The emergence and perils of polarization.

We provide commentaries on the papers included in the Dynamics of Political Polarization Special Feature. Baldassarri reads the contribution of the papers in light of the theoretical distinction between ideological partisanship, which is generally rooted in sociodemographic and political cleavages, and affective partisanship, which is, instead, mostly fueled by emotional attachment and repulsion, rather than ideology and material interests. The latter, she argues, is likely to lead to a runaway process and threaten the pluralistic bases of contemporary democracy. Page sees the contribution of the many distinct models in the ensemble as potentially contributing more than the parts. Individual papers identify distinct causes of polarization as well as potential solutions. Viewed collectively, the papers suggest that the multiple causes of polarization may self-reinforce, which suggests that successful interventions would require a variety of efforts. Understanding how to construct such interventions may require larger models with greater realism.

Market integration accounts for local variation in generalized altruism in a nationwide lost-letter experiment.

What explains variation in levels of prosocial behavior across communities? And are members of the ingroup and outgroup treated differently? According to evolutionary theories of generalized altruism, market integration should lead to greater levels of prosociality: Market exchange forces people to interact with unknown others, thus creating the conditions for the extension of prosocial behavior beyond close-knit circles to include outgroup members and strangers. Moving away from the evolutionary focus on cross-cultural variation, this article uses the market-integration hypothesis to explain intracultural variation in levels of prosociality in an advanced society. Taking advantage of an ideal setting, this study reports results from a large-scale, nationwide lost-letter experiment in which 5,980 letters were dispersed in a sample of 188 Italian communities. The study confirms the relevance of market integration in accounting for differences in levels of prosociality: In areas where market exchange is dominant, return rates are high. It also casts a light on the relationship between ingroup and outgroup prosociality: Return rates for both Italian and foreign recipients are the same; they vary together; and ingroup returns are highly predictive of outgroup returns at the community level.

Centralized sanctioning and legitimate authority promote cooperation in humans.

Social sanctioning is widely considered a successful strategy to promote cooperation among humans. In situations in which individual and collective interests are at odds, incentives to free-ride induce individuals to refrain from contributing to public goods provision. Experimental evidence from public goods games shows that when endowed with sanctioning powers, conditional cooperators can discipline defectors, thus leading to greater levels of cooperation. However, extant evidence is based on peer punishment institutions, whereas in complex societies, systems of control are often centralized: for instance, we do not sanction our neighbors for driving too fast, the police do. Here we show the effect of centralized sanctioning and legitimate authority on cooperation. We designed an adaptation of the public goods game in which sanctioning power is given to a single monitor, and we experimentally manipulated the process by which the monitor is chosen. To increase the external validity of the study, we conducted lab-in-the-field experiments involving 1,543 Ugandan farmers from 50 producer cooperatives. This research provides evidence of the effectiveness of centralized sanctioning and demonstrates the causal effect of legitimacy on cooperation: participants are more responsive to the authority of an elected monitor than a randomly chosen monitor. Our essay contributes to the literature on the evolution of cooperation by introducing the idea of role differentiation. In complex societies, cooperative behavior is not only sustained by mechanisms of selection and reciprocity among peers, but also by the legitimacy that certain actors derive from their position in the social hierarchy.

Cognitive-motivational mechanisms of political polarization in social-communicative contexts.

Healthy democratic polities feature competing visions of a good society but also require some level of cooperation and institutional trust. Democracy is at risk when citizens become so polarized that an 'us versus them' mentality dominates. Despite a vast multidisciplinary literature, no coherent conceptual framework of the microlevel dynamics that increase or decrease polarization has been presented. In this Review, we provide a conceptual framework to integrate scientific knowledge about cognitive-motivational mechanisms that influence political polarization and the social-communicative contexts in which they are enacted. Ego-justifying and group-justifying motives lead individuals to defend their own pre-existing beliefs and those of their in-group, respectively. However, a distinct class of system-justifying motives contributes to asymmetric forms of polarization. Whereas conservative-rightist ideology is associated with valuing tradition, social order and maintenance of the status quo, liberal-leftist ideology is associated with a push for egalitarian social change. These cognitive-motivational mechanisms interact with social influence processes linked to communication source, message and channel factors, all of which might contribute to increased or decreased polarization. We conclude with a discussion of unanswered questions and ways in which our framework can be extended to the study of culture and institutions.

Cultural Anchors and the Organization of Differences: A Multi-method Analysis of LGBT Marches on Washington.

Social scientists describe culture as either coherent or incoherent and political dissent as either unifying or divisive. This article moves beyond such dichotomies. Content, historical, and network analyses of public debates on how to organize four lesbian, gay, bisexual, and transgender (LGBT) Washington marches provide evidence for an integrative position. Rather than just describe consistencies or contradictions, we contend that the key analytic challenge is to explain the organization of differences. We propose one way of doing this using the mechanism of a cultural anchor. Within and across marches, a small collection of ideas remains fixed in the national conversation, yet in a way that allows activists to address their internal diversity and respond to unfolding historical events. These results suggest that activists do not simply organize around their similarities but, through cultural anchors, they use their commonalities to build a thinly coherent foundation that can also support their differences. Situated at the nexus of culture, social movements, sexualities, and networks, this article demonstrates how the anchoring mechanism works in the context of LGBT political organizing.

People use both heterogeneity and minority representation to evaluate diversity.

The term "diversity," although widely used, can mean different things. Diversity can refer to heterogeneity, i.e., the distribution of people across groups, or to the representation of specific minority groups. We use a conjoint experiment with a race-balanced, national sample to uncover which properties, heterogeneity or minority representation, Americans use to evaluate the extent of racial diversity a neighborhood and whether this assessment varies by participants' race. We show that perceived diversity is strongly associated with heterogeneity. This association is stronger for Whites than for Blacks, Latinos, or Asians. In addition, Blacks, Latinos, and Asians view neighborhoods where their own group is largest as more diverse. Whites vary in their tendency to associate diversity with representation, and Whites who report conservative stances on diversity-related policy issues view predominately White neighborhoods as more diverse than predominately Black neighborhoods. People can agree that diversity is desirable while disagreeing on what makes a community diverse.

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.

Gendered Discrimination Against Immigrants: Experimental Evidence.

Recent migration from Muslim-majority countries has sparked discussions across Europe about the supposed threat posed by new immigrants. Young men make up the largest share of newly arrived immigrants and this demographic is often perceived to be particularly threatening. In this article, we compare pro-sociality and trust toward immigrants from Muslim-majority countries, focusing on gender differences in treatment. We study these questions using behavioral games that measure strategic (trusting) and non-strategic (pro-social) behavior. Our data comes from measures embedded in a large survey of residents of Germany's eastern regions, where anti-immigrant sentiments are high. We find that Germans are similarly pro-social toward immigrant men and women in non-strategic situations, but are significantly less likely to trust immigrant men (but not women) in strategic encounters. These findings provide evidence that immigrants' gender can be an important factor conditioning the behavior of the majority population, but also caution that (gendered) ethnic discrimination may be situationally dependent. Future research should further examine the exact mechanisms underlying this variation in discriminatory behavior.

Ethnic diversity, poverty and social trust in Germany: Evidence from a behavioral measure of trust.

Several scholars have concluded that ethnic diversity has negative consequences for social trust. However, recent research has called into question whether ethnic diversity per se has detrimental effects, or whether lower levels of trust in diverse communities simply reflect a higher concentration of less trusting groups, such as poor people, minorities, or immigrants. Drawing upon a nationally representative sample of the German population (GSOEP), we make two contributions to this debate. First, we examine how ethnic diversity at the neighborhood level-specifically the proportion of immigrants in the neighborhood-is linked to social trust focusing on the compositional effect of poverty. Second, in contrast to the majority of current research on ethnic diversity, we use a behavioral measure of trust in combination with fine-grained (zip-code level) contextual measures of ethnic composition and poverty. Furthermore, we are also able to compare the behavioral measure to a standard attitudinal trust question. We find that household poverty partially accounts for lower levels of trust, and that after controlling for income, German and non-German respondents are equally trusting. However, being surrounded by neighbors with immigrant background is also associated with lower levels of social trust.

Cooperative Networks: Altruism, Group Solidarity, Reciprocity, and Sanctioning in Ugandan Producer Organizations.

Repeated interaction and social networks are commonly considered viable solutions to collective action problems. This article identifies and systematically measures four general mechanisms--that is, generalized altruism, group solidarity, reciprocity, and the threat of sanctioning--and tests which of them brings about cooperation in the context of Ugandan producer organizations. Using an innovative methodological framework that combines "lab-in-the-field" experiments with survey interviews and complete social networks data, the article goes beyond the assessment of a relationship between social networks and collective outcomes to study the mechanisms that favor cooperative behavior. The article first establishes a positive relationship between position in the network structure and propensity to cooperate in the producer organization and then uses farmers' behavior in dictator and public goods games to test different mechanisms that may account for such a relationship. Results show that cooperation is induced by patterns of reciprocity that emerge through repeated interaction rather than other-regarding preferences like altruism or group solidarity.

Love Thy Neighbor? Ethnoracial Diversity and Trust Reexamined.

According to recent research, ethnoracial diversity negatively affects trust and social capital. This article challenges the current conception and measurement of "diversity" and invites scholars to rethink "so-cial capital" in complex societies. It reproduces the analysis of Putnam and shows that the association between diversity and self-reported trust is a compositional artifact attributable to residential sorting: non-whites report lower trust and are overrepresented in heterogeneous communities. The association between diversity and trust is better explained by differences between communities and their residents in terms of race/ethnicity, residential stability, and economic conditions; these classic indicators of inequality, not diversity, strongly and consistently predict self-reported trust. Diversity indexes also obscure the distinction between in-group and out-group contact. For whites, heterogeneity means more out-group neighbors; for nonwhites, heterogeneity means more in-group neighbors. Therefore, separate analyses were conducted by ethnoracial groups. Only for whites does living among out-group members--not in diverse communities per se--negatively predict trust.

Neither ideologues nor agnostics: alternative voters' belief system in an age of partisan politics.

How do Americans organize their political beliefs? This article argues that party polarization and the growing prominence of moral issues in recent decades have catalyzed different responses by different groups of Americans. The article investigates systematic heterogeneity in the organization of political attitudes using relational class analysis, a graph-based method for detecting multiple patterns of opinion in survey data. Three subpopulations, each characterized by a distinctive way of organizing its political beliefs, are identified: ideologues, whose political attitudes strongly align with either liberal or conservative categories; alternatives, who are instead morally conservative but economically liberal, or vice versa; and agnostics, who exhibit weak associations between political beliefs. Individuals' sociodemographic profiles, particularly their income, education, and religiosity, lie at the core of the different ways in which they understand politics. Results show that while ideologues have gone through a process of issue alignment, alternatives have grown increasingly apart from the political agendas of both parties. The conflictual presence of conservative and liberal preferences has often been resolved by alternative voters in favor of the Republican Party.

The effect of group attachment and social position on prosocial behavior. Evidence from lab-in-the-field experiments.

Social life is regulated by norms of fairness that constrain selfish behavior. While a substantial body of scholarship on prosocial behavior has provided evidence of such norms, large inter- and intra-personal variation in prosocial behavior still needs to be explained. The article identifies two social-structural dimensions along which people's generosity varies systematically: group attachment and social position. We conducted lab-in-the-field experiments involving 2,597 members of producer organizations in rural Uganda. Using different variants of the dictator game, we demonstrate that group attachment positively affects prosocial behavior, and that this effect is not simply the by-product of the degree of proximity between individuals. Second, we show that occupying a formal position in an organization or community leads to greater generosity toward in-group members. Taken together, our findings show that prosocial behavior is not an invariant social trait; rather, it varies according to individuals' relative position in the social structure.

The Impact of Elections on Cooperation: Evidence from a Lab-in-the-Field Experiment in Uganda.

Communities often rely on sanctioning to induce public goods contributions. Past studies focus on how external agencies or peer sanctioning induce cooperation. In this article, we focus instead on the role played by centralized authorities, internal to the community. Combining "lab-in-the-field" experiments with observational data on 1,541 Ugandan farmers from 50 communities, we demonstrate the positive effect of internal centralized sanctioning authorities on cooperative behavior. We also show that the size of this effect depends on the political process by which authority is granted: subjects electing leaders contribute more to public goods than subjects who were assigned leaders through a lottery. To test the ecological validity of our findings, we relate farmers' behavior in the experiment to their level of cooperation in their community organization. We show that deference to authority in the controlled setting predicts cooperative behavior in the farmers' natural environment, in which they face a similar social dilemma.

Partisan Joiners: Associational Membership and Political Polarization in the United States (1974-2004)*

OBJECTIVES: Associational life may foster political integration or amplify division, depending on how individuals partition themselves into groups and whether their multiple affiliations embed them into concentric or cross-cutting social circles. Starting from this premise, I relate trends in associational membership to political partisanship, and ask if there is any evidence of increased political polarization in the associative patterns of Americans. METHODS: Using GSS data (1974-2004) on affiliations to 16 types of groups, I plot trends and run multilevel models to examine changes over time in the partisan allegiances of group members and patterns of overlapping memberships. RESULTS: The often-lamented decline in group membership affects primarily the category of single-group members and is limited to a few types of groups. The density of the network of overlapping memberships has remained stable over time and there are no real changes in the patterns of shared memberships between group types, nor do Republicans and Democrats differ in their patterns of preferential affiliation. Although political partisanship does not drive patterns of group affiliation, group members, especially those affiliated with multiple groups, are more radical in their partisan identification than nonmembers, and most types of groups have become politically more heterogeneous over time. CONCLUSION: The puzzling finding that group types are not becoming more partisan, while group members are, leads to the hypothesis (to be tested in future research) that civil society polarization is occurring at the level of actual groups, and not group types.

Partisans without Constraint: Political Polarization and Trends in American Public Opinion.

Public opinion polarization is here conceived as a process of alignment along multiple lines of potential disagreement and measured as growing constraint in individuals' preferences. Using NES data from 1972 to 2004, the authors model trends in issue partisanship-the correlation of issue attitudes with party identification-and issue alignment-the correlation between pairs of issues-and find a substantive increase in issue partisanship, but little evidence of issue alignment. The findings suggest that opinion changes correspond more to a resorting of party labels among voters than to greater constraint on issue attitudes: since parties are more polarized, they are now better at sorting individuals along ideological lines. Levels of constraint vary across population subgroups: strong partisans and wealthier and politically sophisticated voters have grown more coherent in their beliefs. The authors discuss the consequences of partisan realignment and group sorting on the political process and potential deviations from the classic pluralistic account of American politics.