What would happen if you asked your Rabbi, Priest, Pastor etc. if it was a sin to sleep with your daughter or cousin? My guess is that you would get a resounding YES! If that is the case then please explain all of the inbreeding that went on in the bible. For example, Cain and Abel, along with three sisters, (who I don't know the names of), had to have had sex in order for us to even be here at all. And that is just the beginning of the book, it gets more sordid. Then you have Lot doing the "Wild Thang" with his daughters in a cave. And I am sure that there are more examples. Is this biblical contradiction? You decide.