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.

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.

[W]hen the ricochets of atomic billiards chance to put together an object that has a certain, seemingly innocent property, something momentous happens in the universe. That property is an ability to self-replicate; that is, the object is able to use the surrounding materials to make exact copies of itself, including replicas of such minor flaws in copying as may occasionally arise. What will follow from this singular occurrence, anywhere in the universe, is Darwinian selection and hence the baroque extravaganza that, on this planet, we call life. Never were so many facts explained by so few assumptions. Not only does the Darwinian theory command superabundant power to explain. Its economy in doing so has a sinewy elegance, a poetic beauty that outclasses even the most haunting of the world's origin myths. Preface

In one way or another, all my books have been devoted to expounding and exploring the almost limitless power of the Darwinian principle-power unleashed whenever and wherever there is enough time for the consequences of primordial self-replication to unfold. Preface

The total amount of suffering per year in the natural world is beyond all decent contemplation. During the minute it takes me to compose this sentence, thousands of animals are being eaten alive; others are running for their lives, whimpering with fear; others are being slowly devoured from within by rasping parasites; thousands of all kinds are dying of starvation, thirst and disease. [...] In a universe of blind physical forces and genetic replication, some people are going to get hurt, other people are going to get lucky, and you won't find any rhyme or reason in it, nor any justice. The universe we observe has precisely the properties we should expect if there is, at bottom, no design, no purpose, no evil and no good, nothing but blind, pitiless indifference. DNA neither knows nor cares. DNA just is. And we dance to its music.

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

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 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 spirit-driven life force, no throbbing, heaving, pullulating, protoplasmic, mystic jelly. Life is just bytes and bytes and bytes of digital information.

Scientific beliefs are supported by evidence, and they get results. Myths and faiths are not and do not.

Never say, and never take seriously anyone who says, "I cannot believe that so-and-so could have evolved by gradual selection". I have dubbed this kind of fallacy "the Argument from Personal Incredulity". Time and again, it has proven the prelude to an intellectual banana-skin experience.

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 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".

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).

Ten years ago, you could have traveled thousands of miles through the United States and never seen a baseball cap turned back to front. Today, the reverse baseball cap is ubiquitous. I do not know what the pattern of geographical spread of the reverse baseball cap precisely was, but epidemiology is certainly among the professions primarily qualified to study it.

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!

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.

Another force driving progressive evolution is the so-called "arms-race." Prey animals evolve faster running speeds because predators do. Consequently predators have to evolve even faster running speeds, and so on, in an escalating spiral. Such arms races probably account for the spectacularly advanced engineering of eyes, ears, brains, bat "radar" and all the other high-tech weaponry that animals display.

It may be that brain hardware has co-evolved with the internal virtual worlds that it creates. This can be called hardware-software co-evolution.

It is an article of passionate faith among "politically correct" biologists and anthropologists that brain size has no connection with intelligence; that intelligence has nothing to do with genes; and that genes are probably nasty fascist things anyway.

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.

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.

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?

With so many mind-bytes to be downloaded, so many mental codons to be replicated, it is no wonder that child brains are gullible, open to almost any suggestion, vulnerable to subversion, easy prey to Moonies, Scientologists and nuns. Like immune-deficient patients, children are wide open to mental infections that adults might brush off without effort.

Think about the two qualities that a virus, or any sort of parasitic replicator, demands of a friendly medium, the two qualities that make cellular machinery so friendly towards parasitic DNA, and that make computers so friendly towards computer viruses. These qualities are, firstly, a readiness to replicate information accurately, perhaps with some mistakes that are subsequently reproduced accurately; and, secondly, a readiness to obey instructions encoded in the information so replicated.

The second requirement of a virus-friendly environment - that it should obey a program of coded instructions - is again only quantitatively less true for brains than for cells or computers. We sometimes obey orders from one another, but also we sometimes don't. Nevertheless, it is a telling fact that, the world over, the vast majority of children follow the religion of their parents rather than any of the other available religions. Instructions to genuflect, to bow towards Mecca, to nod one's head rhythmically towards the wall, to shake like a maniac, to "speak in tongues" - the list of such arbitrary and pointless motor patterns offered by religion alone is extensive - are obeyed, if not slavishly, at least with some reasonably high statistical probability.

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.

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.

It's been suggested that if the super-naturalists really had the powers they claim, they'd win the lottery every week. I prefer to point out that they could also win a Nobel Prize for discovering fundamental physical forces hitherto unknown to science. Either way, why are they wasting their talents doing party turns on television?By all means let's be open-minded, but not so open-minded that our brains drop out.

How do we account for the current paranormal vogue in the popular media? Perhaps it has something to do with the millennium - in which case it's depressing to realise that the millennium is still three years away.

The popularity of the paranormal, oddly enough, might even be grounds for encouragement. I think that the appetite for mystery, the enthusiasm for that which we do not understand, is healthy and to be fostered. It is the same appetite which drives the best of true science, and it is an appetite which true science is best qualified to satisfy.

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.

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.

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.

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.

In fact writing a computer program is a pretty good way to summarize knowledge about any set of rules.

Natural selection is an extremely simple process, in the sense that very little machinery needs to be set up in order for it to work. Of course the effects and consequences of natural selection are complex in the extreme. But in order to set natural selection going on a real planet, all that is required is the existence of inherited information.

To this day, and in quarters where they should know better, Darwinism is widely regarded as a theory of 'chance'.It is grindingly, creakingly, crashingly obvious that, if Darwinism were really a theory of chance, it couldn't work. You don't need to be a mathematician or physicist to calculate that an eye or a haemoglobin molecule would take from here to infinity to self-assemble by sheer higgledy-piggledy luck. Far from being a difficulty peculiar to Darwinism, the astronomic improbability of eyes and knees, enzymes and elbow joints and the other living wonders is precisely the problem that any theory of life must solve, and that Darwinism uniquely does solve.

Mutation may be random, but selection definitely is not.

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.

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.

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.

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 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.

There's nothing nonsensical about saying that what would evolve if Darwinian selection has its head is something that you don't want to happen. And I could easily imagine trying to go against Darwinism.

The world and the universe is an extremely beautiful place, and the more we understand about it the more beautiful does it appear. It is an immensely exciting experience to be born in the world, born in the universe, and look around you and realise that before you die you have the opportunity of understanding an immense amount about that world and about that universe and about life and about why we're here. We have the opportunity of understanding far, far more than any of our predecessors ever. That is such an exciting possibility, it would be such a shame to blow it and end your life not having understood what there is to understand.

Maybe somewhere in some other galaxy there is a super-intelligence so colossal that from our point of view it would be a god. But it cannot have been the sort of God that we need to explain the origin of the universe, because it cannot have been there that early.

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.

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.

It has become almost a cliché to remark that nobody boasts of ignorance of literature, but it is socially acceptable to boast ignorance of science and proudly claim incompetence in mathematics.