…, in the sense of having a Jewish mother, raises an interesting question apart from the tragic moral enigma of a beautiful young actress’s sudden death. Forgive me if it seems impertinent to ask now, but just how many Jews are there in the world? The figure you always hear is about 13 million. But imagine the implications if we were to take seriously the Jewish idea that Jewish identity is passed down through the mother, regardless of whether someone has a Jewish name, practices Judaism, or has any touch of self-understood Jewish identity at all.

Ms. Murphy, who apparently married in some kind of Jewish ceremony, isn’t really a prime example. Here’s a better one. 
I got an email from a reader the other day, Bruce Carpenter, who relates some news about DNA testing upon himself. He had read my review in National Review of Norman  Podhoretz’s book, Why Are Jews Liberals?, where in passing I wrote about speculation that after the expulsion of the Jews from England, many Jews actually stayed on having converted nominally to Christianity. This left a population of Jews-by-birth who gradually faded into the general background. Bruce Carpenter’s family evidently were among them: 

As an aside, my own family relocated  to Massachusetts in 1638 and were active in religious freedom disputes i.e., the Baptist movement. Recently they were show to have Jewish DNA with a history in trade and finance stretching back to the 1200s in England, especially Norfork and Lincolnshire, a center for Jews until the 12th century. 

He goes on with a bit of family history:

William Carpenter of Rehoboth arrived in Massachusetts in 1638. A close relative, also a William Carpenter, arrived previously and later joined Roger Williams and other free thinkers in the new Providence colony. William Carpenter of Rehoboth was also a Baptist free thinker. He joined secret meetings and was subsequently persecuted by the court. Both Carpenters were proven to have Jewish-Levite Y-chromosome DNA.

His story is very far from being unique. At one point or another during the Middle Ages, Jews were expelled from most of the countries in Europe, in a wave running from west to east. So in Spain, for example, again based on a sample from DNA testing, 8 million or so Spaniards have Jewish backgrounds. Their Jewish ancestors stayed on following the Expulsion after “converting” to Catholicism. Tracing lines of mothers exclusively, you will come up with a bona fide Jewish population in Spain smaller than 8 million but still a lot of people, about half men and half women, though only the women can pass on their Jewishness to the next generation.
I’m constantly hearing from friends, friends of friends, acquaintances, and co-workers, about people discovering their lost or forgotten Jewish roots. Countless Jews over the centuries have disappeared into the larger gentile society. Per the traditional matrilineal definition of a Jew, the men among them left no Jewish descendants but the women did. So did their daughters, and their daughters’ daughters down to today. 
That would make for a heck of a lot more Jews in the world than 13 million. The mathematics that it would take to suggest an approximate number is beyond my pay grade. I wouldn’t know where to begin. Can anyone help? Of course this is leaving aside the famous Lost Tribes, wherever in (presumably) central Asia their descendants may be found living today.
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