I never figured the population explosion was a big logical obstacle...there could easily by a huge number of souls who have incarnated at very great intervals, who are coming to earth more frequently.  There could be plenty who've never been here and are just getting started.  There could be a bunch from elsewhere.  It may be that souls can divide like ameoba, making more from the originals (which would also deal with how six people could have been Cleopatra).  There's just way to many reasonable explainations for me to worry about numbers.

I just don't want to go through adolescence again...