The history of the population of the Americas has just been interpreted again. The most extensive and comprehensive study ever conducted on the basis of fossil DNA extracted from ancient human remains found on the continent has confirmed the existence of a single ancestral population for all the Amerindian ethnic groups, past and present.
Over 17,000 years ago this original contingent crossed the Bering Strait from Siberia to Alaska and began to popularize the New World. The fossil DNA shows an affinity between this migratory current and the populations of Siberia and northern China. Contrary to the traditional theory, it had no connection with Africa or Australasia.
The new study also reveals that once they had settled in North America the descendants of this ancestral migratory flow diverged into two lineages some 16,000 years ago.
Members of a lineage crossed the Isthmus of Panama and populated South America in three consecutive waves.
The first wave occurred between 15,000 and 11,000 years ago. The second took place over 9,000 years ago. There are records of fossil DNA from both migrations throughout South America. The third wave is much more recent, but its influence is limited as it was 4,200 years ago. Its members settled in the central Andes.
An article on the study has just been published in the journal Cell a group of 72 researchers from eight countries, affiliated with the University of São Paulo (USP) in Brazil, the Harvard University in the United States and the Max Planck Institute for the Science of Human History in Germany, among others.
According to the researchers' findings, the lineage that made the north-south journey between 16,000 and 15,000 years ago belonged to the Clovis culture, named for a group of archaeological sites excavated in the western United States and dating back to 13,500-11,000 years ago.
Clovis's culture was so called when flint spearheads were discovered in the 30s in an excavation in Clovis, New Mexico. Clovis sites have been identified throughout the United States and Mexico and Central America. In North America, the Clovis hunted the Pleistocene megafaunas like the giant sloth and mammoth. With the decline of the megafauna and its extinction 11,000 years ago, Clovis's culture eventually disappeared. Long before, however, hunter-gatherer groups had traveled south to explore new hunting grounds. They ended up settling in Central America, as evidenced by the 9,400-year-old human fossil DNA found in Belize and analyzed in the new study.
Later, perhaps while pursuing herds of mastodons, Clovis hunter-gatherers crossed the Isthmus of Panama and spread to South America, as evidenced by the genetic records of the burial sites in Brazil and Chile. Genetics corroborates well-known archaeological finds such as the Monte Verde site in southern Chile, where humans slaughtered mastodons 14,800 years ago.
Among the many known sites of Clovis, the only burial site associated with Clovis's instruments is in Montana, where the remains of a child (Anzick-1) dated to 12,600 years ago have been found. The DNA extracted from these bones has links to the DNA of skeletons of people who lived between 10,000 and 9,000 years ago in the caves near Lagoa Santa, in the state of Minas Gerais, in Brazil. In other words, the Lagoa Santa people were descendants of the Clovis migrants of North America.
"From a genetic point of view, Lagoa Santa people are descendants of early Amerindians," said archaeologist André Menezes Strauss, who coordinated the Brazilian part of the study. Strauss is affiliated with the Museum of Archeology and Ethnology of the University of São Paulo (MAE-USP).
"Surprisingly, the members of this first line of South Americans have not left identifiable descendants among today's Amerindians," he said. "About 9,000 years ago their DNA completely disappears from fossil specimens and is replaced by the DNA of the first migratory wave, before the Clovis culture. All living Amerindians are descendants of this first wave. We do not know yet why the genetic heritage of people Lagoa Santa has disappeared. "
One possible reason for the disappearance of DNA from the second migration is that it has been diluted in the DNA of the Amerindians which are descendants of the first wave and which can not be identified with the existing methods of genetic analysis.
According to Tábita Hünemeier, geneticist of the Institute of Biosciences of the University of São Paulo (IB-USP) who took part in the research, "one of the main results of the study was the identification of the people of Luzia as genetically related to the Clovis culture, which dismantles the idea of two biological components and the possibility that there have been two migrations in the Americas, one with African traits and the other with Asian traits. "
"The people of Luzia must be the result of a migratory wave originated in Beringia," he said, referring to the now submerged Bering bridge that joined Siberia in Alaska during the glaciations, when sea levels were more downs.
"Molecular data suggest the substitution of the population in South America 9,000 years ago: the people of Luzia have disappeared and have been replaced by live Amerindians today, even though both had a common origin in Beringia," Hünemeier said.
The contribution of Brazilian researchers to the study was fundamental. Among the 49 individuals from which the fossil DNA was taken, seven skeletons dated between 10,100 and 9,100 years ago came from Lapa do Santo, a rock shelter at Lagoa Santa.
The seven skeletons, along with dozens of others, were found and exhumed in subsequent archaeological campaigns on the site, led initially by Walter Alves Neves, a physical anthropologist at IB-USP and from 2011 by Strauss. The archaeological campaigns led by Neves between 2002 and 2008 were financed by the São Paulo – FAPESP Research Foundation.
Overall, the new study studied the fossil DNA of 49 individuals found in 15 archaeological sites in Argentina (two sites, 11 individuals dated between 8,900 and 6,600 years ago), Belize (one site, three individuals dated between 9,400 and 7,300 years ago ), Brazil (four sites, 15 individuals dated between 10,100 and 1,000 years ago), Chile (three sites, five individuals dated between 11,100 and 540 years ago) and Peru (seven sites, 15 individuals dated between 10,100 and 730 years ago ).
The Brazilian skeletons come from the archaeological sites Lapa do Santo (seven individuals dated to about 9,600 years ago), Jabuticabeira II in the state of Santa Catarina (a sambaqui or shell with five individuals dated about 2000 years ago), as well as from two peaks of the river in the Ribeira valley, in the state of São Paulo: Laranjal (two individuals dated about 6,700 years ago), and Moraes (a person dating back to about 5,800 years ago).
Paulo Antônio Dantas de Blasis, an archaeologist affiliated to the MAE-USP, led the excavation at Jabuticabeira II, which was also supported by FAPESP through a thematic project.
The excavations at the river sites in the state of São Paulo were led by Levy Figuti, also an archaeologist at the MAE-USP, and were also supported by FAPESP.
"The skeleton of Moraes (5,800 years) and the skeleton of Laranjal (6700 years) are among the oldest in the south and south-east of Brazil," said Figuti. "These locations are strategically unique because they are located between the highlands of the Atlantic Plateau and the coastal plain, contributing significantly to our understanding of how the Southeast of Brazil has been populated."
These skeletons were found between 2000 and 2005. From the beginning, they presented a complex mixture of coastal and inland cultural traits, and the results of their analyzes generally varied except in the case of a skeleton diagnosed as paleoindo (the analysis of its DNA is not yet complete).
"The study just published represents an important step forward in archaeological research, exponentially increasing what we knew about the archeogenetics of the Americas population until a few years ago," said Figuti.
Hünemeier also recently made a significant contribution to the reconstruction of human history in South America using paleogenomics.
Not all human remains found in some of the oldest archaeological sites in Central and South America belonged to genetic descendants of Clovis culture. The inhabitants of different sites had no DNA associated with Clovis.
"This shows that, in addition to its genetic contribution, the second wave of migration in South America, associated with Clovis, could have brought with it technological principles that would have been expressed in the famous fishtail points that are found in many parts of South America "Strauss said.
How many human migrations from Asia arrived in the Americas at the end of the Ice Age more than 16,000 years ago was hitherto unknown. The traditional theory, formulated over the years by Neves and other researchers, was that the first wave presented African traits or traits similar to those of Australian aborigines.
The well-known forensic facial reconstruction of Luzia was performed according to this theory. Luzia is the name given to the fossil skull of a woman who lived in the Lagoa Santa region 12,500 years ago and is sometimes referred to as the "first Brazilian".
The bust of Luzia with African characteristics was built on the basis of the skull morphology by the British artist Richard Neave in the years & # 90;
"However, the shape of the skull is not a reliable indicator of ancestral or geographic origin, but genetics is the best basis for this type of inference," Strauss explained.
"The genetic results of the new study show categorically that there was no significant connection between the people of Lagoa Santa and groups from Africa or from Australia, so the hypothesis that the people of Luzia derived from a wave of migration prior to the ancestors of the current Amerindians has been denied, while the DNA shows that the people of Luzia were entirely Amerindos ".
A new bust has replaced Luzia in the Brazilian scientific pantheon. Caroline Wilkinson, a forensic anthropologist from Liverpool John Moores University in the UK and disciple of Neave, produced a facial reconstruction of one of the exhumed people in Lapa do Santo. The reconstruction was based on a digital retrodiform model of the skull.
"Accustomed like us to the traditional facial reconstruction of Luzia with strongly African traits, this new facial reconstruction reflects the physiognomy of the first inhabitants of Brazil in a much more accurate way, showing the generalized and indistinct characteristics from which the great Amerindian diversity has been established by thousands. of years, "Strauss said.
The study published in Cell, he added, also presents the first genetic data on the Brazilian coastal sambaquis.
"These mammoth tumuli were built about 2000 years ago by populous societies that lived on the coast of Brazil: analysis of fossil DNA from mounds of piles of shells in Santa Catarina and San Paolo show that these groups were genetically related to the Amerindians living today in the South of Brazil, especially the Kaingang groups, "he said.
According to Strauss, DNA extraction from fossils is technically very challenging, especially if the material has been found in a tropical climate site. For almost two decades, extreme fragmentation and significant contamination have prevented several research groups from successfully extracting genetic material from the bones found in Lagoa Santa.
This was done thanks to the methodological advances developed by the Max Planck Institute. As Strauss explained enthusiastically, much remains to be discovered.
"The construction of the first archaeological laboratory in Brazil is scheduled for 2019, thanks to a partnership between the Museum of Archeology and Ethnology of the University of São Paulo (MAE) and its Institute of Biosciences (IB) with FAPESP funding. When it is ready, it will give new impetus to research on the populations of South America and Brazil, "Strauss said.
"To a certain extent, this study not only changes what we know about how the region has been populated, but it also considerably changes the way we study human skeletal remains," said Figuti.
The human remains were first found in Lagoa Santa in 1844, when the Danish naturalist Peter Wilhelm Lund (1801-1880) discovered about 30 skeletons in a flooded cave. Almost all these fossils are now at the Museum of Natural History of Denmark in Copenhagen. Only one skull remained in Brazil. It was donated by Lund to the Brazilian Institute of History and Geography of Rio de Janeiro.
Colonization by leaps and bounds
On the same day of Cell article was published (8 November 2018), an article in the journal Science he also reported new discoveries on fossil DNA from the first migrants in the Americas. André Strauss is one of the authors.
Among the 15 ancient skeletons from which the genetic material was taken, five belong to the Lund Collection in Copenhagen. They date back between 10,400 and 9,800 years ago. They are the oldest of the sample, along with a Nevada individual estimated at 10,700 years.
The sample included fossilized human remains from Alaska, Canada, Brazil, Chile and Argentina. The results of its molecular analysis have suggested that the populations of the Americas by the first human groups of Alaska did not happen simply through the gradual occupation of the territory in conjunction with the growth of the population.
According to the researchers responsible for the study, molecular data suggest that the first humans to invade Alaska or the nearby Yukon, divided into two groups. This happened between 17,500 and 14,600 years ago. One group colonized the North and Central America, and South America.
The populations of the Americas followed one another in leaps and bounds, while small bands of hunter-gatherers traveled far and wide to settle in new areas until they reached the Tierra del Fuego in a movement that lasted one or two millennia at most.
Among the 15 people whose DNA was analyzed, three of the five from Lagoa Santa found genetic material from Australasia, as suggested by the theory proposed by Neves for the occupation of South America. Researchers are unable to explain the origin of this Australasian DNA or how it ended up in a few of the population of Lagoa Santa.
"The fact that the genomic signature of Australasia has been present for 10,400 years in Brazil, but is absent in all the genomes tested to date, which are old or old, and found further north, is a challenge considering the his presence at Lagoa Santa, "they said.
Other fossils collected during the twentieth century include the skull of Luzia, found in the 70s. Nearly 100 skulls excavated by Neves and Strauss in the last 15 years are now held at the USP. A similar number of fossils is found at the Pontifical Catholic University of Minas Gerais (PUC-MG).
But the vast majority of these osteological and archaeological treasures, belonging to perhaps more than 100 individuals, were deposited at the National Museum of Rio de Janeiro and presumably destroyed in the fire that raged in this historic building on September 2, 2018.
Luzia's skull was exhibited at the National Museum next to Neave's facial reconstruction. Scientists feared that it had been lost by fire, but fortunately it was one of the first objects to be recovered from the ruins. It was broken but survived. The fire destroyed the original facial reconstruction (of which there are several copies).