Evolutionary roads to syntax

The author is grateful to the Swiss National Science Foundation (Project 31003A_166458) for support.Syntax is habitually named as what sets human language apart from other communication systems, but how did it evolve? Comparative research on animal behaviour has contributed in important ways, with mainly three sets of data. First, animals have been subjected to artificial grammar tasks, based on the hypothesis that human syntax has evolved through advanced computational capacity. In these experiments humans generally outperform animals, but there are questions about validity, as experimental stimuli are (deliberately) kept devoid of semantic content. Second, animal communication has been compared in terms of the surface structures with the aim of developing a typology of animal syntax, based on the hypothesis that syntax is an evolutionary solution to the constraints of small signal repertoires. A wide range of combinatorial phenomena has been described, mainly in nonhuman primates, but there is little support for the hypothesis that syntax has emerged due to repertoire size constraints. A third way of studying the evolution of syntax is to compare how animals perceive and communicate about external events, the mental deep structure of syntax. Human syntax is closely aligned with how we perceive events in terms of agency, action and patience, each with subsidiary functions. The event perception hypothesis has been least explored in animals and requires a serious research programme.PostprintPeer reviewe

Alarm calling

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Social familiarity affects Diana monkey (Cercopithecus diana diana) alarm call responses in habitat-specific ways

The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement no. 283871.Male Diana monkeys produce loud and acoustically distinct alarm calls to leopards and eagles that propagate over long distances, much beyond the immediate group. Calling is often contagious, with neighbouring males responding to each other’s calls, indicating that harem males communicate both to local group members and distant competitors. Here, we tested whether male Diana monkeys responding to each other’s alarm calls discriminated familiar from unfamiliar callers in two populations in Taï Forest (Ivory Coast) and on Tiwai Island (Sierra Leone). At both sites, we found specific acoustic markers in male alarm call responses that discriminated familiar from unfamiliar callers, but response patterns were site-specific. On Tiwai Island, males responded to familiar males’ eagle alarms with ‘standard’ eagle alarm calls, whereas unfamiliar males triggered acoustically atypical eagle alarms. The opposite was found in Taï Forest where males responded to unfamiliar males’ eagle alarm calls with ‘standard’ eagle alarms, and with atypical eagle alarms to familiar males’ calls. Moreover, only Taï, but not Tiwai, males also marked familiarity with the caller in their leopard-induced alarms. We concluded that male Diana monkeys encode not only predator type but also signaller familiarity in their alarm calls, although in population-specific ways. We explain these inter-site differences in vocal behaviour in terms of differences in predation pressure and population density. We discuss the adaptive function and implications of this behaviour for the origins of acoustic flexibility in primate communication.Publisher PDFPeer reviewe

Noninvasive diagnosis of liver fibrosis in NAFLD: Tips tricks

Non-alcoholic fatty liver disease (NAFLD) is highly prevalent, affecting 25% of the general population. Liver fibrosis must be accurately evaluated in NAFLD to determine the severity of the disease and establish patient management. We present the case of a patient with diabetes showing minimal perturbations of liver function tests, but for whom a simple blood fibrosis test suggested the presence of advanced liver fibrosis. The patient was referred to a hepatologist who confirmed the diagnosis using a specialized blood test and transient elastography. Thereafter, a liver biopsy was performed and pathology was positive for cirrhosis. An upper gastrointestinal endoscopy showed no gastrointestinal varices. Simple blood fibrosis tests are very attractive for the first-line evaluation of liver fibrosis by non-specialists in the large populations of NAFLD and diabetic patients, as they are inexpensive, easy to perform, and accurate for the exclusion of advanced liver fibrosis. Non-specialists must however use them appropriately to avoid unnecessary over-referral to hepatologists. These latter can confirm the diagnosis of advanced liver fibrosis via agreement between a specialized blood test and liver elastography. In addition to the diagnosis of liver fibrosis, noninvasive tests are now recommended for the screening of gastrointestinal varices at risk of bleeding. Liver elastography must be interpreted by a specialist because the choice of the probe, the quality of the examination, and many conditions other than liver fibrosis can influence the examination and create a risk of false positives. Noninvasive tests of liver fibrosis have enabled exciting possibilities for widespread screening of advanced forms of chronic liver diseases. This will become particularly relevant in NAFLD when drugs currently in therapeutic trials become available in the next few years

Trade-offs in the production of animal vocal sequences:insights from the structure of wild chimpanzee pant hoots

The study was funded by Swiss National Science Foundation (310030_143359) and European Research Council project grants awarded to KZ (PRILANG 283871).Background Vocal sequences - utterances consisting of calls produced in close succession - are common phenomena in animal communication. While many studies have explored the adaptive benefits of producing such sequences, very little is known about how the costs and constraints involved in their production affect their form. Here, we investigated this issue in the chimpanzee (Pan troglodytes schweinfurthii) pant hoot, a long and structurally complex vocal sequence comprising four acoustically distinct phases – introduction, build-up, climax and let-down. Results We found that in each of these phases, and for the sequence as a whole, there was a negative relationship between the number of calls produced and their average duration. There was also a negative relationship between the total duration of some adjacent phases. Significant relationships between the fundamental frequency of calls and their number or duration were found for some phases of the sequence, but the direction of these relationships differed between particular phases. Conclusions These results indicate that there are trade-offs in terms of signal duration at two levels in pant-hoot production: between call number and duration, and between the relative durations of successive phases. These trade-offs are likely to reflect biomechanical constraints on vocal sequence production. Phase-specific trade-offs also appear to occur between fundamental frequency and call number or duration, potentially reflecting that different phases of the sequence are associated with distinct types of information, linked in different ways to call pitch. Overall, this study highlights the important role of costs and constraints in shaping the temporal and acoustic structure of animal vocal sequences.Publisher PDFPeer reviewe

Why mutual helping in most natural systems is neither conflict-free nor based on maximal conflict

Funding: All authors are funded by individual grants from the Swiss Science Foundation.Mutual helping for direct benefits can be explained by various game theoretical models, which differ mainly in terms of the underlying conflict of interest between two partners. Conflict is minimal if helping is self-serving and the partner benefits as a by-product. In contrast, conflict is maximal if partners are in a prisoner’s dilemma with both having the payoff-dominant option of not returning the other’s investment. Here, we provide evolutionary and ecological arguments for why these two extremes are often unstable under natural conditions and propose that interactions with intermediate levels of conflict are frequent evolutionary endpoints. We argue that by product helping is prone to becoming an asymmetric investment game since even small variation in by-product benefits will lead to the evolution of partner choice, leading to investments and partner monitoring. Second, iterated prisoner’s dilemmas tend to take place in stable social groups where the fitness of partners is interdependent, to the effect that a certain level of helping is self-serving. In sum, intermediate levels of mutual helping are expected in nature, while efficient partner control mechanisms may allow reaching higher levels.PostprintPeer reviewe

Répertoire et contextes sociaux des cris unitaires du colobe vert (procolobus verus) dans le Parc National de Taï (PNT), Côte d\'Ivoire

Pour caractériser l\'environnement social et écologique du Colobe Vert (Procolobus verus), des observations régulières par tranche de 15 minutes d\'animaux focaux dans trois groupes ont été méné. Les observations et les enregistrements de cris occasionnels (Ad libitum) ont permis de répertorier huit (8) types de cris unitaires émis par différentes classes de sexes et d\'âges. Ces cris peuvent être regroupés en quatre catégories selon les contextes sociaux dans lesquels ils interviennent : les cris a, b et c en cas de prédation et de trouble (présence de prédateur, cris d\'alarme d\'autres espèces), les cris f et g en situation de conflit (combat entre individus), les cris b, c et e en contexte de stabilité (calme apparent), et les cris b, c et e pour signaler des rencontres inter-groupes (rencontre avec d\'autres groupes de singes).In order to knod how Olive Colobus monkeys (Procolobus verus) interact with their social and ecological environment, we carried out regular observations by 15 minutes old section of focal animals in three groups. These observations associated with the recordings of occasional calls (Ad libitum) enabled us to index eight (8) types of unit calls emitted by various sex and age classes. These calls can be gathered into four types according to social contexts in which they happened : the calls a, b and c in context of predation and disturbance (presence of predator, alarm calls from other monkey species), the calls f and g in a situation of conflict (fights between individual), the calls b, c and e as a signal of stability (peaceful context), and the calls b, c and e in case of intergroup encounters (encounter with other monkey groups). Keywords: Colobe Vert, vocalisation, cri unitaire, contexte social, communication, Parc National de Taï, Côte d'Ivoire.Olive Colobus, vocalization, unit call, social context, communication, Taï National Park, Ivory Coast.Sciences & Nature Vol. 4 (2) 2007: pp. 137-14

Wild chimpanzees' use of single and combined vocal and gestural signals

We describe the individual and combined use of vocalizations and gestures in wild chimpanzees. The rate of gesturing peaked in infancy and, with the exception of the alpha male, decreased again in older age groups, while vocal signals showed the opposite pattern. Although gesture-vocal combinations were relatively rare they were consistently found in all age groups, especially during affiliative and agonistic interactions. Within behavioural contexts rank (excluding alpha-rank) had no effect on the rate of male chimpanzees’ use of vocal or gestural signals and only a small effect on their use of combination signals. The alpha male was an outlier, however, both as a prolific user of gestures and recipient of high levels of vocal and gesture-vocal signals. Persistence in signal use varied with signal type: chimpanzees persisted in use of gestures and gesture vocal combinations after failure, but where their vocal signals failed they tended to add gestural signals to produce gesture-vocal combinations. Overall, chimpanzees employed signals with a sensitivity to the public/private nature of information, by adjusting their use of signal types according to social context and by taking into account potential out of-sight audiences. We discuss these findings in relation to the various socio-ecological challenges that chimpanzees are exposed to in their natural forest habitats and the current discussion of multimodal communication in great apes.Publisher PDFPeer reviewe

Syntax and compositionality in animal communication

Much of the research reviewed in this article has benefitted from funding by the Leverhulme Trust, the European Research Council, the Royal Zoological Society of Scotland, and the Swiss National Science Foundation.Syntax has been found in animal communication but only humans appear to have generative, hierarchically structured syntax. How did syntax evolve? I discuss three theories of evolutionary transition from animal to human syntax: computational capacity, structural flexibility and event perception. The computation hypothesis is supported by artificial grammar experiments consistently showing that only humans can learn linear stimulus sequences with an underlying hierarchical structure, a possible by-product of computationally powerful large brains. The structural flexibility hypothesis is supported by evidence of meaning-bearing combinatorial and permutational signal sequences in animals, with sometimes compositional features, but no evidence for generativity or hierarchical structure. Again, animals may be constrained by computational limits in short-term memory but possibly also by limits in articulatory control and social cognition. The event categorization hypothesis, finally, posits that humans are cognitively predisposed to analyse natural events by assigning agency and assessing how agents impact on patients, a propensity that is reflected by the basic syntactic units in all languages. Whether animals perceive natural events in the same way is largely unknown, although event perception may provide the cognitive grounding for syntax evolution.PostprintPeer reviewe