[lg policy] DNA Deciphers Roots of Modern Europeans
wfierman at indiana.edu
Thu Jun 11 16:19:51 UTC 2015
DNA Deciphers Roots of Modern Europeans
JUNE 10, 2015
For centuries, archaeologists have reconstructed the early history of Europe by digging up ancient settlements and examining the items that their inhabitants left behind. More recently, researchers have been scrutinizing something even more revealing than pots, chariots and swords: DNA.
On Wednesday in the journal Nature, two teams of scientists - one based at the University of Copenhagen and one based at Harvard University - presented the largest studies to date of ancient European DNA, extracted from 170 skeletons found in countries from Spain to Russia. Both studies indicate that today's Europeans descend from three groups who moved into Europe at different stages of history.
The first were hunter-gatherers who arrived some 45,000 years ago in Europe. Then came farmers who arrived from the Near East about 8,000 years ago.
Matter. It's the stuff of everything - large and small.
Finally, a group of nomadic sheepherders from western Russia called the Yamnaya arrived about 4,500 years ago. The authors of the new studies also suggest that the Yamnaya language may have given rise to many of the languages spoken in Europe today.
A Yamnaya skull found near Samara, Russia, colored with ocher. Yamnaya expansion into Europe was most likely relatively peaceful. Credit Natalia Shishlina
Ron Pinhasi, an archaeologist at University College Dublin who was not involved in either study, said that the new studies were "a major game-changer. To me, it marks a new phase in ancient DNA research."
The two teams worked independently, studying different skeletons and using different methods to analyze their DNA.
The Harvard team collected DNA from 69 human remains dating back 8,000 years and cataloged the genetic variations at almost 400,000 different points. The Copenhagen team collected DNA from 101 skeletons dating back about 3,400 years and sequenced the entire genomes.
Both teams also compared the newly sequenced DNA to genes retrieved from other ancient Europeans and Asians, and to living humans.
Until about 9,000 years ago, Europe was home to a genetically distinct population of hunter-gatherers, the researchers found. Then, between 9,000 and 7,000 years ago, the genetic profiles of the inhabitants in some parts of Europe abruptly changed, acquiring DNA from Near Eastern populations.
Archaeologists have long known that farming practices spread into Europe at the time from Turkey. But the new evidence shows that it wasn't just the ideas that spread - the farmers did, too.
The hunter-gatherers didn't disappear, however. They managed to survive in pockets across Europe between the farming communities.
"It's an amazing cultural process," said David Reich, a geneticist at Harvard Medical School who led the university's team. "You have groups which are as genetically distinct as Europeans and East Asians. And they're living side by side for thousands of years."
Between 7,000 and 5,000 years ago, however, hunter-gatherer DNA began turning up in the genes of European farmers. "There's a breakdown of these cultural barriers, and they mix," said Dr. Reich.
About 4,500 years ago, the final piece of Europe's genetic puzzle fell into place. A new infusion of DNA arrived - one that is still very common in living Europeans, especially in central and northern Europe.
The closest match to this new DNA, both teams of scientists found, comes from skeletons found in Yamnaya graves in western Russia and Ukraine.
Archaeologists have long been fascinated by the Yamnaya, who left behind artifacts on the steppes of western Russia and Ukraine dating from 5,300 to 4,600 years ago. The Yamnaya used horses to manage huge herds of sheep, and followed their livestock across the steppes with wagons full of food and water.
It was an immensely successful way of life, allowing the Yamnaya to build huge funeral mounds for their dead, which they filled with jewelry, weapons and even entire chariots.
A skeleton buried by a Middle Neolithic culture found near Saxony-Anhalt, Germany. A review of DNA from skeletons across Europe indicated that today's Europeans are descended from three groups who moved there at different stages of history. Credit Juraj Lipták/LDA Sachsen-Anhalt
David W. Anthony, an archaeologist at Hartwick College and a co-author on the Harvard study, said it was likely that the expansion of Yamnaya into Europe was relatively peaceful. "It wasn't Attila the Hun coming in and killing everybody," he said.
Instead, Dr. Anthony thought the most likely scenario was that the Yamnaya "entered into some kind of stable opposition" with the resident Europeans that lasted for a few centuries. But then gradually the barriers between the cultures eroded.
The Copenhagen team's study suggests that the Yamnaya didn't just expand west into Europe, however. The scientists examined DNA from 4,700-year-old skeletons from a Siberian culture called the Afanasievo. It turns out that they inherited Yamnaya DNA, too.
Dr. Anthony was surprised by the possibility that Yamnaya pushed out over a range of about 4,000 miles. "I myself have a hard time wrapping my head around explanations for that," he said.
The two studies also add new fuel to a debate about how languages spread across Europe and Asia. Most European tongues belong to the Indo-European family, which also incudes languages in southern and Central Asia.
For decades, linguists have debated how Indo-European got to Europe. Some favor the idea that the original farmers brought Indo-European into Europe from Turkey. Others think the language came from the Russian steppes thousands of years later.
The new genetic results won't settle the debate, said Eske Willerslev, an evolutionary biologist at Copenhagen University who led the Danish team. But he did think the results were consistent with the idea that the Yamnaya brought Indo-European from the steppes to Europe.
The eastward expansion of Yamnaya, evident in the genetic findings, also supports the theory, Dr. Willerslev said. Linguists have long puzzled over an Indo-European language once spoken in western China called Tocharian. It is only known from 1,200-year-old manuscripts discovered in ancient desert towns. It is possible that Tocharian was a vestige of the eastern spread of the Yamnaya.
"We can just say that the expansion fits very well with the geographical spread of the Indo-European language," said Dr. Willerslev.
Paul Heggarty, a linguist at the Max Planck Institute of Evolutionary Anthropology, said that the new studies were important, but were still too limited to settle the debate over the origins of Indo-European. "I don't think we're there yet," he said.
Dr. Heggarty noted that the studies showed the arrival of Yamnaya in Central Europe about 4,500 years ago. But Greek is an Indo-European language, and the oldest evidence of writing in Europe shows that Greek had developed about 3,500 years ago. By then, it was distinct from other Indo-European languages in Southern Europe, like Latin.
If the Yamnaya were the source of Indo-European languages, they would have had to get to southern Europe soon after they made it to Central Europe.
Dr. Heggarty speculated instead that early European farmers, the second wave of immigrants, may have brought Indo-European to Europe from the Near East. Then, thousands of years later, the Yamnaya brought the language again to Central Europe.
More ancient DNA could swing the balance of evidence in favor of one theory over the other, Dr. Heggarty said. A stronger case for a steppe origin of Indo-European might emerge, for example, if scientists discovered that Greeks around 4,500 years ago abruptly acquired Yamnaya DNA.
"Let's see whether they look like the steppe people or not," he said.
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