Just to come back to you David, after you replied to my post earlier. Firstly, I accept your apology, however if I were to start a debate on racism, for example, I wouldn't just come out with a crass statement, based on zero knowledge and a fair degree of stereotyping and hope that people wouldn't be offended by what I had written. I would choose to pose a question and hope to therefore be able to put my opinion across based on the facts I knew, whilst also being open to someone with more knowledge on the subject correcting me on my inaccuracies. I thought you were also of this mindset and not someone who just posted stereotypes and damn the facts the get their point across.
I won't answer all of your questions, but if it helps I will give you a brief answer to the 2nd question, which hopefully explains a little bit of what sport scientists study. Firstly, it wasn't me that used the term biology, we would use physiology, there is a fair amount of crossover, but the whole reason for looking into the human body is for a different purpose. Generally speaking, the point of insertion of the hamstring muscles, which is just below the knee joint, is greater among black people than in white people. Bringing in a bit of biomechanics here, I'm sure you are aware of the principle of moment arms, i.e. the torque generated is equal the force applied multiplied by the distance between the application point of the force and the fulcrum (in this case the joint), this distance is often called the moment arm. A greater torque is effectively more power being generated in the running motion. This is why, physiologically, black athletes have an advantage over their white counterparts (in general).
As to why 'African Americans' tend to perform better at shorter distances than 'African Africans' and vice-versa, this is mainly down to the different physiques and therefore muscular development in different areas of the body that have evolved over time. Along with this is a fair bit of social interest in the different types of distance running meaning that the population in those respective countries are more focused on shorter or longer distances and as such (generally) produce more athletes in that type of event. As you would expect, a nation such as America, for example, produces more basketballers due to the cultural interest in the sport, when compared to populations in the Indian subcontinent, where sports such as cricket are more popular.