New Evidence Pushes Back Peopling of the Americas Almost 20,000 Years
New research supports the idea that the Clovis-first theory is outdated. Two studies published in the journal Nature provide more evidence that the peopling of the Americas took place well before 13,000 years ago. In fact, the studies suggest the date for the arrival of humans into the Americas should be pushed back to as far as 30,000 years ago.
The Clovis-First Theory
The traditional view about the peopling of the Americas is that during the late Pleistocene period Paleo-Indian people crossed from what is now known as north-east Asia into Alaska via the Beringia land-bridge. They were said to have made this epic journey between 12,000 and 15,000 years ago.
Assistant professor Mikkel Winther Pedersen from the University of Copenhagen taking DNA samples in Chiquihuite cave, a key site in researching the peopling of the Americas. (Image: Devlin A. Gandy/ Nature)
The mark of these people was a specific kind of stone tool known as the ‘Clovis point’ – which archaeologists saw as the sign of big game hunters. From the 1920s until the 1970s, the Clovis-first theory reigned. But then researchers started to make discoveries that were older than they were “supposed to be”, clearly questioning the Clovis-first theory . For example, there are sites in Brazil dating back 20,000 years according to many researchers. But studies show that Clovis points were not being used in the southern continent.
The timing and method(s) of the first migration into the Americas became a source of great controversy. Both of the current studies published in Nature are adding new information to the discussion.
Key sites in the peopling of the Americas. Some of these dates are controversial. ( Nature 2020)
Study One: People on the Continent Around the Last Glacial Maximum
In the first study , Lorena Becerra-Valdivia of the University of New South Wales, Sydney, Australia, and Thomas Higham of the University of Oxford, UK, used radiocarbon and luminescence ages from 42 archaeological sites in North America and Beringia to explore what things looked like after people arrived in the region. Their results show that humans were likely present on the continent before, during, and immediately after the Last Glacial Maximum (LGM) (about 26,500–19,000 years ago).
The researchers also combined Bayesian age modelling with genetic and climatic evidence to analyze the data. They write that these analyses show “the near-synchronous commencement of Beringian, Clovis and Western Stemmed cultural traditions.” They also named the Chiquihuite Cave as the earliest pre-Clovis site on their list (33,150–31,405 cal. bp). The Beringian, Western Stemmed, and Clovis lithic traditions start dates are provided at, 14,860–13,065 and 14,210–13,495 cal. bp, respectively, according to this study.
Assistant professor Mikkel Winther Pedersen with team members carefully sampling the different cultural layers in the cave. (Image: Mads Thomsen / Nature)
Some of the major sites the researchers found to be occupied during or just after the LGM are Gault (26,435–17,385 cal. bp), Meadowcroft Rockshelter (24,335–18,620 cal. bp) and Cactus Hill (20,585–18,970 cal. bp). In eastern Beringia, Bluefish Caves was dated to the LGM by a “humanly modified bone sample” (24,035–23,310 cal. bp). The researchers also note that “the biocultural relationship between the humans represented by pre-Clovis sites and later North American and Beringian traditions is largely unknown.”
Map showing the location of the 42 archaeological sites included in the study about the peopling of North America. ( Becerra-Valdivia et al. / Nature )
Another find these researchers made was “an overlap of each [Beringian, Clovis and Western Stemmed cultural traditions] with the last dates for the appearance of 18 now-extinct faunal genera.” This means that humans spreading out over North America likely was “a key factor in the extinction of large terrestrial mammals,” according to the researchers.
Study Two: The Peopling of the Americas was Underway 30,000 Years Ago
In a related study, published in the same issue of Nature, Ciprian Ardelean of the Universidad Autónoma de Zacatecas, Mexico, and colleagues present their findings after excavations in 2016-2017 in the high-altitude Chiquihuite Cave, located in Zacatecas, Mexico. In the cave, they found stone tools, plant remains, and environmental DNA (but no ancient human DNA ) to analyze.
Top: Stone tool found below the Last Glacial Maximum (LGM) layer. Credit: Ciprian Ardelean. Bottom: Stone tool found above the Last Glacial Maximum (LGM) layer. This particular piece was made from a greenish crystallized limestone. Credit: Ciprian Ardelean / Nature
They decided to dig about 50 meters (164 ft.) inward from the cave’s entrance after discoveries were made in that area in 2012 suggesting that humans were using the cave during the Last Glacial Maximum. The excavators unearthed about 1,900 stone artifacts, as well as genetic, palaeoenvironmental, and chemical data to study.
Their results suggest that people were repeatedly, but not consistently, inhabiting the cave between about 30,000 years and 13,000 years ago. In the paper the researchers write that their results “corroborate previous findings in the Americas of cultural evidence that dates to the Last Glacial Maximum […] and which push back dates for human dispersal to the region possibly as early as 33,000–31,000 years ago.”
A 3D model of Chiquihuite Cave excavation X-12 produced via photogrammetry by Devlin Gandy, University of Cambridge. Published in Ardelean et al. (2020) ( Sketchfab)
Another interesting discovery made at the Chiquihuite Cave is linked to the cave’s location. It is 2,740 meters (8989.5 ft.) above mean sea level and about 1,000 meters (3280.8 ft.) above the valley floor in the Astillero Mountains. This high-altitude location sets it apart from other sites in the peopling of the Americas. As the researchers explain, it breaks “the pattern of megafauna kill sites, open sites and shallow rockshelters.”
To the researchers , this means that “The occupants of the cave were seemingly adapted to altitudes and mountain landscapes, showing a behavioural pattern that—to our knowledge—was previously unknown in the archaeological record of the Americas.” Furthermore, they state that “Their lithic industry has no parallel in the continent and its qualitative traits suggest a mature technology, possibly brought in from elsewhere before the LGM.”
These final points about the study make one wonder: Who were the occupants of the Chiquihuite Cave and what were their origins? Hopefully work will continue at this site to shed some light on these matters.
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Examples of lithic artefacts from Chiquihuite Cave.a, Core. b–e, Flakes; inlay in b emphasizes an isolated platform. f–j, Blades. k–o, Points. Scale bar, 3 cm. ( Ardelean et al.,2020 / Nature ) The researchers say that this lithic industry has no parallel in the continent.
We’re Always Learning New Things…
The find in the Mexican cave is not the first to suggest that people were that far south in the Americas so long ago. As Ruth Gruhn, professor emerita in the Department of Anthropology, University of Alberta in Canada, writes in the current issue of Nature, “This Mexican site now joins half a dozen other documented archaeological sites in northeast and central Brazil that have yielded evidence suggesting dates for human occupation between 20,000 and 30,000 years ago.” Many of those sites have been ignored or disputed due to the dates they provide, but Gruhn is hopefully right when she writes “The findings at Chiquihuite Cave will bring about fresh consideration of this issue.”
Although there are still debates to be had about exactly how people reached the Americas , the belief in big game hunters and Clovis-first that were so prominent are now falling by the wayside. Recent discoveries and improved dating techniques show time and again that the old picture doesn’t fit with the new information.
Top Image: Team members entering the Chiquihuite cave, a key site in researching the peopling of the Americas. Source: Devlin A. Gandy