Orlando Patterson has some thoughts for the black middle class in America.

When W. E. B. DuBois, the patrician black leader, predicted in 1903 that the problem of the 20th century would be the color line, he had in mind an ethno-racial problem with a dual character. One side was the near complete exclusion of African-Americans and other minorities from the upper echelons and leadership of American society, public life and national identity. The other was the segregation of blacks from the social, communal and intimate cultural life of white Americans.

America’s resolution of the public side of the color line would have amazed DuBois. The nation stands today as a global model in the sophistication and enforcement of its civil rights laws, the diversity of its elite, the participation of blacks and other minorities in its great corporations and its public cultural life, and in the embrace of blacks as an integral part of the nation and what it means to be an American.

A black man has led the world’s most powerful military machine and stood a good chance of winning the presidency on the Republican ticket had he run; another is now a leading challenger for the Democratic nomination. A black woman, Oprah Winfrey, is perhaps the nation’s most powerful cultural force; another, Secretary of State Condoleezza Rice, is one of the world’s most powerful people and is the nation’s public face before the world. The recent decisive gubernatorial victory of Deval Patrick in Massachusetts is yet another instance of full public integration. And in popular culture, blacks’ presence is out of all proportion to their numbers.

But when we turn to the other side of DuBois’s color line, we find a stunning paradox: accompanying this public integration has been the near complete isolation of blacks from the private life of the white majority. Recent modest improvements notwithstanding, blacks, including the middle class, are nearly as segregated today as they were in DuBois’s day. The typical black child now goes to a school that is more segregated than in the late ’60s. Segregation is the last major race problem because poverty, per se, is no longer mainly the result of discrimination but part of a broader national crisis that includes whites. Poverty’s greater incidence among blacks is largely due to segregation.

Compounding the paradox is the fact that the highest metropolitan segregation rates are now in the “liberal” regions of the Northeast and the Midwest, including New York. The paradox deepens when we learn from repeated polls that whites say they are comfortable living in neighborhoods that are approximately 25 percent black.

The celebrated tipping-point theory of Thomas Schelling, the Nobel Prize-winning economist, has long appeared to offer a pessimistic answer to the puzzle. It holds that even where a majority of whites favor having black neighbors, the all-white preference of just a few will always rapidly escalate into total segregation.

However, the economist William Easterly, after examining data on segregation over the past three decades, has demonstrated conclusively that Schelling’s theory is groundless in regard to race. In the vast majority of neighborhoods studied, Easterly found no pattern of acceleration of white decline, no evidence of a sudden, extreme exodus at the fabled tipping point, but instead a steady, almost constant decline in the proportion of whites from one decade to the next. Moreover, the typical neighborhoods that did change from being predominantly white to predominantly black in this period still had a significant proportion of whites living in them.

So why does segregation persist? The evidence seems clear that, in sharp contrast with the past, the major cause is that blacks generally prefer to live in neighborhoods that are at least 40 percent black. Blacks mention ethnic pride and white hostility as their main reasons for not moving to white neighborhoods. But studies like Mary Pattillo-McCoy’s ethnography of middle-class black ghettos show that the disadvantages, especially for youth, far outweigh the psychic gains.

It would be naïve to discount persisting white racism, but other minorities, like Jews, have faced a similar dilemma and opted, with good reasons, for integration. The Jewish-American experience also shows that identity and integration are not incompatible, and that when the middle class moves, others follow. If America is ever to solve the second part of DuBois’s color problem, it will be on the shoulders of the black middle class.

Orlando Patterson, a professor of sociology at Harvard, is a guest columnist. Maureen Dowd is off today.