**The earliest indisputable evidence of human habitation in northwestern North America dates from nearly 12,000 years ago (about 11,700 BC). **Some South American sites (Monte Verde on the Chilean coast, have recently been date to more than 12,000 years ago). Arrow points and other artifacts from this period found in Alaska and parts of northwestern Canada have been labeled the Paleo-Indian tradition. These are the so-called Clovis fluted arrowheads. No direct evidence of such a culture has come to light in adjacent parts of North Asia, although a possible prototype has been found on Sakhalin Island. Most likely, the people who developed the Paleo-Indian culture crossed over the Bering Strait (the land bridge had by that time already been submerged by rising seawater) into Alaska earlier than 14,000 years ago and there developed a new culture. Another possibility is that the prototype of this culture is to be found beneath the waters of the present day Bering Sea. Whatever the direct origin of their fluted arrows and other technology, these Paleo-Indian big game hunters quickly spread southward into a land teeming with game as a warming climate opened gaps in the ice sheets covering northern Canada. Within 1000 years of the first evidence of human habitation in Alaska, the same Paleo-Indian assemblages of tools appeared in all habitable parts of North and South America, from the Canadian plains to the tip of present day Chile. It has been estimated that if a group of a few hundred humans entered the Americas and moved at a rate of only eight miles per years, their natural increase, as the first inhabitants of a rich land, would have led to a population explosion (for hunter gatherers) and spread throughout all of the habitable portions Western Hemisphere in about a thousand years. This is exactly what seems to have happened.