Erm..... how many left Africa all those years ago? Because without knowing that accurately, any conclusions you make about what today’s population should be are utterly meaningless.That ancient humans migrated out of Africa 300,000 years ago depends on the truth of the theory of evolution.
Even assuming a minimal growth rate and the worst decimations of war and disease, the world population today should be in the trillions! There should be billions of buried skeletons just from the "Stone Age" alone. Yet paleontologists are "perplexed" that the bones and artifacts of this teeming phantom population, whose remains should still be extant, are totally absent!
But according to the Biblical account, all men today are descendants from the eight survivors of Noah's Flood 4000 years ago, which to the present world population of 7 billion, is a perfect exponential growth curve, even with a growth rate of only 0.5% per annum. If skillful, intelligent human beings have been around for one million years, why would they wait almost 10,000 centuries before making written records? That there are none older than 4-5000 years, shows that the Biblical time scale is much more likely!