Interpretative problems with chimpanzee ultimatum game

In an effort to compare fairness preferences in chimpanzees and children, Proctor et al. (1) have devised experiments aimed at replicating the essential features of two common experiments, the dictator game (DG) and the ultimatum game (UG). Here, we present both methodological concerns and broader interpretative issues. In order for an UG to be meaningful, both players must have a clear understanding of the responder’s role. However, in the experiments that Proctor et al. (1) conducted, “neither species was explicitly trained that refusal was an option.” In fact, the authors considered it “unlikely” that chimpanzee responders would reject, and no refusals actually occurred. Despite this, …