Self-recognition in chimpanzees (Pan troglodytes): distribution, ontogeny, and patterns of emergence.

Investigations of mirror self-recognition (SR) in chimpanzees (Pan troglodytes) have had small samples and divergent methods. In Experiment 1, 105 chimpanzees (10 months to 40 years of age) were observed for signs of SR across 5 days of continuous mirror exposure. In Experiments 2 and 3, negative SR adult and adolescent chimpanzees were saturated with mirror exposure in efforts to facilitate SR and a longitudinal study was conducted with a number of young subjects. In Experiment 4, mark tests were administered to groups of positive SR, negative SR, and ambiguous SR subjects. In Experiment 5, we explored whether previous positive SR reports in young chimpanzees were artifacts of increased arousal during mirror exposure. Results suggest that SR typically emerges at 4.5-8 years of age, at the population level the capacity declines in adulthood, and in group settings SR typically occurs within minutes of a subject's exposure to a mirror.