Hajnal line
en.wikipedia.org
en.wikipedia.org
The Origins of WEIRD Psychology
> Recent research not only confirms the existence of substantial psychological variation around the globe but also highlights the peculiarity of populations that are Western, Educated, Industrialized, Rich and Democratic (WEIRD). We propose that much of this variation arose as people psychologically adapted to differing kin-based institutions—the set of social norms governing descent, marriage, residence and related domains. We further propose that part of the variation in these institutions arose historically from the Catholic Church’s marriage and family policies, which contributed to the dissolution of Europe’s traditional kin-based institutions, leading eventually to the predominance of nuclear families and impersonal institutions. By combining data on 20 psychological outcomes with historical measures of both kinship and Church exposure, we find support for these ideas in a comprehensive array of analyses across countries, among European regions and between individuals with different cultural backgrounds.
But if Catholicism plays a role:
a) why is Ireland outside?
b) why is the Non-Catholic part inside?
These marriage patterns changed sometime long before 1500, maybe circa 1000AD -- so if the church had a hand in it, it's the medieval church.
The places where this pattern was strongest went on to invent Protestant religion, and have now largely moved on from formal church. While the places the present-day Catholic church is strongest are outside this zone... or weren't christian at all in at the relevant time (like Spain, and Mexico).
I wonder though why Ireland, Austria and Venice would be outside. In some respects all of them played central roles in European history (Ireland in Christianization).
EDIT: Just figured out, the drawing is off. If drawn correctly it would include Vienna and Venice.
If you mean the Teutonic Order's crusade quickening the Christian baptism of Grand Duchy of Lithuania, I'm sceptical. Not that the region becoming part of the Christian Europe isn't important; it's just that it was inevitable anyway. The paper "The Origins of WEIRD Psychology" [0] linked by another comment proposes that this is likely to do with Catholicism. However, I speculate that the East Baltic's (the Baltic states') embrace of Catholicism is evident in the 20th century, not because of the ?-1410 crusade, but because in the 20th century, they experienced severe antagonisation from the atheist USSR, and went full-throttle in the other direction. A bit like how the US alcohol prohibition backfired. Aggressive suppression of religion led to it growing strong roots. Funnily enough, same thing was happening almost a thousand years ago, only reversed. Region resisting Catholicism peddled by Teutons and suppression of the pre-Christian religion. 20th century -- same region fighting to preserve a Catholic identity.
Also interesting the US seems to have a sort of fertility zone right down the middle https://www.reddit.com/r/MapPorn/comments/84g2n5/states_and_...
The line as it is drawn excludes Venice and Vienna. Correcting that line to actually overlap with St. Petersburg and Trieste gets these epicenters of European culture back "inside".