Ancient mobility as reflected in genetics

View of the remains of the necropolis of the city of Portus Ostiensis Augusti, which, as Rome’s port, was symbolic of the empire’s extensive network. © Parco Archeologico di Ostia Antica – archives, Italy

How intense was the exchange between the peoples of Europe and the Mediterranean in ancient times? Results from the study of genetic material from the remains of people from the area of ​​the former Roman Empire now provide new evidence of the strong mobility during its heyday. Around eight percent of the people examined as part of the study did not originally come from the region in which they were buried. Indirectly, the results also provide evidence that people's mobility declined sharply again in the wake of the fall of the Roman Empire, say the scientists.

For a long time, only special archaeological finds or historical clues provided insight into population developments in the past. But modern genetics has now revolutionized this field of research: through analyzes and comparisons of ancient DNA that can be obtained from human bones, conclusions can be drawn about ethnic affiliations and ancestry. Among other things, archaeogenetics has already provided interesting insights into the prehistoric development of population structure in Europe. For example, the genomes from the period between 14,000 and 3,000 years ago reflect the immigration of Neolithic farmers and Bronze Age steppe inhabitants. Surprisingly, however, less is known about how the population structure in Europe and the Mediterranean region has changed in the historical era since antiquity.

On the trail of newcomers

In the current study, an international research team has now devoted itself to studying population genetics over the last 3,000 years. The focus was on the era of the Roman Empire. The study was based on analyzes of existing DNA data from thousands of skeletal finds from various regions of the Roman Empire, as well as other areas of Europe, Asia and North Africa. In addition, the researchers sequenced 204 new genomes from 53 archaeological sites in 18 countries. Most of them came from people who lived during the heyday of the Roman Empire until the beginning of the Middle Ages.

As the researchers report, the results revealed a surprisingly high level of diversity. The bottom line is that about eight percent of the people included in the study did not originally come from the area of ​​Europe, Africa or Asia in which they were buried. Geographically more isolated areas tended to be less diverse. Overall, however, there were skeletons in most parts of the Roman Empire whose genetic profile differed significantly from that of the rest of the local population. This means that they themselves or their most recent ancestors came or immigrated from distant regions. The researchers report that the particularly “colorful” regions found included Italy, the Balkans and parts of Central and Western Europe. “We were also able to show that there were common ancestry patterns among people who did not come from the area in which they were found,” says co-senior author Ron Pinhasi from the University of Vienna.

The Roman Empire provided dynamism

As the researchers explain, the observed mobility obviously reflects how the peoples involved reconnected on different levels during the era of the Roman Empire. “The expansion of the Roman Empire was a massive undertaking that involved troop movements, trade, labor, slavery and forced relocation,” says co-author Clemens Weiss of Stanford University. “As the empire developed, more and more people were attracted and mobility across entire continents increased,” said the scientist.

Apparently, this period of intensive mobility was only temporary, as can be seen in the results. If people had continued to move around so intensively, the regional differences would have gradually disappeared, say the researchers. At some point, for example, the genomes of people in Eastern Europe would have been difficult to distinguish from those in Western Europe and North Africa and vice versa. Overall, the population structure of Europe has remained stable to this day, say the scientists. The discrepancy probably reflects how much people's mobility declined with the collapse of the Roman Empire. “However, there is not enough data from this time to be able to say this with certainty - this will now be the content of subsequent studies,” says Pinhasi.

Source: University of Vienna

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