File:Cooperation-Norms-and-Revolutions-A-Unified-Game-Theoretical-Approach-pone.0012530.s003.ogv

English: Same as Movie S1, but considering both, interactions within and between the two populations. Assuming no difference between in-group and out-group interactions, we have ba = Ba = B and ca = Ca = C. While the multi-population stag hunt game (first half of the movie) shows a tendency to establish a commonly shared behavior (“behavioral norm”), the snowdrift game (second half) rather delineates situations of conflict between both populations. It is known that conflicts between two populations may sometimes cause a “revolution”. According to our interpretation, this corresponds to the discontinuous transition of the evolutionary equilibrium, when the background color turns from salmon to mustard. The abrupt change of the q-coordinate from 0 to 1 means that all individuals in the weaker population show the non-preferred behavior before the revolution, but their preferred behavior afterwards. The discontinuous transition occurs, when |B| and |C| in the multi-population snowdrift game become the same. (Note that there is no such revolutionary transition, when individuals have compatible preferences.) The dynamics for two interacting populations without self-interactions is clearly less differentiated (see Movie S2). In particular, Movie S2 shows no revolutionary transition in the snowdrift game. It also lacks cases where the phase diagram of the stag hunt game displays three different basins of attraction at the same time, corresponding to a coexistence of three stable fix points. While two of them correspond to the establishment of a commonly shared behavior (a behavioral norm), the third point represents the formation of different behaviors (separate “subcultures”) in each population.