Genesis 5

SAB, Genesis 5

• 5:2 Male and female created he them; and blessed them, and called their name Adam, in the day when they were created.

Ok Reading this I guess we are not supposed to be called Human, but to be called Adam.

• 5:4 And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters:

So heres one answer massive incest.

So this chapter is just lineage, but provides massive thought that the only way adams boys had children was to make their sisters their wifes.