By selection I mean that as fewer people have children, the ones who do have kids will be an increasingly distinctive population — not specifically conservative or religious, necessarily, but couples who will have written new scripts for romance, discovered new models for child rearing and burden-sharing, in a cultural and technological landscape that’s torn the older models up.

So then the children and grandchildren of these trailblazers, inheriting both the new models for family formation and the world itself, would be the ones who drive some future baby boom.

But if the Biden boom is a short-term scenario for fertility recovery, and the conservative turn a 10- or 15-year scenario, this selection-driven scenario would take multiple generations to show up. And in the meantime, America’s present birthrate is by no means the lowest imaginable: South Korea, for instance, now averages less than one child per woman — half replacement rate, with unprecedented depopulation looming.