An Adaptation for Altruism? The Social Causes, Social Effects, and Social Evolution of Gratitude

People feel grateful when they have benefited from someone’s costly, intentional, voluntary effort on their behalf. Experiencing gratitude motivates beneficiaries to repay their benefactors and to extend generosity to third parties. Expressions of gratitude also reinforce benefactors for their generosity. These social features distinguish gratitude from related emotions such as happiness and feelings of indebtedness. Evolutionary theories propose that gratitude is an adaptation for reciprocal altruism (the sequential exchange of costly benefits between nonrelatives) and, perhaps, upstream reciprocity (a payit-forward style distribution of an unearned benefit to a third party after one has received a benefit from another benefactor). Gratitude therefore may have played a unique role in human social evolution. KEYWORDS—gratitude; emotion; evolution; morality; prosocial behavior; reciprocity; altruism Emotions are discrete, time-limited, affective responses to significant environmental changes. Once activated, emotions are thought to coordinate thought, physiology, and behavior so that people can respond to reality in self-protective and self-enhancing ways (Ekman, 1992). Discovering what a particular emotion does—the environmental inputs that activate it and its effects on behavior, for instance—is therefore regarded by many emotion researchers as a royal road to discovering what it is for—that is, why humans evolved to experience that emotion. Gratitude—a positive emotion that typically flows from the perception that one has benefited from the costly, intentional, voluntary action of another person—is an interesting test bed for considering this functional approach to emotion. Western social theorists from Seneca and Cicero to Adam Smith and David Hume, to modern social scientists such as Robert Frank and Robert Trivers, have apprehended the importance of gratitude for creating and sustaining positive social relations (Bartlett & DeSteno, 2006; Harpham, 2004; McCullough, Kilpatrick, Emmons,&Larson, 2001). Oddly, though, psychological science largely neglected gratitude until the 21st century. Fortunately, recent research has explored gratitude’s distinct social causes and effects. These studies may help to shed light on gratitude’s evolutionary history. GRATITUDE AS A PROSOCIAL EMOTION Gratitude is a pleasant emotion, but it is different from simple happiness because gratitude is typically preceded by the perception that one has benefited from another person’s generosity. Because gratitude is predicated upon receiving a benefit from another social agent, McCullough et al. (2001) proposed that gratitude possesses three psychological features that are relevant to processing and responding to prosocial behavior: It is a (a) benefit detector and both a (b) reinforcer and (c) motivator of prosocial behavior. Gratitude as a Benefit Detector First, McCullough and colleagues proposed that gratitude is an affective readout that alerts people that they have benefited from another person’s prosocial behavior. Gratitude is responsive to four types of information about the benefit-giving situation: (a) the benefit’s costliness to the benefactor, (b) its value to the beneficiary, (c) the intentionality with which it was rendered, and (d) the extent to which it was given even without relational obligations to help (for example, parents’ obligations to help their children). Recent experiments support this characterization of gratitude as a benefit detector. For example, Tsang (2006a) found that, consistent with the proposition that gratitude increases proportionally with the benefactor’s intentionality, participants experiencedmore gratitude toward benefactors who helped them out of benevolent rather than self-serving motives. Address correspondence to Michael E. McCullough, Department of Psychology, University of Miami, P.O. Box 248285, Coral Gables, FL 33124-0751; e-mail: [email protected]. CURRENT DIRECTIONS IN PSYCHOLOGICAL SCIENCE Volume 17—Number 4 281 Copyright r 2008 Association for Psychological Science Gratitude as a Reinforcer of Prosocial Behavior McCullough et al. (2001) also proposed that gratitude reinforces prosocial behavior because expressions of gratitude (for example, saying ‘‘thanks’’) increase the likelihood that benefactors will behave prosocially again in the future. Reviewing previous studies, McCullough and colleagues concluded that benefactors who are thanked for their efforts are willing to give more and work harder on behalf of others when future opportunities arise than are benefactors who have not been thanked. Writing ‘‘thank you’’ on a restaurant bill even raises servers’ tips. Why would saying ‘‘thanks’’ reinforce prosocial behavior— and even tipping? Perhaps because the beneficiary’s expression of thanks acknowledges to the benefactor that he or she has noticed a kindness and, thus, might be prone to reciprocate when a future opportunity to do so arises. In other words, expressing gratitude may make beneficiaries seem like safe targets for future investments. Gratitude as a Motivator of Prosocial Behavior This leads to gratitude’s third prosocial characteristic: It motivates people to behave prosocially after receiving benefits. In 2001, when McCullough and colleagues reviewed the literature, gratitude’s efficacy as a motivator of future prosocial behavior was the most speculative of their proposals about gratitude’s effects. More recent research has confirmed their speculation. McCullough, Emmons, and Tsang (2002) found that people who scored higher on selfand peer-report measures of the ‘‘grateful disposition’’ also scored higher on measures of prosocial behaviors during the previous month (and overall) than did people who scored lower on the gratitudemeasures. In addition, Bartlett and DeSteno (2006) discovered that participants made to feel grateful toward a benefactor exerted more effort to help the benefactor on an unrelated task (i.e., completing a boring and cognitively taxing survey) than did nongrateful participants. They were also more likely to help a stranger (that is, someone who had not helped them) than were nongrateful participants. This latter finding shows that gratitude’s effects on prosocial behavior were not simply caused by reminding people of the norm of reciprocity (the norm that dictates that one should return help for help received). Likewise, Tsang (2006b) found that people who received a benefit due to the intentional effort of a partner not only were more grateful than were people who received the benefit by chance but also were more likely to behave generously toward their partner in response. Finally, Emmons and McCullough (2003) found that participants who wrote daily for 2 weeks about things for which they were grateful reported offering more emotional support and (with near-statistical significance) tangible help to others than did participants who wrote about their daily hassles or about ways in which they were more fortunate than others. Gratitude may motivate prosocial behavior by influencing psychological states that support generosity and cooperation. For example, Dunn and Schweitzer (2005, Study 3) found that participants who described a time in the past when they felt grateful toward someone (thereby creating grateful emotion in the present) subsequently reported higher levels of trust toward a third party than did participants who were asked to describe a time they felt angry, guilty, or proud. Similarly, Jackson, Lewandowski, Fleury, and Chin (2001) found that having participants recall a real-life gratitude-inducing experience caused them to attribute another person’s good fortune to stable causes that were under the fortunate person’s control. In other words, gratitude causes one to give people credit for their accomplishments. Trust and a readiness to give people credit for their accomplishments are important lubricants for positive social interaction, so psychological effects such as these may explain how gratitude promotes prosocial behavior. DISTINGUISHING GRATITUDE FROM OTHER EMOTIONS In light of its prosocial characteristics, functional emotion theorists would likely speculate that gratitude was shaped by evolutionary pressures for generosity and helping. However, if gratitude’s prosocial characteristics were not unique to gratitude (for example, if gratitude were indistinguishable in these respects from emotions such as happiness and indebtedness), then the proposition that gratitude was designed specifically to facilitate social exchange would be weakened. Fortunately for the functionalist approach, research shows that gratitude is quite distinct from several kindred emotions in its phenomenology, causes, and effects. Gratitude Versus Other Positive Emotions Psychologists have long held that positive emotions such as happiness and amusement can promote prosocial behavior. What may distinguish gratitude from other positive emotions in this respect is that gratitude stimulates helping even when it is costly to the helper. Bartlett and DeSteno (2006) found that participants in an experimentally induced state of gratitude voluntarily spent more time completing a boring survey as a favor to their benefactor than did participants in an amused emotional state (see also Tsang, 2006b). Additionally, as noted above, Jackson et al. (2001) showed that gratitude causes people to give other people who encounter good fortune more credit for their good fortune than does simple happiness. Gratitude Versus Obligation and Indebtedness Gratitude is also distinct from obligation and indebtedness. Although people often use obligation-related phrases (e.g., ‘‘I owe you one’’) and gratitude-related phrases (e.g., ‘‘I’m grateful to you’’) interchangeably, they are distinct and have distinct 282 Volume 17—Number 4 Gratitude