Figure 1

Average cooperation per generation for type 1 (b), 2 (c) or 3 (d) ostracism. Type 0 (a) represents a scenario without ostracism. Ostracism is performed by each agent i with a probability equal to the agent’s fusion level \(f_i\). Average cooperation indicates the cumulative frequency of cooperative interactions, defined as the total number of donations made in all preceding generations as a proportion of the total number of games played in all preceding generations. Agents interact randomly with the other fused individuals within their in-group with fixed probabilities of \(S_i\) (\(S_i = 0.1, 0.5, 0.9\)), or with a probability equal to their own current fusion level (\(S_i = f_i\)). \(S_{global}\) indicates that all agents mix uniform randomly (i.e., \(S_i = 0\)). The in-group of an agent i is defined as the subset of agents having at least same level of fusion as i (i.e., \(f_i\) or greater). Agents interact randomly with the whole population with a probability equal to \(1 - S_i\). Results are averaged over five randomly seeded runs. Number of agents \(N=100\); number of games per generation \(m=5000\); number of generations \(M=50,000\). Action rules and fusion levels are mutated at the rate of 0.01 per generation.