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ObjectivesChimpanzees (Pan troglodytes) are patrilocal, with males remaining in their natal community and females dispersing when they reach sexual maturity. However, the details of female chimpanzee dispersal, such as their possible origin, are difficult to assess, even in habituated communities. This study investigates the utility of 87Sr/86Sr analysis for (1) assessing Sr baseline differences between chimpanzee territories and (2) identifying the status (immigrant or natal) of females of unknown origin within the territories of five neighboring communities in Taï National Park (Côte d'Ivoire).Materials and methodsTo create a local Sr isoscape for the Taï Chimpanzee Project (TCP) study area, we sampled environmental samples from TCP-established territories (n = 35). To assess dispersal patterns, 34 tooth enamel samples (one per individual) were selected from the Taï chimpanzee skeletal collection. 87Sr/86Sr analysis was performed on all 69 samples at the W.M. Keck Lab. The theoretical density and overlap of chimpanzee communities as well as generalized linear mixed models (GLMMs) were used to test each question.Results87Sr/86Sr ratios for natal male chimpanzees ranged from 0.71662 to 0.72187, which is well within the corresponding environmental baseline range of 0.70774-0.73460. The local Sr isoscapes fit was estimated with the root-mean-square error value, which was 0.0048 (22% of the whole 87Sr/86Sr data range). GLMMs identified significant differences in 87Sr/86Sr ratios between natal and unknown North community origin groups, suggesting that after 1980, females of unknown origin could be immigrants to North community (n = 7, z-ratio = -4.08, p = 0.0001, power = 0.94).DiscussionThis study indicates that 87Sr/86This study indicates that 87Sr/86Sr analysis can successfully identify immigrant females in skeletal collections obtained from wild chimpanzee communities, enabling the tracking of female dispersal patterns historically. There are, however, significant limitations within the scope of this study, such as (1) the absence of reliable maps for the TCP study area, (2) limited capacity for environmental sampling, (3) small sample sizes, and (4) tooth formation in wild chimpanzees.

Objectives: This study tests if femoral and humeral cross‐sectional geometry (CSG) and cross‐sectional properties (CSPs) in an ontogenetic series of wild‐caught chimpanzees (Pan troglodytes ssp.) reflect locomotor behavior during development. The goal is to clarify the relationship between limb bone structure and locomotor behavior during ontogeny in Pan. Materials and Methods: The latex cast method was used to reconstruct cross sections at the midshaft femur and mid‐distal humerus. Second moments of area (SMAs) (Ix, Iy, Imax, Imin), which are proportional to bending rigidity about a specified axis, and the polar SMA (J), which is proportional to average bending rigidity, were calculated at section locations. Cross‐sectional shape (CSS) was assessed from Ix/Iy and Imax/Imin ratios. Juvenile and adult subsamples were compared. Results: Juveniles and adults have significantly greater femoral J compared to humeral J. Mean interlimb proportions of J are not significantly different between the groups. There is an overall decreasing trend in diaphyseal circularity between the juvenile phase of development and adulthood, although significant differences are only found in the humerus. Discussion: Juvenile chimpanzee locomotion includes forelimb‐ and hindlimb‐biased behaviors. Juveniles and adults preferentially load their hindlimbs relative to their forelimbs. This may indicate similar locomotor behavior, although other explanations including a diversity of hindlimb‐biased locomotor behaviors in juveniles cannot be ruled out. Different ontogenetic trends in forelimb and hindlimb CSS are consistent with limb bone CSG reflecting functional adaptation, albeit the complex nature of bone functional adaptation requires cautious interpretations of skeletal functional morphology from biomechanical analyses. Research Highlights: Like adults, juveniles preferentially load their hindlimbs relative to their forelimbs.Diaphyseal shape maps onto locomotor behavior but should be contextualized with other biomechanically relevant properties. [ABSTRACT FROM AUTHOR]

Although chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) share a multi-male/multi-female societal organization and form male-philopatric groups, disparities in terms of male aggression and stability of temporary parties are thought to exist among them. However, existing research in bonobos has mainly focused on the high social status, prolonged receptivity, and characteristic sexual behaviors of females, leaving the behaviors of males understudied. Moreover, prior comparative studies on Pan suffer from methodological inconsistencies. This study addresses these gaps by employing a uniform observation method to explore party attendance and aggressive interactions among male bonobos in Wamba and male chimpanzees in Kalinzu. Unlike male chimpanzees, which exhibit dispersion in the absence of receptive females in the group, male bonobos showed a lesser degree of such dispersion. Although the overall frequency of aggressive interactions per observation unit did not significantly differ between the two species, the nature of these interactions varied. Notably, severe aggressive behaviors such as physical confrontations among adult males were absent in bonobos, with most aggression occurring between the sons of the two highest-ranking females. Additionally, in bonobos, females actively engaged in polyadic aggressive behavior as aggressors, while all instances of coalitionary aggression in chimpanzees originated from male aggressors. These findings underscore the substantial impact of female behaviors on the observed distinctions in male aggressive interactions between the two species. [ABSTRACT FROM AUTHOR]

Comparative studies of great apes provide a window into our evolutionary past, but the extent and identity of cellular differences that emerged during hominin evolution remain largely unexplored. We established a comparative loss-of-function approach to evaluate whether human cells exhibit distinct genetic dependencies. By performing genome-wide CRISPR interference screens in human and chimpanzee pluripotent stem cells, we identified 75 genes with species-specific effects on cellular proliferation. These genes comprised coherent processes, including cell-cycle progression and lysosomal signaling, which we determined to be human-derived by comparison with orangutan cells. Human-specific robustness to CDK2 and CCNE1 depletion persisted in neural progenitor cells and cerebral organoids, supporting the G1-phase length hypothesis as a potential evolutionary mechanism in human brain expansion. Our findings demonstrate that evolutionary changes in human cells reshaped the landscape of essential genes and establish a platform for systematically uncovering latent cellular and molecular differences between species.

Identifying novel medicinal resources in chimpanzee diets has historically presented challenges, requiring extensive behavioral data collection and health monitoring, accompanied by expensive pharmacological analyses. When putative therapeutic self‐medicative behaviors are observed, these events are often considered isolated occurrences, with little attention paid to other resources ingested in combination. For chimpanzees, medicinal resource combinations could play an important role in maintaining well‐being by tackling different symptoms of an illness, chemically strengthening efficacy of a treatment, or providing prophylactic compounds that prevent future ailments. We call this concept the self‐medicative resource combination hypothesis. However, a dearth of methodological approaches for holistically investigating primate feeding ecology has limited our ability to identify nonrandom resource combinations and explore potential synergistic relationships between medicinal resource candidates. Here we present two analytical tools that test such a hypothesis and demonstrate these approaches on feeding data from the Sonso chimpanzee community in Budongo Forest, Uganda. Using 4 months of data, we establish that both collocation and APRIORI analyses are effective exploratory tools for identifying binary combinations, and that APRIORI is effective for multi‐item rule associations. We then compare outputs from both methods, finding up to 60% agreement, and propose APRIORI as more effective for studies requiring control over confidence intervals and those investigating nonrandom associations between more than two resources. These analytical tools, which can be extrapolated across the animal kingdom, can provide a cost‐effective and efficient method for targeting resources for further pharmacological investigation, potentially aiding in the discovery of novel medicines. Highlights: New methods needed for holistically evaluating chimpanzee diets.Collocation and APRIORI analyses are effective tools for finding nonrandom resource combinations.Relatively high level of agreement between methods.Effective tool for exploring feeding ecology data sets and discovering novel self‐medicative resources. [ABSTRACT FROM AUTHOR]

When facing uncertainty, humans often build mental models of alternative outcomes. Considering diverging scenarios allows agents to respond adaptively to different actual worlds by developing contingency plans (covering one's bases). In a pre-registered experiment, we tested whether chimpanzees (Pan troglodytes) prepare for two mutually exclusive possibilities. Chimpanzees could access two pieces of food, but only if they successfully protected them from a human competitor. In one condition, chimpanzees could be certain about which piece of food the human experimenter would attempt to steal. In a second condition, either one of the food rewards was a potential target of the competitor. We found that chimpanzees were significantly more likely to protect both pieces of food in the second relative to the first condition, raising the possibility that chimpanzees represent and prepare effectively for different possible worlds.

The carbohydrate fraction of most mammalian milks contains a variety of oligosaccharides that encompass a range of structures and monosaccharide compositions. Human milk oligosaccharides have received considerable attention due to their biological roles in neonatal gut microbiota, immunomodulation, and brain development. However, a major challenge in understanding the biology of milk oligosaccharides across other mammals is that reports span more than 5 decades of publications with varying data reporting methods. In the present study, publications on milk oligosaccharide profiles were identified and harmonized into a standardized format to create a comprehensive, machine-readable database of milk oligosaccharides across mammalian species. The resulting database, MilkOligoDB, includes 3193 entries for 783 unique oligosaccharide structures from the milk of 77 different species harvested from 113 publications. Cross-species and cross-publication comparisons of milk oligosaccharide profiles reveal common structural motifs within mammalian orders. Of the species studied, only chimpanzees, bonobos, and Asian elephants share the specific combination of fucosylation, sialylation, and core structures that are characteristic of human milk oligosaccharides. However, agriculturally important species do produce diverse oligosaccharides that may be valuable for human supplementation. Overall, MilkOligoDB facilitates cross-species and cross-publication comparisons of milk oligosaccharide profiles and the generation of new data-driven hypotheses for future research.

Recent studies identify a surprising coupling between evolutionarily new sulci and the functional organization of human posteromedial cortex (PMC). Yet, no study has compared this modern PMC sulcal patterning between humans and non-human hominoids. To fill this gap in knowledge, we first manually defined over 2500 PMC sulci in 120 chimpanzee (Pan Troglodytes) hemispheres and 144 human hemispheres. We uncovered four new sulci, and quantitatively identified species differences in sulcal incidence, depth, and surface area. Interestingly, some sulci are more common in humans and others, in chimpanzees. Further, we found that the prominent marginal ramus of the cingulate sulcus differs significantly between species. Contrary to classic observations, the present results reveal that the surface anatomy of PMC substantially differs between humans and chimpanzees-findings which lay a foundation for better understanding the evolution of neuroanatomical-functional and neuroanatomical-behavioral relationships in this highly expanded region of the human cerebral cortex.

Human accelerated regions (HARs) are conserved genomic loci that evolved at an accelerated rate in the human lineage and may underlie human-specific traits. We generated HARs and chimpanzee accelerated regions with an automated pipeline and an alignment of 241 mammalian genomes. Combining deep learning with chromatin capture experiments in human and chimpanzee neural progenitor cells, we discovered a significant enrichment of HARs in topologically associating domains containing human-specific genomic variants that change three-dimensional (3D) genome organization. Differential gene expression between humans and chimpanzees at these loci suggests rewiring of regulatory interactions between HARs and neurodevelopmental genes. Thus, comparative genomics together with models of 3D genome folding revealed enhancer hijacking as an explanation for the rapid evolution of HARs.

Using machine learning (ML), we interrogated the function of all human-chimpanzee variants in 2,645 human accelerated regions (HARs), finding 43% of HARs have variants with large opposing effects on chromatin state and 14% on neurodevelopmental enhancer activity. This pattern, consistent with compensatory evolution, was confirmed using massively parallel reporter assays in chimpanzee and human neural progenitor cells. The species-specific enhancer activity of HARs was accurately predicted from the presence and absence of transcription factor footprints in each species. Despite these striking cis effects, activity of a given HAR sequence was nearly identical in human and chimpanzee cells. This suggests that HARs did not evolve to compensate for changes in the trans environment but instead altered their ability to bind factors present in both species. Thus, ML prioritized variants with functional effects on human neurodevelopment and revealed an unexpected reason why HARs may have evolved so rapidly.

Humans are perhaps the most curious animals on earth, but to what extent our innate motivations for discovering new information are shared with our closest relatives remain poorly understood. To shed light on this question, we presented great apes with two experimental paradigms in which they had to initially choose between an empty opaque cup and a baited opaque cup with rewards invisible to the ape in study 1, or to choose between a transparent cup with rewards or a baited opaque cup with rewards invisible to the ape in studies 2 and 3. We also presented young children with scenarios comparable to the second paradigm (studies 4 and 5). Notably, after the initial choice phase, we presented participants with potential alternatives providing better rewards than the previously secured options. Importantly, those alternatives shared some features with the uncertain options, giving subjects the possibility to relate both options through analogical reasoning. We found that most great apes were not curious about the uncertain options. They only explored those options after they were presented with the alternatives. Children, instead, explored the uncertain options before the alternatives were presented, showing a higher degree of curiosity than the great apes. We argue that differences between children and apes mostly lay in motivational dispositions to explore the unknown.

Cancers occur across species. Understanding what is consistent and varies across species can provide new insights into cancer initiation and evolution, with significant implications for animal welfare and wildlife conservation. We build a pan-species cancer digital pathology atlas (panspecies.ai) and conduct a pan-species study of computational comparative pathology using a supervised convolutional neural network algorithm trained on human samples. The artificial intelligence algorithm achieves high accuracy in measuring immune response through single-cell classification for two transmissible cancers (canine transmissible venereal tumour, 0.94; Tasmanian devil facial tumour disease, 0.88). In 18 other vertebrate species (mammalia = 11, reptilia = 4, aves = 2, and amphibia = 1), accuracy (range 0.57-0.94) is influenced by cell morphological similarity preserved across different taxonomic groups, tumour sites, and variations in the immune compartment. Furthermore, a spatial immune score based on artificial intelligence and spatial statistics is associated with prognosis in canine melanoma and prostate tumours. A metric, named morphospace overlap, is developed to guide veterinary pathologists towards rational deployment of this technology on new samples. This study provides the foundation and guidelines for transferring artificial intelligence technologies to veterinary pathology based on understanding of morphological conservation, which could vastly accelerate developments in veterinary medicine and comparative oncology.

In humans, puberty initiates a period of rapid growth, change, and formative neurobehavioral development. Brain and behavior changes during this maturational window contribute to opportunities for social learning. Here we provide new insights into adolescence as a unique period of social learning and development by describing field studies of our closest living relatives, chimpanzees. Like humans, chimpanzees have a multiyear juvenile life stage between weaning and puberty onset followed by a multiyear adolescent life stage after pubertal onset but prior to socially-recognized adulthood. As they develop increasing autonomy from caregivers, adolescent chimpanzees explore and develop many different types of social relationships with a wide range of individuals in a highly flexible social environment. We describe how adolescent social motivations and experiences differ from those of juveniles and adults and expose adolescents to high levels of uncertainty, risk, and vulnerability, as well as opportunities for adaptive social learning. We discuss how these adolescent learning experiences may be shaped by early life and in turn shape varied adult social outcomes. We outline how future chimpanzee field research can contribute in new ways to a more integrative interdisciplinary understanding of adolescence as a developmental window of adaptive social learning and resilience.

Objectives: Bonobos and chimpanzees do not differ from one another in overall frequencies of arboreality versus terrestriality as much as once thought. Thus, at a broad level, one would predict that there is little difference in foot morphology among Pan taxa. However, behavioral data suggest that bonobos more often use smaller diameter substrates (<10 cm) when climbing whereas western chimpanzees frequently climb larger diameter (>15 cm) substrates. This study tests the hypothesis that if Pan medial cuneiform and talus morphology reflects these substrate preferences, then the morphology of these bones should favor hallucial grasping in bonobos and an inverted foot set in western chimpanzees. Materials and Methods: Three‐dimensional geometric morphometric (3DGM) methods were used to explore shape variation in 126 talus and 127 medial cuneiform 3D surface models acquired from 108 chimpanzees (24 western, four Nigeria‐Cameroon, 33 central, 32 eastern, and 15 captive unknowns) and 22 bonobos Results: The shapes of the talus and medial cuneiform in Pan covary as a functional unit emphasizing hallucial grasping with a less inverted foot set in bonobos and a more inverted foot set with a less abducted hallucial set in western chimpanzees. Other chimpanzee subspecies fall between these two extremes. Discussion: Bonobo and western chimpanzee medial cuneiform and talus shapes are consistent with their differing preferences for using smaller and larger diameter substrates, respectively, when vertically climbing. These results suggest that even among closely related taxa, foot, hand, and other postcranial anatomy may be fine‐tuned for specific locomotor behaviors or preferences. [ABSTRACT FROM AUTHOR]

Chimpanzees (Pan troglodytes) with teeth severely damaged by dental caries and/or periodontal disease are often managed with medication and/or tooth extraction. A common endodontic treatment for severely decayed teeth in a 26-year-old female chimpanzee is reported. The left maxillary central incisor tooth had lost its crown, probably due to trauma that was not recent, and it had a fistula most likely due to chronic apical periodontitis. The diagnosis was confirmed radiographically before treatment. To treat the infected root canal, endodontic treatment used in humans was adapted for a chimpanzee. After the treatment, the tooth was sealed using an adhesive resin composite. At 11-years post-treatment, there were no signs of recurrence of the lesion or of failure of the tooth seal. The results of this case report suggest that common endodontic treatments used in humans are also effective in chimpanzees. [ABSTRACT FROM AUTHOR]

Observations of chimpanzees in their natural habitat show that as well as competing, these primates often cooperate by forming coalitions, patrolling the boundaries of their territories, and hunting in groups. Perhaps because of the important role it is thought to have played in the evolution of our own species, group hunting behaviours have attracted considerable research interest. The underlying question is to what extent do chimpanzees hunt cooperatively in a human-like manner? To answer this question, we must consider not only their behaviour, but also the cognitive abilities required, given that any two similar behaviours may respond to different psychological mechanisms. Research on the cognitive aspect of cooperation has been carried out mainly through experiments with chimpanzees in captivity. The available evidence suggests that, with experience, chimpanzees are capable of coordination between individuals, but it is unclear whether they can also cooperate, i.e., act according to a common strategy. [ABSTRACT FROM AUTHOR]

ABSTRACT The purpose of this review is to highlight the most important aspects of the anatomical and functional uniqueness of the human brain. For this, a comparison is made between our brains and those of our closest ancestors (chimpanzees and bonobos) and human ancestors. During human evolution, several changes occurred in the brain, such as an absolute increase in brain size and number of cortical neurons, in addition to a greater degree of functional lateralization and anatomical asymmetry. Also, the cortical cytoarchitecture became more diversified and there was an increase in the number of intracortical networks and networks extending from the cerebral cortex to subcortical structures, with more neural networks being invested in multisensory and sensory-motor-affective-cognitive integration. These changes permitted more complex, flexible and versatile cognitive abilities and social behavior, such as shared intentionality and symbolic articulated language, which, in turn, made possible the formation of larger social groups and cumulative cultural evolution that are characteristic of our species.

As our closest living relatives, non-human primates uniquely enable explorations of human health, disease, development, and evolution. Considerable effort has thus been devoted to generating induced pluripotent stem cells (iPSCs) from multiple non-human primate species. Here, we establish improved culture methods for chimpanzee (Pan troglodytes) and pig-tailed macaque (Macaca nemestrina) iPSCs. Such iPSCs spontaneously differentiate in conventional culture conditions, but can be readily propagated by inhibiting endogenous WNT signaling. As a unique functional test of these iPSCs, we injected them into the pre-implantation embryos of another non-human species, rhesus macaques (Macaca mulatta). Ectopic expression of gene BCL2 enhances the survival and proliferation of chimpanzee and pig-tailed macaque iPSCs within the pre-implantation embryo, although the identity and long-term contribution of the transplanted cells warrants further investigation. In summary, we disclose transcriptomic and proteomic data, cell lines, and cell culture resources that may be broadly enabling for non-human primate iPSCs research.

Employing orexin-A immunohistochemical staining we describe the nuclear parcellation of orexinergic neurons in the hypothalami of a lar gibbon and a chimpanzee. The clustering of orexinergic neurons within the hypothalamus and the terminal networks follow the patterns generally observed in other mammals, including laboratory rodents, strepsirrhine primates and humans. The orexinergic neurons were found within three distinct clusters in the ape hypothalamus, which include the main cluster, zona incerta cluster and optic tract cluster. In addition, the orexinergic neurons of the optic tract cluster appear to extend to a more rostral and medial location than observed in other species, being observed in the tuberal region in the anterior ventromedial aspect of the hypothalamus. While orexinergic terminal networks were observed throughout the brain, high density terminal networks were observed within the hypothalamus, medial and intralaminar nuclei of the dorsal thalamus, and within the serotonergic and noradrenergic regions of the midbrain and pons, which is typical for mammals. The expanded distribution of orexinergic neurons into the tuberal region of the ape hypothalamus, is a feature that needs to be investigated in other primate species, but appears to correlate with orexin gene expression in the same region of the human hypothalamus, but these neurons are not revealed with immunohistochemical staining in humans. Thus, it appears that apes have a broader distribution of orexinergic neurons compared to other primate species, but that the neurons within this extension of the optic tract cluster in humans, while expressing the orexin gene, do not produce the neuropeptide.

Judgements of wrongdoing in humans often hinge upon an assessment of whether a perpetrator acted out of free choice: whether they had more than one option. The classic inhibitors of free choice are constraint (e.g. having your hands tied together) and ignorance (e.g. being unaware that an alternative exists). Here, across two studies, we investigate whether chimpanzees consider these factors in their evaluation of social action. Chimpanzees interacted with a human experimenter who handed them a non-preferred item of food, either because they were physically constrained from accessing the preferred item (Experiment 1) or because they were ignorant of the availability of the preferred item (Experiment 2). We found that chimpanzees were more likely to accept the non-preferred food and showed fewer negative emotional responses when the experimenter was physically constrained compared with when they had free choice. We did not, however, find an effect of ignorance on chimpanzee's evaluation. Freedom of choice factors into chimpanzees' evaluation of how they are treated, but it is unclear whether mental state reasoning is involved in this assessment.

The ultimatum game (UG) is widely used to investigate our sense of fairness, a key characteristic that differentiates us from our closest living relatives, bonobos and chimpanzees. Previous studies found that, in general, great apes behave as rational maximizers in the UG. Proposers tend to choose self-maximizing offers, while responders accept most non-zero offers. These studies do not rule out the possibility that apes can behave prosocially to improve the returns for themselves and others. However, this has never been well studied. In this study, we offer chimpanzee and bonobo proposers the possibility of taking into account the leverage of responders over the offers they receive. This leverage takes the form of access to alternatives for responders. We find that proposers tend to propose fairer offers when responders have the option to access alternatives. Furthermore, we find that both species use their leverage to reject unequal offers. Our results suggest that great apes mostly act as rational maximizers in an UG, yet access to alternatives can lead them to change their strategies such as not choosing the self-maximizing offer as proposers and not accepting every offer higher than zero as responders.

ObjectiveSpecies-specific pseudogenization of the CMAH gene during human evolution eliminated common mammalian sialic acid N-glycolylneuraminic acid (Neu5Gc) biosynthesis from its precursor N-acetylneuraminic acid (Neu5Ac). With metabolic nonhuman Neu5Gc incorporation into endothelia from red meat, the major dietary source, anti-Neu5Gc antibodies appeared. Human-like Ldlr-/-Cmah-/- mice on a high-fat diet supplemented with a Neu5Gc-enriched mucin, to mimic human red meat consumption, suffered increased atherosclerosis if human-like anti-Neu5Gc antibodies were elicited.Approach and resultsWe now ask whether interventional Neu5Ac feeding attenuates metabolically incorporated Neu5Gc-mediated inflammatory acceleration of atherogenesis in this Cmah-/-Ldlr-/- model system. Switching to a Neu5Gc-free high-fat diet or adding a 5-fold excess of Collocalia mucoid-derived Neu5Ac in high-fat diet protects against accelerated atherosclerosis. Switching completely from a Neu5Gc-rich to a Neu5Ac-rich diet further reduces severity. Remarkably, feeding Neu5Ac-enriched high-fat diet alone has a substantial intrinsic protective effect against atherosclerosis in Ldlr-/- mice even in the absence of dietary Neu5Gc but only in the human-like Cmah-null background.ConclusionsInterventional Neu5Ac feeding can mitigate or prevent the red meat/Neu5Gc-mediated increased risk for atherosclerosis, and has an intrinsic protective effect, even in the absence of Neu5Gc feeding. These findings suggest that similar interventions should be tried in humans and that Neu5Ac-enriched diets alone should also be investigated further.

Emerging evidence links genes within human-specific segmental duplications (HSDs) to traits and diseases unique to our species. Strikingly, despite being nearly identical by sequence (>98.5%), paralogous HSD genes are differentially expressed across human cell and tissue types, though the underlying mechanisms have not been examined. We compared cross-tissue mRNA levels of 75 HSD genes from 30 families between humans and chimpanzees and found expression patterns consistent with relaxed selection on or neofunctionalization of derived paralogs. In general, ancestral paralogs exhibited greatest expression conservation with chimpanzee orthologs, though exceptions suggest certain derived paralogs may retain or supplant ancestral functions. Concordantly, analysis of long-read isoform sequencing data sets from diverse human tissues and cell lines found that about half of derived paralogs exhibited globally lower expression. To understand mechanisms underlying these differences, we leveraged data from human lymphoblastoid cell lines (LCLs) and found no relationship between paralogous expression divergence and post-transcriptional regulation, sequence divergence, or copy-number variation. Considering cis-regulation, we reanalyzed ENCODE data and recovered hundreds of previously unidentified candidate CREs in HSDs. We also generated large-insert ChIP-sequencing data for active chromatin features in an LCL to better distinguish paralogous regions. Some duplicated CREs were sufficient to drive differential reporter activity, suggesting they may contribute to divergent cis-regulation of paralogous genes. This work provides evidence that cis-regulatory divergence contributes to novel expression patterns of recent gene duplicates in humans.

Syntax is considered a key feature distinguishing human language from other non-human animal communication systems. However, evidence for combinatorial capacities in a wide variety of species, such as birds and monkeys, has challenged this assumption. Nevertheless, a contentious debate surrounding the evolutionary origins of syntax remains, specifically whether the combinatorial capacities displayed in animals merely illustrate a case of convergent evolution or whether it could also represent, within the primate lineage, a homologous trait to syntax in humans. In this piece, I review the literature on combinatorial signalling in our closest-living relative, the chimpanzee (Pan troglotytes), central to demonstrating a more ancient evolutionary account of syntax. Specifically, I detail the combinatorial structures highlighted in chimpanzees, the experimental evidence pointing toward the syntactic-like nature of these combinations, as well as the limitations the field needs to overcome to go a step further and address the question of the evolution of syntax more holistically. I discuss future directions building on exciting recent evidence for combinatorial flexibility in chimpanzees and the potential for learning. Finally, by proposing a compositional analysis to documented combinations of gestures with facial expressions, I argue that a promising avenue for the study of the evolution of syntax lies in the understanding of multimodal combinatorial signalling in our closest-living relatives and its ontogeny.

Investment in social interaction and affiliative behaviour is often related to variation in sex-specific dispersal patterns among species but can also vary within species in response to local environmental conditions and feeding competition. Chimpanzee (Pan troglodytes) association patterns have been studied primarily in low and mid-elevation tropical forests. This study adds to our understanding of association patterns in chimpanzees by presenting the first data on association patterns in a high-elevation population at Nyungwe in equatorial Rwanda. Using data on co-occurrence in social parties (party association) and calculating gregariousness indices, we quantified levels of associations among age-sex classes relative to food (fruit) distribution and the presence of oestrous females. Overall, adult females in Nyungwe are less gregarious than males. Female but not male gregariousness increased when feeding on clumped foods, indicating that resource characteristics impact female association tendencies more intensely than males. Despite high elevation forests representing a habitat with relatively fewer fruit resources for chimpanzees, at an edge of range location, we found that gregariousness patterns were driven by similar factors as those in mid and low elevation chimpanzee populations. – We quantified association patterns in a high elevation population of chimpanzees at Nyungwe (Rwanda) – Adult females were less gregarious than males – Female but not male gregariousness increased when feeding on clumped foods, indicating that resource characteristics impact female association tendencies more intensely than males [ABSTRACT FROM AUTHOR]

The evolution of monogamy has been a central question in biological anthropology. An important avenue of research has been comparisons across "socially monogamous" mammals, but such comparisons are inappropriate for understanding human behavior because humans are not "pair living" and are only sometimes "monogamous." It is the "pair bond" between reproductive partners that is characteristic of humans and has been considered unique to our lineage. I argue that pair bonds have been overlooked in one of our closest living relatives, chimpanzees. These pair bonds are not between mates but between male "friends" who exhibit enduring and emotional social bonds. The presence of such bonds in male–male chimpanzees raises the possibility that pair bonds emerged earlier in our evolutionary history. I suggest pair bonds first arose as "friendships" and only later, in the human lineage, were present between mates. The mechanisms for these bonds were co‐opted for male‐female bonds in humans. [ABSTRACT FROM AUTHOR]

Most primate species are highly social. Yet, within species, pronounced individual differences in social functioning are evident. In humans, the Social Responsiveness Scale (SRS) measures variation in social functioning. The SRS provides a quantitative measure of social functioning in natural social settings and can be used as a screening tool for autistic traits. The SRS was previously adapted for use in chimpanzees and recently refined for rhesus macaques, resulting in the macaque Social Responsiveness Scale-Revised (mSRS-R). Here, we performed an exploratory factor analysis on the mSRS-R in a large sample of male rhesus macaques (N = 233). We investigated the relationships of the resulting mSRS-R factors to quantitative social behavior (alone, proximity, contact, groom, and play) and to previously-established personality dimensions (Sociability, Confidence, Irritability, and Equability). Factor analysis yielded three mSRS-R factors: Poor Social Motivation, Poor Social Attractiveness, and Inappropriate Behavior. mSRS-R factors mapped closely to social behavior and personality dimensions in rhesus macaques, providing support for this instrument's convergent and discriminant validity. Animals with higher Poor Social Motivation were more likely to be observed alone and less likely to be observed in contact and grooming with conspecifics. Animals with higher Poor Social Attractiveness were less likely to be observed playing but more likely to be observed grooming with conspecifics. Inappropriate Behavior did not predict any behavioral measure. Finally, animals with higher Poor Social Motivation and higher Poor Social Attractiveness had less sociable personalities, whereas animals with more Inappropriate Behavior were more confident and more irritable. These findings suggest that the mSRS-R is a promising, psychometrically robust tool that can be deployed to better understand the psychological factors contributing to individual differences in macaque social functioning and, with relevant species-specific modification, the SRS may hold promise for investigating variation in social functioning across diverse primate taxa.

Gene regulatory divergence is thought to play a central role in determining human-specific traits. However, our ability to link divergent regulation to divergent phenotypes is limited. Here, we utilized human-chimpanzee hybrid induced pluripotent stem cells to study gene expression separating these species. The tetraploid hybrid cells allowed us to separate cis- from trans-regulatory effects, and to control for nongenetic confounding factors. We differentiated these cells into cranial neural crest cells, the primary cell type giving rise to the face. We discovered evidence of lineage-specific selection on the hedgehog signaling pathway, including a human-specific sixfold down-regulation of EVC2 (LIMBIN), a key hedgehog gene. Inducing a similar down-regulation of EVC2 substantially reduced hedgehog signaling output. Mice and humans lacking functional EVC2 show striking phenotypic parallels to human-chimpanzee craniofacial differences, suggesting that the regulatory divergence of hedgehog signaling may have contributed to the unique craniofacial morphology of humans.

BackgroundA safe and effective vaccine to prevent chronic hepatitis C virus (HCV) infection is a critical component of efforts to eliminate the disease.MethodsIn this phase 1-2 randomized, double-blind, placebo-controlled trial, we evaluated a recombinant chimpanzee adenovirus 3 vector priming vaccination followed by a recombinant modified vaccinia Ankara boost; both vaccines encode HCV nonstructural proteins. Adults who were considered to be at risk for HCV infection on the basis of a history of recent injection drug use were randomly assigned (in a 1:1 ratio) to receive vaccine or placebo on days 0 and 56. Vaccine-related serious adverse events, severe local or systemic adverse events, and laboratory adverse events were the primary safety end points. The primary efficacy end point was chronic HCV infection, defined as persistent viremia for 6 months.ResultsA total of 548 participants underwent randomization, with 274 assigned to each group. There was no significant difference in the incidence of chronic HCV infection between the groups. In the per-protocol population, chronic HCV infection developed in 14 participants in each group (hazard ratio [vaccine vs. placebo], 1.53; 95% confidence interval [CI], 0.66 to 3.55; vaccine efficacy, -53%; 95% CI, -255 to 34). In the modified intention-to-treat population, chronic HCV infection developed in 19 participants in the vaccine group and 17 in placebo group (hazard ratio, 1.66; 95% CI, 0.79 to 3.50; vaccine efficacy, -66%; 95% CI, -250 to 21). The geometric mean peak HCV RNA level after infection differed between the vaccine group and the placebo group (152.51×103 IU per milliliter and 1804.93×103 IU per milliliter, respectively). T-cell responses to HCV were detected in 78% of the participants in the vaccine group. The percentages of participants with serious adverse events were similar in the two groups.ConclusionsIn this trial, the HCV vaccine regimen did not cause serious adverse events, produced HCV-specific T-cell responses, and lowered the peak HCV RNA level, but it did not prevent chronic HCV infection. (Funded by the National Institute of Allergy and Infectious Diseases; ClinicalTrials.gov number, NCT01436357.).

Recent technological advances have expanded the annotated protein coding content of mammalian genomes, as hundreds of previously unidentified, short open reading frame (ORF)-encoded peptides (SEPs) have now been found to be translated. Although several studies have identified important physiological roles for this emerging protein class, a general method to define their interactomes is lacking. Here, we demonstrate that genetic incorporation of the photo-crosslinking noncanonical amino acid AbK into SEP transgenes allows for the facile identification of SEP cellular interaction partners using affinity-based methods. From a survey of seven SEPs, we report the discovery of short ORF-encoded histone binding protein (SEHBP), a conserved microprotein that interacts with chromatin-associated proteins, localizes to discrete genomic loci, and induces a robust transcriptional program when overexpressed in human cells. This work affords a straightforward method to help define the physiological roles of SEPs and demonstrates its utility by identifying SEHBP as a short ORF-encoded transcription factor.

The "drunken monkey" hypothesis posits that attraction to ethanol derives from an evolutionary linkage among the sugars of ripe fruit, associated alcoholic fermentation by yeast, and ensuing consumption by human ancestors. First proposed in 2000, this concept has received increasing attention from the fields of animal sensory biology, primate foraging behavior, and molecular evolution. We undertook a review of English language citations subsequent to publication of the original paper and assessed research trends and future directions relative to natural dietary ethanol exposure in primates and other animals. Two major empirical themes emerge: attraction to and consumption of fermenting fruits (and nectar) by numerous vertebrates and invertebrates (e.g., Drosophila flies), and genomic evidence for natural selection consistent with sustained exposure to dietary ethanol in diverse taxa (including hominids and the genus Homo) over tens of millions of years. We also describe our current field studies in Uganda of ethanol content within fruits consumed by free-ranging chimpanzees, which suggest chronic low-level exposure to this psychoactive molecule in our closest living relatives.

Stable isotope analysis is an increasingly used molecular tool to reconstruct the diet and ecology of elusive primates such as unhabituated chimpanzees. The consumption of C4 plant feeding termites by chimpanzees may partly explain the relatively high carbon isotope values reported for some chimpanzee communities. However, the modest availability of termite isotope data as well as the diversity and cryptic ecology of termites potentially consumed by chimpanzees obscures our ability to assess the plausibility of these termites as a C4 resource. Here we report the carbon and nitrogen isotope values from 79 Macrotermes termite samples from six savanna woodland chimpanzee research sites across equatorial Africa. Using mixing models, we estimated the proportion of Macrotermes C4 plant consumption across savanna woodland sites. Additionally, we tested for isotopic differences between termite colonies in different vegetation types and between the social castes within the same colony in a subset of 47 samples from 12 mounds. We found that Macrotermes carbon isotope values were indistinguishable from those of C3 plants. Only 5 to 15% of Macrotermes diets were comprised of C4 plants across sites, suggesting that they cannot be considered a C4 food resource substantially influencing the isotope signatures of consumers. In the Macrotermes subsample, vegetation type and caste were significantly correlated with termite carbon values, but not with nitrogen isotope values. Large Macrotermes soldiers, preferentially consumed by chimpanzees, had comparably low carbon isotope values relative to other termite castes. We conclude that Macrotermes consumption is unlikely to result in high carbon isotope values in either extant chimpanzees or fossil hominins.

BackgroundHumans life histories have been described as "slow", patterned by slow growth, delayed maturity, and long life span. While it is known that human life history diverged from that of a recent common chimpanzee-human ancestor some ~4-8 mya, it is unclear how selection pressures led to these distinct traits. To provide insight, we compare wild chimpanzees and human subsistence societies in order to identify the age-specific vital rates that best explain fitness variation, selection pressures and species divergence.MethodsWe employ Life Table Response Experiments to quantify vital rate contributions to population growth rate differences. Although widespread in ecology, these methods have not been applied to human populations or to inform differences between humans and chimpanzees. We also estimate correlations between vital rate elasticities and life history traits to investigate differences in selection pressures and test several predictions based on life history theory.ResultsChimpanzees' earlier maturity and higher adult mortality drive species differences in population growth, whereas infant mortality and fertility variation explain differences between human populations. Human fitness is decoupled from longevity by postreproductive survival, while chimpanzees forfeit higher potential lifetime fertility due to adult mortality attrition. Infant survival is often lower among humans, but lost fitness is recouped via short birth spacing and high peak fertility, thereby reducing selection on infant survival. Lastly, longevity and delayed maturity reduce selection on child survival, but among humans, recruitment selection is unexpectedly highest in longer-lived populations, which are also faster-growing due to high fertility.ConclusionHumans differ from chimpanzees more because of delayed maturity and lower adult mortality than from differences in juvenile mortality or fertility. In both species, high child mortality reflects bet-hedging costs of quality/quantity tradeoffs borne by offspring, with high and variable child mortality likely regulating human population growth over evolutionary history. Positive correlations between survival and fertility among human subsistence populations leads to selection pressures in human subsistence societies that differ from those in modern populations undergoing demographic transition.

Domesticated animals experienced profound changes in diet, environment, and social interactions that likely shaped their gut microbiota and were potentially analogous to ecological changes experienced by humans during industrialization. Comparing the gut microbiota of wild and domesticated mammals plus chimpanzees and humans, we found a strong signal of domestication in overall gut microbial community composition and similar changes in composition with domestication and industrialization. Reciprocal diet switches within mouse and canid dyads demonstrated the critical role of diet in shaping the domesticated gut microbiota. Notably, we succeeded in recovering wild-like microbiota in domesticated mice through experimental colonization. Although fundamentally different processes, we conclude that domestication and industrialization have impacted the gut microbiota in related ways, likely through shared ecological change. Our findings highlight the utility, and limitations, of domesticated animal models for human research and the importance of studying wild animals and non-industrialized humans for interrogating signals of host-microbial coevolution.

The mammalian male-specific Y chromosome plays a critical role in sex determination and male fertility. However, because of its repetitive and haploid nature, it is frequently absent from genome assemblies and remains enigmatic. The Y chromosomes of great apes represent a particular puzzle: their gene content is more similar between human and gorilla than between human and chimpanzee, even though human and chimpanzee share a more recent common ancestor. To solve this puzzle, here we constructed a dataset including Ys from all extant great ape genera. We generated assemblies of bonobo and orangutan Ys from short and long sequencing reads and aligned them with the publicly available human, chimpanzee, and gorilla Y assemblies. Analyzing this dataset, we found that the genus Pan, which includes chimpanzee and bonobo, experienced accelerated substitution rates. Pan also exhibited elevated gene death rates. These observations are consistent with high levels of sperm competition in Pan Furthermore, we inferred that the great ape common ancestor already possessed multicopy sequences homologous to most human and chimpanzee palindromes. Nonetheless, each species also acquired distinct ampliconic sequences. We also detected increased chromatin contacts between and within palindromes (from Hi-C data), likely facilitating gene conversion and structural rearrangements. Our results highlight the dynamic mode of Y chromosome evolution and open avenues for studies of male-specific dispersal in endangered great ape species.

The human cerebral cortex contains many cell types that likely underwent independent functional changes during evolution. However, cell-type-specific regulatory landscapes in the cortex remain largely unexplored. Here we report epigenomic and transcriptomic analyses of the two main cortical neuronal subtypes, glutamatergic projection neurons and GABAergic interneurons, in human, chimpanzee, and rhesus macaque. Using genome-wide profiling of the H3K27ac histone modification, we identify neuron-subtype-specific regulatory elements that previously went undetected in bulk brain tissue samples. Human-specific regulatory changes are uncovered in multiple genes, including those associated with language, autism spectrum disorder, and drug addiction. We observe preferential evolutionary divergence in neuron subtype-specific regulatory elements and show that a substantial fraction of pan-neuronal regulatory elements undergoes subtype-specific evolutionary changes. This study sheds light on the interplay between regulatory evolution and cell-type-dependent gene-expression programs, and provides a resource for further exploration of human brain evolution and function.

Optimal foraging theory has guided much of the research on foraging behaviour in the past five decades, with the notion of optimality deeply embedded in most models today. However, assuming that all foragers strive to maximize a certain predefined currency, such as amount of food per unit time, restricts what can be learned about the factors influencing foraging decisions. Here we applied a different approach: the discrete-choice model, which does not assume an optimal strategy as the starting point, but instead examines foraging decisions directly, modelling interpatch movements as the consequence of a choice of destination from a limited set of options. We analysed a set of foraging decisions by both adult male and female chimpanzees, Pan troglodytes , from two habituated communities in the Budongo forest, Uganda, to investigate the influence of foraging variables including food patch characteristics and interpatch distance on patch choice, with a view to identifying the strategy underlying these decisions. Despite differences in habitat between communities, we found that foraging strategies were remarkably similar across both communities and sexes, with chimpanzees exhibiting a clear preference for closer and novel (not previously visited) food patches. Individuals of both communities frequently chose to forage on food patches providing young leaves, highlighting the importance of this food type in their diet. Contrary to expectation, patch size did not predict foraging decisions, except for adult males of one community that chose larger patches, while both sexes aimed to minimize travel distance between consecutive patches. This study provides the first direct evidence that chimpanzees consider travel distance and whether they have recently visited a patch when choosing between potential foraging sites and demonstrates that new insights can be gained (even in a well-studied system) from integrating several important variables describing feeding ecology into a coherent model of patch choice. • Discrete-choice models facilitate direct investigation of animal foraging strategies. • Chimpanzees consider distance and novelty when choosing foraging patches. • Patch size had no impact on choice of patch by adult female chimpanzees. • Both male and female adult chimpanzees aim to minimize travel distance. [ABSTRACT FROM AUTHOR]

Objectives: Chimpanzees (Pan troglodytes) possess a relatively generalized molar morphology allowing them to access a wide range of foods. Comparisons of crown and cusp morphology among the four subspecies have suggested relatively large intraspecific variability. Here, we compare molar crown traits and cusp wear of two geographically close populations of Western chimpanzees, P. t. verus, to provide further information on intraspecific dental variability. Materials and Methods: Micro‐CT reconstructions of high‐resolution replicas of first and second molars of two Western chimpanzee populations from Ivory Coast (Taï National Park) and Liberia, respectively were used for this study. First, we analyzed projected tooth and cusp 2D areas as well as the occurrence of cusp six (C6) on lower molars. Second, we quantified the molar cusp wear three‐dimensionally to infer how the individual cusps alter with advancing wear. Results: Both populations are similar in their molar crown morphology, except for a higher appearance rate of a C6 in Taï chimpanzees. In Taï chimpanzees, lingual cusps of upper molars and buccal cusps of lower molars possess an advanced wear pattern compared to the remaining cusps, while in Liberian chimpanzees this wear gradient is less pronounced. Discussion: The similar crown morphology between both populations fits with previous descriptions for Western chimpanzees and provides additional data on dental variation within this subspecies. The wear pattern of the Taï chimpanzees are in concordance with their observed tool rather than tooth use to open nuts/seeds, while the Liberian chimpanzees may have consumed hard food items crushed between their molars. [ABSTRACT FROM AUTHOR]

While cases of interspecies grooming have been reported in primates, no comprehensive cross-site review has been published about this behavior in great apes. Only a few recorded observations of interspecies grooming events between chimpanzees and other primate species have been reported in the wild, all of which have thus far been in Uganda. Here, we review all interspecies grooming events recorded for the Sonso community chimpanzees in Budongo Forest Reserve, Uganda, adding five new observations to the single, previously reported event from this community. A new case of interspecies play involving three juvenile male chimpanzees and a red-tailed monkey is also detailed. All events took place between 1993 and 2021. In all of the six interspecific grooming events from Budongo, the 'groomer' was a female chimpanzee between the ages of 4–6 years, and the 'recipient' was a member of the genus Cercopithecus. In five of these events, chimpanzee groomers played with the tail of their interspecific grooming partners, and except for one case, initiated the interaction. In three cases, chimpanzee groomers smelled their fingers after touching distinct parts of the receiver's body. While a single function of chimpanzee interspecies grooming remains difficult to determine from these results, our review outlines and assesses some hypotheses for the general function of this behavior, as well as some of the costs and benefits for both the chimpanzee groomers and their sympatric interspecific receivers. As allogrooming is a universal behavior in chimpanzees, investigating the ultimate and proximate drivers of chimpanzee interspecies grooming may reveal further functions of allogrooming in our closest living relatives, and help us to better understand how chimpanzees distinguish between affiliative and agonistic species and contexts. [ABSTRACT FROM AUTHOR]

Recent efforts to comprehensively characterize great ape genetic diversity using short-read sequencing and single-nucleotide variants have led to important discoveries related to selection within species, demographic history, and lineage-specific traits. Structural variants (SVs), including deletions and inversions, comprise a larger proportion of genetic differences between and within species, making them an important yet understudied source of trait divergence. Here, we used a combination of long-read and -range sequencing approaches to characterize the structural variant landscape of two additional Pan troglodytes verus individuals, one of whom carries 13% admixture from Pan troglodytes troglodytes. We performed optical mapping of both individuals followed by nanopore sequencing of one individual. Filtering for larger variants (>10 kbp) and combined with genotyping of SVs using short-read data from the Great Ape Genome Project, we identified 425 deletions and 59 inversions, of which 88 and 36, respectively, were novel. Compared with gene expression in humans, we found a significant enrichment of chimpanzee genes with differential expression in lymphoblastoid cell lines and induced pluripotent stem cells, both within deletions and near inversion breakpoints. We examined chromatin-conformation maps from human and chimpanzee using these same cell types and observed alterations in genomic interactions at SV breakpoints. Finally, we focused on 56 genes impacted by SVs in >90% of chimpanzees and absent in humans and gorillas, which may contribute to chimpanzee-specific features. Sequencing a greater set of individuals from diverse subspecies will be critical to establish the complete landscape of genetic variation in chimpanzees.

Primate lentiviruses encode a Vif protein that counteracts the host antiviral APOBEC3 (A3) family members. The adaptation of Vif to species-specific A3 determinants is a critical event that allowed the spillover of a lentivirus from monkey reservoirs to chimpanzees and subsequently to humans, which gave rise to HIV-1 and the acquired immune deficiency syndrome (AIDS) pandemic. How Vif-A3 protein interactions are remodeled during evolution is unclear. Here, we report a 2.94 Å crystal structure of the Vif substrate receptor complex from simian immunodeficiency virus isolated from red-capped mangabey (SIVrcm). The structure of the SIVrcm Vif complex illuminates the stage of lentiviral Vif evolution that is immediately prior to entering hominid primates. Structure-function studies reveal the adaptations that allowed SIVrcm Vif to antagonize hominid A3G. These studies show a partitioning between an evolutionarily dynamic specificity determinant and a conserved protein interacting surface on Vif that enables adaptation while maintaining protein interactions required for potent A3 antagonism.

Epigenetic age has emerged as an important biomarker of biological ageing. It has revealed that some tissues age faster than others, which is vital to understanding the complex phenomenon of ageing and developing effective interventions. Previous studies have demonstrated that humans exhibit heterogeneity in pace of epigenetic ageing among brain structures that are consistent with differences in structural and microanatomical deterioration. Here, we add comparative data on epigenetic brain ageing for chimpanzees, humans’ closest relatives. Such comparisons can further our understanding of which aspects of human ageing are evolutionarily conserved or specific to our species, especially given that humans are distinguished by a long lifespan, large brain, and, potentially, more severe neurodegeneration with age. Specifically, we investigated epigenetic ageing of the dorsolateral prefrontal cortex and cerebellum, of humans and chimpanzees by generating genome-wide CpG methylation data and applying established epigenetic clock algorithms to produce estimates of biological age for these tissues. We found that both species exhibit relatively slow epigenetic ageing in the brain relative to blood. Between brain structures, humans show a faster rate of epigenetic ageing in the dorsolateral prefrontal cortex compared to the cerebellum, which is consistent with previous findings. Chimpanzees, in contrast, show comparable rates of epigenetic ageing in the two brain structures. Greater epigenetic change in the human dorsolateral prefrontal cortex compared to the cerebellum may reflect both the protracted development of this structure in humans and its greater age-related vulnerability to neurodegenerative pathology.

Visitor effect studies have had inconsistent results, due in part to the inability to control for all confounding variables such as time of day, seasonal weather patterns, and so forth. This study represents the first instance where chimpanzee (Pan troglodytes) wounding frequencies were investigated across extensive time periods in the presence and complete absence of visitors, thus eliminating many visitor-related variables. Additional variables were eliminated through the zoo selection process, based on institutional responses to a 29-question survey, providing a novel approach to the question of visitor effects. The aim of this study was to determine if visitors were associated with a change in chimpanzee wound event frequencies across four 51-day time conditions, three of which occurred prior to the COVID-19 pandemic, and one during the first wave of pandemic-related zoo closures. We analyzed the archival records of 21 chimpanzees housed at three U.S. zoos. Due to the small number of wound events across all study windows, frequencies of “no wound” events were analyzed. A chi-square goodness of fit test was performed to determine whether the frequency of “no wound” events was equal between the “open” and “closed” trials. Results indicate that the frequencies did not differ, suggesting that chimpanzee welfare, as it relates to wounding, may not be adversely affected by zoo visitors.

Depictions of and references to apes (tailless hominoids) are very limited in early historical written accounts. The first known published representations of ape‐like primates appear in Medieval European books during the first century following the invention of printing. Considering the current knowledge of ape iconography, this article examines an unusual image of a couple of ape‐like creatures rendered in a European manuscript and explores the possible links of this challenging illustration with historical accounts and contexts during the late Middle Ages and early Renaissance. The studied manuscript is known as "BL Sloane MS 4016" and is a medieval herbal manuscript (Tratactus de Herbis) of Lombardian origin dated c. 1440. The illustration in question, which also appears in similar manuscripts, represents two primates. However, these representations differ significantly from those in the other manuscripts. The individuals have physical features that suggest attribution to chimpanzees. The location and the date of the manuscript in relation to the extended merchant and travel network between Europe and Africa during the late Medieval times and earlier Renaissance most likely indicate that free‐living or traded chimpanzees or their images may have been the visual source for the illustration. The examination of early depictions and descriptions of apes helps us to understand how we, humans, have represented our own closest zoological relatives. In doing so, this study also provides a review of early ape iconography and historical accounts about African primates during the so‐called Age of Discoveries. Research highlights: ‐An exploration of the earliest depictions of African apes in Medieval times and the early Renaissance, including that of a challenging and novel image of chimpanzees.‐A revision of the historical accounts about African primate diversity during the 15th and 16th centuries.‐Expanding knowledge about primates in the past serves as a tool for ultimately building more robust plans for the future conservation of all endangered primates [ABSTRACT FROM AUTHOR]

Human culture thrives by virtue of communication, yet whether communication plays an influential role in the cultural lives of other animals remains understudied. Here, we investigated whether chimpanzees use communication to engage in a cultural practice by analysing grooming handclasp (GHC) interactions—a socio-cultural behaviour requiring interindividual coordination for successful execution. Previous accounts attributed GHC initiations to behavioural shaping, whereby the initiator physically moulds the partner's arm into the desired GHC posture. Using frame-by-frame analysis and matched-control methodology, we find that chimpanzees do not only shape their partner's posture (22%), but also use gestural communication to initiate GHC (44%), which requires an active and synchronized response from the partner. Moreover, in a third (34%) of the GHC initiations, the requisite coordination was achieved by seemingly effortless synchrony. Lastly, using a longitudinal approach, we find that for GHC initiations, communication occurs more frequently than shaping in experienced dyads and less in mother–offspring dyads. These findings are consistent with ontogenetic ritualization, thereby reflecting first documentation of chimpanzees communicating to coordinate a cultural practice. We conclude that chimpanzees show interactional flexibility in the socio-cultural domain, opening the possibility that the interplay between communication and culture is rooted in our deep evolutionary history. [ABSTRACT FROM AUTHOR]

A 41‐year‐old male vasectomized, zoo‐housed chimpanzee (Pan troglodytes) presented with progressive visual deficits due to bilateral cataract formation. Phacoemulsification and lenticular implant were performed by a veterinary and human board‐certified ophthalmologist team in a field setting. Post‐operative healing occurred without complication, and the patient returned to the troop with improved vision. [ABSTRACT FROM AUTHOR]

Among the many genes involved in the metabolism of therapeutic drugs, human arylamine N-acetyltransferases (NATs) genes have been extensively studied, due to their medical importance both in pharmacogenetics and disease epidemiology. One member of this small gene family, NAT2, is established as the locus of the classic human acetylation polymorphism in drug metabolism. Current hypotheses hold that selective processes favoring haplotypes conferring lower NAT2 activity have been operating in modern humans' recent history as an adaptation to local chemical and dietary environments. To shed new light on such hypotheses, we investigated the genetic diversity of the three members of the NAT gene family in seven hominid species, including modern humans, Neanderthals and Denisovans. Little polymorphism sharing was found among hominids, yet all species displayed high NAT diversity, but distributed in an opposite fashion in chimpanzees and bonobos (Pan genus) compared to modern humans, with higher diversity in Pan species at NAT1 and lower at NAT2, while the reverse is observed in humans. This pattern was also reflected in the results returned by selective neutrality tests, which suggest, in agreement with the predicted functional impact of mutations detected in non-human primates, stronger directional selection, presumably purifying selection, at NAT1 in modern humans, and at NAT2 in chimpanzees. Overall, the results point to the evolution of divergent functions of these highly homologous genes in the different primate species, possibly related to their specific chemical/dietary environment (exposome) and we hypothesize that this is likely linked to the emergence of controlled fire use in the human lineage.

Competition over scarce resources is common across the animal kingdom. Here we investigate the strategies of chimpanzees and children in a limited resource problem. Both species were presented with a tug-of-war apparatus in which each individual in a dyad received a tool to access a reward, but tools could not be used simultaneously. We assessed the equality of tool use as well as the frequency of turn taking. Both species managed to overcome this conflict of interest but used different strategies to do so. While there was substantial variation in chimpanzee behaviour, monopolization was the common course of action: tool use was asymmetric with individual chimpanzees monopolizing the resource. In children, turn-taking emerged as the dominant strategy: tool use was symmetric and children alternated access to the tool at a high rate. These results suggest that while both species possess strategies for solving limited resource problems, humans might have evolved species unique motivations and socio-cognitive skills for dealing with such conflicts of interest.

Comparative analyses of neuronal phenotypes in closely related species can shed light on neuronal changes occurring during evolution. The study of post-mortem brains of nonhuman primates (NHPs) has been limited and often does not recapitulate important species-specific developmental hallmarks. We utilize induced pluripotent stem cell (iPSC) technology to investigate the development of cortical pyramidal neurons following migration and maturation of cells grafted in the developing mouse cortex. Our results show differential migration patterns in human neural progenitor cells compared to those of chimpanzees and bonobos both in vitro and in vivo, suggesting heterochronic changes in human neurons. The strategy proposed here lays the groundwork for further comparative analyses between humans and NHPs and opens new avenues for understanding the differences in the neural underpinnings of cognition and neurological disease susceptibility between species.