> Part of the answer could be that genetics play a larger role than anyone would like. In studies like the Norway study you cite this could be controlled for b

> Part of the answer could be that genetics play a larger role than anyone would like. In studies like the Norway study you cite this could be controlled for by adoptions. Though adoptees, of course, come with their own non-genetic baggage. I would hope that, at the very least, IQ testing would be performed to try to match based on that.