Pitsiladis and his colleagues found a similar pattern in Ethiopia. What was not shared between the Ethiopians and the Kenyans, however, was a particularly large proportion of their genes.
The maternal line of DNA has been found to be more influential in endurance than the paternal, so Pitsiladis's group analyzed that genetic material and found that Ethiopian and Kenyan athletes "could not be more different genetically," Pitsiladis says. The Ethiopian athletes, for example, were much more likely to have blocks of gene variants common in Europe and Asia than were the Kenyan athletes. Pitsiladis's conclusion is that whatever specific genes are necessary for endurance, they aren't exclusive to either Ethiopians or Kenyans.
His work suggests that some sports phenomena that seem on the surface to be entirely based in genetics might not be. (Or at least not in the way we're used to thinking about genetics. A newer science called epigenetics is unraveling how environment and behavior, such as exercise, can actually turn particular genes on and off in patterns that might be passed on through generations.)
Similarly counterintuitive conclusions about the interplay between nature and nurture have come from outside sports: African-Americans are more prone than white Americans to hypertension, but the trend is not found among black people in some of the countries from which black Americans came, such as Jamaica and Nigeria. That points to the U.S., not to genes associated with blackness, as a culprit.
This is not to say that all ethnicities are the same. Nigerians are known for sprinting, and all Nigerians have at least one copy of the sprint gene variant. But so do nearly all Kenyans, as well as 80% of Europeans, two groups not renowned for sprinting.
A decade ago, when Pitsiladis began to study elite athletes, his medical students would ask why East Africans dominate distance running, to which he would reflexively respond that their secret is in their genes. "But after 10 years of work," he says, "I have to say that this is a socioeconomic phenomenon we're looking at." He feels the same way about sprinters in Jamaica, where scores of spike-clad kids hoping to be the next great runner attend sprint practice on Saturday mornings. (In the 1930s some U.S. sportswriters looked at the prominence of Jewish players in college basketball and suggested that Jews had a genetic predisposition for the game. That notion seems laughable today; the phenomenon was more likely due to the fact that inner-city New York, where many Jews lived then, was a basketball hotbed.)
Strong as the socioeconomic argument is, Pitsiladis adds, "This is not to say that genes aren't important. You absolutely must choose your parents correctly." That is facetious, of course, because we can't choose our parents. Nor do humans usually couple because of one another's genetics. We pair up more in the manner of the roulette ball that bounces off a few walls and eventually settles into one of many suitable spots. Williams suggests that if humanity is to produce an athlete with more of the "correct" sporting genes, the best approaches are to keep spinning the wheel (i.e., keep having babies) or to weight the genetic roulette ball with more lineages in which parents and grandparents have obvious athletic prowess and probably a lot of beneficial genes. The witting merger of superstars (think Yao Ming's parents, who were brought together by the Chinese basketball federation) is rare. Yet there is a particular population in which it is the standard.
THE NATURE OF NURTURE
IF THOROUGHBREDS COULD talk, they might explain just how important it is to choose one's parents. Because athletic ability involves a complex mix of genes, champion racehorses tend to result from multiple generations of mating among athletic horses. The more genes that are involved in an athletic trait, the more generations of athlete-to-athlete breeding it will likely take to get a colt that has collected enough of the right gene variants to make the winner's circle.
Thus the one sure bet at the racetrack is that every top horse has good racehorses not only for parents but also for grandparents and great-grandparents. (In some marquee horse races, winning times plateaued in the mid-20th century, leading some scientists to suggest that centuries of breeding for speed have in fact brought thoroughbreds to their physiological terminal velocity).