I think the Kenyan thing is even more specific than that.
I remember hearing something about how upon investigation of a common trait amongst successful Kenyan long distance athletes, it was traced back to a genetic trait of a particular people from quite a specific mountainous region of Kenya, and I think it's some kind of small adaptation in their leg structure, or leg muscle fibres, or something to do with how their leg muscles can get more energy from oxygen than normal because the rugged and elevated region these people are from (kind of like training at higher altitude for generation after generation).