Tuesday, July 16, 2024

Medieval Slavic migration transformed gene pool across Balkans

Ancestry from early medieval Slavic migrations is widespread right across the Balkans, including in Greece and other countries that do not have Slavic national identities, according to the first major study of ancient and modern DNA from the region.

Historical records indicate that during the sixth and seventh centuries, while the Eastern Roman Empire was afflicted by plague and warfare, large numbers of people migrated from Eastern Europe into the Balkan Peninsula. The new research, from an international team, confirms this influx but also shows mixing and continuity with earlier local populations such as ancient Greeks, Thracians and Illyrians.

It indicates that today’s Balkan residents have around 30-60 per cent Slavic ancestry, with the higher levels in the north. “We found this genetic signal of Slavic migration all across the Balkans,” said paleogenomicist Professor Carles Lalueza-Fox of the Institute of Evolutionary Biology and Museum of Natural Sciences in Barcelona, senior author of the study published in Cell. “This could have important social and political implications given that the Balkans has had a long history of conflict associated with their perceived identities.”

Previous studies have investigated the ancestry of people in Italy and Britain during and after the fall of the Western Roman Empire, but little has been known about the genetics and demographics of the Balkans around this time.

The sixth-century Eastern Roman, or Byzantine, emperor Justinian, depicted here in a mosaic at Ravenna, was of Thracian or Illyrian origins in the Balkans. Photo: Shutterstock

To explore the population history of the Balkans and examine the influence of Roman rule, the researchers extracted ancient DNA from remains of 136 individuals excavated from 20 different sites in the region. The sites included large Roman cities, military fortresses and small towns. The team focused on three periods: the expansion and height of the Roman Empire from 1-250AD; the late imperial period, from 250-550; and the period following the Western Roman Empire’s collapse (550-1000).

They studied autosomal DNA, showing an individual’s whole ancestry, as well as Y chromosome and mitochondrial DNA showing lineage along the direct male and female lines only. In order to provide historical and cultural context for the genetic data, the team collaborated with local archeologists and historians. For all the remains, they documented the burial type, as well as any grave goods, such as coins, jewellery, pottery, tools and weapons. The researchers also used radiocarbon dating to verify the age of 38 of the individuals, which generated isotopic data that provides insights into their diets.

The Balkans, stretching from Greece to the Danube frontier zone, and adjacent to Italy, was an important region within the Roman Empire and birthplace of emperors including Diocletian, Constantius Chlorus and Justinian. The researchers were surprised to find very little evidence of Iron Age Italian ancestry in Roman-era Balkan populations. Instead, they showed that there was an influx of people from western Anatolia, in modern-day Turkey, from about 1-300AD.

Roman aqueduct that supplied water to Viminacium, a large and cosmopolitan city in what is now Serbia. Photo: Carles Lalueza-Foz

This DNA was mostly evident in individuals buried at the city of Viminacium in modern-day Serbia, but also at other urban centres including Tragurium (Croatia) and Iader (Croatia).

They said this wasn’t particularly surprising given that the empire’s largest population centres, apart from Rome, were in Anatolia and the Middle East. Moreover, large-scale migration from the eastern provinces to Italy is known from Roman literature and has already been shown in DNA studies. It does indicate that these Anatolian migrants not only travelled to the metropolis but also to frontier regions. Pablo Carrión, of the Institute of Evolutionary Biology, co-first author of the study, said: “What we cannot say is whether the migration into the Balkans came directly from Anatolia or from descendants of Anatolians who had migrated to Rome.”

The team also found evidence of individual long-distance migrations into the Balkans from within and outside the Roman Empire. Notably, a second or third-century male of about 16 years old whose remains were excavated at a necropolis at Viminacium was of 100 per cent East African ancestry. He was buried with an oil lamp depicting an eagle, associated with worship of Jupiter, but isotopic analysis of his teeth indicates that he consumed a lot of seafood in his childhood and probably grew up in a distant location.

Skull of the East African individual, along with the oil lamp with the eagle that he was buried with. Photo: Miodrag Grbic

Carrión said: “We know there was the powerful Kingdom of Kush, just south of the Egyptian provinces of the Roman Empire. And we know that the Roman Empire had really strong links, with people moving and trading across the River Nile. He probably migrated in his early years to arrive in the Balkans from Africa.” The circumstances of his migration aren’t clear, but he might have been a slave or his parents may have travelled for trade or other work opportunities. Two other burials at Viminacium from this period were of men of North African ancestry.

Looking at the late imperial period, from 250-550, the researchers detected migrants in the Balkans with mixed ancestry from Northern Europe and the Pontic-Kazakh steppe. Their predominantly Northern European ancestry suggests they belonged to eastern Germanic groups such as Goths, who are known to have settled in the region in late Roman times. After Goths inflicted a crushing defeat on the Romans at the Battle of Adrianople, many were permitted to settle in the Balkans under a treaty of 382.

The team note that these migrants intermarried with existing populations, were buried in Roman cemeteries and appear to have become Romanised. Unlike the Roman-period Anatolian migrations, which left a small but enduring trace in modern Balkan populations, the Germanic settlers made no longterm mark on the gene pool, however. In contrast, the major influx from Eastern Europe around 600 led to lasting changes.

Eastern Roman, or Byzantine, sources describe Slavic people raiding south of the Danube from the early sixth century and raiding and settling widely in the Balkans thereafter. Human remains from after 700 in the Balkans show similar ancestry compositions to present-day individuals in the region. The researchers said this suggested that large-scale migrations of Slavs were the last major demographic shift — in spite of later movements of people under Ottoman rule, for example.

“There have been debates about how impactful these migrations were and to what extent the spread of Slavic language was largely through cultural influences or movements of people, but our study shows that these migrations had a profound demographic effect,” said senior author and population geneticist Professor David Reich of Harvard University. “More than half of the ancestry of most peoples in the Balkans today comes from the Slavic migrations, with around a third Slavic ancestry even in countries like Greece where no Slavic languages are spoken today.”

It appears that women made up a significant proportion of Slavic incomers, more so than in the case of the Anatolian and Germanic migrations. According to the study, levels of Slavic ancestry are around 50-60 per cent in today’s Serbs, Croats, Bulgarians and Romanians, admixed with ancestry from earlier Balkan populations. The level of Slavic ancestry is 30-40 per cent in mainland Greece, falling to 4-20 per cent in the Aegean islands.

The findings may not be universally welcomed in a region where identity is strongly tied to ideas of descent from historic groups. Carrión said: “National identity there is really linked to ethnicity. So the national identity of Serbs, for example, is that they are pure Slavs and linked to Russia. The Croats’ identity is also of pure Slav. The Albanians say they have this population continuity from the Illyrians and there was no impact from later migration. And the Greeks are the same with the ancient Greeks.

“This paper is just showing that people migrate and they interact with other people and groups and they admix — that is completely natural for human beings and we see that from all studies of ancient DNA. But it will definitely cause some controversy.”

Among its further findings, the study shows that Eastern European ancestry was sporadically present in the Balkans long before the big Slavic migrations. For example, they found that a woman who died in the second or third centuries and was buried at Viminacium was of unmixed Eastern European ancestry. They said this illustrates how small movements into the dynamic economy of the Roman Empire may have preceded larger-scale migration. 

The Byzantine Despot’s Palace at Mystras in the Peloponnese, southern Greece, where today’s population are descended from medieval Slavs as well as ancient Greeks, according to the new research. Photo: Shutterstock

Other outliers in the data illustrating historic mobility include a pair of tenth-century twins buried among a group of warriors of Slavic ancestry at a fort site in Northern Serbia. The twins’ DNA indicates that they were not Slavs but probably from what is now Southern France.

The researchers are already planning a follow-up study that will take advantage of improvements in ancient DNA technologies. “We are now able to sequence hundreds of individuals from the same site, so we can go to another level of resolution and start to understand more about the social interactions and kinship between the different individuals,” said population geneticist Dr Iñigo Olalde, of the University of the Basque Country, co-first author.

The team did not focus on genetic history before Roman times. However, they note in the paper that, during the Bronze Age and Iron Age, people of the southern Balkans, such as ancient Greeks, were genetically closer to Near Easterners than those in the northern Balkans. On the other hand, those in the northern Balkans were closer than southerners to Central, Northern and Eastern European Populations. People in the central Balkans were, genetically, in between the two.

A similar pattern persists in modern-day populations. According to the authors, this points to a degree of local continuity from the Iron Age onwards across the entire region, along with the strong impact of arrivals from outside the Balkans, affecting all groups. They write: “Irrespective of modern nation-state boundaries, populations in our study area have been shaped by similar processes of migration and change.”

The photograph at the top of the article includes the medieval fortress of Golubac in Serbia — where localsare descended both from Slavs and earlier Balkan populations, according to the new study. Photo: Shutterstock

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