Supporting a controversial view of how humans might have populated the Western Hemisphere, geneticists have found that groups from Asia traveled over the Bering Strait into North America in at least three separate migrations beginning more than 15,000 years ago — not in a single wave, as has been widely thought.
"We have various lines of evidence that there was more than one migration," said Dr. Andres Ruiz-Linares, a professor of human genetics at University College London and senior author of a report on the findings that was published Wednesday by the journal Nature.And this from The Science Codex:
The discovery was made possible by the sheer volume of genetic material the team was able to assemble and analyze, he said.
Ruiz-Linares and colleagues around the world analyzed DNA samples, primarily from blood, taken from hundreds of modern-day Native Americans and other indigenous people representing 52 distinct populations. These included Inuits of east and west Greenland, Canadian groups including the Algonquin and the Ojibwa, and a larger variety of people spanning the southern regions of the Americas from Mexico to Peru.
Investigating patterns in more than 350,000 gene variants, the scientists determined that most of the groups they studied did indeed descend from an original "First American" population.
However, they also saw that Eskimo-Aleut populations of the Arctic inherited almost half of their DNA from a second ancestral group, and the Na-Dene-speaking Chipewyans, from Canada, got about 10% of theirs from yet another group.
The results lined up nicely with a controversial model for the colonization of the Americas that was proposed in 1986 by Stanford University anthropological linguist Joseph Greenberg, Ruiz-Linares said.
By examining similarities between many native languages, Greenberg argued that the Americas were populated through three distinct migrations. But his hypothesis was widely rejected by researchers who didn't agree with his classification of languages.
The evidence for a pre-13,000 year old non-Clovis culture in North America includes obsidian and chert artifacts known as Western Stemmed projectile points, and DNA-profiling of dried human excrement — more accurately known as coprolites. Both obsidian projectile points and coprolites were excavated from sediments in the Paisley Caves.
Previous investigations found that human coprolites in the caves predated the Clovis culture by over 1,000 years; however, critics questioned the interpretations by saying that the cave strata had not been sufficiently examined and that no Clovis-age stone tools had been found with the coprolites.
Critics also questioned whether or not younger DNA could have been washed down through the cave's sediments, thereby contaminating non-human coprolites with more recent human DNA. If true, evidence for pre-Clovis human presence would have been bogus.
The new study refutes every one of the critics' arguments and uses overwhelming archaeological, stratigraphic, DNA and radiocarbon evidence to conclusively state that humans — and ones totally unrelated to Clovis peoples — were present at Paisley Caves over a millennium before Clovis.
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It's not the first time that the partners Dr. Jenkins from the US and Professor Willerslev from Denmark rewrite American prehistory.
In 2008, the two researchers presented a DNA-profiling's and radiocarbon dating of coprolites moving the first human settlements in North America back in time by one thousand years, from 13,000 to 14,340 years ago. As if that was not enough, the team showed through DNA analysis of ancient human excrement that these people originated in Asia and were the probable predecessors of modern indigenous Americans.
With the new results the international team has added an important piece to the puzzle of who peopled the Americas — the final continent on Earth to be colonized by humans.
Professor Willerslev says of the new results:
"Our investigations constitute the final blow to the Clovis First theory. Culturally, biologically and chronologically the theory is no longer viable. The dissimilar stone artefacts, as well as the DNA-profiling of the human excrement, show that humans were present before Clovis and that another culture in North America was at least as old as the Clovis Culture itself. Or to put it differently: Either America was populated several thousand years before Clovis by people who created 'mother' technologies to the two very different styles of Clovis tools and Western Stemmed Tradition tools. Or else there must have been two earlier migrations into North America of which one must have predated the Clovis immigration by at least one thousand years. Both assumptions would explain our findings, but trying to distinguish which is more likely is very premature."
Dr Paula Campos, a former postdoc at Willerslev's lab in Copenhagen, now at Science Museum, University of Coimbra, Portugal, elaborates the point:
"When we published the first DNA results from the Paisley Caves four years ago it caused an outcry. Many archaeologists felt that our results must be wrong. They considered it an established fact that Clovis were the first Americans. People would come up with any number of alternative explanations to our data in order to repudiate our interpretation. Today we demonstrate that our conclusions were right."
Thomas Stafford, also of the Centre for GeoGenetics in Copenhagen, and Loren Davies of Oregon State University agree:
"Critics said that the stratigraphy in the Paisley Caves is diffuse and chaotic and that this explains the finding of human coprolites older that Clovis. This couldn't be more wrong. The stratigraphy is well developed, clear and ordered correctly top to bottom."