For decades, my students have been split approximately 50-50 between Americans and those from abroad. As a behavioral scientist specializing in happiness, I pick up on the dispositional differences between the two groups. Early in my career, many of the international students seemed to me to have a certain weariness about them that the Americans did not. My Spanish wife saw it, too: Young Americans were relaxed, happy, and innocent by comparison.

That has reversed in the past decade. Now, I see a greater edge in the American students—more cynicism, less laughter. Today, it is the Asian and South American students who smile more easily. Even the jaded, cosmopolitan Europeans seem happier than my young compatriots. The only ones who seem to be able to give us a run for our gloom are the Brits and the Canadians.