Zach Hambrick has always been fascinated by exceptional performance, or what he calls “the extremes of human capabilities.” Growing up, he’d devour Guinness World Records, noting the feats it described and picturing himself proudly posing in its pages. By the time he reached college, though, he’d moved on to a new obsession: becoming a golf pro. “I was very serious about it,” he told me. “I practiced religiously. It was very deliberate practice.” Every day, for hours, he’d be out swinging and putting. He expected to find himself on his way to glory. Except it didn’t quite ­ work out that way. Instead, young Zach was confronted with an uncomfortable truth: “I just wasn’t very good.” He saw other students, even kids around town—many of them, far less devoted and far less driven—and many of them played a better game. When he tried out for the college team, he didn’t even come close to making it. “I thought, What is the deal here?”

This was Hambrick’s introduction to an age-old debate: nature versus nurture, genetics versus effort. We’ve been having it long before we knew what DNA was. Right around the same time Gregor Mendel was messing about with his famous peas, Charles Darwin’s cousin, Francis Galton, was positing that genius tends to run in families. Take almost any enterprise and find its most famous voices, he argued, and you’re led to family trees of great accomplishment, much like his own. (He would take this notion to an extreme with his eugenics program.) And, while that view hasn’t survived in its extreme form, the basic question still guides modern research—not nature versus nurture so much as just how much nature, and just how much nurture?

After finishing college, Hambrick began graduate work in psychology at Georgia Tech, with Timothy Salthouse, looking at aging and expertise in older adults. Despite his failures at golf, Hambrick was still very much of the belief that, given enough effort, you could reach excellence. Maybe golf just hadn’t been the right thing for him. In 1996, when the Olympics came to Atlanta, the students had to leave campus to make way for the athletes and visitors, and Salthouse suggested that Hambrick spend a few months at Florida State University. There, he ended up working with Anders Ericsson, a professor of psychology. A couple of years earlier, Ericsson and Neil Charness had published a provocative paper arguing that training and so-called deliberate practice could describe performance differences that had been previously ascribed to innate talent. “The traditional view of talent, which concludes that successful individuals have special innate abilities and basic capacities, is not consistent with the reviewed evidence,” Ericsson and Charness wrote. “Differences between expert and less accomplished performers reflect acquired knowledge and skills or physiological adaptations effected by training, with the only confirmed exception being height.” In other words, training was everything. Hambrick could have become a world-class golfer with enough practice. Maybe he’d given up too soon.

It’s a provocative argument, and one that Ericsson still espouses over two decades later, having made a single modification to his list of exceptions: body size joined height as one of only two areas with any possible genetic influence. When we spoke recently, I presented him with multiple papers from different labs, from studies on the heredity of talent in twins to genetics papers on specific gene variants implicated in performance. But he held firm to his argument. He told me he had yet to encounter someone presenting him with evidence that anything other than practice matters. (He did, in a later conversation, add that the age at which one begins practicing can make a difference in someone’s achievement level.) “I have no problem conceptually with this idea of genetic differences,” he said when we first spoke, “but nothing I’ve seen has convinced me this is actually the case. There’s compelling evidence that if it’s length of bones, that cannot be explained by training. We know you can’t influence diameter of bones. But that’s really it.”

If that’s true, it means that the sky is the limit, especially if you’re dealing with areas other than athletics, where length of bones can offer no competitive edge. Follow your dreams and, with enough training—an average of ten thousand hours, as the famous formulation goes—you can reach them, whether they involve golf or poetry. (It’s important to note here that Malcolm Gladwell, who popularized Ericsson’s work in his book “Outliers,” takes a much more nuanced position and has argued that practice isn’t sufficient. “I could play chess for 100 years and I’ll never be a grandmaster,” he has written. “The point is simply that natural ability requires a huge investment of time in order to be made manifest.”)

But Hambrick obviously didn’t become a golf pro. And, if you look closely at ten thousand hours as an average, rather than absolute, number, you can start to see a problem with it. If, as shown even in Ericsson’s own data, some people require fewer hours and some require more to reach an identical point, doesn’t that imply that some individual difference other than practice is at play? When I brought this issue up with Hambrick, he noted that, in his introductory psychology course, some of the students who study very little do better than the ones who study a lot.

So I asked Ericsson if, given all the advances in genetics research and all the work on the science of expertise and élite performance that has taken place since his original formulation, he still believed in the preëminent importance of training. Do natural, heritable abilities really mean nothing? If, for instance, he himself could choose my trainer and design the perfect training plan, could I become a world-class pianist? (I chose this example since I played for many years in my youth and easily have ten thousand hours in hand.) At first, Ericsson demurred, refusing a straight yes-or-no answer in favor of asking questions about my past. Why hadn’t I been better as a child? Perhaps I wasn’t motivated? No, I assured him, I was. Perhaps my teacher wasn’t qualified? No, I responded. She was a former professor at a music conservatory in Russia. Maybe, I countered, I’m just not particularly talented at piano. He refused to accept that, and ultimately blamed my teacher. Clearly, she didn’t provide the right deliberate practice. I’d be in a different profession today if only she’d been better.

Hambrick blames something else. That summer in Florida, in 1996, he and Ericsson grew close. He remembers meeting often at Ericsson’s F.S.U. office, going to his house to peruse his book collection, taking in F.S.U. basketball games on later visits. “It was fantastic. Wonderful, inspiring conversations,” he recalls. Together with one of Ericsson’s own students, Len Hill, they decided to tackle the golf question head-on. Hambrick spent weeks tracking down data for P.G.A. tour stats and running analyses to determine how the pros reached their level of success. The work continued when he returned to Atlanta, and even went on into the first years of his professorship at Michigan State University. But the analyses weren’t turning out quite as expected—training was not explaining nearly as much as it should. So, while the work languished in unpublished state, Hambrick began to focus more and more on the other possible components of expert accomplishment. Of course, training was important—but how important? “I started to ask, Well, wait a second, can these strong claims about the primacy of practice actually hold up—is there the evidence to back it up?” The more he researched, the more he concluded that the answer was no. No matter how much he had practiced as a teen-ager, he would never have reached the P.G.A. tour. Of course, he’d known that all along, on some level—after all, he quit golf. People do have natural ceilings to their talent in any given area, and after a certain point their success arose from things other than deliberate practice.