Another Reason Why the West Is Rich.

• Author: Stroup, Jane Shaw

The WEIRDest People in the World: How the West Became Psychologically Peculiar and Particularly Prosperous

By Joseph Henrich

680 pp.; Farrar, Straus and Giroux, 2020

They never let up. They keep arriving--those big, popular books that you can't resist because they offer a single powerful explanation for the economic prosperity of the West. Jared Diamond pointed to geography, Douglass North and Robert Thomas to property rights, Joel Mokyr to technology, Dierdre McCloskey to bourgeois virtues, and Kenneth Pomeranz to coal and colonies.

Now we have another big, monocausal explanation for Western Europe's rise that is utterly different from the rest, although it has faint echoes of Max Weber. The WEIRDest People in the World, by cultural psychologist Joseph Henrich, gives the credit for European prosperity to the Catholic Church. Why? Because the Church completely obliterated traditional kinship ties through increasingly rigid restrictions on whom one could marry.

The process started in 597 AD when a monk, Augustine of Canterbury, was trying to convert the Anglo-Saxons of England. He wrote to Pope Gregory I (now St. Gregory the Great), asking if some prevalent marriage customs would be allowed once the natives became Christian. The pope's reply was strict. He rejected marriage to close relatives or to close in-laws (in-laws are called "affines" by anthropologists). He banned the adoption of children. He prohibited concubines. (Divorce was already prohibited, based on Jesus's words in Scripture.)

Exactly why the pope gave these answers can be debated, but one effect of the practice was to reduce the number of heirs. And one result of fewer heirs was that more people bequeathed their wealth to the Church, motivated in part by the hope that such gifts could ease their way into heaven.

Individual over clan / To Henrich, the pope's instructions launched the Church's "Marriage and Family Program" (MFP), which ultimately destroyed the extended family. He does not discuss the reasons for this policy, but he presents plenty of evidence for it. He includes a timeline of the steps, both local and centralized, that the Church took to eliminate marriages within one's "clan."

By 1063, the Synod of Rome (the assembly of bishops for Italy) prohibited marriages between all cousins up to sixth cousins. Certainly, that was extreme. Who is your sixth cousin? Someone who has the same great-great-great-great-great-grandparent. It is unlikely that you would know who such a relative is. And if you found a seventh cousin to marry, you had to be sure that he or she was not also an affine or a godparent. (The sixth-cousin "incest" rule was later relaxed to...