London’s mayor, Boris Johnson, drew criticism late last year for saying that economic inequality can be attributed, in part, to IQ. ‘I am afraid that [the] violent economic centrifuge [of competition] is operating on human beings who are already very far from equal in raw ability,” he told an audience at the Centre for Policy Studies.

That’s a satisfying worldview for someone who is successful and considers himself unusually bright. But a quick look at the data shows the limitations of raw smarts and stick-to-itiveness as an explanation for inequality. The income distribution in the United States provides a good example. In 2012 the top 0.01 percent of households earned an average of $10.25 million, while the mean household income for the country overall was $51,000. Are top earners 200 times as smart as the rest of the field? Doubtful. Do they have the capacity to work 200 times more hours in the week? Even more doubtful. Many forces out of their control, including sheer luck, are at play.

But say you’re in that top 0.01 percent-or even the top 50 percent. Would you want to admit happenstance as a benefactor? Wouldn’t you rather believe that you earned your wealth, that you […]