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The primate roots of human language

Final Report Summary - PRILANG (The primate roots of human language)

In this project, we have studied the evolution of human language as a collection of mechanisms: A flexible and socially learned code system; a receiver psychology capable of making relevance judgements about signaller intention; and a signaller psychology governed by a cooperative motivation to share information. We studied these capacities comparatively in non-human primates, with the following discoveries.

First, there is an unprecedented amount of acoustic variability in different primate call types, with evidence for social learning and population-level differences. Furthermore, there are morphologically structured call types and call sequences and considerable flexibility in call use. In the gestural domain we found evidence for multimodal communication in wild apes and gestures that convey intentions and spatial information.

Second, as receivers, primates possess the capacity to make inferences about the relevance and intention of signaller behaviour, as demonstrated by field experiments with wild chimpanzees. For instance, individuals can relate the calls of (unseen) group members to previous social interactions and they routinely take the pragmatic circumstances into account when responding to each other’s signals.

Finally, concerning cooperative motivation and social awareness we found that great apes routinely seek to persuade others to engage in cooperative acts and that, in situations of danger, take others' knowledge into account when deciding what visual and acoustic cues to provide to them.

The overall emerging picture is one of continuation along major components of the language faculty. Yet, no species other than humans appears to have fully formed vocal control and an audience-aware psychological potency that would, in combination, enable individuals to develop an open-ended and conventionalised signalling system to interact with others’ belief systems.