Adam and Eve have sons, Fucker and Shithead. They also have daughters, Bitch and Hag(No, those aren't their names, but whatever).

When it comes time for the children to continue the human race...whoops, they're the only little brats on the planet. Who is there to procreate with. The family, of course.

Holy inbreds.

What a profound realization! I can't believe that no one has ever considered that before. You must be the most intelligent person on the planet![/sarcasm]