Please tell me you're being sarcastic and you seriously don't believe the entire human race was descended from two people, one of whom was made from the rib of the other. . .
If you do, let me ask the question: "did Adam & Eve have navels?"
How 'bout, "if there were only Cain & Abel (and that other guy later), where did the 'third generation' come from?" I guess the implication is that to believe Judeao-Christian myths are to believe it's okay to fornicate with peoples' sisters, mothers, etc.
Makes for good rationalization material. Wonder why this kind of stuff is so common in those "bible-belt" states. Coincidence? Hmmm. I think not. . .