>In Plomin’s study, the young person with the second-highest GPS for intelligence achieved results only slightly above average. That’s not surprising, though: environmental factors still play an important role.
The effect can also be nonlinear.
As far as I know correlation between wide polygenic score (GPS) and intelligence is linear (r ≈ 0.30) only because linear correlation is measured? It would be interesting to see the effect of wide polygenic score to different extremes, very high and low g.
I would hypothesize that genes are more important factor in low intelligence
scores than they are in high IQ. Environmental factors seem to work the same way.
There is some evidence that there is a right skew to the IQ distribution and it's not perfectly normal.
second-highest GPS for intelligence achieved results only slightly above average
This doesn't need much explaining, the correlation between the score and test results just isn't that high. That's all. Saying "environmental factors" here is, I think, nothing more than a polite way of saying "noise".
People think about nonlinearities too. My understanding is that we're a long way from having such good data that it would help our predictions to include them. Steve Hsu writes about this, I can't find the perfect link but here's a start:
The IQ distribution is normal by definition. Test scores are normalised to put them exactly on that curve. In order to say that the distribution is skewed you have to choose some other way of normalizing it that you think is "objective". (If you actually did this though, I think you would be correct. The best scientists and mathematicians aren't just twice as good as everyone else, they're hundreds of times as good. So the high intelligence tail is heavy, in some sense.)
Intelligence researchers don't use normalized IQ for anything serious (they are not comparable across countries, for example). They use raw test data to generate the real distribution.
I tried to avoid using the 'IQ' and use g-factor or intelligence, but I slipped at the end. I'm sorry about that.
>. So the high intelligence tail is heavy
Yes. Intelligence seems to have fat tails on both directions and it's also right skewed.
I would guess that there are lots of places where having one gene be allele A and another allele X would be good or B and Y but having A and Y or B and X would be bad. And I'm not sure if current screening methods would find that except by saying that A is good if X is more prevalent in the population than Y.
If the Flynn effect is real there should be a right skew and vice versa. A skewed distribution is what directional selection or any other directional population shift looks like.
The effect can also be nonlinear.
As far as I know correlation between wide polygenic score (GPS) and intelligence is linear (r ≈ 0.30) only because linear correlation is measured? It would be interesting to see the effect of wide polygenic score to different extremes, very high and low g.
I would hypothesize that genes are more important factor in low intelligence scores than they are in high IQ. Environmental factors seem to work the same way.
There is some evidence that there is a right skew to the IQ distribution and it's not perfectly normal.