As the saying goes "I wouldn't **** you if you where the last man on earth" but say he was, then to repopulate they would need to reproduce, but then the world would of came from an incestrious family if you think about it down the generations, then if adam and eve IS true then arn't we all from an incestrious family?
How about the first man on earth. Adam and Eve begat Cain and Able, Cain killed Able, and then the three of them went ahead and populated the Earth, just a little bit incestuous,
My answer was posted 'tongue in cheek', but to answer mycatis, if your religous, you must believe in the Genisis as written, and all people are descended from Adam and Eve, so in the beginning, there was no-one else around at that time, so incest must have been the order of the day.
I'm not religous chessman :-) but Adam and Eve had loads of children after Cain, Able and Seth. Cain and Abel were married to their sisters Eeeew so they were all related but I suppose we are forgeting that it doesnt matter since after the flood, there was only Noah and his family left anyway!! So there, lol