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Authors thank the Royal Zoological Society Scotland for the core funding they provide to the Budongo Conservation Field Station. Associating with kin provides individual benefits but requires that these relationships be detectable. In humans, facial phenotype matching might help assess paternity; however, evidence for it is mixed. In chimpanzees, concealing visual cues of paternity may be beneficial due to their promiscuous mating system and the considerable risk of infanticide by males. On the other hand, detecting kin can also aid chimpanzees in avoiding inbreeding and in forming alliances that improve kin-mediated fitness. Although previous studies assessing relatedness based on facial resemblance in chimpanzees exist, they used images of captive populations in whom selection pressures and reproductive opportunities are controlled and only assessed maternity or paternity of adult offspring. In natural populations, the chances of infanticide are highest during early infancy, suggesting that young infants would benefit most from paternity concealment, whereas adults and subadults would benefit from the detection of all types of kin, including half-siblings. In our experiment, we conducted an online study with human participants, in which they had to assess the relatedness of chimpanzees based on facial similarity. To address previous methodological constraints, we used chimpanzee images across all ages, as well as maternal and paternal half-siblings. We found that kin status was detected above chance across all relatedness categories, with easier kin detection of father-offspring pairs, females, and older chimpanzees. Together, these findings support the existence of paternity confusion in infant chimpanzees and provide a possible mechanism for incest avoidance and kin-based social alliances in older individuals. Postprint

This project received funding from the European Union's 8th Framework Programme, Horizon 2020 (grant agreement number: 802719) and the St Andrews Restarting Research Funding Scheme (2020). 1. Studying animal behaviour allows us to understand how different species and individuals navigate their physical and social worlds. Video coding of behaviour is considered a gold standard: allowing researchers to extract rich nuanced behavioural datasets, validate their reliability, and for research to be replicated. However, in practice, videos are only useful if data can be efficiently extracted. Manually locating relevant footage in 10,000 s of hours is extremely time-consuming, as is the manual coding of animal behaviour, which requires extensive training to achieve reliability. 2. Machine learning approaches are used to automate the recognition of patterns within data, considerably reducing the time taken to extract data and improving reliability. However, tracking visual information to recognise nuanced behaviour is a challenging problem and, to date, the tracking and pose-estimation tools used to detect behaviour are typically applied where the visual environment is highly controlled. 3. Animal behaviour researchers are interested in applying these tools to the study of wild animals, but it is not clear to what extent doing so is currently possible, or which tools are most suited to particular problems. To address this gap in knowledge, we describe the new tools available in this rapidly evolving landscape, suggest guidance for tool selection, provide a worked demonstration of the use of machine learning to track movement in video data of wild apes, and make our base models available for use. 4. We use a pose-estimation tool, DeepLabCut, to demonstrate successful training of two pilot models of an extremely challenging pose estimate and tracking problem: multi-animal wild forest-living chimpanzees and bonobos across behavioural contexts from hand-held video footage. 5. With DeepWild we show that, without requiring specific expertise in machine learning, pose estimation and movement tracking of free-living wild primates in visually complex environments is an attainable goal for behavioural researchers. Publisher PDF

In most languages, individual words can be ambiguous between several different meanings, but through syntax and context the intended meaning of an ambiguous word usually becomes apparent. Many great ape gestures also have ambiguous meanings, which poses the problem of how individuals can interpret the signaller’s intended meaning in specific instances. We tested the effects of sequence compositionality and situational context (including behavioural and interpersonal contexts) in wild bonobos (Pan paniscus) at Wamba, DRCongo. We found no effect on a gesture’s meaning from its presence and position in sequence. However, two aspects of situational context did affect meaning: behaviour of the signaller immediately prior to gesturing, and relative age/sex of signaller and recipient. The intended meaning of ambiguous gestures was almost completely disambiguated by means of these aspects of context. Our findings suggest that the use of contextual information to interpret ambiguous signals predates the uniquely-human lineage and is not specific to language.

Animal communication has long been thought to be subject to pressures and constraints associated with social relationships. However, our understanding of how the nature and quality of social relationships relates to the use and evolution of communication is limited by a lack of directly comparable methods across multiple levels of analysis. Here, we analysed observational data from 111 wild groups belonging to 26 non-human primate species, to test how vocal communication relates to dominance style (the strictness with which a dominance hierarchy is enforced, ranging from 'despotic' to 'tolerant'). At the individual-level, we found that dominant individuals who were more tolerant vocalized at a higher rate than their despotic counterparts. This indicates that tolerance within a relationship may place pressure on the dominant partner to communicate more during social interactions. At the species-level, however, despotic species exhibited a larger repertoire of hierarchy-related vocalizations than their tolerant counterparts. Findings suggest primate signals are used and evolve in tandem with the nature of interactions that characterize individuals' social relationships. Publisher PDF

Despite important similarities having been found between human and animal communication systems, surprisingly little research effort has focussed on whether the cognitive mechanisms underpinning these behaviours are also similar. In particular, it is highly debated whether signal production is the result of reflexive processes, or can be characterized as intentional. Here, we critically evaluate the criteria that are used to identify signals produced with different degrees of intentionality, and discuss recent attempts to apply these criteria to the vocal, gestural and multimodal communicative signals of great apes and more distantly related species. Finally, we outline the necessary research tools, such as physiologically validated measures of arousal, and empirical evidence that we believe would propel this debate forward and help unravel the evolutionary origins of human intentional communication. This article is part of the theme issue ‘What can animal communication teach us about human language?’

Funding: This study was funded by an European Research Council Consolidator grant (ERC_CoG 2016_724608) awarded to KS (https://erc.europa.eu/funding/consolidator-grants). Joint attention, or sharing attention with another individual about an object or event, is a critical behaviour that emerges in pre-linguistic infants and predicts later language abilities. Given its importance, it is perhaps surprising that there is no consensus on how to measure joint attention in prelinguistic infants. A rigorous definition proposed by Siposova & Carpenter (2019) requires the infant and partner to gaze alternate between an object and each other (coordination of attention) and exchange communicative signals (explicit acknowledgement of jointly sharing attention). However, Hobson and Hobson (2007) proposed that the quality of gaze between individuals is, in itself, a sufficient communicative signal that demonstrates sharing of attention. They proposed that observers can reliably distinguish “sharing”, “checking”, and “orienting” looks, but the empirical basis for this claim is limited as their study focussed on two raters examining looks from 11-year-old children. Here, we analysed categorisations made by 32 naïve raters of 60 infant looks to their mothers, to examine whether they could be reliably distinguished according to Hobson and Hobson’s definitions. Raters had overall low agreement and only in 3 out of 26 cases did a significant majority of the raters agree with the judgement of the mother who had received the look. For the looks that raters did agree on at above chance levels, look duration and the overall communication rate of the mother were identified as cues that raters may have relied upon. In our experiment, naïve third party observers could not reliably determine the type of look infants gave to their mothers, which indicates that subjective judgements of types of look should not be used to identify mutual awareness of sharing attention in infants. Instead, we advocate the use of objective behaviour measurement to infer that interactants know they are ‘jointly’ attending to an object or event, and believe this will be a crucial step in understanding the ontogenetic and evolutionary origins of joint attention. Publisher PDF

Maternal cannibalism, whereby a mother consumes her own offspring, occurs in various animal taxa and is commonly explained by nutritional stress or environmental pressures. It is rare in nonhuman primates and is considered an aberrant behavior only observed under high-stress conditions. It was therefore surprising when, in the first reported case of cannibalism in wild bonobos, a mother consumed part of the dead infant at LuiKotale. Here we report two more cases of maternal cannibalism by wild bonobos at two different study sites, Wamba and Kokolopori. The dead infants' mothers participated in the cannibalism in both cases. At Kokolopori, although the mother did consume part of the carcass, it was held and shared by another dominant female. At Wamba, the mother was a dominant female within the community and was the primary consumer of the carcass. In both cases, cannibalism resembled other meat-eating events, with the dominant female controlling meat consumption. Infanticide was not observed in either case, but its occurrence could not be ruled out. Although rare, the occurrence of maternal cannibalism at three different study sites suggests that this may represent part of the behavioral repertoire of bonobos, rather than an aberrant behavior.

The 11th International Conference on the Evolution of Language (Evolang 11) was hosted at the Lavin-Bernick Center for University Life at Tulane University in New Orleans, LA, USA, from 21 March to 24 March 2016. The University of Southern Mississippi organised the conference, with Heidi Lyn as Chair of the local organising committee. Over 200 delegates gathered for this second American Evolang, and were treated not only to a wide range of current research in language origins and evolution, but also to local ‘NOLA’ food and culture as well. Evolang hosted a reception at Mardi Gras World—a stylised warehouse storing numerous Mardi Gras floats and costumes, where guests were serenaded with a brass band and committee members threw beads into the amused, cocktail-sipping crowd. The conference banquet was held at the colonial-era-style Audubon Tea Room with live jazz and a swing dancing lesson led by Thom Scott-Phillips. Post-conference events included a ghost tour, swamp tours, and a plantation tour. This was the 20th anniversary of the very first Evolang, held in Edinburgh in 1996, and saw the release of the first issue of the Journal of Language Evolution . With a 20-year history, it is hardly surprising that there has been a strong ‘self-reflective’ tendency at recent Evolang conferences, as witnessed, for example, in the ‘Perspectives on Evolang’ section in the proceedings of Evolang 10 (Cartmill et al. 2014), as well as in some of the contributions in the first issue of JoLE (Dediu and de Boer 2016; Hammarstrom 2016). Something that is repeatedly mentioned in these publications is the observation that ‘work on language evolution has become much more rigorous: we are discovering methods by which questions we could formerly only speculate about can now be investigated empirically’ (de Boer 2014). These ‘self-reflective’ tendencies were also exemplified …

Cross-species comparison of great ape gesturing has so far been limited to the physical form of gestures in the repertoire, without questioning whether gestures share the same meanings. Researchers have recently catalogued the meanings of chimpanzee gestures, but little is known about the gesture meanings of our other closest living relative, the bonobo. The bonobo gestural repertoire overlaps by approximately 90% with that of the chimpanzee, but such overlap might not extend to meanings. Here, we first determine the meanings of bonobo gestures by analysing the outcomes of gesturing that apparently satisfy the signaller. Around half of bonobo gestures have a single meaning, while half are more ambiguous. Moreover, all but 1 gesture type have distinct meanings, achieving a different distribution of intended meanings to the average distribution for all gesture types. We then employ a randomisation procedure in a novel way to test the likelihood that the observed between-species overlap in the assignment of meanings to gestures would arise by chance under a set of different constraints. We compare a matrix of the meanings of bonobo gestures with a matrix for those of chimpanzees against 10,000 randomised iterations of matrices constrained to the original data at 4 different levels. We find that the similarity between the 2 species is much greater than would be expected by chance. Bonobos and chimpanzees share not only the physical form of the gestures but also many gesture meanings., Author summary Bonobos and chimpanzees are closely related members of the great ape family, and both species use gestures to communicate. We are able to deduce the meaning of great ape gestures by looking at the ‘Apparently Satisfactory Outcome’ (ASO), which reflects how the recipient of the gesture reacts and whether their reaction satisfies the signaller; satisfaction is shown by the signaller ceasing to produce more gestures. Here, we use ASOs to define the meaning of bonobo gestures, most of which are used to start or stop social interactions such as grooming, travelling, or sex. We then compare the meanings of bonobo gestures with those of chimpanzees and find that many of the gestures share the same meanings. Bonobos and chimpanzees could, in principle, understand one another’s gestures; however, more research is necessary to determine how such gestures and gesture meanings are acquired.

Summary Some scientists have suggested that, among Hominidae, prolonged postmenopausal longevity evolved uniquely in humans [1], while others disagree [2]. There have, however, been few empirical studies on how physiological aging and somatic durability in humans compare to our closest relatives — chimpanzees and bonobos [3]. If prolonged lifespan is selected for in humans, physiological aging, including reproductive and somatic senescence, might be different for Pan and Homo . But it seems that the parameters of reproductive senescence, such as the age of having their final offspring and the number of years between generations, are not very different between chimpanzee and human females [4]. Here, we report evidence for five cases of long-sightedness (presbyopia) in old wild bonobos, exhibited during grooming. Our results suggest that senescence of the eye has not changed much since the divergence of Pan and Homo from their common ancestor.

Research on great ape gestural communication has hitherto prioritised the signaller, focusing on the expressed repertoire, the set of gesture types that an individual deploys. In this study of wild bonobos (Pan paniscus), we also examine the understood repertoire, the set of gesture types that a recipient understands: a recipient understands a gesture if they respond to the signaller with an Apparently Satisfactory Outcome (ASO). Combining the understood and expressed repertoires substantially expands an individual’s overall repertoire. Hence, we propose that including the understood repertoire better represents an individual’s actual communicative repertoire, and may for the first time reveal gesture types received exclusively by specific subsets of individuals. Significant differences between expressed and understood repertoires might result from two things: (1) gestures are ritualised between signallers and recipients and may therefore be unidirectional in some cases, or (2) the circumstances of use differ among age-sex groups, limiting the need for an individual to use a certain gesture type. In the latter, we expect consistency in particular age-sex groups whereas unidirectional comprehension as a result of ritualization would predict random distribution among individuals. We further compare our dataset with and without gesture instances occurring in play, as play may be a context in which individuals deploy gestures that they rarely or never use otherwise. Assessing the understood repertoire is a useful tool for animal communication researchers, not only allowing shorter study-periods, but also to discover gesture types specific to subsets of individuals, which may reveal much about a species’ social behaviour.

Great apes give gestures deliberately and voluntarily, in order to influence particular target audiences, whose direction of attention they take into account when choosing which type of gesture to use. These facts make the study of ape gesture directly relevant to understanding the evolutionary precursors of human language; here we present an assessment of ape gesture from that perspective, focusing on the work of the "St Andrews Group" of researchers. Intended meanings of ape gestures are relatively few and simple. As with human words, ape gestures often have several distinct meanings, which are effectively disambiguated by behavioural context. Compared to the signalling of most other animals, great ape gestural repertoires are large. Because of this, and the relatively small number of intended meanings they achieve, ape gestures are redundant, with extensive overlaps in meaning. The great majority of gestures are innate, in the sense that the species' biological inheritance includes the potential to develop each gestural form and use it for a specific range of purposes. Moreover, the phylogenetic origin of many gestures is relatively old, since gestures are extensively shared between different genera in the great ape family. Acquisition of an adult repertoire is a process of first exploring the innate species potential for many gestures and then gradual restriction to a final (active) repertoire that is much smaller. No evidence of syntactic structure has yet been detected.

Medidas morfometricas foram tomadas, foi estimada abundância e feitas observacoes ecologicas para Sibon annulatus, S. argus, S. longifrenis e S. nebulatus em dois habitats neotropicais: Uma floresta pantanosa de baixada na Costa Rica e uma floresta de neblina no Panama. Quarenta e quatro e 58 serpentes adultas foram registradas na Costa Rica e no Panama, respectivamente. Diferencas morfologicas e na condicao corporal significativas foram minimas entre as especies para ambas as localidades. Sao discutidas as observacoes sobre alimentacao, reproducao, abundância, distribuicao e um registro de um novo tamanho maximo para S. annulatus.

Funding was provided by the Wenner-Gren Foundation Dissertation Fieldwork Grant, Japan Society for the Promotion of Science (JSPS) Grant in Aid for Scientific Research, JSPS Core-to-Core Program, and University of St Andrews 600th Anniversary Scholarship. In animal communication, signallers and recipients are typically different: each signal is given by one subset of individuals (members of the same age, sex, or social rank) and directed towards another. However, there is scope for signaller-recipient interchangeability in systems where most signals are potentially relevant for all age-sex groups, such as great ape gestural communication. In this study of wild bonobos (Pan paniscus), we aimed to discover whether their gestural communication is indeed a mutually understood communicative repertoire, in which all individuals can act as both signallers and recipients. While past studies have only examined the expressed repertoire, the set of gesture types that a signaller deploys, we also examined the understood repertoire, the set of gestures to which a recipient reacts in a way that satisfies the signaller. We found that most of the gestural repertoire was both expressed and understood by all age and sex groups, with few exceptions, suggesting that during their lifetimes all individuals may use and understand all gesture types. Indeed, as the number of overall gesture instances increased, so did the proportion of individuals estimated to both express and understand a gesture type. We compared the community repertoire of bonobos to that of chimpanzees, finding an 88% overlap. Observed differences are consistent with sampling effects generated by the species’ different social systems, and it is thus possible that the repertoire of gesture types available to Pan is determined biologically. Publisher PDF