Chimps scratch out grooming requests

Pairs of adult males in a community of wild African chimps often communicate with gestures, indicating that they possess a basic knowledge of one another’s wants and intentions, two researchers contend. Many scientists attribute the capacity to discern others’ thoughts and feelings only to people.

The chimp encounters proceed as follows: One animal makes an exaggerated scratching movement on part of his body, such as his forehead, in front of a comrade, who then grooms the indicated spot. Gesturing of this type frequently occurs during social grooming, causing the provider to shift his activities to where the recipient scratched himself.

Simone Pika of the University of St. Andrews in Fife, Scotland, and John Mitani of the University of Michigan in Ann Arbor spent several months in Uganda observing male chimps’ grooming behavior in a community of more than 140 animals. The scientists recorded 186 instances in which one chimp used scratching to request grooming of a particular spot on his body from another chimp. The animal that viewed the scratching display usually began to groom the indicated spot, even if he was already grooming another part of the gesturing chimp.

Pairs of high-ranking male chimps were most likely to use and respond to exaggerated scratches as grooming requests, highlighting the importance of the symbolic gestures, Pika and Mitani report in the March 21 Current Biology.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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