There a lot more variability between individuals then between ethnic origins. Sure, the Olympics have demonstrated that at very high levels, black people win much more often than white people at a 100m race. But pick one black guy and one white guy completely at random on this planet. What's the likelihood of the black guy winning a 100m race? I'd say about 50%. The variability across individuals is just too much. Even if you had a precise way of measuring intelligence and managed to prove with 99.9% confidence that people of origin X are on average more intelligent than people of origin Y, it would mean absolutely nothing at the individual level.