For nearly a century, Harlem has been synonymous with black urban America. Given its magnetic and growing appeal to younger black professionals and its historic residential enclaves and cultural institutions, the neighborhood’s reputation as the capital of black America seems unlikely to change soon.

But the neighborhood is in the midst of a profound and accelerating shift. In greater Harlem, which runs river to river, and from East 96th Street and West 106th Street to West 155th Street, blacks are no longer a majority of the population  a shift that actually occurred a decade ago, but was largely overlooked.

By 2008, their share had declined to 4 in 10 residents. Since 2000, central Harlem’s population has grown more than in any other decade since the 1940s, to 126,000 from 109,000, but its black population  about 77,000 in central Harlem and about twice that in greater Harlem  is smaller than at any time since the 1920s.

In 2008, 22 percent of the white households in Harlem had moved to their present homes within the previous year. By comparison, only 7 percent of the black households had.