Ph. Crowley, Dangerous games and the emergence of social structure: evolving memory-based strategies for the generalized hawk-dove game, BEH ECOLOGY, 12(6), 2001, pp. 753-760
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.