Population Learning of Cooperative Behavior in a Three-Person Centipede Game

We consider mixed populations (N 1/4 21) of genuine (humans) and arti.cial (robots) agents repeatedly interacting in small groups whose composition is changed randomly from round to round. Our purpose is to study the spread of cooperative or non-cooperative behavior over time in populations playing a 3-person centipede game by manipulating the behavior of the robots (cooperative vs. noncooperative) and their proportion in the population. Our results convey a positive message: adding a handful of cooperative robots increases the propensity of the genuine subjects to cooperate over time, whereas adding a handful of non-cooperative agents does not decrease this propensity. If there are enough hard-core cooperative subjects in the population, they not only negate the behavior of the non-cooperative robots but also induce other subjects to behave more cooperatively.