That's a solid question too. Very interesting.
It would be very interesting to do a series of studies about the genetic and cultural pieces that make up running prowess in different cultures.
Presumably the genetic gifts of Kenyan and Ethiopian runners come from their ancestors living, running, and hunting at altitude for thousands of years (please correct me if there is an incorrect assumption and they come from somewhere else).
I wonder how other cultural groups around the world who also lived, ran, and hunted at altitude compare genetically and in actual performance to East African athletes. American Indian tribes living in Colorado, Utah, Montana, parts of Mexico, etc. likely had a similar historical situation and placed a high cultural value on running.
Second, it would be interesting to compare the performance differences between two cultures where children running to school is very common. Many people like to attribute the success of East African distance runners to their running to school everyday as a child. Kenya and Ethiopia cannot be the only countries in the world where this is common. What are others, and how do they compare in performance in distance events?