Figure 4.

Emergence of Reciprocal Strategy and Polarization in a Stochastic Evolutionary Model

(A) shows how the fraction of successful groups does not vary significantly with timing uncertainty (left y axis), while the predominance of the reciprocal strategy over the strategies that contribute to reach the target increases (right y axis and boxes with slashes). (B) shows that the polarization increases when there is timing uncertainty. These results reproduce the trend observed in the experimental data. (Z = 50, N = 6, r = 0.9, E = 40, τ = 120, β = 0.004, with Z being the population size, N the number of group members, r the risk of losing the remainder of the endowment when not reaching the threshold, E the initial endowment, t the threshold that needs to be achieved, and β the selection strength in the stochastic evolutionary dynamic. See Transparent Methods for a detailed explanation of this dynamic model and Figures S6–S8 for additional results).