It seems that this question demonstrates that the Mosaic laws, both dietary and moral, went back long before Moses. In Genesis 26, God told Isaac that the covenant would be perpetuated through him because Abraham kept his laws, ordinances, and precepts. So obviously there were moral standards that were verbal/common knowledge long before the Pentateuch was written. Also the mere statements that Noah was righteous in his generation and that Enoch walked with God indicate standards.

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Mary Vanderkooi
Kale Heywott Church (KHC)
Soddo, Ethiopia