Beyond aerodigestion: exaptation of feeding-related mouth movements for social communication in human and non-human primates

Three arguments are advanced from human and non-human primate infancy research for the exaptation of ingestive mouth movements (tongue-protrusion and lip-smacking) for the purposes of social communication: Their relation to affiliative behaviours; their sensitivity to social context; and their role in social development. Although these behaviours may have an aerodigestive function, such an account of their occurrence is only partial