Compared the abilities of 3 mother-reared and 3 human-raised (enculturated) chimpanzees and 16 human toddlers to imitatively learn novel actions on objects. Found that mother-reared chimpanzees were poorer imitators than both enculturated chimpanzees and human children, who did not differ from one another in imitative learning. On time delay trials, the enculturated chimpanzees performed better than the other groups. (MDM)