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http://www.nature.com/scitable/knowledge/library/primate -communication -67560503 Primate Communication By: Klaus Zuberbuhler (School of Psychology, University of St Andrews and Cognitive Science Centre, University of Neuchatel ) © 2012 Nature Education Citation: Zuberbuhler, K. (2012) Primate Communication. Nature Education Knowledge 3(10) :83 Why Do Primates Communicate? Like other animals, primates communicate to satisfy their biological and social needs, such as avoiding predators, interacting with o ther group members, or maintaining cohesion during travel. To this end, they use a range of different signals, many of which have directly evolved as ritualised abbreviations of more basic behavioural or physiological processes. For example, chimpanzees so metimes react with pilo -erection (bristling of hair) during conflicts, which makes them appear bigger and more dangerous and conveys their willingness to escalate (van Hooff 1973). Communication signals have thus evolved partly to be psychologically effect ive on receivers (Guilford & Dawkins 1991). Is Primate Communication More Complex Compared to Other Groups of Animals? Most primates live in groups in which members know each other individually and maintain multifaceted social relations; factors which ar e thought to favour the evolution of advanced communication skills (McComb & Semple 2005). However, other animals with complex social behaviour, such as dolphins, also show sophisticated communication skills, suggesting that complex communication is not li mited to primates (Janik 2009). Do Primates ‘Cry Wolf'? Monkeys sometimes produce terrestrial predator alarms when competing over food, even though no predator is around. As a result, other group members run to safety, which then gives the caller a foragi ng advantage (Wheeler 2009). In general, however, primates rarely produce such dishonest signals, or ‘cry wolf'. Why is dishonest signalling not more common? One solution has been given by Zahavi's (1975) ‘handicap principle', which states that receivers w ill only attend to signals that are difficult to fake by low -quality or poorly motivated individuals. It has also been argued that, in primates, individuals know and need each other and thus gain little from deception (Silk et al . 2000). Moreover, primates can learn to ignore unreliable signallers (Cheney & Seyfarth 1988), suggesting that ‘reputation' acts as a further safeguard against dishonest signalling. Honest signalling prevails because of sceptical receivers. Channels of Primate Communication Primat e communication takes place in all major modalities. Olfaction is one of the least researched modalities, partly because it is difficult to measure and manipulate olfactory cues, especially in the wild. Nevertheless, probably all primates secrete scents th at influence others. An interesting human example is women apparently influencing each other's ovulation through odourless cues (Stern & McClintock 1998). Another remarkable example is the ‘stink fights' of male ring -tailed lemurs. During conflicts, males rub their tails across their wrist and chest glands before waving them at each other (Jolly 1966). Generally, olfactory cues play important roles in stating claims over resources and displaying individual characteristics, such as reproductive state, social rank, immuno -compatibility, and other genetic traits (Wedekind et al . 1995). One difficulty with research on olfactory communication is that it is often unclear whether scent - bearing substances are actively and strategically released into the environment, or whether they are mere by -products of general metabolic processes. Active scent marking and self -anointment (applying scent -bearing substances onto a substrate or body) are notable exceptions, but in many cases it is unclear whether olfactory cues quali fy as proper communication signals. Figure 1: Gestural communication. Gestural communication in the Sonso chimpanzee community of Budongo Forest, Uganda. The young infant ‘Cathy’ reaches out to the older infant ‘Zak’, who interprets and accepts this gesture as a play invitation. ‘Zak’ responds with a ‘play -face’ and both begin to wrestle. Primate gestures have been defined as 'discrete, mechanically ineffe ctive physical movements of the body observed during periods of intentional communication' (Hobaiter & Byrne 2011). © 2012 Nature Education Courtesy of C. Hobaiter. All rights reserved. In the visu al domain, primates use a range of facial displays and body part movements as communication signals, sometimes combined with tactile components. Gorilla chest beating and Rhesus monkeys bared -teeth displays are examples of how different species express soc ial rank with visual signals. Current research has focused much on gestures, which are interesting because of their partly flexible, partly species -specific use in a variety of social contexts. Gestures have been studied mainly in great apes, where conside rable variation between individuals and groups has been found. Whether some of this variation is socially learned and thus potentially ‘cultural' is still an unresolved question. A more established finding is that, during gesturing, apes take into account each other's attention and deploy their signals accordingly (Call & Tomasello 2007; Figure 1). Interestingly, however, there is almost no evidence that primate gestures, or combinations thereof, carry symbolic meaning by referring to external entities (Car tmill & Byrne 2010). Instead, they appear to function primarily to facilitate ongoing social interactions, to bond with others, or to persuade others to behave in a desired way. For many primates, vocalizations are the main channel of communication. Vocal repertoires tend to be species -specific, indicating that they develop under strong genetic control. Humans also possess a specific repertoire of such context -specific calls but, in addition, they also possess extensive control over vocal production, an ab ility that develops early and is crucial for the acquisition of speech. Such high degrees of vocal control is not seen in other primates and one interesting hypothesis is that it is the product of relatively recent genetic changes during human evolution (E nard et al . 2002). If this is correct then our hominid ancestors must have relied on a primate -like communication system. In sum, primates communicate using all major modalities. Olfactory communication is poorly researched but is probably widespread, mostly inflexible and contextually confined to basic biological functions. Within the visual modality, gestures are somewhat of an exception because of their flexibility and socially targeted use. Finally, vocal communication is based on species - specific r epertoires, with some flexibility in use but little in structure. The Origins of Syntax and Meaning What are the evolutionary origins of syntax? A persistent claim has been that human languages are the product of a genetically endowed, universal grammatic al deep structure that — amongst other things — enables children to acquire language without much help (Chomsky 2005). Although extremely influential, it has been impossible to find convincing empirical support for this idea, for example by identifying gra mmatical features that are shared amongst all the world's languages (Evans & Levinson 2009). Nevertheless, humans possess the capacity for syntactic communication, so what are the biological roots of this ability? At a basic level, various primates produce utterances that consist of combinations of calls that can be meaningful to others. For example, male putty -nosed monkeys produce series of two basic loud calls to external threats, such as eagles and leopards. In addition, males sometimes combine the two calls into a unique sequence, which conveys its own meaning (‘move away'), regardless of the nature of the external disturbance (Arnold & Zuberbühler 2006; Figure 2). Similarly, adult male Campbell's monkeys produce different loud call types, which they co mbine into structurally unique context -specific sequences (Ouattara et al . 2009). Meaning at the sequence level has also been found in ape vocalisations, including gibbons and more recently bonobos (Clay & Zuberbühler 2011), suggesting that syntactically o rganised sequences are widespread in primate communication. In contrast to human language, there is no evidence that primates use such call combinations in a generative and creative way to ‘make infinite use of finite means' (von Humboldt 1836). Figure 2: Putty -nosed monkeys combine two call types. Putty -nosed monkeys combine two call types (‘pyows’ and ‘hacks’) into meaningful sequences. Females travelled further after hearing playbacks of ‘pyow -hack’ combinations of their own male (both real and synth etically composed) compared to his ‘pyow’ series (indicating a disturbance on the ground) or ‘hack’ series (indicating the presence of a crowned eagle). © 2012 Nature Education Data from Arnold & Zuberbühler (2008). All rights reserved. Another feature of human communication is that speech acts can be symbolic by referring to both mental entities and events in the outside world. Furthermore, humans make ample use of indexical and iconic signals, s uch as pointing or pantomiming, and from an early age, infants understand that symbolic and indexical signals complement each other in their capacity to refer to external objects (Gliga & Csibra 2009). Although laboratory research has shown that great apes can learn a considerable number of arbitrary symbols and follow indexical signals, there is little evidence that they use such acquired skills in creative ways or when communicating with each other (e.g., Savage -Rumbaugh et al . 1986). Figure 3: Diana m onkeys understand the predator -alarm calls of other monkeys. Diana monkeys understand the predator -alarm calls of other monkeys, (within and across species) and perceive them as representations of the corresponding predator class. Top panel: baseline - eag le alarm calls by female Diana monkeys given in response to playback of eagle shrieks; intermediate panel: test condition – eagle alarm calls given by female Diana monkeys in response to a male’s eagle alarm calls followed by eagle shrieks; bottom panel: c ontrol condition – leopard alarm calls given by female Diana monkeys in response a male’s leopard alarm calls followed by eagle shrieks. Females only ceased to respond to probe stimuli if they were primed with a semantically corresponding stimulus (baselin e and test conditions). © 2012 Nature Education Data from Zuberbühler et al . (1999). All rights reserved. In sum, although primates sometimes combine different call types into complex utterances th at are meaningful to others, it is still unclear how this behaviour is related to syntax in human language. One key difference appears to be that human languages, and their grammars, are socially learned, while there is no such evidence for primate call se quences. The difference between human and primate communication is less obvious in the domain of call comprehension.

Both human and non -human primates extract meaning by relating arbitrary sound structures to real -world events and their mental representati ons. Do Primates Actively Inform Each Other? Another contentious issue in the evolution of language debate is whether primates communicate to actively inform each other. Humans tend to interpret communicative acts as an underlying intention to be informat ive (Grice 1969). Thus, meaning does not solely emerge from the speech signal, but also from the ‘common ground' shared by the interlocutors. There is currently no good evidence that primate communication operates this way, although some key abilities seem to be present. For example, primates can predict the impact of their signals on others (e.g., Hopkins et al . 2007). Similarly, both apes and monkeys have demonstrated considerable audience awareness that suggest that they have some understanding of the ef fects of their calls and gestures (e.g., Wich & de Vries 2006, Laporte & Zuberbühler 2010, Genty et al . 2009; Crockford et al. 2012; Figure 4). Humans, however, go a step further, with signallers and receivers communicating in relation to their shared int entions (Tomasello 2008). As a consequence, human communication is bi - directional, conversational, and based on conventions as to how intentions are to be communicated. A particularly interesting example is pointing, which emerges early and universally dur ing human development, with no direct equivalent in primate communication. Although the pointing gesture has no independent meaning, it is very effective in triggering shared attention between signallers and receivers in relation to an external referent. A pes also produce gestures to request objects, but there is no good evidence that they point for others solely to be informative. The degree to which primates perceive and share each other's intentions, and to communicate as part of this cooperative experie nce, is the object of much ongoing research. Results are likely to delineate more clearly the relationship between primate communication and human language. As such they will provide progress towards one of the most interesting questions in science. What p art of our biology is uniquely human and what is part of our primate heritage? Figure 4: Female chimpanzees produce copulation calls during sexual interactions with males. Call rates are affected by the social rank of the male partner and the composition of the nearby audience. Both mating with low -ranking males and the presence of large female audiences tend to inhibit copulation calls in different females. © 2012 Nature Education Data from Townsend et al . (2008). All rights reserved. References and Recommended Reading Arnold, K. & Zuberbühler, K. Language evolution: Semantic combinations in primate calls.

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