http://en.wikipedia.org/wiki/Minnesota_Twin_Family_Study#The...

This indicates that genetics certainly play a very important role here. It might not be PC to say so but the science is pretty clear.

Actually, the science of broad heritability, which is what you are talking about here, is anything but clear. The concept of heritability (it originated with Francis Galton) is a pre-Mendelian concept, an example of the saying that a person with a hammer treats any problem as a nail.

Heritability says NOTHING about malleability of a particular trait in populations, as any professionally edited genetics textbook will remind you. And there is already plenty of empirical evidence that IQ scores, and real-world intelligent behavior outside the testing room, and rationality (which is distinct from IQ) are exquisitely sensitive to environmental influences, many of those influences being cultural or educational rather than nutritional. That's what the book under review is about: providing a large number of citations to primary research literature on the malleability of IQ and educational achievement.