sure why the Cain story doesn't belong in a biography article. If it's notable, then it belongs somewhere. Where else would you suggest? It's either got to go in (1) it's own article; (2) this article; or (3) the article about Cain and Abel. Of those three options, I think this one's clearly the most appropriate. There's nothing that says certain notable anecdotes can't be included in a biographical article. On the contrary, is that not where they belong?

I'm not