A while ago, I realized that it is actually ALL nature, in that the child's brain will only learn what it is shown and not what it is told.
So in other words, if you are walking through the store with your child and he keeps asking for things and grabbing at them and you keep telling him no and he keeps doing it and you wonder why he would do this even though you know a lot about discipline, but then once you leave that store, you go out and trade your car in for a new one for the third time this year, it means that the child does learn from you, but rather, it's what you do and not what you say that he will pick up. I have seen this happen so many times now, that it is not even any kind of revelation anymore.
So yeah on one side you have a child's biological connection to their parents that deicides behavior, but on the other hand you have the child who does actually learn from their parents behavior, which does count as a kind of nurture, but since it is the child's mimicking brain in action rather than his listening to what is being told, I see it as more of a nature thing. A child will only respond to education if he sees that his parents respond to it and see it as a worthy enterprise. He will only use proper manners when he sees them in use, rather than just being nagged at to act proper.
Yes there is some nurture, but it's a natural nurture.