Chimpanzees warn each other about danger.

Chimpanzees may be able to determine whether their partners know they are in danger, researchers at Ohio State University, Columbus, have found. This suggests that these primates are able to decide how ignorant or informed their peers are about an unexpected situation. If the findings are accurate, chimps may share with humans the ability to perceive the knowledge state of a peer, and perhaps the intention to protect that peer. Earlier experiments with rhesus and Japanese macaque monkeys failed to show the same abilities in those animals, strengthening the argument that, in some ways, chimpanzees are closer to humans than they are to other primates.

Sally Boysen, associate professor of psychology, and her colleagues studied three pairs of chimpanzees: two adult males, Kermit and Darrell, who had been together for 18 years; a pair of females, Sarah and Abagail; and a male and female, Bobby and Sheba. For the tests, Boysen modeled both a treat and a threat to the chimps. She used grapes, a food the chimps highly desired, as the hidden treat. A member of the research group hiding with a tranquilizer dart was the threat. All of the animals previously had been sedated by a dart or had seen a tranquilizer dart used, and thus saw it as a threat.

In half of the test conditions, both animals in the pair were able to watch as either the grapes were hidden in the cage or a researcher with the tranquilizer dart hid as a predator. For the rest of the experiments, one animal was placed in an adjoining cage with a clear view of the food or threat while the other was kept oft in a nearby room. Boysen wanted to know if one animal would "tell" the other about the reward or threat. If it did, this would mean one animal would have to decide how well-informed the other was about a given situation.

When she tested the animals with the hidden grapes, absolutely nothing happened. No information was exchanged between the two chimps. "You wouldn't expect it to work with the food...