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From mouth to hand: Gesture, speech, and the evolution of right-handedness

Corballis, Michael C. (2003) From mouth to hand: Gesture, speech, and the evolution of right-handedness.

Short Abstract:

The marked species-specific bias toward right-handedness in humans may have been driven by a left-hemispheric dominance for vocalization, which appears to have a much earlier evolutionary origin, perhaps going back to the beginnings of vocalization itself. The influence of vocalization on hand preference may have come about because language evolved initially from manual gestures, but gradually incorporated vocal elements. Although autonomous speech eventually prevailed, probably with or after the emergence of Homo sapiens, the long association of vocal and manual elements in the evolution of language left us the legacy of right-handedness.

Long Abstract:

The strong predominance of right-handedness appears to be a uniquely human characteristic, whereas the left-cerebral dominance for vocalization occurs in many species, including frogs, birds, and mammals. Right-handedness may have arisen because of an association between manual gestures and vocalization in the evolution of language. I argue that language evolved from manual gestures, gradually incorporating vocal elements. The transition may be traced through changes in the function of Broca’s area. Its homologue in monkeys has nothing to do with vocal control, but contains the so-called “mirror neurons,” the code for both the production of manual reaching movements onto the perception of those same movements performed by others. This system is bilateral in monkeys, but predominantly left-hemispheric in humans, and in humans is involved with vocalization as well as manual actions. There is evidence that Broca’s area is enlarged on the left side in Homo habilis, suggesting that a link between gesture and vocalization may go back at least 2 million years, although other evidence suggests that speech may not have become fully autonomous until Homo sapiens appeared some 170,000 years ago, or perhaps even later. The removal of manual gesture as a necessary component of language may explain the rapid advance of technology, allowing late migrations of Homo sapiens from Africa to replace all other hominids in other parts of the world, including the Neanderthals in Europe and Homo erectus in Asia. Nevertheless, the long association of vocalization with manual gesture left us a legacy of right-handedness.