Traditionally sociologists have thought about the consequences of ethnic diversity in one of two ways. The conflict model claims that the more that diverse groups interact, the more social tension there will be. The contact model, on the other hand, suggests that the more that different groups interact, the less they will fear each other. Unsurprisingly the first model is favoured by conservatives to justify restrictions on immigration, while liberals often call on the second in arguing for multicultural education.
New research from the American sociologist Robert Putnam suggests that both models are wrong. Putnam's data, published in the journal Scandinavian Political Studies, shows that greater diversity creates neither conflict nor cooperation but anomie. Putnam and his colleagues interviewed 30,000 people in 41 communities across America. The more diverse a community, the less socially engaged were its members - they voted less, did less community work, gave less to charity, and had fewer friends.
Most strikingly, people in more diverse society people are more distrustful not just of members of other ethnic groups but of their own, too. 'It's not just that we don't trust people who are not like us', Putnam says. 'In diverse communities, we don't trust people who do look like us.'
One of the most influential social scientists in the world, Putnam has the ear of politicians as widely different as Bill Clinton, George Bush, Gordon Brown and even Muammar Gaddaffi. He worries that his new research will undermine his liberal message about immigration and multiculturalism. Putnam actually conducted the research in 2000, but has only just published the results because of its potentially explosive political message.
The implications of the data are, however, far from straightforward. The real problem with the study, as Putnam himself has pointed out, is that it offers only a snapshot of attitudes at one moment in time. Diversity, though, is not static phenomena. The character of diversity changes over time, as does our political response to it.
A broader view of diversity helps puncture the myth that contemporary Western societies are particularly diverse. 'When I was a child', the Ghanaian born American philosopher Kwame Appiah recalls, 'we lived in a household where you could hear at least three mother tongues spoken each day. Ghana, with a population close to that of New York State, has several dozen languages in active use and no one language that is spoken at home - or even fluently understood - by a majority of the population.' So why is it, he asks, that in America 'which seems so much less diverse than most other societies are we so preoccupied with diversity and inclined to conceive of it as cultural?'
The diversity of American society is small in comparison, not just to most third world countries, but also to its past. The proportion of foreign-born Americans is far less than it was at the beginning of the twentieth century. Intermarriage between immigrant groups continues to increase. More than 97 per cent of Americans speak English.
A century ago new immigrants did not simply speak their own language, they also read their own newspapers, ate their own food and lived their own lives. In 1923, for instance, the Polish community alone published 67 weekly newspapers, and 19 dailies, the largest of which had a circulation of more than a hundred thousand. Today, not just language, but the shopping mall, the sports field, the Hollywood film and the TV sitcom all serve to bind differences and create a set of experiences and cultural practices that is more common than at any time in the past.
The European experience reveals another problem with the current debate on diversity - our tendency to equate diversity simply with the presence of peoples from the third world. That just reflects our current obsessions with race and culture. In the past, diversity was often seen in economic or social terms. The indigenous working class and rural poor were as alien to the nineteenth century political elite as third world immigrants often seem today. How come, the Christian socialist Phillipe Buchez asked in 1857, that the French countryside was full of 'races so miserable, inferior and bastardised that they may be classed below the most inferior savage races'? An article in Saturday Review, an English liberal magazine, described the poor of East London as 'a race of whom we know nothing, whose lives are of quite different complexion from ours, persons with whom we have no point of contact'. What we now see as homogenous societies were felt then as deeply diverse.
There is nothing new in plural societies. What is different today is the perception of greater diversity and the sense that such diversity is a problem because social differences cannot or should not be overcome. Or to put it another way, the real problem is not diversity or immigration but the political context in which we think about such issues - in particular, the loss of belief in the possibility of universal values and of a common culture. This inevitably leads to civic disengagement and a sense of anomie - and is why greater diversity leads to greater distrust of everyone, whatever their ethnic or cultural background.
Both sides in the diversity debate pigeonhole people into distinct ethnic and cultural compartments and assume little possibility of creating commonalities. Multiculturalists argue that the presence in a society of diversity of peoples precludes the possibility of common values. Nativists suggest that such values are possible only within an ethnically homogenous society. Both, in other words, confuse the diversity of peoples and the diversity of values. And both are wrong. There is no reason why different peoples should not accept common values - so long as we stop subscribing to the absurd notion that cultural distinctions cannot, or should not, be overcome. The real problem is not immigration or diversity as lived experience. It is the political process that transforms diversity into division and disengagement.