One must either concede that laws were given to Adam that aren’t in the text, or accept the God is unjust in meting out punishment to those ignorant of His desires.
Deut. 32:7 Remember the days of old, consider the years of many generations; ask thy father, and he will declare unto thee, thine elders, and they will tell thee.
8 When the Most High gave to the nations their inheritance, when He separated the children of men, He set the borders of the peoples according to the reckoning of the children of Israel.
9 For the portion of the LORD is His people, Jacob the lot of His inheritance.
Look back. What did Jews of old believe? What do acknowledged teachers say that is consistent with ancient understandings?
Also see:
http://www.jewishpath.com/parsha/bereishis/the_seven_noach_commands.html
If you are a thoughtful reader of scriptures you’d see immediately that two ignorant innocents expelled from the Garden in Eden wouldn’t know a thing about basic survival. Clearly, there’s more to the story.
I completely agree that the Ten Commandments are a reinstitution of what must have been lost or forgotten.