[resegooredo]

Since there is still no clear understanding of how envirement and genes combine to form a certain level of intelligence how exactly are the researchers controlling for different environments.

Also I'd be very curios to see studies of identical twins separated at birth and placed in very different environments. (different cultures, different social status, education, etc.) I doubt that there is a large enough sample size of such twins.

Additionally there is the question of how meaningful/useful IQ is in the first place.