Referential-gesture communication in wild chimpanzees (Pan troglodytes)

Humans commonly use referential gestures that direct the attention of recipients to particular aspects of the environment. Because the recipient of a referential gesture must infer the signaler’s meaning, the use of these gestures has been linked with cognitive capacities such as the ability to recognize another individual’s mental state. Researchers have now found evidence that such referential gesturing is a natural part of chimpanzee behavior. The observations, which shed light on the communicative abilities of wild apes, are reported in the March 21st issue of Current Biology by Dr. Simone Pika of the University of St. Andrews, Scotland, and Dr. John Mitani of the University of Michigan.

Among the non-human primates–our closest living relatives–referential gestures have been reported only in captive chimpanzees interacting with their human experimenters and in human-raised or language-trained apes. In the new work, the researchers provide evidence for the widespread use of a referential gesture by chimpanzees (Pan troglodytes) in the wild. The animals were observed in the Ngogo community of chimps in Kibale National Park, Uganda.

The gesture studied by the researchers–a “directed scratch”–involved one chimpanzee making a relatively loud and exaggerated scratching movement on a part of his body that could be seen by his grooming partner. In the majority of cases, the indicated spot was groomed immediately afterward by the recipient of the gesture. The scratch gesture occurred between pairs of adult males and was used more often in pairs consisting of high-ranking males. On the basis of their observations, the researchers suggest that the “directed scratch” gesture may be used communicatively to indicate a precise spot on the body and to depict a desired future action, namely grooming. The findings also suggest that the recipient of the signal has an understanding of the intended meaning of the gesture. “Directed scratches” therefore qualify as referential and iconic, in the technical sense, and might provide support for the hypothesis that some form of mental-state attribution may be present in our closest living relatives.