Historically to sustain that a Jewish ethnicity exists for real ... well, that's not that correct. The Jewish People is a kind of mix built on a filtered selection. If you visit Israel, meeting Jews from Russia, Europe, America, Africa ... you will realize that a Jewish ethnicity isn't.
Jewish is a real ethnic group, and their ethnicity is much existent than the "ethnicity" of a German and French (which are only modern period products). Try to share loudly your (laughable) opinion about non-existent Jewish ethnicity in the streets of Tel-Aviv. I do not guarantee that you can avoid even physical attrocities. They would (correctly) interpret (this nonsense) as an agressive attack on their identity. Next time learn population genetics too.