Today is National DNA Day. DNA testing has become increasingly popular for genealogy purposes, and the Jewish community is no exception to this trend. This is clear from this year's IAJGS conference on Jewish Genealogy, which is boasting in-depth DNA workshops and has more than 20 lectures related to DNA on its schedule.
But DNA testing for genealogy purposes poses a special problem for Jews, often called the Ashkenazi Problem: Jews tend to marry Jews, and Jews who do not marry Jews tend to drop out of the Jewish community, and we have been doing that for so long in such a small population that we all tend to have a lot of DNA in common. The technical term for this is "endogamy," or in other words, inbreeding. As a result, one study found that the average Jewish DNA tester matched 54% of all testers with any Jewish heritage! Compare this with gentile testers, who matched less than 1% of all testers with gentile ancestry.
But if you are Jewish and interested in DNA testing, don't give up hope! It is possible to make real connections with real relatives through DNA testing. One of my great-grandfathers (Joseph Spigler) had seven siblings, four of whom married and had children, and I have successfully identified DNA matches from three of his siblings! Although two of those matches did not appear until six months after I took my test, and I have had less success so far on other branches. DNA testing can be particularly valuable if you are from a family separated by the Holocaust (discussed further below) or by adoption (discussed further below). But you have to come into it with proper expectations, and you have to meet your relatives halfway if you expect to have any success.