Somalia is a flat, hot place at sea level with no running culture. Yet, so many Somalis abroad have become the world's fastest runners. Why?
Somalis are linguistically and genetically very closely related to the Oromo of Ethiopia. Most Ethiopian runners are actually Oromo. Somalis are very well aware of this relationship and often talk about their "Cushitic heritage" on Internet forums.
And ta-da! Look at this. Looks like a map of where all the fast runners come from, but it's a map of shared genes. Morocco, Algeria, and Tunisia are on there too. And why the fastest Arabs mostly from Morocco, Algeria, and Tunisia, but not other Arab countries?
http://www.thegeneticatlas.com/E1b1b.png
https://en.wikipedia.org/wiki/Haplogroup_E-M215_(Y-DNA)
Any other explanations are welcome here.