Why Did Mormon Fertility Rates Fall?

Mormon fertility rates fell once the community grew big enough to live in close contact with ordinary society, Leopold Aschenbrenner says. High-fertility religious subgroups normalize, and the force of modernity pulls the birth rate down.

People had treated Mormons as the group that would keep a high birth rate and replace everyone else. Aschenbrenner says the decline still reached them, and that is what clinched the broader fertility-decline story. He does not remember the exact numbers. He puts the drop at roughly four children to two over the course of 10 or 20 years. Fertility rates among Mormons remain important, and they are still going down.

The same limit applies to the next group people name. He says the Amish are probably not a scalable exception. A religious community that grows large enough runs into modernity and loses the high rate.