Study site duration and all cumulative infanticides (i.e., male or female, within or between groups) reported for chimpanzees (C), mountain gorillas (G), and orangutans (O). Four out of six long-term chimpanzee study sites show a strong positive correlation between study site duration and cumulative number of infanticides observed. The other two long-term chimpanzee sites considered, Kanyawara and Tai, have reported only one and zero confirmed infanticides, respectively. Mountain gorilla observations at Karisoke show a similarly strong relationship, whereas no orangutan study sites have reported infanticide in spite of comparable study site durations at Ketambe and Tanjung Puting. Data sources: Chimpanzees (C), for reviews see Wrangham et al. 2006 and Wilson et al. 2004; more recent infanticides reported in Murray et al. 2007; Townsend et al. 2007; Sherrow and Amsler 2007. Mountain gorillas (G): Fossey 1984; Watts 1989; Harcourt and Stewart 2007. Orangutans (O): Gunung Palung, Mitani 1991; Knott et al. 2008; Ketambe, Wich et al. 2004; Kutai, Rodman 1973; Mitani 1985; Lokan, Horr 1972; Suaq Balimbing, van Schaik 2004; Sebangau, estimated; Tanjung Puting, Rodman and Mitani 1987; Galdikas pers. comm.; Tuanan, Jaeggi et al. 2008; Ulu Segama, MacKinnon 1974