Now it came about, when men began to multiply on the face of the land, and daughters were born to them, that the sons of God saw that the daughters of men were beautiful; and they took wives for themselves, whomever they chose.
The popular theory on the identity of the sons of God in Genesis 6:1-2 is the sons of Seth. And the daughters of men are the daughters of Cain. But is this view correct? Without resorting to the Book of Enoch or other extra-Biblical book, this video answers this question clearly using only Biblical references.