DNA recovered from ancient skeletons reveals that the genetic makeup of modern Europe was established around 4,500 B.C. in the mid-Neolithic—or 6,500 years ago—and not by the first farmers who arrived in the area around 7,500 years ago or by earlier hunter-gatherer groups. (Read about Europe's oldest known town.)
"The genetics show that something around that point caused the genetic signatures of previous populations to disappear," said Alan Cooper, director of the Australian Centre for Ancient DNA at the University of Adelaide, where the research was performed. "However, we don't know what happened or why, and [the mid-Neolithic] has not been previously identified as [a time] of major change," he said. Furthermore, the origins of the mid-Neolithic populations that did form the basis of modern Europe are also unknown.
"This population moves in around 4,000 to 5,000 [B.C.], but where it came from remains a mystery, as we can't see anything like it in the areas surrounding Europe," Cooper said. The surprising findings are part of a new study, published in this week's issue of the journal Nature Communications, that provides the first detailed genetic history of modern Europe. The study shows that "relatively recent migrations seem to have had a significant genetic impact on the population of Central Europe," said study co-author Spencer Wells, who leads National Geographic's Genographic Project. (Read about Europe's "Wild Men" in National Geographic magazine.)
In the study, Cooper and his colleagues extracted mitochondrial DNA—which children inherit only from their mothers—from the teeth and bones of 39 skeletons found in central Germany. The skeletons ranged in age from about 7,500 to 2,500 years old. The team focused on a group of closely related mitochondrial lineages—mutations in mitochondrial DNA that are similar to one another—known as haplogroup H, which is carried by up to 45 percent of modern Europeans.
Cooper and his colleagues focused on haplogroup H because previous studies have indicated the mutations might have been present in Europeans' genetic makeup for several thousand years. It's unclear how this haplogroup became dominant in Europe. Some scientists have proposed that it spread across the continent following a population boom after the end of the last ice age about 12,000 years ago. But the new data paint a different picture of the genetic foundation of modern Europe: Rather than a single or a few migration events, Europe was occupied several times, in waves, by different groups, from different directions and at different times.
The first modern humans to reach Europe arrived from Africa 35,000 to 40,000 years ago. By about 30,000 years ago, they were widespread throughout the area while their close cousins, the Neanderthals, disappeared. Hardly any of these early hunter-gatherers carried the H haplogroup in their DNA.
About 7,500 years ago during the early Neolithic period, another wave of humans expanded into Europe, this time from the Middle East. They carried in their genes a variant of the H haplogroup, and in their minds knowledge of how to grow and raise crops. (Related: "Egypt's Earliest Farming Village Found.")
Archeologists call these first Central European farmers the linear pottery culture (LBK)—so named because their pottery often had linear decorations. The genetic evidence shows that the appearance of the LBK farmers and their unique H haplogroups coincided with a dramatic reduction of the U haplogroup—the dominant haplogroup among the hunter-gatherers living in Europe at that time.
Farmers Move In
The findings settle a longstanding debate among archaeologists, said Wells, who is also a National Geographic explorer-in-residence. Archaeology alone can't determine whether cultural movements—such as a new style of pottery or, in this case, farming—were accompanied by the movements of people, Wells said in an email. "In this study we show that changes in the European archaeological record are accompanied by genetic changes, suggesting that cultural shifts were accompanied by the migration of people and their DNA." The LBK group and its descendants were very successful and spread quickly across Europe. "They became the first pan-European culture, if you like," Cooper said. Given their success, it would be natural to assume that members of the LBK culture were significant genetic ancestors of many modern Europeans. But the team's genetic analysis revealed a surprise: About 6,500 years ago in the mid-Neolithic, the LBK culture was itself displaced. Their haplogroup H types suddenly became very rare, and they were subsequently replaced by populations bearing a different set of haplogroup H variations.
The details of this "genetic turnover" event are murky. Scientists don't know what prompted it, or even where the new colonizers came from. "The extent or nature of this genetic turnover are not clear, and we don't know how widespread it is," Cooper said. If this turnover were widespread, it could have been prompted by climate change or disease, he said. "All we know is that the descendants of the LBK farmers disappeared from Central Europe about 4,500 [B.C.], clearing the way for the rise of populations from elsewhere, with their own unique H signatures."
Peter Bogucki, an archeologist at Princeton University who has studied early farming societies in Europe, called the finding "really interesting" and noted the timing of the genetic turnover is curious. "At the end of the fifth millennium—[about] 4,000 B.C.—there are a lot of changes in the archeological record," said Bogucki, who was not involved in the study. For example, the long houses that LBK farmers and their descendants favored became less common. Also, the settlement patterns of people living in Central Europe began changing, as did their stone tools. "There are major transformations during this time that haven't really been all that well explained in interior Central Europe," Bogucki said. "It looks like the whole system of agricultural settlement that got established with the LBK ran its course through the fifth millennium and something caused people to change."
Of Unknown Origins
Bogucki agrees that climate change might have been a trigger for the change in Europe's genetic makeup, but he thinks it was only a factor and not the sole cause. One thing that is clear from the genetic data is that nearly half of modern Europeans can trace their origins back to this mysterious group. "About [4,500 B.C.], you start seeing a diversity and composition of genetic signatures that are beginning to look like modern [Central] Europe," Cooper said. "This composition is then modified by subsequent cultures moving in, but it's the first point at which you see something like the modern European genetic makeup in place." Whatever prompted the replacement of genetic signatures from the first pan-European culture, Cooper is clearly intrigued. "Something major happened," he said in a statement, "and the hunt is now on to find out what that was." (That is of course a lie, they know very well where they came from).
Correction: The original version of this article stated that the genetic makeup of modern Europeans emerged 4,500 years ago. The text has been updated to reflect the correct timing as 4,500 B.C., or 6,500 years ago.
The Conversation Media Group
23 March 2015, 6.11am AEDT
Authors: Alan Cooper - Director, Australian Centre for Ancient DNA at University of Adelaide: Wolfgang Haak - University of Adelaide
Map depicting the two major hypotheses of the spread of Indo-European languages (white arrows)
and geographic distribution of the archaeological cultures described in the text.
Europe is famously tesselated (having a checkered appearance), with different cultural and language groups clustering in different regions. But how did they all get there? And how are they related?
One way of answering these questions comes from digging up relics of the past. Europe has a rich archaeological record, ranging from periods well before the famous metal ages (i.e. copper, bronze and iron) to the recent adventures of the Romans, Vandals, Huns and Vikings.
Distinctive types of pottery and cultural practices associated with burials and settlements have been used to group the ancient populations into individual “archaeological cultures”. However, it hasn’t been clear whether there is a genetic basis for these group boundaries or whether they’re just cultural.
Another line of evidence to illuminate how various groups are related comes from their languages. There is the well known Indo-European language tree – ranging from Hindi to Russian to Spanish. But it’s also quite unclear how the languages spread to their present regions.
Now we have another layer of information to help us reveal the history of European peoples: DNA sequencing.
Along with our colleagues, we have been using genome sequencing technology to analyse the vast array of ancient skeletons recovered from across Europe, ranging from the original hunter-gatherer inhabitants to the first farmers who appear around 8,000 years ago, and right up to the early Bronze Age 3,500 years ago.
The genetic results paint a fascinating picture, and were published in a recent series of papers in Nature and Science.
What we have found is that, in addition to the original European hunter-gatherers and a heavy dose of Near Eastern farmers, we can now add a third major population: steppe pastoralists. These nomads appear to have “invaded” central Europe in a previously unknown wave during the early Bronze Age (about 4,500 years ago).
This event saw the introduction of two very significant new technologies to western Europe: domestic horses and the wheel. It also reveals the mysterious source for the Indo-European languages.
The genetic results have answered a number of contentious and long-standing questions in European history. The first big issue was whether the first farmers in Europe were hunter-gatherers who had learnt farming techniques from neighbours in southeast Europe, or did they instead come from the Near East, where farming was invented.
The genetic results are clear: farming was introduced widely across Europe in one or two rapid waves around 8,000 years ago by populations from the Near East -– effectively the very first skilled migrants.
At first the original hunter-gatherer populations appear to have retreated to the fringes of Europe: to Britain, Scandinavia and Finland. But the genetics show that within a few thousand years they had returned, and significant amounts of hunter-gatherer genomic DNA was mixed in with the farmers 7,000 to 5,000 years ago across many parts of Europe.
But there was still a major outstanding mystery. Apart from these two groups, the genomic signals clearly showed that a third -– previously unsuspected – large contribution had been made sometime before the Iron Age, around 2,000 years ago. But by whom?
We have finally been able to identify the mystery culprit, using a clever new system invented by our colleagues at Harvard University.
Instead of sequencing the entire genome from a very small number of well preserved skeletons, we analysed 400,000 small genetic markers right across the genome. This made it possible to rapidly survey large numbers of skeletons from all across Europe and Eurasia.
This process revealed the solution to the mystery. Our survey showed that skeletons of the Yamnaya culture from the Russian/Ukrainian grasslands north of the Black Sea, buried in large mounds known as kurgans, turned out to be the genetic source we were missing.
This group of pastoralists, with domestic horses and oxen-drawn wheeled carts, appear to be responsible for up to 75% of the genomic DNA seen in central European cultures 4,500 years ago, known as the Corded Ware Culture. This must have represented a major wave of people, along with all their cultural and technological baggage.
This discovery also answered another major archaeological conundrum: who or what was the source of the Indo-European language family, which is wide-spread across Eurasia and the world, and includes English, Spanish, French, Greek, Russian and Hindu?
Archaeologists had two major hypotheses: the language family came with either the invading Near East farming wave more than 8,000 years ago, or some form of steppe population sometime much later. Evidence in support of the first hypothesis was the large scale cultural turnover evident with farming.
The second hypothesis was supported by linguistic evidence of common words across Indo-European languages for things like wheeled vehicles and transport that would match the economy and toolkit of the steppe herders.
Our new genomic data finally provides a smoking gun – or a wheeled cart in this case – as the missing evidence of a major cultural contribution from the steppe in the early Bronze Age. While we can’t definitively prove that the Yamnaya were the first to introduce Indo-European language to Europe, the size of the genetic input suggests that it brought at least major parts, if not the whole thing.
So for those of us with European heritage, the next time you see an oxen-drawn cart, or a domestic horse, think “that’s my heritage”, along with a good chunk of hunter-gatherer and a firm base of early farmer.
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