Long-run cooperation in the one-shot Prisoner's Dilemma: a hierarchic evolutionary approach

This paper proposes a hierarchic evolutionary model leading to long-run cooperation in the Prisoner's Dilemma. The population is segmented into groups, and evolution and interaction take place 'in parallel' at two levels: (i) within groups at the lower level; (ii) among groups at the higher one. At each of these levels, what performs currently best tends to be imitated. On the other hand, occasionally, individuals also experiment with (or mutate to) some new strategy. If the number of groups is sufficiently large, the long-run (invariant) distribution of the process is shown to be concentrated on the cooperative outcome.