Ooooh, that kind of linkage is a fallacy.
We differ off humanoid apes at less than 2% of DNA, just like we differ
off rabbits in less than 8% of DNA.
We have different jaws, different bone structre which supports different
standing, and different attributes such as hairiness.
The difference in intellectual capacity is the clearest to us, but its
greatest cause isn't the brain, which only swelled about 2 times bigger,
but actually the tongue bone - this inch-by-inch piece which enable us
to humm something greater than "haba haba".
There are kinds of innate defects. Some Mongoloids for example have
intellectual problems. But those have nothing much to do with the
evolutionary branching of Homo-Sapiens-Sapiens of other apes.
We have much clearer evidence of nutrition's effect over intelligence.
Why not care for balanced nutrition before we start your suggested
dilution? It's cheaper and more efficient.
Lior.