patrick.net

I'm a quarter Jewish by ethnicity (maternal grandfather) but almost all of my "relatives" on 23andme are Jewish. How can this be?

The answer is that Ashkenazi (European) Jews are all descended from a fairly small group of Jewish merchants (about 300 people) who moved north from Italy to Germany in about 900 AD, and later into Eastern Europe. The numbers and dates are not certain, but it's something like that. They married some European women at first, but closed things off after that. You can see evidence of these European women in mitochondrial DNA of modern Jews.

Those 300 people have literally millions of descendants now, and most of them are close to 100% descended from that initial group, which made a point of intermarrying only among themselves. You can see this in that almost every Ashkenazi Jew on 23and me is classified as almost 100% Jewish.

Before and during WWII, and even now, Jews were anxious to say that they are not a particular race:

https://encyclopedia.ushmm.org/content/en/article/nazi-racism

The Nazis tried to use science to prove their racial theories. They recruited doctors and other scientists to help them. These officials tried to categorize people into races. They measured and described people’s physical features, like noses, skulls, eyes, and hair.

These attempts at categorization failed to prove Nazi racial theories. In fact, their efforts revealed that human beings could not be scientifically categorized into races. Humankind is simply too naturally diverse.

23andme proves that the above claim is definitely false, even though it's still being repeated on sites like that one. Jews are actually even closer genetically to each other than any race is, and race is also definitely real and provable genetically. To call Jews a "race" is to understate the extremely close genetic relation among Jews. Traditionally, Jews even recognized this relationship with a saying in Yiddish: "Alle yiden seyn mishpochim." Meaning "All Jews are family." That was not a metaphor and everyone knew it.

The Nazis could have very easily proved who was and who wasn't a Jew with 23andme. They just didn't have the technology at the time, and that's a good thing.

Since it is so overwhelmingly obvious that all Ashkenazi Jews are related at a level even smaller than a race, 23andme treats Jews differently:

https://customercare.23andme.com/hc/en-us/articles/212170958-DNA-Relatives-Detecting-Relatives-and-Predicting-Relationships

Are you categorizing cousins differently for people with Ashkenazi ancestry?

Yes, we are making relationship predictions that take into account the higher than average DNA sharing found in people with Ashkenazi ancestry. In many of these cases, this results in a "distant" cousin prediction.

None of this is to say anything bad about Ashkenazi Jews, only that they are all clearly relatives to each other with a very small gene pool. We should not deny the truth just because it is politically incorrect.

PS The idea that Jews are descendants of the Khazars is also proven wrong by the same data. Khazars are Turkic, Jews are not.

PPS Sephardic (Spanish) and Mizrahi (Middle-eastern) Jews are yet something else. They are probably related to that group of 300 way back, but they definitely not Ashkenazi.