¹⁵A simple model of anger in our framework is that it is a reaction that comes on top of frustration when another agent is causing, at least partly, the frustration. But this does not yet explain the evolutionary meaning of anger, and in particular why angry people can behave extremely “irrationally” in the sense of causing great damage to themselves. A well-known evolutionary explanation is as follows. Imagine a gangster comes to you and asks you to give him all your money. The rational thing to do would be to give the money. This is rational in the sense that otherwise, he might kill you or inflict some bodily harm, and certainly it is better for you to just give the money. However, this behavior has the downside that then the gangster can come to you any time he wishes and always take your money. The evolutionary explanation of anger is that it is a program that makes you behave irrationally. In this case, you would just get “mad”, and physically attack the gangster, even if you know he will kill you as a consequence. Surprisingly, having such a program may be good from an evolutionary viewpoint, because if the gangster knows you have such a program installed, he might decide not to bother you. It is not good, from an evolutionary viewpoint, to actually attack the gangster; what is good here evolutionarily is having such a program installed, and signalling this to the gangster. If the gangster knows about the program, it may never be actually used, because it works as a powerful deterrent. This is a well-known game-theoretic model in evolutionary theory, it was originally used for modelling the behavior of animals who fight over mating opportunities, territory, or other scarce resources (Smith and Price, 1973; Pinker, 1999), which is why it is often called the hawk-dove game (Hirshleifer, 1987; Nowak et al., 2016). It is actually equivalent to another game-theoretical model called the game of chicken, which, despite sharing an avian name, has a very different story and motivation behind it. — Let me also note that social interaction creates many further emotions, such as shame and guilt, some of which are moral emotions (Haidt, 2003); that is, they enforce behavior conforming to ethical norms.