, and Ardipithecus-often referred to as facultative bipeds-and examine the debates on the extent of bipedality and arboreality in these taxa. Moreover, the question of Middle Pliocene hominin locomotor diversity is addressed based on information derived from the 'Little Foot' specimen from Sterkfontein, footprints from Laetoli, and the Burtele Foot in Ethiopia. Our review suggests that the most convincing evidence for locomotor diversity comes from Burtele, whereas the evidence from Sterkfontein and Laetoli is unconvincing and equivocal, respectively. Finally, we address the decades old issue of the significance of arboreality in the otherwise habitual biped, Australopithecus, with emphasis on Australopithecus afarensis and its implications for the paleobiology of these creatures. We conclude that many of the apelike features encountered, mostly in the upper part of the Australopithecus skeleton, were retained for their significance in climbing. Approaches that have investigated character plasticity and those exploring internal bone structure have shown that the shoulder and limbs in Au. afarensis and Australopithecus africanus were involved in arboreal activities that are thought to be key for feeding, nesting, and predator avoidance. We conclude that many of the so-called retained ape-like features persisted due to stabilizing selection, that early hominins engaged in a considerable amount of arboreality even after Australopithecus had become a habitual biped, and arboreality only ceased to be an important component of hominin locomotor behavior after the emergence of Homo erectus.