well if blacks get better nutrition now today than whites did a hundred years ago, then it wouldn't prove anything, it would just prove that good nutrition = higher intelligence than bad nutrition
I'm not denying there are environmental factors
I am only claiming that there is evidence there are genetic factors

there are many genes that affect intelligence, like these:
http://www.sciencedaily.com/releases...0427161424.htm
http://www.physorg.com/news91799494.html
http://www.wellesley.edu/Chemistry/c...elligence.html
each gene affects IQ by 2-4 points and there are about 50-100 genes that affect intelligence

and of course different people have different versions of these genes
the more intelligent ones have the better versions, the less intelligent ones have the worse versions