What would make a man physically attracted to his own minor daughter?

What kind of childhood do you think he would of had? What if he seems like he loves his daughter naturally to everyone else, but to you behind closed doors you sense something is not right, but can pinpoint it? What signs would you look for in a young girl under 10. What if you sense it is about to happen, what are the signs? I read that some parents who have been abandoned by their spouse often look to their kids as a fill-in, is this true?