Spin Cycle--Nature/Nurture, Which Is It?

Last week I mentioned that Bruiser twists his hair, kind of like I do and that he has done it since he could reliably put hand to hair.  This got Jen to thinking and this week's Spin Cycle topic is Nature vs. Nurture.
Just looking at my boys I know there is a lot to be said for nature.  It is easy to see the physical traits that each boy has gotten and from whom they got them.  The less tangible traits are a bit harder to see, but they are there.
Turbo has Nick's out going personality, has since he could talk.  He's the kid who would say Hi to any kid he saw in the grocery store, can make friends with anyone and will with everyone.  The confidence and friendliness Turbo has comes directly from Nick.  A love of visual things--having to see something, then being able to create something else from it, is a trait from me.  I need a guide of some sort, then I can be creative.
Bruiser, well his personality is more like mine--a bit cautious initially, but once we are comfortable we are just as friendly as Nick and Turbo.  However, Bruiser has a drive to create and this comes directly from Nick.  They both love to draw on anything, with anything.  This is a good thing, but less good for my walls (however, Nick does know not to draw on the walls, we're still working on Bruiser).  Bruiser is also fascinated with books.  This, I think, comes from me.  While Trubo loves to hear a story, Bruiser has been interested in looking at, carrying around, and most recently sleeping with books.  He has been "reading" them to himself and his stuffed animals for a while now.
We see the differences in the attitude toward bikes.  Turbo has not really been all that interested in his bike.  He likes it now that he has learned how to ride, but it is not a passion.  Bruiser on the other hand, loves his bike.  He likes nothing better than to zoom up and down the side walk.  He will be riding a two wheeler far sooner than Turbo did.  The love of biking--that is a Nick trait.  I learned to ride my bike at about the same age as Turbo.  It was never more that a means to get around.
I see a lot of nature in the interests and traits that my kids have.  I'm sure as they grow nurture will come to play a bigger part in who they become.  And that right there is what the whole nature vs. nurture thing comes down to.  When they are little nature wins out.  As they grow nurture becomes more important.  My boys are still small, so I see more nature in them, it has not been covered up by nurture (peer pressure, incidents that leave their mark in one way or another, influence of other authority figures, etc.).
So what do you think--nature or nurture?