Michael Shermer speaks with the energy and passion of an evangelist, so it's not too surprising to learn that he used to be one. What is surprising is that he has made a 180-degree turn in his approach to belief. As a college student at Pepperdine University, he knocked on doors to spread the word of the gospel to anyone who would listen. Now he preaches the power of skepticism in the true sense of the word.

Like a war hero who becomes an anti-war activist, this turnaround is both curious and inspiring. His story underscores the complexity of the concept of belief and our need to hold on to some form of validation.

Shermer is the publisher of Skeptic Magazine. He is quick to point out that what many people think of as skepticism is really cynicism. Being skeptical has nothing to do with being a grumpy curmudgeon who discounts any idea that disrupts his world view. It is less a position and more an approach using science and reason.

Skeptics are open to looking into anything and everything, but are reluctant to latch on to theories without sufficient evidence to back them up. Skeptics don't sit around trashing the ideas of others--that would be a waste of thinking time. Instead, they luxuriate in the opportunity to further explore interesting notions.

The motto of the Skeptics Society and Skeptic Magazine is a statement made by the 17th-century Dutch philosopher Baruch Spinoza: "I have made a ceaseless effort not to ridicule, not to bewail, not to scorn human actions, but to understand them."

This is a fabulous approach to life, even though it may require more patience than most of us can muster. If we can't count on any absolute truths and we don't want to get bogged down by the muddy thinking of relativism, we've got to do our best to establish what Shermer calls "provisional" truths. He uses the word "provisional" a lot to refer to those pretty good truths and almost universal ideas we tend to think of as fairly consistent. Is infanticide bad? Yes, almost always. There could be, in some cultures and in some specific circumstances, ethical reasons to justify infanticide, but we recognize that those are few and far between. Provisional ethics allows for continued discussion and exploration in a way that a black and white view never will.

Shermer was in town recently to talk about the third book in his trilogy on the power of belief: The Science of Good and Evil: Why People Cheat, Gossip, Share, Care and Follow the Golden Rule. He offered compelling theories and groundbreaking scientific results regarding the evolution of human ethics. Thanks to magnetic resonance imaging, we can now see what's going on in the brain while we perform certain tasks. It turns out that the pleasure centers of our brain "light up" when we engage in activities that are cooperative- sharing, being generous, helping others. Just as though we were eating our favorite comfort foods, getting a massage, or making love, our brains register this activity as highly pleasurable. There is (some) reason to believe that cooperation has evolved as a highly prized survival skill, and thus we are "rewarded" by feeling good about it.

Engaging in competitive activities--trying to beat a rival, striving to gain control--shows up in an entirely different area of the brain. Of course, this is also a very important survival skill, but it tends to come with its own tangible rewards--more food, more wealth, the mate of your choice, etc.

I'm still waiting for research on highly competitive individuals. Do their brains light up in the pleasure zone when they win? Is there some sort of shift that happens? What about sociopaths? Do their pleasure centers flare when they lie, cheat, steal, or harm someone?

There's just no end to thinking when you view the world with a healthy dose of skepticism. Socrates observed that the only thing he knew for sure is that he knew nothing. Sticklers are all too happy to point out that this, in fact, suggests that he knows that nothing exists, knows that he knows this, knows that he knows that he knows this, ad nauseum. By the same token, if you are skeptical about everything, you must be skeptical of your own skepticism! Just when you think you've got something figured out, it's time to be skeptical again.

This isn't the mainstream approach to thinking. We tend to like having ideas we can hang on to. We choose a couple of stable concepts, tie up a hammock and swing there contentedly.

That's one way to live.

Another way is to hang that hammock on a couple of sturdy ideas, sway there a bit, and then go off and find another place to swing. It's a lot more work, but you cover a lot more territory in the process. Your intellectual journey may be arduous but infinitely rewarding.

Because there are limitations in scientific investigation and plenty of mysteries remaining, the Skeptics keep in mind the words of Albert Einstein: "All our science, measured against reality, is primitive and childlike--and yet it is the most precious thing we have."

Einstein believed in the power of the unknown and reveled in the right to figure things out as best we can. He valued imagination over knowledge, but persisted in searching for evidence that what we dream can be described and reported scientifically.

Skeptics are cautious believers. They hope for magnificence, they dream of infinite truths and they doggedly pursue their right to be wrong. They are forever moving their hammocks and testing untried trees.

And they are downright evangelical about it.