Charles Mlingwa, Erasmus Tarimo, Edeus Massawe, A.K. Seki, M. Mbaga and their staff for their friendship and encouragement; We thank Michio Nakamura, Gaku Ohashi, Tetsuya Sakamai, Crickette Sanz and Dave Morgan for allowing us to use their precious video clips; Tamotsu Asou, Richard Byrne, Satoshi Hirata, Michio Nakamura, Yukimaru Sugiyama, Rikako Tonooka, Caroline Tutin and Moyo Uehara for allowing us to use their precious photos or illustrations; Tamotsu Asou, Miho Nakamura, Mitsue Matsuya and the late Masayasu Mori for allowing us to use their videos for study; Toshimichi Nemoto and Asami Kanayama for helping us in various ways in Tanzania. We thank our colleagues who have studied chimpanzees at Mahale for sharing information on the behavioral patterns, in particular, the late Kenji Kawanaka, the late Shigeo Uehara, Hitoshige