Machines Like Us

As Corballis mentions in his 2003 BBS article, even the great apes -- our closest relatives in the animal kingdom -- tend not to show a right-hand preference unless raised in captivity, suggesting handedness is learned through imitation of caregivers. So why should humans be the only species to show clear manual asymmetry, 9:1 in favor of righties?

While manual asymmetry may be unique to humans, cerebral asymmetry is not. Corballis reviews how animals as diverse as frogs, birds, mice, rats, gerbils and marmosets tend to show more reliance on their left hemispheres in producing and recognizing their species' vocalizations. Even in humans, right-handed adults are more likely to show greater activity in their left cerebral hemispheres on language tasks. And the only situation in which chimpanzees show clear handedness is during pointing -- when chimpanzees point, they tend to do so (around 2/3 of the time) with their right hands (some chimps have even been observed to point spontaneously in the wild, suggesting this behavior is not due merely to imitating humans.)

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