There are differences. We don't JUST have different paint jobs as the nurture/behaviorist types would have us believe. This being said, the caste system is real. Its most obvious manifestations are in American football and American sprinting. Running back is the most extreme example. This is pure, 100% racism. There is enough evidence from history, e.g., Borzov, to indicate that it is possible for a white man to reach the top in sprinting. There is also enough evidence to show that that top person will usually be black. That blacks are slightly faster isn't such a bad thing when you weigh it against all the things that whites are way better at. When you talk about the far right end of the bell curve, very slight differences will matter big time in sprinting where hundredths of seconds separate ranks.