Anthropologists recognize both the close similarities and distinct differences between the human species and the great apes, especially the chimpanzee and the bonobo. Besides acknowledging the obvious biological characteristics, primatologists needed to also investigate the psychological and social similarities between the human animal and the two Pan species. Jane Goodall pioneered the close-range and long-term observations of wild chimpanzees in their natural habitats. Likewise, Harold Coolidge and Frans de Waal contributed to understanding and appreciating bonobos as a result of their ground-breaking research. These studies clearly attest to a striking contrast between the aggressive chimpanzee and the peaceful bonobo. Furthermore, our own species shares some psychological and social aspects with both of these pongids. Consequently, anthropologists can now confidently place all three species within an evolutionary framework.