dude, ***** this topic... go further back in the bible... read the first chapter in the book of matthew. It mearly discusses the 28 generations leading up to Jesus Christ himself. The geneology went from Abraham to Jesus Christ. According to the old bible school song I learned when I actually did go to church, we are all children of Abraham. If not Abraham, at least we are all sons and daughters of Adam and Eve... providing the bible is truth.
Eve never gave birth to any girls... only three sons. Cain killed Able and was banished from the Garden of Eden. Then Adam and Eve bit from the tree of knowledge and had forsaken God's word. At this point, God abolished the Garden of Eden as we were not worthy enough for it. So following this story, we now have 3 males and 1 female in the world. So wouldn't any relationship we get into be incestious? Further more, did Eve reproduce with her own offspring? or did the bible just leave out mention of other females during this era?