I think trying to categorize it as one or the other us where we fail. Both nature and nurture have an impact on your personality as a whole.

I was born liking pain and with thought processes that would lead me to being sub, but my experiences have refined those rough ideas. Some are born exactly what they will always be, some have no idea until much later in life.

There isn't a one-size-fits-all answer, any more than there's a one-size-fits-all kink.