Why couldn’t the earliest people live where there were severe winters?

The most ancient people could not live where there are severe winters, because they did not yet have the opportunity to warm themselves and their homes sufficiently. For example, the fire that they learned to produce and maintain in a cave would not be enough for a temperature of minus 30. Also, they did not learn to sufficiently process animal skins for sewing warm clothes or shoes. Plus, in a harsh climate, plants used for food by the most ancient people during gathering do not grow for more than six months.