What about Adam and Eve's children? They would have to marry their sisters and brothers, since no other people would be available. (And if there were other people there as well, then the creation of Adam and Eve just wouldn't be all that it is cracked up to be.) I've heard that they married apes. 
"You need me. You wouldn't be much of a hero without a villain. And you do love being the hero, don't you. The cheering children, the swooning women, you love it so much, it's made you my most reliable accomplice." -- Lex Luthor to Superman, Question Authority, Justice League Unlimited
| 
