This Guardian Article suggests that the actual identifier of an expert is the ability to spend 20-30 hours a week practicing your chosen subject to achieve at least 10,000 hours of practice. At this point you are an expert. They go on to support this suggestion with music, computer programming and mathematics.
The old addage that Practice makes Perfect may be true after all - there are no 'born genius' found in their article. Only people who were able to put in the practice, were around at the right time and the right place and has some increadible luck! Nice (but long) article.
