From Mathematical Expertise Brian Butterworth Chapter on Mathematical expertise. In K. A. Ericsson's (Ed.), Cambridge Handbook of Expertise and Expert Performance. (pp. 553-568) Cambridge: Cambridge University Press (150k) (2006), URL: http://www.mathematicalbrain.com/
Charles Darwin, in a letter to Galton, wrote "I have always maintained that excepting fools, men did not differ much in intellect, only in zeal and hard work; I still think this an eminently important difference."
The article concludes:
"It may also be the case that some of us are born with a disposition to enjoy or even be obsessed with an orderly domain like mathematics. However, there is no evidence at the moment for differences in innate specific capacities for mathematics"
P.S. For such an eminent publisher, proof reading is poor. The formula on page 561 is wrong but can be easily corrected.
(via Evolutionary Psychology discussion group)
P.S (via 3quarksdaily) Another article in similar vein:
The truth about grit.
Maybe now one can try to find out about what makes some gritty: topic, person,environment, some gene expression...? But from the stories of various abnormal cases, it seems to me that most humans have enoramous potential if only we know how to tap it.
P.P.S.The Making of an Expert is drawing some attention in blogs.