Absence of knowledge attribution and self-recognition in young chimpanzees (Pan troglodytes)

Mirror self-recognition in chimpanzees (Pan troglodytes) is typically delayed until 4 1/2-8 years of age. Also, species capable of mirror self-recognition may be capable of some forms of mental state attribution related to intentions and knowledge. Previous investigations of knowledge attribution by chimpanzees used adolescents and adults but did not explicitly test for self-recognition. We report an investigation of knowledge attribution in 6 young chimpanzees previously tested for self-recognition. Subjects were required to discriminate between a person who had seen where food was hidden and another person who had not. The results are consistent with the proposition that most chimpanzees younger than 4 1/2 years of age show neither mirror self-recognition nor knowledge attribution. The results are also consistent with the idea that, just as in humans, development of self-recognition in chimpanzees may precede development of knowledge attribution.