Remember that 74,000 years ago the Toba explosion left (alive) only 2-5,000 humans worldwide.
There was also a huge genetic split at that time and produced many more 'branches' on the human tree. This occured again about 18k years ago during the Last Glacial Maximum (LGM).
Yes, that's like what I was thinking of..
What was the population before Toba?
What about similar global / continental disasters?
Example:
Sea level rise at the end of last ice age..
How many lives can we guess were lost as the Indonesian plateau (savannah? land bridge?) was submerged, isolating the Australian continent and turning myriad Indonesian mountain ranges into islands?
It seems logical to me that the world population has probably gotten fairly large at least once, maybe several times, only to be diminished by some disaster or disease..
(Hope that makes sense..)