Anyways I think it's not a question of intelligence but the capacity for work you can enjoy putting in and that dosen't feel like work but like you are doing what you like doing, and you can do it for many hours on end...
Those who were mature enough to reach this level of seriousness and passion, combined with work ethic, at early age become prodigies (in chess, music, math, anything)
Prodigies are those children who show an unusual aptitude for something and so are encouraged and trained in that field. No one knows the way it occurs; probably the way their neural pathways developed are unusually well-suited for the thought processes inherent in the understanding of the subject. Five-year-old Aram Khachaturian had just started piano lessons when he displayed the ability to play a piece he had just heard and compose some variations on it. There are rare individuals like this that just seem to pick up math or music or chess "at first glance".
As for work (even if it is fun for someone) being the key, remember that chess prodigies Capablanca and Spassky both admitted to being lazy and not bothering to study the game much. And there are people who can solve difficult, multi-step math exercises in their head faster than they can be typed into a calculator. No amount of work will give most mathematicians the ability to do this.
I'm not saying dedication and work are not helpful, but they don't provide the total explanation.
Fair enough.. the reason we are all here right now is some kind of obsession/passion for chess.. to the extent we are enjoying just talking about it.. maybe the "born this way" thing is right... In regards to Capa and what you describe I could compare to Arthur Rubinstein who was always saying how he loved to eat choclate and cherries while practicing and he wouldn't practice alot.. he even went to Juliard where everyone practices 8h a day and told them more than 3 is too much in a lecture he gave..
But his point I agree with, the amount of work is not what makes or breaks.. but the quality.. like what Rubinstein could go through and the types of exercises and deconstructions he did in 3 h + the other 16h a day in which he was thinking mostly about music was more than enough..
You need muscles to lift weights and you also need things like bones. Does that make the idea that you need muscles wrong?
No, but that doesn't mean that it is the total and unique factor that will yield a definitive correspondence. Of course in the case of something as simple as lifting weights it is more important (and obvious) than in an endeavor such as chess that requires a wider range of talents