Research Article

The Church, intensive kinship, and global psychological variation

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Science  08 Nov 2019:
Vol. 366, Issue 6466, eaau5141
DOI: 10.1126/science.aau5141

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Cultural evolution

There is substantial variation in psychological attributes across cultures. Schulz et al. examined whether the spread of Catholicism in Europe generated much of this variation (see the Perspective by Gelfand). In particular, they focus on how the Church broke down extended kin-based institutions and encouraged a nuclear family structure. To do this, the authors developed measures of historical Church exposure and kin-based institutions across populations. These measures accounted for individual differences in 20 psychological outcomes collected in prior studies.

Science, this issue p. eaau5141; see also p. 686

Structured Abstract

INTRODUCTION

A growing body of research suggests that populations around the globe vary substantially along several important psychological dimensions and that populations characterized as Western, Educated, Industrialized, Rich, and Democratic (WEIRD) are particularly unusual. People from these societies tend to be more individualistic, independent, and impersonally prosocial (e.g., trusting of strangers) while revealing less conformity and in-group loyalty. Although these patterns are now well documented, few efforts have sought to explain them. Here, we propose that the Western Church (i.e., the branch of Christianity that evolved into the Roman Catholic Church) transformed European kinship structures during the Middle Ages and that this transformation was a key factor behind a shift towards a WEIRDer psychology.

RATIONALE

Our approach integrates three insights. First, anthropological evidence suggests that diverse kin-based institutions—our species’s most fundamental institutions—have been the primary structure for organizing social life in most societies around the world and back into history. With the origins of agriculture, cultural evolution increasingly favored intensive kinship norms related to cousin marriage, clans, and co-residence that fostered social tightness, interdependence, and in-group cooperation. Second, psychological research reveals that people’s motivations, emotions, and perceptions are shaped by the social norms they encounter while growing up. Within intensive kin-based institutions, people’s psychological processes adapt to the collectivistic demands of their dense social networks. Intensive kinship norms reward greater conformity, obedience, and in-group loyalty while discouraging individualism, independence, and impersonal motivations for fairness and cooperation. Third, historical research suggests that the Western Church systematically undermined Europe’s intensive kin-based institutions during the Middle Ages (for example, by banning cousin marriage). The Church’s family policies meant that by 1500 CE, and likely centuries earlier in some regions, Europe lacked strong kin-based institutions and was instead dominated by relatively independent and isolated nuclear or stem families.

Our theory predicts that populations with (i) a longer historical exposure to the medieval Western Church or less intensive kin-based institutions will be more individualistic, less conforming, and more impersonally prosocial today; and (ii) longer historical exposure to the Western Church will be associated with less-intensive kin-based institutions.

RESULTS

We test these predictions at three levels. Globally, we show that countries with longer historical exposure to the medieval Western Church or less intensive kinship (e.g., lower rates of cousin marriage) are more individualistic and independent, less conforming and obedient, and more inclined toward trust and cooperation with strangers (see figure). Focusing on Europe, where we compare regions within countries, we show that longer exposure to the Western Church is associated with less intensive kinship, greater individualism, less conformity, and more fairness and trust toward strangers. Finally, comparing only the adult children of immigrants in European countries, we show that those whose parents come from countries or ethnic groups that historically experienced more centuries under the Western Church or had less intensive kinship tend to be more individualistic, less conforming, and more inclined toward fairness and trust with strangers.

CONCLUSION

This research suggests that contemporary psychological patterns, ranging from individualism and trust to conformity and analytical thinking, have been influenced by deep cultural evolutionary processes, including the Church’s peculiar incest taboos, family policies, and enduring kin-based institutions.

Cross-country relationship between exposure to the medieval churches, kin-based institutions, and psychology.

As predicted by our theory, countries with a longer exposure to the medieval Western Church have lower rates of cousin marriage (A); countries with lower rates of cousin marriage have a more individualistic and impersonally prosocial psychology (B); and countries with a longer exposure to the medieval Western Church have a more individualistic and impersonally prosocial psychology (C). Blue dots, green diamonds, and gray triangles denote countries primarily exposed to the Western Church, to the Eastern Church, and with no church exposure, respectively. ρ^ denotes Spearman correlation.

Abstract

Recent research not only confirms the existence of substantial psychological variation around the globe but also highlights the peculiarity of many Western populations. We propose that part of this variation can be traced back to the action and diffusion of the Western Church, the branch of Christianity that evolved into the Roman Catholic Church. Specifically, we propose that the Western Church’s transformation of European kinship, by promoting small, nuclear households, weak family ties, and residential mobility, fostered greater individualism, less conformity, and more impersonal prosociality. By combining data on 24 psychological outcomes with historical measures of both Church exposure and kinship, we find support for these ideas in a comprehensive array of analyses across countries, among European regions, and among individuals from different cultural backgrounds.

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