The Selfish Gene (Kindle highlights)

Living organisms had existed on earth, without ever knowing why, for over three thousand million years before the truth finally dawned on one of them. His name was Charles Darwin. (p. 1)
Today the theory of evolution is about as much open to doubt as the theory that the earth goes round the sun, but the full implications of Darwin’s revolution have yet to be widely realized. (p. 1)
The argument of this book is that we, and all other animals, are machines created by our genes. (p. 2)
Much as we might wish to believe otherwise, universal love and the welfare of the species as a whole are concepts that simply do not make evolutionary sense. (p. 2)
This book is mainly intended to be interesting, but if you would extract a moral from it, read it as a warning. Be warned that if you wish, as I do, to build a society in which individuals cooperate generously and unselfishly towards a common good, you can expect little help from biological nature. Let us try to teach generosity and altruism, because we are born selfish. Let us understand what our own selfish genes are up to, because we may then at least have the chance to upset their designs, something that no other species has ever aspired to. (p. 3)
I shall argue that the fundamental unit of selection, and therefore of self-interest, is not the species, nor the group, nor even, strictly, the individual. It is the gene, the unit of heredity. (p. 11)
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. (p. 12)
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. (p. 12)
The earliest form of natural selection was simply a selection of stable forms and a rejection of unstable ones. There is no mystery about this. It had to happen by definition. (p. 13)
In the lifetime of a man, things that are that improbable can be treated for practical purposes as impossible. That is why you will never win a big prize on the football pools. But in our human estimates of what is probable and what is not, we are not used to dealing in hundreds of millions of years. If you filled in pools coupons every week for a hundred million years you would very likely win several jackpots. (p. 15)
Can we reconcile the idea that copying errors are an essential prerequisite for evolution to occur, with the statement that natural selection favours high copying-fidelity? The answer is that although evolution may seem, in some vague sense, a ‘good thing’, especially since we are the product of it, nothing actually ‘wants’ to evolve. 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. (p. 17)
Jacques Monod made this point very well in his Herbert Spencer lecture, after wryly remarking: ‘Another curious aspect of the theory of evolution is that everybody thinks he understands it!’ (p. 18)
Human suffering has been caused because too many of us cannot grasp that words are only tools for our use, and that the mere presence in the dictionary of a word like ‘living’ does not mean it necessarily has to refer to something definite in the real world. (p. 18)
This may have been how the first living cells appeared. Replicators began not merely to exist, but to construct for themselves containers, vehicles for their continued existence. The replicators that survived were the ones that built survival machines for themselves to live in. (p. 19)
In the eye colour example just given, the person would actually have brown eyes: the instructions for making blue eyes would be ignored in the building of the body, though this does not stop them being passed on to future generations. A gene that is ignored in this way is called recessive. The opposite of a recessive gene is a dominant gene. The gene for brown eyes is dominant to the gene for blue eyes. A person has blue eyes only if both copies of the relevant page are unanimous in recommending blue eyes. (p. 25)
When two genes, like the brown eye and the blue eye gene, are rivals for the same slot on a chromosome, they are called alleles of each other. For our purposes, the word allele is synonymous with rival. (p. 26)
I have described the normal division of a cell into two new cells, each one receiving a complete copy of all 46 chromosomes. This normal cell division is called mitosis. But there is another kind of cell division called meiosis. This occurs only in the production of the sex cells; the sperms or eggs. Sperms and eggs are unique among our cells in that, instead of containing 46 chromosomes, they contain only 23. (p. 26)
The process of swapping bits of chromosome is called crossing over. (p. 27)
A gene is defined as any portion of chromosomal material that potentially lasts for enough generations to serve as a unit of natural selection. (p. 28)
If we wish, we can define a single gene as a sequence of nucleotide letters lying between a START and an END symbol, and coding for one protein chain. The word cistron has been used for a unit defined in this way, and some people use the word gene interchangeably with cistron. (p. 28)
The chance coming together, through crossing-over, of previously existing sub-units is the usual way for a new genetic unit to be formed. Another way—of great evolutionary importance even though it is rare—is called point mutation. A point mutation is an error corresponding to a single misprinted letter in a book. It is rare, but clearly the longer a genetic unit is, the more likely it is to be altered by a mutation somewhere along its length. (p. 31)
The genes are not destroyed by crossing-over, they merely change partners and march on. Of course they march on. That is their business. They are the replicators and we are their survival machines. When we have served our purpose we are cast aside. But genes are denizens of geological time: genes are forever. (p. 35)
Conversely, what are the properties that instantly mark a gene out as a ‘bad’, short-lived one? There might be several such universal properties, but there is one that is particularly relevant to this book: at the gene level, altruism must be bad and selfishness good. This follows inexorably from our definitions of altruism and selfishness. 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. (p. 36)
The true ‘purpose’ of DNA is to survive, no more and no less. The simplest way to explain the surplus DNA is to suppose that it is a parasite, or at best a harmless but useless passenger, hitching a ride in the survival machines created by the other DNA. (p. 45)
With reservations, the gene pool plays the same role for the modern replicators as the primeval soup did for the original ones. Sex and chromosomal crossing-over have the effect of preserving the liquidity of the modern equivalent of the soup. Because of sex and crossing-over the gene pool is kept well stirred, and the genes partially shuffled. Evolution is the process by which some genes become more numerous and others less numerous in the gene pool. (p. 45)
As far as the gene is concerned, the gene pool is just the new sort of soup where it makes its living. All that has changed is that nowadays it makes its living by cooperating with successive groups of companions drawn from the gene pool in building one mortal survival machine after another. (p. 45)
It seems that some people, educationally over-endowed with the tools of philosophy, cannot resist poking in their scholarly apparatus where it isn’t helpful. I am reminded of P. B. Medawar’s remark about the attractions of ‘philosophy-fiction’ to ‘a large population of people, often with well-developed literary and scholarly tastes, who have been educated far beyond their capacity to undertake analytical thought’. (p. 278)
If simulation is such a good idea, we might expect that survival machines would have discovered it first. After all, they invented many of the other techniques of human engineering long before we came on the scene: the focusing lens and the parabolic reflector, frequency analysis of sound waves, servo-control, sonar, buffer storage of incoming information, and countless others with long names, whose details don’t matter. What about 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. You may see them vividly in your mind’s eye, or you may see and manipulate stylized abstractions of them. In either case it is unlikely that somewhere laid out in your brain is an actual spatial model of the events you are imagining. But, just as in the computer, the details of how your brain represents its model of the world are less important than the fact that it is able to use it to predict possible events. 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. (p. 58)
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. (p. 59)
It was this macabre habit, in the related Ichneumon wasps, that provoked Darwin to write: ‘I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of Caterpillars . . .” He might as well have used the example of a French chef boiling lobsters alive to preserve the flavour. (p. 283)
The general conclusions which are important are that ESS is will tend to evolve, that an ESS is not the same as the optimum that could be achieved by a group conspiracy, and that common sense can be misleading. (p. 75)
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. (p. 69)
Similarly, the fact that genes are selected for mutual compatibility does not necessarily mean we have to think of groups of genes as being selected as units, as they were in the case of the butterflies. Selection at the low level of the single gene can give the impression of selection at some higher level. (p. 85)
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. (p. 86)
As a first approximation I said that what makes a gene good is the ability to build efficient survival machines—bodies. We must now amend that statement. The gene pool will become an evolutionarily stable set of genes, defined as a gene pool that cannot be invaded by any new gene. Most new genes that arise, either by mutation or reassortment or immigration, are quickly penalized by natural selection: the evolutionarily stable set is restored. Occasionally a new gene does succeed in invading the set: it succeeds in spreading through the gene pool. There is a transitional period of instability, terminating in a new evolutionarily stable set—a little bit of evolution has occurred. (p. 86)
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. (p. 96)
It is hard to believe that this simple truth is not understood by those leaders who forbid their followers to use effective contraceptive methods. They express a preference for ‘natural’ methods of population limitation, and a natural method is exactly what they are going to get. It is called starvation. (p. 111)
According to Lack, therefore, individuals regulate their clutch size for reasons that are anything but altruistic. They are not practising birth-control in order to avoid over-exploiting the group’s resources. They are practising birth-control in order to maximize the number of surviving children they actually have, an aim which is the very opposite of that which we normally associate with birth-control. (p. 116)
Contraception is sometimes attacked as ‘unnatural’. So it is, very unnatural. The trouble is, so is the welfare state. (p. 117)
Individual humans who have more children than they are capable of rearing are probably too ignorant in most cases to be accused of conscious malevolent exploitation. Powerful institutions and leaders who deliberately encourage them to do so seem to me less free from suspicion. (p. 118)
Our conclusion from this chapter is that individual parents practise family planning, but in the sense that they optimize their birth-rates rather than restrict them for public good. They try to maximize the number of surviving children that they have, and this means having neither too many babies nor too few. Genes that make an individual have too many babies tend not to persist in the gene pool, because children containing such genes tend not to survive to adulthood. (p. 122)
The phrase ‘the child should cheat’ means that genes that tend to make children cheat have an advantage in the gene pool. If there is a human moral to be drawn, it is that we must teach our children altruism, for we cannot expect it to be part of their biological nature. (p. 139)
Since each sperm is so tiny, a male can afford to make many millions of them every day. This means he is potentially able to beget a very large number of children in a very short period of time, using different females. This is only possible because each new embryo is endowed with adequate food by the mother in each case. This therefore places a limit on the number of children a female can have, but the number of children a male can have is virtually unlimited. Female exploitation begins here. (p. 142)
But the selection pressure to lock out exploiters would have been weaker than the pressure on exploiters to duck under the barrier: the exploiters had more to lose, and they therefore won the evolutionary battle. The honest ones became eggs, and the exploiters became sperms. (p. 143)
Males, then, seem to be pretty worthless fellows, and on simple ‘good of the species’ grounds, we might expect that males would become less numerous than females. (p. 143)
The selfish gene theory, on the other hand, has no trouble in explaining the fact that the numbers of males and females tend to be equal, even when the males who actually reproduce may be a small fraction of the total number. (p. 143)
Since she starts by investing more than the male, in the form of her large, food-rich egg, a mother is already at the moment of conception ‘committed’ to each child more deeply than the father is. She stands to lose more if the child dies than the father does. (p. 146)
More to the point, she would have to invest more than the father in the future in order to bring a new substitute child up to the same level of development. If she tried the tactic of leaving the father holding the baby, while she went off with another male, the father might, at relatively small cost to himself, retaliate by abandoning the baby too. (p. 146)
Any male who is not patient enough to wait until the female eventually consents to copulate is not likely to be a good bet as a faithful husband. By insisting on a long engagement period, a female weeds out casual suitors, and only finally copulates with a male who has proved his qualities of fidelity and perseverance in advance. (p. 149)
As we have already seen, a long engagement can also benefit a male where there is a danger of his being duped into caring for another male’s child. (p. 149)
Maynard Smith explores these historical networks in a brief survey of mating patterns throughout the animal kingdom, ending with the memorable rhetorical question: ‘Why don’t male mammals lactate?’ (p. 302)
Any male who can pass himself off as a good loyal domestic type, but who in reality is concealing a strong tendency towards desertion and unfaithfulness, could have a great advantage. As long as his deserted former wives have any chance of bringing up some of the children, the philanderer stands to pass on more genes than a rival male who is an honest husband and father. Genes for effective deception by males will tend to be favoured in the gene pool. (p. 154)
Natural selection, by sharpening up the ability of each partner to detect dishonesty in the other, has kept large-scale deceit down to a fairly low level. Males have more to gain from dishonesty than females, and we must expect that, even in those species where males show considerable parental altruism, they will usually tend to do a bit less work than the females, and to be a bit more ready to abscond. (p. 155)
Now comes the part of Zahavi’s theory that really sticks in the throat. He suggests that the tails of birds of paradise and peacocks, the huge antlers of deer, and the other sexually-selected features which have always seemed paradoxical because they appear to be handicaps to their possessors, evolve precisely because they are handicaps. A male bird with a long and cumbersome tail is showing off to females that he is such a strong he-man that he can survive in spite of his tail. Think of a woman watching two men run a race. If both arrive at the finishing post at the same time, but one has deliberately encumbered himself with a sack of coal on his back, the women will naturally draw the conclusion that the man with the burden is really the faster runner. (p. 159)
Eggs are a relatively valuable resource, and therefore a female does not need to be so sexually attractive as a male does in order to ensure that her eggs are fertilized. A male is perfectly capable of siring all the children born to a large population of females. Even if a male has a short life because his gaudy tail attracts predators, or gets tangled in the bushes, he may have fathered a very large number of children before he dies. An unattractive or drab male may live even as long as a female, but he has few children, and his genes are not passed on. (p. 162)
A male, on the other hand, has less to lose if he mates with a member of the wrong species, and, although he may have nothing to gain either, we should expect males to be less fussy in their choice of sexual partners. (p. 163)
What this astonishing variety suggests is that man’s way of life is largely determined by culture rather than by genes. (p. 164)
Bird alarm calls have been held up so many times as ‘awkward’ for the Darwinian theory that it has become a kind of sport to dream up explanations for them. As a result, we now have so many good explanations that it is hard to remember what all the fuss was about. (p. 169)
Suicidal self-sacrifice therefore seldom evolves. But a worker bee never bears offspring of its own. All its efforts are directed to preserving its genes by caring for relatives other than its own offspring. The death of a single sterile worker bee is no more serious to its genes than is the shedding of a leaf in autumn to the genes of a tree. (p. 172)
Ants have their own domestic animals as well as their crop plants. Aphids—greenfly and similar bugs—are highly specialized for sucking the juice out of plants. They pump the sap up out of the plants’ veins more efficiently than they subsequently digest it. The result is that they excrete a liquid that has had only some of its nutritious value extracted. Droplets of sugar-rich ‘honeydew’ pass out of the back end at a great rate, in some cases more than the insect’s own body-weight every hour. The honeydew normally rains down on to the ground—it may well have been the providential food known as ‘manna’ in the Old Testament. But ants of several species intercept it as soon as it leaves the bug. The ants ‘milk’ the aphids by stroking their hind-quarters with their feelers and legs. (p. 181)
A lichen appears superficially to be an individual plant like any other. But it is really an intimate symbiotic union between a fungus and a green alga. Neither partner could live without the other. (p. 181)
Recently it has been plausibly argued that mitochondria are, in origin, symbiotic bacteria who joined forces with our type of cell very early in evolution. Similar suggestions have been made for other small bodies within our cells. (p. 182)
We are gigantic colonies of symbiotic genes. (p. 182)
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! (p. 182)
In general, associations of mutual benefit will evolve if each partner can get more out than he puts in. This is true whether we are speaking of members of the same hyena pack, or of widely distinct creatures such as ants and aphids, or bees and flowers. (p. 182)
It is even possible that man’s swollen brain, and his predisposition to reason mathematically, evolved as a mechanism of ever more devious cheating, and ever more penetrating detection of cheating in others. Money is a formal token of delayed reciprocal altruism. (p. 188)
I am an enthusiastic Darwinian, but I think Darwinism is too big a theory to be confined to the narrow context of the gene. (p. 191)
This is the law that all life evolves by the differential survival of replicating entities. (p. 191)
The first ten chapters of The Selfish Gene had concentrated exclusively on one kind of replicator, the gene. In discussing memes in the final chapter I was trying to make the case for replicators in general, and to show that genes were not the only members of that important class. Whether the milieu of human culture really does have what it takes to get a form of Darwinism going, I am not sure. But in any case that question is subsidiary to my concern. Chapter 11 will have succeeded if the reader closes the book with the feeling that DNA molecules are not the only entities that might form the basis for Darwinian evolution. (p. 322)
What is it about the idea of a god that gives it its stability and penetrance in the cultural environment? The survival value of the god meme in the meme pool results from its great psychological appeal. It provides a superficially plausible answer to deep and troubling questions about existence. It suggests that injustices in this world may be rectified in the next. The ‘everlasting arms’ hold out a cushion against our own inadequacies which, like a doctor’s placebo, is none the less effective for being imaginary. (p. 193)
The old gene-selected evolution, by making brains, provided the soup’ in which the first memes arose. Once self-copying memes had arisen, their own, much faster, kind of evolution took off. We biologists have assimilated the idea of genetic evolution so deeply that we tend to forget that it is only one of many possible kinds of evolution. (p. 194)
The memes are being passed on to you in altered form. This looks quite unlike the particulate, all-or-none quality of gene transmission. It looks as though meme transmission is subject to continuous mutation, and also to blending. (p. 195)
Each individual has his own way of interpreting Darwin’s ideas. He probably learned them not from Darwin’s own writings, but from more recent authors. Much of what Darwin said is, in detail, wrong. Darwin if he read this book would scarcely recognize his own original theory in it, though I hope he would like the way I put it. Yet, in spite of all this, there is something, some essence of Darwinism, which is present in the head of every individual who understands the theory. (p. 195)
The human brain, and the body that it controls, cannot do more than one or a few things at once. If a meme is to dominate the attention of a human brain, it must do so at the expense of ‘rival’ memes. (p. 197)
Other commodities for which memes compete are radio and television time, billboard space, newspaper column-inches, and library shelf-space. (p. 197)
The human brain, and the body that it controls, cannot do more than one or a few things at once. If a meme is to dominate the attention of a human brain, it must do so at the expense of ‘rival’ memes. Other commodities for which memes compete are radio and television time, billboard space, newspaper column-inches, and library shelf-space. (p. 197)
Suppose, for the sake of argument, it happened to be the case that marriage weakened the power of a priest to influence his flock, say because it occupied a large proportion of his time and attention. This has, indeed, been advanced as an official reason for the enforcement of celibacy among priests. If this were the case, it would follow that the meme for celibacy could have greater survival value than the meme for marriage. Of course, exactly the opposite would be true for A gene for celibacy. If a priest is a survival machine for memes, celibacy is a useful attribute to build into him. Celibacy is just a minor partner in a large complex of mutually-assisting religious memes. (p. 198)
Selection favours memes that exploit their cultural environment to their own advantage. This cultural environment consists of other memes which are also being selected. The meme pool therefore comes to have the attributes of an evolutionarily stable set, which new memes find it hard to invade. (p. 199)
When we die there are two things we can leave behind us: genes and memes. (p. 199)
Elizabeth II is a direct descendant of William the Conqueror. Yet it is quite probable that she bears not a single one of the old king’s genes. We should not seek immortality in reproduction. (p. 199)
Socrates may or may not have a gene or two alive in the world today, as G. C. Williams has remarked, but who cares? The memecomplexes of Socrates, Leonardo, Copernicus and Marconi are still going strong. (p. 199)
We have the power to defy the selfish genes of our birth and, if necessary, the selfish memes of our indoctrination. (p. 200)
So, we have identified two characteristics of winning strategies: niceness and forgivingness. This almost utopian-sounding conclusion—that niceness and forgivingness pay—came as a surprise to many of the experts, who had tried to be too cunning by submitting subtly nasty strategies; while even those who had submitted nice strategies had not dared anything so forgiving as Tit for Two Tats. (p. 213)
But once again nastiness didn’t pay. Once again, Tit for Tat, submitted by Anatol Rapoport, was the winner, and it scored a massive 96 per cent of the benchmark score. (p. 213)
Sadly, however, when psychologists set up games of Iterated Prisoner’s Dilemma between real humans, nearly all players succumb to envy and therefore do relatively poorly in terms of money. It seems that many people, perhaps without even thinking about it, would rather do down the other player than cooperate with the other player to do down the banker. (p. 220)
Many situations in real life are, as a matter of fact, equivalent to nonzero sum games. Nature often plays the role of ‘banker’, and individuals can therefore benefit from one another’s success. They do not have to do down rivals in order to benefit themselves. (p. 224)
We are, of course, entirely familiar with the idea of unconscious strategists, or at least of strategists whose consciousness, if any, is irrelevant. Unconscious strategists abound in the pages of this book. Axelrod’s programs are an exellent model for the way we, throughout the book, have been thinking of animals and plants, and indeed of genes. (p. 228)
Nobody would ever claim that a bacterium was a conscious strategist, yet bacterial parasites are probably engaged in ceaseless games of Prisoner’s Dilemma with their hosts and there is no reason why we should not attribute Axelrodian adjectives—forgiving, non-envious, and so on—to their strategies. (p. 229)
Needless to say, there is no suggestion that the bacteria work all this out in their nasty little heads! Selection on generations of bacteria has presumably built into them an unconscious rule of thumb which works by purely biochemical means. (p. 229)
What the Darwinian corpus gives us is not detailed expectations about particular organisms. It gives us something subtler and more valuable: understanding of principle. (p. 233)
All genes look alike, just as all recording tapes look alike. The important differences between genes emerge only in their effects. This usually means effects on the processes of embryonic development and hence on bodily form and behaviour. Successful genes are genes that, in the environment influenced by all the other genes in a shared embryo, have beneficial effects on that embryo. Beneficial means that they make the embryo likely to develop into a successful adult, an adult likely to reproduce and pass those very same genes on to future generations. (p. 235)
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. (p. 235)
What if a mutant gene arose that just happened to have an effect, not upon something obvious like eye colour or curliness of hair, but upon meiosis itself? Suppose it happened to bias meiosis in such a way that it, the mutant gene itself, was more likely than its allelic partner to end up in the egg. There are such genes and they are called segregation distorters. They have a diabolical simplicity. When a segregation distorter arises by mutation, it will spread inexorably through the population at the expense of its allele. It is this that is known as meiotic drive. (p. 236)
The phenotypic effects of a gene are normally seen as all the effects that it has on the body in which it sits. This is the conventional definition. But we shall now see that the phenotypic effects of a gene need to be thought of as all the effects that it has on the world. (p. 238)
Just imagine the banner headlines if a marine biologist were to discover a species of dolphin that wove large, intricately meshed fishing nets, twenty dolphin-lengths in diameter! Yet we take a spider web for granted, as a nuisance in the house rather than as one of the wonders of the world. (p. 239)
All that genes can really influence directly is protein synthesis. A gene’s influence upon a nervous system, or, for that matter, upon the colour of an eye or the wrinkliness of a pea, is always indirect. (p. 240)
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. If any genes of an organism, such as a human, could discover a way of spreading themselves that did not depend on the conventional sperm or egg route, they would take it and be less cooperative. (p. 245)
We’ve already seen examples of genes that bias meiosis in their own favour. Perhaps there are also genes that have broken out of the sperm/egg ‘proper channels’ altogether and pioneered a sideways route. (p. 245)
We are losing cells continually from our skin; much of the dust in our houses consists of our sloughed-off cells. We must be breathing in one another’s cells all the time. If you draw your fingernail across the inside of your mouth it will come away with hundreds of living cells. The kisses and caresses of lovers must transfer multitudes of cells both ways. (p. 246)
Some plasmids are capable of splicing themselves seamlessly into a chromosome. So smooth is the splice that you can’t see the join: the plasmid is indistinguishable from any other part of the chromosome. The same plasmids can also cut themselves out again. This ability of DNA to cut and splice, to jump in and out of chromosomes at the drop of a hat, is one of the more exciting facts that have come to light since the first edition of this book was published. (p. 246)
Or perhaps, as I speculated on page 182, all ‘own’ chromosomal genes should be regarded as mutually parasitic on one another. (p. 247)
An orthodox chromosomal gene and a venereally transmitted virus agree with one another in wanting their host to copulate. It is an intriguing thought that both would want the host to be sexually attractive. More, an orthodox chromosomal gene and a virus that is transmitted inside the host’s egg would agree in wanting the host to succeed not just in its courtship but in every detailed aspect of its life, down to being a loyal, doting parent and even grandparent. (p. 247)
Beaver lakes are extended phenotypic effects of beaver genes, and they can extend over several hundreds of yards. A long reach indeed! (p. 248)
The point is summed up in one of Aesop’s fables: ‘The rabbit runs faster than the fox, because the rabbit is running for his life while the fox is only running for his dinner.’ (p. 250)
We showed that the very idea of an ‘own’ body was a loaded assumption. In one sense, all the genes in a body are ‘parasitic’ genes, whether we like to call them the body’s ‘own’ genes or not. (p. 250)
For ants, matricide is an act of special genetic madness and formidable indeed must be the drug that drives them to it. In the world of the extended phenotype, ask not how an animal’s behaviour benefits its genes; ask instead whose genes it is benefiting. (p. 252)
It doesn’t matter in which body a gene physically sits. The target of its manipulation may be the same body or a different one. Natural selection favours those genes that manipulate the world to ensure their own propagation. (p. 253)
This leads to what I have called the Central Theorem of the Extended Phenotype: 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. (p. 253)
The vehicles that we know best are individual bodies like our own. A body, then, is not a replicator; it is a vehicle. I must emphasize this, since the point has been misunderstood. Vehicles don’t replicate themselves; they work to propagate their replicators. (p. 254)
Nowadays this cooperation between genes goes on within cells. It must have started as rudimentary cooperation between self-replicating molecules in the primeval soup (or whatever primeval medium there was). Cell walls perhaps arose as a device to keep useful chemicals together and stop them leaking away. (p. 258)
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. (p. 258)
The only difference between the two species is that splurgeweed reproduces by hiving off chunks of itself consisting of indeterminate numbers of cells, while bottle-wrack reproduces by hiving off chunks of itself always consisting of single cells. (p. 259)
There is only a limited amount of change that can be achieved by direct transformation in the ‘swords to ploughshares’ manner. Really radical change can be achieved only by going ‘back to the drawing board’, throwing away the previous design and starting afresh. (p. 260)
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. (p. 261)
One important thing about a ‘bottlenecked’ life cycle is that it makes possible the equivalent of going back to the drawing board. (p. 261)
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. In the same way, the endlessly repeated growth rhythms imposed by a bottlenecked life cycle will—it seems almost inevitable—be used to order and structure embryology. (p. 262)
We can think of an individual organism as a ‘group’ of cells. A form of group selection can be made to work, provided some means can be found for increasing the ratio of between-group variation to within-group variation. Bottle-wrack’s reproductive habit has exactly the effect of increasing this ratio; splurge-weed’s habit has just the opposite effect. (p. 263)
Two other ideas that have dominated this chapter. Firstly the idea that parasites will cooperate with hosts to the extent that their genes pass to the next generation in the same reproductive cells as the genes of the hosts—squeezing through the same bottleneck. And secondly the idea that the cells of a sexually reproducing body cooperate with each other only because meiosis is scrupulously fair. (p. 263)