Nor can we accurately quantify the genetic contribution in the first place. It depends. Some things are discrete (eg, genetic diseases like huntington's). Mos

Nor can we accurately quantify the genetic contribution in the first place. It depends. Some things are discrete (eg, genetic diseases like huntington's). Most things are on a continuum--there's no IQ gene, for instance. I suspect that, in a rough way, almost every non-junk aspect of the human genome has some effect on intelligence, large or small. The best tests are perhaps still separated twin studies. Identical DNA + different environments makes for a convenient way to quantify the genetic influence of characteristics... Of course, once genetic engineering is in full bloom, all of this will be quite non-controversial.