The Selfish Gene

Dawkins explains the origins of life. From the physical universe, common molecules evolved into complex biological organisms, following Darwin’s theory of evolution. Dawkins maintains that stable entities persist: “A stable thing is a collection of atoms that is permanent enough or common enough to deserve a name” (16). From simple atoms combining into molecules in stars, to water forming shapes on Earth or in space, to mountains forming, matter forms stable shapes.

Biological organisms tend to include more complex molecules, such as proteins. Proteins consist of chains of smaller molecules, called amino acids. Hundreds of amino acids fold into a precise protein form. Trillions of proteins form each second in a single person, without failure.

Before biological organisms, physical and chemical processes evolved molecules from simpler to more complex forms. Without any planning, atoms take on their stable forms: molecules. Randomly shaking atoms can yield complex molecules, but to form a human would require too much time. Darwin’s theory of evolution explains human origins.

Dawkins writes that before biological organisms developed, Earth probably contained plentiful water, carbon dioxide, methane, and ammonia, which also exist on other planets. Chemists have replicated the conditions of early Earth and applied the equivalent of lightning. This results in a “soup” containing amino acids. A comparable process produced early life on

Earth. In the seas, the “primeval soup” (18) formed into clumps, growing into yet more complex molecules. The molecules traveled freely, before bacteria evolved that could break them down:

At some point a particularly remarkable molecule was formed by accident. We will call it the Replicator. It may not necessarily have been the biggest or the most complex molecule around, but it had the extraordinary property of being able to create copies of itself (18).

As unlikely as the formation of a self-replicating molecule would be in a human lifespan, over hundreds of millions of years it becomes quite likely. The replicator acts as a machine to assemble building blocks. Numerous building blocks filled the “soup” and attracted each other. When any building blocks approach the replicator, they automatically follow the template of the replicator. Therefore, their stable shape copies the replicator, they become replicators themselves, and they make yet more copies.

Biological replication functions like crystal formation. If instead of like attracting like building blocks, they attract opposite kinds, then the replicators form negative copies, or inverses. DNA, comparable to the first replicators, uses this flipping as its stable form. From a fairly random soup of molecules, the replicators rapidly took over the seas. These replicators used up the building block molecules.

Replication occurs imperfectly, as with any copying process. Dawkins compares written texts, which when copied by hand include numerous mistakes, and even when copied by modern methods contain errors. The more generations of copies, the more mistakes. Dawkins writes that the mistranslation of “young woman” into “virgin” yielded the biblical prophecy: “Behold a virgin shall conceive and bear a son” (16).

Individual copying errors generally cause deterioration. Replication errors over evolutionary time, however, enabled the variation of life. Instead of identical replicas, different breeds varied in their relative levels of stability. The more stable replicators lived longer and made more copies. Therefore, they became predominant. The faster-breeding replicators rapidly outbred the slower ones, and accurate replicators produced more children and descendants than inaccurate replicators.

Evolution selected replicators for “longevity,” “fecundity,” and “accuracy” (17). While some replication errors are necessary for evolution, the tendency generally involves minimizing errors:

Evolutionary trends toward these three kinds of stability took place in the following sense: if you had sampled the soup at two different times, the later sample would have contained a higher proportion of varieties with high longevity/fecundity/copying-fidelity. This is essentially what a biologist means by evolution when he is speaking of living creatures, and the mechanism is the same-natural selection (20).

Dawkins writes that the replicators could be considered living. Regardless of terminology, they evolve comparably to plants and animals. Because of finite resources, such as space and building blocks, the original “soup” could only support limited numbers of replicators. Therefore, competition determined which varieties survived.

Some replicators may have formed so as to consume others. Other replicators formed chemical and physical defenses, possibly forming the first biological cells. Replicators built functional containers—machines—enabling greater survival. Competition drove the cumulative improvement of these survival machines. Billions of years later, the replicators survive. Instead of living freely in the ocean, they transport themselves in large robots, or people:

They are in you and in me; they created us, body and mind; and their preservation is the ultimate rationale for our existence. They have come a long way, those replicators. Now they go by the name of genes, and we are their survival machines (22).

The machines to protect replicators include not only humans, but all animals, plants, bacteria, and viruses. Countless “survival machines” (22) of different types populate the planet. Despite the vast differences in form among various machines, such as an octopus or a mouse or a tree, they carry the same basic replicators (genes). The DNA takes on different forms according to its roles: “A monkey is a machine that preserves genes up trees, a fish is a machine that preserves genes in the water; there is even a small worm that preserves genes in German beer mats. DNA works in mysterious ways” (22).

Dawkins notes that genetic DNA may have changed somewhat from the first replicators. DNA may even have destroyed a predecessor or evolved from clay crystals. At any rate, only modern DNA survives as a replicator today. DNA molecules are chains of building blocks called nucleotides. This compares with proteins composed of amino acid building blocks. DNA forms into invisibly small double helix shapes, “the immortal coil” (22).

The coils of DNA contain four types of nucleotide, abbreviated C, A, T, G. One of these building blocks is the same regardless of the organism it inhabits. However, the sequence of nucleotides differs among organisms. DNA resides in cells throughout the body. Almost every one of the quadrillion cells in a human contains a complete copy of the DNA:

This DNA can be regarded as a set of instructions for how to make a body, written in the A, T, C, G alphabet of the nucleotides. It is as though, in every room of a gigantic building, there was a book-case containing the architect's plans for the entire building. The 'book-case' in a cell is called the nucleus. The architect's plans run to 46 volumes in man—the number is different in other species. The 'volumes' are called chromosomes. They are visible under a microscope as long threads, and the genes are strung out along them in order. It is not easy, indeed it may not even be meaningful, to decide where one gene ends and the next one begins (23).

Dawkins reminds that instead of an architect, natural selection crafts the DNA. A person starts life as a single cell, containing the master plan. The cell repeatedly divides into two copies, each containing complete DNA. In addition to replication, DNA constructs the body by instructing the sequence of converting amino acids into proteins. The proteins provide the structure and function of the entire body. Characteristics that a body acquires in the environment do not get transferred back into the genes: “No matter how much knowledge and wisdom you acquire during your life, not one jot will be passed on to your children by genetic means. Each new generation starts from scratch” (24).

Because the genes depend on the body they produce for their own survival, genes control their own survival rate and evolution through the bodies they produce. Natural selection continues to increase the “longevity, fecundity, and copying-fidelity” (24) of replicators. However, instead of a direct competition among replicators, the competition now takes place indirectly among their products: organisms.

The replicators themselves remain unthinking. Their resultant organisms have however developed organs, such as brains, muscles, hearts, and eyes. These organs group together numerous genes, working so closely that they blend together. One gene can have involvement in various parts of the body, and one part of the body can have involvement from various genes.

Therefore, the genes generally operate as a complex, rather than as individual genes. However, over evolutionary time, individual genes do remain stable. Through sex, genes repeatedly intermix. The genes that survive across generations develop individual identities.

The 46 chromosomes in a human come in 23 pairs. In the book-case analogy, there are 23 sets of alternative volumes, such as 5a and 5b. Half come from the mother, half from the father. While the two halves of a pair can sit at a distance, they control for the same characteristics. If both chromosomes send the same instruction, such as for brown hair, then the body follows. If the chromosomes differ, then the body could ignore a “recessive” gene or combine the two different genes.

Two rival genes, such as for brown or blonde hair, are called alleles. One allele (or page in the book-case analogy) belongs at a certain location on each chromosome (volume). At conception, one receives at each chromosome location a pair of genes, one from each parent. However, in a broader sense, the species population contains a “gene pool” consisting of all the possible genes:“The gene pool is a worthwhile abstraction because sex mixes genes up, albeit in a carefully organized way. In particular, something like the detaching and interchanging of pages and wads of pages from loose-leaf binders really does go on” (26).

The regular division of a cell into two identical copies is called “mitosis.” In another form of cell division, “meiosis,” sex cells get produced. Sperms or eggs contain 23 chromosomes instead of 46. When sperm and egg fuse, they combine to yield 46 chromosomes. In the production of a sperm, segments of each chromosome from 1 to 23 are mixed and matched from maternal and paternal origins. Each sperm contains a unique sequence over the full 23 chromosomes and likewise for eggs.

Small parts of paternal and maternal chromosomes mechanically detach themselves, and exchange places, in a process called “crossing-over” (27). Therefore, unlike in the other cells of a body, sex cells do not contain neatly divided paternal and maternal chromosomes. Genetic instructions differ from texts, at finer details than the gene-page analogy: “In a loose-leaf binder a whole page may be inserted, removed or exchanged, but not a fraction of a page. But the gene complex is just a long string of nucleotide letters, not divided into discrete pages in an obvious way at all” (27).

The CATG code does include special sequences to start and finish protein production messages. One can define a gene as the sequence between such a set, encoding the production of a single protein. This definition also has the name “cistron.” However, crossing-over can break apart cistrons:

It is as though the architect's plans were written out, not on discrete pages, but on 46 rolls of ticker tape. Cistrons are not of fixed length. The only way to tell where one cistron ends and the next begins would be to read the symbols on the tape, looking for end of message and start of message symbols. Crossing-over is represented by taking matching paternal and maternal tapes, and cutting and exchanging matching portions, regardless of what is written on them (27).

Dawkins borrows his definition of “gene” in the title of The Selfish Gene from G. C. Williams: “A gene is defined as any portion of chromosomal material that potentially lasts for enough generations to serve as a unit of natural selection. In the words of the previous chapter, a gene is a replicator with high copying-fidelity” (27).

When genes copy accurately, they yield longevity in terms of molecular structure. Longer genetic sequences are more likely to get split during meiosis (sexual cell division). Therefore, shorter genetic sequences are likely to survive longer periods of time. Cistrons (segments encoding individual proteins) take less than one percent of a chromosome, and therefore survive numerous generations of crossing-over. One chromosome lasts for one generation before being broken up during meiosis.

Smaller subunits of a chromosome survive over numerous generations before being broken apart. Very small genetic sequences have survived from before humans even existed and can survive far into the future. Because of common ancestry, genetic subunits also get shared across relatives. Therefore, any two humans, and even other species, share genetic snippets. These small genetic sequences can also get reproduced independently by chance. Generally, smaller sequences occur more commonly.

Most new sequences get made through crossing-over. Occasionally, a point mutation produces a new sequence. A point mutation refers to a copy error, equivalent to a misprinted character in a book. Longer sequences are more likely to experience point mutations because they have more coding. Other mutations involve segments detaching themselves from a chromosome, and then reattaching in different configurations.

Most sizable mutations have harmful effects. However, a few improve function. These new genetic sequences have greater likelihood of transmission. Over evolutionary time, effective sequences take shape.

Dawkins describes biological mimicry. Some butterflies taste bad to birds, and bear warning colors. Other butterfly species that birds would otherwise eat have adopted these warning colors as a defense. Mimic species often copy a single unpleasant-tasting species. In some mimic species, however, one organism will mimic a particular target species, while a different organism will mimic a different target species. Offspring mimic one or another of the target species, as any intermediate would fail and get eaten.

A gene controls the colors, patterns, and other traits of mimicry. However, a cistron (encoding a single protein) would be quite small for this task. The overall shaped sequence of coding however can control all of these traits. Dawkins refers to the genetic cluster as a “gene.”A gene, or cluster of cistrons, has alleles. In the butterfly species, the organisms that mimic one target have one set of cistrons, while the organisms that mimic another target have a different set of cistrons. The clusters generally get preserved against crossing-over, making intermediate butterflies uncommon:

The butterfly mimicry cluster is a good example. As the cistrons leave one body and enter the next, as they board sperm or egg for the journey into the next generation, they are likely to find that the little vessel contains their close neighbours of the previous voyage, old shipmates with whom they sailed on the long odyssey from the bodies of distant ancestors (30).

The genes evolve over time through the accumulation of slight variations: “To be strict, this book should be called not The Selfish Cistron nor The Selfish Chromosome, but The slightly selfish big bit of chromosome and the even more selfish little bit of chromosome” (31).Natural selection promotes entities that survive effectively. Dawkins defines the gene as the biological unit that survives effectively. Therefore, these genes get selected and become selfish: “It was the great achievement of Gregor Mendel to show that hereditary units can be treated in practice as indivisible and independent particles” (31).

In practice, even small segments like cistrons do get broken up, or forced together. The Dawkins definition of a gene more closely reflects Mendel’s hereditary ideal. Genes travel through generations, generally untouched. Darwin had thought that heredity involved blending. Mendel and Darwin did not straighten out this difference in their lifetimes. Later biologists realized that Mendel’s individual genes could explain heredity in accordance with Darwin’s evolution:

Another aspect of the particulateness of the gene is that it does not grow senile; it is no more likely to die when it is a million years old than when it is only a hundred. It leaps from body to body down the generations, manipulating body after body in its own way and for its own ends, abandoning a succession of mortal bodies before they sink in senility and death (31).

While humans live a few decades, genes live for millions and millions of years. Therefore, evolution takes place primarily at the genetic level:

In sexually reproducing species, the individual is too large and too temporary a genetic unit to qualify as a significant unit of natural selection. The group of individuals is an even larger unit. Genetically speaking, individuals and groups are like clouds in the sky or dust-storms in the desert. They are temporary aggregations or federations (32).

Populations do not remain stable over long periods of time. Instead, they blend together and transform within. As a result, populations do not get selected over evolutionary time. Individuals vary and do not have numerous copies to select among. They do not get selected over evolutionary time, similar to chromosomes, which get rapidly remixed, like individuals and populations. Genes, however, replicate accurately, across numerous copies in numerous generations. They survive, while chromosomes and individuals and populations die: “They are the replicators and we are their survival machines” (32). Genes, unlike long-lasting substances, survives as a sequence rather than in material form. Individual DNA molecules only last months, but they make accurate copies.

Dawkins considers the extremely long duration of genetic code, hundreds of millions of years, its defining property. He argues that evolutionary theory requires this understanding of the gene, because natural selection takes so much time. Natural selection requires “longevity,” “fecundity,” and “accuracy” (17). The gene is the largest entity that could have these, making it an effective replicator: “The gene is defined as a piece of chromosome which is sufficiently short for it to last, potentially, for long enough for it to function as a significant unit of natural selection” (33).

Generally, genes fit between the cistron and chromosome in scale. Most genes die out after a single generation. Some get lucky, and others have advantages that let them survive. Genes producing effective “survival machines” (22) live longer, improving their vehicles. Certain traits, such as long legs for running animals or short legs for moles, confer advantages. Generally speaking, “good genes” enable survival machines to live longer, and “bad genes” cause survival machines to have less longevity:

Can we think of any universal qualities that we would expect to find in all good (i.e. long-lived) genes? 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 (33).

Alleles compete for positions on their chromosome. Genes that improve their likelihood of survival will by definition live longer: “The gene is the basic unit of selfishness” (33). Due to the complexity of embryonic developments, genes interact with each other and the environment in often unpredictable ways. Therefore, a “gene” for a particular attribute often refers instead to a set of genes with environmental influence. Dawkins likens the process to growing wheat with nitrate fertilizer. The nitrate (or gene) alone isn’t enough to produce a plant (or leg), yet given all the other prerequisites, nitrate (or a particular gene) can enlarge a plant (or leg). Small genetic differences determine evolution.

Genes compete fiercely among alleles, for example brown versus blonde hair. Other genes contribute to the environment, having subtler effects on the competition. Each gene on its own has important characteristics, as does an oarsman on a boat. On different teams (sets of genes), and in different weather (environments), an oarsman may perform differently.

Good genes sharing the same body as bad genes get killed. However, because of having numerous copies in bodies without the bad genes, the good genes still survive better statistically. Bad genes or harmful environments often kill good genes. However, chance gets drowned out by quality over evolutionary time.

A gene that cooperates with other genes in the gene pool will perform better with the genes it encounters, surviving longer. For example, carnivores and herbivores have different gene pools. A gene for sharp teeth would fit with the carnivore but not herbivore gene pool, and therefore, improve the former but not the latter.

Dawkins reiterates that the gene, a small sequence of the chromosome capable of reproducing indefinitely, is the main unit of natural selection—not the individual or species, which die frequently. Explanations of why people die include the accumulation of genetic damage, which could particularly accumulate after the reproductive years: “No doubt some of your cousins and great-uncles died in childhood, but not a single one of your ancestors did” (36).

Dawkins speculates about how to extend human lives. A gradually increasing minimum age for childbearing could extend the point at which lethal genes get activated, which he dismisses as unpalatable. Artificially signaling the body with chemicals often found in youth could also trigger genetic extension of lifespan.

Dawkins next notes that crossing-over does not theoretically have to occur. If it did not, then chromosomes would be stable, and would take the place of genes as the basic unit of natural selection and evolution. The entire chromosome would the fit the definition of “gene” that Dawkins uses.

Many plants and some animals reproduce non-sexually. Biologists often struggle to explain mathematically why sexual reproduction makes sense from an evolutionary perspective. Dawkins notes that most attempts start from the assumption of individuals maximizing their genes, rather than genes maximizing their individuals. Sexual reproduction (and crossing-over) could benefit a single gene, which would thus survive by propagating sexually. Because sex and crossing-over do occur, the gene as Dawkins defines it represents the basic unit of natural selection.

The selfish gene perspective can also explain “junk DNA.” Much DNA does not actually produce proteins. Traditional biology struggles to explain its presence. Yet, according to the selfish gene understanding, it exists merely to survive, hitchhiking with the rest of the survival machine.

Dawkins reconciles his gene-centric view with the individual-centric view of evolution. Over the course of an individual lifetime, the person experiences the manifestations of evolution. Yet, over generations, the genes shape the machines that bear them: “The gene pool plays the same role for the modern replicators as the primeval soup did for the original ones” (39). Sex and crossing-over mix up the genes: “Evolution is the process by which some genes become more numerous and others less numerous in the gene pool” (39). In investigating the evolution of any characteristic, Dawkins stresses the importance of its effect on the frequency of genes in the gene pool:

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 (40).