Adam and Eve did not re-populate the world. According to the story they Had 2 sons and that was all. So here we have 3 men and 1 female and they are all family. Sounds like incest to me. It shouldn't matter what adam and eve did because their offspring were killed and the world was re-populated by Noah and his family which again is a story of incest. Creation and the stories of the bible don't add up, they say one thing and do another.