<<Is it really that clear? While I admit that this is, of course, the
traditional interpretation, there are a number of difficulties with this
view. For instance: who did the sons of Adam and Chava marry?>>
Each of them had a twin sister born with them, whom they married. They
permission from God, and therefore it wasn't a problem with incest. The
same applied to the children of Yaakov. Each shevet, except for Yosef had a
twin sister. Yosef married his step-niece.