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Crusader Sequences Point to Temporary Mixing With Local Population in Lebanon

Crusader bones, Lebanon

NEW YORK (GenomeWeb) – A Wellcome Sanger Institute-led team used ancient DNA sequencing to dig into the genetics at play during the Crusades — work that demonstrated the broader feasibility of using sequencing to complement available historical documents, even in parts of the world with sub-par DNA preservation.

"Historical records are often very fragmentary and potentially very biased," senior author Chris Tyler-Smith, a genetics researcher at the Wellcome Sanger Institute, said in a statement. "But genetics gives us a complementary approach that can confirm some of the things that we read about in history and tell us about things that are not recorded in the historical records."

For a study published online today in The American Journal of Human Genetics, he and his colleagues did DNA sequencing on ancient samples from a burial pit in Lebanon, believed to contain the remains of Crusaders who died in the 1200s, and on four pre-Crusade, Roman-period individuals buried in Lebanon as far back as the 3rd century. The Crusaders at that site were genetically diverse, the researchers reported, and included three Europeans, four individuals with Near Eastern ancestry, and two individuals with mixed European and Near Eastern ancestry.

The results suggested Crusaders "originated from western Europe and recruited local people of the near East to join them in battle," Tyler-Smith said. "The Crusaders and near Easterners lived, fought and died side by side."

Even so, the Christian Crusaders did not leave a lasting genetic imprint on populations in the Near East after the Crusades — a series of bloody invasions and related religious wars that took place over a nearly 200 years, from around 1100 to the late 1200s. Instead, contemporary Lebanese Christians appeared to be more genetically related to the ancient individuals who lived in the region roughly 2,000 years ago, during the Roman period.

"[A]fter the fighting had finished, the mixed [Crusader-Near East] generation married into the local population and the genetic traces of the Crusaders were quickly lost," first author Marc Haber, a post-doctoral fellow in Tyler-Smith's Sanger lab, said in a statement.

Starting with remains from 25 individuals at a Crusader cemetery near Sidon, Lebanon, the researchers successfully sequenced nine individuals with Illumina short reads. They were confident that the remains came from Crusaders based on the burial location and estimated age, as well as the presence of European-style coins and accoutrements.

Those sequences were analyzed alongside those from four Lebanese individuals from the Roman period, as well as available data for hundreds more ancient individuals sequenced previously and thousands of modern-day humans with array-based genotypes and sequences reported in past studies.

The DNA data indicated that just three of the nine Crusaders were Europeans, including individuals with Sardinian and Spanish ancestry. The remaining Crusaders came from Near Eastern populations or had mixed. Moreover, the team noted that the long-term impact that Europeans had on local populations was minimal.

"Our findings suggest that it's worthwhile looking at ancient DNA even from periods when it seems like not that much was going on genetically," Tyler-Smith said, noting that "history may be full of these transient pulses of genetic mixing that disappear without a trace."

Beyond insights about Crusader interactions, the results point to the possibility of doing additional studies on ancient DNA in the region, which has a climate that is unfavorable for DNA preservation. In particular, members of the team are reportedly interested in investigating genetic features in Near Eastern populations as they moved from the Bronze Age into the Iron Age.

"There has been a lot of long-term interest in the genetics of this region, because it has this very strategic position, a lot of history, and a lot of migrations," Haber said. "But previous research has focused mainly on present-day populations, partly because recovering ancient DNA from warm climates is so difficult." 

"Our success shows that studying samples in a similar condition is now possible because of advances in DNA extraction and sequencing technology," he added.