when trying to think through a chemical problem, he would ask himself what he would do if he were an electron.

Personification of this kind is not just a quaint didactic device. It can also help a professional scientist to get the right answer, in the face of tricky temptations to error.

Our brains have evolved to the point where we are capable of rebelling against our selfish genes. The fact that we can do so is made obvious by our use of contraceptives. The same principle can and should work on a wider scale.

In the opening pages of The Extended Phenotype I explained this using the metaphor of the Necker cube.

I now think that this metaphor was too cautious. Rather than propose a new theory or unearth a new fact, often the most important contribution a scientist can make is to discover a new way of seeing old theories or facts.

Expounding ideas that have hitherto appeared only in the technical literature is a difficult art. It requires insightful new twists of language and revealing metaphors. If you push novelty of language and metaphor far enough, you can end up with a new way of seeing.

The argument of this book is that we, and all other animals, are machines created by our genes. Like successful Chicago gangsters, our genes have survived, in some cases for millions of years, in a highly competitive world. This entitles us to expect certain qualities in our genes. I shall argue that a predominant quality to be expected in a successful gene is ruthless selfishness.

universal love and the welfare of the species as a whole are concepts that simply do not make evolutionary sense.

As a corollary to these remarks about teaching, it is a fallacy—incidentally a very common one—to suppose that genetically inherited traits are by definition fixed and unmodifiable.

One of the surprising consequences of the modern version of the Darwinian theory is that apparently trivial tiny influences on survival probability can have a major impact on evolution. This is because of the enormous time available for such influences to make themselves felt.

Often altruism within a group goes with selfishness between groups. This is a basis of trade unionism.

Darwin’s theory of evolution by natural selection is satisfying because it shows us a way in which simplicity could change into complexity, how unordered atoms could group themselves into ever more complex patterns until they ended up manufacturing people.

Darwin’s ‘survival of the fittest’ is really a special case of a more general law of survival of the stable. The universe is populated by stable things. A stable thing is a collection of atoms that is permanent enough or common enough to deserve a name.

The haemoglobin of our blood is a typical protein molecule. It is built up from chains of smaller molecules, amino acids, each containing a few dozen atoms arranged in a precise pattern. In the haemoglobin molecule there are 574 amino acid molecules. These are arranged in four chains, which twist around each other to form a globular three-dimensional structure of bewildering complexity.

The earliest form of natural selection was simply a selection of stable forms and a rejection of unstable ones.

If they all copied from a single master original, meaning would not be greatly perverted. But let copies be made from other copies, which in their turn were made from other copies, and errors will start to become cumulative and serious.

I suppose the scholars of the Septuagint could at least be said to have started something big when they mistranslated the Hebrew word for ‘young woman’ into the Greek word for ‘virgin’, coming up with the prophecy: ‘Behold a virgin shall conceive and bear a son …’*

Evolution is something that happens, willy-nilly, in spite of all the efforts of the replicators (and nowadays of the genes) to prevent it happening.

To return to the primeval soup, it must have become populated by stable varieties of molecule; stable in that either the individual molecules lasted a long time, or they replicated rapidly, or they replicated accurately. Evolutionary trends toward these three kinds of stability took place in the following sense: if you had sampled the soup at two different times, the later sample would have contained a higher proportion of varieties with high longevity/ fecundity/ copying-fidelity.

mould, we supposed it to be bathed in a soup rich in the small building block molecules necessary to make copies. But when the replicators became numerous, building blocks must have been used up at such a rate that they became a scarce and precious resource.

Ways of increasing stability and of decreasing rivals’ stability became more elaborate and more efficient. Some of them may even have ‘discovered’ how to break up molecules of rival varieties chemically, and to use the building blocks so released for making their own copies. These proto-carnivores simultaneously obtained food and removed competing rivals.

Replicators began not merely to exist, but to construct for themselves containers, vehicles for their continued existence.

They have come a long way, those replicators. Now they go by the name of genes, and we are their survival machines.

We are all survival machines for the same kind of replicator—molecules called DNA—but there are many different ways of making a living in the world, and the replicators have built a vast range of machines to exploit them.

A body is the genes’ way of preserving the genes unaltered.

Sperms and eggs are unique among our cells in that, instead of containing 46 chromosomes, they contain only 23.

Therefore every sperm cell made by an individual is unique, even though all his sperms assembled their 23 chromosomes from bits of the same set of 46 chromosomes. Eggs are made in a similar way in ovaries, and they too are all unique.

Even if there were, there is nothing sacred about definitions. We can define a word how we like for our own purposes, provided we do so clearly and unambiguously.

A gene is defined as any portion of chromosomal material that potentially lasts for enough generations to serve as a unit of natural selection.

a gene is a replicator with high copying-fidelity. Copying-fidelity is another way of saying longevity-in-the-form-of-copies and I shall abbreviate this simply to longevity. The definition will take some justifying.

Now comes the important point. The shorter a genetic unit is, the longer—in generations—it is likely to live. In particular, the less likely it is to be split by any one crossing-over. Suppose a whole chromosome is, on average, likely to undergo one cross-over every time a sperm or egg is made by meiotic division, and this cross-over can happen anywhere along its length. If we consider a very large genetic unit, say half the length of the chromosome, there is a 50 per cent chance that the unit will be split at each meiosis. If the genetic unit we are considering is only 1 per cent of the length of the chromosome, we can assume that it has only a 1 per cent chance of being split in any one meiotic division. This means that the unit can expect to survive for a large number of generations in the individual’s descendants. A single cistron is likely to be much less than 1 per cent of the length of a chromosome. Even a group of several neighbouring cistrons can expect to live many generations before being broken up by crossing-over.

The life-span of a chromosome is one generation.

The smaller a genetic unit is, the more likely it is that another individual shares it—the more likely it is to be represented many times over in the world, in the form of copies.

This includes the mimics, and so genes for mimicry are favoured by natural selection. That is how mimicry evolves.

What I am doing is emphasizing the potential near-immortality of a gene, in the form of copies, as its defining property.

Genes are competing directly with their alleles for survival, since their alleles in the gene pool are rivals for their slot on the chromosomes of future generations. Any gene that behaves in such a way as to increase its own survival chances in the gene pool at the expense of its alleles will, by definition, tautologously, tend to survive. The gene is the basic unit of selfishness.

Expressions like ‘gene for long legs’ or ‘gene for altruistic behaviour’ are convenient figures of speech, but it is important to understand what they mean. There is no gene which single-handedly builds a leg, long or short. Building a leg is a multigene cooperative enterprise.

As an analogy, think of the influence of a fertilizer, say nitrate, on the growth of wheat. Everybody knows that wheat plants grow bigger in the presence of nitrate than in its absence. But nobody would be so foolish as to claim that, on its own, nitrate can make a wheat plant.

But by definition luck, good and bad, strikes at random, and a gene that is consistently on the losing side is not unlucky; it is a bad gene.

It is complicated because the ‘environment’ of a gene consists largely of other genes, each of which is itself being selected for its ability to cooperate with its environment of other genes.

But the long-term consequences of non-random individual death and reproductive success are manifested in the form of changing gene frequencies in the gene pool.

A major branch of survival machines, now called plants, started to use sunlight directly themselves to build up complex molecules from simple ones, re-enacting at much higher speed the synthetic processes of the original soup. Another branch, now known as animals, ‘discovered’ how to exploit the chemical labours of the plants, either by eating them or by eating other animals. Both main branches of survival machines evolved more and more ingenious tricks to increase their efficiency in their various ways of life, and new ways of life were continually being opened up.

But most plant movement is really irreversible growth. Animals, on the other hand, have evolved ways of moving hundreds of thousands of times faster. Moreover, the movements they make are reversible, and repeatable an indefinite number of times.

The workings of the sensory systems are particularly baffling, because they can achieve far more sophisticated feats of pattern-recognition than the best and most expensive man-made machines; if this were not so, all typists would be redundant, superseded by speech-recognizing machines, or machines for reading handwriting. Human typists will be needed for many decades yet.

A notable advance was the evolutionary ‘invention’ of memory. By this device, the timing of muscle contractions could be influenced not only by events in the immediate past, but by events in the distant past as well. The memory, or store, is an essential part of a digital computer too. Computer memories are more reliable than human ones, but they are less capacious, and enormously less sophisticated in their techniques of information-retrieval.

Each one of us knows, from the evidence of our own introspection, that, at least in one modern survival machine, this purposiveness has evolved the property we call ‘consciousness’.

All the programmer can do is to set the computer up beforehand in the best way possible, with a proper balance between lists of specific knowledge and hints about strategies and techniques. The genes too control the behaviour of their survival machines, not directly with their fingers on puppet strings, but indirectly like the computer programmer.

Just as the Andromedans had to have a computer on earth to take day-to-day decisions for them, our genes have to build a brain.

The reason why they cannot manipulate our puppet strings directly is the same: time-lags. Genes work by controlling protein synthesis. This is a powerful way of manipulating the world, but it is slow. It takes months of patiently pulling protein strings to build an embryo. The whole point about behaviour, on the other hand, is that it is fast. It

Like the chess programmer, the genes have to ‘instruct’ their survival machines not in specifics, but in the general strategies and tricks of the living trade.*

Prediction in a complex world is a chancy business. Every decision that a survival machine takes is a gamble, and it is the business of genes to program brains in advance so that on average they take decisions that pay off. The currency used in the casino of evolution is survival, strictly gene survival, but for many purposes individual survival is a reasonable approximation.

Here the program may take the form of the following instructions to the survival machine: ‘Here is a list of things defined as rewarding: sweet taste in the mouth, orgasm, mild temperature, smiling child. And here is a list of nasty things: various sorts of pain, nausea, empty stomach, screaming child. If you should happen to do something that is followed by one of the nasty things, don’t do it again, but on the other hand repeat anything that is followed by one of the nice things.’ The advantage of this sort of programming is that it greatly cuts down the number of detailed rules that have to be built into the original program; and it is also capable of coping with changes in the environment that could not have been predicted in detail.

One of the most interesting methods of predicting the future is simulation.

Well, when you yourself have a difficult decision to make involving unknown quantities in the future, you do go in for a form of simulation. You imagine what would happen if you did each of the alternatives open to you. You set up a model in your head, not of everything in the world, but of the restricted set of entities which you think may be relevant.

Survival machines that can simulate the future are one jump ahead of survival machines who can only learn on the basis of overt 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. Simulation is both safer and faster.

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. There is no reason to suppose that electronic computers are conscious when they simulate, although we have to admit that in the future they may become so. Perhaps consciousness arises when the brain’s simulation of the world becomes so complete that it must include a model of itself.*

Genes are the primary policy-makers; brains are the executives. But as brains became more highly developed, they took over more and more of the actual policy decisions, using tricks like learning and simulation in doing so.

The genes are master programmers, and they are programming for their lives. They are judged according to the success of their programs in coping with all the hazards that life throws at their survival machines, and the judge is the ruthless judge of the court of survival.

The traditional story of ethologists is that communication signals evolve for the mutual benefit of both sender and recipient.

Whenever a system of communication evolves, there is always the danger that some will exploit the system for their own ends.

Natural selection favours genes that control their survival machines in such a way that they make the best use of their environment. This includes making the best use of other survival machines, both of the same and of different species.

Moles and blackbirds may compete for worms, but blackbirds and blackbirds compete with each other for worms and for everything else. If they are members of the same sex, they may also compete for mating partners.

evolutionarily stable strategy, an idea that he traces back to W. D. Hamilton and R. H. MacArthur.

An evolutionarily stable strategy or ESS is defined as a strategy which, if most members of a population adopt it, cannot be bettered by an alternative strategy.*

best strategy for an individual depends on what the majority of the population are doing.

It is possible for humans to enter into pacts or conspiracies that are to every individual’s advantage, even if these are not stable in the ESS sense. But this is only possible because every individual uses his conscious foresight, and is able to see that it is in his own long-term interests to obey the rules of the pact. Even in human pacts there is a constant danger that individuals will stand to gain so much in the short term by breaking the pact that the temptation to do so will be overwhelming.

A retaliator is a conditional strategist. His behaviour depends on the behaviour of his opponent.

In the war of attrition, telling lies is no more evolutionarily stable than telling the truth. The poker face is evolutionarily stable.

Territorial ‘defence’ may simply be an ESS which arises because of the asymmetry in time of arrival that usually characterizes the relationship between two individuals and a patch of ground.

have a hunch that we may come to look back on the invention of the ESS concept as one of the most important advances in evolutionary theory since Darwin.* It is applicable wherever we find conflict of interest, and that means almost everywhere.

Genes are selected, not as ‘good’ in isolation, but as good at working against the background of the other genes in the gene pool. A good gene must be compatible with, and complementary to, the other genes with whom it has to share a long succession of bodies.

The gene pool is the long-term environment of the gene. ‘Good’ genes are blindly selected as those that survive in the gene pool. This is not a theory; it is not even an observed fact: it is a tautology.

Genes are selected on ‘merit’. But merit is judged on the basis of performance against the background of the evolutionarily stable set which is the current gene pool.

Well-integrated bodies exist because they are the product of an evolutionarily stable set of selfish genes.

Genetically speaking, your first cousin is equivalent to a great-grandchild. Similarly, you are just as likely to ‘take after’ your uncle () as after your grandfather ().

When a man throws a ball high in the air and catches it again, he behaves as if he had solved a set of differential equations in predicting the trajectory of the ball. He may neither know nor care what a differential equation is, but this does not affect his skill with the ball. At some subconscious level, something functionally equivalent to the mathematical calculations is going on. Similarly, when a man takes a difficult decision, after weighing up all the pros and cons, and all the consequences of the decision that he can imagine, he is doing the functional equivalent of a large ‘weighted sum’ calculation, such as a computer might perform.

What really happens is that the gene pool becomes filled with genes that influence bodies in such a way that they behave as if they had made such calculations.

Living bodies are machines programmed by genes that have survived. The genes that have survived have done so in conditions that tended on average to characterize the environment of the species in the past. Therefore ‘estimates’ of costs and benefits are based on past ‘experience’, just as they are in human decision-making.

According to him, groups whose individual members restrain their own birth rates are less likely to go extinct than rival groups whose individual members reproduce so fast that they endanger the food supply. Therefore the world becomes populated by groups of restrained breeders.

If the population gets too big, some individuals will not get territories, and therefore will not breed. Winning a territory is therefore, to Wynne-Edwards, like winning a ticket or licence to breed. Since there is a finite number of territories available, it is as if a finite number of breeding licences is issued. Individuals may fight over who gets these licences, but the total number of babies that the population can have as a whole is limited by the number of territories available.

populations use formal contests over status and territory as a means of limiting their size slightly below the level at which starvation itself actually takes its toll.

ambitions. She has to strike a balance between bearing and caring. The total amount of food and other resources which an individual female, or a mated pair, can muster is the limiting factor determining the number of children they can rear.

Contraception is sometimes attacked as ‘unnatural’. So it is, very unnatural. The trouble is, so is the welfare state.

The welfare state is perhaps the greatest altruistic system the animal kingdom has ever known. But any altruistic system is inherently unstable, because it is open to abuse by selfish individuals, ready to exploit it.

predictor. A female starling can in principle know that, when she comes to feed her babies in the coming spring, she will be competing for food with rivals of the same species. If she can somehow estimate the local density of her own species in winter, this could provide her with a powerful means of predicting how difficult it is going to be to get food for babies next spring. If she found the winter population to be particularly high, her prudent policy, from her own selfish point of view, might well be to lay relatively few eggs: her estimate of her own optimum clutch size would have been reduced.

Genes are selected for their ability to make the best use of the levers of power at their disposal: they will exploit their practical opportunities.

When a gene is sitting in a juvenile body its practical opportunities will be different from when it is sitting in a parental body. Therefore its optimum policy will be different in the two stages in its body’s life history.

there is one fundamental feature of the sexes which can be used to label males as males, and females as females, throughout animals and plants. This is that the sex cells or ‘gametes’ of males are much smaller and more numerous than the gametes of females. This is true whether we are dealing with animals or plants. One group of individuals has large sex cells, and it is convenient to use the word female for them. The other group, which it is convenient to call male, has small sex cells.

So we can think of two divergent sexual ‘strategies’ evolving. There was the large-investment or ‘honest’ strategy. This automatically opened the way for a small-investment exploitative strategy. Once the divergence between the two strategies had started, it would have continued in runaway fashion. Medium-sized intermediates would have been penalized, because they did not enjoy the advantages of either of the two more extreme strategies.

Is there anything a female can do to reduce the extent to which her mate exploits her in the first place? She has a strong card in her hand. She can refuse to copulate. She is in demand, in a seller’s market. This is because she brings the dowry of a large, nutritious egg. A male who successfully copulates gains a valuable food reserve for his offspring. The female is potentially in a position to drive a hard bargain before she copulates.

Courtship rituals often include considerable pre-copulation investment by the male. The female may refuse to copulate until the male has built her a nest. Or the male may have to feed her quite substantial amounts of food.

Could females force males to invest so heavily in their offspring before they allow copulation that it would no longer pay the males to desert after copulation?

A business man should never say ‘I have already invested so much in the Concorde airliner (for instance) that I cannot afford to scrap it now.’ He should always ask instead whether it would pay him in the future, to cut his losses, and abandon the project now, even though he has already invested heavily in it.

Our two female strategies will be called coy and fast, and the two male strategies will be called faithful and philanderer.

She begs from the male, using the same gestures as a young bird would use. It has been supposed that this is automatically attractive to the male, in the same way as a man finds a lisp or pouting lips attractive in an adult woman.

However, it is still possible that human males in general have a tendency towards promiscuity, and females a tendency towards monogamy, as we would predict on evolutionary grounds. Which of these two tendencies wins in particular societies depends on details of cultural circumstance, just as in different animal species it depends on ecological details.

True warfare in which large rival armies fight to the death is known only in man and in social insects.

Members of different species often have much to offer each other because they can bring different ‘skills’ to the partnership.

The other side of this coin is that viruses may be genes who have broken loose from ‘colonies’ such as ourselves. Viruses consist of pure DNA (or a related self-replicating molecule) surrounded by a protein jacket. They are all parasitic. The suggestion is that they have evolved from ‘rebel’ genes who escaped, and now travel from body to body directly through the air, rather than via the more conventional vehicles—sperms and eggs.

If this is true, we might just as well regard ourselves as colonies of viruses!

The benefit to a large fish of being able to return repeatedly to the same ‘barber’s shop’, rather than continually searching for a new one, must outweigh the cost of refraining from eating the cleaner.

A long memory and a capacity for individual recognition are well developed in man. We might therefore expect reciprocal altruism to have played an important part in human evolution. Trivers goes so far as to suggest that many of our psychological characteristics—envy, guilt, gratitude, sympathy, etc.—have been shaped by natural selection for improved ability to cheat, to detect cheats, and to avoid being thought to be a cheat. Of particular interest are ‘subtle cheats’ who appear to be reciprocating, but who consistently pay back slightly less than they receive.

During most of the time Jenkins was there, there was a fixed number of songs on the island, a kind of ‘song pool’ from which each young male drew his own small repertoire. But occasionally Jenkins was privileged to witness the ‘invention’ of a new song, which occurred by a mistake in the imitation of an old one.

in a number of cases the variant was transmitted accurately in its new form to younger recruits so that a recognizably coherent group of like singers developed.’ Jenkins refers to the origins of new songs as ‘cultural mutations’.

will there still be any general principle that is true of all life? Obviously I do not know but, if I had to bet, I would put my money on one fundamental principle. This is the law that all life evolves by the differential survival of replicating entities.*

value? Remember that ‘survival value’ here does not mean value for a gene in a gene pool, but value for a meme in a meme pool.

What is it about the idea of a god that gives it its stability and penetrance in the cultural environment?

God exists, if only in the form of a meme with high survival value, or infective power, in the environment provided by human culture.

Some memes, like some genes, achieve brilliant short-term success in spreading rapidly, but do not last long in the meme pool.

An ‘idea-meme’ might be defined as an entity that is capable of being transmitted from one brain to another.

Throughout this book, I have emphasized that we must not think of genes as conscious, purposeful agents. Blind natural selection, however, makes them behave rather as if they were purposeful, and it has been convenient, as a shorthand, to refer to genes in the language of purpose.

Any user of a digital computer knows how precious computer time and memory storage space are. At many large computer centres they are literally costed in money; or each user may be allotted a ration of time, measured in seconds, and a ration of space, measured in ‘words’. The computers in which memes live are human brains.* Time is possibly a more important limiting factor than storage space, and it is the subject of heavy competition.

Other commodities for which memes compete are radio and television time, billboard space, newspaper column-inches, and library shelf-space.

The idea of hell fire is, quite simply, self perpetuating, because of its own deep psychological impact. It has become linked with the god meme because the two reinforce each other, and assist each other’s survival in the meme pool.

Another member of the religious meme complex is called faith. It means blind trust, in the absence of evidence, even in the teeth of evidence.

Blind faith can justify anything.*

One unique feature of man, which may or may not have evolved memically, is his capacity for conscious foresight.

another unique quality of man is a capacity for genuine, disinterested, true altruism.

our conscious foresight—our capacity to simulate the future in imagination—could save us from the worst selfish excesses of the blind replicators.

We have the power to defy the selfish genes of our birth and, if necessary, the selfish memes of our indoctrination.

We are built as gene machines and cultured as meme machines, but we have the power to turn against our creators. We, alone on earth, can rebel against the tyranny of the selfish replicators.*

This amounts to a quest for possible ways in which Tit for Tat individuals might happen to cluster together in sufficient numbers that they can all benefit at the banker’s expense.

It is only a mistake in certain kinds of game. Games theorists divide games into ‘zero sum’ and ‘nonzero sum’. A zero sum game is one in which a win for one player is a loss for the other.

Prisoner’s Dilemma, however, is a nonzero sum game.

What is to be done? The Shakespeare option is messy. It would be cleaner to get the law changed. But most parliamentarians are drawn from the legal profession, and have a zero sum mentality. It is hard to imagine a more adversarial atmosphere than the British House of Commons. (The law courts at least preserve the decencies of debate. As well they might, since ‘my learned friend and I’ are cooperating very nicely all the way to the bank.) Perhaps well-meaning legislators and, indeed, contrite lawyers should be taught a little game theory. It is only fair to add that some lawyers play exactly the opposite role, persuading clients who are itching for a zero sum fight that they would do better to reach a nonzero sum settlement out of court.

The locally stable strategy in any particular part of the trench lines was not necessarily Tit for Tat itself. Tit for Tat is one of a family of nice, retaliatory but forgiving strategies, all of which are, if not technically stable, at least difficult to invade once they arise. Three Tits for a Tat, for instance, grew up in one local area according to a contemporary account.

So it is natural to ask whether his optimistic conclusions—about the success of non-envious, forgiving niceness—also apply in the world of nature. The answer is yes, of course they do. The only conditions are that nature should sometimes set up games of Prisoner’s Dilemma, that the shadow of the future should be long, and that the games should be nonzero sum games. These conditions are certainly met, all round the living kingdoms.

Darwinian corpus gives us is not detailed expectations about particular organisms. It gives us something subtler and more valuable: understanding of principle. But if we must have myths, the real facts about vampires could tell a different moral tale. To the bats themselves, not only is blood thicker than water. They rise above the bonds of kinship, forming their own lasting ties of loyal blood-brotherhood. Vampires could form the vanguard of a comfortable new myth, a myth of sharing, mutualistic cooperation. They could herald the benignant idea that, even with selfish genes at the helm, nice guys can finish first.

Natural selection favours some genes rather than others not because of the nature of the genes themselves, but because of their consequences—their phenotypic effects.

as far as natural selection is concerned. The benefits that actually count are the benefits to those genes that give the shell its protective properties.

In that case there must have been genes controlling variation in caddis houses, for selection cannot produce adaptations unless there are hereditary differences among which to select.

genes in one organism can have extended phenotypic effects on the body of another organism.

Giantism in beetle larvae is an extended phenotypic effect of protozoan genes.

Genes, then, reach outside their ‘own’ body to influence phenotypes in other bodies.

Are its genes transmitted to future generations via the same vehicles as the host’s genes? If they are not, I would expect it to damage the host, in one way or another. But if they are, the parasite will do all that it can to help the host, not only to survive but to reproduce. Over evolutionary time it will cease to be a parasite, will cooperate with the host, and may eventually merge into the host’s tissues and become unrecognizable as a parasite at all.

we are all relics of ancient parasitic mergers.

We can take this argument to its logical conclusion and apply it to normal, ‘own’ genes. Our own genes cooperate with one another, not because they are our own but because they share the same outlet—sperm or egg—into the future.

When we have a cold or a cough, we normally think of the symptoms as annoying byproducts of the virus’s activities. But in some cases it seems more probable that they are deliberately engineered by the virus to help it to travel from one host to another.

Viruses may well, indeed, have originated as collections of breakaway genes. If we want to erect any distinction, it should be between genes that pass from body to body via the orthodox route of sperms or eggs, and genes that pass from body to body via unorthodox, ‘sideways’ routes.

Rivals with a genetic tendency to resist manipulation would actually be less successful in passing on genes, because of the economic costs of resisting.

Natural selection favours those genes that manipulate the world to ensure their own propagation.

An animal’s behaviour tends to maximize the survival of the genes ‘for’ that behaviour, whether or not those genes happen to be in the body of the particular animal performing it.

Vehicles don’t replicate themselves; they work to propagate their replicators. Replicators don’t behave, don’t perceive the world, don’t catch prey or run away from predators; they make vehicles that do all those things.

The essential quality that an entity needs, if it is to become an effective gene vehicle, is this. It must have an impartial exit channel into the future, for all the genes inside it. This is true of an individual wolf.

Why did genes gang up in cells? Why did cells gang up in many-celled bodies? And why did bodies adopt what I shall call a ‘bottlenecked’ life cycle?

Each of these enzymes is made by one gene. If a sequence of six enzymes is needed for a particular synthetic pathway, all six genes for making them must be present. Now it is quite likely that there are two alternative pathways for arriving at that same end-product, each needing six different enzymes, and with nothing to choose between the two of them.

But when the ways of making a living that are open to small organisms have all been filled, there are still prosperous livings to be made by larger organisms. Large organisms can eat smaller ones, for instance, and can avoid being eaten by them.

The advantages of being in a club of cells don’t stop with size. The cells in the club can specialize, each thereby becoming more efficient at performing its particular task. Specialist cells serve other cells in the club and they also benefit from the efficiency of other specialists. If there are many cells, some can specialize as sensors to detect prey, others as nerves to pass on the message, others as stinging cells to paralyse the prey, muscle cells to move tentacles and catch the prey, secretory cells to dissolve it and yet others to absorb the juices.

We must not forget that, at least in modern bodies like our own, the cells are a clone. All contain the same genes, although different genes will be turned on in the different specialist cells.

Really radical change can be achieved only by going ‘back to the drawing board’, throwing away the previous design and starting afresh.

Living things, of course, were never designed on drawing boards. But they do go back to fresh beginnings. They make a clean start in every generation. Every new organism begins as a single cell and grows anew. It inherits the ideas of ancestral design, in the form of the DNA program, but it does not inherit the physical organs of its ancestors. It does not inherit its parent’s heart and remould it into a new (and possibly improved) heart. It starts from scratch, as a single cell, and grows a new heart, using the same design program as its parent’s heart, to which improvements may be added.

One important thing about a ‘bottlenecked’ life cycle is that it makes possible the equivalent of going back to the drawing board.

Bottlenecking of the life cycle has a second, related consequence. It provides a ‘calendar’ that can be used to regulate the processes of embryology. In a bottlenecked life cycle, every fresh generation marches through approximately the same parade of events.

So, the stereotyped growth cycle provides a clock, or calendar, by means of which embryological events may be triggered. Think of how readily we ourselves use the cycles of the earth’s daily rotation, and its yearly circumnavigation of the sun, to structure and order our lives.

Such well-tempered regulations of gene activity are a prerequisite for the evolution of embryologies capable of crafting complex tissues and organs. The precision and complexity of an eagle’s eye or a swallow’s wing couldn’t emerge without clockwork rules for what is laid down when.

If life cycles become bottlenecked, living material seems bound to become boxed into discrete, unitary organisms. And the more that living material is boxed into discrete survival machines, the more will the cells of those survival machines concentrate their efforts on that special class of cells that are destined to ferry their shared genes through the bottleneck into the next generation.

As time goes by, the world becomes filled with the most powerful and ingenious replicators.

Replicators survive, not only by virtue of their own intrinsic properties, but by virtue of their consequences on the world. These consequences can be quite indirect. All that is necessary is that eventually the consequences, however tortuous and indirect, feed back and affect the success of the replicator at getting itself copied.

At some point in the evolution of life on our earth, this ganging up of mutually compatible replicators began to be formalized in the creation of discrete vehicles—cells and, later, many-celled bodies. Vehicles that evolved a bottlenecked life cycle prospered, and became more discrete and vehicle-like.

The only kind of entity that has to exist in order for life to arise, anywhere in the universe, is the immortal replicator.

‘A gene is defined as any portion of chromosomal material that potentially lasts for enough generations to serve as a unit of natural selection.’

sexually reproducing population is a cartel of mutually compatible, cooperating genes: cooperating today because they have flourished by cooperating through many generations of similar bodies in the ancestral past.

the key to the cooperation is that, in every generation, all the genes in a body share the same ‘bottlenecked’ exit route to the future: the sperms or eggs in which they aspire to sail into the next generation.

To look at it another way, every living individual has been built, during its embryonic development, by genes which can trace their ancestry through a very large number of generations, in a very large number of individuals.

Living animals have inherited the genes that helped huge numbers of ancestors to survive. That is why living animals have what it takes to survive—and reproduce.

From R. Dawkins and Y. Wong (2006) The Ancestor’s Tale, 2nd edition Image courtesy of Y. Wong

So powerful is the gene’s eye view, the genome of a single individual is sufficient to make quantitatively detailed inferences about historical demography. What else might it be capable of? As foreshadowed by the Nigerian comparison, future analyses of individuals from different parts of the world could give a geographic dimension to these demographic signals from the past.

Dead’. The gene pool of a species is a mutually supportive cartel of genes that have survived in particular environments of the past, both distant and recent. This makes it a kind of negative imprint of those environments. A sufficiently knowledgeable geneticist should be able to read out, from the genome of an animal, the environments in which its ancestors survived.