Peopling of the Americas

It is believed that the peopling of the Americas began when Paleolithic hunter-gatherers (Paleo-Indians) entered North America from the North Asian Mammoth steppe via the Beringia land bridge, which had formed between northeastern Siberia and western Alaska due to the lowering of sea level during the Last Glacial Maximum (26,000 to 19,000 years ago). These populations expanded south of the Laurentide Ice Sheet, either by sea or land, and spread rapidly southward, occupying both North and South America no later than 14,000 years ago, and possibly before 20,000 years ago. The earliest populations in the Americas, before roughly 10,000 years ago, are known as Paleo-Indians. Indigenous peoples of the Americas have been linked to Siberian populations by the distribution of blood types, and in genetic composition as reflected by molecular data, such as DNA. While there is general agreement that the Americas were first settled from Asia, the migration patterns and the place(s) of origin in Eurasia of the peoples who migrated to the Americas remain unclear. The most generally accepted theory is that Ancient Beringians moved when sea levels were significantly lowered due to the Quaternary glaciation, following herds of now-extinct Pleistocene megafauna along ice-free corridors that stretched between the Laurentide and Cordilleran ice sheets. Another proposed route has them migrating down the Pacific coast to South America as far as Chile, either on foot or using boats. Any archaeological evidence of coastal occupation during the last Ice Age would now have been covered by the sea level rise, up to a hundred meters since then. The precise date for the peopling of the Americas is a long-standing open question. While advances in archaeology, Pleistocene geology, physical anthropology, and DNA analysis have progressively shed more light on the subject, significant questions remain unresolved. The Clovis First theory refers to the hypothesis that the Clovis culture represents the earliest human presence in the Americas about 13,000 years ago. Evidence of pre-Clovis cultures has accumulated and pushed back the possible date of the first peopling of the Americas. Academics generally believe that humans reached North America south of the Laurentide Ice Sheet at some point between 15,000 and 20,000 years ago. Current debates center around four glacial-age openings which could have allowed entry into North America: coastal around 24,000 and 15,000 years ago, inland around 14,000 years ago, and coastal around 12,000 years ago. The Swan Point Archaeological Site located in Alaska has yielded the oldest evidence of human habitation that is not disputed, with artifacts that have radiocarbon dates of 14,000 years, indicating the site was occupied around 12,000 BCE.

Scholarly debate

Historically, researchers thought a single theory explained the peopling of the Americas, focusing on findings from Blackwater Draw, New Mexico, where human artifacts dated from the last ice age were found alongside the remains of extinct animals in the 1930s. This led to the widespread assent to the Clovis First theory, proposing that the first Americans migrated over the Beringia land bridge from Asia during a time when glacial passages opened. This model linked the first inhabitants to distinctive spear points, known as Clovis points, dating to 13,250 to 12,800 years ago. Numerous claims of earlier human presence began to challenge the Clovis first model beginning in the 1990s, culminating in significant discoveries at Monte Verde, Chile, dating back 14,500 years. At Oregon's Paisley Caves, fossilized human feces date back 14,300 years. In Texas, at Buttermilk Creek complex, stone tool fragments date back 15,500 years. At Arroyo Seco 2 in Argentina, archaeologists discovered 14,000-year-old butchered animal bones. Meadowcroft Rockshelter in Pennsylvania may have a history of at least 16,000 years. However, firm dates for key sites like Monte Verde, Chile are still an ongoing debate. The Swan Point Archaeological Site in eastern central Alaska has yielded the oldest evidence of human habitation that is not disputed. Artifacts, faunal remains, and hearths at the site have radiocarbon dates of 14,000 years, indicating the site was occupied around 12,000 BCE. As research progressed in the 2000s, the narrative shifted from a single migration event to multiple small, diverse groups entering the continent at various points in time. This indicates that people might have populated North and South America as early as 15,000 to 20,000 years ago, which some think supports a coastal migration route. The genetic history of the Indigenous peoples of the Americas has highlighted populations that adapted over tens of thousands of years. Geneticists discovered that a Beringian population split from Siberian groups about 36,000 years ago. Around 25,000 years ago, they became isolated, forming a new genetic group linked to today's Indigenous populations, which divided into two main lineages between 14,500 and 17,000 years ago reflecting the dispersal associated with the early peopling of the Americas. The Chiquihuite Cave in Mexico is a possible Upper Paleolithic archaeological site in the Astillero Mountains, Zacatecas State, in North-Central Mexico. Chiquihuite Cave may provide evidence of early human presence in the Western Hemisphere dating back as far as 33,000 years ago. Stones discovered here, thought to be lithic artifacts, have been dated to 26,000 years ago based on more than 50 samples of animal bone and charcoal found in association with these stones. However, there is scholarly debate over whether the stones are truly artifacts (human-made tools that are evidence of human presence) or if they were formed naturally. No evidence of human DNA or hearths has been unearthed.

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