I have read about the sex that fell man in the garden was Eve did it first, then took Adam to experience it and Satan literally had a three-way with them inclusive of homosexual acts between Adam and Satan and thus wound up with the impregnation of Eve by both Adam and Satan. Cain was cast away into a populated world of other "humans" somehow outside/separate from the Garden. They were already there as he feared being killed by the outsiders everywhere he went so God marked him to preserve him...remember?

P.S.A. The tree of "knowledge" was what the word implied in the Old Testament times/jargon/lingo. If you had sexual contact with someone then it was called "knowing" them. Put two and two together...sex was the sin it has horrifically plagued us in every way since! Pedophelia=maligned sexual acts outside of nature/God's intention for the act is not what we do with it! They took from the tree of knowledge/sex for pleasure. This was NOT God's plan for us to know sex tTHAT way.