THE psychological traits of people in developed countries in the West — individualism, independence, and willingness to trust strangers — can be traced to the Church’s teachings on the family, and, in particular, its proscription of incest, a new study suggests.

The study, The Church, Intensive Kinship, and Global Psychological Variation, was published in the journal Science last week. It was led by Dr Joseph Henrich, who chairs the Department of Human Evolutionary Biology at Harvard, with collaborators from George Mason University and the Canadian Institute for Advanced Research.

Noting the “substantial variation in psychological attributes across cultures”, the study’s authors explore the impact of the spread of Christianity in Europe. They conclude that “longer exposure to the Western Church is associated with less intensive kinship, greater individualism, less conformity, and more fairness and trust toward strangers”.

The paper traces how the Church “broke down extended kin-based institutions”, and produced, by 1500, “relatively independent and isolated nuclear or stem families”. By the Early Middle Ages, the authors write, the Church had become “obsessed with incest, and began to expand the circle of forbidden relatives”. It also eliminated from Europe legal adoption, remarriage, and all forms of polygamous marriage.

It is this, they suggest, that explains the fact that people in WEIRD (Western, Educated, Industrialised, Rich, and Democratic) countries tend to be “more individualistic, independent, and trusting of strangers, while revealing less conformity and in-group loyalty”.

In Italy, they studied data for blood donations, and concluded that a higher rate of marriages of cousins was associated with a reduction in blood donations. Italians from provinces that had higher rates of cousin marriage were found both to take more loans from family and friends (instead of from banks), and to keep more of their wealth in cash instead of in banks, stocks, or other financial assets.

“If the authors are right, or even in the vicinity of being right, it couldn’t be bigger,” Dr Stephen Stich, Distinguished Professor of Philosophy and Cognitive Science at Rutgers University, told Science. “What they are offering to explain is the emergence of democratic institutions, of individualism in the West.”