That`s a very interesting question.
One thing that brings to my mind is that the relationship with Cain & Abel reminds about the hero path and contests that Joseph Campbell discussed in Hero With Thousand Faces. There are several very old myths in history (Gilgamesh for example) that tells a story about a hero and a champion. Another one is favoured due to his/her achievements and feats, another one has lesser favour but cleaner morale. First one`s lust for power becomes clear when they contest, and the other gets more followers... Joseph Campbell tried to point out there is a same basic structure with the path that can be found in different cultures around the world, in most of theist pantheons, primitive cultures and children`s stories.
Well, we know JS reads a lot and it would be a wonder if he hasn`t heard about the book. But all in all, I think there`s a certain amount of a mundane drama with Cain and Abel`s story that brings a lot of imagination to us every one.
