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From chimps, new clues to language origins

Nov. 16, 2009
Courtesy Elsevier journals
and World Science staff

Chimps seem to use the left half of the brain when com­mu­ni­cat­ing with ges­tures—just as hu­mans do when us­ing lan­guage, re­search­ers have found.

The find­ings, in a species con­sid­ered one of the two clos­est rela­tives of hu­mans in the animal king­dom, sug­gest that our left-brain dom­i­nance for lan­guage comes from our ape-like an­ces­tors, the sci­en­tists said. The results also sup­port a the­o­ry that spo­ken lan­guage evolved from ges­tur­al com­mu­nica­t­ion, they added.

A chimp, spe­cies Pa­n Troglodytes. Chimps are be­lieved to be among the clos­est rel­a­tives to hu­mans in the an­i­mal king­dom. (Im­age cour­te­sy Uni­ver­si­ty of Il­li­nois at Urbana-Champaign)

Most hu­man lin­guis­tic func­tions are con­trolled by the left hem­i­sphere, or half, of the brain. The study of cap­tive chim­panzees at the Yer­kes Na­tional Pri­mate Re­search Cen­ter in At­lan­ta, Ga. found that a large ma­jor­ity of the chimps showed a “sig­nif­i­cant” bi­as to­wards right-hand­ed ges­tures, the in­ves­ti­ga­tors said. In gen­er­al, the right half of the body is con­trolled by the left half of the brain.

The study is re­ported in the Jan­u­ary is­sue of the re­search jour­nal Cor­tex.

The sci­en­tists, su­per­vised by Wil­liam D. Hop­kins of Ag­nes Scott Col­lege in Geor­gia, stud­ied hand use in 70 cap­tive chim­panzees over a pe­ri­od of 10 months, re­cord­ing a va­ri­e­ty of com­mu­nica­tive ges­tures spe­cif­ic to chimps.

These in­clud­ed ac­tions clas­si­fied as “arm threat,” “ex­tend arm” or “hand-slap,” pro­duced in dif­fer­ent so­cial con­texts, such as at­ten­tion-get­ting, shared ex­cita­t­ion, threat, ag­gres­sion, greet­ing, rec­on­cilia­t­ion or in­vita­t­ions for groom­ing or play. The ges­tures were di­rect­ed both at oth­er chimps and at hu­man ob­servers.

“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,” Hop­kins said.

Co-authors Adrien Meguerditchian and Jacques Vau­clair of Aix-Marseille Un­ivers­ity in France said the find­ings of­fer “ad­di­tion­al sup­port” to the idea that speech evolved in­i­tially from a ges­tur­al com­mu­nica­tive sys­tem in our an­ces­tors. Apes’ ges­tur­al com­mu­nica­t­ion shares some key fea­tures with hu­man lan­guage, such as in­ten­tion­al­ity, ref­er­en­tial prop­er­ties and flex­i­bil­ity of learn­ing and use, they ar­gued.

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Chimps seem to use the left half of the brain when communicating with gestures—just as humans do when using language, researchers have found. The findings suggest that our left-brain dominance for language comes from our ape ancestors, and support a theory that spoken language evolved from gestural communication, scientists said. Most human linguistic functions are controlled by the left hemisphere, or half, of the brain. The study of captive chimpanzees at the Yerkes National Primate Research Center in Atlanta, Ga. found that a large majority of the chimps showed a “significant” bias towards right-handed gestures, the investigators said. In general, the right half of the body is controlled by the left half of the brain. The study is reported in the January issue of the research journal Cortex. The scientists, supervised by William D. Hopkins of Agnes Scott College in Georgia, studied hand-use in 70 captive chimpanzees over a period of 10 months, recording a variety of communicative gestures specific to chimps. These included actions classified as “arm threat,” “extend arm” or “hand-slap,” produced in different social contexts, such as attention-getting, shared excitation, threat, aggression, greeting, reconciliation or invitations for grooming or play. The gestures were directed both at other chimps and at human observers. “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,” Hopkins said. Co-authors Adrien Meguerditchian and Jacques Vauclair of Aix-Marseille University in France added that the findings offer “additional support” to the idea that speech evolved initially from a gestural communicative system in our ancestors. Apes’ gestural communication also shares some key features with human language, such as intentionality, referential properties and flexibility of learning and use, they argued.