This paper will discuss a role of anger from the perspective of game theory. Primarily, by adopting a responder in a standard ultimatum game as an example, we highlight that anger has a rational role as a commitment device and a signaling device from an evolutional point of view. Game theory has clarified theoretical conditions, such as incentive compatibility, to make a commitment and/or signaling function. However, there are few arguments as to whether emotions such as anger satisfy those requirements. Thus, in this paper, we show that anger expressed by the responder who was offered an unfair offer in an ultimatum game actually satisfies those requirements.
