Wednesday, November 21, 2018

Extremely Fast Peopling of the Americas

Ed Yong
A skull from Lagoa Santa, Brazil (Natural History Museum of Denmark)
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Were the Native Americans "human"?
Two genetic studies show how the first Native Americans spread through their new continent with incredible speed.

Tens of thousands of years ago, two gigantic ice sheets smothered the northernmost parts of what has since been named North America.

They towered more than two kilometers high and contained 1.5 times as much water as Antarctica does today. They were daunting, impassable barriers to the early humans who had started moving east from Asia, walking across a land bridge that once connected the regions now known as Russia and Alaska.

Flowering azaleasBut once the ice started to melt, these peoples -- [allegedly] the ancestors of the Americas’ Indigenous groups -- spread southward into new lands. What happened next?

 
Genetic studies, based on ancient remains, had already suggested that once the first American Indians got south of the ice, 14,600 to 17,500 years ago, they split into two main branches.
 
One stayed north, giving rise to the Algonquian-speaking peoples of Canada. The other headed south, giving rise to the widespread Clovis culture, and to Central and South Americans. That’s a very rough outline, but a new study from J. Víctor Moreno-Mayar and his colleagues fleshes it out. They showed that whatever happened south of the ice, it happened fast.
 
They sequenced the genomes of 15 ancient humans, who came from sites ranging all the way from Alaska to Patagonia. One person from Spirit Cave in Nevada and five from Lagoa Santa in Brazil were especially instructive.
 
They were all just over 10,000 years old, and though they lived 6,300 miles apart, they were strikingly similar in their DNA. Genetically, they were also closely matched to Anzick-1 -- a famous Clovis infant from Montana, who was about 2,000 years older.

The International Space Station, with Earth belowAll this suggests that, about 14,000 years ago, the southern lineage of early American Indians spread through the continent with blinding speed. To picture their movements, don’t think of a slowly growing tree, incrementally sending out new branches and twigs. Instead, imagine a starburst, with many rays zooming out simultaneously and rapidly.
 
In a matter of centuries, these people had gone down both sides of the Rockies, across the Great Basin, and into Mexico’s highlands. Within a couple more millennia, they had zipped down the Andes, through the Amazon, and as far south as the continent allowed. “Once they were south of the ice, they found a territory that was open, vast, and full of resources,” says Moreno-Mayar, who is based at the University of Copenhagen. “They were adept hunter-gatherers, so they expanded very quickly.”
 
This pattern confirms the suspicions of archaeologists, whose finds had long suggested that... More
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