I'll bite. This isn't an official answer and I'm just having fun with your assumptions. DNA testing shows that at some point homosapiens and neanderthals cross bred. In the Book of Genesis, Cain kills Able and is cast out into the "land of Nod", which is basically an area outside of the Garden. Then it says that Cain "knew his wife" and had kids. Some people assume that she had to have been a daughter of Adam and Eve. But she could have been a neanderthal.