Well I have a fairly good idea. In the early days I would bet that the hominids would have a very high rate of infant mortality. We do know that the peoples of around 10,000 years ago had a hard time just replacing themselves (having 2 children that lived).<quoted text>
Right. But do you ever wonder why the first civilizations did not occur until about 10,000 BC? Why is that?
Also, they were starting from scratch in everything. They had no accumulated knowledge from which to draw. No language to enable them to pass along vital information and knowledge. A scratch could kill them from sepsis because they didn't know the germ theory.
It has been estimated from the bones found that many many of them didn't live past 18-25 years old. That in itself is an impediment to passing along knowledge. For a long time they had no effective weapons to use against wild animals. In Africa, where we came from , there are many things that can kill you.
Then for the longest time we were hunter-gatherers and didn't stay in one place very long...we followed the food. It is only after many people realized we could grow lots of food if we stayed in one place that civilizations/cities started forming.
Another thing to consider is that there were several natural 'disasters' that wiped out lots of the world-wide populations occasionally. Ice ages, volcanoes....those kind of things. 75,000 years ago, when Mount Toba in Sumatra/Malaysia exploded, it may have brought population down to less than 10-20 thousand people.
The US government census bureau has estimated that world population around the time farming commenced in the middle east was 10-20 million people world-wide. All continents (except Antarctica) were populated by this time.