Genetic legacies of human invasions

Really interesting stuff: according to the BBC, a paper published in the American Journal of Human Genetics reports that a faint genetic legacy of the Crusades appears in Lebanon, mostly among Lebanese Christians. And while Lebanese Christians and Muslims are overwhelmingly of the same stock genetically, Lebanese Muslim populations showed a genetic signature originating in the Arabian peninsula.

Update: The original paper is even more interesting than the BBC summary suggests. They looked at Y-chromosome diversity in four areas of the country – Mount Lebanon, the Bekaa, north Lebanon and south Lebanon, excluding Beirut because its population reflects recent migration from all over the country and classified people as Muslim (Shiite or Sunni), Christian or Druze.

Even in as small a country as Lebanon, they found that there was significant genetic differences between regions of the country. But there was about three times as much difference between religious groups as there was between regions.

Apparently it’s rare to find genetic differences between religious groups within a country, but for Lebanon the Arab invasion introduced Arab Y-chromosomes to what became the Lebanese Muslim population, but not the Lebanese Christians. Similarly, the Crusades introduced European Y-chromosome lineages to the Lebanese Christian population. They failed to find any genetic signature associated with the Ottoman conquest of Lebanon.

I have wondered in the past if the Crusaders left descendants in the Middle East. Most popular histories of the Crusades end with their cities falling, one by one, and the massacres that followed the fall of each city. But sometimes you come across an account that talks about peaceful surrenders. Still, the much larger crusader armies are likely to have left as large an imprint as the far smaller groups who stayed behind and tried to hold the conquests.

1. Zalloua et al., Y-Chromosomal Diversity in Lebanon Is Structured by Recent Historical Events, The American Journal of Human Genetics (2008), doi:10.1016/j.ajhg.2008.01.020 (If that link isn’t working, try this one).