Who Is a Jew? DNA Can Hold the Key

     

Who is a Jew? As the recent passport row shows, that question can be murky, with elements of belief, values, descent and nationality mixed in.

It also has dark reminders of a terrible time in history when Jewish blood meant death; and science, or pseudo-science, claimed to be able to sniff it out.

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Things have changed. A decade ago, I was passing through Ben Gurion airport in Tel Aviv carrying a box filled with small tubes. Alerted by the Syrian stamp in my passport, the security staff gave me a hard time. After emptying my case, she asked what was in the box. I replied, irritably: "Arab spit". "What?" she said. "I’m a geneticist, I explained, I have been sampling Palestinian DNA. At once, her face brightened – ah, DNA. Had I heard the then novel stuff on the shared male chromosomes of priestly Jewish families such as the Cohens? I had, and we parted on amicable terms.

The conversation gave me pause for thought. Joseph Mengele himself wrote his doctoral thesis on the relationship between jaw shape and racial identity. His ideas were pernicious rubbish and even 20 years later the thought of a genetic test for Jewish descent would have been treated with horror. Now, one has emerged and is not despised but hailed by many Jews themselves.

A scan of half a million variable sites across the genomes of several hundred Europeans and Americans, each aware from their family history of having had a recent Jewish or a non-Jewish ancestry, gave an absolute separation between Jews and others: even a single Jewish grandparent was enough to provide an unambiguous identity, written in DNA. A carefully chosen sample of just 300 of those sites does almost as well, and a test based on that would be cheap.

Judaism is inherited down the female line – as are mitochondria. Their DNA shows that today’s Jews from the largest group, the eight million Ashkenazim – most of whom once found their home in central and eastern Europe, and who now represent the majority of American Jews – have few grandmothers. Around half descend from just four women who bear mitochondrial types found almost exclusively in that population. Two million trace their descent from just one of those ancient predecessors.

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March 20, 2010