REVIEW

Diversity and prosocial behaviorDelia Baldassarri* and Maria Abascal

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-groupsolidarity that glues homogeneous communities together. Social cohesion in multiethnic societies depends onwhether prosocial behavior extends beyond close-knit networks and in-group boundaries. We identify twofeatures of modern societies—social differentiation and economic interdependence—that can set the stage forconstructive interactions with dissimilar others. Whether societal adaptations to diversity lead towardintegration or division depends on the positions occupied by minorities and immigrants in the social structureand economic system, along with the institutional arrangements that determine their political inclusion.

Most Western countries already are orare destined to become multiethnicsocieties thanks to recent patterns ofmigration and globalization. Growingimmigration to North America and

Western Europe (Fig. 1A) has commanded par-ticular attention. Increased ethnic heterogeneityhas renewed scholarly interest in intergroupdynamics of cooperation and discriminationand spurred debates over the consequences ofethnic diversity for social trust and de-mocratic integration. Many scholarshave concluded that ethnic diversitynegatively affects overall levels of trust,social capital, and public goods provi-sion. Instead, we see these changes asan opportunity to ask amore importantquestion: How does prosocial behaviorextend beyond the boundaries of the in-group and to unknown and dissimilar others?Answering this question is the key to achievingsolidarity and cooperation in the heterogeneouscommunities we increasingly inhabit today.

Cooperation in heterogeneous versushomogeneous societies

To function, large collectivities need to fostersolidarity and cooperation among their mem-bers. Most theories of political order—fromEnlightenment theories of the social contract(Hobbes and Rousseau) and Tocqueville’sDemocracy in America to recent work on civilsociety and social capital—acknowledge theneed for a sense of collective identity thatallows trust and solidarity to extend beyondthe boundaries of the family or clan to thelarger community or nation. How does thiscome about? According to popular models ofhuman behavior, repeated interactions withingroups and close-knit networks facilitate theemergence of a shared culture, norms of rec-iprocity and cooperation, and peer sanctioning,inducing positive outcomes for the collectiv-ity (1). Homogeneous communities readily nur-

ture trust and solidarity through these avenues.In heterogeneous communities, by contrast,social ties between noncoethnics are sparser,which limits coordination and social control. Inaddition, socialnormsmightnotbe sharedacrossethnic boundaries, or there might be uncertaintyamong members regarding the extent to whichthey are shared (2). Seen in this light, it makessense to think of diversity as a challenge to thefoundations of our collective social contract.

Nevertheless,most heterogeneous communi-ties still manage to get along. As homogeneouscommunities become less prevalent and morepeople experience life in diverse contexts, weneed tomove beyond traditional understandingsof prosociality. In order to achieve solidarity andcooperation, diverse communities may not relyon the samemechanisms as homogeneous ones.More than a century ago, in fact, Durkheim ar-gued that solidarity in complex, differentiatedsocieties relies primarily on interdependenceand the division of labor rather than on culturalsimilarity and mutual acquaintanceship (3).Following this lead, we identify two featuresof modern societies that have the potential tofoster generalized prosociality.The first feature is social differentiation,

which refers to the growing number of iden-tities and group affiliations that people havein their lives. As first theorized by Simmel, inmodern societies individuals become less de-termined by a few ascribed categories—such asrace, class, or gender—and experience a greaterability to choose their group affiliations. Aspeople emancipate from family and commu-nity ties, out of choice or necessity, the numberof unknown, distant others they will interactwith increases, and this has been shown to

foster generalized prosociality (4, 5). A second,related feature is economic interdependence:Market-integrated societies inwhich strangersregularly engage in mutually beneficial tran-sactions exhibit greater levels of generalizedsolidarity and trust (6, 7).We should not take for granted that so-

cieties will inevitably adapt to increasing di-versity in ways that further social integration.Critically important for social integration isthe extent to which ethnic differences maponto class, religious, gender, or other differ-ences. Differentiation brings about socialintegration when lines of social division arecross-cutting—that is, when ethnic groupmem-bership does not wholly predict member-ship in specific class, religious, gender, or othergroups. By contrast, when social cleavages areconsolidated, differentiation poses a threatto social integration (8) and democratic sta-bility (9). Ethnic diversity may thereby fostersocial division.Indeed, existing studies on the effects of

ethnic diversity tend to highlight its negativeconsequences for social capital, economic growth,and public goods provision. We start by re-viewing this literature, which has dominated

the debate regarding the consequencesof ethnic diversity in Western socie-ties. However, to fully understand theconditions under which heterogeneoussocieties can achieve social cohesionacross lines of ethnic differentia-tion, we also need to take stock ofthe status of immigrants and nativeminorities. Then, we discuss how dif-

ferentiation and economic interdependence—two core features that emerge in modernsocieties—set the stage for a new kind of pro-sociality that extends beyond the confines ofthe in-group by enhancing the opportunitiesfor intergroup contact, encouraging superordi-nate identification, and inhibiting in-group–out-group thinking. Overall, we argue that thetype of prosociality that helps heterogeneoussocieties function likely derives from positiveexperiences in the context of strategic inter-actions, such as those in the workplace, and isdifferent from the in-group solidarity that glueshomogeneous communities together.

The “problem” of diversity

Political economy scholars have looked to ethnicdiversity in their attempts to explain societalproblems in developing countries, includingviolent conflicts and stalled economic growth(10). On the whole, however, studies paint anuanced picture, one in which poverty andpolitical instability, rather than ethnic or re-ligious divisions, increase the risk of civil war(11) and in which ethnic fractionalization isassociated with lower growth only in the ab-sence of robust democratic institutions andpolicies (12, 13).

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Baldassarri et al., Science 369, 1183–1187 (2020) 4 September 2020 1 of 5

Department of Sociology, New York University, New York, NY10012, USA.*Corresponding author. Email: delia.b@nyu.edu

“The key to solidarity and cooperation... is the extension of prosociality beyond

close-knit networks...”

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A second line of work, which focuses mainlyon Western European and North Americancountries, instead probes within-country dif-ferences across homogeneous and heteroge-neous communities. These studies typicallyreport negative associations between ethnicdiversity anddesirable outcomes, including civicengagement (14), public goods provision (15),and self-reported trust (16). On the associationbetween diversity and trust alone, a recentreview covers nearly 90 studies (17). Althougheffect sizes are minimal, this scholarship oftenreaches alarming conclusions about the erosionof civic life at the hands of ethnic diversity.However, in Western countries, homoge-

neous and heterogeneous communities differin systematic ways, which cautions against con-cluding that diversity per se has negative ef-fects. For one, heterogeneous communities aredisproportionally nonwhite, economically dis-advantaged, and residentially unstable. Com-positional effects related to these differenceslargely account for the relationship betweenethnic diversity and collective outcomes. Forexample, nonwhites and immigrants tend to re-port lower trust, and they are overrepresentedin heterogeneous communities. Once analysesaccount for the fact that native whites, who aredisproportionately represented in homogeneouscommunities, also score higher on prosocialindicators, negative associations with ethnicdiversity are strongly reduced and even dis-appear. Similarly, economic hardship takes a tollon prosocial engagement, and diverse commu-nities have much higher rates of concentratedpoverty (18). Overall, economic indicators areby far stronger predictors of collective out-comes than are ethnoracial indicators (3, 19).More generally, the consequences of ethnic

diversity likely depend on the extent to whichethnicity constitutes one of many lines of dif-ferentiation or instead operates as an organiz-ing principle around which resources aredistributed. It matters whether ethnicity inter-sects with other lines of division and, especial-ly, economic inequality. In their investigationof public goods provision, Baldwin and Huberfound that economic inequality betweengroups—rather than ethnolinguistic or cul-tural differences—undermines welfare pro-vision (20). They speculate that this happensbecause richer, more powerful groups prioritizedifferent public goods and exclude others fromaccess. Therefore, resource asymmetries betweenethnic groups, and not the multiplicity of ethnicgroups per se, undermine collective efforts.Ethnic fractionalization has been and re-

mains relatively low in Western Europe andNorth America compared with several coun-tries in Africa and Asia (Fig. 1B). The focus onWestern countries is mostly driven by grow-ing immigration (Fig. 1A). Hence, to date,systematic ethnoracial differences betweenhomogeneous and heterogeneous commu-

nities are an artifact of studying diversity incontexts such as North America and Europe,where heterogeneity is relatively low and homo-geneous communities are, by and large, homo-geneously native majority communities.It follows that although they use measures

of heterogeneity andmake claims about diver-sity, studies in Western countries are unableto attribute observed associations to hetero-geneity, as opposed to immigrant or minorityshare. As a result, studies of ethnic diversityrehash the findings of a long-standing liter-ature on how native majorities react to thegrowing presence of immigrants and minor-ities. This literature links the size and growthof immigrant and minority populations toperceived threat and greater hostility towardthem. For example, survey and laboratory ex-periments found that U.S. whites who are ex-posed to information about the growing shareof nonwhites express greater opposition topolicies and parties seen to benefit nonwhites(21). Observed effects are theorized to stemfrom broad concerns about native majorities’economicwell-being, their cultural dominance,and their symbolic status within an intergrouphierarchy from which they derive social andpsychological benefits (22).Diversity, as both a concept and measure,

treats groups interchangeably; a communitythat is 80% white and 20% Black is as diverseas one that is 80% Black and 20% white andone that is 80% Latino and 20% Asian (18).However, where there is differentiation, thereis hierarchy: Native majorities, native minorities,and immigrants occupy different positions inthe social order. Because intergroup dynamicstend to reproduce status and power asymmetries(23), the dynamics of similarly heterogeneouscommunities likely vary according to the specificgroups represented and their relative sizes.Hierarchy raises another consideration: Inheterogeneous contexts, we need to distinguishbetweenbenefits that accrue to single groups andthose that extend to the whole collectivity (3).Taken together, these observations caution

against making generic claims about the ef-fects of diversity. To ascertain the challengesand possibilities posed by diversity, we firstneed to disentangle its effects from those ofinequality. This entails understanding the so-cial cleavages and asymmetries that governintergroup relationships in diverse societies.

Immigrants and native minorities inWestern countries

To what extent and in what domains haveimmigrants and native minorities achievedeconomic, political, and social membershipin Western countries?In the United States, immigrants (primarily

from Latin America and Asia) and native mi-norities (primarily Black Americans) con-tribute to present-day diversity. Regarding the

experience of immigrants, scholars are splitbetween those who contend that today’s im-migrants are on the same upward trajectoryas earlier Europeans (24) and those who read,from some groups’ experiences, evidence ofstalled or even downward mobility (25). Evi-dence of integration comes from the advancesmade by members of the second generationover their immigrant parents (26). However,longer-term views into the third generation orlater reveal remarkable marital homogamy aswell as network and residential segregation forsome groups, such as Mexican Americans (27).The experience of Black Americans, the

largest native minority group in the UnitedStates, challenges the expectation that fulleconomic, political, and social membershipnecessarily await later-generation Americans.Black households have less wealth and lowerincomes than do Asian or Latino households.And despite recent gains, Blacks are still lesslikely to marry whites and more likely to beresidentially segregated from whites thanare Asians or Latinos. Persistent, intergen-erational disadvantage among Blacks is aconsequence of past institutional practices,including Jim Crow segregation and red-lining (28), present institutional practicessuch as mass incarceration, and contempo-rary discrimination in the labor market andother domains (29).In Europe, immigrants from Turkey, Africa,

and other regions, including former colonies,contribute to diversity. Their prospects for in-tegration are sobering (30). Evidence of upwardeconomic mobility is tempered by gaps inemployment and earnings that may persistinto later generations (31). A growing body offield experimental research uncovers discrim-ination against immigrants, especiallyMuslimimmigrants and/or those of Arab origin, informalmarkets such as those for employmentand housing (32) and informal, everyday in-teractions (33, 34). Hostility toward certainimmigrant groups is sometimes motivated bytheir observance and transmission of religiouspractices and cultural norms that are seento conflict with liberal principles of genderequality and individual freedom (33, 35). Thesefindings fuel the view that European societiesare converging on a “discriminatory equilib-rium” in which discrimination toward somegroups drives underinvestments in humancapital (30) and furthers the reproduction ofvalues and practices that stall integration ineconomic and other domains.The picture is not all negative, however. First,

it is worth acknowledging that persistent,later-generation gaps in educational attain-ment, employment, and earnings coexist withsubstantial upward mobility, especially betweenthe first and second generations (24). Second,legal status can go a long way toward securingeconomicmobility, as evidenced by the diverging

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earnings trajectories of undocumented im-migrants and legal permanent residents in theUnited States as well as the rise in earningsinduced by amnesty laws (26). When it comes topolitical incorporation, government efforts topromote citizenship, whether aimed directlyat immigrants or at the community organiza-tions that serve them, boost naturalization andparticipation through material and symbolicchannels—that is, by signaling immigrants’suitability for inclusion (36).When such resources are not available or

when discrimination is prevalent, attachmentto a protective “ethnic core” may provide im-migrants andminorities one path to economic,political, and cultural mobility (27, 37). How-ever, insofar as enclaves reproduce segregationand contribute to discrimination by nativemajorities toward immigrants and minorities,they are a suboptimal and short-term reprieveto the challenges posed by diversity. A morerobust solution for the successful integrationof immigrants and minorities in multiethnicsocieties builds on the features of modernsocieties that facilitate cooperative encountersand shared interests across group boundaries.

Toward a theory of prosociality inmultiethnic societies

The key to solidarity and cooperation in het-erogeneous communities is the extension ofprosociality beyond close-knit networks andin-group boundaries to unknown, dissimilarothers. The large-scale interdependence of lifein modern societies requires that individualsfollow universal norms of reciprocity andcooperation rather than rely on mutual ac-quaintanceship or group identification. The ob-servance of suchnorms is assured by thepresenceof strong coordinating institutions; for example,we rely on public transportation not because weknow the bus driver or identify with them butbecause we trust that they will competently per-form the job that corresponds to their role (3).The type of prosociality that helps hetero-

geneous communities function is differentfrom the in-group solidarity that glues homo-geneous communities together. A large schol-arship has documented the parochial natureof human altruism, convincingly showing thatin-group preferences are a staple of humanbehavior (38). From an evolutionary perspec-tive, parochial altruism emerged from thecoevolution of intergroup favoritism and out-group hostility during periods of violent in-tergroup conflict (39). Although in-groupfavoritism may have served us well in small-scale societies, it cannot get us far in complex,large-scale societies characterized by hetero-geneity. For diverse societies to function, theymust to some extent suppress members’ reli-ance on in-group identification as the primarybasis for prosocial behavior (40). Prosocial be-havior in complex societies likely derives from

positive experiences in the context of strategicinteractions, such as those in the workplace,rather than empathic identification (41). Peoplein modern societies are often pushed outsidethe comfort zones of their familiar networksto constructively interact with unknown anddissimilar others. We have learned, from arich literature on intergroup contact, that suchinteractions have the potential to reduceprejudice, especially under favorable condi-tions, including equal status, common goals,and lack of competition (42). Here, we discusshow social differentiation, a macrostructuralfeature of modern societies, may favor theemergence of generalized prosociality and thespecial role that market integration and eco-

nomic interdependence can play in facilitatingproductive intergroup interactions.Differentiation may be the key, not an ob-

stacle, to social cohesion in modern societiesbecause an increase in the dimensions of dif-ferentiation might bring about greater socialintegration. A greater number of identitiesand affiliations brings about distinct combina-tions that can foster even greater cooperation(8). This, however, occurs onlywhen the linesof differentiation are cross-cutting, whereasdivision follows from consolidated lines ofdifferentiation (Fig. 2). Ethnic heterogeneitycan push societies toward either pole. On theone hand, when ethnic differences overlapwithstatusandresourcedifferences, in-group favoritism

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Ethnoracial fractionalization (2013)

0.76 – 0.890.65 – 0.760.53 – 0.650.38 – 0.530.26 – 0.380.17 – 0.260.02 – 0.17No Data

Ratio of migrant stock(2015/1990)

1.91 – 25.901.47 – 1.911.14 – 1.470.90 – 1.140.74 – 0.900.50 – 0.740.03 – 0.50No Data

A

B

Fig. 1. Ratio of migrant stock and ethnoracial fractionalization by countries. (A) Ratio of international migrantstock (1990/2015). Europe and North America saw relatively large increases in national stocks of internationalmigrants in the past two decades. International migrant stock refers to the percentage of foreign-born residentsin a given year. Orange indicates higher ratios of migrant stock; teal indicates lower ratios of migrant stock.[Data source: United Nations Population Division] (B) Ethnoracial fractionalization (2013). Fractionalization is higherin sub-Saharan Africa and parts of Asia than in Europe or North America. Fractionalization corresponds to theprobability that two randomly chosen residents belong to the same ethnoracial group. Darker colors represent higherethnoracial fractionalization. [Data source: Historical Index of Ethnoracial Fractionalization]

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can operatemore efficiently. But far from bind-ing people together (as it does in homogeneoussocieties), in-group favoritism would deepeninequality and division in heterogeneous ones.On the other hand, when heterogeneity alongethnic lines cross-cuts differences in terms ofclass, politics, and other dimensions, it bothneutralizes in-group favoritism and deepensinterdependence, fostering cohesion.

Social differentiation

Social differentiation refers to the multiplicityof identities and roles that individuals mayacquire and inhabit in their day-to-day livesand often leads to greater individualization.Namely, people’s ability to choose, with relativefreedom, their identities and group affiliationsincreases, and their profiles becomedistinctive.When lines of differentiation are cross-cutting,the process of differentiation and individu-alization sets the stage for broad-based cohe-sion through at least three pathways.The first is by facilitating interpersonal con-

tact beyond close-knit, kinship ties and withothers who are dissimilar in terms of someidentities, including, most notably, ethnicity.Research supports the claim that generalizedtrust and other benefits flow from interactionsoutside dense networks, such as those basedon kinship. Cross-societal comparisons havedocumented greater generalized trust and co-operation in an individualistic society such asthe United States than in Japan, where moni-toring and sanctioning happenprimarilywithinthe confines of close, long-term relationships(4). According to Yamagishi’s emancipatorytheory of trust, strong ties, which are typicalof collectivist societies such as Japan, producea sense of security within the group butprevent trust from developing beyond groupboundaries. Similarly, people with strong fam-ily and group ties display lower levels of trust

toward generalized others in incentivized ex-periments. By contrast, people who are lessembedded in family networks and those whohave experienced uprooting events, such asdivorce, are more likely to trust strangers,possibly because they have more opportuni-ties and incentives to engage in relationshipswith unknown others (5). More broadly, semi-nal work on social networks has exposed thelimits of strong ties and close-knit social rela-tionships (43, 44). This work shines a positivelight on weak ties and network positions ofbrokerage for their ability to connect parts of asocial network that would be otherwise dis-connected, facilitating access to a broader rangeof information and opportunities. To quoteGranovetter, “Weak ties, often denounced asgenerative of alienation...are here seen asindispensable to individuals’ opportunitiesand to their integration into communities;strong ties, breeding local cohesion, lead tooverall fragmentation” [(43), p. 1378].The second pathway through which social

differentiation may foster cohesion is throughidentification, with or without direct interper-sonal contact. In laboratory studies, proceduresthat encourage identification with a common(or “superordinate”) identity have been shownto reduce prejudice across group boundaries(45). This is possible when cross-cutting affi-liations enable identification with a categorythat spans ethnic boundaries. An outstandingquestion is whether identificationwith a super-ordinate category can somehow achieve deepertrust and cooperation than can lower-level eth-nic identification, perhaps by “training” indi-viduals to bemore flexible about categorizationin general. If not, superordinate identificationmay be an imperfect solution that trades favor-itism toward one group for favoritism towardanother, larger group. These aspects are ripe forfurther testing in field settings (46).

A third pathway consists in subvertinghumans’ deep-seated capacity to think (andact) in terms of in-group–out-group catego-ries. Category-based inconsistencies—for ex-ample, the Harvard-educated, first-generationLatina—inhibit the cognitive processes thatcompel us to frame encounters in “us versusthem” terms, opening the door to more elab-orate cognitive processes in which an alter ismore likely to be perceived as “an individualrather than an (oppositional) group member”[(40), p. 854]. The distinction between thispathway and one that hinges on a commonidentity is subtle: Category-based inconsisten-cies can subvert “us versus them” thinkingeven if we do not share identities or exper-iences with a target—that is, even if we areneither Ivy League–educated, nor Latino, northe first in our family to attend college.Critically, the most effective way to secure

multiethnic cohesion through this channelis not to promote a few minorities but ratherto weaken the covariance between ethnic cat-egory membership and life chances writ large—that is, to cultivate a system in which a first-class education is equally accessible to whitesand nonwhites, regardless of their familybackground. There is growing evidence thatcross-cutting affiliations can mitigate biasagainst immigrants and minorities. Experi-mental evidence shows that U.S. Americansreport greater willingness to admit immigrantswho are highly educated or have high-statusjobs (47). Relatedly, high socioeconomic sta-tus mitigates mistrust toward Blacks in acooperative investment game (48), and signalsof cultural integration mitigate bias towardMuslims in Germany (33).Taken together, the hypothesized pathways

are consistent with a model of social cohesionin which cross-cutting differentiation, ratherthan social closure, is the unifying force.Whensocial cleavages are not cross-cutting but in-stead consolidated—for example, whenminori-ties and immigrants are systematically deprivedof educational and employment opportunitiesand thereby relegated to the lower tiers of thesocial hierarchy—disadvantaged groupswill con-tinue to be cast in a separate and marginalizedsocial category and discriminated against.

Economic interdependence

Economic exchanges are the quintessentialsetting for meaningful, cooperative interac-tions between dissimilar others. This is partlybecause of the specific nature of economictransactions: They occur between parties whohave different goods (or skills) to exchangeand thereby bring together people who maynot belong to the same social circles. Alongthese lines, workplace relationships tend tobe less homophilious than relationships inother settings. Moreover, intergroup encount-ers in economic settings seem to be particularly

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Ethnicity

Class

Sexuality

Social network

A B C

Fig. 2. Social differentiation leads to greater integration when dimensions of differentiation are cross-cutting. (A to C) The top layers represent various group identities that individuals might have in modern societies(such as ethnicity, class, or sexuality), and the bottom layer describes the social network that emerges from sharedmembership in these groups. In (A), the two dimensions of differentiation are consolidated and thus bring aboutsocial fragmentation. In (B) and (C), the dimensions are cross-cutting, thus favoring social integration. As the numberof cross-cutting dimensions increases [(comparing (C) with (B)], so does overall network integration.

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conducive to generalized prosociality. In aseries of cross-cultural studies, Henrich andhis colleagues uncovered less prosocial behav-ior in small-scale societies based on kinshipnetworks than in market-integrated socie-ties in which strangers regularly engage inmutually beneficial transactions. In theirwords, “The more frequently people experi-ence market transactions, the more they willalso experience abstract sharing principlesconcerning behaviors toward strangers” [(6),p. 76)]. Market integration not only fostersprosociality toward unknown others; it canalso shift boundaries to include noncoeth-nics. In a nationwide field experiment in Italy,market integration explained variation inprosocial behavior toward both natives andimmigrants (7). Similar effects are imputed toglobalization, understood as greater world-wide connectedness (49).Workplaces, more than homes or neighbor-

hoods, may be crucial for fostering the type ofprosociality that holds modern societies to-gether. Minorities’ and immigrants’ positionsin the productive system and their prospectsfor socialmobility—including employment op-portunities in complementary sectors, anda legal regime that protects their rights asworkers—are therefore important not onlyfor their own material success but for societyas a whole. The economic integration of mi-norities and immigrants also determines theextent to which they come to identify withmainstream society (50).Most economic exchanges—for example,

hiring someone or renting an apartment fromthem—are strategic in nature, in the sensethat a person’s behavior is affected by theirexpectations of the alter. These types of inter-action entail risk and uncertainty becausepeople have to overcome difficulties relatedto coordination, lack of information, and mis-trust. Cooperative and prosocial behavior inthese settings may still be affected by in-groupfavoritism but are also based on consider-ations that go beyond whether an ego likes ordislikes the alter, to encompass the alter’strustworthiness, competence, and reputation(40). This calls for a deeper understandingof intergroup dynamics, and the institutionalarrangements, that favor prosocial outcomesin the context of strategic interactions. Somefield experimental work has made progress inthis direction; for example, in a study of pub-lic goods provision in diverse Ugandan neigh-borhoods, Habyarimana and colleagues usedbehavioral games to disentangle the variousmotives and mechanisms that bring aboutcollective action in multiethnic contexts (2).Although they did not find evidence of ethnicfavoritism, they found that the reciprocitynorms and sanctioning opportunities that fa-cilitate cooperation in risky interactions arestronger among coethnics than noncoethnics.

Market integration enhances opportuni-ties for productive interactions across groupboundaries. Additionally, the strategic natureof economic exchanges elicits decision-makingprocesses that go beyond in-group favoritism,therefore providing new venues for institu-tional intervention.

Conclusion

We can approach ethnic diversity through thelens of lost homogeneity. From this perspec-tive, we understand thatmembers of thewhitemajority tend to react negatively to the growthof immigrants and minorities in their com-munities. However, it would be premature toconclude that diversity or diversification perse are to blame for declining levels of trust andcooperation. In the Western European andNorth American context, diversity is synon-ymous with immigrant and minority shareand economic disadvantage, and statisticalattempts at disentangling their effects willnot get us very far.Beyond questioning the effects of ethnic di-

versity, scholars should develop a theory ofsocial cohesion in multiethnic societies thatconsiders intergroup dynamics, social cleav-ages, and asymmetries in resources and power.Crucial to this effort is understanding the con-ditions under which prosocial behavior extendsbeyond close-knit networks and the safe con-fines of the in-group. Here, we have high-lighted two features ofmodern societies, socialdifferentiation and economic interdependence,that set the stage for generalized prosocialityto develop. We argue that, in contrast with thein-group solidarity that glues homogeneouscommunities together, prosociality in heter-ogeneous societies likely derives from posi-tive experiences in the context of strategicinteractions. Further research is needed onthe mechanisms and institutional arrange-ments that foster this higher-level form ofcooperation.The experience of immigrants and minori-

ties is instructive regarding the conditions andinstitutions that facilitate integration and mo-bility in Western societies. Of primary im-portance are employment opportunities inmainstream labor markets, especially underconditions of economic expansion, along withlegal and political inclusion. Regrettably, itis precisely these conditions that are in shortsupply in a historical moment characterizedby the rise of right-wing movements, an eco-nomic recession induced by a global pandemic,and long-standing institutional practices,such as those of law enforcement, that deepenthe divides between ethnoracial groups.Wheth-er societal adaptation to diversitymoves towardintegration or social division depends asmuchonmicrointeractions on the ground as on theeconomic and political institutions that gov-ern these processes.

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ACKNOWLEDGMENTS

The authors thank B. Park for work on the figures and the referees forhelpful comments. Funding: D.B. acknowledges support from theEuropean Research Council (639284) and M.A. from the NationalScience Foundation (1845177). Author contributions: D.B. and M.A.wrote the Review. Competing interests: The authors have nocompeting interests. Data and materials availability: Data for Fig. 1Acame from the United Nations Population Division and are available athttps://migrationdataportal.org/?i=stock_abs_&t=2015. Data for Fig.1B were collected by L. Drazanova and posted (51).

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