Ontogeny of mirror behavior in two species of great apes.

Mirror image reactions of two infant apes, a female chimpanzee (Pan troglodytes) and a male orangutan (Pongo pygmaeus), born at the Zoo de Vincennes and the Jardin des Plantes of Paris, France, respectively, were studied and compared with those of children. Self-recognition was also tested following 46.5 hours of mirror exposure by application of red marks on parts of the body invisible to the animal without the aid of the mirror. Results indicated that the behavior of the two young apes followed a developmental trend similar to that of human babies. At the end of the study, the female chimpanzee (11 months of age) expressed social behavior, searched for the image behind the mirror, and showed interest in imaged movement. The orangutan (2 years and 5 months old) had begun to test movement synchronism and to display self-directed behaviors. The tests of self-recognition yielded negative results in both animals.