THE WORLD OF SPORTS runs on merit, right?

If you're an athlete, your skills, ambition and work ethic are supposed to determine your career path, rather than nepotism or insider connections. Which means you can come from anywhere and succeed. Clint Dempsey grew up in a trailer park in South Texas, playing soccer with migrant kids from across the Mexican border. LeBron James shuttled among apartments in the worst neighborhoods of Akron as a child, with a teen mother and no father. Starting at age 7, Michael Oher of The Blind Side fame bounced from foster home to foster home to the Memphis streets. Their rise from humble beginnings, along with the triumphant tales of many other athletes, are core chapters of the great sports mythology. It's from competition, in fact, that we get the phrase "level playing field."

If only it were so. Yes, talent and grit drive sports success. But so does an athlete's background, and more than you might think. That's the lesson from research published recently in the International Review for the Sociology of Sport. Joshua Kjerulf Dubrow of the Polish Academy of Sciences and Jimi Adams of Arizona State University studied NBA players from 1994 to 2004. They found that among African-Americans, a child from a low-income family has 37 percent lower odds of making the NBA than a child from a middle- or upper-income family. Poor white athletes are 75 percent less likely to become NBA players than middle-class or well-off whites. Further, a black athlete from a family without two parents is 18 percent less likely to play in the NBA than a black athlete raised by two parents, while a white athlete from a non-two-parent family has 33 percent lower odds of making the pros. As Dubrow and Adams put it, "The intersection of race, class and family structure background presents unequal pathways into the league."

Contrary to popular perception, poverty and broken homes are underrepresented in the NBA, not overrepresented. For example, while 45 percent of black male children in the U.S. live in households earning no more than 150 percent of the poverty line ($22,050 for a family of four in 2010), just 34 percent of black athletes in the NBA grew up in that financial situation, according to Dubrow and Adams. Thirty percent of white American males come from below-average-income homes without two parents, but not one white NBA player had that background. Economics and family boost or drag an athlete, like in other professions.

The NBA of our imagination -- a league that functions as a conveyor of inner-city hoop dreams -- actually did exist at one point. In the 1960s and '70s, more than 90 percent of NBA players were from urban areas. But as the game grew more popular and attracted more corporate sponsors, pro teams and colleges expanded the search for talent, and suburban (and foreign) high schools began strengthening their programs. As a result, it now takes more resources -- a lot more -- to compete at the highest level. "You need facilities, equipment and transportation, not to mention coaches and volunteers," says Peter Roby, former director of the advocacy group Sport in Society and the athletic director at Northeastern University. "And what we've found is that kids in cities are now much less likely to participate in sports than kids in suburbs."

According to research conducted in 2009 by The Mag, NBA players come from hometowns with a median population of around 110,000, and that population is 59 percent white and as educated as the U.S. as a whole.

Pro basketball simply doesn't conform to many old stereotypes anymore. Just look at Kyrie Irving, the No. 1 overall pick in this year's draft: He was born in Melbourne, Australia, was raised by his international-hoops-playing dad and grew up in suburban West Orange, N.J.

Athletes and fans invest so much emotion into sports that we convince ourselves that they possess some kind of transformative power. We believe that skills always trump circumstances. But that's a myth. With funding for school athletic programs on chopping blocks across the country, it's important to understand what the numbers actually tell us. Yes, your talent is important. But your very first teams -- your family and your earliest support structures -- matter an awful lot too.