For at least the last twenty years the cultural and political elites of the United States have championed the cause of multiculturalism by claiming that diversity was something that made all of us better. Little effort was ever made to define precisely just what was meant by diversity, difference or most crucially "better." Nor was there any significant research that provided empirical support for the claim that multiculturalism and diversity translated into better people, better communities, better organizations and businesses or a better country. But now a considerable amount of solid evidence about multiculturalism is in, and it suggests that...