From hand to mouth in the evolution of language:: the influence of vocal behavior on lateralized hand use in manual gestures by chimpanzees (Pan troglodytes)

Studies in human subjects indicate that manual gestures accompanied by speech are produced more often by the right compared to the left hand. Additional studies indicate that the production of sign language is controlled by the same brain areas as speech, suggesting similar neurobiological substrates for language that are not modality specific. We report evidence that chimpanzees exhibit preferential use of the right hand in gestural communication. Moreover use of the right hand in gestural communication is significantly enhanced when accompanied by a vocalization, particularly among human-reared chimpanzees. Taken together, the data suggest that the lateralization of manual and speech systems of communication may date back as far as 5 million years ago.