Christians will say that people had no concept of morals before God gave it to them. Not only were murder, purgery, rape and adultery permitted, they were the favorite past times of all ancient civilizations.
No, I'd say that God's desires and laws were pretty much written on the hearts of Adam and Eve. For instance, although the 10 commandments had not yet been given in the way we see in Exodus, when Adam and Eve sinned they knew they had done something "wrong."
Even before Cain murdered Able scripture shows that God was talking about what was right and wrong...even sin.
Gen 1:6-7 Then the LORD said to Cain, "Why are you angry? Why is your face downcast? If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must rule over it."