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The study of non-human animals, in particular primates, can provide essential insights into language evolution. A critical element of language is vocal production learning, i.e. learning how to produce calls. In contrast to other lineages such as songbirds, vocal production learning of completely new signals is strikingly rare in non-human primates. An increasing body of research, however, suggests that various species of non-human primates engage in vocal accommodation and adjust the structure of their calls in response to environmental noise or conspecific vocalizations. To date it is unclear what role vocal accommodation may have played in language evolution, in particular because it summarizes a variety of heterogeneous phenomena which are potentially achieved by different mechanisms. In contrast to non-human primates, accommodation research in humans has a long tradition in psychology and linguistics. Based on theoretical models from these research traditions, we provide a new framework which allows comparing instances of accommodation across species, and studying them according to their underlying mechanism and ultimate biological function. We found that at the mechanistic level, many cases of accommodation can be explained with an automatic perception-production link, but some instances arguably require higher levels of vocal control. Functionally, both human and non-human primates use social accommodation to signal social closeness or social distance to a partner or social group. Together, this indicates that not only some vocal control, but also the communicative function of vocal accommodation to signal social closeness and distance must have evolved prior to the emergence of language, rather than being the result of it. Vocal accommodation as found in other primates has thus endowed our ancestors with pre-adaptations that may have paved the way for language evolution., (© 2017 Cambridge Philosophical Society.)

Language is a cognitively demanding human trait, but it is also a fundamentally cooperative enterprise that rests on the motivation to share information. Great apes possess many of the cognitive prerequisites for language, but largely lack the motivation to share information. Callitrichids (including marmosets and tamarins) are highly vocal monkeys that are more distantly related to humans than great apes are, but like humans, they are cooperative breeders and all group members help raising offspring. Among primates, this rearing system is correlated with proactive prosociality, which can be expressed as motivation to share information. We therefore propose that the unique coincidence of these two components in humans set the stage for language evolution: The cognitive component inherited from our great ape-like ancestors, and the motivational one added convergently as a result of cooperative breeding. We evaluate this scenario based on a review of callitrichd vocal communication and show that furthermore, they possess many of the mechanistic elements emphasized by the mirror system hypothesis of language evolution. We end by highlighting how more systematic phylogenetic comparisons will enable us to further promote our understanding of the role of cooperative breeding during language evolution. [ABSTRACT FROM AUTHOR]