Sociality as a defensive response to the threat of loss Tim Johnson Max Planck Institute for Human Development Lentzeallee 94 14195 Berlin Germany tjohnson@mpib-berlin.mpg.de Mikhail Myagkov, PhD Department of Political Science University of Oregon Eugene, OR 97403 USA myagkov@darkwing.uoregon.edu John Orbell, PhD Department of Political Science University of Oregon Eugene, OR 97403 USA jorbell@darkwing.uoregon.edu ABSTRACT . Laboratory research studying behavior in the Prisoner’s Dilemma (PD) game is consistent with the commonplace perception that social exchange is risky. Although they often do cooperate, people also often defect. Thus, the decision to enter a PD game with a stranger, about whom one has no good basis for predicting behavior, is a bet on cooperation. Many investigators have explored a range of cognitive processes and individual differences putatively bearing on the choice to enter such games, but few have asked how people perceive, assess, and respond to social risk in general. That is what we ask here. From the well known finding that people are risk-averse in the domain of gains and risk-tolerant in the domain of losses, we predict that, with game incentives constant, people will be more willing to enter social relationships when game payoffs are framed as losses than when they are framed as gains. We tested this prediction in a student population playing PD games. Results strongly supported the prediction, suggesting that human sociality may have evolved more as a defensive response to the possibility of loss than as an opportunistic attempt to capture gain. L aboratory research into choice behavior during Prisoner’s Dilemma (PD) game play long focused on testing the prediction that, absent external incentives supporting cooperation, rational people would choose the dominant defect alternative. However, findings disconfirming this prediction are, by now, un- ambiguous and well accepted. People often do cooperate in PD games, 1, 2, 3, 4 choosing against their private interest and, thereby, producing greater social welfare. Nevertheless, universal cooperation is seldom, if ever, observed in such laboratory work, meaning that players first decide how others are likely to behave in a PD-type game and only then whether such a game should be entered. This question has also been addressed by a modified laboratory paradigm giving subjects the option of playing or not playing PD as well as a within-game choice of cooperation or defection. The findings are diverse; researchers have reported 13 P OLITICS AND THE L IFE S CIENCES d 25 J ULY 2005 d VOL. 23, NO.2