Richer people are more civilized than poor ones. This thought struck me during last night's Steaua Bucharest-Arsenal game. 
Arsenal's black players were loudly booed - a fact only the Mirror saw fit to report. This is not something that happens in England, or even much in north west Europe. But it is common in the poorer parts of Europe, or in poorer parts of richer countries - at Lazio but not Milan, for example.
Which raises the possibility - that economic growth helps reduce racism. Benjamin Friedman shows in this book that the Ku Klux Klan gained strength during recessions and declined during periods of growth. And this paper shows a correlation between individual prosperity and liberalism.
But what's the mechanism?
One possibility is that the rich are more relaxed than the poor, so don't feel threatened by people who look different from them.
I'm not sure. A combination of habit formation and loss aversion mean the rich are just as keen as the poor to protect what they have.
Another possibility is that immigrants compete with the poor for unskilled work and so drive down wages for the poor but not the rich.
I'm not sure this true. And even if it is, it can't explain Steaua fans' racism. Bucharest is not a poor city because an influx of Togolese has driven down wages.
Instead, I suspect one mechanism is that the rich know better than the poor that diversity is a source of wealth. Differences in tastes and abilities are what lie behind the division of labour, comparative advantage and hence prosperity. As the cliche goes, it takes differences of opinion to make a market. Instinctively, therefore, we rich people regard people of different ethnicities as providing opportunities to get rich, not threats to our status. We know better than the poor - and certainly better than those brought up under Communism - that the economy is a positive-sum game.
This mechanism predicts that those who got rich from trading will be more tolerant, on average, than those who got rich in other ways - through inheritance, say. How much evidence is there for this? Here's one datapoint.
What's more, this suggests there might be another growth trap. Poverty causes intolerance. But intolerance also retards growth.