In the first few decades after the Holocaust, scholars argued that it was unique as a genocide in its reach and specificity. This began to change in the 1980s during the West German Historikerstreit ("historians' dispute"), an attempt to re-position the Holocaust within German historiography. Ernst Nolte triggered the dispute in June 1986 with an article in the Frankfurter Allgemeine Zeitung: "Vergangenheit, die nicht vergehen will: Eine Rede, die geschrieben, aber nicht mehr gehalten werden konnte" ("The past that will not pass: A speech that could be written but not delivered"), in which he compared Auschwitz to the Gulag and suggested that the Holocaust was a response to Hitler's fear of the Soviet Union: "Was the Bolshevik murder of an entire class not the logical and factual prius of the 'racial murder' of National Socialism? ... Was the source of Auschwitz a past that would not go away?"[aa]
Gentiles whose status placed them on the periphery of a community generally had fewer social constraints and a higher level of independence. This sense of independence, in turn, seems to have made many rescuers more likely to act in accordance with their personal values and moral precepts, even when these standards were in opposition to societal norms. Such rescuers were propelled by values connected to self-approval. In interviews, they insisted again and again that they had to be at peace with themselves, with their ideas of what was right or wrong.
According to the Yad Vashem Holocaust Martyrs' and Heroes' Remembrance Authority in Jerusalem, "[a]ll the serious research" confirms that between five and six million Jews died. Early postwar calculations were 4.2 to 4.5 million from Gerald Reitlinger; 5.1 million from Raul Hilberg; and 5.95 million from Jacob Lestschinsky. In 1986 Lucy S. Dawidowicz used the pre-war census figures to estimate 5.934 million. Yehuda Bauer and Robert Rozett in the Encyclopedia of the Holocaust (1990) estimated 5.59–5.86 million. A 1996 study led by Wolfgang Benz suggested 5.29 to 6.2 million, based on comparing pre- and post-war census records and surviving German documentation on deportations and killings. Martin Gilbert arrived at a minimum of 5.75 million. The figures include over one million children.
In 1935, Mengele earned a PhD in anthropology from the University of Munich. In January 1937, he joined the Institute for Hereditary Biology and Racial Hygiene in Frankfurt, where he worked for Dr. Otmar Freiherr von Verschuer, a German geneticist with a particular interest in researching twins. As von Verschuer's assistant, Mengele focused on the genetic factors that result in a cleft lip and palate, or a cleft chin. His thesis on the subject earned him a cum laude doctorate in medicine (MD) from the University of Frankfurt in 1938. (Both of his degrees were revoked by the issuing universities in the 1960s.) In a letter of recommendation, von Verschuer praised Mengele's reliability and his ability to verbally present complex material in a clear manner. The American author Robert Jay Lifton notes that Mengele's published works were in keeping with the scientific mainstream of the time, and would probably have been viewed as valid scientific efforts even outside Nazi Germany.