Dear little Six Billionth Living Person: As one of the newest members of a notoriously inquisitive species, it probably won't be too long before you start asking the two $64,000 questions with which the other 5,999,999,999 of us have been wrestling for some time:

How did we get here? And, now that we are here, how shall we live?

Oddly - as if six billion of us weren't enough to be going on with - it will almost certainly be suggested to you that the answer to the question of origins requires you to believe in the existence of a further, invisible, ineffable Being "somewhere up there", an omnipotent creator whom we poor limited creatures are unable even to perceive, much less to understand. That is, you will be strongly encouraged to imagine a heaven, with at least one god in residence.

This sky god, it's said, made the universe by churning its matter in a giant pot. Or, he danced. Or, he vomited Creation out of himself. Or, he simply called it into being, and lo, it Was. In some of the more interesting creation stories, the single mighty sky god is subdivided into many lesser forces - junior deities, avatars, gigantic metamorphic "ancestors" whose adventures create the landscape, or the whimsical, wanton, meddling, cruel pantheons of the great polytheisms, whose wild doings will convince you that the real engine of creation was lust: for infinite power, for too easily broken human bodies, for clouds of glory. But it's only fair to add that there are also stories which offer the message that the primary creative impulse was, and is, love.

Many of these stories will strike you as extremely beautiful, and therefore seductive. Unfortunately, however, you will not be required to make a purely literary response to them. Only the stories of dead religions can be appreciated for their beauty. Living religions require much more of you. So you will be told that belief in "your" stories, and adherence to the rituals of worship that have grown up around them, must become a vital part of your life in the crowded world. They will be called the heart of your culture, even of your individual identity.

It is possible that they may at some point come to feel inescapable, not in the way that the truth is inescapable, but in the way that a jail is. They may at some point cease to feel like the texts in which human beings have tried to solve a great mystery, and feel, instead, like the pretexts for other properly anointed human beings to order you around. And it's true that human history is full of the public oppression wrought by the charioteers of the gods. In the opinion of religious people, however, the private comfort that religion brings more than compensates for the evil done in its name.

As human knowledge has grown, it has also become plain that every religious story ever told about how we got here is quite simply wrong. This, finally, is what all religions have in common. They didn't get it right. There was no celestial churning, no maker's dance, no vomiting of galaxies, no snake or kangaroo ancestors, no Valhalla, no Olympus, no six-day conjuring trick followed by a day of rest. Wrong, wrong, wrong.

But here's something genuinely odd. The wrongness of the sacred tales hasn't lessened the zeal of the devout in the least. If anything, the sheer out-of-step zaniness of religion leads the religious to insist ever more stridently on the importance of blind faith.

As a result of this faith, by the way, it has proved impossible, in many parts of the world, to prevent the human race's numbers from swelling alarmingly. Blame the overcrowded planet at least partly on the misguidedness of the race's spiritual guides. In your own lifetime, you may well witness the arrival of the nine billionth world citizen.

(If too many people are being born as a result, in part, of religious strictures against birth control, then too many people are also dying because religious culture, by refusing to face the facts of human sexuality, also refuses to fight against the spread of sexually transmitted diseases.)

There are those who say that the great wars of the new century will once again be wars of religion, jihads and crusades, as they were in the middle ages. I don't believe them, or not in the way they mean it. Take a took at the Muslim world, or rather the Islamist world, to use the word coined to describe Islam's present-day "political arm". The divisions between its great powers (Afghanistan vs lran vs Iraq vs Saudi Arabia vs Syria vs Egypt) are what strike you most forcefully. There's very little resembling a common purpose. Even after the non-Islamic Nato fought a war for the Muslim Kosovan Albanians, the Muslim world was slow in coming forward with much-needed humanitarian aid.

The real wars of religion are the wars religions unleash against ordinary citizens within their "sphere of influence". They are wars of the godly against the largely defenceless - American fundamentalists against pro-choice doctors, Iranian mullahs against their country's Jewish minority, Hindu fundamentalists in Bombay against that city's increasingly fearful Muslims.

The victors in that war must not be the closed-minded, marching into battle with, as ever, God on their side. To choose unbelief is to choose mind over dogma, to trust in our humanity instead of all these dangerous divinities. So, how did we get here? Don't look for the answer in storybooks. Imperfect human knowledge may be a bumpy, pot-holed street, but it's the only road to wisdom worth taking. Virgil, who believed that the apiarist Aristaeus could spon taneously generate new bees from the rotting carcass of a cow, was closer to a truth about origins than all the revered old books.

The ancient wisdoms are modern nonsenses. Live in your own time, use what we know, and as you grow up, perhaps the human race will finally grow up with you, and put aside childish things.

As the song says, "It's easy if you try."

As for mortality, the second great question - how to live? What is right action, and what wrong? - it comes down to your willingness to think for yourself. Only you can decide if you want to be handed down the law by priests, and accept that good and evil are somehow external to ourselves. To my mind religion, even at its most sophisticated, essentially infantilises our ethical selves by setting infallible moral Arbiters and irredeemably immoral Tempters above us: the eternal parents, good and bad, light and dark, of the supernatural realm.

How, then, are we to make ethical choices without a divine rulebook or judge? Is unbelief just the first step on the long slide into the brain death of cultural relativism, according to which many unbearable things - female circumcision, to name just one - can be excused on culturally specific grounds, and the universality of human rights, too, can be ignored? (This last piece of moral unmaking finds supporters in some of the world's most authoritarian regimes, and also, unnervingly, on the editorial page of the Daily Telegraph.)

Well, no, it isn't, but the reasons for saying so aren't clear-cut. Only hard-line ideology is clear-cut. Freedom, which is the word I use for the secular-ethical position, is inevitably fuzzier. Yes, freedom is that space in which contradiction can reign, it is a never-ending debate. It is not in itself the answer to the question of morals, but the conversation about that question. And it is much more than mere relativism, because it is not merely a never-ending talk show, but a place in which choices are made, values defined and defended. Intellectual freedom, in European history, has mostly meant freedom from the restraints of the Church, not the state.

This is the battle Voltaire was fighting, and it's also what all six billion of us could do for ourselves, the revolution in which each of us could play our small, six-billionth part: once and for all we could refuse to allow priests, and the fictions on whose behalf they claim to speak, to be the policemen of our liberties and behaviour. Once and for all we could put the stories back into the books, put the books back on the shelves, and see the world undogmatised and plain.

Imagine there's no heaven, my dear Six Billionth, and at once the sky's the limit.

 Extract from Letters to the Six Billionth World Citizen, published in English by Uitgeverij Podium, Amsterdam. Copies available at Dutch internet bookshops including www.nl.bol.com and www.boeknet.nl