I worked for a manager who was also a pastor. I raised a similar question to him. He said Cain & Abel weren't their only 2 sons. Really? You have 100s of kids and only two are ever worth mentioning: the murderer and his victim? Just how dull were those other kids?
Kid 1: "Hey dad, I invented the wheel!"
Kid 2: "Hey dad, I discovered fire!"
Kid 3 to kid 4: discovers the power of "I'm not touching you!"
Adam: "......"

It's not in "the book" but god pulled off another creation in the next valley and that's where these wives came from. They have their own "book". And ever since humans have been coveting whatever the people in the next valley have. Either game, gathering food, material resources or the women. It's still going on today but at a much larger scale

Cain and Eve hooked up, hence the word for it, MF's.

No, no, No! You cannot challenge their delusions with logic!!!
That is not allowed.

It is amazing how believers ignore the obvious.