Orangutans try to communicate by gesturing in the same way as people do, researchers find.
In a series of sessions with captive female orangutans, Richard Byrne and his colleagues at the University of St. Andrews in Scotland offered individual animals a whole serving of a favorite food, a half serving, or a food that the apes didn’t prefer. The scientists recorded signals that the animals made before food appeared, when it was offered, and after the food was given over.
“They have gestures that have more or less precise meanings,” Byrne says. He notes that such abilities are often considered uniquely human.
“It’s what orangutans do when they’re thwarted that reveals what’s in their minds,” Byrne says.
He and his colleagues found that when presented with half a portion of a favorite food, the ape would typically increase the frequency of whatever gesture it was making before the food appeared—signaling that it wanted more, the researchers infer.
When the offered food wasn’t a favorite, the animal changed the motion that it had been making before food appeared, which the researchers interpret as a message that the food giver didn’t understand the animal.
The observations reveal that orangutans were “reacting to the mental state” of the food giver, Byrne says. This is the same method used by people when playing the party game charades, he adds.
“The ability to understand the audience and to do something appropriate about it may go back a long way in evolution,” says Byrne. The report appears in the Aug. 7 Current Biology.