Heritability is a technical measure of how much of the variance in a quantitative trait (such as IQ) is associated with genetic differences, in a population with a certain distribution of genotypes and environments. Under some very strong simplifying assumptions, quantitative geneticists use it to calculate the changes to be expected from artificial or natural selection in a statistically steady environment. It says nothing about how much the over-all level of the trait is under genetic control, and it says nothing about how much the trait can change under environmental interventions. If, despite this, one does want to find out the heritability of IQ for some human population, the fact that the simplifying assumptions I mentioned are clearly false in this case means that existing estimates are unreliable, and probably too high, maybe much too high.
Jason’s blog reference goes on:
So: Do I really believe that the heritability of IQ is zero? Well, I hope by this point I’ve persuaded you that’s not a well-posed question. What I hope you really want to ask is something like: Do I think there are currently any genetic variations which, holding environment fixed to within some reasonable norms for prosperous, democratic, industrial or post-industrial societies, would tend to lead to differences in IQ? There my answer is “yes, of course”.
For the record, the estimate I cited is exactly the same estimate that Jason’s blog’s author repeatedly refers to as the best existing estimate in the literature. The author goes on to argue that that estimate is either biased up or meaningless. Nonetheless, even the blog author clearly does not actually disagree with the mainstream position among relevant scientists that there is a substantial genetic component to intelligence: “of course” there is.
I did particularly enjoy, I must say, the bit where the blogger chastises geneticists for failing to use rigorous statistical methods developed by econometricians.
Congratulations, you’ve all been trolled.