Abstract

Humans regularly help others upon seeing them in trouble, often almost impulsively. Help may be given even to strangers or to different species, with no return expected. Studies have reported that not only humans but also non-human primates show prosocial behaviours, such as helping and cooperation, in both natural and captive settings. Some researchers suggest that these behaviours relate to a sense of fairness and an ability to empathize. However, it is still not clear what kinds of affective states and motivation non-human species have and how they are involved in prosocial behaviours. In this chapter, we introduce our studies on cooperative behaviour, food sharing, and third-party evaluation in captive tufted capuchin monkeys, a New World monkey species. These studies demonstrated that the dominant monkeys behave prosocially towards subordinate monkeys, that capuchins are sensitive to partners’ efforts and rewards, and that they refuse food from humans who show anti-social behaviour towards others. From these results, we propose that advantageous inequality aversion may promote prosocial behaviour only towards subordinates and that empathy may not be important in food contexts.