I've been a christian all my life and i'm trying to pull down God and make stupid silly questions for you to answer.
But there has been this one thing which has been puzzling me.
When Kane killed his brother he decided (or god told him to) to leave. Then kane told god that he was afraid that someone might try to hurt him, then god put a mark on his head and told that whoever hurts him, god will revenge for him.
Since back then there was only Adam's family, who else was there for kane to be afraid of?