The figure summarizes analytical predictions for empathy evolution under three different social norms, using adaptive dynamics in a population of discriminators, compared to Monte Carlo simulations in finite populations. (a, c, e) White areas in the pairwise invasibility plots show values of for which the invader’s expected payoff exceeds the mean payoff of the resident population. Orange arrows indicate the direction of predicted evolution. (b, d, f) Monte Carlo simulations in small populations of 100 individuals with recurring mutations to reflect the predictions of adaptive-dynamics analysis. For each norm, sample trajectories showing all values in three independent populations are show in colors (red, blue, yellow), with the population means shown in gray.