what about this:
(Genesis 4:16) Then Cain went away from the presence of the LORD, and dwelt in the land of Nod, east of Eden. 17 Cain knew his wife, and she conceived and bore Enoch; and he built a city, and called the name of the city after the name of his son, Enoch.


point being, just because it says adam and eve were first, it doesn't say "only" (if it does, show where)