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Political mobilization messages delivered to 61 million Facebook users during the 2010 US congressional elections directly influenced political self-expression, information seeking and real-world voting behaviour of millions of people and their friends, with social transmission occurring mainly between close friends and having a greater effect than the direct effect of the messages themselves. An off-line side to online social networking Online social networks are everywhere. They must be influencing the way society is developing, but hard evidence is scarce. For instance, the relative effectiveness of online friendships and face-to-face friendships as drivers of social change is not known. In what may be the largest experiment ever conducted with human subjects, James Fowler and colleagues randomly assigned messages to 61 million Facebook users on Election Day in the United States in 2010, and tracked their behaviour both online and offline, using publicly available records. The results show that the messages influenced the political communication, information-seeking and voting behaviour of millions of people. Social messages had more impact than informational messages and 'weak ties' were much less likely than 'strong ties' to spread behaviour via the social network. Thus online mobilization works primarily through strong-tie networks that may exist offline but have an online representation. Human behaviour is thought to spread through face-to-face social networks, but it is difficult to identify social influence effects in observational studies 9 , 10 , 11 , 12 , 13 , and it is unknown whether online social networks operate in the same way 14 – 19 . Here we report results from a randomized controlled trial of political mobilization messages delivered to 61 million Facebook users during the 2010 US congressional elections. The results show that the messages directly influenced political self-expression, information seeking and real-world voting behaviour of millions of people. Furthermore, the messages not only influenced the users who received them but also the users’ friends, and friends of friends. The effect of social transmission on real-world voting was greater than the direct effect of the messages themselves, and nearly all the transmission occurred between ‘close friends’ who were more likely to have a face-to-face relationship. These results suggest that strong ties are instrumental for spreading both online and real-world behaviour in human social networks.

The widespread existence of cooperation is difficult to explain because individuals face strong incentives to exploit the cooperative tendencies of others. In the research reported here, we examined how the spread of reputational information through gossip promotes cooperation in mixed-motive settings. Results showed that individuals readily communicated reputational information about others, and recipients used this information to selectively interact with cooperative individuals and ostracize those who had behaved selfishly, which enabled group members to contribute to the public good with reduced threat of exploitation. Additionally, ostracized individuals responded to exclusion by subsequently cooperating at levels comparable to those who were not ostracized. These results suggest that the spread of reputational information through gossip can mitigate egoistic behavior by facilitating partner selection, thereby helping to solve the problem of cooperation even in noniterated interactions.

We review emerging research on the psychological and biological factors that underlie social group formation, cooperation, and conflict in humans. Our aim is to integrate the intergroup neuroscience literature with classic theories of group processes and intergroup relations in an effort to move beyond merely describing the effects of specific social out-groups on the brain and behavior. Instead, we emphasize the underlying psychological processes that govern intergroup interactions more generally: forming and updating our representations of \"us\" and \"them\" via social identification and functional relations between groups. This approach highlights the dynamic nature of social identity and the context-dependent nature of intergroup relations. We argue that this theoretical integration can help reconcile seemingly discrepant findings in the literature, provide organizational principles for understanding the core elements of intergroup dynamics, and highlight several exciting directions for future research at the interface of intergroup relations and neuroscience.

Identifying social influence in networks is critical to understainding how behaviors spread. We present a method that uses in vivo randomized experimentation to identify influence and susceptibility in networks while avoiding the biases inherent in traditional estimates of social contagion. Estimation in a representative sample of 1.3 million Facebook users showed that younger users are more susceptible to influence than older users, men are more influential than women, women influence men more than they influence other women, and married individuals are the least susceptible to influence in the decision to adopt the product offered. Analysis of influence and susceptibility together with network structure revealed that influential individuals are less susceptible to influence than noninfluential individuals and that they cluster in the network while susceptible individuals do not, which suggests that influential people with influential friends may be instrumental in the spread of this product in the network.

Societal change and personal life events sometimes make one feel uncertain about one's self and identity. According to uncertainty-identity theory, this self-uncertainty can motivate people to identify with social groups, particularly groups that provide a distinctive and clearly defined identity and associated normative beliefs and behavioral prescriptions. This process can make more extreme groups and behaviors attractive as a source of identification-contingent uncertainty reduction. People may zealously identify with highly distinctive groups that have strong and directive leadership and ideological and ethnocentric belief systems that proscribe dissent and prescribe group-normative behavior. This analysis has been extended to help illuminate how extremism may emerge in the context of religion, politics, gangs, leadership, and adolescent risk taking. This article describes uncertainty-identity theory, overviews empirical support for its main tenets, and outlines some directions for future research.

The mechanisms underlying the association between positive emotions and physical health remain a mystery. We hypothesize that an upward-spiral dynamic continually reinforces the tie between positive emotions and physical health and that this spiral is mediated by people's perceptions of their positive social connections. We tested this overarching hypothesis in a longitudinal field experiment in which participants were randomly assigned to an intervention group that self-generated positive emotions via loving-kindness meditation or to a waiting-list control group. Participants in the intervention group increased in positive emotions relative to those in the control group, an effect moderated by baseline vagal tone, a proxy index of physical health. Increased positive emotions, in turn, produced increases in vagal tone, an effect mediated by increased perceptions of social connections. This experimental evidence identifies one mechanism—perceptions of social connections—through which positive emotions build physical health, indexed as vagal tone. Results suggest that positive emotions, positive social connections, and physical health influence one another in a self-sustaining upward-spiral dynamic.

Decades of research in social and political psychology have demonstrated that political conservatives appear more intolerant toward a variety of groups than do political liberals. Recent work from our three independent labs has challenged this conventional wisdom by suggesting that some of the psychological underpinnings of intolerance are not exclusive to people on either end of the political spectrum. These studies have demonstrated that liberals and conservatives express similar levels of intolerance toward ideologically dissimilar and threatening groups. We suggest directions for future research and discuss the psychological and political implications of our conclusions.

With over 800 million active users, Facebook is changing the way hundreds of millions of people relate to one another and share information. A rapidly growing body of research has accompanied the meteoric rise of Facebook as social scientists assess the impact of Facebook on social life. In addition, researchers have recognized the utility of Facebook as a novel tool to observe behavior in a naturalistic setting, test hypotheses, and recruit participants. However, research on Facebook emanates from a wide variety of disciplines, with results being published in a broad range of journals and conference proceedings, making it difficult to keep track of various findings. And because Facebook is a relatively recent phenomenon, uncertainty still exists about the most effective ways to do Facebook research. To address these issues, the authors conducted a comprehensive literature search, identifying 412 relevant articles, which were sorted into 5 categories: descriptive analysis of users, motivations for using Facebook, identity presentation, the role of Facebook in social interactions, and privacy and information disclosure. The literature review serves as the foundation from which to assess current findings and offer recommendations to the field for future research on Facebook and online social networks more broadly.

The U.S. Census Bureau projects that racial minority groups will make up a majority of the U.S. national population in 2042, effectively creating a so-called majority-minority nation. In four experiments, we explored how salience of such racial demographic shifts affects White Americans' political-party leanings and expressed political ideology. Study 1 revealed that making California's majority-minority shift salient led politically unaffiliated White Americans to lean more toward the Republican Party and express greater political conservatism. Studies 2, 3a, and 3b revealed that making the changing national racial demographics salient led White Americans (regardless of political affiliation) to endorse conservative policy positions more strongly. Moreover, the results implicate group-status threat as the mechanism underlying these effects. Taken together, this work suggests that the increasing diversity of the nation may engender a widening partisan divide.

Persuasive messages are more effective when they are custom-tailored to reflect the interests and concerns of the intended audience. Much of the message-framing literature has focused on the advantages of using either gain or loss frames, depending on the motivational orientation of the target group. In the current study, we extended this research to examine whether a persuasive appeal's effectiveness can be increased by aligning the message framing with the recipient's personality profile. For a single product, we constructed five advertisements, each designed to target one of the five major trait domains of human personality. In a sample of 324 survey respondents, advertisements were evaluated more positively the more they cohered with participants' dispositional motives. These results suggest that adapting persuasive messages to the personality traits of the target audience can be an effective way of increasing the messages' impact, and highlight the potential value of personality-based communication strategies.