First off one persons visual comparisions are about worth as much as handtiming the olympic 100m dash, or couting in your head to time the marathon.
Next average differences you would be talking about the middle of the distribution (average human) which may have no effect on outlier conditions (elite athletes).
Next show me the studies that say all of these conditions are bell curved, and with your hypothesis of africans and whites differing in these areas they should not be bell curved.
Show me a study that says white athletes have more body fat than black athletes, what athletes were used?
Dont use sketchy arguements to argue an important topic like this.
I am not saying it isnt true that africans are dominating the track events, but if you are going to give a reasoning for it, at least use strong arguements.
Chances are its probably not 100% genetic or 100% environmental, maybe its something else no one has thought of, hell I know I see 500 places on the internet that if it was chance it had like .0000000000000000001 chance ofhappening, well whats the chance life would occur on the earth out of all the planets, and the chance that humans would evolve, create the internet, and in 2007 we would have this conversation right now, probably a lot less than the chance of .000000000000000001.