Joseph Henrich
Henrich argues that Western populations' historically unusual psychology arose in part from medieval Catholic marriage rules that weakened clan ties over generations.
People from WEIRD cultures possess a peculiar psychology characterized by intense individualism, a focus on personal intentions over social context, and a reliance on internal guilt rather than external shame.
The Catholic Church helped trigger this psychological transformation by enforcing strict marriage prohibitions that weakened the dense, kinship-based clans that dominated human history.
As extended families became less central, Westerners increasingly formed voluntary associations like guilds, universities, and charter towns that operated on more impartial rules rather than blood ties.