The Kohanic Gene

A number of years ago, researchers delighted the Jewish world by discovering that the Y-chromosome of Jewish kohanim points to one unique ancestor. The Y-chromosome is, of course, passed patralinially, and thus can serve as proof of familial relation for males.

The science is fascinating. However, I never felt that the purported religous implications claimed by some were strong at all. Throughout history, there were undoubtedly families who were priestly who, over years of secularism and the pressures of the exile, forgot their lofty status. Certainly, there were also families that accidentally or not, took on the kohanic traditions mistakenly. It seemed too pat, and worked out only too well, that all kohanim tested seemed to point to one ancestor. Support for this reservation can be found in the mishna Midot 5:4, where the Oral Law records the fact that the Jewish High Court had to sometimes sit in judgement on questions of priestly lineage, and would attempt to clarify a family's status: a man who was found to be an authentic Kohen would wear white, and one found to be unpriestly wore black. Furthermore, in Eduyot, 8:7, Rabbi Yehoshua states that in the times of the redemption, Eliyahu the prophet will not come to confirm or deny the legitimacy of families accidentally mixed, but only to do so regarding families that attempted to mix themselves in with higher station willfully. (See Kehati's commentary here that expressly includes the kohanic honor as one of the items that this statement includes.) For all these reasons, the kohanic Y-chromosome was never much more than a curiosity to me. I found the underlying science much more compelling and fascinating than the religous implications.

Today, I have learned that my reasoning to be less than impressed was well-guided. New research seems to agree that there was not one ancestor for the kohanim, but a number of ancestors. Those who feel this to be a blow to the authenticity of the Torah's narrative would do well to remember the line of thought I mentioned in the previous paragraph. For if in 2008, a (for example, reubenic) family is erroneously assumed to be kohanic, they would be, in the eyes of the study, full kohanim, just as authentic kohanim would be. Thus, when the study looks at the Y-chromosomes of true kohanim and faux kohanim that they assume to be true kohanim, they would find that some of these Y-chromosomes trace back 3000 years ago to kohanic roots, and some to reubenic roots. However, because the study in 2008 does not know that the reubenic Y-chromosome is being mistaken for kohanic, it will assume that both Y-chromosomes have equal claim to kehuna, and thus conclude that there are multiple ancestors for the kohanic tribe. This is not a deficiency in the genetics or the science, but an epistemological deficiency; we simply cannot guarantee that everyone who claims (even in good faith) to be a kohen, is indeed a kohen!

Of course, it does not matter when the error was introduced; whenever this occurred, the Y-chromosome of the "new kohen" would automatically join the genetic pool of "known kohanim" and wait patiently to be discovered.

(It is important to note that people who are halachikally Jewish can still come from differring Y-chromosome branches, since Judaism has always accepted converts, even at the time of the Exodus. However, converts could never become kohanim, as this was strictly a birthright.)

Thus, the new study should not at all be seen in any way as denying or disproving the Torah traditions. It is however interesting to note that, "Cohanim Y chromosomes from both Ashkenazi and non-Ashkenazi Jewish communities, is virtually absent in non-Jews..."