Sadly, the stupid tend to breed prolifically, and anti-vax idiots often have a gaggle of spawn, and are keen to whelp more litters as the others die from perfectly preventable diseases

I think about that often. The people who have the most kids are generally the ones who can’t afford them and have a harder time providing extra-curricular activities or those with more extreme religious beliefs who may opt out of scientific education. If your average Mormon has 3-4 kids and your average astrophysicist has 1-2, the population trend must eventually follow.