Robert Putnam's recent article is bound to generate a lot of discussion among academics as well as politicians. Abstract:
"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."
A nice summary of the article by Madeleine Bunting and interesting comments in The Guardian.
I came across Putnam's article through a post of Andrew Leigh in his blog. Andrew Leigh also links to asimilar study by himself. Another summary of Putnam's study here.