From Mardi Gras to rock and roll, Barbara Ehrenreich celebrates collective joy in Dancing in the Streets.

Your book Blood Rites was about the human impulse to wage war. Your new book deals with collective joy. Is there any connection?

Oh, yes. In Blood RitesI became intrigued with the question of collective excitement. There's a public excitement that goes together with war. Before World War I, there was true delirium. People really were dancing in the streets! As for collective joy, it's a human capacity we don't make much use of. I would tell people that I was writing about ecstatic ritual, and they would give me a blank look and say, "What's that?" And that's a shame.

Why haven't more people written about it?

There has been a general Western scholarly disdain of revelry. It's perceived as something that white, European, civilized people don't do. Whenever European colonizers encountered ecstatic ritual in other parts of the world, the reaction was always, "Oh, my God! Look at these heathens!" But fortunately it survives. A few weeks ago I was in San Francisco, and there was a Love Fest, I think it was inspired by the Love Parade in Berlin, with floats and naked people. I really wanted to join in, it was great. But I'm a grandmother now.

What about ecstatic ritual makes it the object of such disdain?

The very old civilizations are hierarchical, and hierarchy tends to be hostile to collective joy because it's an egalitarian impulse. You see that in the significance of masking—you take away normal marks of status and you create new ones. In carnival, people would dress up as the white slaveowners, mock the white power structure. And the elites would not join in the celebrations. They would go off and hide, have their own private celebrations, masked balls. Eventually, it goes even further, and they start banning public celebrations.

What's the link between collective joy and politics?

When people lower down in the social hierarchy celebrate their bonds to each other, celebrate their solidarity, that's very threatening to the powers that be. But my stance in the book is that ecstatic ritual is a social good in and of itself—it doesn't have to be justified by social goals. It's not a bad idea to start discovering forms of happiness and satisfaction that are not derived from the accumulation of material objects and start deriving it from within ourselves. It's easier on the environment, for one thing.