Sometimes people will say that the reason we're all doomed is that stupid people outbreed smart people. For this to be true you need three things:
- intelligence can be defined in a useful way;
- intelligence is largely genetic;
- more intelligent people have fewer children than less intelligent people.
Let's just assume all those things are true, and see where it leads us. A little bit of maths will show you that, if there are two groups, where couples from one group have on average cs children, and couples from the second group have cd children, then after n generations the ratios between the groups will change by
en(ln cs - ln cd)
So, OK, what does this mean? Well, let's assume a generation is 20 years, and 10,000 years ago there were equal numbers of intelligent and dumb people. Let's also assume that cs = 2.1 and cd = 2.2 (so each dumb couple has 2.2 children and each smart couple has 2.1).
Today there would be about 1 smart person for every 12 billion stupid people. There are about 7 billion people in the world. In other words there would be no smart people left.
Well, in fact there are lots of smart people in the world. So at least one of the assumptions above is false. I suspect that, insofar as intelligence can be usefully defined, very intelligent people do tend to have fewer children than average. So that leaves, really, two options: either intelligence can't usefully be defined in any useful way, intelligence is not genetic, or both. I think both.
It took me less long to do the maths involved here than it did to work out how to format it in markdown, and I am not a god-like genius: the only safe thing you can say is that people who believe in eugenics are not very smart (Dominic Cummings: I'm looking at you).