"Long before it's in the papers"
June 04, 2013


Scientists explore whether some apes shake heads for “no”

May 5, 2010
Special to World Science  

In com­mu­ni­cating with each oth­er, apes known as bono­bos some­times shake their heads—and one of the pur­poses for which they do this may be anal­o­gous to say­ing “no,” a study has found.

Re­search­ers say the find­ing could be sig­nif­i­cant be­cause bono­bos are al­so hu­mans’ clos­est ev­o­lu­tion­ary rel­a­tives, along with com­mon chim­panzees.

To com­mu­ni­cate with each oth­er, apes known as bono­bos some­times shake their head­s—and one of the pur­poses for which they do this may be anal­o­gous to say­ing “no,” a study has found. Above, an ad­ult bono­bo (cour­tesy Ka­bir Ba­kie)

The sci­en­tists doc­u­mented 49 head shakes among bono­bos in Euro­pean zoos, 13 of which they said oc­curred while the head-shaker was try­ing to stop anoth­er bonobo from do­ing some­thing.

“Do these ges­tures re­flect a prim­i­tive pre­cur­sor of the hu­man head shake that de­notes nega­t­ion? This is an in­tri­guing pos­si­bil­ity, but ad­di­tion­al data” is needed, the re­search­ers wrote in de­scrib­ing their find­ings. 

The re­port, by re­search­ers Chris­tel Schnei­der and Kat­ja Lie­bal of the Free Uni­vers­ity Ber­lin and Jo­sep Call of the Max Planck In­sti­tute for Ev­o­lu­tion­ary An­thro­po­l­ogy in Leip­zig, Ger­ma­ny, ap­pears in the April 24 is­sue of the re­search jour­nal Pri­ma­tes.

Bono­bos—en­dan­gered Af­ri­can apes per­haps best known for their free­wheel­ing sex life—are close ev­o­lu­tion­ary rel­a­tives of com­mon chim­panzees. The two spe­cies are be­lieved to con­sti­tute branches of a sin­gle ape line­age. Be­fore this di­vi­sion oc­curred, though, sci­en­tists be­lieve the line­age spawned anoth­er branch, the one that even­tu­ally gave rise to hu­mans. This ear­li­er separa­t­ion took place an es­ti­mat­ed six mil­lion years ago.

The in­ves­ti­ga­tors video­taped 25 ape in­fants dur­ing their first 20 months of life, as well as in­ter­ac­tions be­tween in­fants and their moth­ers, as part of a study on ape ges­tures. A to­tal of 190 hours of video­tape were cap­tured. The study in­clud­ed four types of apes—bono­bos, chim­panzees, orangutans and go­ril­las—but head shak­ing was seen only in bono­bos, the re­search­ers said. 

Elev­en of the 13 “pre­ven­tive” head shakes were cases of moth­ers shak­ing their heads at in­fants, Schnei­der and col­leagues said. 

In one instance, for ex­am­ple, a moth­er re­peat­edly grabbed her ba­by and brought it back to her­self as it was try­ing to get away from her and climb a tree. Twice the moth­er, af­ter seiz­ing the in­fant, looked at it and shook her head. The ul­ti­mate out­come seems to have been un­suc­cess­ful for the moth­er, as the ba­by started head­ing to the tree again af­ter the moth­er turned her at­ten­tion away to anoth­er group mem­ber.

The two “pre­ven­tive” head-shak­ing cases not be­tween a moth­er and in­fant, both in­volved a bono­bo shak­ing its head when anoth­er tried to take its food, Schnei­der and col­leagues wrote. 

Then there were the 36 cases in which head-shak­ing served no ap­par­ent pre­ven­tive func­tion, the in­ves­ti­ga­tors not­ed. These shakes “were used to in­i­ti­ate or to main­tain be­hav­ior in var­i­ous con­texts,” such as in play­ing, they wrote, and in some cases “to ap­proach and greet a group mem­ber.”

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To communicate with each other, apes known as bonobos sometimes shake their heads—and one of the purposes for which they do this may be analogous to saying “no,” a study has found. Researchers say the finding could be significant because bonobos are also humans’ closest evolutionary relatives, along with common chimpanzees. Scientists documented 49 head shakes among members of the species. Thirteen of the gestures were deemed to have occurred while the head-shaker was trying to stop another bonobo from doing something. “Do these gestures reflect a primitive precursor of the human head shake that denotes negation? This is an intriguing possibility, but additional data” is needed, the researchers wrote in describing their findings. The report, by researchers Christel Schneider and Katja Liebal of the Free University Berlin and Josep Call of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, appears in the April 24 issue of the research journal Primates. Bonobos—endangered African apes perhaps best known for their freewheeling sex life—are close evolutionary relatives of common chimpanzees. The two species are believed to represent branches of a single ape lineage. Before this division occurred, though, scientists believe the lineage spawned another branch, the one that eventually gave rise to humans. This earlier separation took place an estimated six million years ago. The investigators videotaped 25 ape infants during their first 20 months of life, as well as interactions between infants and their mothers, as part of a study on ape gestures. A total of 190 hours of videotape were captured. The study included four types of apes—bonobos, chimpanzees, orangutans and gorillas—but head shaking was seen only in bonobos, the researchers said. Eleven of the 13 “preventive” head shakes were cases of mothers shaking their heads at infants, Schneider and colleagues said. In one case, for example, a mother repeatedly grabbed her baby and brought it back to herself as it was trying to get away from her and climb a tree. Twice the mother, after seizing the infant, looked at it and shook her head. The ultimate outcome seems to have been unsuccessful for the mother, as the baby started heading to the tree again after the mother turned her attention away to another group member. The two “preventive” head-shaking cases not between a mother and infant, both involved one bonobo shaking its head when another one tried to take its food, Schneider and colleagues wrote. Then there were the 36 cases in which head-shaking served no apparent preventive function, the investigators noted. These “were used to initiate or to maintain behavior in various contexts,” such as in playing, they wrote, and in some cases “to approach and greet a group member.”