And the Lord said to him,"Therefore, whoever kills Cain, vengeance shall be taken on him sevenfold." And the Lord set a mark on Cain, lest anyone finding him should kill him.
Genesis 4:15
Cain knew there were people "out there". God acknowledged that there were. I've pondered this for years without finding any good answers. You mentioned "two creations" awhile back and this came to mind again. Do you have some more missing pieces for me? Some scriptures to pass on?