Over the past few decades, American society has been transformed in a fit of absence of mind. First, we’ve gone from a low immigrant nation to a high immigrant nation. If you grew up between 1950 and 1985, you grew up at a time when only about 5 percent or 6 percent of American residents were foreign born. Today, roughly 13 percent of American residents are foreign born, and we’re possibly heading to 15 percent.

Moreover, up until now, America was primarily an outpost of European civilization. Between 1830 and 1880, 80 percent of the immigrants came from Northern and Western Europe. Over the following decades, the bulk came from Southern and Central Europe. In 1960, 75 percent of the foreign-born population came from Europe, with European ideas and European heritage.

Soon, we will no longer be an outpost of Europe, but a nation of mutts, a nation with hundreds of fluid ethnicities from around the world, intermarrying and intermingling. Americans of European descent are already a minority among 5-year-olds. European-Americans will be a minority over all in 30 years at the latest, and probably sooner.

If enacted, the immigration reform bill would accelerate these trends. It would further increase immigration levels. According to the Census Bureau, roughly 20 million immigrants will come to this country under current law. The Congressional Budget Office expects another 16 million under the new provisions.

It would boost the rise of non-Europeans. Immigration would be more global. Hispanics are now projected to make up 30 percent of the U.S. population by 2050. We would hit that mark sooner with reform.

In other words, immigration reform won’t transform America. It will just speed up the arrival of a New America that is already guaranteed.

As we stand on the cusp of this New America, it’s understandable to feel some anxiety. If you take sociology and culture seriously, it’s sensible to wonder whether this is the sort of country we want to be. Can we absorb this many immigrants without changing something fundamental?Let’s make some educated guesses about what the New America will look like. It will almost certainly be economically dynamic. Immigration boosts economic dynamism, and more immigration would boost it more. There would also be a lot of upward striving. Immigrant groups tend to work harder than native groups. They save more. They start business at higher rates than natives.

My colleague Anne Snyder delineates several possible changes to the social fabric. Basically we are witnessing the end of the old ethnic-racial order. Traditionally, mainstream America has been defined by the big block of whites, while other big blocks — blacks, Hispanics, Asians — occupied different places on the hierarchy.

Soon there will be no dominant block, just complex networks of fluid streams — Vietnamese, Bengalis, Kazakhs. It’s a bit like the end of the cold war when bipolar thinking had to give way to a radically multipolar mind-set.

Because high immigration is taking place at a time of unprecedentedly low ethnic hostility, we’re seeing high rates of intermarriage. This creates large numbers of hybrid individuals, biracial or triracial people with names like Enrique Cohen-Chan. These people transcend existing categories and soften the social boundaries between groups.

This won’t lead to a bland mélange America but probably a move to ethnic re-orthodoxy. As Alvaro Vargas Llosa points out in his book, “Global Crossings,” the typical pattern is that the more third-generation people assimilate, the more they also value their ethnic roots. We could soon see people with completely unaccented English joining Chinese-American Federations and Honduran-American Support Networks.

The big divides could be along educational lines, not ethnic ones. Because educated people intermarry at higher rates, we could have an educated cosmopolitan class with low ethnic boundaries and a fair bit of integration in white-collar workplaces. Then, underneath, there could be a less-educated, more-balkanized layer, with high residential and professional segregation and more ethnic hostility.

We could also see more ethnic jostling between groups. The most interesting and problematic flashpoint may be between immigrants and African-Americans. We now have this bogus category, “minority,” in which we lump the supposed rainbow coalition of immigrants and blacks. But, in fact, tensions between “minority” groups could soon be more plainly obvious than any solidarity.

Finally, it would make sense that the religion of diversity, which dominates the ethos of our schools, would give way to an ethos of civic cohesion. We won’t have to celebrate diversity because it will be a fact. The problem will be finding the 21st-century thing that binds the fluid network of ethnic cells.

On the whole, this future is exciting. The challenge will be to create a global civilization that is, at the same time, distinctly American. Immigration reform or not, the nation of mutts is coming.