Sev­er­al years ago, if some­one had asked me who count­ed as Jew­ish in Nazi Ger­many, I would have been sure of the answer: any­one with at least one Jew­ish grand­par­ent. That, after all, is what I was taught in my Jew­ish day school and in the var­i­ous Jew­ish pro­grams I par­tic­i­pat­ed in through­out my child­hood. How­ev­er, while work­ing on my new book Rav­en­ous, I was sur­prised to dis­cov­er that what I had been taught was not cor­rect. Not exactly.

Rav­en­ous tells the sto­ry of Otto War­burg, the famed bio­chemist who made a break­through can­cer dis­cov­ery in 1923. Warburg’s father was Jew­ish but his moth­er was not, mean­ing he had two Jew­ish grand­par­ents. The Civ­il Ser­vice Law was the first anti-Jew­ish leg­is­la­tion passed by the Nazis in 1933, and it applied (with some excep­tions) to any­one with a sin­gle Jew­ish grand­par­ent. But the pass­ing of the Nurem­berg Laws in 1935 made things more complicated.

In the orig­i­nal draft of the Nurem­berg leg­is­la­tion that banned rela­tions between Jews and those con­sid­ered ​“Ger­man-blood­ed,” there was a crit­i­cal line: ​“This law only applies to full Jews.” And ​“full Jews” were defined as some­one with three or four Jew­ish grand­par­ents. Hitler left this men­tion of ​“full Jews” in place in the draft of the leg­is­la­tion that was sent to the gov­ern­ment press agency. But he removed the line in the draft sent to the Reich­stag, indi­cat­ing that the new laws would apply to any­one with even one Jew­ish grandparent.

There is no ques­tion that in 1935 Hitler want­ed to per­se­cute every­one of Jew­ish descent. The Nazis called those with one or two Jew­ish grand­par­ents Mis­chlinge, which trans­lates to some­thing like ​“mon­grel.” Hitler despised the Mis­chlinge, call­ing them ​“mon­strosi­ties halfway between man and ape.” That the Mis­chlinge would even­tu­al­ly meet what­ev­er fate await­ed ​“full Jews” was a giv­en. Hitler allowed the line stat­ing that the leg­is­la­tion applied strict­ly to ​“full Jews” to remain in the pub­lic announce­ment of Nurem­berg Laws only out of con­cern for Germany’s inter­na­tion­al rep­u­ta­tion — the Berlin Olympic games were less than a year away.

The two dif­fer­ent ver­sions of the leg­is­la­tion led to con­sid­er­able con­fu­sion. In Novem­ber of 1935, a sup­ple­men­tary decree was added to the Nurem­berg Laws in an effort to bring more clar­i­ty. Some­one like War­burg, who had two Jew­ish grand­par­ents, was defined as a ​“first-degree Mis­chling.” (Mis­chling is the sin­gu­lar of Mis­chlinge.) A per­son with only one Jew­ish grand­par­ent was labeled a ​“sec­ond-degree Mis­chling.”

Though not sub­ject to all the same decrees as ​“full Jews,” Mis­chlinge were still per­se­cut­ed and treat­ed as pari­ahs in Ger­man soci­ety. In the imme­di­ate after­math of the pas­sage of the Nurem­berg Laws, they could be draft­ed into the army, but they would now be restrict­ed to the low­est ranks; they could enroll in uni­ver­si­ties but were barred from the study of some subjects.

Con­sid­ered nei­ther ​“true” Jews nor ​“true” Ger­mans, the Mis­chlinge were trapped in the mid­dle of the Nazis’ twist­ed racial ide­ol­o­gy. The Mis­chlinge, who often did not iden­ti­fy as Jew­ish, were shocked to be clas­si­fied as sec­ond-class cit­i­zens. One offi­cial at the Reich Min­istry of the Inte­ri­or com­ment­ed that the Mis­chlinge had it worse than the ​“full” Jews, who at least belong to a true com­mu­ni­ty. The Mis­chlinge were strand­ed between two worlds: half-oppressed, half-oppressor.

While work­ing on Rav­en­ous, I learned anoth­er sur­pris­ing detail about Nazi racial clas­si­fi­ca­tions: it was pos­si­ble to have one’s offi­cial sta­tus changed. The process was infor­mal­ly known as Aryaniza­tion. The exact num­ber of half- and quar­ter-Jews who applied to have their legal sta­tus changed in Nazi Ger­many remains unknown. Records of the Reich Min­istry of the Inte­ri­orindi­cate that­by May 1941 near­ly 10,000 Mis­chlinge had applied for an upgrad­ed legal sta­tus of one type or anoth­er; 263 had been suc­cess­ful. Schol­ars now believe the true num­bers of those who applied are con­sid­er­ably higher.

In 1941, after being evict­ed from his Kaiser Wil­helm insti­tute, Otto War­burg sub­mit­ted his own appli­ca­tion for Aryaniza­tion. The appli­ca­tion required pho­tos (front and pro­file), mil­i­tary records, a writ­ten fam­i­ly his­to­ry, and a state­ment of the applicant’s polit­i­cal views. Hitler was known to per­son­al­ly review such appli­ca­tions. Grow­ing frus­trat­ed with the num­ber of spe­cial cas­es he was asked to con­sid­er, Hitler once com­plained that Nazi Par­ty mem­bers ​“seem to know more respectable Jews than the total num­ber of Jews in Germany.”

Giv­en that War­burg was a Nobel Prize win­ner, Hitler was like­ly involved in review­ing his appli­ca­tion for Ayraniza­tion. But Warburg’s case lin­gered for months with­out an offi­cial deci­sion. In the mean­time, the ques­tion of what to do about the Mis­chlinge remained a source of frus­tra­tion for the Nazis. On Jan­u­ary 20, 1942, Nazi lead­ers gath­ered at the infa­mous Wannsee Con­fer­ence to plan the ​“Final Solu­tion of the Jew­ish ques­tion.” It was decid­ed that half-Jews (first-degree Mis­chlinge) were to be treat­ed as full Jews. Quar­ter-Jews (sec­ond-degree Mis­chlinge) would be assim­i­lat­ed into Aryan society.

The deci­sions made that Jan­u­ary after­noon might have doomed War­burg and oth­er first-degree Mis­chlinge, but some Ger­man offi­cials con­tin­ued to make the case that the Mis­chlinge should be ster­il­ized rather than deport­ed. Six weeks after the Wannsee Con­fer­ence, senior Nazi offi­cials gath­ered again, this time to arrive at a ​“Final Solu­tion” to the Mis­chling ques­tion. At this sec­ond con­fer­ence, over­seen by Adolf Eich­mann, the senior Nazis dis­cussed the logis­ti­cal prob­lem of ster­il­iz­ing tens of thou­sands of Mis­chlinge, even won­der­ing about whether there was enough hos­pi­tal space to do all the pro­ce­dures. By the end of this sec­ond ​“Final Solu­tion” con­fer­ence, the Mis­chling ques­tion still had no defin­i­tive answer.

Though War­burg was nev­er offi­cial­ly Aryanized, the Nazi lead­er­ship chose to pro­tect him, seem­ing­ly in the hope that he would arrive at a cure for can­cer, a dis­ease Hitler and oth­er high-rank­ing Nazis dread­ed. Though the records are incon­clu­sive, Her­mann Göring, whose pow­er and influ­ence was then sec­ond only to Hitler’s, may have inter­vened on Warburg’s behalf. Göring once claimed that it was up to him to decide ​“who is a Jew and who is Aryan” — a state­ment that speaks to the under­ly­ing fic­tion of the Nazi racial clas­si­fi­ca­tions. In the end, whether some­one count­ed as a Jew had less to do with one’s grand­par­ents than with one’s per­ceived use­ful­ness to the Nazis.