Genetic differences that give an advantage in certain tasks. If the rules of different sports, for example, were different we might see different results. In boxing, for example, the rules favor black boxers who can use hand and foot speed to an advantage coupled with less chance of bleeding and a general ability to absorb punches to the chin with less harm than with whites. Suppose, however, that boxing were changed so that rabbit punches to the neck were the most common punch thrown. We'd no doubt see more blacks being knocked out, because it is this neck area in particular, and the cardiovascular system in general that is the weak spot that makes blacks more susceptible to choke holds, and other attacks to this system.
Whites tend to have slower hand and foot speed.
The way boxing and many other sports are played gives blacks an advantage over white athletes. As in all things in life it is important to know one's strengths and one's weaknesses and to play to one's strengths. This doesn't mean that whites should stop competing in those sports where they are at a disadvantage nor that blacks should stop competing in those areas of life where they are at a disadvantage, but that one should consider genetic differences in all things. And, in the real world there are good white boxers and bad black boxers and there are very intelligent blacks and some pretty dumb whites, because in every racial population where most members of that population are clustered under the center of the bell curve, there are still members of that racial population out towards the lips of the bell where the bell curve of one group intersects with the bell curve of another group. Still, the exceptions do not disprove the rule and the rule is that statistically, we can say that the members of the races of man are generally much more like other members of their own race than they are like members of other races.