News — The tales of humanity’s distant past were once revealed only by digging up ancient settlements, bones, and artifacts or by reading ancient texts, from the cuneiform clay tablets of the Hittites to the vivid chronicles of Herodotus.
In the past decade, however, a powerful new window has opened into humanity’s past, in the stories written in the genes of our distant ancestors. Since 2014, the number of individuals from thousands of years ago whose DNA has been analyzed has leapt from a mere handful to more than 8,000. That has ushered in what Kristian Kristiansen, professor of archaeology at University of Gothenburg in Sweden, calls a major scientific revolution. “It has created a new kind of independent evidence to answer questions in archeology that had never before been resolved,” Kristiansen explains.
Indeed, “the first results were quite shocking,” Kristiansen says. For 50 years, scientists had assumed that our ancestors were mostly homebodies, so that recent populations in many countries were largely the descendants of those who had lived in the same general areas for thousands of years. Wrong. Beginning in 2015, ancient DNA pioneer , a Howard Hughes Medical Institute Investigator at Harvard Medical School, and others published genetic data showing that the story of humanity is actually one of vast and frequent migrations. About 5,300 years ago, in detail, nomadic herders called the Yamnaya used newly invented horse-drawn carts to journey from the steppes for far eastern Europe (present-day Ukraine and western Russia) westward across Europe—even to Britain—and eastward to India. As they roamed, they carried with them the seeds of the Indo-European languages spoken by billions of people around the world today. “The DNA evidence was a breakthrough, showing how the languages trace the path of the migration,” explains Reich.
Deeper mysteries
Yet the evidence for the wandering Yamnaya raised deeper mysteries. Where did the closely related languages in ancient Anatolia (modern-day Turkey), such as Hittite, come from? And where was the origin of the parent language to Indo-European and these Anatolian languages? The leading theory was that the steppe population had travelled southeast through the Balkans into Anatolia, bringing an early version of Indo-European. Finding genetic evidence, however, was challenging, says Reich. “The region is hot, and DNA does not do well in a warm environment.”
But then in 2018, geneticists at the University of Copenhagen reported that they’d been able to sample the genes of a few individuals from ancient Anatolia. They found no trace of steppe ancestry, says Guus Kroonen, professor of linguistics at the University of Copenhagen and University Lecturer at the Leiden University Centre for Linguistics. That was unexpected evidence for another theory—that the Anatolian languages came not from the steppe but could rather be traced back to people who lived in the Caucasus highlands, north of the Fertile Crescent.
Now comes a far more complete and detailed answer to that question and others in a trio of papers (and cover image) in the 26 August issue of Science from Reich and a huge team of co-authors. Using advanced techniques for extracting and studying ancient DNA from bones found in the warm climate, the researchers analyzed the genes of 727 individuals across the entire Southern Arc (including modern-day Cyprus, Greece, the Balkans, Turkey, and Armenia), representing a sweeping 11,000 years of human history.
“Points like an arrow”
The new results demolish the previous leading theory—the idea of migrations into Anatolia from the north and west—while providing overwhelming evidence for what the Copenhagen team had suggested. “Our data show almost no DNA from the steppe in Anatolia,” explains Reich. Instead, the genetic analysis “points like an arrow to the Caucasus as the origin of movements that spread populations and languages both north into the steppe and west into Anatolia,” he says. It also reveals that the Caucasus “has been a place that has harbored a lot of diversity for a long time,” says Reich, bolstering the idea that the region has been a crucible for languages and cultures.
“With the DNA, we can see things, like the Anatolian influx in Rome, that that text writers might not have known about or chosen to record due to the biases of the time.”
David Reich, HHMI Investigator at Harvard Medical School
Despite the large number of samples, the genetic signatures in the region don’t provide absolute proof of the origins and spread of languages, linguists caution. They point out that the linguistic evidence doesn’t correlate with the genetic evidence, because the reconstructed Proto-Indo-European lexicon does not reflect the predominantly farming lifestyle that was dominant in the East Mediterranean, including the Caucasus, from an early stage. It’s still conceivable that a small group from the steppe might have traveled to Anatolia, bringing their language, before their genetic signal was lost as they mixed into the existing populations, says Kroonen. But the massive new evidence from Reich’s team for the Caucasus origin of both Hittite (and related languages) in Anatolia and Indo-European in the steppe makes that scenario increasingly unlikely. “It makes a lot of sense, and to me it looks convincing,” says Kristiansen.
The new solutions to major mysteries like the origin and spread of languages is just one of the findings in Reich’s three Science papers, however. The new data also are full of nuggets that fill other gaps in our stories of the past. Some 10,000-12,000 years ago, for example, the first evidence for farming appears in Anatolia. DNA extracted from those farmers shows that their genes are similar to those of contemporary people from Mesopotamia, suggesting a common ancestry. But a bit later, pottery appears in archeological sites in Anatolia for the first time. That’s when new DNA appears in the Anatolian farmers as well, a genetic signature that’s more like that from farmers in the Levant (modern-day Israel and Jordan) rather than Mesopotamia. The conclusion: “There is a migration associated with the arrival of pottery that is really connected to the Levant,” explains Reich.
Another result sheds new light on Roman history, thousands of years after the stories of Anatolian farmers and the steppe migrations. During the heyday of the Roman Empire, Rome was a huge, diverse city. But where did most of the people and their ancestors hail from? Previous studies had shown that they were genetically different from the Italians who initially founded the city but couldn’t pinpoint their origin. “Now we know the answer,” says Reich. The genetic mix found in Romans about 2000 years ago is almost identical to that from Anatolia, suggesting that the people in Imperial Rome were largely descended from Anatolians. That’s not something that the ancient historians mentioned in their voluminous writings. “With the DNA, we can see things, like the Anatolian influx in Rome, that that text writers might not have known about or chosen to record due to the biases of the time,” says Reich.
Ancestry and power
At the same time, though, some of the new evidence adds to the mysteries and complexities. The genetic data show overwhelmingly that Greece was one of many destinations for the Yamnaya nomads as they spread across Europe 5,000-4,000 years ago, bringing with them the precursor of today’s Greek language. And yet the remains of the so-called Griffin Warrior, a wealthy man buried in an incredibly elaborate grave near the ancient city of Pylos in 1450 BC, show that he had nary a trace of steppe ancestry. One might think that the newer arrivals from the steppe might be more privileged and powerful than those they replaced genetically, says Reich. “But here one of the wealthiest people is not associated with the big change,” he says. “It shows there is complexity in the relationship between ancestry and power.”
More broadly, one of the key contributions of the new papers is a technical innovation—a statistical framework that makes it possible for all of the published ancient DNA from many parts of the world to be compared and analyzed together. “That allows us to think about people from diverse regions who are usually studied separately,” Reich explains. The artifacts and settlements unearthed by archeologists often don’t point to possible connections among far-flung populations, he says, but the genetics can, making it possible to tell stories that before were unknown. Thanks to the analysis of ancient DNA, “we can write a much more detailed history of how human populations changed over time and place,” says Reich.
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Citation
Lazaridis I, Alpaslan-Roodenberg S et. al. “,” Science. 2022 Aug 26. doi: 10.1126/science.abm4247
Lazaridis I, Alpaslan-Roodenberg et. al., “,” Science. 2022 Aug 26. doi: 10.1126/science.abq0755.
Lazaridis I, Alpaslan-Roodenberg S et. al. “,” Science. 2022 Aug 26. doi: 10.1126/science.abq0762.
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