[Nathan Zachary]

What "time"? Do you have conclusive evidence as to when snow and ice either receeded enough to make the land habitable, or increased to make life more difficult?

Goelogical evidence suggests the later.

[muawiyah]

Just as soon as lichen and mushrooms could row, the reindeer could move in, and the Sa'ami with them.

Although you need a digestive system that can handle a high fat/high protein diet, and there's not much in the way of carbohydrates around, people were able to move into Alpine, subarctic and Arctic regions for the last 180,000 years (maybe more).