Settlement of The Americas - Understanding The Debate

Understanding The Debate

The chronology of migration models is currently divided into two general approaches. The first is the short chronology theory with the first movement beyond Alaska into the New World occurring no earlier than 15,000 – 17,000 years ago, followed by successive waves of immigrants. The second belief is the long chronology theory, which proposes that the first group of people entered the hemisphere at a much earlier date, possibly 21,000–40,000 years ago, with a much later mass secondary wave of immigrants.

One factor fueling the debate is the discontinuity of archaeological evidence between North and South America Paleo-Indian sites. A roughly uniform techno-complex pattern known as Clovis appears in North and Central American sites from at least 13,500 years ago onwards. South American sites of equal antiquity do not share the same consistency and exhibit more diverse cultural patterns. Archaeologists conclude that the "Clovis-first", and Paleo-Indian time frame do not adequately explain complex lithic stage tools appearing in South America. Some theorists seek to develop a colonization model that integrates both North and South American archaeological records.

Indigenous Amerindian genetic studies indicate that the "colonizing founders" of the Americas emerged from a single-source ancestral population that evolved in isolation, likely in Beringia. Age estimates based on Y-chromosome micro-satellite place diversity of the American Haplogroup Q1a3a (Y-DNA) at around 10,000 to 15,000 years ago. This does not address if there were any previous failed colonization attempts by other genetic groups, as genetic testing can only address current population ancestral heritage.

Migrants from northeastern Asia could have walked to Alaska with relative ease when Beringia was above sea level. But traveling south from Alaska to the rest of North America may have posed significant challenges. The two main possible routes proposed south for human migration are: down the Pacific coast; or by way of an interior passage (Mackenzie Corridor) along the eastern flank of the Rocky Mountains. When the Laurentide and Cordilleran ice sheets were at their maximum extent, both routes were likely impassable. The Cordilleran sheet reached across to the Pacific shore in the west, and its eastern edge abutted the Laurentide, near the present border between British Columbia and Alberta. Geological evidence suggests the Pacific coastal route was open for overland travel before 23,000 years ago and after 15,000 years ago. During the coldest millennia of the last ice age, roughly 23,000 to 19,000 years ago, lobes of glaciers hundreds of kilometers wide flowed down to the sea. Deep crevasses scarred their surfaces, making travel across them dangerous. Even if people traveled by boat—a claim for which there is currently no direct archaeological evidence as sea level rise has hidden the old coastline — the journey would have been difficult with abundant icebergs in the water. Around 15,000 to 13,000 years ago, the coast is presumed to have been ice-free. Additionally, by this time the climate had warmed, and lands were covered in grass and trees. Early Paleo-Indian groups could have readily replenished their food supplies, repaired clothing and tents, and replaced broken or lost tools.

Coastal or "watercraft" theories have broad implications, one being that Paleo-Indians in North America may not have been purely terrestrial big-game hunters, but instead were already adapted to maritime or semi-maritime lifestyles. Additionally, it is possible that "Beringian" (western Alaskan) groups migrated into the northern interior and coastlines only to meet their demise during the last glacial maximum, approximately 20,000 years ago, leaving evidence of occupation in specific localized areas. However, they would not be considered a founding population unless they had managed to migrate south, populate and survive the coldest part of the last ice age.