̽��ֱ�� of Cambridge - North America

Trump voters believe American values and prosperity are ‘under threat’

fpjl2 — Mon, 11 Nov 2024 08:31:40 +0000

Data also suggests that Democrat appeals to unity were popular across the board, but “politicians need to do more to understand why some people feel under threat”.

Direct genetic evidence of founding population reveals story of first Native Americans

tdk25 — Wed, 03 Jan 2018 18:00:05 +0000

̽��ֱ��data, which came from archaeological finds in Alaska, also points to the existence of a previously unknown Native American population, whom academics have named “Ancient Beringians”.

̽��ֱ��findings are being published in the journal Nature and present possible answers to a series of long-standing questions about how the Americas were first populated.

It is widely accepted that the earliest settlers crossed from what is now Russia into Alaska via an ancient land bridge spanning the Bering Strait which was submerged at the end of the last Ice Age. Issues such as whether there was one founding group or several, when they arrived, and what happened next, are the subject of extensive debate, however.

In the new study, an international team of researchers led by academics from the Universities of Cambridge and Copenhagen sequenced the full genome of an infant – a girl named Xach'itee'aanenh t'eede gay, or Sunrise Child-girl, by the local Native community - whose remains were found at the Upward Sun River archaeological site in Alaska in 2013.

To their surprise, they found that although the child had lived around 11,500 years ago, long after people first arrived in the region, her genetic information did not match either of the two recognised branches of early Native Americans, which are referred to as Northern and Southern. Instead, she appeared to have belonged to an entirely distinct Native American population, which they called Ancient Beringians.

Further analyses then revealed that the Ancient Beringians were an offshoot of the same ancestor population as the Northern and Southern Native American groups, but that they separated from that population earlier in its history. This timeline allowed the researchers to construct a picture of how and when the continent might have been settled by a common, founding population of ancestral Native Americans, that gradually divided into these different sub-groupings.

̽��ֱ��study was led by Professor Eske Willerslev, who holds positions both at St John’s College, ̽��ֱ�� of Cambridge, and the ̽��ֱ�� of Copenhagen in Denmark.

“ ̽��ֱ��Ancient Beringians diversified from other Native Americans before any ancient or living Native American population sequenced to date. It’s basically a relict population of an ancestral group which was common to all Native Americans, so the sequenced genetic data gave us enormous potential in terms of answering questions relating to the early peopling of the Americas,” he said.

“We were able to show that people probably entered Alaska before 20,000 years ago. It’s the first time that we have had direct genomic evidence that all Native Americans can be traced back to one source population, via a single, founding migration event.”

̽��ֱ��study compared data from the Upward Sun River remains with both ancient genomes, and those of numerous present-day populations. This allowed the researchers first to establish that the Ancient Beringian group was more closely related to early Native Americans than their Asian and Eurasian ancestors, and then to determine the precise nature of that relationship and how, over time, they split into distinct populations.

Until now, the existence of two separate Northern and Southern branches of early Native Americans has divided academic opinion regarding how the continent was populated. Researchers have disagreed over whether these two branches split after humans entered Alaska, or whether they represent separate migrations.

̽��ֱ��Upward Sun River genome shows that Ancient Beringians were isolated from the common, ancestral Native American population, both before the Northern and Southern divide, and after the ancestral source population was itself isolated from other groups in Asia. ̽��ֱ��researchers say that this means it is likely there was one wave of migration into the Americas, with all subdivisions taking place thereafter.

According to the researchers’ timeline, the ancestral population first emerged as a separate group around 36,000 years ago, probably somewhere in northeast Asia. Constant contact with Asian populations continued until around 25,000 years ago, when the gene flow between the two groups ceased. This cessation was probably caused by brutal changes in the climate, which isolated the Native American ancestors. “It therefore probably indicates the point when people first started moving into Alaska,” Willerslev said.

Around the same time, there was a level of genetic exchange with an ancient North Eurasian population. Previous research by Willerslev has shown that a relatively specific, localised level of contact between this group, and East Asians, led to the emergence of a distinctive ancestral Native American population.

Ancient Beringians themselves then separated from the ancestral group earlier than either the Northern or Southern branches around 20,000 years ago. Genetic contact continued with their Native American cousins, however, at least until the Upward Sun River girl was born in Alaska around 8,500 years later.

̽��ֱ��geographical proximity required for ongoing contact of this sort led the researchers to conclude that the initial migration into the Americas had probably already taken place when the Ancient Beringians broke away from the main ancestral line. José Víctor Moreno-Mayar, from the ̽��ֱ�� of Copenhagen, said: “It looks as though this Ancient Beringian population was up there, in Alaska, from 20,000 years ago until 11,500 years ago, but they were already distinct from the wider Native American group.”

Finally, the researchers established that the Northern and Southern Native American branches only split between 17,000 and 14,000 years ago which, based on the wider evidence, indicates that they must have already been on the American continent south of the glacial ice.

̽��ֱ��divide probably occurred after their ancestors had passed through, or around, the Laurentide and Cordilleran ice sheets – two vast glaciers which covered what is now Canada and parts of the northern United States, but began to thaw at around this time.

̽��ֱ��continued existence of this ice sheet across much of the north of the continent would have isolated the southbound travellers from the Ancient Beringians in Alaska, who were eventually replaced or absorbed by other Native American populations. Although modern populations in both Alaska and northern Canada belong to the Northern Native American branch, the analysis shows that these derive from a later “back” migration north, long after the initial migration events.

“One significant aspect of this research is that some people have claimed the presence of humans in the Americas dates back earlier – to 30,000 years, 40,000 years, or even more,” Willerslev added. “We cannot prove that those claims are not true, but what we are saying, is that if they are correct, they could not possibly have been the direct ancestors to contemporary Native Americans.”

Reference:

Willerslev, E, et al. Terminal Pleistocene Alaskan genome reveals first founding population of Native Americans. Nature. 3 Jan 2018. DOI: 10.1038/nature25173

Direct genetic traces of the earliest Native Americans have been identified for the first time in a new study. ̽��ֱ��genetic evidence suggests that people may have entered the continent in a single migratory wave, perhaps arriving more than 20,000 years ago.

It’s the first time that we have had direct genomic evidence that all Native Americans can be traced back to one source population, via a single, founding migration event

Eske Willerslev

Ben Potter.

Excavations at the Upward Sun River archaeological site in Alaska. ̽��ֱ��new study shows that the remains found there belonged to members of a previously unknown Native American population, whom academics have named “Ancient Beringians”.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Textbook story of how humans populated America is “biologically unviable”, study finds

tdk25 — Wed, 10 Aug 2016 17:00:08 +0000

̽��ֱ��established theory about how Ice Age peoples first reached the present-day United States has been challenged by an unprecedented study which concludes that their supposed entry route was “biologically unviable”.

̽��ֱ��first people to reach the Americas crossed via an ancient land bridge between Siberia and Alaska but then, according to conventional wisdom, had to wait until two huge ice sheets that covered what is now Canada started to recede, creating the so-called “ice-free corridor” which enabled them to move south.

In a new study published in the journal Nature, however, an international team of researchers used ancient DNA extracted from a crucial pinch-point within this corridor to investigate how its ecosystem evolved as the glaciers began to retreat. They created a comprehensive picture showing how and when different flora and fauna emerged and the once ice-covered landscape became a viable passageway. No prehistoric reconstruction project like it has ever been attempted before.

̽��ֱ��researchers conclude that while people may well have travelled this corridor after about 12,600 years ago, it would have been impassable earlier than that, as the corridor lacked crucial resources, such as wood for fuel and tools, and game animals which were essential to the hunter-gatherer lifestyle.

If this is true, then it means that the first Americans, who were present south of the ice sheets long before 12,600 years ago, must have made the journey south by another route. ̽��ֱ��study’s authors suggest that they probably migrated along the Pacific coast.

Who these people were is still widely disputed. Archaeologists agree, however, that early inhabitants of the modern-day contiguous United States included the so-called “Clovis” culture, which first appear in the archaeological record over 13,000 years ago. And the new study argues that the ice-free corridor would have been completely impassable at that time.

̽��ֱ��research was led by Professor Eske Willerslev, an evolutionary geneticist in the Department of Zoology and Fellow of St John’s College, ̽��ֱ�� of Cambridge, who also holds posts at the Centre for GeoGenetics, ̽��ֱ�� of Copenhagen, and the Wellcome Sanger Institute in Cambridge.

“ ̽��ֱ��bottom line is that even though the physical corridor was open by 13,000 years ago, it was several hundred years before it was possible to use it,” Willerslev said.

“That means that the first people entering what is now the US, Central and South America must have taken a different route. Whether you believe these people were Clovis, or someone else, they simply could not have come through the corridor, as long claimed.”

Mikkel Winther Pedersen, a PhD student at the Centre for GeoGenetics, ̽��ֱ�� of Copenhagen, who conducted the molecular analysis, added: “ ̽��ֱ��ice-free corridor was long considered the principal entry route for the first Americans. Our results reveal that it simply opened up too late for that to have been possible.”

̽��ֱ��corridor is thought to have been about 1,500 kilometres long, and emerged east of the Rocky Mountains 13,000 years ago in present-day western Canada, as two great ice sheets – the Cordilleran and Laurentide, retreated.

On paper, this fits well with the argument that Clovis people were the first to disperse across the Americas. ̽��ֱ��first evidence for this culture, which is named after distinctive stone tools found near Clovis, New Mexico, also dates from roughly the same time, although many archaeologists now believe that other people arrived earlier.

“What nobody has looked at is when the corridor became biologically viable,” Willerslev said. “When could they actually have survived the long and difficult journey through it?”

̽��ֱ��conclusion reached by Willerslev and his colleagues is that the journey would have been impossible until about 12,600 years ago. Their research focused on a “bottleneck”, one of the last parts of the corridor to become ice-free, and now partly covered by Charlie Lake in British Columbia, and Spring Lake, Alberta – both part of Canada’s Peace River drainage basin.

̽��ֱ��team gathered evidence including radiocarbon dates, pollen, macrofossils and DNA taken from lake sediment cores, which they obtained standing on the frozen lake surface during the winter season. Willerslev’s own PhD, 13 years ago, demonstrated that it is possible to extract ancient plant and mammalian DNA from sediments, as it contains preserved molecular fossils from substances such as tissue, urine, and faeces.

Having acquired the DNA, the group then applied a technique termed “shotgun sequencing”. “Instead of looking for specific pieces of DNA from individual species, we basically sequenced everything in there, from bacteria to animals,” Willerslev said. “It’s amazing what you can get out of this. We found evidence of fish, eagles, mammals and plants. It shows how effective this approach can be to reconstruct past environments.”

This approach allowed the team to see, with remarkable precision, how the bottleneck’s ecosystem developed. Crucially, it showed that before about 12,600 years ago, there were no plants, nor animals, in the corridor, meaning that humans passing through it would not have had the resources that were essential for their survival.

Around 12,600 years ago, steppe vegetation started to appear, followed quickly by animals such as bison, woolly mammoth, jackrabbits and voles. Importantly 11,500 years ago, the researchers identified a transition to a “parkland ecosystem” – a landscape densely populated by trees, as well as moose, elk and bald-headed eagles, which would have offered crucial resources for migrating humans.

Somewhere in between, the lakes in the area were populated by fish, including several identifiable species such as pike and perch. Finally, about 10,000 years ago, the area transitioned again, this time into boreal forest, characterised by spruce and pine.

̽��ֱ��fact that Clovis was clearly present south of the corridor before 12,600 years ago means that they could not have travelled through it. David Meltzer, an archaeologist at Southern Methodist ̽��ֱ�� and a co-author on the study, said: “There is compelling evidence that Clovis was preceded by an earlier and possibly separate population, but either way, the first people to reach the Americas in Ice Age times would have found the corridor itself impassable.”

“Most likely, you would say that the evidence points to their having travelled down the Pacific Coast,” Willerslev added. “That now seems the most likely scenario.”

̽��ֱ��paper Postglacial viability and colonization in North America's ice-free corridor is published in the journal Nature on 10. August 2016. DOI: 10.1038/nature19085

Inset images: Map outlining the opening of the human migration routes in North America revealed by the results presented in this study. / Mikkel W. Pedersen and colleague preparing for coring of the lake sediments. All images provided by Mikkel Winther Pedersen, Centre for GeoGenetics, Natural History Museum of Denmark, ̽��ֱ�� of Copenhagen.

Using ancient DNA, researchers have created a unique picture of how a prehistoric migration route evolved over thousands of years – revealing that it could not have been used by the first people to enter the Americas, as traditionally thought.

̽��ֱ��first people entering what is now the US, Central and South America must have taken a different route to the one that has long been claimed

Eske Willerslev

Mikkel Winther Pedersen, Centre for GeoGenetics, Natural History Museum of Denmark, ̽��ֱ�� of Copenhagen

̽��ֱ��fieldwork was conducted during the winter because the frozen lake surface provided the researchers with a solid (but freezing) platform for drilling into the sediment

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes