 What is the true explanation for Charles being the last man on Earth?
There should be an epitaph for every man, big or little, but a really grand and special one for Loner Charlie. New York lay quietly below him. Within a year it was obvious to everyone that man was the only animal left on earth. Within six months, half of the world's population was gone. Less than a month ago no more than a few thousand people remained in New York. And now.... "I've got to find out," Charles told himself. Once a year the Bureau issued The Index, an exact accounting of Earth's four billion inhabitants. Charles activated the switches that would flash a schematic map of New York on the screen. Charles was by himself, the last person alive in all of New York City.
 The invisible aliens exterminated people in alphabetical order, according to the the Bureau of Vital Statistics index. Charles happens to be last on the list, with the last name Zzyzst.
 The invisible aliens exterminated people according to chance and probability. Charles just so happened to be killed last.  The invisible aliens exterminated people in alphabetical order, according to the the Bureau of Vital Statistics index. Charles happens to be last on the list, with the last name Zzyzst.  The invisible aliens exterminated people according to how normal they were. Charles just so happened to be the most normal human alive.  The invisible aliens exterminated people in the order of a foretold prophecy. Because he was a prophet, Charles was killed last.