Emergence and Collapse of Peace with Friend Selection Strategies

A society consisting of agents who can freely choose to attack or not to attack others inevitably evolves into a battling society (a \'war of all against all\'). We investigated whether strategies based on C. Schmitt\'s concept of the political, the distinction of a friend and an enemy, lead to the emergence and collapse of social order. Especially, we propose \'friend selection strategies\' (FSSs), one of which we called the \'us-TFT\' (tit for tat) strategy, which requires an agent to regard one who did not attack him or his \'friends\' as a \'friend\'. We carried out evolutionary simulations on an artificial society consisting of FSS agents. As a result, we found that the us-TFT results in a peaceful society with the emergence of an us-TFT community. In addition, we found that the collapse of a peaceful society is triggered by another FSS strategy called a \'coward\'.