Human and Monkey Responses in a Symmetric Game of Conflict with Asymmetric Equilibria

To better understand the evolutionary history of human decision-making, we compare human behavior to that of two monkey species in a symmetric game of conflict with two asymmetric equilibria. While all of these species routinely make decisions in the context of social cooperation and competition, they have different socio-ecologies, which leads to different predictions about how they will respond. Our prediction was that anti-matching would be more difficult than matching in a symmetric coordination with simultaneous moves. To our surprise, not only do rhesus macaques frequently play one asymmetric Nash equilibrium, but so do capuchin monkeys, whose play in the coordination game was literally not distinguishable from randomness (in simultaneous play). Humans are the only species to play both asymmetric equilibria in a repeated game

Anything for a Cheerio: Brown Capuchins (\u3cem\u3eSapajus [Cebus] apella\u3c/em\u3e) Consistently Coordinate in an Assurance Game for Unequal Payoffs

Unequal outcomes disrupt cooperation in some situations, but this has not been tested in the context of coordination in economic games. To explore this, we tested brown capuchins (Sapajus [Cebus] apella) on a manual version of the Stag Hunt (or Assurance) Game, in which individuals sequentially chose between two options, Stag or Hare, and were rewarded according to their choices and that of their partner. Typically, coordination on Stag results in an equal highest payout, whereas coordinating on Hare results in a guaranteed equal but lower payoff and uncoordinated play results in the lowest payoff when playing Stag. We varied this structure such that one capuchin received double the rewards for the coordinated Stag outcome; thus, it was still both animals\u27 best option, but no longer equally rewarding. Despite the inequality, capuchins coordinated on Stag in 78% of trials, and neither payoff structure nor their partner\u27s choice impacted their decision. Additionally, there was no relationship between self-scratching, a measure of stress in capuchins, and choices. After completing the study, we discovered our reward, cheerios, was sufficiently valuable that in another study, capuchins never refused it, so post hoc we repeated the study using a lower value reward, banana flavored pellets. Capuchins completed only 26% of the pellet trials (compared to 98% with cheerios), constraining our ability to interpret the results, but nonetheless the monkeys showed a decrease in preference for Stag, particularly when they received fewer rewards for the coordinated Stag outcome. These results reinforce capuchins\u27 ability to find coordinated outcomes in the Stag Hunt game, but more work is needed to determine whether the monkeys did not mind the inequality or were unwilling to sacrifice a highly preferred food to rectify it. In either case, researchers should carefully consider the impact of their chosen rewards on subjects\u27 choices

Prevention of early childhood caries

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97473/1/j.1600-0528.1988.tb02094.x.pd

Behaviour 152 (2015) 941-961 Oxytocin reduces food sharing in capuchin monkeys by modulating social distance

Abstract Recent evidence indicates that oxytocin plays an important role in promoting prosocial behaviour amongst humans and other species. We tested whether oxytocin affected cooperation and foodsharing in capuchin monkeys, a highly cooperative New World primate. Subjects received either 2IU oxytocin or an inert adjuvent intranasally prior to each session. Oxytocin influenced food sharing in capuchins in ways we did not anticipate. Recipients were less likely to passively acquire food from possessors when either individual had received OT than in the control, and also spent less time in proximity to their partner. Passive food sharing requires proximity, and oxytocin decreased the capuchins' typical congregating behaviour, apparently resulting in decreased sharing. We propose that the likely mechanism for increased social distance is the known anxiolytic effect of oxytocin. Our results indicate a need to consider how oxytocin affects the context of interactions and interacts with modes of sociality unique to each species