'Unwilling' versus 'unable': chimpanzees' understanding of human intentional action.

Understanding the intentional actions of others is a fundamental part of human social cognition and behavior. An important question is therefore whether other animal species, especially our nearest relatives the chimpanzees, also understand the intentional actions of others. Here we show that chimpanzees spontaneously (without training) behave differently depending on whether a human is unwilling or unable to give them food Chimpanzees produced more behaviors and left the testing station earlier with an unwilling compared to an unable (but willing) experimenter These data together with other recent studies on chimpanzees' knowledge about others' visual perception show that chimpanzees know more about the intentional actions and perceptions of others than previously demonstrated