The heritability of human intelligence is estimated to be around 0.5. There are of course various estimates, some lower, some higher. But let's work with this value of 0.5 for the moment.
I wanted to know how this relates to the trait value of future generations and read a bit about it. For example, in some related posts:
how should one interpret heritability is it related to r2
why is a heritability coefficient not an index of how genetic something is
how to interpret the breeders equation
Turns out the breeders equation gives us an idea about that. But we need a second variable: Selection. I read that selection is based on the reproductive success of individuals with a certain trait value. But how would I calculate this value? Let's assume that the reproductive success is higher, for humans with higher intelligence. Let's simplify and say, the fertiliy rate of above average indivdiduals is 2.10 and the same value for below average individuals is 1.90. How would I plug those numbers into the breeders equation?
I tried the other way around. We know that intelligence is increasing over generations in western civilizations (see Flynn effect). Again, estimates vary (and can actually be negative) but we can work with an increase of 2 IQ points per decade. So lets say 5 IQ points increase from one generation to the next in a western civilization population. That would mean:
S = R/h²
S = 5/0.5 = 10
What would this value of 10 mean? How does this boil down to the reproductive success of individuals with certain trait values?