Catholic Marriage Rules May Explain Why Western Societies are So WEIRD

Catholic Marriage Rules May Explain Why Western Societies are So WEIRD April 4, 2019

Catholic Marriage

People in North America and Western Europe are WEIRD. That is, they’re Western, Educated, Industrialized, Rich, and Democratic – and as such, very different, psychologically speaking, than the rest of the world. People from WEIRD societies are more individualistic, think more analytically, are less conformist, and are more “impersonally prosocial,” trusting and cooperating easily with strangers rather than relying only on close-knit families, tribe members, or friends. Recently, a group of researchers released a paper preprint investigating the historical origins of WEIRD psychology. Their conclusion? The origins of psychological WEIRDness may be found in – wait for it – Catholic rules about marriage.

In order to understand why historical Catholic marriage practices have anything to do with 21st-century patterns in cultural psychology, two things are in order: a little history and a little anthropology.

Some Useful Background

First, the anthropology. Religions aren’t just belief systems, or mechanisms for coping with existential dread, or tools for oppressing the proletariate. They might be all these things at different times, but they’re also cultural systems that impose norms for marriage, family, and kinship. 

Family and kinship differ greatly from society to society. In some cultures, it’s okay to marry your first cousin, or for men to have two wives. In others, you can’t marry close relatives, or monogamy might be the rule. In fact, kinship patterns vary so widely across societies, and are so important for understanding other aspects of culture, that a major chunk of anthropologists’ work consists of simply cataloguing the kinship systems of the cultures they study. 

Importantly, religious taboos and norms always have an influence on these systems. In small-scale societies, the beliefs and rituals that we’d call “religious” are fully integrated into the social structure of the group, helping to reinforce and stabilize the ways family and group members are supposed to related to each other. But larger-scale religions have a lot to say about family, too. Part of what it means to be a Muslim is to accept that a man can only have four wives at maximum (and, according to many Muslims, ideally only one). Christianity has always been strict on marital monogamy. And so on.

Now, the history. Roughly speaking, there are traditionally two “halves” to Christianity: the Western and Eastern churches. This division more or less stems from the Emperor Diocletian’s 3rd-century partition of the Roman Empire into Western and Eastern halves. The Western Church evolved into what we know today as the Roman Catholic Church (and its Protestant offspring), while the Eastern Church became Eastern Orthodoxy.* 

Although they shared a basic theology, these two versions of Christianity differed in important ways. One was that the Western Church was much more internally unified and hierarchically coherent throughout the Middle Ages than the Orthodox churches were, thanks to the Roman papacy. Another is that, while both Eastern and Western versions of Christianity were strongly opposed to cousin marriage (as compared to most other religions), the Western church was much stricter and more serious about this than the Eastern church was. And because of its centralized organization and integration with secular medieval governments, the Western church was in a position to enforce its preferences that people not marry relatives.

So that’s the background. Cultures differ in their kinship norms. Religions have a lot to do with forming and enforcing kinship norms. And while both Eastern and Western Christianity strongly disapproved of cousin marriage, the Western church was a lot more adamant about it, and in a better position to enforce its values. What’s this got to do with WEIRD psychology?

Cousin Marriage and WEIRDness

When people marry their close relatives, they create thick, tightly woven kinship networks. We sometimes call them clans. In part, this is because cousin marriage increases the amount by which members of a family are related, which may in turn increase the extent to which cooperation and mutual aid are restricted to within the clan. But cousin marriage can also work to concentrate property by consolidating inheritances within a single lineage, which only further magnifies in-group collectivism. 

By contrast, exogamy – the practice of marrying partners from outside the family or clan – loosens up the social fabric, which in turn can weaken people’s obligations to extended family and facilitate more contact between different in-groups or regions, increasing impersonal trust across longer distances.

In turn, cultural psychology has shown that tightly networked, clannish in-groups are strongly associated with collectivism, obedience, holistic cognitive styles, and other cognitive and behavioral traits. Looser kinship and social networks are usually associated with the opposite traits: individualism, originality, and analytical thinking. In other words, WEIRD psychology is a good fit for diffuse, non-clannish social environments.

Given these patterns, the authors of the preprint, “The Origins of WEIRD Psychology” – Jonathan Schulz, Duman Bahrami-Rad, Jonathan Beauchamp, and Joseph Henrich,** – posited that cousin marriage might play an important role in understanding psychological differences across societies. That is, low levels of cousin marriage, thanks to the influence of the Western church, might explain why Europeans and North Americans are so WEIRD.

The Study. Jeez.

I’m not even going to try to talk about everything that this paper contains. For one thing, the PDF is over 170 pages long, most of which is detailed, richly documented supplementary materials and analyses. For another, those 170 pages are so dense with statistical analyses and hefty doses of historical background that it would be pointless to try to do it justice in a single blog post. So let me just give the overview. 

The authors tested two basic hypotheses. First, kinship intensity would be inversely correlated with WEIRD psychological and behavioral traits (individualism, analytical thinking, disinterested economic cooperation, etc.) across different societies. Second, historical exposure to Christianity – with its frowning disapproval of cousin marriage – would positively predict those same traits, and would also predict less cousin marriage. Moreover, exposure to Western Christianity would have a stronger impact on these outcomes than exposure to Eastern Christianity.

Schulz and his colleagues used data from the well-known Ethnographic Atlas – a database of coded information about more than 1,100 societies across the world – to generate a “Kinship Intensity Index” (which I’ll just call consanguinity for simplicity’s sake). The items they used for their consanguinity measure included prevalence of polygamy (because polygamous societies tend to have higher in-group relatedness than monogamous ones) and reported preference for cousin marriage, as well as other related variables. Importantly, the data for this measure were mostly collected around a century ago, during the first heyday of ethnographic research. Thus, these data reflect historical, not necessarily current, family patterns.

The authors also secured actual information about 20th-century cousin marriages from the Catholic Church’s records in Spain, France, and Italy, as well as cousin marriage data from another source in Turkey. (The Catholic Church keeps records on cousin marriage because it historically has required people to ask for “dispensations” – special permission – to marry cousins.) 

For a measure of historical exposure to the Church, they looked at records of the geographic prevalence of bishoprics, or seats of Church administration, throughout the European and Mediterranean world, at fifty-year intervals, between 550 and 1500 CE. In English, this means that they recorded what proportion of the land’s surface lay within a 100-km radius of a bishop’s seat, extended over nearly a thousand years. A portion of land that lay within a bishopric for that entire time would be coded as having 950 years’ worth of exposure to the Church. A portion of land that only got a bishopric in 1350 would be coded as having 150 years’ worth of exposure to the Church.

Next, they gathered data from the World Values Survey and other global databases on just about everything: individualism/collectivism, social trust, creativity, traditionalism, conformity, and “cultural tightness,” which refers to adherence to social norms. They also found data on impartial honesty and generosity in economics games, blood donation levels, and even the number of traffic tickets given to UN diplomats by New York City traffic cops (as a measure of impersonal institution norm-following).

The Results

To a remarkably consistent extent, their results corroborated their predictions across all measures. The extent to which a given country’s inhabitants preferred cousin marriage positively predicted their average conformity and traditionalism, while negatively predicting individualism, creativity, analytical thinking, and disinterested cooperation. Within Christian regions, exposure to Western Christianity predicted WEIRD cognitive styles, individualism, and disinterested cooperation. Western church exposure also predicted less consanguinity and modern cousin marriage. Exposure to the Eastern church also had many of these effects, but usually more weakly, and the effects for the Eastern church weren’t as robust to statistical controls.

Church exposure even (strongly) predicted fewer unpaid New York City traffic tickets given to UN diplomats prior to 2002. Just let that sink in: these authors found that the number of half-centuries that the historical population of a country had been exposed to the Catholic Church’s bureaucracy and norms, five hundred years ago, was a strong predictor of whether the diplomats from those countries would mostly obey (impersonal, institutionalized) traffic laws in New York City in the 20th century, despite the fact that until 2002 diplomatic immunity meant that they never needed to pay their tickets. 

The authors included many statistical controls to ensure that their results weren’t due to confounding factors such as climate, agricultural fertility, irrigation, or parasite stress, all of which have been suggested to have a role in shaping cultural psychology. They also zoomed in and conducted their analyses between regions within Europe, and found essentially the same results. In all cases, longer exposure to the Western church meant less consanguinity, which meant more WEIRDness and more disinterested prosocial cooperation.

What Does This Mean?

There’s one issue in the analyses I can’t quite figure out: in their statistical models, the authors never actually tested to see whether historical exposure to the Western church was associated with contemporary WEIRDness via decreased cousin marriage. This was the overall hypothesis they set out to test, so I’m not quite sure why they opted not to include both Church exposure and consanguinity in a single model. After all, their results show pretty conclusively that Church exposure predicts less consanguinity and more WEIRDness, and also that less consanguinity predicts more WEIRDness. I could be missing something here. Like I said, the paper is 170 pages long. But it seems to me that the final “t” isn’t crossed or final “i” dotted.

That aside, the findings still raise a lot of interesting – and sometimes uncomfortable – questions. Let’s just touch on the most obvious issue: this research seems to suggest that Western Europe came to have the (mostly) stable social institutions, individualism, and creativity that people have often associated with it because of Catholicism. The opportunities for jingoism and cultural triumphalism abound. The authors write that the Western church’s disassembly of older, clannish kinship systems

left many regions of Western Europe dominated by independent, monogamous, nuclear families – a peculiar configuration called the European Marriage Pattern.

…and so,

Our work…suggests that contemporary psychological patterns, ranging from individualism and trust to conformity and analytic thinking, have been influenced by enduring family structures, particular religious practices and deep cultural evolutionary practices.

The authors even suggest that the Catholic Church spread across the world to become the largest branch of Christianity precisely because of the way that less-intensive kinship systems altered Europeans’ psychology (although, again, I can’t see where they tested precisely this causal model):

The Church’s [suppression of cousin marriage] thus constitutes part of the success story of the Catholic Church. In addition, a changing psychology (fostering creativity, analytical thinking and entrepreneurial activity) and an increase in the scope of trust (which allowed for division of labor and trade expansion) may have contributed to the rise of the West and with it the expansion of the Catholic Church.

While all these things may be true (or “something like the truth,” in Socrates’ famous phrasing), it’s pretty obvious that they might also cause eyebrows to raise. Haven’t we had enough of European culture crowing about its own virtues? 

The best way to circumvent this problem, I think, is to emphasize that psychological WEIRDness and individualism come with a lot of their own problems. As numerous researchers have pointed out, the societies dominated by WEIRD people are often not especially happy, and loneliness has become an epidemic problem in many developed societies. The individualism that (apparently) emerged out of the less-consanguineous, less clan-based European Middle Ages is not an unadulterated good. Kids growing up in other parts of the world might not enjoy the stable governments and economic dynamism that seems to often go along with WEIRD psychology, but they also often have much stronger bonds with their families, and are often nestled in tight communities with longstanding, meaningful traditions. 

I won’t dwell on this question extensively. I think it’s clear that different cultural patterns offer distinct advantages and disadvantages, and that no one society has the right to claim that its own package is somehow perfect. Not to mention that societies are made of lots of individuals, each of whom are very different from the others – so generalizations about society-level trends are only that, generalizations.

All the same, it’s worthwhile to think about where the norms, values, and expectations that characterize modern WEIRD societies came from. Remember that, within WEIRD societies, liberals and progressives are even more WEIRD – more individualistic, more analytical, less traditionalistic. At the same time, working-class people and farmers (especially rice farmers) are typically less WEIRD, while professionals and the college-educated are more so. So, even within societies, there are distinctive breakdowns by class and ideology when it comes to the predispositions that Schulz and his colleagues are interested in. Kinship structures may influence cognitive styles, but so do economic modes, religious values, and educational mores. 

In turn, once a particular cognitive style or value system takes hold, it might long outlast the original conditions that produced it. For example, in Protestant European societies such as England and the Netherlands, marriage between first cousins is still vanishingly rare, despite the fact that the Reformation mostly ended the formal restrictions on consanguineous marriage. The Catholic habit was already engrained.***

Similarly, in China, residents of historically rice-farming regions today are more collectivistic and cognitively holistic than residents of wheat-farming regions (due to rice farming’s intensive demands for coordination between farmers), even if nobody actually farms either of those crops in a given region anymore. The social patterns and the value systems that were suited to particular ways of life kept running for centuries – being tacitly inherited, passed down, from generation to generation. As William James said, “Habit…is the enormous fly-wheel of society.”

That’s all I’ve got to say for now. Check out the preprint here.


* There’s more to the story than this, of course. The Coptic Churches (like the Egyptian Coptic Church) are technically Eastern, I suppose, but they weren’t in communion with either Orthodox or the Roman churches during the Middle Ages. So they don’t really count for the West-East division we’re discussing here. However, the Coptic Churches and Churches of the East only account for a small percentage of all Christians, so the generalization mostly stands, at least for our purposes.

** Joe Henrich, the senior author, presented on the data in this paper at my colloquium at the Center for Mind and Culture last month. I’d skimmed the preprint before then, but his presentation got me thinking I needed to write a blog post on it. Or several. There’s enough in there to sustain a separate blog on its own for a while. I wish I didn’t have to sleep.†

*** This raises the question: why did this norm – not marrying one’s cousin – stick around after the Reformation, while other Catholic norms and value evaporated? 

† Not that I get that much sleep anyway. Everyone who knows me, especially my remarkably patient wife, encounters my insomniac self about twice a week – a suddenly less talkative, less gregarious, but loopier and less filtered person who sulks about the hours he spent fruitlessly trying to nod off the previous evening, while trying not to resent all the morning people who walk around looking viciously perky and chipper .

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