Emilie Genty

Gestural communication of the gorilla (Gorilla gorilla): repertoire, intentionality and possible origins

Social groups of gorillas were observed in three captive facilities and one African field site. Cases of potential gesture use, totalling 9,540, were filtered by strict criteria for intentionality, giving a corpus of 5,250 instances of intentional gesture use. This indicated a repertoire of 102 gesture types. Most repertoire differences between individuals and sites were explicable as a consequence of environmental affordances and sampling effects: overall gesture frequency was a good predictor of universality of occurrence. Only one gesture was idiosyncratic to a single individual, and was given only to humans. Indications of cultural learning were few, though not absent. Six gestures appeared to be traditions within single social groups, but overall concordance in repertoires was almost as high between as within social groups. No support was found for the ontogenetic ritualization hypothesis as the chief means of acquisition of gestures. Many gestures whose form ruled out such an origin, i.e. gestures derived from species-typical displays, were used as intentionally and almost as flexibly as gestures whose form was consistent with learning by ritualization. When using both classes of gesture, gorillas paid specific attention to the attentional state of their audience. Thus, it would be unwarranted to divide ape gestural repertoires into ‘innate, species-typical, inflexible reactions’ and ‘individually learned, intentional, flexible communication’. We conclude that gorilla gestural communication is based on a species-typical repertoire, like those of most other mammalian species but very much larger. Gorilla gestures are not, however, inflexible signals but are employed for intentional communication to specific individuals.

Why do gorillas make sequences of gestures

Great ape gestures have attracted considerable research interest in recent years, prompted by their flexible and intentional pattern of use; but almost all studies have focused on single gestures. Here, we report the first quantitative analysis of sequential gesture use in western gorillas (Gorilla gorilla gorilla), using data from three captive groups and one African study site. We found no evidence that gesture sequences were given for reasons of increased communicative efficiency over single gestures. Longer sequences of repeated gestures did not increase the likelihood of response, and using a sequence was seldom in reaction to communicative failure. Sequential combination of two gestures with similar meanings did not generally increase effectiveness, and sometimes reduced it. Gesture sequences were closely associated with play contexts. Markov transition analysis showed two networks of frequently co-occurring gestures, both consisting of gestures used to regulate play. One network comprised only tactile gestures, the other a mix of silent, audible and tactile gestures; apparently, these clusters resulted from gesture use in play with proximal or distal contact, respectively. No evidence was found for syntactic effects of sequential combination: meanings changed little or not at all. Semantically, many gestures overlapped massively with others in their core information (i.e. message), and gesture messages spanned relatively few functions. We suggest that the underlying semantics of gorilla gestures is highly simplified compared to that of human words. Gesture sequences allow continual adjustment of the tempo and nature of social interactions, rather than generally conveying semantically referential information or syntactic structures.

Spatial Reference in a Bonobo Gesture

Great apes frequently produce gestures during social interactions to communicate in flexible, goal-directed ways [1-3], a feature with considerable relevance for the ongoing debate over the evolutionary origins of human language [1, 4]. But despite this shared feature with language, there has been a lack of evidence for semantic content in ape gestures. According to one authoritative view, ape gestures thus do not have any specific referential, iconic, or deictic content, a fundamental difference versus human gestures and spoken language [1, 5] that suggests these features have a more recent origin in human evolution, perhaps caused by a fundamental transition from ape-like individual intentionality to human-like shared intentionality [6]. Here, we revisit this human uniqueness claim with a study of a previously undescribed human-like beckoning gesture in bonobos that has potentially both deictic and iconic character. We analyzed beckoning in two groups of bonobos, kept under near natural environmental and social conditions at the Lola Ya Bonobo sanctuary near Kinshasa, Democratic Republic of Congo, in terms of its linguistic content and underlying communicative intention.

Great ape gestures: intentional communication with a rich set of innate signals

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.

Iconic gesturing in bonobos.

We comment on a recent behavioral study in which we describe a human-like beckoning gesture in 2 groups of bonobos, used in combination with sexual solicitation postures. The beckoning gesture fulfils key criteria of deixis and iconicity, in that it communicates to a distant recipient the desired travel path in relation to a specific social intention, i.e., to have sex at another location. We discuss this finding in light of the fact that, despite the documented great ape capacity and obvious communicative advantage, referential gestures are still surprisingly rare in their natural communication. We address several possibilities for this peculiar underuse and are most compelled by the notion that non-human primates are generally not very motivated to share their experiences of external objects or events with others, which removes most reasons for referential signaling.

Complex patterns of signalling to convey different social goals of sex in bonobos, Pan paniscus

Sexual behaviour in bonobos (Pan paniscus) functions beyond mere reproduction to mediate social interactions and relationships. In this study, we assessed the signalling behaviour in relation to four social goals of sex in this species: appeasement after conflict, tension reduction, social bonding and reproduction. Overall, sexual behaviour was strongly decoupled from its ancestral reproductive function with habitual use in the social domain, which was accompanied by a corresponding complexity in communication behaviour. We found that signalling behaviour varied systematically depending on the initiator’s goals and gender. Although all gestures and vocalisations were part of the species-typical communication repertoire, they were often combined and produced flexibly. Generally, gestures and multi-modal combinations were more flexibly used to communicate a goal than vocalisations. There was no clear relation between signalling behaviour and success of sexual initiations, suggesting that communication was primarily used to indicate the signaller’s intention, and not to influence a recipient’s willingness to interact sexually. We discuss these findings in light of the larger question of what may have caused, in humans, the evolutionary transition from primate-like communication to language.

Bonobos modify communication signals according to recipient familiarity

Human and nonhuman primate communication differs in various ways. In particular, humans base communicative efforts on mutual knowledge and conventions shared between interlocutors. In this study, we experimentally tested whether bonobos (Pan paniscus), a close relative to humans, are able to take into account the familiarity, i.e. the shared interaction history, when communicating with a human partner. In five experimental conditions we found that subjects took the recipients’ attentional state and their own communicative effectiveness into account by adjusting signal production accordingly. More importantly, in case of communicative failure, subjects repeated previously successful signals more often with a familiar than unfamiliar recipient, with whom they had no previous interactions, and elaborated by switching to new signals more with the unfamiliar than the familiar one, similar to what has previously been found in two year-old children. We discuss these findings in relation to the human capacity to establish common ground between interlocutors, a crucial aspect of human cooperative communication.

Brown Lemurs (Eulemur fulvus) Can Master the Qualitative Version of the Reverse-Reward Contingency

Behavioral flexibility that requires behavioral inhibition has important fitness consequences. One task commonly used to assess behavioral inhibition is the reverse-reward task in which the subject is rewarded by the non selected items. Lemurs were tested for their ability to solve the qualitative version of the reverse-reward task with the choice between identical quantities of different food items instead of different quantities of the same food. Two of four subjects mastered the task without a correction procedure and were able to generalize the acquired rule to novel combinations of food. One of the two subjects competent on the quality version of the task could transfer this ability to different quantities of the same food. Our results are compared to lemurs’ performances when tested under the quantitative version in a previous study and those of capuchin monkeys tested under a similar paradigm. The whole results suggest that the qualitative version of the reverse-reward task may be easier to master than its quantitative counterpart and that lemurs perform better than capuchin monkeys as they were able to later transfer the learning rule to the quantitative version of the task.

Social play as joint action: A framework to study the evolution of shared intentionality as an interactional achievement

Social play has a complex, cooperative nature that requires substantial coordination. This has led researchers to use social games to study cognitive abilities like shared intentionality, the skill and motivation to share goals and intentions with others during joint action. We expand this proposal by considering play as a joint action and examining how shared intentionality is achieved during human joint action. We describe how humans get into, conduct, and get out of joint actions together in an orderly way, thereby constructing the state of “togetherness” characteristic of shared intentionality. These processes play out as three main phases, the opening (where participants are ratified and joint commitments are established), the main body (where progress, ongoing commitments, and possible role reversals are coordinated), and the closing (where the intention to terminate the action is coordinated and where participants take leave of each other). We use this process in humans as a framework for examining how various animal species get into, maintain, and get out of play bouts. This comparative approach constitutes an alternative measure of those species’ possession of shared intentionality. Using this framework, we review the play literature on human children and different social species of mammals and birds in search of behavioral markers of shared intentionality in the coordination of play bouts. We discuss how our approach could shed light on the evolution of the special human motivation to cooperate and share psychological states with others.

Social learning in bonobos: Learning of individual food preferences and copying despite better knowledge

Over the past few decades there has been a growing interest into social learning in animals. The importance of social influence on food choice has been demonstrated across a number of species including humans. Many more recent studies into social learning and conformity have looked into the influence of group social norms on the behaviour of individuals and it’s relevance in cultural evolution. The present study’s primary aim was to investigate bonobos’ capacity for social learning of food preferences from one or two demonstrators. We first wished to test whether bonobos in a captive social group could learn a food colour preference through mere observation of two conspecific demonstrators and the time-scale required for such learning. Secondly, we wished to investigate how these same individuals would perform in a reverse social learning task with one of the same demonstrators. In order to manipulate the demonstrators’ food preferences we used pink and blue artificial colouring and sweetening or bittering agents. In experiment 1, the ‘simple social learning’ task, two demonstrators consistently made a biased food colour choice (pink) in front of the subjects who were subsequently presented with the two, coloured, but palatable food items to choose from. In experiment 2, the ‘reverse social learning’ task, we used just one of the two demonstrators who consistently made the opposite colour choice (blue) with a different food type. Having observed the demonstrator, the subjects were tested once again. Overall, in the ‘simple social learning’ task, subjects preferentially chose the colour most consumed by the demonstrators (pink). In the ‘reverse social learning’ task, subjects preferentially chose the colour most consumed by the demonstrator (blue), but only after the additional 4 days of exposure. The results from experiment 1 followed our predictions and are in accordance with the literature on social learning and social facilitation of acceptance of novel foods. The results from experiment 2 showed that longer exposure was necessary in order to achieve a similar result, indicating that the ‘reverse social learning’ task was more difficult for the bonobos to manage. This corresponds nicely with previous studies of bonobos in which experimental paradigms were reversed. Furthermore, and perhaps of more interest is the fact that despite gaining knowledge that both colours were palatable during testing, subjects chose to eat more of the food consumed by the demonstrator. We discuss these findings in light of previous studies and considering influential factors such as the social status of the demonstrator.