Heritability of ultimatum game responder behavior

Abstract

Experimental evidence suggests that many people are willing to deviate from materially maximizing strategies to punish unfair behavior. Even though little is known about the origins of such fairness preferences, it has been suggested that they have deep evolutionary roots and that they are crucial for maintaining and understanding cooperation among non-kin. Here we report the results of an ultimatum game, played for real monetary stakes, using twins recruited from the population-based Swedish Twin Registry as our subject pool. Employing standard structural equation modeling techniques, we estimate that >40% of the variation in subjects' rejection behavior is explained by additive genetic effects. Our estimates also suggest a very modest role for common environment as a source of phenotypic variation. Based on these findings, we argue that any attempt to explain observed ultimatum bargaining game behavior that ignores this genetic influence is incomplete.

Fig. 1.

Distribution of acceptance thresholds in the ultimatum game for MZ and DZ twins. The distributions do not differ significantly.

Fig. 2.

Scatterplot of ultimatum game acceptance thresholds for twin pairs. (A) Scatterplot for MZ twin pairs. The acceptance thresholds are highly correlated. (B) Scatterplot for DZ twin pairs. There was no significant correlation in acceptance thresholds.