You contain a trillion copies of a large, textual document written in a highly accurate, digital code, each copy as voluminous as a substantial book. I'm talking, of course, of the DNA in your cells.

Nature is not cruel, only pitilessly indifferent. This is one of the hardest lessons for humans to learn. We cannot admit that things might be neither good nor evil, neither cruel nor kind, but simply callous - indifferent to all suffering, lacking all purpose.

The likelihood is that, in 100,000 years time, we shall either have reverted to wild barbarism, or else civilisation will have advanced beyond all recognition - into colonies in outer space, for instance. In either case, evolutionary extrapolations from present conditions are likely to be highly misleading.

If you want to do evil, science provides the most powerful weapons to do evil; but equally, if you want to do good, science puts into your hands the most powerful tools to do so. The trick is to want the right things, then science will provide you with the most effective methods of achieving them.

The world becomes full of organisms that have what it takes to become ancestors. That, in a sentence, is Darwinism.

Mutation may be random, but selection definitely is not.

There is one particular property of living things, however, that I want to single out as explicable only by Darwinian selection. This property is the one that has been the recurring topic of this book: adaptive complexity.

McDonald: Now a lot of people find great comfort from religion. Not everybody is as you are - well-favored, handsome, wealthy, with a good job, happy family life. I mean, your life is good - not everybody's life is good, and religion brings them comfort.Dawkins: There are all sorts of things that would be comforting. I expect an injection of morphine would be comforting - it might be more comforting, for all I know. But to say that something is comforting is not to say that it's true.

Like computer viruses, successful mind viruses will tend to be hard for their victims to detect. If you are the victim of one, the chances are that you won't know it, and may even vigorously deny it. Accepting that a virus might be difficult to detect in your own mind, what tell-tale signs might you look out for? I shall answer by imaging how a medical textbook might describe the typical symptoms of a sufferer (arbitrarily assumed to be male).

You don't have to be a scientist - you don't have to play the Bunsen burner - in order to understand enough science to overtake your imagined need and fill that fancied gap. Science needs to be released from the lab into the culture.

We humans are an extremely important manifestation of the replication bomb, because it is through us - through our brains, our symbolic culture and our technology - that the explosion may proceed to the next stage and reverberate through deep space.

Scientific and technological progress themselves are value-neutral. They are just very good at doing what they do. If you want to do selfish, greedy, intolerant and violent things, scientific technology will provide you with by far the most efficient way of doing so. But if you want to do good, to solve the world's problems, to progress in the best value-laden sense, once again, there is no better means to those ends than the scientific way.

But perhaps the rest of us could have separate classes in science appreciation, the wonder of science, scientific ways of thinking, and the history of scientific ideas, rather than laboratory experience.

Each generation is a filter, a sieve; good genes tend to fall through the sieve into the next generation; bad genes tend to end up in bodies that die young or without reproducing.

The attitude that living things are placed here for our benefit still dominates our culture, even where its underpinnings have disappeared. We now need, for purposes of scientific understanding, to find a less human-centered view of the natural world.

If we want to postulate a deity capable of engineering all the organized complexity in the world, either instantaneously or by guiding evolution, that deity must have been vastly complex in the first place. The creationist, whether a naive Bible-thumper or an educated bishop, simply postulates an already existing being of prodigious intelligence and complexity. If we are going to allow ourselves the luxury of postulating organized complexity without offering an explanation, we might as well make a job of it and simply postulate the existence of life as we know it!

It is a very helpful insight to say we are vehicles for our DNA, we are hosts for DNA parasites which are our genes. Those are insights which help us to understand an aspect of life. But it's emotive to say, that's all there is to it, we might as well give up going to Shakespeare plays and give up listening to music and things, because that's got nothing to do with it. That's an entirely different subject.

The patient typically finds himself impelled by some deep, inner conviction that something is true, or right, or virtuous: a conviction that doesn't seem to owe anything to evidence or reason, but which, nevertheless, he feels as totally compelling and convincing. We doctors refer to such a belief as "faith".

Natural selection is like artificial selection, but without the human chooser. Instead of a human deciding which offspring shall die in which shall reproduce, nature 'decides'. The quotation marks are vital because nature doesn't consciously decide. This might seem too obvious to emphasize, but you'd be surprised by the number of people who think natural selection implies some kind of personal choice. They couldn't be more wrong. It just is the case that some offspring are more likely to die while others have what it takes to survive and reproduce. Therefore, as the generations go by, the average, typical creature in the population becomes ever better at the arts of surviving and reproducing. Ever better, I should specify, when, when measured against some absolute standard.

Most of what we strive for in our modern life uses the apparatus of goal seeking that was originally set up to seek goals in the state of nature.

I have just discovered that without her father's consent this sweet, trusting, gullible six-year-old is being sent, for weekly instruction, to a Roman Catholic nun. What chance has she?

It really comes down to parsimony, economy of explanation. It is possible that your car engine is driven by psychokinetic energy, but if it looks like a petrol engine, smells like a petrol engine and performs exactly as well as a petrol engine, the sensible working hypothesis is that it is a petrol engine.

The river of my title is a river of DNA, and it flows through time, not space. It is a river of information, not a river of bones and tissues.

There is no general reason to expect evolution to be progressive - even in the weak, value-neutral sense. There will be times when increased size of some organ is favoured and other times when decreased size is favoured. Most of the time, average-sized individuals will be favoured in the population and both extremes will be penalised. During these times the population exhibits evolutionary stasis (i.e., no change) with respect to the factor being measured. If we had a complete fossil record and looked for trends in some particular dimension, such as leg length, we would expect to see periods of no change alternating with fitful continuations or reversals in direction - like a weathervane in changeable, gusty weather.

I don't want to sound callous. I mean, even if I have nothing to offer, that doesn't matter, because that still doesn't mean that what anybody else has to offer therefore has to be true.

If you have a faith, it is statistically overwhelmingly likely that it is the same faith as your parents and grandparents had. No doubt soaring cathedrals, stirring music, moving stories and parables, help a bit. But by far the most important variable determining your religion is the accident of birth. The convictions that you so passionately believe would have been a completely different, and largely contradictory, set of convictions, if only you had happened to be born in a different place. Epidemiology, not evidence.

Orb webs in real life do their business largely in two dimensions. If the mesh is too coarse, flies pass straight through. If the mesh is too fine, rival spiders will achieve nearly the same result at less cost in silk, and will therefore leave behind more progeny to carry on their economically more prudent genes. Natural selection finds the efficient compromise.

I think it is not helpful to apply Darwinian language too widely. Conquest of nation by nation is too distant for Darwinian explanations to be helpful. Darwinism is the differential survival of self-replicating genes in a gene pool, usually as manifested by individual behaviour, morphology, and phenotypes. Group selection of any kind is not Darwinism as Darwin understood it nor as I understand it. There is a very vague analogy between group selection and conquest of a nation by another nation, but I don't think it's a very helpful analogy. So I would prefer not to invoke Darwinian language for that kind of historical interpretation.

Even sticking to the higher plane of love, is it so very obvious that you can't love more than one person? We seem to manage it with parental love (parents are reproached if they don't at least pretend to love all their children equally), love of books, of food, of wine (love of Chateau Margaux does not preclude love of a fine Hock, and we don't feel unfaithful to the red when we dally with the white), love of composers, poets, holiday beaches, friends . . . why is erotic love the one exception that everybody instantly acknowledges without even thinking about it?

I am not advocating a morality based on evolution. I am saying how things have evolved. I am not saying how we humans morally ought to behave.

It is fashionable to wax apocalyptic about the threat to humanity posed by the AIDS virus, "mad cow" disease, and many others, but I think a case can be made that faith is one of the world's great evils, comparable to the smallpox virus but harder to eradicate.

I am often accused of expressing contempt and despising religious people. I don't despise religious people, I despise what they stand for. I like to quote the British journalist Johann Hari who said, "I have so much respect for you, that I cannot respect your ridiculous ideas."

Darwin made it possible to be an intellectually fulfilled atheist.

But if you can breed cattle for milk yield, horses for running speed, and dogs for herding skill, why on Earth should it be impossible to breed humans for mathematical, musical or athletic ability? Objections such as "these are not one-dimensional abilities" apply equally to cows, horses and dogs and never stopped anybody in practice. I wonder whether, some 60 years after Hitler's death, we might at least venture to ask what the moral difference is between breeding for musical ability and forcing a child to take music lessons. Or why it is acceptable to train fast runners and high jumpers but not to breed them. I can think of some answers, and they are good ones, which would probably end up persuading me. But hasn't the time come when we should stop being frightened even to put the question? From the Afterword, The Herald

The selfish gene theory is Darwin's theory, expressed in a way that Darwin did not choose but whose aptness, I should like to think, he would instantly have recognized and delighted in. It is in fact a logical outgrowth of orthodox neo-Darwinism, but expressed as a novel image. Rather than focus on the individual organism, it takes a gene's eye view of nature. It is a different way of seeing, not a different theory.

Faith is the great cop-out, the great excuse to evade the need to think and evaluate evidence. Faith is belief in spite of, even perhaps because of, the lack of evidence.

We don't need fossils - the case for evolution is watertight without them; so it is paradoxical to use gaps in the fossil record as though they were evidence against evolution.

Survival machines that can simulate the future are one jump ahead of survival machines that who can only learn of the basis of trial and error. The trouble with overt trial is that it takes time and energy. The trouble with overt error is that it is often fatal. ...The evolution of the capacity to simulate seems to have culminated in subjective consciousness. Why this should have happened is, to me, the most profound mystery facing modern biology.

The fact that life evolved out of nearly nothing, some 10 billion years after the universe evolved out of literally nothing, is a fact so staggering that I would be mad to attempt words to do it justice.

Evidence is the only good reason to believe anything.

There has been progress in design, but not progress in accomplishment.

I'm not one of those who wants to stop Christian traditions. This is historically a Christian country. I'm a cultural Christian the same way as many of my friends call themselves cultural Jews or cultural Muslims. So, yes, I love singing carols along with everybody else. I'm not one of those who wants to purge our society of our Christian history.

Let us try to teach generosity and altruism, because we are born selfish. Let us understand what our own selfish genes are up to, because we may then at least have a chance to upset their designs, something that no other species has ever aspired to do.

More generally it is completely unrealistic to claim, as Gould and many others do, that religion keeps itself away from science's turf, restricting itself to morals and values. A universe with a supernatural presence would be a fundamentally and qualitatively different kind of universe from one without. The difference is, inescapably, a scientific difference. Religions make existence claims, and this means scientific claims.

I don't believe you until you tell me, do you really believe, for example, if they say they are Catholic, "Do you really believe that when a priest blesses a wafer, it turns into the body of Christ? Are you seriously telling me you believe that? Are you seriously saying that wine turns into blood?" Mock them. Ridicule them. In public. Don't fall for the convention that we're all too polite to talk about religion. Religion is not off the table. Religion is not off limits. Religion makes specific claims about the universe which need to be substantiated and need to be challenged and, if necessary, need to be ridiculed with contempt.

However many ways there may be of being alive, it is certain that there are vastly more ways of being dead.

Even the constantly reiterated insistence that we are miserable offenders, born in sin, is a kind of inverted arrogance: such vanity, to presume that our moral conduct has some sort of cosmic significance, as though the Creator of the Universe wouldn't have better things to do than tot up our black marks and our brownie points. The universe is all concerned with me. Is that not the arrogance that passeth all understanding? The Intellectual and Moral Courage of Atheism

We are survival machines-robot vehicles blindly programmed to preserve the selfish molecules known as genes. This is a truth which still fills me with astonishment.

It is often said, mainly by the 'no-contests', that although there is no positive evidence for the existence of God, nor is there evidence against his existence. So it is best to keep an open mind and be agnostic. At first sight that seems an unassailable position, at least in the weak sense of Pascal's wager. But on second thoughts it seems a cop-out, because the same could be said of Father Christmas and tooth fairies. There may be fairies at the bottom of the garden. There is no evidence for it, but you can't prove that there aren't any, so shouldn't we be agnostic with respect to fairies?

Unfortunately, instead of working out that they have probably misunderstood evolution, creationists conclude, instead, that evolution must be false.