We've all seen people walking down the street talking on their cell phones and waving their hands. The person on the other end of the line can't see them, but the behavior just goes to show gestures are an integral part of human communication. Many apes gesture, too. A study of orangutans shows that they modify their gestures to be better understood--a finding that may have implications for the evolution of human language.
Recent research has shown that apes attempt to communicate with people by gesturing, especially when the people have food. For example, a 2005 study led by primatologist William Hopkins of the Yerkes National Primate Research Center in Atlanta, Georgia, found that chimps point their fingers or hold out their hands when an experimenter is carrying a banana, and continue to gesture if they are given only half of it.
Erica Cartmill and Richard Byrne of the University of St. Andrews in Scotland set out to see if orangutans behaved the same way, and how effective gestures are in helping them to communicate. Cartmill tested six animals, three at Twycross Zoo in England and three at the Durrell Wildlife Conservation Trust on Jersey in the Channel Islands. She placed two dishes in front of the orangutans' cages, one filled with a food they liked--bread at Twycross and bananas at the Durrell facility--and the other with food they detested--leeks at Twycross and celery at Durrell. Cartmill then left the area, and the orangutans' keeper sat down in a chair in front of the bars. The encounter was videotaped.
The keeper sat still for 30 seconds while the orangutans engaged in a wide variety of gestures, including puckering their lips, extending one or two fingers, banging on the cage with an object, and spitting through the bars. The keeper then gave them the food they wanted, half of the food they wanted, or the food they did not like. When the orangutans got what they wanted, they stopped gesturing and ate it. When given only half of the food, they continued to gesture, using on average 60% of the same gestures they used before the food was delivered. But when given the food they did not like, only 10% of their gestures were repeats, and the orangs were much more likely to try new ones instead.
Cartmill and Byrne conclude that the orangutans were able to distinguish between being partially understood, when they were given half the food, and being entirely misunderstood, when they were given the undesirable food, and to modify their gesturing accordingly. They liken this behavior to a game of "charades," in which human players repeat and refine their gestures when the members of their team seem close to guessing the name of a film or a famous person, but try something different if the team does not understand. Since apes appear able to do this, too, gesturing may have been part of a "prelinguistic" communication that eventually led to human language, the researchers report in the 2 August issue of Current Biology.
"These results clearly show that the orangutans are intentionally communicating," says Hopkins, who agrees that gesturing may have been "critical to the evolution of language, just as it is critical to the development of language in modern human children."