No, I'm questioning the whole basis of many of these twin studies, because some of the more famous ones that get cited were "pre-loaded" to get certain results.
MANY different studies have studied identical twins (monozygotic) raised apart and found a 0.70 correlation for intelligence. This is enormous.
Great, if true.
Question: did they correct for the nurture end of things?
I've bumped into too many identical twins with very different overall temperments (intelligence, WHAT they're good at, personality, et cetera) to buy in that intelligence is that strongly determined by genetics. I have one rather smart sister, and two fair-to-middlin' brothers--and in mathematics, I'm the best of breed in my family. My sister and brothers are very coordinated; I'm something of a klutz. We're all over whatever charts you want to look at.
Yes, that's why they do studies on monozygotic twins RAISED APART, i.e. in different environments.