Legions of athletes, sports gurus, and scientists have tried to figure out why Kenyans dominate long-distance running. In this short, we stumble across a surprising, and sort of terrifying, explanation.

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.