Opinion

Book tackles controversial search for the ‘athlete gene’

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Glance through a list of the Boston Marathon winners, and you see a sea of Kenyan flags. In the last two decades, 16 of the 20 top finishers hailed from Kenya and three from Ethiopia.

Compare the populations of America (313 million) to Kenya (41 million), and the results are even more astounding.

Only 17 American men have run a marathon in less than two hours, 10 minutes (that’s 4:58 per mile). In October 2011 alone, 32 Kenyan men accomplished this feat.

Five American high-school students in history have run under a four-minute mile. In one Kenyan high school, there were four sub-four milers attending class at the same time.

The statistics don’t lie — but what exactly are they telling us? Some point to cultural and socioeconomic reasons for Kenya’s long-distance dominance — the fact that children there run great distances simply to get to school, their diet, even going barefoot.

But according to a new book on the science of athleticism, that’s only part of the story. “It would be blind and silly to ignore the importance of access to equipment and coaching. But . . . it would be just as blind to ignore the conspicuously thorough dominance of people with particular geographic ancestry in certain sports,” writes David Epstein in “The Sports Gene” (Current), out Aug. 1.

“Namely, of course, that the athletes who are fleetest of foot, in both long and short distances, are black.”

In his book, Sports Illustrated journalist Epstein tackles the controversial question of how much athleticism derives from genes and how much is molded by training and environment.

In the last 10 years, scientists have found 23 gene variants strongly linked to endurance athletes and around 200 genes that have been associated with physical performance.

But these are only tenuous links at best. “Just as tough as it is to find genes for height — even though we know they exist — it is extraordinarily difficult to pin down genes for even one physiological factor involved in running, let alone all of them,” writes Epstein.

A single trait — speed, for example — likely requires “hundreds, if not thousands of gene variants” to account for it. When you think about the whole athlete, it’s a “dizzying number of combinations,” Dr. Ross Tucker, exercise physiologist at the University of Cape Town, South Africa, told The Post.

Yet you don’t necessarily need gene studies to spot the differences.

“Every study that has examined race differences in body types has documented disparity between black and white people that remains whether they reside in Africa, Europe or the Americas,” writes Epstein.

According to a 2010 study conducted by a racially diverse team of scientists, black adults have a center of mass (the belly button, approximately) that is about 3% higher than whites. The higher center of gravity, which translates to longer legs, equals about a 1.5% running-speed advantage. Conversely, a lower belly button, or a longer torso, gives whites a better swimming-speed advantage.

Those of African descent have “linear” builds and “longer legs and a more narrow pelvic breadth,” which are key to endurance and speed running, writes Epstein. Kenya’s elite runners, largely made up of a specific group of people called the Kalenjin, have been studied most intensely. Two Danish studies show that Kenyan children regularly outperform their European counterparts and had far better “running economy” and endurance without training.

The Kalenjin boys were, on average, 2 inches shorter than the Danes but had legs that were three quarters of an inch longer. In addition, their lower legs were 15% to 17% thinner than the Danish boys’ legs. (Weight on lower legs is important. Add 4 pounds to each ankle and a person burns energy 24% more rapidly, writes Epstein.)

But these physical differences are not yet seen on the genetic level, explains University of Glasgow biologist Yanni Pitsiladis, who’s featured in the book and has spent 15 years studying the genetics of East African runners. He believes it’s “environmental,” chalking up their running superiority to Kenya’s socioeconomic profile, the high altitude, the fact that three-quarters of Kenyan professional runners had to run or walk six miles to school, and other non-biological reasons.

With a similar environmental profile, “anyone could have the same outcome” as the Kenyan athletes, he believes. “You absolutely must have the right genes. But after 10 years of work, I have to say that this is a socioeconomic phenomenon.”

The entire issue of sports physiology is a thorny one.

TV commentator Jimmy the Greek Snyder was fired in 1988 after offering up a theory on the success of black athletes. “The slave owner would breed his big black to his big woman so that he could have a big black kid, you see?” he infamously said.

But others have expressed similar beliefs in less racially insensitive terms. In a 2012 documentary, African-American sprinting champion Michael Johnson said that slavery has helped black physiology.

“It is impossible to think that being descended from slaves hasn’t left an imprint through the generations. I believe there is a superior athletic gene in us,” he said.

While researching his book, Epstein says he talked to many scientists who were fearful of the implications of their own studies.

“One of them told me that he actually has data on ethnic differences with respect to a particular physiological trait but that he would never publish the data because of the potential controversy,” he writes.

A psychologist told the author that he purposely marginalizes the role of genes in order to “send a positive message” to the masses.

“But maybe it’s dangerous, too,” the sports psychologist said, “to say that you’re stuck where you are because you’re not working hard enough.”