If I said to you, the most useful thing that North Americans could do right now is learn to restrain themselves a little, how might you react?

If you were a good conservative you might think, yes! This is just what I’ve been talking about - an end to wild leftover ‘60s behavior. No more promiscuity! Stop piercing things! But if you thought about it a little more, you might grow wary: what if people restrained their desire to buy stuff on credit? Wouldn’t that undermine our sanctified economy?

And if you were a good progressive you might think: about time! Shut down K-Mart! Save the planet! But what if it went a little deeper? If it meant, say, restraining your desire to travel, or to reinvent yourself on the spur of the moment? To take vows more seriously, commit to a particular community?

We’ve spent the last couple of centuries being liberated – from gender roles, from geographic constraint, it goes on. Some of that’s been good, and some of it has eroded community, turned us into more-or-less free agents. We don’t have to put up with an abusive spouse any more; that’s an advance. Half our children deal with divorce while they’re growing up – what about that? Credit has freed us to buy almost anything. The spread of industrial agriculture has liberated us from the need to grow our own food, and made it so inexpensive that we can and do eat to our hearts’ content (and then to our hearts’ discontent). If you wanted a poster child for our unrestrained age, you could do worse than Bill Clinton, who seems to have rarely met a desire (Mickey D’s! Monica! NAFTA!) to which he didn’t yield. And now he’s got a six-inch scar on his chest.

Thus it has always been, you might say. But the momentum has clearly accelerated. By some measures humans have used more physical resources since World War II than in all of history before it. It’s now taking a toll beyond anything we could ever have imagined. What does it mean when one-sixth of the world’s population consumes without any real restraint? It means that so far we’ve raised the temperature of the planet one degree Fahrenheit. The computer modeling is very clear: if we continue on this path, and if we are joined on it by some significant fraction of the world’s population, then we will raise the planet’s temperature something like a further five degrees before the century ends. That a further fi ve degrees before the century ends. That is to say, Earth will be warmer than it’s been since is to say, Earth will be warmer than it’s been since well before the dawn of primate evolution.

We’ve also begun to intuit the damage to humans, and to human society, from that kind of endless binge. We’re experimenting right now with what it means to live as a hyperindividual, living for yourself, never saying no. Judging from the mountain of Paxil scrips, the experiment is not going entirely successfully. Plastic surgery is way up (and genetic enhancement looms on the not-too-distant horizon). But satisfaction?

Which makes sense, I think. Because we’ve so completely denied one part of our nature, the part that embraces restraint. In the last couple of centuries we’ve decided our true human nature is the beavering, ambitious, grasping, curious, pedal-to-the-floor part. It’s certainly there; all of us can feel it. But humans were also built for restraint. In a way it may be the greater of our gifts, the one thing that makes us different, as flight makes birds different. We’re the animal that can decide not to do something we’re capable of. Decide, as individuals, that we don’t need a big car, or a car at all. Decide that something else – our family, our tribe, our community, the rest of creation, the divine – matters as much as we do, and thus sets limits on our behavior. Taboos, we call them, and taboo has become a dirty word. Our wants and needs have become coterminous. But taboos were what kept us from fishing out all the salmon in the river. Taboos, if we can develop them, are what will keep us from firing off nuclear weapons or building designer babies.

In individuals, learning restraint is the process of maturing. After a couple of generations of embracing everything young and dynamic and innovative, maturity starts to look more attractive: we could use some elders right about now. In societies, maturation will be even more difficult. But it’s clearly time to find out: we’ve grown very, very large, larger than we should be. The chest pains are beginning. A certain kind of party may be over. But a better and deeper (if quieter) party beckons.

Bill McKibben is a scholar-in-residence at Middlebury College, Vermont.