The NY Times had an article about population long, long ago. Like more than a million years ago.
"From the composition of just two human genomes, geneticists have computed the size of the human population 1.2 million years ago from which everyone in the world is descended.
They put the number at 18,500 people, but this refers only to breeding individuals, the “effective” population. The actual population would have been about three times as large, or 55,500."
So according to geneticists and the NY Times, 1.2 million years ago (lol), the number of people was 18,500, only for "breeding" individuals. LOL again. I guess those other persons remained celibate, lol. Or hybrids? Or unbreeding? Or unbreedable.
And, of course, there are caveats and disagreements among scientists.
But 18,000 or so more than a million years ago.