Monkeys recognize the faces of group mates in photographs
Jennifer J. Pokorny and Frans B. M. de Waal show that "Monkeys recognize the faces of group mates in photographs" (PNAS December 22, 2009 vol. 106 no. 51 21539-21543).
Subjects need to select the odd facial image from among four. On this trial, the odd image is a member of group 1 (Top Left) ...