Where Are the Tibetan Marathoners?

I ask because a flurry of papers in the last month or two has shown that they've racked up a bunch of oxygen-efficiency mutations, unsurprisingly. What's interesting is it shows that where humans live can have rapid evolutionary effects on us, even in just a few thousand years (Tibetan and Han Chinese populations split less than three millennia ago). Most interesting is that one of the mutations much more common in Tibetans was already associated with improved athletic performance. (Science paper wasn't up yet so here's an article from the lay press; here are two more.)

So why don't we see more of these guys and gals out on the course? My prediction is that before long we will, although I'm presuming (since I haven't read the paper either) that these are genes which improve aerobic metabolism rather than muscle mass and will therefore enhance performance in endurance sports.