Just found this article by Robert Putnam, PhD, of Bowling Alone fame.
E Pluribus Unum: Diversity and Community in the Twenty-first Century
Robert D. Putnam (2007)
The 2006 Johan Skytte Prize Lecture
Scandinavian Political Studies 30 (2), 137–174.
Volume 30 Issue 2 Page 137-174, June 2007
Ethnic diversity is increasing in most advanced countries, driven mostly by sharp increases in immigration. In the long run immigration and diversity are likely to have important cultural, economic, fiscal, and developmental benefits. In the short run, however, immigration and ethnic diversity tend to reduce social solidarity and social capital. New evidence from the US suggests that in ethnically diverse neighbourhoods residents of all races tend to ‘hunker down’. Trust (even of one’s own race) is lower, altruism and community cooperation rarer, friends fewer. In the long run, however, successful immigrant societies have overcome such fragmentation by creating new, cross-cutting forms of social solidarity and more encompassing identities. Illustrations of becoming comfortable with diversity are drawn from the US military, religious institutions, and earlier waves of American immigration.