Dangerous games and the emergence of social structure: evolving memory-based strategies for the generalized hawk-dove game

How can stable relationships emerge from repeated, pairwise interactions am ong competing individuals in a social group? In small groups, direct assess ment of resource-holding potential, which is often linked to body size, can sort individuals into a dominance hierarchy. But in larger groups, memory of behavior in previous interactions may prove essential for social stabili ty. In this study, I used a classifier-system model (similar to a genetic a lgorithm) to evolve strategies that individuals play in pairwise games that are potentially dangerous (i.e., fitness benefits of winning are outweighe d by losing costs that result mainly from risk of injury). When the two pos sible responses by each player in a single interaction are designated C (= careful) and D (= daring), the average gain is highest if responses are com plementary (i.e., one plays C and the other plays D). Stable dominance rela tionships, which depend on such complementarity across a sequence of intera ctions, are more common when both sizes are known to the contestants, when strategies are based on memory, and when combat is especially dangerous. Tw o key memory-based strategies generated by the classifier system (DorC and CAD) are particularly adept at achieving and maintaining complementarity; t hese strategies, which represent building blocks from which social structur e can arise, are linked here with pairwise contests for the first time. Whe n most individuals in the group differ in size, stable dominance relationsh ips generally yield transitive hierarchies consistent with size. Empirical tests of these predicted patterns are proposed.