Today’s GEITP pages provide a lesson in history, gleaned from DNA-sequencing. The attached article offers an example of what can be learned from whole-genome sequencing (WGS) of individuals from mass graves many centuries ago. Human migrations are often accompanied by historical battles and invasions that have profoundly reshaped genetic diversity of local populations in many regions (e.g. the Mongols during the time of Genghis Khan, spreading male lineages throughout Asia from the Pacific to the Caspian Sea; colonial Iberians in South America, resulting in European ancestry seen today among Latinos).
From 1095 to ~1300 A.D., hundreds of thousands of Europeans arrived in the Near East to fight in the Crusades and to settle in the newly established European states along the Eastern Mediterranean coast. Historical records from this period report varying episodes of forced displacement of the local people — or co-existence and mixing with them. Ancient DNA (aDNA) from medieval Crusaders who traveled to the Near East, and from local people who were their contemporaries and interacted with them, can potentially resolve the discrepancy between historical records reporting admixed descendants of Crusaders in the Near East versus the genetics of modern populations not displaying such a signal; aDNA from this period can also resolve uncertainties in the demographic processes that accompanied the Crusades, providing insight. What was the origin of Crusaders’ armies and extent to which they were from genetically and geographically diverse groups? How genetically similar are modern Near Easterners to the Medieval populations, and what genetic changes occurred after the Crusades?
These questions can potentially be answered today in great detail using ancient genomics; however, obtaining aDNA from Crusaders is challenging and hindered by two major technical factors: the hot and humid climate in the Near East makes it difficult for aDNA to survive; and burials of individuals who can be linked to the Crusaders are rare. One of the few known Crusader burial sites is located in the city of Sidon (south of present-day Lebanon), an important stronghold in the Crusaders’ Kingdom of Jerusalem, and scene of major battles between the Crusaders and Arabs from 1110 CE to 1249 A.D. A recent archaeological excavation in Sidon near the ruins of a Crusader castle uncovered two mass burials consisting of skeletal remains from at least 25 individuals who had signs of inter-personal violent injuries and dated (using radiocarbon) to 1025–1283 A.D.
Authors [see attached report] sequenced the whole genomes of 13 individuals who lived in what is today known as Lebanon between the 3rd and 13th centuries A.D.; these included nine individuals from the ‘‘Crusaders’ pit’’ in Sidon. Authors show that all the Crusaders’ pit individuals were males; some were Western Europeans from diverse origins, some were locals (genetically indistinguishable from present-day Lebanese), and two individuals were a mixture of European and Near Eastern ancestries, providing direct evidence that the Crusaders admixed with the local population. However, Lebanese Christians today are mostly genetically similar to local people who lived during the Roman period — which had preceded the Crusades by more than four centuries.
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Am J Hum Genet 2 May 2o19; 104: 1-8