The rationality of splitting equally

Conventional economic models seem unable to capture the propensity for 50-50 bargaining divisions observed in the lab. Experiments further suggest that something outside the usual set of economic parameters systematically influences bargaining settlements. I examine a simple bargaining model from a biological perspective. A limit evolutionarily stable strategy, FAIRMAN, makes 50-50 offers, punishes demands for more, and exploits demands for less. Fairman involves strategy perturbations resembling probes for concessions. When bargainers can use a signal to discriminate among partners, 50-50 is the unique limit evolutionarily stable outcome. The results suggest that some social conventions persist because they promote efficiency in an evolutionarily stable manner.