The time scales of these migrations are staggering. Our most familiar time scale is from the time of Christ, Mesopotamia, the Roman Empire, Egypt — 2,000 to 5,000 years ago.
I wonder how these migrations occurred. Did a tribal leader convene a council and said “It’s time we moved on”? Did they just move a few miles away? A few tens of miles? Did they know they were constantly moving in a particular direction? Was it just animated by the need for a new food supply? Were they nomadic like the North American Indians?
I would imagine they were a lot like Baptists.
Every time a Baptist Church gets a new preacher half the congregation doesn’t like him, and so leave and start a new church..............
They followed the animals they preyed upon, and responded to pressure from other tribes, not to mention increasing population pressures.
It is not hard to see an average movement of a couple of miles a year.
Periodic Ice Ages forced migration and advanced intelligence - only the smart survive in the cold.
Simple. The chiefs eldest son or the strongest warrior became the next chief. Either kowtow or collect your familiar group and move out of range.
My guess is that early humans were continually exploring for food, especially in directions where there weren’t already competing (and territory-defending) humans.
Consider an early tribe. They settle in an area where there is good hunting, and plentiful food allows them to have many surviving children. The kids grow up, and groups set out to explore what’s available a few miles away. Over a generation, people can spread a hundred miles. Over several generations, a thousand miles.