Every time I hear Jacqueline du Pré play the Elgar Cello Sonata, I am moved to tears. The credit for my tears go to both du Pre and Edward Elgar-Elgar for composing such a masterpiece, and du Pré for expressing it so well. The combination is nothing short of breathtaking.
Are both of their musical attainments solely a result of practice? Jacqueline du Pré was given the Elgar concerto by her teacher when she was 13. Not only did she memorize the concerto in 4 days, but she was described by her teacher as performing it "almost impeccably." Is practice during the course of those 4 days the sole explanation for her brilliance?
As mentioned in my last post, K. Anders Ericsson has proposed a model of expertise acquisition in which deliberate practice is the single factor responsible for elite attainment. Researchers adopting this extreme environmental position generally use case studies as evidence, and make the point that it even took Mozart 10 years to compose anything that we would wish to call a masterpiece. Often this is dubbed the 10-year rule.
The problem with focusing on the Mozart's of the world though is that they already have been selected for high levels of general intelligence and musical ability. In fact, Cox  estimated that Mozart, Bach, and Beethoven all had IQ's that fall somewhere between 125 and 155. Even those with an IQ of 125 are more intelligent than approximately 95% of the general population. Therefore, while Mozart may have required lots and lots of practice to produce his great works, his high intellect may have also contributed to his musical genius.
In a recent journal article called Becoming an expert in the musical domain: It takes more than just practice , the authors scientifically address this issue.
According to their Summation Theory, general intelligence, domain-specific skills, and deliberate practice are all factors that independently contribute to music achievement. According to the researchers, "if Ericsson's practice theory is true, then general intelligence and musical ability should not add predictive value after accounting for practice time, nor should expert musicians differ from lower-level musicians in general intelligence or raw musical talent (p.332)." The following equation represents their model:
Musical achievement = general intelligence + domain-specific skills + practice
They tested this model using a statistical technique called regression and found that general intelligence (as measured by a test of asbtract reasoning), music ability (as measured by a test of tonal and rhythmic differentiation), and time devoted to musical practice and lessons significantly accounted for more of the variance in music achievement than practice alone. In other words, even with practice entered into the equation, both general intelligence and domain-specific music ability added to the prediction of the variance in musical achievement above what would be expected by chance.
According to their Summation Theory, as individuals enter into more competitively selected musical groups, their average levels of general intelligence and music ability will be elevated compared to individuals in less selective musical groups. The researchers indeed found that higher-level musicians had higher average levels of all three factors than the high school band members. This is all the more reason for scientific studies to investigate the predictors of musical achievement among samples diverse in ability, as a sample with a restricted range may cause the correlation between two variables to be severely reduced. This could result in researchers finding no significant relationship between abilities and achievement when they actually do exist.
Can anyone be a Mozart?
The authors conclude that not everyone can be a Mozart.
While I think this study is an important step toward understanding the contributions to music achievement, I think there are lots more questions to answer. For instance, the authors do concede that correlation doesn't necessarily mean causation. Perhaps achievement motivates musicians to practice more, and lack of achievement causes musicians to practice less. Then you have what has been referred to as The Matthew Effect, where the rich get richer and the poor get poorer.
Another interesting question the authors raise is the extent to which people with a minimum level of general intelligence and music ability are capable of improving their skills through practice. I think it would also be interesting to determine more precisely what those "minimum levels" are, and the extent to which practice can modify innate proclivities and brain structures. There is some exciting research with taxi drivers showing that experience can indeed affect brain structure such as the amount of gray matter volume in the hippocampus . More such studies should be conducted in various domains of expertise.
Without a doubt though, these questions can and should be investigated using scientific methodology. Also, it is my view that multi-factor views of achievement are the way forward. Another important factor not mentioned here is the environment, but I'll take that up in later posts.
 Cox, C. (1926). Genetic studies of genius. Vol. II. The early mental traits of three-hundred geniuses. Stanford, CA: Stanford University Press.