Medieval Catholic Church Family Policies Molded Western Society As We Know It Today, Study Claims


A medieval-era stained glass window in an old castle in Toledo, Spain, shows a Spanish royal court member and a Roman Catholic bishop facing each other. Arnold O. A. Pinto/Shutterstock

The Catholic Church’s "obsession" with banning incest during the Medieval Ages may be responsible for molding western society into the “weird” culture that it is today, new research claims.

Over time, cultures evolve and change. Perhaps one of the most revolutionary evolutions of social norms and values occurred between the fifth and 15th centuries when the Western Church, later to become the Roman Catholic Church, imposed strict rules on marriage. These rules banned practices like marriages between cousins and polygyny (the most common form of polygamy, where multiple women share a husband), which ultimately led to “systematically undermin[ing] Europe’s intensive kin-based institutions" to encourage a “nuclear family structure”. In return, society in North America and Europe evolved to be “western, educated, industrialized, rich, and democratic, or WEIRD.


“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,” write the authors in Science.

To explain how social groups like the church molded psychology and values of its members, especially family dynamics, researchers compared how the Catholic religion spread across Europe against rates of co-residence on extended families, data on cousin marriage rates, and other measures they used to determine what they called a “kinship intensity index”. Researchers tested at three levels: globally, within Europe, and among adult children of European immigrants whose parents came from countries or ethnic groups exposed to the Western Church. They found that banning incest exponentially grew monogamous marriages between non-relatives. For every 500 years society was under the church, marriages between cousins declined by 91 percent.

(A) Exposure to the medieval Western (blue shading) and Eastern (green shading) Churches at the country level. (B) The kinship intensity index (KII) for ethnolinguistic groups around the world. Science

“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,” write the authors.

Spread of the Western Church loosened tribe-like family structures as norms and ideas were put upon people attending the Catholic Church, changing the psychology of an entire society. In situations of extended families, members typically work together toward a common goal, such as working the family farm, and favor tradition, nepotism, obedience to authority – all of which largely kept families safe from outsiders. Breaking down these large units promoted individualism, independence, and creativity while creating a need to cooperate with others, particularly strangers who might help or benefit individuals. The authors note that one is not necessarily better than the other, but there are trade-offs between the two.


It is unclear whether this shift was intentionally designed by the church or simply a byproduct of a new belief system. The researchers contend that there may have been a material incentive to the shift as shrinking family networks could have meant those without heirs would leave their wealth to the church.


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