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New research challenges a previous view that humans got to America via this area, where an ice-free corridor existed during the last ice age.

Textbook Story of How Humans Populated America is Biologically Unviable, Study Finds

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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.

The 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”.

The 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.

The 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. The study’s authors suggest that they probably migrated along the Pacific coast.

Opening of human migration routes in North America.

Opening of human migration routes in North America. Credit: Pedersen et al., 2016. Nature

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

“The 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, University of Copenhagen, who conducted the molecular analysis, added: “The 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.”

The 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. The 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?”

The 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.

The 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.

Mikkel W. Pedersen and colleague preparing for coring of the lake sediments.

Mikkel W. Pedersen and colleague preparing for coring of the lake sediments. Image provided by Mikkel Winther Pedersen, Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen.

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.

The 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 University 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.”

The 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

​Top image: New research challenges a previous view that humans got to America via this area, where an ice-free corridor existed during the last ice age. Credit: Mikkel Winther Pedersen

The article ‘ Textbook Story of How Humans Populated America is Biologically Unviable, Study Finds’ was originally published by Cambridge University and has been republished under a Creative Commons license.

Comments

And I think it is very probable that when they did come South there were already peoples there. This chart shows that it is beyond a doubt that the most common indigenous Blood Type “O” originated in South America and spread North.. No way it could have happened any other way!

  http://anthro.palomar.edu/vary/vary_3.htm

Roberto Peron's picture

Frankly, I think man has been sailing the waves for a long, long time!  The land route was not viable but the water route was.  So they made boats and came south with little to no problem. Ancient man was NOT the stereotypical “cave man” but was far more intelligent and industrious than we might wish to think.  It’s time to give our ancestors some credit and stop painting this absurb picture of them as club carrying  dolts!! 

Natve American's have nothing to do with that Middle Eastern religious Clap trap! They didnt exist in that fairy tale, keep them out of it! Also, all the Pacific fishing Cultures did grow beards . Haida, Aleuts, Bella Coola, Yuki, Chumash, Peicue, Fuegans. Even the Paiute and some AmaInians had heavy beards. The Chumash and the Yuki in Califirnia had the most full bears. Look up Fernando Librado a full blooded Chumash Indian from Santa Cruz Island off the Coast of Southern California, when the Spanish came they called the island , Island of the Bearded Men. Fernando Librado had a beard that would put a white man to Shame the Chumash Indians were the First Natives to have a true Maritime culture and the only Indians to make and issue true money, they were also the only ones that had guilds to make Boats out of planks. They have lived ob Santa Rosa and Santa Cruz islands continuously for over 13,000 years. Arlington Springs woman is most likely their ancestor. Google the Chumash and Fernando Librado if you dont believe me. Youll never say Indians cant grow beards again.

The gods brought the Canaanites here when Cain was exiled from the Edin. The gods also marked them genetically so they could not grow beards.

Thank you for your reply!, I agree, the refusal to recognize that everything natural does indeed cycle is a problem. There have been Five "Ice Ages" over the last 500,000 years of Mankind yet we refuse to look beyond the very last one. Man could have advanced and declined during every one of these.

http://www.ncdc.noaa.gov/paleo/abrupt/data2.html

I'm just having trouble with the overall sureness that Early Man would never try to stick his toes in the Water. Removing just this concept alone would open huge barriers in thought and discovery. I am very sure that many very early Symbols do indeed share Round Earth and Seafaring knowledge.

But because if the Firewall Mental Block the theories are tossed to the side and never investigated further. Why is the "What if they could?" form of investigation so Radical and Irrational? The theory that man absolutely feared water and would never touch it until only about 4,000 years ago is just as Radical and Irrational and down right lacks any Proof in Fact.

You are right...Those who have proven the Earth Round now once again view it as flat without further discussion. So without any facts to support their own sureness then it could only originate from Superstition, Blindness or Ignorance and is unfortunately a huge loss for Science...

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