At the 1968 summer Olympics in Mexico City, Kipchoge Keino overcame a gall bladder infection to win gold in the 1500 meter race. Since then, one particular group of Kenyans—the Kalenjin—has produced an astonishing number of great long-distance runners. Gregory Warner, NPR's East Africa correspondent, takes Jad and Robert down a rabbit hole of theories about what exactly is going on in Kalenjin country. 

David Epstein and John Manners help Greg untangle a web of potential factors - from something in the cornmeal to simple economics. And, after talking to a young Kalenjin runner named Elly Kipgogei, Greg discovers a somewhat disturbing explanation for Kalenjin running prowess that actually makes him want to get on the treadmill and push himself just a little harder.