One St. Patrick’s Day in Chicago, back when I was working as a television reporter there in the 1980s, I wandered up and down the famous parade route on Dearborn Street and asked people in green plastic derbies and kelly-green sweatshirts about the content of Irishness. What were the markers? What did it mean to be Irish? Almost no one had an answer that made any sense. Several people cited devotion to family. Many mentioned the Catholic Church. But most could not name anything that made being ethnically Irish different from being anything else.

As an admirer and student of Irish culture and history, I was stunned that I could talk to as many people as I did, all self-identifying as ethnically Irish, and come away with so little. Literature? Art? Joyce? Yeats? Ireland’s suffering at the hands of the British? If family devotion and fealty to the Church were the only markers of Irishness, then being Irish was no different from being Italian, Polish, or Croatian. Or Mexican, for that matter.

On another day, I was assigned to cover the approaching end of farming in Cook County. I headed out to a remote corner of the county once solely devoted to growing corn, wheat, and soybeans. On the way to the farm, I noticed that one of the streets we passed had the same Germanic name as the farmer we were set to interview, and made a mental note to ask him about it.

I walked through the neat rows of corn with a pleasant man in his late twenties as he talked about where he was going to move after the rented land he was farming was graded for a subdivision. I asked about the street and whether it was named for his family. He said it was, that his family had settled in that part of Cook County just before the Civil War.

“Where did they come from?” I asked.

He paused. “Uhhhh…Germany, I guess.”

I guess? I chewed on that answer for a long time afterwards. Would some future Suarez descendant, when asked whether he or she was Mexican or Central American or Caribbean, tell the questioner that one Raul Suarez came at some point in the twentieth century from “Puerto Rico, I guess”?

In Not Fit for Our Society, Peter Schrag takes us back to the immigration battles that rocked the early United States, as successive waves of newcomers forced the young nation, again and again, to confront difficult questions about assimilation and acculturation. Schrag, a naturalized American who came here as a Jewish refugee from Hitler’s Germany, makes a simple proposition: that just as it is true that the United States has always been a nation of immigrants, it has also always been a nation of immigration restrictionists. There is a centuries-long history of immigration battles the happy parade-goers in Chicago, the presumably German-American farmer in the Cook suburbs, and millions more Americans across the country forget, or want to forget. “Our contemporary immigration battles,” Schrag writes, “particularly the ideas and proposals of latter-day nativists and immigration restrictionists resonate with the arguments of more than two centuries of that history.” The nineteenth- and twentieth-century arguments got as nasty, racist, and hyperbolic as anything we’re hearing today with regard to Arizona’s new law.

But Schrag’s discussion goes beyond a mere retelling of the immigrant story into a probing meditation on race and ethnicity. He argues that just as assimilation and acculturation eventually broadened the definition of whiteness and American identity, so too will it happen with the coming generations of immigrants. Schrag notes the rapid changes in Latino families already in the United States, and presents the provocative proposal that they may someday resemble the Irish and the Germans in their ability to set aside, forget, and sentimentalize who they once were. The only question is whether the rest of America will let them join earlier arrivals in the act of forgetting.

In a quick sprint of some 232 pages, Not Fit for Our Society lays out a gripping history of nineteenth- and twentieth-century immigration and sets the scene for the new immigration battles about to be staged on Capitol Hill and across the country. Schrag draws strong parallels between the eugenicist arguments of early twentieth-century scientists like Lothrop Stoddard and Henry Goddard and the recent work of Charles Murray and the late Richard Herrnstein. In 1912, Goddard warned of the birth of “more feeble-minded children with which to clog the wheels of human progress.” Eight decades later, Herrnstein and Murray, writing in The Bell Curve, maintained that high levels of immigration lower the country’s brainpower. In a March speech to a Tea Party convention in Nashville, former Congressman Tom Tancredo put it more bluntly: “People who could not even spell the word ‘vote,’ or say it in English, put a committed socialist ideologue in the White House.”

Schrag walks the reader through the science and pseudoscience of race in nineteenth-century America. Using the new “sciences” of intelligence testing, racial anthropology, and eugenics, researchers claimed to discover a racial hierarchy among the world’s peoples, and their findings swept through universities and scientific institutes. It found “Nordic” Europeans superior to so-called “Alpine” people, who were in turn superior to “Mediterranean” types. Writing in a journal called The Survey, Goddard found 82 percent of Russian immigrants, 80 percent of Hungarians, 79 percent of Italians, and 76 percent of Jews to be morons, and backed up his statistics by noting that Ellis Island was sending home more immigrants as feeble-minded every year.

Once the academy opened the Pandora’s box of racial and ethnic pseudoscience, it did not sit quiet and frozen on the pages of learned journals. By the 1920s, race science had a powerful audience among American politicians (and, more disturbingly, avid students in the new National Socialist Party in Germany). An immigration bill passed in 1917 created something called the “Asiatic Barred Zone,” a swath of the planet from which no one could immigrate to the United States. It began in Turkey and ran through the Middle East across Asia, through the Indian subcontinent to the Pacific Ocean, excluding Japan. Since the Fourteenth and Fifteenth Amendments to the Constitution now guaranteed the rights of citizenship to “persons of African descent,” the new law was bound to launch court cases to clear up the rules. As Schrag asks, “Who was white and thus entitled to naturalization and, by extension, to immigration, and who was something else?”

There was never a “once and for all” sorting of America’s immigrant stock. Instead there was a gradual accumulation of a jurisprudence of race, if you will, that neatly reflected the constantly shifting boundaries of whiteness. Schrag details the typically muddled conclusions reached by the courts about the “otherness” of Asians:

Lawsuits seeking to answer the racial question had begun in 1878, three decades before the creation of the barred zone–suits in which the courts ruled repeatedly that the Chinese weren’t white, that the Japanese weren’t white, that Hawaiians weren’t white, that Filipinos weren’t white, and that Burmese weren’t white.…In 1919 two courts ruled that Asian Indians were white (one other court, in 1919, ruled they probably weren’t).…Four pre-1917 decisions had ruled that Syrians were white, and three that they weren’t. Then came rulings that Koreans weren’t white; Afghanis weren’t white, followed in 1945 by a decision that they were; and that “Arabians” weren’t white, again followed by a Board of Immigration Appeals ruling (in 1941) that, because European civilization had originated in the Middle East, they were white.

All this uncertainty has led to peculiar outcomes. Schrag tells of an appellate court in Alabama that overturned a miscegenation conviction involving a black man and a white woman “because there had been no proof that the woman, a Sicilian, was white.” These cases are not only part of some long ago past. Shereen Marisol Meraji, a young producer at NPR, told of her difficulty in filling out the racial identity section of the 2010 census form. Her father is an immigrant from Iran, her mother, Puerto Rican. “I call myself a Puerto-Ranian.…But there isn’t a Puerto-Ranian category on the census. So I check Hispanic,” she said. Meraji called other Middle Easterners, including her father, and found they disliked having to declare a race on the census. Iranians, Kuwaitis, and Iraqis are all from Asia, but these Americans assume the “Asian” categories are not meant for them.

Up until the 1920s, the Irish were not white in the way we use the term today, and were instead commonly referred to as members of another “race” by native-born American Protestants. The same went for Italians, who were also assigned another racial category. The Jews of Eastern Europe were most certainly not white in the schematic diagrams of race created by “scientists” at America’s temples of scientific rigor, Harvard and Columbia.

But assimilation and social change let all these groups gradually leave the waiting rooms of whiteness. The discovery of new places, peoples, and enemies to worry about also moved the guardians of whiteness to wave some through the gates and keep others out. As the feeder countries of European immigration shifted south to the Mediterranean and east past the Balkans by the early years of the twentieth century, Schrag writes, questions about the Irish began to fade, only to be replaced by speculation about whether Orthodox Christian Serbs and Lithuanian Jews would ever become real Americans.

Of all the foreign-born in the United States, half are from Spanish-speaking countries. Of that portion, half are from just one country, Mexico. It is no wonder modern debates over immigration have centered on Spanish speakers who live as legal and illegal immigrants in this country. Schrag challenges anti-immigrant forces and Latino activists alike with his argument that it is not altogether clear what it will mean to be a Latino in the United States later this century, when large chunks of that population will be the descendants of families in the country for more than a hundred years. Will Latinos be like the kelly green-clad revelers on St. Patrick’s Day, or keep real and abiding links to their country of origin?

Demographers project that by 2042, the United States will no longer be home to a European-descended majority. (We’re getting the first glimpse of that next country this year, with the forecast that the birth cohort for 2010 will be the first ever to have a “non-white” majority.) Latinos, like Asians, are “marrying out” at very high rates. Latinos are acquiring mastery of English in the second and third generations in much the way immigrant descendants of earlier generations did.

Recent statistics indicate Latinos are no different from other Americans in shedding or shifting away from the church of their ancestors. The Pew Forum on Religion & Public Life found that about half of American adults have changed religious affiliation at least once in their lives, and that many have done it more than once. Latinos are just embarking on that part of the American journey. Some two-thirds still self-identify as Roman Catholics, but a growing portion, 15 percent, is Evangelical Protestant (half are converts), and about one in ten are religiously unaffiliated.

Take away language through assimilation, genetic “stock” through intermarriage, and religion through conversion, and what will it mean to be Latino 40 years from now? Schrag notes that the writer Richard Rodriguez has observed that California Latinos don’t look like their own grandparents. Once the grandchildren and great-grandchildren of the rest of the hemisphere are “whitened” by American life, what will this coming Latino majority consist of? Will it simply be taste in food or sports? The historical accidents of names like Ramos, Gomez, and Suarez?

Just as Americans have sentimentalized immigration history, bathing the Ellis Island arrivals in a golden light, we have also sentimentalized ethnicity. For millions of Americans, ethnicity is a near-empty signifier, a container for “identity” that holds little beyond foods, family stories, and a few half-remembered phrases in the tongue of the Old Country. The ahistorical warm feelings about past generations of immigrants will not pay forward to a sympathy for, or understanding of, the next wave of new Americans.

But the news isn’t all bad. Latinos are already successfully navigating currents in American life. While hardly new on the American scene, Latinos are more numerous and more successful than ever before. What’s unclear, however, is whether Latinos are smashing the binary concept of race in America, or playing by its long-established rules and will become white over time as other immigrant groups have. Economics has something to do with this uncertainty. Historically, when an immigrant group starts out on the bottom of the socioeconomic ladder, room is made higher up in response to the group’s gradual economic success. Yet globalization and the offshoring of more and more American jobs may have created an immigrant class that cannot rise as earlier groups have.

The bigger picture is thus more muddled, and less susceptible to absolutist interpretations, than before. Latinos may end up as both subverters of the Great American Skin Game and victims of it. As a matter of cultural tradition, Latinos are very conscious of the broad continuum of color and appearance their mixed gene pool has created, resulting in something much subtler than the American one-drop rule, which made anyone with black ancestry black. (There’s an old joke: A young woman in Latin America brings a date home to meet the family. The wily grandmother, seeing the European-looking young man, says to him, “Y tu abuela, donde esta?”–“And your grandmother, where is she?” The joke, of course, is that a more thorough examination of the family tree is needed before identifying the relative whiteness of an individual.)

If the new mixed-race arrivals from the Caribbean and the darker, more Indian immigrants from Mexico and Central America are left behind, while Latinos who look more like Eva Longoria race ahead in intermarriage, acculturation, and economic success, then the rigidities of the American way of race will not have been demolished, only modified to fit a new reality. Just as in the nineteenth century, the category of “white” will once again be broadened, rather than smashed for good, leaving “non-white” people on the outside once again.

But if Latinos of all hues and statures, “good” and “bad” hair alike, merge with the American whole, then their arrival will have done something different. They will have become the first mixed-race immigrant group to become part of the country’s mainstream, and by doing so, change what an “average” American looks like to their fellow citizens and to the rest of the world. That’s big, and it will have happened under anomalous historical circumstances: Unlike previous immigrant flows that peaked, spiked, then subsided, the arrival of Spanish speakers from the rest of the hemisphere has mostly remained high. There will be no shared memory of coming to a particular place at a particular time, because this is an immigrant group whose arrival will span centuries.

Latinos of earlier generations will almost certainly peel off and become part of the American mainstream. However, the steady flow of new arrivals, without the spike and subsidence of Italians, Norwegians, Eastern European Jews, and others could open doors faster and make more and more Americans more and more comfortable with this changing country.

The debate that is shaping up over the roughly 12 million illegal immigrants in the United States looks like it will fit within the pattern Schrag identifies: It is already heavily freighted with accusations that today’s new arrivals will never fit in, don’t understand American democracy, and refuse to assimilate.

The lovely irony is that even as immigration restrictionists speculate about the coming loss of American identity, culture, and language, the ground continues to shift under their feet. Native-born Latinos are driving American demographic change, and changing the makeup of the electorate in the states that determine who becomes president. If Schrag is right, and I expect he is, the United States will just be wrapping its head around a new brown future around the same time millions of Latinos have put aside Spanish, and the Old Country has become a fading and distant memory.