I don't think I commit sins with higher-than-average frequency, but after accumulating them for five decades, I could sure use a born-again experience. Just a quick cleansing and a fresh start.

Actually, make that four decades. In the mid 1960s, when I was 8 or 9, I did get born again. At a southern Baptist church in Texas, I felt the tug of God and responded to the altar call, and several weeks later got baptized. But within a few years I was losing my Christian faith, and it finally disappeared. So that's about 40 years of sin accretion since the last bath.

Which raises the question: If I no longer believe in a personal God, looking down and judging me, why do I still feel guilt over my wrongdoings and shortcomings? Why do I still want some father figure (a God, ideally, though a resurrected version of my dad would do) to pat me on the shoulder and tell me I've done O.K. and can now go play golf for a millennium or so? Is godlessness not, in fact, as some born-again atheists seem to promise, a path to happiness? And, anyway, where did this need for forgiveness and affirmation come from?

I spent much of the last decade researching ancient, and even prehistoric, religion for my book The Evolution of God, and I now have some clues as to how I got into this predicament.

In the beginning, back in prehistoric hunter-gatherer days, religion wasn't concerned with moral infractions -- at least, not if the many hunter-gatherer societies observed by anthropologists over the past 150 years are any indication. Hunter-gatherer gods don't generally focus their firepower on things like lying, cheating, coveting, or lusting.

There are violations of the divine code, to be sure. The Semang hunter-gatherers of Southeast Asia thought that the god Karei would punish them if they combed their hair during a thunderstorm. But that's not a moral infraction. Besides, it's no great challenge to confine coiffing to fair weather.

Now fast-forward through the invention of agriculture and writing, to ancient Egypt. The Book of the Dead tells us what kinds of things an Egyptian said to the gods to secure a happy afterlife in the second millennium B.C.E.:

I have not encroached on the land of others. I have not added weights to the scales to cheat buyers. I have not misread the scales to cheat buyers. I have not stolen milk from the mouths of children. I am pure. I am pure. I am pure. I am pure.

I think she doth protest too much, but you get the picture: By the time of urban civilization -- social organization on a scale that's hard to maintain if people don't behave themselves -- religion has started upholding the precarious social order by stressing truly moral strictures. And that's a problem, from the standpoint of individual happiness, because it's hard to fulfill your desires and lead a morally impeccable life, too. (The Book of the Dead says, "I have not caused pain... I have made no one weep." Speak for yourself!)

Of course, you don't need religion to feel guilty about harming people. Natural selection built the conscience, hence guilt, into our brains. But it may be religion that transformed pangs of guilt into a chronic sense of sin.

This, in fact, was the view of one influential sin theorist, the Apostle Paul. Paul articulated, and may have invented, the Christian doctrine of salvation, which accords cleansing power to belief in Christ. And Paul -- who seems to have had a more-active-than-average conscience -- attributed his own sense of sin to his upbringing in the Torah, the Jewish Law. "If it had not been for the law, I would not have known sin. I would not have known what it is to covet if the law had not said, ‘You shall not covet.' "

The burden of sin is even heavier when divine punishment can come not just in the afterlife, but in real time; now every misfortune is cause to wonder what you've done wrong. In India at about the time those passages in the Book of the Dead took shape, a hymn to the sky god Varuna, upholder of the moral order, asked, "O Varuna, what was the terrible crime for which you wish to destroy your friend who praises you? Proclaim it to me so that I may hasten to prostrate myself before you and be free from sin."

So it's no wonder that by the time of Paul, humanity was ripe for born-again experience. And certainly Christianity wasn't the only religion in the Roman Empire that offered dramatic rituals of salvation. But Paul's version of salvation proved the easiest to, as they say, scale. Hence my salvation in the Immanuel Baptist Church in El Paso, Texas.

But why, now that El Paso and Christianity are both in the rear view mirror, do I still feel that I could use a born-again experience? Why, if I don't believe in heaven, do I still want something you could call salvation?

Maybe it's a tribute to childhood impressionability. And maybe it's because, actually, trudging around under the burden of sin, in pursuit of ever-receding salvation, isn't such a bad life.

The sense I got back in El Paso was that salvation wasn't just about taking the bath and believing in Christ. Sure, that was the technical pre-requisite for getting to heaven. But a thoroughgoing sense of salvation -- a sense of being a truly good Christian -- depended on, for example, pursuing a "calling," finding the career path that allows you to do the most good for the world.

Obviously, thinking you're doing God's work -- or even that you're trying to -- carries the danger of self-dramatization and self-delusion. But it beats ennui! And it takes at a little of the sting out of, say, a tanking global economy, since having more stuff isn't the point anyway.

Besides, it's the sense of sin, the sense of human frailty, the deep Calvinist suspicion of yourself, that can keep the self-dramatization in check. Salvation, at the most abstract level, is the sense that you're on the right side of the moral law, and the sense of sin is what keeps you not-quite-sure that you are. It also keeps you longing for that final affirmation -- the true born-again experience, the one that will end the uncertainty. But don't hold your breath.

If salvation is indeed about feeling that you're on the right side of the law, then you don't need God -- or even, as in my case, the looming memory of God -- to seek it. You can be an atheist and feel that there's such a thing as right and wrong, and that you'll try to align your life with this moral axis. In fact, I think you can make a sheerly intellectual, non-faith-based case that there is some such transcendent source of meaning, and even something you could call a moral order "out there." I even think it's fair to suspect that there's a purpose unfolding on this planet, leaving aside the much tougher question of what's behind the purpose.

But, for my money, there's nothing quite like the idea that what's behind that purpose is something that can approve or disapprove of you. It keeps you on your toes, and it keeps your life mattering, even when it's only a feeling, and no longer a belief.