After reading the abstract of the paper mentioned here I started wondering, why did human groups migrate away from southerner (warmer) places towards the north which is far colder and has less possibilities to grow crops and wild animals to hunt?
Was the population density too high?
And after they migrated, what did they mostly survive on? Were they hunters-gatherers? Did they cultivate? Was it not more difficult to survive in colder climates?
Pre agriculture you need a lot of land to support a small amount of humans.
It’s not like someone walked from Africa to Norway. A group would expand a little North, settle, then another group would move a little further north.
It was a slow gradual migration. So people slowly got used to the changes.
But like you said, the further North the less food, so they had to spread further and further each time.