than studies on chimpanzees. Therefore, behavioral comparisons between chimpanzee, bonobo and human can be made to some extent. Many authors have pointed out behavioral similarities and differences between human and chimpanzee. Some behavioral patterns are common to both human and chimpanzee but not bonobo, as well as patterns common to both human and bonobo but not chimpanzee. 10 Introduction These behavioral patterns are either those of the LCA of Pan and Homo, which either chimpanzee or bonobo has lost, or patterns that were lacking in the LCA but evolved in both man and only one species of Pan in parallel after the split of chimpanzee and bonobo. In such cases, we tentatively show 3, the status of which remains ambiguous. The behavioral patterns of the LCA more likely