Answers to Quora Questions by Yair Davidiy (27 August 2017, 5 Elul, 5777)
How did Nazis in World War II identify Jews? What did they resort to if they were just suspicious of someone being a Jew?
The numerous other answers to this question have answered the main points very well.
Here and there existed a measure of self-identification.
The Mixed-Breeds (Mischling) who were half Jews would be considered as full Jews if they belonged to a Jewish Religious body.
Most Mischling identified as Aryans. Half-castes would be kept alive though there are reports that towards the end they too were to be done away with.
The way to get out of this was to deny Jewish ancestry altogether.
If their mother was Aryan a neighbor or friend would be asked to testify that he had seduced the woman and therefore biologically the offspring were full blood Aryan bastards and so, in the eyes of the Nazis, Kosher (pun intended).
There are cases of the real (Jewish) father being asked to leave by the rest of the family since his presence compromised them.
Erich von Manstein, born Eduard Lewinski, apparently believed himself to be a mischling. He went out of his way to defend the rights of Mischling in Germany. Nevertheless von Manstein supported the extermination of Jews in the east.
Probably the most virulent enemy of the Jews in Germany was Julius Streicher. He gave Jew-Hatred a pornographic appeal and was himself a sex pervert. Striecher claimed on at least one occasion to himself have in part Jewish blood! So did Hitler.
Occasionally one meets Afro-Americans who hate other black people. They have internalized the prejudices of the mainstream.
So too, physically impaired individuals are known in some cases to adopt extreme eugenic type viewpoints against people such as themselves. The Germans hated Jews and invented a 'scientific' rationale for their belief. This was the result.