>>3587401>but there's less of a difference between a white and black brain than a white and chimpanzee brain
Small differences matter when they're in the head. Some brains build space rockets, some brains hang their pants low and sell drugs at the street corner.
Consider, there's not much of a difference between a brain with a mental illness, and a normal brain. Just some few genes gone wrong and you become an idiot or a lunatic. Brains are the least likely to change through evolution because even small changes make them go completely wrong - so evolution has made brains that resist change in their fundamental workings. That's why you can take a monkey out of the jungle, but you can't take the jungle out of the monkey.