From Grasping to Grooming to Gossip: Innovative Use of Chimpanzee Signals in Novel Environments Supports Both Vocal and Gestural Theories of Language Origins

The unique challenges posed by ecologically novel situations can illuminate the limits of flexibility in animal signalling systems. Here we describe the innovative application of species-typical calls by chimpanzees exposed to the novel circumstances in which the animals are dependent upon others to act on the world for them, what we have previously termed “the Referential Problem Space”. When chimpanzees are put into the Referential Problem Space, they display attention-getting calls and other auditory signals, and they tailor these signals to the state of attention of the receiver. Here we report that the kinds of calls that chimpanzees use in these evolutionarily novel circumstances are, generally, amplified versions of the same calls that they display in grooming contexts. Thus, this class of auditory signals, used in affiliative, grooming contexts, is chosen overwhelmingly by chimpanzees for application towards novel ends. This is consistent with Dunbar’s (Grooming, gossip and the evolution of language. Faber and Faber, London, 1996) hypothesis that early humans substituted auditory contact for manual grooming as group sizes exceeded ca. 150 people. Moreover, these calls are primarily produced by supralaryngeal modulation of the airstream. This is consistent with Corballis’s (From hand to mouth: The origins of language. Princeton University Press, Princeton, 2002) hypothesis that intentional communication in humans moved from the hands to the mouth and then into the larynx. In contemporary chimpanzees, we find intentional modulation of calls focused at the fronts of their oral cavities, for most grooming calls.