Crusader DNA in the Middle East

http://news.bbc.co.uk/1/hi/sci/tech/7316281.stm  Quoting:

Scientists have detected the faint genetic traces left by medieval crusaders in the Middle East. The team says it found a particular DNA signature which recently appeared in Lebanon and is probably linked to the crusades. The finding comes from the Genographic Project, a major effort to track human migrations through DNA. Details of the research have been published in the American Journal of Human Genetics.

The researchers found that some Christian men in Lebanon carry a DNA signature hailing from Western Europe. Four crusades came through Lebanon between the 11th and 13th Centuries - the first, second, third and sixth. The bulk of the crusader armies came from England, France, Germany and Italy; many of the men stayed to build castles and settlements, mixing with the local populations. The scientists also found that Lebanese Muslim men were more likely than Christians to carry a particular genetic signature. But this one is linked to expansions from the Arabian Peninsula which brought Islam to the area in the 7th and 8th Centuries. But they emphasise that the differences between the two communities are minor, and that Christians and Muslim Arabs in Lebanon overwhelmingly share a common heritage . . .

The study focused on the Y, or male, chromosome, a package of genetic material carried only by men that is passed down from father to son more or less unchanged, just like a surname. But over many generations, the chromosome accumulates small changes, or copying errors, in its DNA sequence. These can be used to classify male chromosomes into different groups (called haplogroups) which, to some extent, reflect a person's geographical ancestry.

The team analysed the Y chromosomes of 926 Lebanese males and found that patterns of male genetic variation in Lebanon fell more along religious lines than along geographical lines. A genetic signature on the male chromosome called WES1, which is usually only found in west European populations, was found among the Lebanese men included in the study.

"It seems to have come in from Europe and is found mostly in the Christian population," said Dr Spencer Wells, director of the Genographic Project. "This is odd because typically we don't see this sort of stratification by religion when we are looking at the relative proportions of these lineages - and particularly immigration events." He told BBC News: "Looking at the same data set, we saw a similar enrichment of lineages coming in from the Arabian Peninsula in the Muslim population which we didn't see [as often] in the Christian population." Lebanese Muslim men were found to have high frequencies of a Y chromosome grouping known as J1. This is typical of populations originating from the Arabian Peninsula, who were involved in the Muslim expansion.

This doesn't surprise me at all. I have little to add, other than modern people tend to exaggerate mixing between populations that don't share core values and/or cultures. For example, if a Christian girl married a Muslim man, she would be considered Muslim and so would her children, so they wouldn't marry back into the Christian community. If this goes on for enough generations, then you get two similar, but distinct genetic groups as you see above.

Two other historical examples: This explains why there isn't as much North African in the Iberian peninsula as people previously thought (going back), or as much Viking or Roman in England proper as previously thought as well.