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See Inside March / April 2010

Chimps Talk with Their Hands

Right-handed gesturing in apes hints at the origins of human language

The origins of language have long been a mystery, but mounting evidence hints that our unique linguistic abilities could have evolved from gestural communication in our ancestors. Such gesturing may also explain why most people are right-handed.

Researchers at the Yerkes National Primate Research Center recently ex­am­ined captive chimpanzees and found that most of them predominantly used their right hand when communicating with one another—for example, when greeting another chimp by extending an arm. The animals did not show this hand preference for noncommunicative actions, such as wiping their noses. Such lateralized hand use suggests that chimpanzees have a system in their left brain hemisphere that is coupled to the production of com­municative gestures, says study author William Hopkins. The same cerebral hemisphere is host to most language functions in humans, which hints that an ancestral gestural system could have been the precursor for language, he says.

That notion is supported by previous studies that have shown anatomical asymmetries in chimpanzees’ brains in areas that are considered to be ho­mo­logues of human language centers, such as Broca’s area, Hopkins says. ­“Chimps that gesture with their right hand typically have a larger left Broca’s area, and those that don’t show a [hand] bias typically don’t show any asymmetry in the brain,” he notes.

The idea that language emerged from an ancestral gestural system located in the left brain hemisphere could explain why the vast majority of people are right-handed, Hopkins says. If gesturing was strongly selected for in human evolution, then the fact that most people are right-handed is a consequence of that. This hypothesis challenges the long-held view that the opposite scenario is true: that right-handedness emerged for motor skills such as tool use and that communi­cation built on the developed asymmetry in the motor system later.

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