Murder is old. We can’t call it the oldest profession simply because, well, it wasn’t really a profession when it was invented, at least according to one set of accounts. There just weren’t enough people around, which became a problem later, as we’ll get into. Murder most foul, it was, brother against brother. The incident with Cain and Abel is interesting for a lot of reasons.
For one, it's happening in the first generation. Adam and Eve got kicked out of the Garden, and their first two sons turn out like this. It’s not really fair to call it bad parenting, either; I mean they got 50% right. Not bad for a couple of kids freshly kicked out of Paradise, especially considering there were no parenting books yet.
What we have with Cain and Abel is a simple crime of passion. Abel got recognition for what he did, Cain felt slighted. Cain kills Abel. End of story, right? Pack up, go home. Not quite. See, what we also have here is the first act of pre-meditation.