Not sure about this one. I think that Gheng and Bug Smasher are correct when it comes to motor skills and academia but I think it falls short where artistic endeavour is concerned. Yes you can teach someone perspective as an artist or teach someone how to play scales as a musician but there is definitely an 'unlearnable' bit when it comes to artistic pursuits. All of the top musicians have undoubtedly put in the hours of practise and sweat, but so do a lot of other musicians who never get within artillery distance of the top guys. There's something else that you need. Would you call it natural talent or aptitude? Difficult one and something that my colleagues and I often discuss.
Personally at the moment I tend to lean towards the nurture argument. If you are exposed from birth to good music or any other category of the arts and are encouraged by parents and siblings who share that interest then you have a head start.