>>725457014
It because phenotypically-determiniative genetics don't mesh very well with "ethnicity" as variously defined. You can easily observe admixture between "color groups" or "races" because of superficial features. Jewish is a terrible example for your argument, however, because the ethnic component of Jewish-ness is something like, "has this person's ancestors lived in the Levant at some point in the last 6000 years Y/N?". Jewish-ness is akin to Americans claiming a divine right to return to New York City because on of their ancestors came through Ellis Island at some point, despite the fact that people claiming that could have an actual ethnicity from literally anywhere on Earth, and their brief stint in NYC wasn't at all a genetic or cultural bottleneck. Ethnic studies of Jews have some merit, though; they are the most self-selective group in the world, so they have extremely conservative genetics. A unpublished study in Scotland found that Jews were 6 times more likely to have a father-daughter offspring AT THAT MOMENT in the late 2010's. Unpublished, because the findings were "controversial".
