>>3
Incorrect.
Science 297(5580) front cover (2002) had a story about a gene all mammals carry, a mutated version of which approximately triples brain mass and does very impressive things for rats and mice.
The brain is the organ of cognition. Its structure and function are determined by the genes.
Barring brain damage or severe malnutrition in childhood, intelligence--which we define for convenience as the net information-processing power of a given brain--is 100% genetic. This has been known for well over a century.
People get all pissy about it, but H. Sapiens is an animal, like a horse or dog. We can breed animals for any trait we can imagine. Our ancestors were doing this during the Iron Age. And we have vastly more sophisticated tools at our disposal today.
Why wouldn't intelligence be genetic? How could it be any different from lung capacity or the length of the long bones in the limbs?