Have we come, at last, to the end of morally instructive Nazis? After eight decades, Nazis may seem to have retreated into a class with orcs and cable-TV sharks, fantastic creatures representing evil, rather than historical figures who actually were evil. It is fine to say we should look past the History Channel Nazis—“Hitler and the Occult”—to the real thing, but there comes a time when the iconic imagination really does overwhelm the historical imagination. No one any longer objects to jokes about the Spanish Inquisition, which burned skeptics and Jews alive, but which exists now first of all as a Monty Python sketch (“Nobody expects the Spanish Inquisition!”), while Henry VIII and the Tudors, who burned men, too, and brutalized thousands, are a soap opera before they are a sermon.

Two new books suggest that we may not have come to the end, and that, on the contrary, our struggle to understand how evil happens is still best helped by understanding how evil happened. The subject of David G. Marwell’s “Mengele” (W. W. Norton) is one of the leading orcs: Josef Mengele, the Angel of Death at Auschwitz, who oversaw selections on the train ramp—sending some family members off to be gassed or worked to death, while conducting bizarre medical experiments on others—and who then escaped scot-free to a secret life in South America. Mengele’s name became synonymous with pure evil of the sinister, educated sort: the movie “Marathon Man,” with Laurence Olivier as the Dustin Hoffman-torturing dentist, making dental visits difficult for a generation, was inspired by Mengele.

Marwell’s life has much new to tell us, both about Mengele himself and, more significant, about the social and scientific milieu that allowed him to flourish. There is nothing surprising in educated people doing evil, but it is still amazing to see how fully they construct a rationale to let them do it, piling plausible reason on self-justification, until, like Mengele, they are able to look themselves in the mirror every morning with bright-eyed self-congratulation. Mengele, though he had a medical degree, thought of himself as a scientist. He trained as a physical anthropologist at the highest levels of German academia. The offspring of a solid Bavarian Catholic family—during his later years in exile, he wrote tearful memoirs about his mother’s Catholic pieties—he studied in Bonn and Vienna, and, in 1933, worked in Munich, under the Scottish-German anthropologist Theodor Mollison. It was Mollison, Marwell writes, who “perfected a series of measuring and recording devices that helped to standardize and increase the precision of the essential measurements that were the basis of physical anthropology.” Even in the early thirties, Mollison was an eager Nazi, and the particular kind of anthropology he taught turned very easily to a völkisch ideology; it was a purely descriptive science that easily lent itself to pseudoscience, what Stephen Jay Gould memorably dubbed “the mismeasure of man.” Mollison became famous for his “deviation curves,” graphs that seemed to show differences among racial kinds.

All ideas, and ideals, are capable of being twisted into their opposites. Religious doctrines preaching nonviolence and loving thy enemy quickly turn into a search for enemies not to love. The intention and its perversion are usually transparent. We even have a good word for this bad practice: hypocrisy. But scientific theories, which get their credibility from their ability to explain the action of a limited domain of objects, can explode into false models for unrelated subjects without conscious hypocrisy. The Darwinian idea of the struggle for existence, designed to explain the chiselling of birds’ beaks, becomes in a generation the idea that poor people deserve to be poor. Einstein’s idea that the measurement of time is relative can warp into the idea that morality is. The missteps can be hard to track. The perversion of a scientific practice takes a second; its rectification takes a semester.

The German anthropological practice of measuring people and typing them according to race, in which Mengele was trained, had, as the Columbia historian Andrew Zimmerman has shown, begun on a large scale half a century before Mengele was schooled in it. It was pioneered in the eighteen-seventies, under the direction of the impeccably liberal scientist Rudolf Virchow, who was a leading voice against anti-Semitism at the time, vying with a notorious anti-Semitic agitator for a seat in the Reichstag, and winning. And, indeed, dividing schoolchildren into “Blonds” (Nordic types) and “Brunets” (everyone else), Virchow found that “Brunets occurred among all the schoolchildren a bit more than 14 percent; among the Jews it was 42 percent.” Looking at the numbers, we might think that there was remarkably little measurable uniformity among Jews. But people make numbers mean what they want them to mean, as in baseball negotiations, and in this case the numbers were taken to mean that the Jews were not subtly different but utterly Other. Analyzing the numbers with sufficient acuity to see what they really did or didn’t show was complicated, like explaining why high batting averages aren’t a good guide to winning baseball games: you have to be willing to hang around for the explanation, rather than rushing to sign the contract. And so the idea of objectifying standards of human measurement was easily married to the (anti-Darwinian) idea that what you were measuring was not individual variations but racial essences—that races were like species, and came in fixed, unchanging kinds, discernible and deducible from fixed measures.

Mengele, studying human mandibles under Mollison’s supervision, concluded that “the jaws of the examined racial groups indicate in their front sections such distinct differences that they permit one to distinguish between the races.” It was like trying to study the internal-combustion engine by surveying all the parked cars on a street. You would end up with a significant-seeming taxonomy of windshield sizes and bumper dents, but you would have no idea that they all had the same motor inside, much less how it worked.

Even by the politicized standards of the field, Mengele was a mediocre student. His doctoral thesis, Mollison judged, though it “suffers from a somewhat clumsy manner of presentation and expression, may be described as fulfilling the requirements”—academese, in any era, for a B-minus. Mengele was good enough to study with the big names and win their support, but not good enough to go far in their world.

He went on to write another doctoral dissertation, in medical genetics, studying the heritability of cleft palates, which reinforced Nazi legislation requiring the sterilization of Germans with genetic disorders. By the late nineteen-thirties, he had been put to work as an expert consultant on racial types, evaluating such variables as blood types, eye color, eyebrow shapes, and fingerprints, to determine if a subject in a court case was a full Jew or a half Jew. In one instance, a Jew named Heinz Alexander was accused of the racial crime of miscegenation for having had an affair with an Aryan. He defended himself by insisting that he was not, in fact, fully Jewish but the bastard of an Aryan father. (Mengele wasn’t convinced.)

Reading about Mengele’s prewar training, one is struck by the enormous investment of resources, intellectual and financial, that was poured into this weirdly minute and futile science of racial difference. When Mengele, newly enlisted in the S.S. on the brink of war in 1938, sought to marry a twenty-one-year-old named Irene Schönbein, the Racial Office of the S.S. traced her ancestry back to 1648 to look for any signs of non-Aryan taint, and, unable to confidently establish the racial identity of her paternal grandfather, refused to enter her into its “clan registry.” (Nazi rules about “racial purity” were inspired by, but did not go as far as, American “one drop” and “blood fraction” laws, enacted in the South, which stipulated that even a remote black ancestor rendered an individual nonwhite. As with Hitler’s likening of his conquest of the East to the American conquest of the West, our worst history encouraged the Nazis’ worst instincts.)

Racism doesn’t, one would think, normally demand quantitative data on quite this scale in order to prosper. Anti-Semitism in medieval times managed with gossip about blood-based matzo. But this racial stuff was not merely instrumental; it was obsessive. The Nazi intelligentsia really believed. An obsessive anatomy and a specialized language of racial difference created an essential intellectual armor, a shield from scrutiny. An alternative intellectual universe was constructed, with its own sciences and academic establishment, to insure that everyone involved would see himself as normal, as a scientist doing science. It was this self-sealing intellectual wholeness that distinguished the Nazis from the commerce-minded conservatives with whom they often allied, and eventually consumed. Mengele’s career is a reminder that Nazism was not, as the left long insisted, capitalism with the gloves off. It was craziness with a white coat on—a faith driven, as most big historical movements are, by passionate ideas, not parsable interests.

Mengele, after serving with the Waffen S.S. Viking division—creepy even by Nazi standards, it was made up largely of foreign Aryan volunteers—was finally posted to Auschwitz, in May of 1943. This was regarded as a plum assignment for S.S. troops; you could kill people there without the threat of being killed. Once in Auschwitz, Mengele became famous as the worst of villains precisely because he seemed to love his job. Tributes to his calm spirits and good humor morbidly fill the pages of recollections, including those of the Jewish scientists who were press-ganged into his service.

Marwell does show, however, that Mengele gets the “credit” for more selections than he could possibly have made on his own. As one survivor wrote, “If a member of the SS is repeatedly named in public in connection with especially monstrous deeds, it is possible that survivors will project their experiences on to him. . . . More than once I heard survivors say that Mengele did this or that to them, even though Mengele had not yet arrived in Auschwitz at the time.” Crimes committed by the entirety of the Auschwitz staff were ascribed to him. He appears to have been singled out because of the sinister calm and scrupulous care with which he approached the task of sorting out the soon-to-die from the (briefly) saved, a sangfroid that he maintained, as one less confident colleague suggested, because he alone accepted that all of the Jews were already “dead upon arrival.” He was sorting out ghosts, not people.

It was Mengele’s conduct of experiments that made his reputation for pure evil so potent. He established his own research institute at Auschwitz, affiliated with a traditionally respectable academic one, the Kaiser Wilhelm Institute of Anthropology, in Berlin. And his sincerely constructed carapace of normal science is what makes the work especially chilling. His notorious twin studies, for example, have often been imagined to be wild efforts to increase German fecundity by finding a secret method by which all German women would have twins. In fact, Marwell shows, these studies were a continuation of the kind of research that was going on elsewhere in the world. Identical twins were widely seen as the Rosetta stone of genetics, which would allow scientists to crack the code of culture versus nature. Working with an equally appalling woman scientist named Karin Magnussen, Mengele “harvested” eyes from Sinti twins in the camp who had a condition called heterochromia of the iris, resulting in eyes with different colors. The aim was not one of fiendish engineering, to change eye color, which would have been merely cosmetic. No, it was to collect hard data in advance of discovering “the applied genetics” of “paternity and ancestry determinations,” which would sort out Übermenschen from Untermenschen. Mengele’s work in Auschwitz was what we would call “pure research.” Marwell, who clearly did not entirely expect to find what he did find, writes:

He pursued his science not as some renegade propelled solely by evil and bizarre impulses but rather in a manner that his mentor and his peers could judge as meeting the highest standards. . . . The notion of Mengele as unhinged, driven by demons, and indulging grotesque and sadistic impulses should be replaced by something even more unsettling. Mengele was, in fact, in the scientific vanguard, enjoying the confidence and mentorship of the leaders in his field. The science he pursued in Auschwitz, to the extent that we can reconstruct it, was not anomalous but rather consistent with research carried out by others in what was considered to be the scientific establishment.

To this, one might add a single footnote: the German “scientific establishment” had long ago sold its soul, and measuring stick, to the Devil. The scientists in Berlin and Graz who readily accepted disembodied heads and eyes and skeletons from Mengele’s institute had been morally corrupted long before the samples arrived. No one suggests that Mengele’s twin or eye-color research was of lasting value, despite its diabolical origins. (This might be said, for instance, of the Nazis’ rocket research: the science was sound, even if the missiles went to the wrong cities.) The genetics of eye color was never going to be cracked by the gruesome business of collecting a lot of eyes. The anthropologists in Berlin and Munich had already convinced themselves that their fanatic inventorying and artifact-collecting impulse was so virtuous that it made questions of morality empty. Mengele was not, it turns out, a mad scientist. It was worse than that. He was participating in a mad science.

Marwell surveys, with a kind of aghast wonder, the comforts of life for Nazi doctors living amid so much death. They had a special “subcamp,” twenty miles from the gas chambers, that served as a rustic retreat. There were regular conjugal visits, and a steady flow of dinner parties among the S.S. officers and their wives. All this as the smoke rose in the camp nearby. Mengele was happy in this world—photographs show him smiling, and even the inmate-slave who drew his baths called him “polite.” Whenever some sense of morality intruded on this tightly enclosed communal sphere, the special unity of the bad actors held the group together. Again and again, the S.S. leaders, from Himmler on down, emphasized to their followers that they had already crossed the bar: if they failed in their task, the children of the survivors would come for them. It is the collective logic of all extremism. Within a group of killers, only acts of sadistic cruelty in which all are made to join can guarantee solidarity. And so we see the omnipresence of hazing rituals among motorcycle gangs and mafiosi: you make your bones by burning your bridges. The fanatic leader convinces his adherents not that this is the only way forward but that there is no way of turning back.

Mengele’s flight from Europe after the war was startlingly slow. Stopping off in Munich, perhaps to collect records of his research which he had sent on from Auschwitz, he spent more than three years under an assumed name as a hired hand at a Bavarian farm. (One of perhaps a hundred bitter ironies in his post-Auschwitz life: most S.S. men, like their victims, had been tattooed, in their case to receive the right blood type if they were wounded and needed a transfusion. This made them easy to identify after the war, but Mengele had managed to evade the marking, probably out of vanity.)

He made his way, in 1949, to South America, with the help of the Red Cross—along with the Catholic clergy’s “ratline,” one of the two most efficient escape routes for ex-Nazis—obtaining a passport more or less on demand. Once he arrived in South America, moving from Argentina to Paraguay and eventually settling in Brazil, he was protected by a makeshift network of German and Austrian expats. Mengele shared a coffee-and-cattle operation for years in Brazil with a Hungarian couple who kept his secret in exchange for a new farm, paid for by his protectors.

The Israelis tried to keep track of him, but never tried to kidnap him. This was, in part, a matter of politics. No doubt Israel had to balance its desire to capture war criminals against the price of alienating potentially helpful South American governments. And, logistically, Mossad, like any government agency, had limited means and many missions. Infuriatingly, Mengele’s life on the run did not include much running: he managed the farm, kept a wary eye on his imagined pursuers, and had plenty of time to get married, go on holidays, and even correspond regularly with his son, Rolf, who lived in Germany. Mengele died in 1979, during one of those holidays; he had a stroke while swimming.

His friends buried him, under his assumed name of Wolfgang Gerhard, and then, pressured by the West German and Brazilian police, disclosed the location of his grave. But the Germans and the Israelis—as well as Americans, who by now had taken up the Mengele hunt, at the political urging of the New York senator Al D’Amato—were unconvinced that they had the right corpse. They gave Mengele and his associates too much credit for fiendish movie-style secrecy—extensive plastic surgeries and faked deaths—when he had mostly been kept safe by lassitude on the part of his pursuers and moral indifference on the part of his protectors.

In June of 1985, teams of pathologists, forensic anthropologists, and other investigators from both Germany and the United States—including Marwell himself, working for the Justice Department’s Office of Special Investigations—descended on São Paulo to determine if the body was indeed Mengele’s. In the strangest irony, the methods used to identify the criminal were essentially versions of the physical anthropology that Mengele had been trained in. Measurements were taken, the pubic symphysis was examined for wear; femurs were cross-sectioned, and ribs were inspected to assess how “cupped” they had become. Finally, the Germans introduced a brand-new technique: two high-resolution videos—one of the corpse’s skull, the other of a photograph of Mengele when alive—were superimposed. It was Mengele, and “closure,” that strange beast, was captured at last. All that microscopic Teutonic precision was now directed not to the malignant fantasy of creating racial categories but to distinguishing one man from all others. What exists is individuals, and what we can capture is their quiddities; the larger collectivities—of nation, class, mind, character—to which they belong are still too manifold for measurement.

Götz Aly, the German historian whose “Hitler’s Beneficiaries” is one of the more highly praised works on the Third Reich published in the past two decades, has just brought out a new book in English, “Europe Against the Jews: 1880-1945” (Metropolitan), and it throws some postscript-like light on the Mengele case. Aly has two motives in writing his book. First, to show just how widespread, pan-European, and ideologically complete European anti-Semitism was. From France through Poland and on into Romania and Hungary, each country had, in the nineteenth century, an anti-Semitic establishment, often anchored in the Catholic right but just as often in the Socialist left, which was, in its language, as virulent as the later, Hitlerian kind. Anti-Semitism that envisioned the removal and, implicitly, the extermination of the Jews was everywhere. Nobody needed encouragement to persecute Jews. The circumstances of war made it possible, but many, throughout Europe, had been eager to do so as soon as they could.

His second line of inquiry is more subtle: Why did they want to persecute the Jews so badly? He distinguishes classic medieval-style anti-Semitism, in which Jews were simply aliens, from a modern strain, in which they had become, unacceptably, betters. A new sort of competition had arisen in which the Jews had seized a first-mover advantage. In the nineteenth century, they arrived, before anyone else, at an understanding that, in the new world of modernity, competitive advancement—doing well on exams—would provide an alternative to advancement through bloodlines. Why the Jews did so well in societies that depended on some form of test-taking is a complicated historical question, though it may be as simple as that the tradition of Talmudic study could easily be “exapted” for the purpose. Paradoxically, only when the “national” groups entered this competition themselves and began to catch up did their hatred of the Jews take on a new ferocity. “As the gap in education closed, the degree of friction between Jews and majority populations increased,” Aly writes. “Envy is born of social proximity, not of the distance between two cleanly separated groups.”

The 1894 Dreyfus case, the original falling domino of what was to come, fits this pattern perfectly, and it makes sense that it happened in France, the first European nation to insure “careers open to talent.” Captain Dreyfus’s great sin was not being a Dreyfus but being a captain. And though Aly doesn’t cite this instance, his scheme maps perfectly onto the lives of the Nazis: Hitler was enraged at the Jews in Vienna not because Jews were practicing the arts instead of agriculture but because they wouldn’t let him into art school. Goebbels was a failed philosophical novelist, not a rabble-rouser. The circles of populist authoritarians, then and now, tended to be filled with embittered B-minus competitors.

And so we come to the last and still the most morally instructive thing about studying the Nazis now: we can see how tightly the elimination of the Jews was bound to a hatred of cosmopolitanism. Although huge numbers of the Jews who perished in the mass killings were poor religious Jews from Eastern Europe, many peasants and peddlers and small merchants, the main enemy, as Mengele understood, had always been the educated Jews of Western Europe. When an S.S. doctor wondered aloud why all the poor Jews of the East had to be killed, he recalled Mengele explaining that “it was precisely from this reservoir of people that the Jews drew new power and refreshed their blood. Without the poor but supposedly harmless Eastern Jews, the civilized West European Jews would not be capable of survival. Therefore, it is necessary to destroy all Jews.” The masses of poor religious Jews in Poland were almost accidental to the effort; the real target was the élite, who brought with them the bacillus of cosmopolitanism.

In Tom Stoppard’s great new play, “Leopoldstadt,” the study of a thoroughly assimilated Jewish family which begins in Vienna’s golden period before the Great War—a Star of David sits atop their Christmas tree—the final, shattering scene is set in the nineteen-fifties. A man whose immediate family escaped in time comes home and asks, happily, about the relatives he had known as a boy. He lists one name after another: Ernst? Auschwitz. Hanna? Auschwitz. All his flawed and idiosyncratic relatives turn out to have been murdered by the Mengeles of the world. The audience, unique in my experience, is silent at the end, almost unable to applaud the actors. But the invocation is exact: it was the destruction of such harmless and happy Viennese cosmopolitan families that Hitler, who discovered anti-Semitism as a cure-all for his frustrations as a young and unsuccessful artist in Vienna, most desired. He was willing to destroy European civilization in order to achieve it, and he did.