viernes, 4 de mayo de 2007

Like humans, apes can communicate manually

The Atlanta Journal-Constitution
Published on: 05/01/07

Before there was speech, there was the gesture — a hand outstretched to beg for food, or a "come hither" sweep of a beckoning forearm.

Monkeys may see. But when it comes to gestures, only apes — and humans — do.

That discovery, by researchers at Emory University's Yerkes National Primate Research Center, offers new fuel for the theory that the evolution of human language began, not with words, but with a wave of the hand or a flick of the wrist.

"Our research suggests that just as human babies can learn certain gestures before they speak, our ancestors may have been gesturing to each other before they talked," says Yerkes researcher Frans B.M. de Waal.

Language, the fundamental mechanism by which humans share information, is thought to have emerged about 100,000 years ago. But the study by de Waal and Yerkes co-researcher Amy Pollick, published Monday in the Proceedings of the National Academy of Science, suggests that nonvocal communication — perhaps hand gestures exchanged by prehistoric hunters — may have appeared much earlier.

Although monkeys and other primates have a wide range of facial expression and body postures, de Waal says only the apes — chimps, bonobos, gorillas and orangutans — use controlled manual gestures. Those gestures, like spoken language, are flexible enough to have different meanings in different contexts and vary from group to group.

"The difference in control is dramatically illustrated by past failure to teach chimpanzees to speak, even though they have no trouble learning the gestures of American sign language."

From their daily observations of two groups of chimps at the Yerkes center in Atlanta and two groups of bonobos at the San Diego Zoo, the researchers documented 31 distinct manual gestures — including pointing, waving, beckoning, and rapping knuckles, whose meanings varied enormously from group to group.

"A chimpanzee stretching out an open hand toward a possessor of food, for instance, signals a desire for food, but stretching out an open hand toward a third party during a fight signals a need for support," explains de Waal. "You can see similar contextual differences in someone begging on the street."

The British primatologist Jane Goodall first noted gesturing among chimpanzees in the wild in the 1960s. But de Waal, the author of "Our Inner Ape," "Chimpanzee Politics," "Peacemaking Among Primates," and other books, says the ability has since been documented in all apes, which are humans' closest relatives on the evolutionary tree.

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