CHICAGO -- A new study has shown that chimpanzees may be able to determine whether their partners know they are in danger. This suggests that these primates are able to decide how ignorant or informed their peers are about an unexpected situation.

The finding, made by a team of researchers at Ohio State University's Comparative Cognition Project, suggests that chimps share with humans the ability to perceive the knowledge state of a peer, and perhaps the intention to protect that peer.

Earlier experiments with both rhesus and Japanese macaque monkeys failed to show the same abilities in those animals. These new results strengthen the argument that in some ways, chimpanzees are closer to humans than they are to other primates.

The studies were presented Aug. 16 in Chicago at the annual meeting of the American Psychological Association.
Sally Boysen, associate professor of psychology at Ohio State and director of the project, said the fundamental question for the test was whether one chimpanzee could tell if another was ignorant of a specific situation, in this case, of a threat or a reward.

Boysen and her colleagues tested three pairs of chimpanzees at the Ohio State colony. Two adult males, Kermit and Darrell, who had been together for 18 years, were tested, along with 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 in the study had previously been sedated by a dart or had seen a tranquilizer dart used, and 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.