The attached article posts so many interesting facts on this issue and explains the African dominance in long distance running from a genetic perspective.
It discusses their superior BMI's for running and bone densities, their differing limb lengths that aid their speed and running precision and why, for an Ethnic population of only 4.4 million, they're so incredibly good at distance running.
HERE ARE SOME FACTS TO WET THE APPETITE!:
"The statistics are hard to ignore. This medium-size country of 41 million dominates the world in competitive running. Pick any long-distance race. You'll often find that up to about 70 or 80 percent of its winners since the late 1980s, when East African nutrition and technology started catching up with the West, have been from Kenya. Since 1988, for example, 20 of the 25 first-place men in the Boston Marathon have been Kenyan. Kenyan women appear to have had a later start, winning none of marathons before 2000 (possibly due to discriminatory laws and a tradition of forcing girls into marriages, both of which were partially rolled back by 1990s reforms) and 9 of 13 since then. Of the top 25 male record holders for the 3000-meter steeplechase, 18 are Kenyan. Seven of the last 8 London marathons were won by Kenyans, and the sole outlier was from neighboring Ethiopia*. Their record in the Olympic men's marathon is more uneven, having placed in the top three in only four of the last six races. Still, not bad for one country. And even more amazing is that three-fourths of the Kenyan champions come from an ethnic minority of 4.4. million, or 0.06% of global population."