I doubt that a man trying to write about people is any more interested in blood relationships than in the shape of their noses, unless they are necessary to help the story move. If the writer concentrates on what he does need to be interested in, which is the truth and the human heart, he won't have much time left for anything else, such as ideas and facts like the shape of noses or blood relationships, since in my opinion ideas and facts have very little connection with truth.