I’ve heard people reference this study a number of times recently and finally decided to track it down. For an expanded explanation of Mr. Putnam’s findings, see his article E Pluribus Unum: Diversity and Community in the Twenty-first Century.

Boston.com – The downside of diversity

It has become increasingly popular to speak of racial and ethnic diversity as a civic strength. From multicultural festivals to pronouncements from political leaders, the message is the same: our differences make us stronger.

But a massive new study, based on detailed interviews of nearly 30,000 people across America, has concluded just the opposite. Harvard political scientist Robert Putnam — famous for “Bowling Alone,” his 2000 book on declining civic engagement — has found that the greater the diversity in a community, the fewer people vote and the less they volunteer, the less they give to charity and work on community projects. In the most diverse communities, neighbors trust one another about half as much as they do in the most homogenous settings. The study, the largest ever on civic engagement in America, found that virtually all measures of civic health are lower in more diverse settings.

“The extent of the effect is shocking,” says Scott Page, a University of Michigan political scientist.

The study comes at a time when the future of the American melting pot is the focus of intense political debate, from immigration to race-based admissions to schools, and it poses challenges to advocates on all sides of the issues. The study is already being cited by some conservatives as proof of the harm large-scale immigration causes to the nation’s social fabric. But with demographic trends already pushing the nation inexorably toward greater diversity, the real question may yet lie ahead: how to handle the unsettling social changes that Putnam’s research predicts.

“We can’t ignore the findings,” says Ali Noorani, executive director of the Massachusetts Immigrant and Refugee Advocacy Coalition. “The big question we have to ask ourselves is, what do we do about it; what are the next steps?”

The study is part of a fascinating new portrait of diversity emerging from recent scholarship. Diversity, it shows, makes us uncomfortable — but discomfort, it turns out, isn’t always a bad thing. Unease with differences helps explain why teams of engineers from different cultures may be ideally suited to solve a vexing problem. Culture clashes can produce a dynamic give-and-take, generating a solution that may have eluded a group of people with more similar backgrounds and approaches. At the same time, though, Putnam’s work adds to a growing body of research indicating that more diverse populations seem to extend themselves less on behalf of collective needs and goals.