Conversation among primate species

Abstract

The literature in psychology and sociolinguistic suggests that human interlocutors, when conversing, virtually sign a sort of contract that defines the exchange rules in both structural and social domains. These rules make the messages more understandable and the interaction more predictable, but they may also act as a social bond regulator. These rules can be very basic such as speech overlap avoidance, respect of response delays, turn-taking and vocal accommodation to the context and interlocutor’s social status. Interestingly, these rules are universally spread among human cultures questioning their biological basis and motivating the search for possible parallels with our primate cousins. Here, we will review the available literature on monkeys and apes. We will describe the different forms of vocal interactions, the temporal rules underlying these coordinated interactions, the non-random social selection of interlocutors and the context-dependent acoustic plasticity associated to these exchanges. The fact that primate species are socially varied, in terms of both social structure and social organisation, is another interesting aspect, since different social needs may predict different vocal interaction patterns and conversational rules. For example, duets, choruses and dyadic exchanges are not randomly distributed in the primate phylogeny and may even show different functions. Also, age proximity, kin membership, social affinity and hierarchy seem to play species-specific roles. Regarding plasticity, cases of vocal sharing and acoustic matching have been described in some species, notably in contact calls which are the calls the most frequently involved in dyadic exchanges. At last, a few studies also show that these ‘primitive’ conversational rules are often broken by juveniles and that the appropriate way to vocally interact with others may be socially learned, thus another aspect that do not seem strictly human.