It’s official. Africans rule the world. At least the world of marathon running, that is.

It comes as no surprise to hear that a runner from Africa — particularly Kenya and Ethiopia in East Africa — has won a marathon in any given place of the world.

Geoffrey Mutai, a Kenyan, made history when he won the ING New York Marathon on Sunday, in a record 2 hours, 5 minutes and 6 seconds. Mutai, who also made history by setting a record in this year’s Boston Marathon, beat the New York Marathon record set by Ethiopia’s Tesfaye Jifar in 2001.

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Coming in second in New York was Kenya’s Emmanuel Mutai, winner of the London Marathon and no relation to the champion (the second and third place winners in London’s men’s race in April were from Kenya, as were the first and third place women champions). And Tsegaye Kebede of Ethiopia, the 2008 Beijing Olympic bronze medalist, came in third.

All in all, African runners won the top five spots and six of the top seven places. In the men’s race, only one American has won since 1983, and no American woman has won since 1977.

Meanwhile, In Saturday’s Savannah Rock ‘n’ Roll Half Marathon, Reuben Mwei of Kenya won the men’s race, as Mula Seboka of Ethiopia won for the women’s contest.

With the 2012 London Olympics soon approaching, runners from East Africa are expected to dominate and make it hard for Americans and other to gain a foothold in the sport. Something’s going on here. But what exactly explains the African dominance in long distance running?

There are numerous explanations, depending on who’s doing the talking. Somewhere in there, facts are mixed in with stereotypes and anecdotal evidence. But essentially, it comes down to a discussion of Nurture”>nature vs. nurture is a common reason given for African prowess in marathon races, though the explanation is at times overdone.

For example, one sports columnist suggests that Americans, unlike Africans, simply aren’t interested in marathons. Their heart isn’t in it. American children want to play basketball, football and baseball, and they don’t dream of running.

Others cite the work ethic in nations such as Kenya. There are the stories of Kenyans training at an earlier age, of walking five kilometers every day to school, and their willingness to endure punishment through hours of hard training at high altitudes. Further, in East African nations with high poverty and high unemployment, there is an economic incentive to train to win and remove oneself from a tough economic condition.

For example, Geoffrey Mutai claimed $200,000 for his recent victory in New York. A strong argument can be made that commercial factors — the high level of endorsements — are driving the popularity of distance running over track.

In addition, whereas Western nations have surpassed other countries in certain sports due to their technological superiority, poor, low tech East Africans have bridged the gap by dominating in this most accessible sport that requires legs and a place to run.

At least one American writer and former marathon champion takes the concept of nurture a step further by suggesting that some nations have a strategy of throwing a team of dozen runners into major marathons, in the hopes that one will win. He offers that a “slightly more totalitarian” U.S. government would be able to win marathons, or at least see more Americans in the top ten, by conscripting its top NCAA cross-country runners and sending them to a training camp.

Nurture can explain why certain ethnic, racial or socioeconomic groups gravitate towards other sports and excel — or don’t. For example, many boxers of all racial backgrounds grew up poor. Whites once dominated basketball, which later became the purview of the black athlete — despite gains made by players from Eastern Europe and China.

Sports such as golf and tennis were once considered “white sports,” and racism was a barrier to entry for African-Americans. Meanwhile, pioneers such as Arthur Ashe and Althea Gibson broke barriers, while Tiger Woods and the Williams sisters have sparked interest and paved the way for a younger generation of black athletes.

Baseball has seen the decline of the African-American player — who excelled under the Negro Leagues yet was barred from the major leagues until Jackie Robinson — and the rise of the Dominican player. The U.S. major league teams established academies in the Dominican Republic, where children are cultivated, housed, and trained in modern facilities.

A more controversial reason than nurture that is offered for the supremacy of African marathoners is nature, in other words genetics. The idea that Kenyans are natural athletes, in what would amount to an evolutionary and Darwinian process, has its followers.

There are observers who would attribute genetics to the strength of northern European power lifters, the ability of Asians to excel in diving and gymnastics, the sprinting prowess of West Africans, and the advantage that northern Africans have in middle distance running.

And for East African endurance runners, suggested genetic factors in their favor include the nature of their muscle fibers, thin build, naturally low body fat levels and narrow hips, lung capacity, and superior gait.

In the case of athletic prowess among Kenyans and Ethiopians, some writers reject the role of nurture entirely, and believe it’s all about the DNA — the same DNA that makes it more likely for blacks to suffer from sickle cell disease, and makes whites more vulnerable to cystic fibrosis.

However, recent studies have found no genetic explanation for the East African running phenomenon. One could argue that the genetic argument tends to belittle the accomplishments of these Kenyan and Ethiopian runners, as if their hard work and perseverance mean nothing, and they owe their success to little more than the luck of birth and DNA.

The risk of this school of thought is that blacks are pigeonholed as great athletes, and stereotyped as intellectually inferior — even as the president of the United States, the son of a Kenyan father, is one of the most brilliant individuals around.

So is it an accident of birth, good genes, hard work, a hunger to win or social environment that produces these superior East African marathon athletes? The truth may very well lie somewhere in there.

In the meantime, these men and women are stepping up their game, and changing the game for runners around the world. And there’s no hint that this will change anytime soon.