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Orangutan communication resembles “charades”

Aug. 1, 2007
Courtesy Current Biology
and World Science staff

When orang­u­tans use ges­tures to com­mu­ni­cate, they use the same bas­ic strat­e­gy that peo­ple fol­low in play­ing the game cha­rades, re­search­ers have found. 

In cha­rades, peo­ple act out a word or phrase with­out speak­ing. For ex­am­ple, “foot­ball” could be bro­ken down in­to “foot” and “bal­l.” Play­ers com­pete over who can get oth­ers to un­der­stand them most quick­ly. To help, play­ers of­ten al­so give their lis­ten­ers hints to how closely they’ve come to get­ting it. They tend to re­peat sig­nals that seem to be work­ing while stop­ping those that are cre­at­ing con­fu­sion.

A Su­ma­tran orang­u­tan, Julitta, and her 2-year-old daugh­ter, Pu­tri, for­age at the Dur­rell Wild­life Conserva­tion Trust in Jer­sey, U.K. (Cred­it: Er­i­ca Cart­mill)


In a si­m­i­lar vein, cap­tive orang­u­tans in­ten­tion­ally mod­i­fy or re­peat hand or oth­er sig­nals based on the suc­cess or fail­ure of a first at­tempt, a new study finds. The re­search ap­pears in the Aug. 2 is­sue of the re­search jour­nal Cur­rent Bi­ol­o­gy.

“We were sur­prised that the orang­u­tans’ re­sponses so clearly sig­naled their as­sess­ment of the au­di­ence’s com­pre­hen­sion,” said Rich­ard Byrne of The Un­ivers­ity of St. An­drews, Scot­land, one of the re­search­ers. “Look­ing at the tapes of the an­i­mal’s re­sponses, you can easily work out wheth­er the orang­u­tan thinks it has been ful­ly, par­tially, or not un­der­stood.”

To learn wheth­er orang­u­tans in­ten­tion­ally com­mu­ni­cate with peo­ple through ges­tures, a skill ear­li­er at­trib­ut­ed to chim­panzees, Byrne and col­league Er­i­ca Cart­mill pre­sented six cap­tive orang­u­tans with situa­t­ions in which one tempt­ing and one less tempt­ing food item had to be reached with hu­man help.

But rath­er than co­op­er­ate ful­ly, the ex­pe­ri­menter some­times pur­pose­fully mis­un­der­stood the orang­u­tan’s re­quests. The ex­pe­ri­menter some­times pro­vid­ed only half of the de­li­cious treat, or hand­ed over the yuck­ier item in­stead.

When the hu­man part­ner failed to meet the orang­u­tans’ aims, the apes per­sisted in fur­ther tries, the re­search­ers re­ported. When par­tially un­der­stood, the an­i­mals nar­rowed down their range of sig­nals by fo­cus­ing on ges­tures al­ready used and re­peating them. When com­pletely mis­un­der­stood, orang­u­tans elab­o­rat­ed their range of ges­tures and avoided rep­e­ti­tion of failed sig­nals. The strat­e­gy is one way to con­struct a shared lex­i­con from learn­ed or rit­u­al­ized sig­nals, the re­search­ers con­clud­ed, and may give new clues to help recon­struct the ori­gins of lan­guage.

* * *

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When orangutans use gestures to communicate, they use the same basic strategy that people follow in playing the game charades, researchers have found. In charades, people act out a word or phrase without speaking. For example, “football” could be broken down into “foot” and “ball.” Players compete over who can get others to understand them most quickly. To help, players often also give their listeners hints to how closely they’ve come to getting it. They tend to repeat signals that seem to be working while stopping those that are creating confusion. In a similar vein, captive orangutans intentionally modify or repeat hand or other signals based on the success or failure of a first attempt, a new study find. The research appears in the Aug. 2 issue of the research journal Current Biology. “We were surprised that the orangutans’ responses so clearly signaled their assessment of the audience’s comprehension,” said Richard Byrne of The University of St. Andrews, Scotland, one of the researchers. “Looking at the tapes of the animal’s responses, you can easily work out whether the orangutan thinks it has been fully, partially, or not understood.” To learn whether orangutans intentionally communicate with people through gestures, a skill earlier attributed to chimpanzees, Byrne and colleague Erica Cartmill presented six captive orangutans with situations in which one tempting and one less tempting food item had to be reached with human help. But rather than cooperate fully, the experimenter sometimes purposefully misunderstood the orangutan’s requests. The experimenter sometimes provided only half of the delicious treat, or handed over the yuckier item instead. When the human partner failed to meet the orangutans’ aims, the apes persisted in further tries, the researchers reported. When partially understood, the animals narrowed down their range of signals by focusing on gestures already used and repeating them. When completely misunderstood, orangutans elaborated their range of gestures and avoided repetition of failed signals. The strategy is one way to construct a shared lexicon from learned or ritualized signals, the researchers concluded, and may gives new clues to help reconstruct the origins of language.