"It certainly doesn't undermine the similarities among the various Lebanese communities, but it does agree with oral tradition—that some Lebanese Christians are descendents of Crusaders—and points to a genetic connection to the Crusaders," he added.
"We have a correspondence between what we knew about the history of the region from written documents and what we're starting to see that in the genetic patterns as well."
The researchers noticed a similar pattern when they looked at Y-chromosome lineages in the Muslim population.
"We found that a lineage that is very common in the Arabian Peninsula—Hg J*—is found in slightly higher frequencies preferentially in the Muslim population," said Wells, who also heads the Genographic Project.
Wells said that even though the genetic matches are found only in about 2 percent of the population, they provide a detectable impact of two historical migrations into Lebanon.
"What is cool is that we found this lineage in the Lebanese Christians that we don't see elsewhere in the Middle East, or at least we haven't seen it yet," Wells said. "So it seems to have migrated from Western Europe relatively recently into the Lebanese population of Christians, but not Muslims.
"Now what historical events would have brought a substantial number—2 percent—of Y chromosomes in the Christian population in from Western Europe?" he added. "The most likely answer is the Crusades."
The Genographic researchers say their discoveries suggest, in particular, that Crusaders from the 11th to 13th centuries A.D. introduced their lineages into the Lebanese population.
The expansion of Islam from the Arabian Peninsula beginning in the seventh century A.D. likely introduced lineages into people who subsequently became Lebanese Muslims, they add.
Peter Underhill is a senior research scientist at Stanford University who has previously analyzed Y chromosomes to study human migrations out of Africa.
He says the treasure trove of data from the new study will be helpful in studying historical human migrations. But he is not fully convinced about the findings.
"I must admit that I hesitate to fully embrace the assumptions and the conclusions of major historic Crusader and Muslim influences being the major forcing factors modulating the genetic landscape in Lebanon," Underhill said.
"I am always tempted to ask the question, What if the Crusaders or Muslim events never happened? Is it feasible that one would still see similar patterns?"
Christians were established and converting "locals" in the Middle East prior to the arrival of the Crusaders, Underhill pointed out. The Greeks also had a pre-Crusade presence, so the chromosome match could have come from Greece rather than France or England.
But Wells and his colleagues disagree.
"The fact that we do detect significant excesses of the lineages Hg J* and R1b in the relevant Lebanese subpopulations requires explanation," Wells said.
"The documented Muslim and Crusader migrations could, following Underhill's line of reasoning, have left no genetic impact, but in that case, other undocumented migrations of significant numbers of men from the same source regions must have taken place."
Wells said such an alternative explanation is more complicated and less plausible than the simpler explanation that the migrations known from history are responsible for the observed genetic effects.
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