It is true that there are quite a number of ways of making a living–flying, swimming, swinging through the trees, and so on. But, however many ways there may be of being alive, it is certain that there are vastly more ways of being dead, or rather not alive.

The answer we have arrived at is that complicated things have some quality, specifiable in advance, that is highly unlikely to have been acquired by random chance alone. In the case of living things, the quality that is specified in advance is, in some sense, ‘proficiency’; either proficiency in a particular ability such as flying, as an aero-engineer might admire it; or proficiency in something more general, such as the ability to stave off death, or the ability to propagate genes in reproduction.

If they fail they die. More generally, if living things didn’t work actively to prevent it, they would eventually merge into their surroundings, and cease to exist as autonomous beings. That is what happens when they die.

The body is a complex thing with many constituent parts, and to understand its behaviour you must apply the laws of physics to its parts, not to the whole.

If we wish to understand how a machine or living body works, we look to its component parts and ask how they interact with each other. If there is a complex thing that we do not yet understand, we can come to understand it in terms of simpler parts that we do already understand.

For any given level of complex organization, satisfying explanations may normally be attained if we peel the hierarchy down one or two layers from our starting layer, but not more. The behaviour of a motor car is explained in terms of cylinders, carburettors and sparking plugs.

A satisfying explanation has to be in terms of a manageably small number of interactions. This is why, if we want to understand the workings of computers, we prefer a preliminary explanation in terms of about half a dozen major subcomponents–memory, processing mill, backing store, control unit, input–output handler, etc.

Only specialist engineers are likely to go down to the level of AND gates and NOR gates, and only physicists will go down further, to the level of how electrons behave in a semiconducting medium.

the aptest name for my approach to understanding how things work is probably ‘hierarchical reductionism’. If you read trendy intellectual magazines, you may have noticed that ‘reductionism’ is one of those things, like sin, that is only mentioned by people who are against it.

The nonexistent reductionist–the sort that everybody is against, but who exists only in their imaginations–tries to explain complicated things directly in terms of the smallest parts, even, in some extreme versions of the myth, as the sum of the parts!

goes without saying–though the mythical, baby-eating reductionist is reputed to deny this–that the kinds of explanations which are suitable at high levels in the hierarchy are quite different from the kinds of explanations which are suitable at lower levels.

We concluded that the behaviour of a complicated thing should be explained in terms of interactions between its component parts, considered as successive layers of an orderly hierarchy.

A complicated thing is one whose existence we do not feel inclined to take for granted, because it is too ‘improbable’. It could not have come into existence in a single act of chance. We shall explain its coming into existence as a consequence of gradual, cumulative, step-by-step transformations from simpler things, from primordial objects sufficiently simple to have come into being by chance.

I am a biologist. I take the facts of physics, the facts of the world of simplicity, for granted.

I am aware that my characterization of a complex object–statistically improbable in a direction that is specified not with hindsight–may seem idiosyncratic.

Natural selection is the blind watchmaker, blind because it does not see ahead, does not plan consequences, has no purpose in view. Yet the living results of natural selection overwhelmingly impress us with the appearance of design as if by a master watchmaker, impress us with the illusion of design and planning.

Bats have a problem: how to find their way around in the dark. They hunt at night, and cannot use light to help them find prey and avoid obstacles. You might say that if this is a problem it is a problem of their own making, a problem that they could avoid simply by changing their habits and hunting by day. But the daytime economy is already heavily exploited by other creatures such as birds.

The engineer who sets about designing an efficient sonar or radar device soon comes up against a problem resulting from the need to make the pulses extremely loud.

The intensity of the sound is distributed and, in a sense, ‘diluted’ over the whole surface of the sphere. The surface area of any sphere is proportional to the radius squared. The intensity of the sound at any particular point on the sphere therefore decreases, not in proportion to the distance (the radius) but in proportion to the square of the distance from the sound source, as the wavefront advances and the sphere swells. This means that the sound gets quieter pretty fast, as it travels away from its source, in this case the bat.

Bats developed ‘send/ receive’ switching technology long long ago, probably millions of years before our ancestors came down from the trees.

The bat called Tadarida is capable of alternately contracting and relaxing its switching muscles 50 times per second, keeping in perfect synchrony with the machine gun-like pulses of ultrasound.

Actually some bats play a trick that is more interesting than simply emitting hoots of constant pitch and measuring the pitch of the returning echoes. They carefully adjust the pitch of the outgoing hoots, in such a way as to keep the pitch of the echo constant after it has been Doppler-shifted.

That is no more what it is like to be a bat than the following is a good picture of what it is like to see colour: use an instrument to measure the wavelength of the light that is entering your eye: if it is long, you are seeing red, if it is short you are seeing violet or blue. It happens to be a physical fact that the light that we call red has a longer wavelength than the light that we call blue.

We are such thoroughly visual animals that we hardly realize what a complicated business seeing is. Objects are ‘out there’, and we think that we ‘see’ them out there. But I suspect that really our percept is an elaborate computer model in the brain, constructed on the basis of information coming from out there, but transformed in the head into a form in which that information can be used.

The sensation of seeing is, for us, very different from the sensation of hearing, but this cannot be directly due to the physical differences between light and sound. Both light and sound are, after all, translated by the respective sense organs into the same kind of nerve impulses.

It is impossible to tell, from the physical attributes of a nerve impulse, whether it is conveying information about light, about sound or about smell. The reason the sensation of seeing is so different from the sensation of hearing and the sensation of smelling is that the brain finds it convenient to use different kinds of internal model of the visual world, the world of sound and the world of smell.

It is because we internally use our visual information and our sound information in different ways and for different purposes that the sensations of seeing and hearing are so different. It is not directly because of the physical differences between light and sound.

But a bat uses its sound information for very much the same kind of purpose as we use our visual information. It uses sound to perceive, and continuously update its perception of, the position of objects in three-dimensional space, just as we use light. The type of internal computer model that it needs, therefore, is one suitable for the internal representation of the changing positions of objects in three-dimensional space.

That model will be designed, in evolution, for its suitability for useful internal representation, irrespective of the physical stimuli that come to it from outside.

The fact that bats construct their internal model with the aid of echoes, while we construct ours with the aid of light, is irrelevant.

Yet the mathematical calculations that would be necessary to explain the principles of vision are just as complex and difficult, and nobody has ever had any difficulty in believing that little animals can see.

Of course, a sophisticated conscious brain did the wiring up (or at least designed the wiring diagram), but no conscious brain is involved in the moment-to-moment working of the box.

Our experience of electronic technology prepares us to accept the idea that unconscious machinery can behave as if it understands complex mathematical ideas. This idea is directly transferable to the workings of living machinery. A bat is a machine, whose internal electronics are so wired up that its wing muscles cause it to home in on insects, as an unconscious guided missile homes in on an aeroplane.

our intuition, derived from technology, is correct. But our experience of technology also prepares us to see the mind of a conscious and purposeful designer in the genesis of sophisticated machinery. It is this second intuition that is wrong in the case of living machinery. In the case of living machinery, the ‘designer’ is unconscious natural selection, the blind watchmaker.

We have seen that living things are too improbable and too beautifully ‘designed’ to have come into existence by chance. How, then, did they come into existence? The answer, Darwin’s answer, is by gradual, step-by-step transformations from simple beginnings, from primordial entities sufficiently simple to have come into existence by chance. Each successive change in the gradual evolutionary process was simple enough, relative to its predecessor, to have arisen by chance. But the whole sequence of cumulative steps constitutes anything but a chance process, when you consider the complexity of the final end-product relative to the original starting point. The cumulative process is directed by nonrandom survival. The purpose of this chapter is to demonstrate the power of this cumulative selection as a fundamentally nonrandom process.

The waves and the pebbles together constitute a simple example of a system that automatically generates non-randomness.

The simple sieves we have been considering so far in this chapter are all examples of single-step selection. Living organization is the product of cumulative selection.

There is a big difference, then, between cumulative selection (in which each improvement, however slight, is used as a basis for future building), and single-step selection (in which each new ‘try’ is a fresh one).

Chance is a minor ingredient in the Darwinian recipe, but the most important ingredient is cumulative selection which is quintessentially nonrandom.

The ‘watchmaker’ that is cumulative natural selection is blind to the future and has no long-term goal.

We have assembled our two program modules, then, labelled DEVELOPMENT and REPRODUCTION. REPRODUCTION passes genes down the generations, with the possibility of mutation. DEVELOPMENT takes the genes provided by REPRODUCTION in any given generation, and translates those genes into drawing action, and hence into a picture of a body on the computer screen. The time has come to bring the two modules together in the big program called EVOLUTION.

But although the mutations are random, the cumulative change over the generations is not random.

The progeny in any one generation are different from their parent in random directions. But which of those progeny is selected to go forward into the next generation is not random. This is where Darwinian selection comes in.

In true natural selection, if a body has what it takes to survive, its genes automatically survive because they are inside it. So the genes that survive tend to be, automatically, those genes that confer on bodies the qualities that assist them to survive.

nature, the usual selecting agent is direct, stark and simple. It is the grim reaper. Of course, the reasons for survival are anything but simple–that is why natural selection can build up animals and plants of such formidable complexity.

There is a definite set of biomorphs, each permanently sitting in its own unique place in a mathematical space. It is permanently sitting there in the sense that, if only you knew its genetic formula, you could instantly find it; moreover, its neighbours in this special kind of space are the biomorphs that differ from it by only one gene. Now that I know the genetic formula of my insects, I can reproduce them at will, and I can tell the computer to ‘evolve’ towards them from any arbitrary starting point.

When you first evolve a new creature by artificial selection in the computer model, it feels like a creative process. So it is, indeed.

All the creatures in Biomorph Land have a definite spatial relationship one to another. What does that mean? What meaning can we attach to spatial position? The space we are talking about is genetic space. Each animal has its own position in genetic space. Near neighbours in genetic space are animals that differ from one another by only a single mutation.

The triangle lies on a flat two-dimensional ‘plane’ that cuts through the nine-dimensional hypervolume

Jumping could theoretically get you the prize faster–in a single hop. But because of the astronomical odds against success, a series of small steps, each one building on the accumulated success of previous steps, is the only feasible way.

substitute. For those, like me, who are not mathematicians, the computer can be a powerful friend to the imagination. Like mathematics, it doesn’t only stretch the imagination. It also disciplines and controls it.

One kind of answer suggests that bird vision has been improving over the same evolutionary timespan as insect camouflage. Perhaps, to be a little facetious, an ancestral insect that looked only 5 per cent like a turd would have fooled an ancestral bird with only 5 per cent vision.

The important thing about light intensity, distance of insect from predator, distance of image from centre of retina, and similar variables, is that they are all continuous variables. They vary by insensible degrees all the way from the extreme of invisibility to the extreme of visibility. Such continuous variables foster continuous and gradual evolution.

Although it probably began as a lung, over the course of evolution it has become the swimbladder, an ingenious device with which the fish maintains itself as a hydrostat in permanent equilibrium.

There is no hard-and-fast divide between water-breathing and air-breathing animals. Different animals may spend 99 per cent of their time in water, 98 per cent, 97 per cent, and so on all the way to 0 per cent. At every step of the way, some fractional increase in lung area will be an advantage. There is continuity, gradualism, all the way.

They provide most impressive demonstrations of the power of natural selection to put together good designs. Yet the fact that the superficially similar designs also differ, testifies to their independent evolutionary origins and histories.

if a design is good enough to evolve once, the same design principle is good enough to evolve twice, from different starting points, in different parts of the animal kingdom.

It follows that the echolocation technology has been independently developed in bats and birds, just as it was independently developed by British, American and German scientists.

We really don’t know what is special about 13 and 17 years. What matters for our purposes here is that there must be something special about those numbers, because three different species of cicada have independently converged upon them.

the dinosaurs (with the exception of the group of dinosaurs that we now call birds) went extinct, they went extinct all over the world.

In all three areas the mammals that happened to be around at the start fanned out in evolution, and produced a specialist for each trade which, in many cases, came to bear a remarkable resemblance to the corresponding specialist in the other two areas.

Each trade, the burrowing trade, the large hunter trade, the plains-grazing trade, and so on, was the subject of independent convergent evolution in two or three separate continents.

The animals are often very large, and they frequently go about in great herds. Each one of these big herbivores is a mountain of valuable food to any predator that can exploit it. As a consequence of this there is, as we shall see, a whole trade devoted to the difficult task of catching and killing them. These are the predators.

The basic requirement for an advanced information technology is some kind of storage medium with a large number of memory locations.

That is the diagnostic feature of a digital system: its fundamental elements are either definitely in one state or definitely in another state, with no half measures and no intermediates or compromises.

The main storage medium inside willow seeds, ants and all other living cells is not electronic but chemical. It exploits the fact that certain kinds of molecule are capable of ‘polymerizing’, that is joining up in long chains of indefinite length.

DNA is ROM. It can be read millions of times over, but only written to once–when it is first assembled at the birth of the cell in which it resides.

The difference is that each location is stuck with its contents, once and for all.

What matters is that a particular location in my DNA corresponds precisely to one particular location in your DNA: they have the same address.

All of us, all human beings, have the same set of DNA addresses, but not necessarily the same contents of those addresses. That is the main reason why we are all different from each other. Other species don’t have the same set of addresses.

species. The thing that defines a species is that all members have the same addressing system for their DNA.

Of course, at any particular time, every copy has to be inside an individual body. But what matters in evolution is changes in frequency of alternative possible contents at each address in populations.

Before they can be involved in any kind of action, the code symbols of DNA have to be translated into another medium. They are first transcribed into exactly corresponding RNA symbols.

There are 20 kinds of amino acids in living cells. All biological proteins are chains made of these 20 basic building-blocks.

There is a sense, therefore, in which the three-dimensional coiled shape of a protein is determined by the one-dimensional sequence of code symbols in the DNA.

Many of the amino acids are coded by more than one triplet (as you might have guessed from the fact that there are 64 triplets and only 20 amino acids).

The whole translation, from strictly sequential DNA ROM to precisely invariant three-dimensional protein shape, is a remarkable feat of digital information technology.

Protein molecules called enzymes are machines in the sense that each one causes a particular chemical reaction to take place.

Since all body cells contain the same genes, it might seem surprising that all body cells aren’t the same as each other. The reason is that a different subset of genes is read in different kinds of cells, the others being ignored.

The shape and behaviour of a cell depend upon which genes inside that cell are being read and translated into their protein products. This in turn depends on the chemicals already in the cell, which depends partly on which genes have previously been read in the cell, and partly on neighbouring cells.

When one cell divides into two, the two daughter cells aren’t necessarily the same as each other. In the original fertilized egg, for instance, certain chemicals congregate at one end of the cell, others at the other end. When such a polarized cell divides, the two daughter cells receive different chemical allocations. This means that different genes will be read in the two daughter cells, and a kind of self-reinforcing divergence gets going.

These diverging processes are best thought of as locally autonomous in the manner of the ‘recursive’ procedure of Chapter 3, rather than as coordinated in some grand central design.

You can think of horizontal transmission and vertical transmission as corresponding to the two sub-programs called DEVELOPMENT and REPRODUCTION in Chapter 3.

If there is no natural selection, therefore, we might expect that there would be no evolution. Conversely, strong ‘selection pressure’, we could be forgiven for thinking, might be expected to lead to rapid evolution. Instead, what we find is that natural selection exerts a braking effect on evolution. The baseline rate of evolution, in the absence of natural selection, is the maximum possible rate. That is synonymous with the mutation rate.

The DNA-copying procedure incorporates various ‘proofreading’ drills.

We seem to have two kinds of ‘existenceworthiness’: the dewdrop kind, which can be summed up as ‘likely to come into existence but not very durable’; and the rock kind, which can be summed up as ‘not very likely to come into existence but likely to last for a long time once there’. Rocks have durability and dewdrops have ‘generatability’. (I’ve tried to think of a less ugly word but I can’t.)

It is not a substance at all, it is a property, the property of self-replication. This is the basic ingredient of cumulative selection.

But modern DNA replication is a high-technology affair, with elaborate proofreading techniques that have been perfected over many generations of cumulative selection.

It is possible for an error to result in an improvement.

I dare say many an exquisite new dish has been created because a cook made a mistake while trying to follow a recipe.

So the factory is hijacked by these self-interested blueprints. In a sense it was crying out to be hijacked. If you fill your factory with machines so sophisticated that they can make anything that any blueprint tells them to make, it is hardly surprising if sooner or later a blueprint arises that tells these machines to make copies of itself.

DNA can be said to exert power over its own future, and bodies and their organs and behaviour patterns are the instruments of that power.

This is that, once life (i.e. replicators and cumulative selection) originates at all, it always advances to the point where its creatures evolve enough intelligence to speculate about their origins.

The basic idea of The Blind Watchmaker is that we don’t need to postulate a designer in order to understand life, or anything else in the universe.

Cairns-Smith believes that the original life on this planet was based on self-replicating inorganic crystals such as silicates.

Stonehenge is incomprehensible until we realize that the builders used some kind of scaffolding, or perhaps ramps of earth, which are no longer there. We can see only the end-product, and have to infer the vanished scaffolding. Similarly, DNA and protein are two pillars of a stable and elegant arch, which persists once all its parts simultaneously exist.

Graphite and diamonds, for instance, are both crystals of pure carbon. Their atoms are identical.

But–and here is the vital point–there are flaws. Right in the middle of an expanse of orderly herringbone there can be a patch, identical to the rest except that it is twisted round at a different angle so that the ‘weave’ goes off in another direction. Or the weave may lie in the same direction, but each row has ‘slipped’ half a row to one side. Nearly all naturally occurring crystals have flaws. And once a flaw has appeared, it tends to be copied as subsequent layers of crystal encrust themselves on top of it.

Although laser discs are used today mainly for music, you could pack the whole Encyclopaedia Britannica onto one of them, and read it out using the same laser technique.

Flaws in crystals at the atomic level are far smaller than the pits etched in a laser disc’s surface, so crystals can potentially pack more information into a given area.

So, we have a speculative picture of mineral crystals on the primeval Earth showing some of the properties of replication, multiplication, heredity and mutation that would have been necessary in order for a form of cumulative selection to get started.

The new replicators are not DNA and they are not clay crystals. They are patterns of information that can thrive only in brains or the artificially manufactured products of brains–books, computers, and so on. But, given that brains, books and computers exist, these new replicators, which I called memes to distinguish them from genes, can propagate themselves from brain to brain, from brain to book, from book to brain, from brain to computer, from computer to computer.

Evolution under the influence of the new replicators–memic evolution–is in its infancy. It is manifested in the phenomena that we call cultural evolution.

Cultural evolution is many orders of magnitude faster than DNA-based evolution,

The conclusion to this part of the argument is that we can calculate our way into regions of miraculous improbability far greater than we can imagine as plausible.

We are equipped to make mental calculations of risk and odds, within the range of improbabilities that would be useful in human life. This means risks of the order of, say, being gored by a buffalo if we shoot an arrow at it, being struck by lightning if we shelter under a lone tree in a thunderstorm, or drowning if we try to swim across a river.

Evolution has equipped our brains with a subjective consciousness of risk and improbability suitable for creatures with a lifetime of less than one century.

But from each gene’s point of view, perhaps the most important part of its environment is all the other genes that it encounters.

The genes themselves don’t evolve, they merely survive or fail to survive in the gene pool. It is the ‘team’ that evolves.

It is difficult for a minority team to break in, even a minority team which would, in the end, have done the job more efficiently. The majority team has an automatic resistance to being displaced, simply by virtue of being in the majority. This doesn’t mean that the majority team can never be displaced. If it couldn’t, evolution would grind to a halt. But it does mean that there is a kind of built-in inertia.

When you tell a computer to delete a file, it appears to obey you. But it doesn’t actually wipe out the text of that file. It simply wipes out all pointers to that file.

They achieve these large-scale indirect manipulations via their more direct effects on the miniature scale of cells. For instance, they change the shape of the cell membrane. The cells then interact with one another in huge populations to produce large-scale group effects such as an arm or a leg or (more indirectly) a beaver’s dam.

Most of the properties of an organism that we are equipped to see with our naked eyes are so-called ‘emergent properties’. Even the computer biomorphs, with their nine genes, had emergent properties.

Evolution will come to a standstill until something in the conditions changes: the onset of an ice age, a change in the average rainfall of the area, a shift in the prevailing wind.

And, just as long-term fluctuations in the weather are ‘tracked’ by evolution, so long-term changes in the habits or weaponry of predators will be tracked by evolutionary changes in their prey. And vice versa, of course.

The principle of zero change in success rate, no matter how great the evolutionary progress in equipment, has been given the memorable name of the ‘Red Queen effect’ by the American biologist Leigh van Valen.

Why, for instance, are trees in forests so tall? The short answer is that all the other trees are tall, so no one tree can afford not to be. It would be overshadowed if it did.

although all would be better off if none of them escalated, so long as one of them escalates none can afford not to.

A symmetric arms race is one between competitors trying to do roughly the same thing as each other. The arms race between forest trees struggling to reach the light is an example. The different species of trees are not all making their livings in exactly the same way, but as far as the particular race we are talking about is concerned–the race for the sunlight above the canopy–they are competitors for the same resource.

The arms race between cheetahs and gazelles, however, is asymmetric. It is a true arms race in which success on either side is felt as failure by the other side, but the nature of the success and failure on the two sides is very different. The two sides are ‘trying’ to do very different things. Cheetahs are trying to eat gazelles. Gazelles are not trying to eat cheetahs, they are trying to avoid being eaten by cheetahs.

and it vividly illustrates the point about equipment improving while its net effectiveness stands still (and its costs increase).

the EQ is standardized against, say, the whole of the mammals.

The price is measured as what economists call ‘opportunity cost’. The opportunity cost of something is measured as the sum of all the other things that you have to forgo in order to have that something.

genes are selected, not for their intrinsic qualities, but by virtue of their interactions with their environments.

An especially important component of a gene’s environment is other genes.

They cooperate because they all stand to gain from the same outcome–the survival and reproduction of the communal body–and because they constitute an important part of the environment in which natural selection works on each other.

The point about different species is that their genes don’t mix–because members of different species can’t mate with one another.

Each new genetic improvement selected on one side of the arms race–say predators–changes the environment for selection of genes on the other side of the arms race–prey.

Bodies evolve integrated and coherent purposefulness because genes are selected in the environment provided by other genes within the same species. But because genes are also selected in the environment provided by other genes in different species, arms races develop.

On the other hand, some of the greatest advances in science have come about because some clever person spotted an analogy between a subject that was already understood, and another still mysterious subject. The trick is to strike a balance between too much indiscriminate analogizing on the one hand, and a sterile blindness to fruitful analogies on the other.

But I suspect that this amounts, in practice, to a difference, not so much in ability to notice analogies as in ability to reject foolish analogies and pursue helpful ones.

A useful engine should deliver rotational power at a constant rate, the right rate for the job in hand, milling, weaving, pumping or whatever it happens to be.

Watt’s governor was an automatic valve regulating the flow of steam to the piston.

Slight initial perturbations are increased, and they run away in an ever-increasing spiral, which culminates either in disaster or in an eventual throttling down at some higher level due to other processes.

The most noticeable and spectacular positive feedbacks are those that result, not in a decrease, but in a runaway increase in something: a nuclear explosion, a schoolmaster losing his temper, a brawl in a pub, escalating invective at the United Nations

In the total absence of such checks, it is easy to see that the speed of development will be proportional to the development already attained, which will therefore increase with time exponentially, or in geometric progression.

Darwin, although he laid his main stress on survival and the struggle for existence, recognized that existence and survival were only means to an end. That end was reproduction.

A male has a great deal to gain by being attractive to females. A female has little to gain by being attractive to males, since she is bound to be in demand anyway.

The idea of genes failing to express themselves is not a difficult one. If a man has genes for a long penis, he is just as likely to pass those genes on to his daughter as to his son. His son may express those genes whereas his daughter, of course, will not, because she doesn’t have a penis at all. But if the man eventually gets grandsons, the sons of his daughter may be just as likely to inherit his long penis as the sons of his son.

Genes may be carried in a body but not expressed.

By the same reasoning, if you have inherited the genes for a short tail, the chances are that you have also inherited the genes for making females prefer a short tail.

So, the genes for male qualities, and the genes for making females prefer those qualities, will not be randomly shuffled around the population, but will tend to be shuffled around together.

We can express this by saying that there is a utilitarian optimum tail length, which is different from the sexually selected optimum:

In a society where only one in six males mates at all and the fortunate males have large harems, pandering to the majority tastes of females will have enormous benefits, benefits that are well capable of outweighing the utilitarian costs in energy and flight efficiency.

each male body will tend to contain copies of genes that make females prefer his own characteristics.

So, when a female exercises her choice of male, whichever way her preference lies, the chances are that the genes that bias her choice are choosing copies of themselves in the males. They are choosing copies of themselves using male tail length as a label, in a more complicated version of the way the hypothetical green-beard gene uses the green beard as a label.

Whenever small minorities tend to become even smaller minorities, and small majorities tend to become bigger majorities, we have a recipe for positive feedback:

The strong analogy with sexual selection notes that the essence of the Fisher/ Lande theory is the ‘green beard’-like phenomenon whereby genes for female choice automatically tend to choose copies of themselves, a process with an automatic tendency to go explosive. It is not clear that there are examples of this kind of phenomenon other than sexual selection itself.

Genes island-hop in the bodies of birds, just as words island-hop in canoes.

Languages, then, evolve. But although modern English has evolved from Chaucerian English, I don’t think many people would wish to claim that modern English is an improvement on Chaucerian English.

language. Indeed, to the extent that they do, we often see change as deterioration, as degeneration. We tend to see earlier usages as correct, recent changes as corruptions.

To a lesser extent, the same phenomenon of popularity being popular for its own sake is well known in the worlds of book publishing, womens’ fashions, and advertising generally.

One of the best things an advertiser can say about a product is that it is the best-selling product of its kind.

When a book’s sales ‘go critical’, the numbers reach the point where word-of-mouth recommendations et cetera cause its sales suddenly to take-off in a runaway fashion. Rates of sales suddenly become dramatically larger than they were before critical mass was reached, and there may be a period of exponential growth before the inevitable levelling out and subsequent decline.

Basically we have here yet more examples of positive feedback. A book’s, or even a pop record’s, real qualities are not negligible in determining its sales but, nevertheless, wherever there are positive feedbacks lurking, there is bound to be a strong arbitrary element determining which book or record succeeds, and which fails.

If critical mass and take-off are important elements in any success story, there is bound to be a lot of luck, and there is also plenty of scope for manipulation and exploitation by people that understand the system.

Peahens that prefer long-tailed peacocks are favoured solely because other females have the same preference. The male’s qualities themselves are arbitrary and irrelevant.

Darwin’s view was that a complete fossil record, if only we had one, would show gentle rather than jerky change. But since fossilization is such a chancy business, and finding such fossils as there are is scarcely less chancy, it is as though we had a cine film with most of the frames missing.

of a microscope which is almost, but not quite perfectly, in focus and otherwise well adjusted for distinct vision. What are the odds that, if we make some random change to the state of the microscope (corresponding to a mutation), we shall improve the focus and general quality of the image?

It is sufficiently obvious that any large derangement will have a very small probability of improving the adjustment, while in the case of alterations much less than the smallest of those intentionally effected by the maker or the operator, the chance of improvement should be almost exactly one half.

The assumption flows from the role of the microscope in the analogy. The microscope after its random adjustment stands for a mutant animal. The microscope before its random adjustment stands for the normal, unmutated parent of the supposed mutant animal. Since it is a parent, it must have survived long enough to reproduce, and therefore it cannot be all that far from being well-adjusted. By the same token, the microscope before the random jolt cannot be all that far from being in focus, or the animal that it stands for in the analogy couldn’t have survived at all.

The greater the number of simultaneous improvements we consider, the more improbable is their simultaneous occurrence.

So natural selection penalizes any predilection, on the part of individuals on either side, towards hybridizing with the other species or even race. Natural selection thereby finishes off the process of ‘reproductive isolation’ that began with the chance intervention of a mountain range. ‘Speciation’ is complete. We now have two species where previously there was one, and the two species can coexist in the same area without interbreeding with one another.

large breeding populations have an inherent tendency to resist evolutionary change. A suitable analogy is the inertia of a large heavy object; it is hard to shift. Small, outlying populations, by virtue of being small, are inherently more likely, so the theory goes, to change, to evolve.

In a sense it had no ‘need’ to evolve because these animals had found a successful way of life deep in the sea where conditions did not change much. Perhaps they never participated in any arms races. Their cousins that emerged onto the land did evolve because natural selection, under a variety of hostile conditions including arms races, forced them to.

This is because after some generations of selective breeding the available genetic variation runs out, and we have to wait for new mutations.

suggests to me that, if lineages go for many generations in the wild without changing, this is not because they resist change but because there is no natural selection pressure in favour of changing.

They don’t change because individuals that stay the same survive better than individuals that change.

There are people in the world who desperately want not to have to believe in Darwinism. They seem to fall into three main classes. First, there are those who, for religious reasons, want evolution itself to be untrue. Second, there are those who have no reason to deny that evolution has happened but who, often for political or ideological reasons, find Darwin’s theory of its mechanism distasteful. Of these, some find the idea of natural selection unacceptably harsh and ruthless; others confuse natural selection with randomness, and hence ‘meaninglessness’, which offends their dignity; yet others confuse Darwinism with Social Darwinism, which has racist and other disagreeable overtones. Third, there are people, including many working in what they call (often as a singular noun) ‘the media’, who just like seeing applecarts upset, perhaps because it makes good journalistic copy; and Darwinism has become sufficiently established and respectable to be a tempting applecart.

The books in a large library are nearly useless unless they are organized in some nonrandom way so that books on a particular subject can be found when you want them. The science, or it may be an art, of librarianship is an exercise in applied taxonomy.

Librarians can have sensible disagreements with one another about classification policy, but the criteria by which arguments are won or lost will not include the ‘truth’ or ‘correctness’ of one classification system relative to another.

the pattern of evolutionary descent is hierarchical.

Another way of representing this idea of strict hierarchy is in terms of ‘perfect nesting’.

Chimpanzees and we share more than 99 per cent of our genes. If, in various forgotten islands around the world, survivors of all intermediates back to the chimp/ human common ancestor were discovered, who can doubt that our laws and our moral conventions would be profoundly affected, especially as there would presumably be some interbreeding along the spectrum?

The species that we see in the world will tend to have whatever it takes to come into the world in the first place–to ‘be speciated’–and whatever it takes not to go extinct.

Evolving is something that species do, not something that individual organisms do: you can’t talk of an organism as evolving.

The genetic code is universal. I regard this as near-conclusive proof that all organisms are descended from a single common ancestor.

most of the evolutionary change that goes on at the molecular level is neutral. This means that it is not due to natural selection but is effectively random, and therefore that, except through occasional bad luck, the bugbear of convergence is not there to mislead the taxonomist.

probably most evolutionary change, when seen at the molecular level, is non-functional.

Natural selection can act only on the range of variation thrown up by mutation. Mutation is described as ‘random’ but this means only that it is not systematically directed towards improvement. It is a highly nonrandom subset of all the variation that we can conceive of. Mutation has to act by altering the processes of existing embryology. You can’t make an elephant by mutation if the existing embryology is octopus embryology.