Both. But I think Nurture more, because you can take a wild wolf pup from the wild and nurture it to be tame. It's nature would be to rip your face off when hungry (as you're meat), but nurture told it not to. So it waits for its feed at the bowl or something.
So with humans, I think it's similar. How can you learn something that's never shown? If you're brought up in a violent and angered way/family, then you're not going to know much else, and it's not entirely that individual fault. We don't get to choose our families.
Influence. From parents, media, other people....all helps to shape who we are.