Q. How can you really be certain that you are a Kohen?
A. A family surname is some help. Not just Cohen, but also Cahn, Kahn, Kahan, etc.; even Katz (or any of its variations): this stands for kohen tzedek, righteous priest. But none of these names is a guarantee of priestly lineage, nor is family tradition.
Few of us can trace our descent back more than three generations, though some families have always been scrupulous in preserving genealogical records. One such priestly family is the Adlers: father and son, Nathan Marcus Adler and Hermann Adler, occupied the British Chief Rabbinate from 1845 to 1911, and they traced their yichus back through centuries of kohanim.
But genetic research has come to our aid. “Geographical”, the magazine of the Royal Geographical Society (September, 1998), carries an article entitled “Bodies of Evidence”, in which Dr Mark Thomas of University College London reports on genetic investigation into Jews who claim to be kohanim.
“We looked at the Y chromosome,” says Dr Thomas, “which is only passed on through men, of Cohens from Jewish communities worldwide. We found they’re all much the same. And, since part of the Y chromosome is known to mutate at a regular rate (at about 0.2 per cent per generation), we’ve been able to estimate the time distance from the common ancestor of all Cohens by looking at the number of changes between the different Cohens. We’ve now done this in Ashkenazi Cohens and in Sephardi Cohens and got the same date.”
The date has been traced to about 3000 years ago (Jewish tradition considers the Exodus was about 3300 years ago; the priestly office came into being shortly thereafter).