Collaborating Authors

Can playing together help us live together?


The contact hypothesis in psychology predicts that prejudice can be reduced when rival groups come together under optimal circumstances of cooperation and equal status. To date, the weight of real-world evidence for this hypothesis comes from self-reported attitudes after self-initiated contact, not from preregistered randomized trials that take intergroup contact as seriously as one would take a potential vaccine for conflict ([ 1 ][1], [ 2 ][2]). Consequently, on page 866 of this issue, the results of Mousa's ([ 3 ][3]) new field experiment are breaking news. Mousa intervened in amateur Christian soccer leagues across Northern Iraqi cities affected by ISIS violence. To assess the impact of this ambitious real-world intervention, she randomly assigned Muslim players to half of the teams, measured players' behavior up to 6 months later, and posted her preregistered analysis plan and data alongside the report. Mousa finds that having Muslim teammates causes Christian players to change their behavior for the better toward Muslim players, by including them, working with them, and awarding them material signs of respect. Team-based contact with minority group members reduced prejudiced behavior toward other minority group players. Given its relevance for policy (Mousa notes that $877 million was allocated in 2020 toward “social cohesion” programming by the U.S. Agency for International Development) and that the contact hypothesis has been studied for many years, some may classify this research as an application of a well-known finding. This would be inaccurate. Previous research has not demonstrated cause and effect with real-world interventions or measured behaviors or otherwise leveraged the most robust research methodologies. These methods are crucial, given that the anticipated effects of contact range from positive change to backlash, in which contact stirs latent resentments. This makes Mousa's research more similar to basic science that makes progress toward fundamental evidence than to applied research that tests policy interventions based on a robust foundation of scientific evidence. Work in the field, which is often mistaken for applied research because of its location outside the laboratory, performs the function of basic science when it comes to the question of whether intergroup contact increases social cohesion. The study presents a fundamental theoretical puzzle: Why don't the positive behavioral effects generalize out of context, or to positive intergroup attitudes? The first piece of the puzzle is that the observed changes are limited to behaviors and not attitudes. A growing number of field experiments on prejudice reduction uncover this pattern ([ 4 ][4], [ 5 ][5]), which counters both lay and scientific notions that attitudes guide behavior. One could argue that between attitudes and behaviors, it is better to change behavior because prejudicial action is worse than harboring prejudicial attitudes. Additionally, public behaviors may cause more downstream change because they are more easily observable than private attitudes ([ 6 ][6]). More work is needed to measure these kinds of spillover effects, following on Mousa's finding that community members who attended more games were more likely to view religious and ethnic divisions as arbitrary. Future work can also disentangle whether attitudes are simply more difficult to change or whether current research is not measuring the correct attitudes. Perhaps the nature of intergroup contact is useful for changing a more limited range of attitudes than those measured in the present study. Mousa observes one instance of attitude change among players: the item regarding arbitrary religious and ethnic divisions. She points out that it represents a change in “abstract attitudes rather than concrete policy positions.” As it was originally conceived, the contact hypothesis was a salve for prejudice or animus, not for antagonistic political opinion or behavior ([ 7 ][7]). Since then, psychological evidence has grown, suggesting that prejudice-reduction interventions have inconsistent and even unintended effects on related political attitudes ([ 8 ][8]). Mousa defines and measures the target of her intervention, social cohesion, as a more compound concept than prejudice, involving intergroup cooperation and policy attitudes. Interventions such as contact that are intended to soften attitudes toward outgroups may need to be combined with additional activities to channel newfound goodwill into a political or policy position. Early work on interracial contact in the United States recognized this point. For example, in addition to creating ideal contact conditions for Black and White individuals working in teams, one study using Black actors to mention instances of discrimination and race-based hardship helped White participants connect their experience to larger societal issues ([ 9 ][9]). The second piece of the theoretical puzzle is that changes in behavior toward other Muslim players in the league did not generalize to changes in behavior toward Muslim strangers. Mousa offers possible explanations, including ongoing threat from recent anti-Christian violence, the fragile quality of the contact with other players, and the possibility that behavior change takes longer to manifest. Another possibility rests in the basic math of the league's intergroup contact: Christian leaders allowed a maximum of three Muslim players on treatment teams. This limitation represents a hard-won insight about the difficulty of implementing intergroup contact interventions in post-conflict settings but may have limited the generalizability of behavioral effects. Psychological theory predicts that individuals can make positive generalizations from one prototypical group member to the rest of the group ([ 10 ][10]). The handful of Muslim players may have been seen as exceptional, not prototypical, in the eyes of the Christian players, similar to other contexts with a token number of outgroup individuals. If the Muslim players were considered an exception to the rule, psychological theory would not predict that positive impressions of Muslim players would generalize to their group. Another consequence of the small number of Muslim players is that it inhibits the research from exploring effects on both sides of the intergroup contact. Mousa's data suggest that Muslim players' prejudice did not change over time, but there are too few Muslims and no Muslim control group to rigorously test this claim. Leaving out the perspectives of minority group members, who are often instrumentalized for the purpose of attitude change among the majority, is a pattern in intergroup contact research. There is much to learn by studying reactions to intergroup contact among minority group participants. This landmark study cuts a clear path for future scholarship. Generalized answers will only emerge after more experimental work that may seem like policy application but is actually basic science, working systematically toward robust conclusions. Mousa is one of a cohort ([ 2 ][2]) of young scientists who are leading the way. 1. [↵][11]1. E. L. Paluck, 2. S. A. Green, 3. D. P. Green , Behav. Pub. Pol. 3, 129 (2019). [OpenUrl][12] 2. [↵][13]1. E. L. Paluck , Harvard Dataverse (2020); doi:10.7910/DVN/ODACR5. 3. [↵][14]1. S. Mousa , Science 369, 866 (2020). [OpenUrl][15][Abstract/FREE Full Text][16] 4. [↵][17]1. A. Scacco, 2. S. S. Warren , Am. Polit. Sci. Rev. 112, 654 (2018). [OpenUrl][18][CrossRef][19] 5. [↵][20]1. E. L. Paluck , J. Pers. Soc. Psychol. 96, 574 (2009). [OpenUrl][21][CrossRef][22][PubMed][23][Web of Science][24] 6. [↵][25]1. T. Kuran , Private Truths, Public Lies (Harvard Univ. Press, 1997). 7. [↵][26]1. G. Allport , The Nature of Prejudice (Addison Wesley, 1954). 8. [↵][27]1. J. Dixon, 2. M. Levine, 3. S. Reicher, 4. K. Durrheim , Behav. Brain Sci. 35, 411 (2012). [OpenUrl][28][CrossRef][29][PubMed][30] 9. [↵][31]1. S. W. Cook , J. Res. Dev. Educ. 55, 647 (1978). [OpenUrl][32] 10. [↵][33]1. J. C. Turner, 2. M. A. Hogg, 3. P. J. Oakes, 4. S. D. Reicher, 5. M. S. Wetherell , Rediscovering the Social Group, A Self-Categorization Theory (Basil Blackwell, 1987). Acknowledgments: The authors thank the Rita Allen Foundation for funding and R. Porat and D. Green for comments. 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Diversity and prosocial behavior


Immigration and globalization have spurred interest in the effects of ethnic diversity in Western societies. Most scholars focus on whether diversity undermines trust, social capital, and collective goods provision. However, the type of prosociality that helps heterogeneous societies function is different from the in-group solidarity that glues homogeneous communities together. Social cohesion in multiethnic societies depends on whether prosocial behavior extends beyond close-knit networks and in-group boundaries. We identify two features of modern societies--social differentiation and economic interdependence--that can set the stage for constructive interactions with dissimilar others. Whether societal adaptations to diversity lead toward integration or division depends on the positions occupied by minorities and immigrants in the social structure and economic system, along with the institutional arrangements that determine their political inclusion. Most Western countries already are or are destined to become multiethnic societies thanks to recent patterns of migration and globalization. Growing immigration to North America and Western Europe (Figure 1A) has commanded particular attention. Increased ethnic heterogeneity has renewed scholarly interest in intergroup dynamics of cooperation and discrimination and spurred debates over the consequences of ethnic diversity for social trust and democratic integration.

Most humans are naturally inclined to help strangers and share limited resources

Daily Mail - Science & tech

From relentless online trolling to this summer's appalling terror attacks, it's hard to remember humans are (mostly) kind. But that's the message of a new study that shows groups of humans do not clash as much with their peers as other primates do. Researchers found humans are far more open to exploring relationships with strangers, which helps us secure limited resources and may have helped our ancestors thrive. Researchers from the University of California Santa Barbara and the Max Planck Institute for Evolutionary Anthropology studied human kindness and cooperation in Bolivia. In 2014, researchers from the University of Minnesota declared chimpanzees to be inherently violent, with males in particular proving to be the most aggressive of the sexes.

A Scholar of Extremism on How Religious Conflict Shapes Sri Lanka

The New Yorker

On Easter Sunday, terrorists slaughtered nearly three hundred people in Sri Lanka, in coördinated attacks at three churches and three luxury hotels. The government has said that the attacks were the work of suicide bombers from a single extremist group, and that thirteen people are being held in police custody. On April 11th, the country's deputy inspector general had issued a letter to government officials saying that National Thowheed Jama'ath, a radical Islamist group based in South India, was planning a terrorist attack, but the Prime Minister, Ranil Wickremesinghe, has said that he did not receive the warning. Since the attack, the government has shut down Facebook and other social-media platforms, which recently were used to incite anti-Muslim violence in the country. Sri Lanka has experienced intermittent violence since the end of a brutal civil war, which lasted from 1983 to 2009.

Indirect Reciprocity and the Evolution of Prejudicial Groups


Prejudice is a human attitude involving generally negative and unsubstantiated prejudgement of others. When acted upon, this results in wide-ranging behaviours such as sexism, ageism and discrimination against sexual preference1,2,3 through to ethnic, racial, nationalistic and religious extremism4,5, with bias and intergroup conflict characterised as a "problem of the century"6. Most recently, prejudice has been highlighted in connection to global political events: for example anti-immigration prejudice was a strong correlate of support for Brexit7. The human disposition to categorize others through their group identity creates an opportunity for discrimination8,9,10. As a consequence of in-group formation11, which occurs through cultural or biological identification with others, or as a consequence of identity-less strangers mutually cooperating12, bias can take hold in two ways.