Imitative learning of actions on objects by children, chimpanzees, and enculturated chimpanzees.

In this study we compared the abilities of chimpanzees and human children to imitatively learn novel actions on objects. Of particular interest were possible differences between chimpanzees raised mostly with conspecifics (mother-reared) and chimpanzees raised in a human-like cultural environment (enculturated). Subjects were thus 3 enculturated and 3 mother-reared chimpanzees, along with 8 18-month-old and 8 30-month-old human children. Each subject was tested over a 2-day period with 16 novel objects. The introduction of each object was preceded by a baseline period in which the subject's natural proclivities toward the object were determined. For 12 objects, a human experimenter demonstrated first a simple and then a complex novel action, instructing the subject in each case to "Do what I do" (chimpanzees were prepared for the task behaviorally as well). For the other 4 objects, demonstration of a single action took place on the first day and the subject's opportunity to imitate was delayed until the second day, 48 hours later. Actions that a subject produced in baseline were excluded from further analysis. For each analyzed action, the subject's behavior was scored as to whether it successfully reproduced (1) the end result of the demonstrated action, and (2) the behavioral means used by the demonstrator. Results showed that in immediate imitation the mother-reared chimpanzees were much poorer imitators than the enculturated chimpanzees and the human children, who did not differ from one another. Surprisingly, on the delay trials, the enculturated chimpanzees significantly outperformed the other 3 groups. We conclude from these results that a human-like sociocultural environment is an essential component in the development of human-like social-cognitive and imitative learning skills for chimpanzees, and perhaps for human beings as well.