Tim Radford
Genetics researchers have confirmed something which has been Holy Writ in Israel for 3 300 years. They have examined the Y chromosomes of Jewish priests and found they are, indeed, different from the rest of the Jewish people.
According to Jewish tradition, priests – as distinct from rabbis –are descended from Aaron, brother of Moses, through the male line. Priesthood is only by descent, and possibly 5% of male Jews are therefore hereditary priests, called the cohanim, and often carry the surname Cohen, meaning priest.
But although by tradition all the 14- million Jews in the world are the children of Abraham, molecular biologists find the biblical connections harder to make. There are two separate populations of Ashkenazi and Sephardic Jews with different genetic make-ups, and both of these have been increasingly blurred by 2 000 years of mixing with populations of other faiths.
But Karl Skorecki of the Technion-Israel Institute of Technology in Haifa and colleagues at University College London and the universities of Toronto and Arizona report in Nature magazine that certain genes tell a different story.
The human Y chromosome is inherited from the father and most of it does not alter, except by random mutation – mistakes in copying of the DNA. They identified little telltale bits of the chromosome – haplotypes – that could be recognised as “markers” and went looking for them in 188 unrelated Jewish male priests in Israel, North America and Britain. Because priests were identified by other Jews as such, they had religious and social obligations which tended to preserve their identity and sense of lineage, the scientists reckoned.
They found that in a number of ways priests in different communities differed from their own lay neighbours, and in some respects were much more like each other.
The research does two things: it helps confirm that the Y chromosome could be calibrated as a kind of father-to-son genetic “clock”, to be used alongside an already well-known “mitochondrial DNA” clock passed from mother to daughter.
This mother-daughter clock was used, some years ago, to show that everybody alive today could have descended from one woman, probably in Africa, about 250 000 years ago, who was immediately dubbed the “African Eve”.
But the priesthood study also supports a long religious tradition that dates from the biblical Book of Exodus. The Jewish priesthood may indeed have had one founding father, or a “founding modal haplotype”, as the researchers put it.
“This result is consistent,” they say, “with an origin for the Jewish priesthood antedating the division of world Jewry into Ashkenazi and Sephardic communities, and is of particular interest in view of the genetic diversity displayed between the two communities.”