I'm gonna throw out a theory here that really hasn't been discussed before.
I can't speak for non-American white runners, but in the U.S., our lifestyle is not at all conducive to producing fast distance runners. There are 15-year-old kids living in U.S. suburbs who have more pressure on them than CEOs of large companies. Our current system is to have teenagers work around the clock to pad their high school credentials, just so their families can pay $200,000 to get an undergraduate degree at a respectable school. It's a system that breeds stress, which is incredibly unhealthy and thus bad for running.
Let's compare two equally talented teenage runners, one from the U.S. and one from a less wealthy part of the world:
U.S. Teen - Wakes up at 6am to go to school after staying up late to finish a paper. Dad has already left for work because he's working extra hours to afford his son's future college tuition. Mom is stressed because she's barely seen dad all week, so she scolds teen for getting a 'B' on a quiz. 'B's aren't going to get her son into a top school.
Teen, already stressed, heads off to seven hours of classes based on memorization and regurgitation of material. He has a test and quiz today, on top of the paper that was due. He spends the entire day seated at a desk, wracking his brain to remember names, dates, and terms. His only fuel for the day has been a bowl of Frosted Flakes with factory-farmed milk and chicken nuggets/fries from his school cafeteria.
At 4:00, his cross-country team has a duel meet. He finishes first overall, but his time has not improved at all from last year. He and his coach can't figure out why. He goes home to his stressed parents, who continue to fight as they crunch numbers to afford their son's $49,000 tuition the next year.
Teen from a Less Wealthy Country - Wakes up at 4am to help his family with the farm. Is on his feet working until 7am, at which time he runs two miles to school. Classes are based on real-world skills, and the teen is grateful to have the opportunity to learn.
Teen runs home at noon to do more chores. Around 2pm, he's allowed to train. His dream is to be an elite runner one day, so on this day he puts in 10 miles across rolling dirt roads, with pick ups every few minutes.
He comes home at 4pm, does homework for two hours, then spends the rest of the night relaxing. His family eats dinner together, grateful for the meal and each other. He is in bed at 8pm to read for an hour, then asleep by 9pm to be charged up for the next day.
Which lifestyle sounds like it would be better at breeding talent?