Figure 5. Resilient cooperators stabilize cooperation in an agent-based model.

In both cases, T₁–T₁₀ refer to threshold strategies, where a player playing strategy T_x will cooperate conditionally up to round x and then will defect unilaterally. T₁ corresponds to defection on every round and CC corresponds to full conditional cooperation (also known as ‘grim trigger') (a) Individual strategies for 100 simulated agents over the course of 400 games in the absence of resilient cooperators (that is, all agents are rational cooperators who selfishly best-respond to the inferred distribution of strategies in the population). In this case cooperation unravels completely. (b) Individual strategies for the same model but with 40% resilient cooperators and 60% rational agents. In this case cooperation stabilizes after 100–150 games (equivalent to 5–8 days)