There is a line of men who have been taught to listen to the voice of the LORD, the bible calls them sons of God. You say they are all descendants of Adam and Eve, and that is your belief. How you accord that belief with evidence that the human race is millions of years old (rather than 6,000 years) is up to you. If you take that approach, then all men were taught to listen to the voice of the LORD by Adam, but some fell away, which prefigures the apostasy. Where in scripture does God go through the trouble of setting up a negative outcome as a type-antitype pair? In my belief, God called out from the multitude of men one single family of men (the line of Adam-Seth-Enoch-Noah etc) and taught them to listen to his word. This prefigures the calling of Abraham, of Moses, the priesthood of Aaron, of all the prophets, and of the Church in general. This belief allows for evolution and an old earth, but it also explains where Cain got his wife, and how he built a whole city in only a few generations...not all the citizens were from his loins.