Keeping up cooperation: A group of 20 players (circles) encounter each other at random. When they meet they can choose to pay a cost to engage in cooperative behavior, or withold cooperation and hope to gain at their opponent's expense. Blue players want to cooperate and red players do not. Each player chooses whether to cooperate at a given time using a strategy that takes acount of their history of past encounters with their current opponent. The size of a circle indicates their wealth, which is determined by the average payoff they recieve in all their encounters with other players. Players' strategies evolve, so that players tend to copy the strategies of opponents more wealthy than themselves. They also mutate, so that sometimes players randomly try a brand new strategy. If you press "m" you can change the length of the players' memories from long to short and back. Once cooperation is lost, it is hard to get back. Press "q" to reset.