The Flynn effect contradicts this, and not just superficially in that IQ scores have been rising for the last 20 years and the next 20 years aren't going to be that different, but that it points to a strong non-genetic component of IQ. The cultures who become wealthy and have fewer children have pretty much the same code as cultures that are a little behind, same within countries. Lastly, 20 years is barely a single generation. You'd have to pretty much wipe out large sections of the population to see a 1 generation change.