Bonobos converse and pay attention to breaking conversational rules
Résumé
Human languages are deeply associated with the capacities to be engaged in social actions and cooperative communication. Despite their diversity, they all share the respect of conversational rules such as speech overlap avoidance, turn-taking and socially-based interlocutor preferences. Among primate species, such orderly vocal exchanges have been found in a diversity of monkey species, though surprisingly, not in great apes. Social functions of vocal exchanges have been largely evidenced and thus the absence of antiphony in great apes is puzzling regarding their complex social life and their evolutionary proximity with humans. The present study investigates whether bonobos – a highly social and cooperative species – present spontaneous coordinated vocal turn-taking and whether social factors affect these vocal productions. We monitored the vocal output of a captive group at La Vallée des Singes (France). Nearly 200 exchanged calls have been analyzed for which the caller identity and context of emission were known. We found the existence of temporally- and socially- ruled vocal exchanges, such as call overlap avoidance. Call repertoire sharing between exchanging partners was explained by social factors and not by their age, sex or kinship. Bonobos were also capable of immediate acoustic matching during interactions. These findings allowed testing whether the conversational rule-respect is significant for listeners or not. We played back four types of stimuli of vocal exchanges creating call overlap and/or modifying the caller identities. In total 10 bonobos have been tested. We found that the audience were sensitive to temporal rule-breaking of antiphony. This study demonstrates for the first time that great apes, like monkeys, apply some simple conversational turn-taking rules and that the audience pay attention to third-party vocal exchanges. Finding these shared traits between monkeys, apes and humans fills a significant gap and will be of high interest in the discussions of speech evolution.