Social Rationality

It has long been argued that chimpanzees and other nonhuman primates do not understand the psychological states of others, such as their goals, perceptions, knowledge, and beliefs (Heyes, 1998; Povinelli & Vonk, 2003, 2004; Tomasello & Call, 1997). Hare et al. (2000, 2001) highlighted that negative results often came from cooperative tasks with humans, whereas positive findings arose from competitive interactions among conspecifics in natural settings. Indeed, studies in competitive contexts confirmed chimpanzees' ability to understand what conspecifics have or have not seen (Hare et al., 2001; Kaminski et al., 2008). These studies concluded that chimpanzees know what others know (but not what others believe). In the current study, we will investigate whether chimpanzees also know how others know. We will examine whether chimpanzees track whether another’s belief is based on evidence or not, and if they compare this to whether or not they based their own belief on evidence, especially when their choice conflicts with that of the competitor.