Primatological and archaeological evidence along with anthropological accounts of hunter-gatherer societies indicate that lethal between-group violence may have been sufficiently frequent during our ancestral past to have shaped our evolved behavioral repertoire. Two simulations explore the possibility that heroism (risking one's life fighting for the group) evolved as a specialized form of altruism in response to war. We show that war selects strongly for heroism but only weakly for a domain-general altruistic propensity that promotes both heroism and other privately costly, (...) group-benefiting behaviors. A complementary analytical model shows that domain-specific heroism should evolve more readily when groups are small and mortality in defeated groups is high, features that are plausibly characteristic of our collective ancestral past. (shrink)

Cohesion may be based primarily on interpersonal ties or rely instead on the connection between member and group, while groups may cohere temporarily based on the immediate alignment of interests among members or may be tied together more permanently by socio-emotional bonds. Together, these characteristics define four prototypical group types. Cliques and coalitions are based primarily on dyadic ties. Groups of comrades or colleagues rely instead on the connection of members to the group for cohesion, which reduces the marginal cost (...) of increasing group size. The strong glue of socio-emotional cohesion binds cliques and comrades, while coalitions and groups of colleagues are often based on weaker forms of cohesion. The mix of strong and weak adhesives and the greater scalability offered by the member-group bond provide the building blocks for assembling very large societies without overtaxing the social brain. (shrink)