The Cain and Abel story like virtually all the stories in Genesis are allegorical. They all had a purpose though. For the most part every story in the bible was written to deliver a message, even the ones that were based on actual events. Historical accuracy was never high on the authors priority list. Literal interpretation of the bible is a fairly modern idea. Origen of Alexandrea in the 2nd century discovered that there never was a city named Cana,(so no wedding) for example.

Why even question biblical texts? Magical thinking is all that this is about and you are arguing with people who like talking snakes. Instead, I would ask what is the lesson there in and deal with that reality. Just be kind and gentle in the process and remember, we lead by example.

Why are you asking questions for christians on an agnostic site? Seems counter-intuitive to me.

Here's another bit of trivia: I am an amateur orchardist. As such I have learned Apples did not exist until the last several hundred years. They came from a rose type plant in Kazakhstan. There was no apple in the supposed garden. What was most probably the fruit was a Pomegranate. Not so easy to eat out of hand.

I think the key to understanding all religious scripture (which most Christians miss) is that it never actually describes God. Scriptures only describe the relationship people have had with God based on their own understanding. If they were Warriors then God was a Warrior etc.