When I was a kid, you heard more about the Tarahumara Indian runners of Copper Canyon in Mexico than you heard about the Kalenjin of Kenya. The Tarahumara were supposed to be the great runners of the world, able to run a hundred miles without stopping. But Tarahumara runners have only competed once in the Olympics, with indifferent success, while the Kalenjin have consistently won medals.
Here's an article comparing the two groups. The sports-obsessed British colonial administrators tried to get the young Kalenjin men to redirect their excess energy from cattle-rustling to track, while Mexico wasn't terribly interested in track, and the Uto-Aztecan-speaking Tarahumara didn't want anything to do with Mexicans, anyway.
The author argues that the Tarahumara's strong suit is distances farther than the 26 miles of the marathon. In contrast, by my calculations, the Kalenjin's best distance is about 3000 meters, which is why Kenyans really aren't that all-conquering at the marathon, a distance at which there are a wide variety of winners. (Here's my 1997 chart showing the best running race distances for different groups.)
In 1993, a 55-year-old Tarahumara showed up at the high-altitude 100 mile ultramarathon in Leadville, Colorado and won, running in sandals made from old tires. But since then they haven't really shown much interest in running professionally outside their canyons.
In this decade, an American named Micah True has organized an annual ultramarathon trail run deep in Copper Canyon. Organizers award as prizes 30,000 pounds of corn and $6,000 cash. In 2007, the top American ultramarathoner, Scott Jurek, participated, winning in a time of 6 hours and 32 minutes. But Arnulfo, a Tarahumara finished second in 6 hours and 50 minutes. In 2008, Americans won the top two spots, and local Indians the next eight.
So, it's hard to figure out just how good as runners the Tarahumara really are. There are only about 50,000 of them, so there isn't a big enough sample size for there to be many running prodigies. And they are sometimes malnourished (eating mostly corn), they chain-smoke, and they regularly get falling down drunk. A common estimate is that 100 days per year are devoted to either heavy drinking or recovering from benders. (Like the Japanese, they're emotionally reticent except when they've had a snootfull.) So, they're pretty darn good, but it's hard to get a precise sense of how good.
It's now theorized that their running style (very short strides, landing on the ball off the foot rather than the heel, as is necessary with a long stride) helps them avoid injuries while running on rugged trails. And their running in crummy sandals instead of cushioned supershoes means that their foot muscles don't atrophy, so they don't get the many injuries suffered by American runners.
Indeed, it occurs to me that there might be a hint of an explanation here for one of the more curious trends in sports history. Americans used to be outstanding distance runners. In the 1960s, three American high school boys, Jim Ryun, Marty Liquori, and Tom Danielson, running in low-tech shoes broke the four minute barrier for the mile, but it was 32 years before it happened again (Alan Webb). In 1972, Frank Shorter won the Olympic marathon, which opened the door to the famous running fad of the 1970s. Soon, everybody was running. The Nike Corporation began selling enormous numbers of ever more technologically advanced running shoes.