Weird lands of the tails

Yesterday's post on the speed of Jamaican sprinters, and Genetic Future's skepticism of a one-gene answer for their dominance. The discussion brought up some adaptive talk; I'm not against adaptation, and I think it's entirely plausible that populations differ enough in the distribution of phenotypes that there are different genetic potentialities...but, I have some issues with the intersection of the two in this particular case. Here's my logic.... Sprinters at the Olympic level are the best of the best. They're not just good, they're not just superior, they are the pushing the limits of human capabilities in a particular direction. In other words, they're the extreme tail of a distribution. What's that distribution? I suspect it's approximately normal (or can be so with easy scaling, I wouldn't be surprised if the "fast" end of the tail is very long while the median is rather low; positive skew). Let's just go ...