Like many others who read Malcolm Gladwell's book "Outliers" when it came out five years ago, I was impressed by the 10,000-hour rule of expertise. I wrote a column espousing the rule, which holds that to become a world-class competitor at anything from chess to tennis to baseball, all that's required is 10,000 hours of deliberate practice.

David Epstein has convinced me I was wrong. His thoroughly researched new book, "The Sports Gene," pretty much demolishes the 10,000-hour rule - and much of "Outliers" along with it.

Epstein's book suggests that while real elite athletes have put in plenty of practice time, their aptitude is enhanced by their genes.

If 10,000 hours of deliberate practice is necessary and sufficient for world-class performance, Epstein asks, why do some people reach the master level in chess after 3,000 hours while others require 23,000? The average number of hours needed for many pros may be about 10,000, but it varies widely.

The reason for the variation is genetic, Epstein says. In one study, researchers at Indiana University, University of Minnesota, Texas A&M University, Washington University, Pennington Biomedical Research Center, and Laval University in Quebec measured changes in VO2 max, an indicator of aerobic capacity, in people who followed a strict exercise regimen. About 5 percent of participants boosted their VO2 max levels by an astonishing 40 percent to 50 percent. Another 5 percent, however, saw almost no gain at all, and the rest fell in between.

The clincher was that, although a subject's rate of improvement had little to do with how fit he or she was to start with, members of a family showed somewhat similar gains. The rate of improvement varied 2.5 times as much between families as within families, highlighting the importance of genes in determining how much improvement occurred. As one of the researchers told Epstein, "Unfortunately for the low responders in these studies, the predetermined (genetic) alphabet soup just may not spell 'runner.'"

The research does not suggest that genes are dominant and training is irrelevant; instead, it says that the benefit from training is partially driven by genetics, so that a combination is required for top performance.

Consider professional baseball players. A batter needs years of practice to recognize subtle clues about pitches and thereby have a better chance of hitting them. This is why even the best baseball players tend not to hit well when they face softball pitchers; their accumulated clues are of little use.

Yet professional batters also tend to have extremely good vision - they can see the small nuances in a pitcher's delivery to begin with. One study of minor- and major-league players found that their average vision measures 20/13, which means they can read a letter at 20 feet that a normal person could make out only at 13 feet. To see how rare this is, consider that, in a large sample of eye tests from China, vision better than 20/17 occurred in only 1 in 200 people.

Epstein says that the specific genes and attributes associated with high performance vary from sport to sport (raising the question of whether his book should be more appropriately titled "The Sports Genes"). Basketball players tend not only to be tall, but also to have long arm spans. In a controversial theory, Epstein suggests a disproportionate share of sprinters and jumpers carry sickle-cell trait and/or low hemoglobin, which may boost fast-twitch muscle fibers. High jumpers tend to have very long Achilles tendons. And so on.

Ultimately, Epstein's book is consistent with the literature about IQ. Neither athletic nor intellectual performance is solely a matter of nature or nurture. Instead, the two interact. We can all improve with practice, but some will see will bigger gains than others.

Peter Orszag is vice chairman of corporate and investment banking at Citigroup.

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