I just finished shaking the last of the desert dust out of the bags I brought to this year’s Burning Man, an annual week-long event in Nevada’s Black Rock Desert that takes its name from the burning of a giant effigy at the end of the week. According to popular perception, Burning Man is a non-stop rave thrown by a bunch of drugged-out naked hippies. That’s not entirely false, admittedly, but it’s only a small piece of the picture.

Burning Man is also a large-scale social experiment. The 50,000 people who converge on the desert each year create a temporary but legitimate city – roughly the size of Santa Cruz, CA or Flagstaff, AZ -- with its own street grid, laws, and social mores. In the process, they attempt to do away with several of the most fundamental institutions underlying modern civilization. Clothing, for example, is optional at Burning Man, and many people opt out of it.

Money, on the other hand, is not optional: it’s explicitly banned. People exchange goods and services constantly, but money never changes hands, except in one specially designated central tent which sells coffee and tea. I’ve heard Burning Man sometimes described as a "barter economy," but that’s not quite right. It’s more of a "gift economy," in which people give strangers food, drinks, clothing, massages, bike repairs, rides back to camp, and more, all without any expectation of reciprocation. Many attendees also invest a great deal of their own time and money beforehand to make other people’s experiences at Burning Man more beautiful, interesting, and comfortable, setting up tents or couches for public use or crafting elaborate art installations out in the desert for others to discover.

Serendipitously, behavioral economist Dan Ariely was at this year’s Burning Man and made an appearance at their TEDx conference to talk about why the gift economy works so well. There are two different frameworks people use to negotiate exchanges, he explained, the economic and the social. If we’re in economic mode, we’re willing to give away goods and services only if we get something we value in exchange. In social mode, we give goods and services because it’s socially expected of us. So if I ask you to help me push my car out of a ditch, you may well agree. But if I offer you $10 to help me push my car out of a ditch, you’ll likely think: Are you kidding? My time is worth much more than that. In other words, the mere act of putting a price tag on a good or a service bumps people from the social to the economic mode, and reduces their natural inclinations towards altruism and generosity.

So it seems that Burning Man has managed to create an entire city operating in the social framework rather than the economic one. We give each other goods and services not because we stand to gain, but because we want to be good citizens of Black Rock City. Of course, you could make the case that this isn’t "true" altruism, that our gifts are motivated by a desire to show off or to win social status. There’s surely some truth to that, but for this purpose, it doesn’t matter; people are still being motivated to help each other out and to create enormous value without any financial incentives, and without succumbing to the temptation to free ride on other people’s efforts.

But even if you count the Burning Man experiment a success, the tricky question is what, if anything, we should take away from it. Is there something the outside world should be learning from Black Rock City’s thriving gift economy? Unfortunately, I don’t think our experiment’s results are as extrapolatable as they might seem at first. I think it’s a mistake to interpret the Burning Man experience as a proof of concept that people can be conditioned, through social expectation, to be generous to total strangers. That’s because, although it’s true that the people who gave me food and massages and rides all week were technically strangers, they weren’t just any strangers. They were my fellow tribe members.

And Burning Man is unquestionably a tribe. It’s got its own lingo (everyone in attendance is a "burner," and you’re supposed to greet new people with a hearty "Welcome home!"). It’s got its own customs, from the major (the burning of the Man) to the minor (hugging replaces handshakes). It’s got its own shared value system (open-mindedness, celebration, creativity, sustainability). It’s got its own uniforms – not technically, of course, but there is a very distinct Burning Man aesthetic roughly consisting of some combination of dreadlocks, goggles, body paint, wings, cross-dressing, tattoos, fur, glow sticks, and nudity. And most of all, it’s got its own out-group against which it defines itself: the rest of the world, which from the vantage point of Black Rock City looks awfully dull and uptight.

In other words, Burning Man is an in-group. There’s nothing wrong with that, but when it comes to the age-old, million-dollar question of how to get people to live together in harmony, fostering cooperation within an in-group has never been the hard part. Being in the same tribe, whether that’s an extended family or a particular culture, has always greased the wheels of cooperation. As a species that evolved in tribes, we humans are wired for that. No, the hard part has always been: How do we foster cooperation between different in-groups? And that’s a question about which Burning Man, all its wonderful qualities notwithstanding, is silent.