People of West African descent have longer legs and shorter torsos on average. This allows them to run faster and jump higher. This is why they dominate sprinting, basketball, American football, etc. This is also why you don't see elite black swimmers - in swimming, shorter legs and longer torsos are advantageous. Take a look at Michael Phelps' freakish leg/torso ratio some time.
People of East African descent dominate long-distance running because they have smaller calves on average. This means their legs weigh less, so they need to expend less energy per step.