By the way, there are tens of studies on this subject. They are all very interesting. Please grab the book Sports Gene sometime and give it a read. It is very interesting.
Speaking of gifts, there ARE certain things that you are born with, that's for sure. Like a longer and stiffer achilles tendon, which can make you jump higher. Also speed is something interesting. Every sprinter have the ACTN3, a gene that allows for the production of alpha-actinin-3, a protein found in the fast-twitch muscles of almost every top sprinter who has ever been tested for the gene. And in one study that involved thousands of kids, none who was slow as a kid got faster as an adult. No practice can apparently get you extra fast twitch muscle fibers.
Those are the natural things I do not disagree. My point is, once you pick up a racket, basketball, violin or whatever, that's where the nurture part pulls ahead in my opinion.