Orang-utan charades foreshadow evolution of language


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By Elsa Youngsteadt
Photo by Malene Thyssen

Orang-utans can tell whether you know what they mean, and will modify their signals to try to make you understand better. This is the conclusion of a study published online August 2 in the journal Current Biology. Although the apes in the study used gestures rather than sounds, the authors say that the way the apes establish shared meaning could be a step in the evolution of language.

In the study, a zookeeper sat in front of an orang-utan in a cage. The keeper displayed two foods—one yummy, like a banana, and the other icky, like celery. The orang would gesture at the keeper to try to get him to pass over the good food. The keeper would respond in one of three randomly pre-determined ways. He would hand over all the good food, half the good food, or all the bad food. This would give the ape the impression that the keeper had understood her request, partly understood it, or misunderstood.

If they got all of the good food, the orangs would generally cease to gesture. If they got half the good food or the wrong food they continued to gesture, but the movements they made differed. Given half the good food, they would continue with whatever gestures they had made before that got them part of the food. Given the bad food, they switched to different movements they had not made previously in the session.

The authors liken the orang's behavior to a game of charades, and say the process of establishing shared meaning through feedback would be an important step in one possible route toward the evolution of language.


Cartmill, E.A. and Byrne, R.W. 2007. Orangutans Modify Their Gestural Signaling According to Their Audience's Comprehension. Current Biology Vol 17(15):1345-1348. doi:10.1016/j.cub.2007.06.069.

"Orangutan Communication is Like Charades" from The New Scientist

Two Fingers Means "Give Me a Banana" from ScienceNOW Daily News

Background information on language evolution from psychologist C.George Boeree (Shippensburg University)

Questions for Review and Discussion

1. What experiment did the biologists conduct to find out if orang-utans modify gestures depending on how well they've been understood?

2. What results led the authors to conclude that the apes do modify their gesturing?

3. Can you think of alternative explanations for the results?

4. Are the gestures themselves language? Why or why not? Where might they fit as a stage in the evolution of language?

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