I think you misunderstood him. He was referring to the fact that America used to be the "promise land", because of the freedom it used to have, and why so many

I think you misunderstood him. He was referring to the fact that America used to be the "promise land", because of the freedom it used to have, and why so many people wanted to flee there, and create their own opportunities thanks to that freedom. It has nothing to do with genetics.