this article perfectly describes what happened to the mythical black "community" at the end of legal segregation...,

theatlantic |  In his State of the Union address, President Obama lamented how Washington “has been consumed by ... rancorous argument,” which over the past year has prevented us “from carrying out even the most basic functions of our democracy.” The vast ideological chasm that separates politicians on the left from those on the right shows little sign of narrowing, and the midterm elections this fall promise to be extremely contentious. Most observers expect the environment will guarantee that Congress will achieve next to nothing between now and November. Why has political polarization in our country reached such dangerous levels?

A familiar explanation for our deepening partisan divide is Bill Bishop’s Big Sort hypothesis. He contends that over the past 40 years, Americans have been sorting themselves into communities where people increasingly live, think, and vote like their neighbors. In 1976, for example, just more than a quarter of Americans resided in counties where presidential candidates won the election by a margin of 20 percent or more; but by the year 2004, nearly half of Americans lived in these more politically homogeneous counties.

Bishop’s idea is a convincing description of what is happening. But why is it happening? Thanks to research in demographics and anthropology, it’s now possible to get a clearer picture of the underlying reasons: education and evolution.