Sorry, Crimson Lizard, but Lot's daughters actually didn"t have that as an legitimate excuse to engage in their incestuous behavior. They had, in fact, just left a small city called "Zoar", where they had taken refuge from the destruction. So they did know their were other people. I personally suspect that they had just used the incest as a means of humiliation and disgrace of dear old Dad for giving them up to a mob as rape-bait.