Only on this MB a couple of weeks so forgive me if I reiterate something that may already have been stated here before. If there is heaven above and hell below then what is our plane of existence? I think I've heard it put as purgatory, if this is the case couldn't all the souls that exist past, present, and future be reincarnating continuously through all time until they find redemption or enlightenment which ever the religion dictates for escaping the cycle and going to paradise or heaven. This could cover the difference between population totals throughout time. I'm thinking this because of God kicking Adam & Eve out of paradise and putting them on Earth as punishment for disobeying his commands. Thus I don't think Earth was intended as a luxurious vacation location but a place for the "lost souls" to prove their worthiness and until they did they would continue to stew in their misery.
(lobo for short)