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.

In one study, for instance, Hambrick looked at pianists and measured their working memory, or the ability to keep chunks of information in mind and accessible for short periods of time. In the past, working-memory capacity has been found to be heritable. In his sample, it predicted success even when you accounted for the effects of practice; pianists with better working memory were better at sight reading—and increased practice did not alter the effect. When he looked back to one of the most frequently studied groups in expertise research, chess players, he found that, in addition to working or short-term memory, three more components of cognitive ability—fluid reasoning, comprehension knowledge, and processing speed, all abilities that are, to some extent, heritable—were related to performance. This was especially true of younger and less experienced players. If you’re naturally better, you don’t have to practice quite as much to get good.

So how much did practice actually explain? In a 2014 meta-analysis that looked specifically at the relationship between deliberate practice and performance in music, games like chess, sports, education, and other professions, Hambrick and his team found a relationship that was even more complex than they had expected. For some things, like games, practice explained about a quarter of variance in expertise. For music and sports, the explanatory power accounted for about a fifth. But for education and professions like computer science, military-aircraft piloting, and sales, the effect ranged from small to tiny. For all of these professions, you obviously need to practice, but natural abilities matter more.

What’s more, the explanatory power of practice fell even further when Hambrick took exact level of expertise into account. In sports—one of the areas in which deliberate practice seems to make the most difference—it turned out that the more advanced the athlete, the less of a role practice plays. Training an average athlete for a set number of hours yields far more results than training an élite athlete, which, in turn, yields greater results than training a super-élite athlete. Put differently, someone like me is going to improve a great deal with even a few hundred hours of training. But within an Olympic team tiny differences in performance are unlikely to be the result of training: these athletes train together, with the same coach, day in and day out. Those milliseconds come from somewhere else. Some may be due to the fact that genetic differences can account for some of the response to training. At Stanford’s ELITE study, which looks at the most accomplished athletes in the world, Euan Ashley, a professor of medicine and genetics, is studying how an Olympian’s body may respond differently to a given training regimen. Some changes are due to genetic variants that may affect blood transport or oxygen uptake or fat metabolism, or any other number of factors. Some are due to sheer luck—How much sleep did you get? How are you feeling? And some, of course, are due to hours of training. But at the top of the top of the top, the power of additional training falls off sharply.

So where else, exactly, do performance differences come from? While Hambrick’s work has been focussed more explicitly on practice and genetics, David Lubinski, a professor of psychology at Vanderbilt University, has been approaching the question from a slightly different angle: through what’s called the Study of Mathematically Precocious Youth (SMPY), a longitudinal study of the lives of students who, by the age of thirteen, had scored in the top one per cent of mathematical-reasoning ability and were then selected to take part in an enriched educational environment. (The study, co-directed for many years by Lubinski and his wife, Vanderbilt’s education-school dean, Camilla Benbow, was described in detail in a recent article in Nature.) It’s a crucial supplement to work like Hambrick’s; the data you get from close observation of the same sample and the same individuals over time can answer questions other approaches can’t. “What kinds of practice are more effective? What approaches more effective for some people than others?” Hambrick asks. “We need all the pieces to the puzzle to maximize people’s potential. Lubinski’s work on mathematically precocious youth is an essential piece.”

Now, more than four decades since the SMPY observation began, we are beginning to see some answers. Perhaps not surprisingly, kids in both the SMPY sample and an unrelated cohort of talented students identified by Duke University excel at measures like academic accomplishment, patents, publications, academic tenure, and organizational leadership. They reach full professorship and C.E.O. status at rates far above any population norm. They were selected on nothing more than measurable intellectual promise, and here they are.

That is not the whole story, though, as Lubinski points out. To him, the interesting finding is the striking range of abilities within this élite sample. “Individual differences in the top one per cent matter,” Lubinski told me. “People think of the top one per cent, whether in I.Q. or reasoning or what have you, as categorical. But that top contains one-third of the ability range you see in other samples. There is a huge amount of psychological diversity among the gifted.” Some accomplish a lot, but some, even with all their promise, end up indistinguishable from their initially less gifted counterparts. Genes give everyone a possible peak, but whether you reach that peak depends on a constellation of other factors.

Part of the difference in accomplishment, it turns out, really is due to practice, just like Ericsson argues. “What separates intellectually talented kids from their intellectual peers when it comes to actual creative advances? A lot of it is how much people are willing to work,” Lubinski told me. Some people are gifted, or “intellectually talented,” as he prefers to refer to them, but don’t want to work forty hours a week, while some want to work more than sixty hours. “That has huge implications. Chance always favors the prepared mind.” Practice, work ethic: differences that aren’t apparent at age thirteen will, in their presence or absence, become magnified by the time you hit your forties or fifties. (As it turns out, though, even work ethic may be heritable. Hambrick has recently published a study on the heritability of practice, using eight hundred pairs of twins. “Practice is actually heritable. There have now been two reports of this—ours, and one using ten thousand twins. And practice is substantially heritable.”)

Also crucially important is one of the first things that critics of studies like this point out: environment. These kids aren’t just identified young; they are then nurtured in a way others are not. How much of their success lies in opportunity? It’s a question Lubinski and Benbow have studied in some detail. In three educational–intervention studies, they have demonstrated that, if you compare intellectually talented children who have had the sorts of developmental opportunities the SMPY affords, they end up doing better in terms of measurable intellectual achievements like number of patents and publications than their intellectual peers—individuals matched on general intellectual ability—who have not had that enriched experience.

Opportunity must be there. Genes are great, but they need to have the right environment in which to flourish. You don’t just give birth to a “genius,” whether an academic or an athletic or an artistic one. You also give her the right environment, train her, encourage her, support her, challenge her, respond to her individuality. And who knows what else may ultimately matter. “All the abilities we assess, we still miss things,” Lubinski points out. Lewis Terman, the intellectual forefather of giftedness studies, famously missed two Nobel laureates in his selection. They were cut from the initial samples for not being gifted enough and never had a chance to take part in his study. “You’re tapping potential, but there’s also passion, commitment to work, people who want to do any one thing. People really vary. The diversity of human individuality is breathtaking.”

That diversity originates in our genetic code. But it becomes infinitely more complex as you add life into the mix. We cannot predict with accuracy who will become élite in a given field, but we know that genes and environment matter and that we all have different natural peaks that we can reach through application and training. Saying that training is everything may be tempting, but it’s wrong. “One of the criticisms people direct at us is that we’re killing people’s dreams,” Hambrick says. “But I think in fact it’s the contrary: the more we can know about the origins of expertise, including training but everything else, the more we can help people be their best selves.” Perhaps it’s just enough to know that no matter how many hours I spend in the pool, I won’t be Katie Ledecky. And I’m pretty sure I’m not going to become Brad Mehldau, either, even if I get a better teacher.