A high level mathematician most likely won't be able to play chess at a grandmaster even if he devoted as much time to the endeavor. Likewise a chess grandmaster will never develop the insight of a musical virtuoso with the same level of dedication to the craft etc. etc.
Clearly all of these things require an appreciable degree of mantel acuity yet can't be translated or converted into one another. Despite this people claim that an I test is an accurate measure of intelligence. Why?