Fair and unfair punishers coexist in the Ultimatum Game Brañas Garza, Pablo Espín Martín, Antonio Manuel Exadaktylos, Filippos Herrmann, Benedikt Evolutionary ecology Human behaviour In the Ultimatum Game, a proposer suggests how to split a sum of money with a responder. If the responder rejects the proposal, both players get nothing. Rejection of unfair offers is regarded as a form of punishment implemented by fair-minded individuals, who are willing to impose the cooperation norm at a personal cost. However, recent research using other experimental frameworks has observed non-negligible levels of antisocial punishment by competitive, spiteful individuals, which can eventually undermine cooperation. Using two large-scale experiments, this note explores the nature of Ultimatum Game punishers by analyzing their behavior in a Dictator Game. In both studies, the coexistence of two entirely different sub-populations is confirmed: prosocial punishers on the one hand, who behave fairly as dictators, and spiteful (antisocial) punishers on the other, who are totally unfair. The finding has important implications regarding the evolution of cooperation and the behavioral underpinnings of stable social systems. 2014-09-12T06:40:41Z 2014-09-12T06:40:41Z 2014 journal article Brañas-Garza, P.; et al. Fair and unfair punishers coexist in the Ultimatum Game. Scientific Reports, 4: 6025 (2014). [http://hdl.handle.net/10481/32990] 2045-2322 http://hdl.handle.net/10481/32990 10.1038/srep06025 eng open access Nature Publishing Group