October 10, 2013
In genetics, it’s not just the living who advance the field: DNA preserved in the brittle bones of our ancestors can provide significant insight into our genetic history. Such is the case with a new genetic history of Europe, traced by an international team of researchers and published today in Science. By creating a seamless genetic map from 7,500 to 3,500 years ago in one geographic region, scientists discovered that the genetic diversity of modern day Europe can’t be explained by a single migration, as previously thought, but by multiple migrations coming from a range of areas in modern day Europe.
To write the genetic history of Europe is to glance into the evolution of a Western culture and, often, to be greeted with more questions than answers: Why do 45 percent of Europeans share a distinct kind mitochondrial DNA (DNA passed down through the maternal line) known as haplogroup H? What causes one type of mitochondrial DNA to become dominant over another kind? Can changes in an archaeological record mirror changes in a genetic record?
The new genetic history might provide some answers to these questions. To attempt to piece together Europe’s vast genetic history, researchers from the Australian Centre for Ancient DNA (ACAD) at the University of Adelaide, the University of Mainz, the State Heritage Museum in Halle (Germany), and National Geographic Society’s Genographic Project extracted mitochondrial DNA from the teeth and bones of 396 prehistoric skeletons. These skeletons were found in a rather small and confined area within the German state of Saxony-Anhalt, an area which in previous studies had proved to hold a number of usable skeletal samples.
“We collected over 400 samples from skeletal individuals and extracted DNA. And for 396 of them, we got unambiguous results that could be confirmed,” says Dr. Wolfgang Haak of ACAD, a
lead author of the study. “DNA is not preserved in all individuals, so that was a fantastic success rate.”
The study included a wealth of data not seen before
–ten times as much mitochondrial DNA was examined as in previous studies, making it the largest examination of ancient DNA to date. Such a large amount of data allowed the researchers to create a “a gapless record…from the earliest farmers to the early Bronze Age,” says Haak in a press statement.
One of the ways researchers were able to piece together this gapless genetic record was by narrowing their skeletal samples to a single region. The region in Saxony-Anhalt is especially fruitful when it comes to ancient skeletal samples due to recent political history: after the Berlin Wall was torn down, part of former East Germany underwent a tremendous amount of infrastructural revitalization. In the process of digging new roads and motorways, a number of ancient skeletons were uncovered, boosting the archeological record so much that researchers have access to a sample of specimens ranging from 7,500 years ago to present-day. Moreover, by confining their search within distinct geographic parameters, the researchers were able to construct a real transect of what happened through time in a specific place, instead of a “patchy record of here and there,” as Haak describes the alternative.
What they found surprised them. In an earlier study, Haak and his colleagues used ancient DNA to show that lifestyles in Central Europe switched from hunting and gathering to farming around 5,500 BCE soon after a wave of migration from the Near East, evidenced
by a visible change in the genetic makeup when farming enters the archeological record. But the genetic diversity of modern Europe is too complex to be explained by this migration event alone.
The conundrum that left Haak and researchers puzzled–until now. By taking samples from specimens that create a complete timeline in Saxony-Anhalt, the researchers could pinpoint when changes within the mitochondrial DNA occurred. Confirming their past finding, they saw that while the DNA patterns changed with the influx of farming, they also changed thousands of years later.
By comparing the timing of these genetic changes with a timeline of archaeological finds in central Europe, and by looking up the cultural origins of new artifacts that pop up in the timeline when these genetic changes happened, researchers suggest that the genetic history of Europeans was not only affected by a migration of farmers from the Near East, but by subsequent migrations from cultures in to the west (what is now the Iberian Peninsula) and east (what is now Latvia, Lithuania, the Czech Republic and other modern Eastern European countries).
“With this genetic timeline, we can confirm that the first genetic change occurred between hunter-gatherers and farmers, and it’s surprisingly stable for about two thousand years, when farming is completely established,” Haak explains. “Then, towards the end of the Neolithic, we gain a bit of momentum and see a bunch of early hunter-gatherer lineages coming back. And then again, shortly after that, we see new impulses, coming both from the East and the West. There are suddenly these additionally elements that make-up most of the modern-day diversity. By the time that we reach the early Bronze Age, we have mostly everything in place that we see today.”
The authors’ hypotheses on where these waves of migrations came from relies on the idea that new cultural artifacts, if found in a specific region, must have been brought by travelers far away. But new tools and artifacts, by themselves, don’t automatically mean that migrations have happened to freshen the gene pool: as Haak notes, just because one uses an iPod does not make one distinctly American, or European, or anything else. Nonetheless it seems that, at least in ancient times, new tools and technologies might have gone hand in hand with genetic influxes as migrants brought old techniques to their new lands.
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