Chimpanzees play the ultimatum game

Abstract

Is the sense of fairness uniquely human? Human reactions to reward division are often studied by means of the ultimatum game, in which both partners need to agree on a distribution for both to receive rewards. Humans typically offer generous portions of the reward to their partner, a tendency our close primate relatives have thus far failed to show in experiments. Here we tested chimpanzees (Pan troglodytes) and human children on a modified ultimatum game. One individual chose between two tokens that, with their partner's cooperation, could be exchanged for rewards. One token offered equal rewards to both players, whereas the other token favored the chooser. Both apes and children responded like humans typically do. If their partner's cooperation was required, they split the rewards equally. However, with passive partners-a situation akin to the so-called dictator game-they preferred the selfish option. Thus, humans and chimpanzees show similar preferences regarding reward division, suggesting a long evolutionary history to the human sense of fairness.inequity aversion | equality | reciprocity | sharing | behavioral economics

Payoff-based learning explains the decline in cooperation in public goods games

“…It has been argued that this robust result demonstrates that humans have a unique regard for the welfare of others, termed pro-social preferences, which cannot be explained by kin selection [9], reciprocity [10] and/or via improved reputation [11][12][13][14]. Consequently, economic games are also increasingly being used in non-human primates in attempts to explore the evolutionary origins of such puzzling social behaviours [15][16][17].…”

Chimpanzee responders still behave like rational maximizers

“…Furthermore, because of an order confound (the preference test only occurred before testing), and because analyses were based on pooled data (figure 2 in ref. 4), these results cannot be entirely trusted.…”

“…The ultimatum game (1) is a powerful and widely used test of bargaining behavior that has only recently been applied to nonhuman animals (2)(3)(4). The key feature of this game is the power the responder has; the threat of rejections-the ultimatum-typically induces proposers to be more generous than they would be otherwise.…”

“…These controls were absent in ref. 4. It is conceivable that responders were not aware of the social consequences of their actions (or inactions), in which case they were not playing an ultimatum game.…”

Bonobos (Pan paniscus) vocally protest against violations of social expectations.

“…protest in cases where their perceived expectations are violated (Brosnan & de Waal, 449! 2003Price & Brosnan, 2012;Proctor et al, 2013;Range et al, 2009, Wascher & 450! Bugnyar, 2013.…”