The Right Way To CommunicateBy Michael Bell22/11/2009
Researchers at Yerkes National Primate Research Center (Atlanta, Georgia) have shown that in a population of 70 chimpanzees, a substantial majority of the animals showed a significant bias towards right-handed gestures when communicating.
As is well known, linguistic functions in humans are controlled by the left cerebral hemisphere, and for a long time it has seemed possible that there is some connection between this fact and the predominance of right handedness in humans (resulting equally from left-hemisphere dominance). Anatomical differences at the cellular level between left and right hemispheres have been demonstrated. Many researchers also believe that spoken language had its origins in gestural communication, so that evidence of right-handedness in pre-linguistic communication by chimpanzees is significant.
As reported in the January 2010 issue of Elsevier's Cortex, a team of researchers, supervised by Prof. William D. Hopkins of Agnes Scott College (Decatur, Georgia), studied hand-use in 70 captive chimpanzees over a period of 10 months, recording a variety of communicative gestures specific to chimpanzees. These included 'arm threat', 'extend arm' or 'hand-slap' gestures produced in different social contexts, such as attention-getting interactions, shared excitation, threat, aggression, greeting, reconciliation or invitations for grooming or for play. The gestures were directed at the human observers, as well as toward other chimpanzees.
"The degree of predominance of the right hand for gestures is one of the most pronounced we have ever found in chimpanzees in comparison to other non-communicative manual actions. We already found such manual biases in this species for pointing gestures exclusively directed to humans. These additional data clearly showed that right-handedness for gestures is not specifically associated to interactions with humans, but generalizes to intraspecific communication", notes Prof. Hopkins.
The French members of the team, Dr. Adrien Meguerditchian and Prof. Jacques Vauclair, from the Aix-Marseille University, say: "This finding provides additional support to the idea that speech evolved initially from a gestural communicative system in our ancestors. Moreover, gestural communication in apes shares some key features with human language, such as intentionality, referential properties and flexibility of learning and use".
Hemispheric lateralization of linguistic, and presumably pre-linguistic skills is a fact, but there is no satisfactory answer to the question of why it should have evolved. It doesn't seem likely that it was to solve a capacity problem, although that remains a possible explanation. More convincing is the idea that there is an advantage to handedness. William H. Calvin, in The Throwing Madonna: Essays on the Brain, speculated that one-handed throwing could have been the crucial advance that gave early humans their survival advantage as against other apes, and that the requirement for intricate sequencing of motor actions was best fulfilled in one hemisphere and was then taken advantage of by language when it came along. But really this is just an elaboration of the capacity argument, and more convincing (but only just) is the idea that in gestural communication there is a group advantage if everyone gestures with the same hand, to avoid the need to apply a mirror transformation to the gestures you see when they are made by a left handed person, with some possible dangers of misinterpretation.
Whatever the original reasons for handedness, meaning left-brain dominance in certain functions, the fact that humans are mostly right-handed is of course just a random result. Evolution had to pick either left or right, and metaphorically it spun a coin, which happened to land right side up.