There can be little doubt that the majority of the area through which the Arctic Small Tool horizon spread was unoccupied by human populations. This is particularly true of the Eastern Arctic, with the exception of the southern fringes where they may have come into contact with Archaic peoples near the ecotone between the tundra and the taiga.

In the Western Arctic, it is apparent that there had been earlier human populations in many areas, but these later migrants appear to have occupied a previously unoccupied ecological niche. Geographically, they spread along the Arctic coasts until they had reached the maximum extent of seasonally frozen coasts, usually with adjacent tundra. While it may be that the rising sea level had flooded earlier evidence of such a coastal occupation arid that this habitat had not been unoccupied as it now appears, the present data support the inference that Arctic Small Tool populations were the first to accomplish a successful adaptation to these particular conditions in the American Arctic. For the present, I wish to focus on this coastal aspect of Arctic Small Tool peoples, ignoring (or not modeling) the expanded distribution of sites in interior Alaska which also occurred at this time.