> I find it fascinating that South Korea [..] is very religious. I thought [..] religion was supposed to raise [fertility].

South Korea: 1.1 fertility rate, 56% no religion - https://en.wikipedia.org/wiki/South_Korea

USA: 1.8 fertility rate, 29% no religion - https://en.wikipedia.org/wiki/United_States

Mexico: 2.1 fertility rate, 15% no religion: https://en.wikipedia.org/wiki/Mexico

Niger: 6.6 fertility rate, 0.1% no religion: https://en.wikipedia.org/wiki/Niger

Granted these are randomly chosen countries. If you want to invest the effort and plot fertility rate vs. religion for all countries where data are available to see what correlation (!= causation) emerges, be my guest.

Source for fertility rates: https://en.wikipedia.org/wiki/List_of_sovereign_states_and_d...