Why did the West rise above the rest? Over the last two decades, academics and pundits have tried to answer this question. Most begin their search for the birth of the modern world somewhere over the last few centuries: the discovery of the Americas, the invention of the steam engine, perhaps the outbreak of the French Revolution.

Yet the research of two pathbreaking economists suggests that these answers are misplaced. In separate works, they argue that the invention of capitalism and liberalism in Western Europe should be traced to one surprising source: the medieval Catholic Church.

The research program of Jonathan Schultz, an economist currently attached to the Culture, Cognition, and Coevolution research group at Harvard, is built on a simple observation: Western Europeans—and their cultural descendants in places like North America and Australia—think differently from people raised in other cultures. This is not a unique observation. Over the last two decades, psychologists have asked questions like “Do you think most people can be trusted?” and “Is it important to think up ideas and be creative, to do things one’s own way?” They’ve complimented these questionnaires with games cleverly designed to test how willing subjects are to trust strangers, punish rule breakers, break rules themselves, and treat friends and family impartially.

Schultz and his team drew on 20 of these cross-cultural experiments (including several “natural” experiments, such as the likelihood that a diplomat at the U.N. from a given country would call on diplomatic immunity to get out of a parking ticket) to sketch a psychological profile of the Western mind. They found that on average, Westerners are more individualistic, more trusting of strangers and public institutions, more likely to donate anonymously, less concerned with the opinions and judgments of their peers, less likely to cheat or bend rules (especially for the sake of friends and relatives), and far less tolerant of nepotism than those from other parts of the world.

This will come as little surprise to anyone who has lived both in and outside the West. It also won’t shock psychologists, who have even invented an acronym to label this unique psychological type: “W.E.I.R.D.”—Western, Educated, Industrial, Rich, and Developed. But in contrast to past research, which tended to emphasize the gap between Europe and the rest of the globe, Schultz and his team have focused their attention on differences within Europe itself. They have found that WEIRDness is not uniform across Europe. Some European populations are far WEIRDer than others. What explains this variation in WEIRD psychology? Schultz provides a simple answer: the date at which a region first fell under the influence of the Catholic Church. To predict how civic-minded, individualist, and trusting a population is today, you need only check whether a Catholic bishopric had been established there by the 7th century AD.

Family structure is the link that connects Catholicism to social trust. Most of us are not inclined to think deeply about this. If you are an American, the fact that your kids will leave their childhood home when they grow up to establish their own households is utterly banal. The expectation that your son will only be married to one wife at a time, or that your daughter will not consider marrying her cousin, is so obvious that it is rarely articulated. Yet these commonsense assumptions are not human universals. Most traditional cultures expected their sons and daughters to continue living on their parents’ estate after marriage. In imperial China, for example, it was common practice for all of a family’s sons, as well as its wives, children, and concubines, to live together with their father and mother in one giant community until both parents had passed away (daughters were sent to live with the in-laws). Likewise, cultures that accept polygamous marriage are far more common than those that prohibit it. From the Western point of view, even odder is a marriage practice common to many cultures—like most in the modern Middle East—where parents eagerly arrange marriages between their nephews and daughters.

Marriage practices like these are not just cultural trivia. Schultz’s research advances the claim that these differences have decided the fate of entire civilizations. Those who marry within their families, marry more than one wife, and live together in large communities of extended kin learn from an early age that they are embedded in powerful networks of extended relations. Varied terms are used to describe these networks: among the Romans, they were known as gen; among the Scottish, clans; among the Norse, lines; in Arabia, tribes; in China, lineages; in Sicily, cosca. These kin-groups are the central organizing unit of their societies. A clansman in need turns first to kinsmen for succor and relief. A clansman wronged turns first to kinsmen for revenge. To live in a clan is to equate the family honor with personal interest. These societies put the family before the man and the community behind the clan. Healthy civic life is hard to sustain in such a restricted social world. There simply is no sense of shared civic identity that can supersede the claims of private family interests. In this respect, ancient Rome and modern Warizstan have more in common than either does with the modern West.

For this, Westerners have the Catholic Church to thank. In the early days of Europe’s darkest age, the Church waged a tireless war against the clans of Western Europe. The first step was broadening the doctrinal definition of incest to include marriage to almost all kin relations. Starting with the Synod of Agde in 517 AD, more than 15 synods on the subject were held in France, Spain, and Northern Italy over two centuries.

In kingdoms where the Church was strong, kings were eager to incorporate the new Catholic understanding of marriage and incest into their laws. By the end of the seventh century, legislation against incestuous marriages was written into the Merovingian, Visigothic, and Lombard legal codes. No one, however, was as active a promoter of the new understanding as Charlemagne. He decreed that all prospective spouses must undergo interviews by local bishops or priests before they were allowed to marry. These churchmen would investigate the family relations of both parties; if they were found to violate Church statutes, Charlemagne’s decrees empowered authorities to end the marriage. The power of the clans was being destroyed one marriage at a time. What followed was one of the greatest social transformations in European history: Western Europeans stopped thinking of themselves as kinsmen and started thinking of themselves as neighbors.

Why were leaders like Charlemagne so eager to encode Catholic social teaching into law? This question is the starting point of the research of economist Jared Rubin, whose work traces the origin of modern economic growth to the history of medieval and early modern Europe. In his recent book Rulers, Religion, and Riches: Why the West Got Rich and the Middle East Did Not, Rubin argues that the Catholic Church’s unique position in medieval European society determined the unique trajectory of Europe’s modern economy. In the days of Charlemagne, European kingdoms had the least developed economies of Eurasia. Governments were weak and agents of the crown were few. To maintain power, political leaders needed the support of the Catholic clergy. Laws like those banning plural and cousin marriages were the price of their support.

The kings of Western Europe were not unique in their use of religious authority. The rulers of Byzantium and the Middle East also relied on religious leaders as sources of political legitimacy. What separates the Catholic experience from its Orthodox and Islamic counterparts was the increasingly weak influence Catholic leaders had on secular leaders as the Middle Ages came to a close. The waning authority of the Church had powerful economic effects. In Byzantium, the Arab kingdoms, and the Ottoman Empire, religious leaders retained more than enough political power to frustrate financial and technological innovations that threatened to violate religious doctrines or subvert their cultural authority. The hierarchy of the Catholic Church, in contrast, had little choice but to adapt themselves to unwelcome changes. Rubin’s case studies include the invention of modern banking and the printing press. In both cases, religious leaders across Europe and the Middle East opposed the spread of these new technologies. Only in Western Europe were the protests of the churchmen ignored. The foundations of modern trade were laid on the unique relationship between the Catholic Church and Catholic states.

Rubin traces the origins of Catholic political weakness back to the Church’s first centuries. Unlike Islam, born in conquest and endowed from its origins with political power, Christianity began as the religion of a persecuted minority. The notion that different things might be rendered unto God and unto Caesar made no sense to the jurists of the early Caliphates. This ancient Christian distinction between secular and sectarian was buttressed by the curious institutional history of the Latin West. In contrast to the Arab and Turkic kingdoms, which had no formal religious hierarchy capable of spanning the many Sunni lands, or Byzantium, whose strong Orthodox hierarchy was married to an equally vigorous state bureaucracy, the Catholic Church had a stronger institutional foundation than any kingdom in medieval Europe. This state of affairs led European kingdoms to cling to the Church for support. But if the divisions of feudal Europe brought the princes to the Church’s altars, Rubin shows how these same divisions would eventually lead them into open conflict with the Church itself.

“For Christians it is not possible to have a Church and not have an emperor,” wrote the patriarch of Constantinople in 1393, “for the empire and the church have a great unity and a commonalty, and it is impossible to separate them.” This crude equation of an individual kingdom with all of Christendom was not possible in the Latin West. The Western kingdoms were too fractious for this, the papacy’s claims too catholic. Byzantine emperors and Eastern patriarchs were not without conflict, but they shared a sense of common self-interest. An emperor might worry that the Orthodox hierarchy might favor a popular general or royal relative over him; he did not worry that they would favor an enemy kingdom over his own. Catholic kings had no such assurance. The result was that, as their power increased over the centuries, the kings of the Latin West grew less and less comfortable with their dependence on the papacy.

What followed from this is well known: the Investiture Crisis, the Avignon Papacy, Charles VIII’s march on Rome, and eventually the Protestant Reformation. For Rubin, these events have more than just religious significance. By refusing the blessing of the churchmen, the kings of Europe had to turn elsewhere for support. They turned to a new European social group: the merchants. This nascent business class was happy to legitimize Western monarchs; in return, Western monarchs were happy to promote laws and institutions that favored cross-border trade and finance. The late medieval eclipse of the Church by the market, Rubin concludes, set the scene for Western Europe’s capitalist revolution. Only the political threat posed by a cross-national religious hierarchy could have prompted medieval leaders into the arms of the merchant class. Thus it was only in Western Europe that the development of modern markets began.

Though the methods used by Rubin and Schultz differ (in his papers, Rubin employs game theory and calculus to model the calculations of popes and princes; Schultz and his co-authors rely on statistical methods to correlate modern outcomes with Europe’s medieval heritage) when placed together, their work presents a compelling account of the origins of modernity. Capitalism and liberalism are the twin pillars upon which the modern world was built. And both of them were built, unconsciously, by the priests and popes of the medieval Catholic Church.

Tanner Greer is a writer and analyst formerly based out of Beijing. His research focuses on the relationship between traditional Asian history and modern Asian politics.