First and foremost, I must state that this write-up is hatched out of my own little brain and is not intended to be truly scientific. It probably does not even qualify as a SWAG (scientific wild-assed guess).
That said, perhaps it will ring true through plain ordinary logic with a few facts mixed in. Please let me know where I have gone wrong on this. I have attempted to deliberately over-estimate the population to come up with what would be considered a less unpleasant number by all but the most misanthropic among us.