Most people living in Western, developed countries are psychologically distinct from the rest of the world.
For one, they tend to be more individualistic and think of themselves as being independent of other people.
"There is a stronger sense of autonomy and agency," says Ara Norenzayan, a psychologist at the University of British Columbia, who in 2010, along with some colleagues published a study describing these psychological attributes of people in so-called Western Educated Industrialized Rich Democratic (WEIRD) countries.
On the other hand, people in other parts of the world tend to be more "collectivistic," says Norenzayan, because their lives are embedded in extended family networks and obligations. They "are more embedded in relationships," he says. "People see themselves as being part of this larger context."
So how did people in the West come to be so different?
A new study published Thursday in Science suggests it all began in the Middle Ages, when the predecessor of the Catholic Church pushed a way of life that broke up extended family networks and paved the way for nuclear families, weaker family ties and a more individualistic mindset.
"If you eliminate adoption and remarriage, you prevent lineages from getting heirs and lineages literally die out," he says.
The researchers don't know the precise motivations behind these bans, but they think they had a dramatic impact on how society was organized.
That restructuring of societies in Western Europe in turn also benefited the Church, notes Henrich.
"In some sense, the Church is killing off clans, and they're often getting the lands in wealth," he says. "So this is enriching the Church. Meanwhile, Europeans are broken down into monogamous, nuclear families and they can't recreate the complex kinship structures that we [still] see elsewhere in the world."
"This is the first comprehensive attempt that I can see, where the authors try to explain why is it that Westerners are so unusual or why they're the outliers?" says Norenzayan, who worked with Henrich on the 2010 study, but wasn't involved in the new one.
The study is "incredible in scope and very novel to link specific practices in the Church with psychology centuries later," said University of Maryland psychologist Michele Gelfand in an email. Gelfand, who studies cultural norms and diversity, was not involved in the new study.
Despite the strong evidence of association between the Catholic Church's marriage bans and WEIRD psychology, she thinks future studies need to illustrate exactly how these policies paved the way for this kind of psychology.
And there are likely other factors at play, too, she adds.
"It's not the only practice that has an impact on WEIRD psychology," she wrote, "so we need to also compare its relative impact to other ecological, historical and socio-political variables. There are a lot of open questions."
One question pertains to the fact that the Catholic Church's influence in Europe has declined in the past century, says Norenzayan. "How do you still get these repercussions, when the institution itself is taking more of a backseat?"
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