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The idea that language evolved from manual gestures rather than primate calls dates back at least to the 18th century, and was revived in modern form by the anthropologist, Gordon W. Hewes, in 1973. The main sources of current evidence are: (1) Signed languages invented by deaf communities share with speech the essential characteristics of language, including such properties as reference, generativity, grammar, and prosody; (2) Great apes in captivity are much better able to learn intentional communication systems based on manual gestures than to acquire speech; (3) The manual gestures of chimpanzees in the wild are more flexible and context-independent than their vocalizations; (4) The mirror system in the primate brain provides a natural platform for the evolution of language; it represents manual gestures and some nonvocal oral movements, but not vocalizations. Vocal gestures were probably incorporated into the mirror system late in hominin evolution, perhaps only with the emergence of our own species, Homo sapiens. Copyright © 2009 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs website.
Michael C. Corballis (Fri,) studied this question.