Genesis 4:17

17Cain knew his 4:17 The simplest explanation for the origin of Cain’s wife is that she was one of his sisters, whom Scripture does not mention specifically, but implies (5:4). It is also possible that she was a niece or more distant relative descended from the original family, but in any case it is evident that the unrecorded children of Adam and Eve married each other. This was possible because the human gene pool was at its purest with Adam and Eve, so at some point their children could begin families of their own.wife [one of Adam’s descendants] and she conceived and gave birth to Enoch; and Cain built a city and named it Enoch, after the name of his son.