Lateralization of communicative signals in nonhuman primates and the hypothesis of the gestural origin of language

This article argues for the gestural origins of speech and language based on the available evidence gathered in humans and nonhuman primates and especially from ape studies. The strong link between motor functions (hand use and manual gestures) and speech in humans is reviewed. The presence of asymmetrical cerebral organization in nonhuman primates along with functional asymmetries in the perception and production of vocalizations and in intentional referential gestural communication is then emphasized. The nature of primate communicatory systems is presented, and the similarities and differences between these systems and human speech are discussed. It is argued that recent findings concerning neuroanatomical asymmetries in the chimpanzee brain and the existence of both mirror neurons and lateralized use of hands and vocalizations in communication necessitate a reconsideration of the phylogenic emergence of the cerebral and behavioral prerequisites for human speech.