Scientists explore whether some apes shake heads for “no”

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.”