Anti-intellectualism in America. It is impossible to study any specific person and figure out how much of their intelligence is due to genes versus the environment. The human population overall, can be studied, and from what I have seen, the evidence is roughly 50% of intelligence is inherited, which means 50% is not, and that is huge. I'm referring to Adam Rutherford's latest book on the History of Everyone, I'm not sure the exact title, but he is a geneticist and basically gave an overview of human evolution and what modern genetics tells us about how we evolved. He specifically denied any races among humans, and explained in detail why this was true. Every other book I have read by a geneticist takes this position. I have a beginning biology textbook used in colleges, it is about ten years old, and it specifically states no races exist, as well. The American Anthropological Association takes the position that no races exist.
The only people I am aware of who make the claim that races exist and there are differences among them regarding intelligence are non-scientists, like the journalist who authored the book, The Troubling Inheritance. His book was so full of errors that Scientific American thrashed it on its website, and Massimo Pigliucci, a man with two Ph.Ds in biology and one in philosophy also wrote a blog post shredding it. Basically, the racists have no hard-core science backing them up, but rely upon ignorance and prejudices people hold.