This is the classic "Nature/Nurture" debate, which has engaged philosophers and evolutionary biologists since time immemorial. The "Nature" side says that we are born with all the facilities we will ever need. The "Nurture" side says we are born as a tabula rasa (blank slate) which is filled in by our experiences. Common sense, which both philosophers and evolutionary biologists have little of (I belong in the latter category), suggests that our aptitudes for the tasks that face us in life are a mixture of both - someone with no innate genetic ability can, with diligence become reasonably profficient at a task or vice versa.

A good recent example of this (Navigation-Related Structural Change In the Hippocampi of Taxi Drivers) was published in Proceedings of the National Academy of Sciences, vol. 97, no. 8, April 11, 2000, pp. 4398-403. The study by scientists fron University College London presented evidence that the brains of London taxi drivers are more highly developed than those of their fellow citizens. More experienced drivers had larger hippocampi suggesting that Nurture had a strong effect. In other words - practice makes perfect.

Incidently the study won an Ignoble Prize along with the paper: An Analysis of the Forces Required to Drag Sheep over Various Surfaces."
[PUBLISHED IN: Applied Ergonomics, vol. 33, no. 6, November 2002, pp. 523-31.

For more details on the Ignobles see:

http://www.improbable.com/ig/ig-pastwinners.html

It is hilarious.