Kenyans excel at running not only due to genetics but due to economic and environmental factors. They are built long and lean, to be sure, but Kenya also has a high altitude that they benefit from when training. Kenya is a very poor country as well, and as soon as a few pioneering Kenyans started winning races and getting relatively rich, running quickly became one of the few ways average Kenyans could escape grueling poverty, and has since become a definite cultural signpost, much like basketball in the inner-city US.
Genetics tends to be a field, like religion, that people dwell on as THE ONE defining factor in a culture's success or failure, ignoring every other facet of human existence.Like religion, it's easy to twist around to support an insane, unscientific ideology, so draw your conclusions very carefully in regards to how much "smarter" you think it actually makes a given race. Here's a clue, though, IQ differences in individuals AND groups of people only average out to be a few points, so the differences are negligible. A person would be on much firmer scientific footing to say our differences are largely physical to deal with different types of climate. For white people this translates into light skin to maximize vitamin e production, larger noses to warm air before it reaches sensitive lung tissue, light colored eyes to deal with extend periods of darkness and shorter legs to maintain core temperature in the cold. When you start taliking about differences in mental capacity you've entered dangerous territory, and some conclusions are easily hijacked by those with bad idealogies. Genetics counts for a lot, but so do natural resources, population density and everything else. BEWARE OVERSIMPLIFICATION.
P.S. Kenyans WON'T take over cycling because the only bikes they can afford are single speeds made with plumber's pipe, whereas running is comparitively cheap.