The Selfish Gene (1989 edition)

By Richard Dawkins

Chapter-by-Chapter Anaylsis, Part I

Why are people?

In his first chapter, Dawkins sets the scene for his book. He makes a clear statement of the purpose of the book, which is to argue that "the best way to look at evolution is in terms of selection occurring at the lowest level of all", by which he means the gene. He claims that other authors, including Lorenz, Ardrey and Eibl-Eibesfeldt, totally misunderstood how evolution works because they assumed that the important thing in evolution is the good of the species (or group) rather than the individual (or gene).

He illustrates how this group selection theory cannot be correct by considering a particular scenario in a group. The group selection theory postulates that individual members of a group would be prepared to sacrifice themselves for the welfare of the group and that these groups may be less likely to go extinct than a rival group, whose individual members put their own selfish interests first. Therefore the world would become populated mainly by groups consisting of self-sacrificing individuals. However, Dawkins argues that even in this group of self-sacrificers, there will almost certainly be a few individuals who refuse to make the sacrifice. Even if there is only one selfish rebel, he will benefit from exploiting the selfless individuals in the group and therefore have a greater chance of surviving and having children than them. Each of his children will tend to inherit his selfish traits and consequently go on to be successful in reproduction as well. After several generations of this natural selection, the group that was originally dominated by self-sacrificers will now be over-run by selfish individuals and will be indistinguishable from the selfish group. Therefore, he argues that groups consisting of self-sacrificers would eventually die out, thus demonstrating that the group selection theory fails to work.

Dawkins proposes that the fundamental unit of selection is not the species, nor the group, nor even strictly speaking the individual, but is in fact the gene - the unit of heredity. He argues that humans, and all other animals, are machines created by their genes. These genes have survived for millions of years in a highly competitive world and in order to do this, they have developed certain qualities - one of which is ruthless selfishness. Dawkins argues that this gene selfishness enables the genes to propagate themselves into the next generation and ultimately ensure their survival. However, he goes on to point out that, "there are special circumstances in which a gene can achieve its own selfish goals best by fostering a limited form of altruism at the level of individual animals". He defines altruism as acting "to increase another such entity's welfare at the expense of its own" or more specifically for the purpose of this book, as acting to increase another individual's lifetime number of offspring at a cost to one's own survival and reproduction. Selfish behaviour has exactly the opposite effect. He points out that "an apparently altruistic act is one that looks, superficially, as if it must tend to make the altruist more likely (however slightly) to die, and the recipient more likely to survive" but in fact "it often turns out on closer inspection that acts of apparent altruism are really selfishness in disguise". Therefore, he sums up that the book will show how both individual selfishness and individual altruism are explained by the fundamental law that he calls gene selfishness.

He goes on to describe some examples of "apparently" altruistic and "apparently" selfish behaviour. One example of apparently altruistic behaviour that he quotes is the stinging behaviour of worker bees, which is a very effective defence against the honey robbers but is also fatal to the worker bee. The example of apparently selfish behaviour he uses is that of the macabre cannibalism of female praying mantises who, if they get the chance, will eat the male during mating, the benefit being a good meal!

The replicators

Dawkins explains how natural selection can explain the beginning of the universe. He claims the prerequisites for life on earth were:

  1. The existence of certain kinds of atoms
  2. The presence of energy, ultimately from the sun

Atoms did not "exist" in the sense that they had conscious experience of "life", they just were: solitary units. The excitation of these building block atoms, caused by exposure to an energy source (that of the sun or perhaps even lightening) presumably lead to the atoms adopting their simplest collective form: that of invariant patterns or stable structures. Something is considered stable if it is significantly permanent or common enough to deserve a name. It is assumed that these stable structures took the form of chains and that single free floating building block atoms had a natural affinity towards building block atoms of the same kind. Thus attraction and coupling of "same-kind" building blocks lead to the development of larger, more complex stable structures.

Perhaps due to chance (or due to the larger molecules becoming unstable), divisions began to occur. Splits occurred in such a way that one molecule became two individual chains: each chain being an exact copy of the other. In this way, chains become replicators. Replication occurred and continued to occur because it was stable. The stable survived and replicated while the unstable failed to continue to exist because their instability prevented them from replicating. Thus, Dawkins speculated that the earliest form of natural selection was simply a selection of stable forms and the rejection of unstable ones.

The survival of molecules depended on their successfulness at duplicating themselves. Molecules that faithfully produced replicas of themselves ensured the survival of that molecule "type" into the next generation. Occasionally, rare copying errors which were stable occurred that increased the diversity within the "replicator pool".

Dawkins views stability, and hence success, as having 3 constituents:

  1. Longevity: molecules that survived long enough to reproduce must be successful
  2. Fecundity: molecules that replicate rapidly tend to become more numerous and hence have a larger proportion of replicas entering the next generation
  3. Copying Fidelity: molecules that copy themselves accurately guarantee their own molecular structure's survival into the next generation

The success of the replicators lead to increasing demand on the smaller solitary building blocks, which in turn led to competition. Replicators were selected simply because they were more successful and hence survived to replicate again. This struggle for existence among the replicator varieties led to a process of improvement that was cumulative. Ways of increasing stability and decreasing rivals' stability became more elaborate and efficient. Some may have discovered how to break up molecules of rival varieties chemically, others perhaps learnt how to protect themselves, either chemically or by building a physical wall of protein around themselves. These were the first survival machines, which also became more and more developed and competition became stiffer. Eventually these survival machines evolved into the "survival machines" present today, namely ourselves and all other animals, plants, bacteria and viruses, and the replicators now go by the name of "genes".

Immortal coils

"Different sorts of survival machine appear very varied on the outside and in their internal organs… Yet in their fundamental chemistry they are rather uniform, and, in particular, the replicators that they bear, the genes, are basically the same kind of molecules in all of us - from bacteria to elephants. 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."

In order to summarise this chapter, it is best to divide it into two different sections, according to its title. The first part of the chapter is concerned with the "coils" of DNA, their structure, and their functions. The second part of the chapter is concerned with the "immortality" of these coils and how this immortality labels them as the obvious unit of natural selection. I will discuss these two topics separately.

A DNA molecule is a long chain of building blocks - small molecules called nucleotides - arranged in an alpha helical formation (a pair of nucleotide chains twisted together in an elegant spiral). There are four different kinds of nucleotides, whose names are shortened to A, T, C and G. These are the same in all animals and plants differing simply by the order in which they are strung together.

Our DNA lives inside our bodies, distributed among the cells so that, with a few exceptions, each cell contains a complete copy of that body's DNA. The DNA is present in each cell in the form of chromosomes. These are visible under a microscope as long threads. Each chromosome consists of two identical chromatids which are held together at a narrow region called the centromere. Each chromatid contains one DNA molecule.

Each DNA molecule is made up of a series of genes, where Dawkins defines a gene as "any portion of chromosomal material that potentially lasts for enough generations to serve as a unit of natural selection". This may be confused with a cistron, which is a short portion of the DNA molecule made up of the four- letter nucleotide alphabet coding for one protein. And in some cases the word cistron can be used interchangeably with the word gene, but there are some cases where the cistron cannot fit Dawkins definition of a gene in the sense that they can last for several generations because cistrons can be broken up by the process of crossing over which will be discussed later. Each gene for a particular characteristic can be said to occupy the same position on a chromosome, called the locus. In the gene pool (all the genes of the population in general available) there are several different possible genes for each locus, which are called alleles. They can be considered rivals for same slot on one chromosome.

The number of chromosomes an organism has is characteristic of the species. For example, in humans, there are 46 and in fruit flies there are 8. These chromosomes consist of matching pairs, so humans in fact have two sets of 23 chromosomes, one set coming from the mother and the other from the father. Each chromosome in the pair can be regarded as direct alternatives to the other, with the gene "for" eye colour occupying the same loci on both chromosomes. These genes may be the same (i.e. both coding "for" brown eyes), and therefore considered homozygous, or they may be different, and therefore called heterozygous, depending on the parents. Therefore, each cell contains 23 pairs of chromosomes in its nucleus which make up a complete copy of the bodies DNA.

DNA molecules do two important things: replicate (make copies of themselves) and indirectly supervises the manufacture of the body's proteins. The former is how we develop from a single cell at conception to the thousand million million cells that make up our body as an adult. The process that takes place is called mitosis. This is when the DNA replicates before the cell divides into two so that each daughter cell receives the same number and type of chromosomes as the original. DNA also holds a central role in protein synthesis because the coded message of the DNA, written in the four-letter nucleotide alphabet, is translated into the alphabet of amino acids which then form a chain to produce protein molecules.

The cells undergo another kind of cell division, other than mitosis, called meiosis. This occurs only in the production of the sex cells and results in halving the number of chromosomes rather than straight replication. This is so that when the two sex cells fuse at conception, the new egg only receives the norm 46 chromosomes and does not double up every generation. Each sex cell contains one of each pair of chromosomes, but not in exactly the same form as they exist in the parents because during the manufacturing of the sex cells, chunks from one chromosome are detached and swapped with the corresponding chunk from its paired chromosome. Therefore, each chromosome in a sperm or egg would be a patchwork of maternal and paternal genes. This process of swapping bits is called crossing over and it promotes variation because it produces new combinations of genes in the new individual. Other ways of achieving genetic variation is through point mutations (when an error occurs that is analogous to a single misprinted letter in a book) and inversion (when a piece of chromosome detaches itself at both ends, turns head over heels, and reattaches itself in the inverted position).

Therefore, before moving on to the second half of the chapter, Dawkins emphasises what he means when he uses the term "gene". He is using the word "gene" to describe a portion of a chromosome that is small enough to survive processes such as crossing over and last for enough generations to serve as a unit of natural selection. He writes; "The more likely a length of chromosome is to be split by crossing- over, or altered by mutations of various kinds, the less it qualifies to be called a gene in the sense in which I am using the term". He points out that a cistron may qualify as a gene under this definition, but then so may larger units. For example, a dozen cistrons may be so close to each other on a chromosome that for our purposes they constitute a single long-lived genetic unit.

In the second half of the chapter, Dawkins argues that it is the genes that are the immortals. He says: "We, the individual survival machines in the world, can expect to live a few more decades. But the genes in the world have an expectation of life that must be measured not in decades but in thousands and millions of years." He argues that this is why the individual cannot be considered as the unit of natural selection. They are just unique temporary entities that are only present in one "human" lifetime and it is not possible to get evolution by selecting between entities when there is only one copy of each entity. But the genes survive from one generation to the next, albeit in different bodies and different environments but they themselves are unchanged.

However, one can really only talk of the gene's potential immortality. A gene could live for millions of years, existing in the form of many duplicate copies, but many new genes do not make it past their first generation. Those that do survive are partly lucky (because they have not found themselves in the same body as a lethal gene), but mainly because they have what it takes, i.e. they are good at making survival machines. This means they "build" themselves (through embryonic development) bodies that are equipped with as many beneficial characteristics for their environment as possible, whether this is long legs for running, or sharp teeth for eating meat. More universal properties that are particularly relevant for this book are; altruism is bad and selfishness is good. Dawkins reiterates this idea when he says: "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, tend to survive. The gene is the basic unit of selfishness."

However, having said this, Dawkins points out that the effect of each individual gene is largely dependent on the other genes in the same body, and therefore the success of the gene will be affected by it's compatibility with them. He illustrates this idea with the analogy of the Oxford-Cambridge boat race. One oarsman cannot win the race on his own; he needs eight colleagues. Rowing the boat is a co-operative venture but invariably some men are better at rowing than the others. Selection for the oarsmen depends on the individuals rowing expertise and their compatibility with the other eight members of the boat. Dawkins uses the oarsmen to represent the genes and the boat to represent the chromosome. The gene for each seat in the boat is chosen from the rival alleles, and the gene is selected for its successful survival machine and because it can cooperate well with most of the other genes.