The Selfish Gene

The phrase “nice guys finish last” could apply to biology. A person who assisted other people to pass on genes at the expense of his own genes would reduce his genetic survival. However, in another sense, nice people who groom each can increase their genetic survival. Reciprocal altruism appears within and among species.

Political scientist Robert Axelrod has written about reciprocal altruism. He refers to the famous “Prisoner’s Dilemma” (155), a math game with widespread applications. Two players can cooperate or defect. A player wins the most by cooperating against a defector. Two cooperating players both win a smaller prize. Defecting against a cooperator receives a harsh punishment. Two defectors both receive a smaller punishment. One can reason on the basis of expected payoffs that the best strategy is always to defect. Two rational players would both defect, receiving a poor outcome. Yet had they cooperated, they would both have won prizes.

A variant called the “Iterated Prisoner’s Dilemma” (155) involves repeated rounds. Over ensuing rounds, the two players develop trust or distrust. Over time, it becomes possible for the players to receive better average payoffs. Birds removing ticks from each other play the equivalent of the Iterated Prisoner’s Dilemma. The possible outcomes of mutual grooming or refusal to groom equal the rules of the game. Organisms face numerous versions of the Iterated Prisoner’s Dilemma. Iteration makes various strategies possible.

Axelrod ran a competition among game theory experts. Each could send in rules for a computer to follow. Axelrod also added a random strategy. Running the strategies against each other in a computer for hundreds of rounds, one of the simplest strategies won: Tit for Tat. This approach involves cooperating on the first round, and then copying the previous move of the opponent. The least successful strategy had the most complex rules. Axelrod categorized the entries. A “nice” (157) strategy does not defect first. This includes Tit for Tat. A “nasty” (157) strategy can defect spontaneously. The top eight strategies were nice. Far behind, the bottom seven strategies were nasty.

Another category was “forgiving” (157), for ignoring misdeeds in the distant past. Unforgiving strategies did poorly. An even more forgiving variant of Tit for Tat could have done better:

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 (157).

Axelrod ran a sequel tournament. Entrants knew the previous results. Some entered nice and forgiving programs. Others submitted nasty strategies, to exploit the expected nice entrants. Again, Tit for Tat won. Nice strategies outperformed nasty strategies. This time, however, any nicer variant of Tit for Tat would have been exploited.

Dawkins connected Axelrod with W.D. Hamilton, who collaborated on a prize-winning paper. Combining ideas from biology with the Iterated Prisoner’s Dilemma, Axelrod and Hamilton promoted the concept of evolutionarily stable strategies. An evolutionarily stable strategy continues to survive as the environment develops, unlike a robust Prisoner’s Dilemma entrant which only wins in certain environments.

Axelrod ran a third tournament, this time reusing the second tournament entrants but by giving winners clones for the subsequent round, instead of points. After a thousand rounds, a stable environment emerged. The nasty strategies at first exploited the nice strategies. After consuming the nice ones, the nasty ones went extinct, leaving only the nice but not excessively so. Tit for Tat won.

Tit for Tat does not technically qualify as an evolutionarily stable strategy because nice and nasty strategies can temporarily invade: “There are probably lots of mixtures of slightly nasty strategies with nice and very forgiving strategies that are together capable of invading. Some might see this as a mirror for familiar aspects of human life” (161).

Different strategies can achieve stability, partly through luck. Always Defect or Tit for Tat could spread to stability, if it grows first. In biology, kinship brings together closely related “entrants” so that they can swing the environment in their favor. Closely related people could be more likely to play Tit for Tat. A small core of Tit for Tat people could then grow to overtake a larger Always Defect population. Always Defect is technically an evolutionarily stable strategy, while Tit for Tat is not. However, because the latter can spread to larger populations, over the long term it could still overtake the former.

Another category Axelrod introduced refers to “envious” strategies, which aim for more money (points) than their opponents, instead of a high score. Tit for Tat generally lags behind its particular opponent, while doing better overall: “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” (163).

Games can be considered “zero sum” or “nonzero sum” (163). In the former, wins balance losses. In the latter, players can both win different amounts. A marriage generally has mutual benefit, making it nonzero sum. Dawkins writes that a couple can make divorce nonzero sum too, avoiding costly lawyers and fights over children. Zero sum games promote competition, while nonzero sum games promote cooperation.

Sports games are usually zero sum, as one team wins and the other team loses. Dawkins gives the example of an important match, when news of another match that affected the outcome arrived. Suddenly, it became in the interest of both teams to prevent a goal, and the game became extremely defensive, non-competitive.

Dawkins likens nature to a banker in a game. Many games in life are nonzero sum: “Without departing from the fundamental laws of the selfish gene, we can see how cooperation and mutual assistance can flourish even in a basically selfish world. We can see how, in Axelrod's meaning of the term, nice guys may finish first” (166).

Cooperation depends on iteration. As long as the players do not know when the game will end, they must prepare for further encounters. Any suspicion that the game may end soon would lead one to defect, for fear of being defected by the opponent. The longer the game, the more cooperative (nicer, more forgiving, less envious).

In World War I, non-aggression pacts such as the British and German troops gathering peacefully in no-man’s land, occurred spontaneously. In the trenches with no immediately expected end, the opponents developed cooperation like Tit for Tat. The game can differ among participants. For example, British generals wanted to see their soldiers attacking Germans, in a zero sum game. British soldiers, however, wanted to survive, in a nonzero sum game.

The possibility of retaliation is necessary for “nice” strategies such as Tit for Tat: “Crack shots on both sides would display their deadly virtuosity by firing, not at enemy soldiers, but at inanimate targets close to the enemy soldiers, a technique also used in Western films (like shooting out candle flames)” (167). Forgiveness is important to prevent future defections, and regularity maintains the cooperation. Some British and German artillery fired at the same time and place every day.

Strategies of cooperation or competition arise unconsciously, as strategies run on a computer unconsciously. Dawkins likens plants, animals, and genes to these unconscious strategists. Therefore, life also produces non-envious, forgiving, nice entities. Bacteria and hosts face off in regular games of Prisoner’s Dilemma. In an injured person, beneficial bacteria can become harmful. Rather than through reduced resistance, the attack could be attributed to a nearer expected end of the game for the bacteria to exploit.

Axelrod and Hamilton have also argued that plants can act vengefully. Figs are full of small holes, containing tiny flowers that fig wasps pollinate. A wasp could lay an excess of eggs, or pollinate too few flowers, to “defect.” In such figs, the tree aborts growth early, “retaliating” by destroying the baby wasps. In sea bass, hermaphroditic fish, pairs take turns playing male and female roles. This matches the prediction of Tit for Tat: “Defection is vulnerable to retaliation: the partner can refuse to play the female role next time it is 'her' (his?) turn to do so, or 'she' can simply terminate the whole relationship” (170).

At night, vampire bats feed on blood. Some consume more blood than they need, others do not find blood. Bats regurgitate some blood to share, particularly from mothers to offspring and among other relatives. Unrelated roost mates face a Prisoner’s Dilemma, producing cooperative sharing. In numerous forms throughout biology, selfish genes strategically produce mutual kindness.

The selfish gene theory has at its core a conflict between genes and individuals: “A body doesn't look like the product of a loose and temporary federation of warring genetic agents who hardly have time to get acquainted before embarking in sperm or egg for the next leg of the great genetic diaspora” (173).

Dawkins attempts to resolve the paradox. Selection occurs on genes indirectly, via bodies in environments. By producing an embryo, successful genes reproduce. A “phenotype” refers to the body produced by genes: “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” (173).

Biologists often discuss genotypes and phenotypes of the entire body, making it easy to confuse genetic and individual differences. However, genes can survive by improving themselves at the expense of other genes in the same body. Some genes can make themselves more likely to get reproduced during sex, called “segregation distorters” (174). These can expand in “meiotic drive,” harming other genes, as well as “cheat” (174) against other genes, resulting in having far more than half of the alleles.

Mice can have a segregation distorter called “t gene.” The gene rapidly takes over mouse chromosomes. However, when a mouse carries two of the genes it cannot reproduce. The gene can spread so fast that it drives a population of mice extinct: “Natural selection (which, after all, works at the genic level) favours the segregation distorter, even though its effects at the level of the individual organism are likely to be bad” (174). Organisms function so neatly that biologists often think about organisms as life. However, genes are more fundamental than organisms:

Why isn't the sea still a primordial battleground of free and independent replicators? Why did the ancient replicators club together to make, and reside in, lumbering robots, and why are those robots-individual bodies, you and me-so large and so complicated? (175).

Dawkins describes the “extended phenotype” (175) as the effects of a gene on its body and the environment. A gene can exert effects outside of its body. Genes can produce animal nests, not just animals. Caddis flies reside around rivers. As larvae, they build tubular mobile homes from items on the river bottom. Spiders weave immense webs.

Dawkins notes that these animal feats can surprise people, even though the animals themselves have more elaborate designs such as the eye. Evolution selects genes that build protective covers. This applies whether the cover arises biologically as a lobster shell, or through behavior as the caddis house: “The geneticist should recognize genes 'for' house shape in precisely the same sense as there are genes for, say, leg shape” (176).

Genes directly affect protein synthesis. The rest, whether in bodies or in stones, has mediation. Genes can likewise affect the bodies of other organisms. Snails grow their shells as protection. Flatworms called flukes can become snail parasites. Affected snails have thicker shells. Dawkins speculates that the fluke genes may pressure the snail to grow extra thickness as protection.

A gene can have extended phenotype effects outside of the gene’s body. Parasites often manipulate their hosts. The Nosema parasite mimics a flour beetle hormone, preventing the larva from growing into an adult. The Sacculina parasite destroys the reproductive organs of crabs. In these cases, the victim becomes food for the genes of the parasite.

The genes inside one body may transfer to another through the body reproducing, or by parasites. Parasite genes may reproduce through the host, in which case the parasite could even assist the host in reproduction. Over evolutionary times, such parasites can merge with their hosts: “Maybe, as I suggested earlier, our cells have come far across this evolutionary spectrum: we are all relics of ancient parasitic mergers” (179).

Wood-boring ambrosia beetles get infected by a parasite that rides their eggs. Dawkins predicts that they cooperate. The parasites in fact initiate the birth of male beetles. The two species may eventually merge. Small aquatic animals with tentacles often have algal parasites. On one end of the spectrum, the parasites sicken these animals, while on the other end the parasites cohabit with the animals. The beneficial parasites transport themselves by the eggs of the animal, whereas the harmful parasites do not: “The key point, to repeat it, is that a parasite whose genes aspire to the same destiny as the genes of its host shares all the interests of its host and will eventually cease to act parasitically” (180). Dawkins extends the arguments that genes collaborate across organisms to genes collaborating within an organism:

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 (180).

Small segments of DNA reside in the fluid of cells instead of in chromosomes. These “plasmids” (181) can insert and remove themselves in chromosomes. Dawkins describes how a “rebel” (181) part of DNA could escape from a human chromosome, copy itself, and then reattach itself to chromosomes, possibly through the air into another body. Common human interactions, such as breathing the same air or kissing, could transfer DNA: “If genes could discover a chink of an unorthodox route through to another body (alongside, or instead of, the orthodox sperm or egg route), we must expect natural selection to favour their opportunism and improve it” (181).

Such rebel DNA could travel by the same means as viruses. People having a virus cough. Instead of a side effect, the cough can represent a travel method. Rabies travels by saliva, and makes dogs walk far, bite other dogs, and spread the infectious foam from their mouth. Dawkins speculates that sexually transmitted diseases could increase libido: “The point of comparing rebel human DNA with invading parasitic viruses is that there really isn't any important difference between them” (182). Viruses may have started as rebel genes, or vice versa.

Dawkins distinguishes between genes that transfer via sex cells (sperm or eggs), versus genes that transfer through other routes. Regardless of whether a gene started on a chromosome or as a virus, its interests reside in propagating via its exit, sex cells or otherwise:

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 (182).

The extended phenotype can reach large distances. Beavers build protective areas of water to reside and travel. These lakes can reach hundreds of yards: “Whatever its benefits, a beaver lake is a conspicuous and characteristic feature of the landscape. It is a phenotype, no less than the beaver's teeth and tail, and it has evolved under the influence of Darwinian selection” (182).

Cuckoos act parasitically, although not directly within their hosts. Manipulating host nests counts as an extended phenotype. Dawkins speculates that Cuckoos may also affect the nervous systems of the victims, as do drugs, pornography, or junk food. The evolutionary arms race between parasites and hosts often favors parasites because they have survived exclusively through exploitation while hosts have to defend themselves and also provide their own food.

Parasites can have their effect from inside or outside the body of a host. All the genes in a body can be considered parasites. A gene can act on the phenotype of the body it is in, or on the extended phenotype of any other body. Some ant species have other ant species as parasites. The parasite queen decapitates the host queen and takes over the colony. In another species, the parasite queen convinces the host workers, possibly through chemicals, to decapitate the host queen.

Some caterpillars act as parasites in ant nests. One caterpillar species can produce sounds to call ants, excrete nectar for ants, and produce a drug that makes ants attack anyone other than the caterpillar while following the caterpillar for days. In numerous species of plants and animals, genes act on their extended phenotypes through other organisms:

Natural selection favours those genes that manipulate the world to ensure their own propagation. 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 (186).

Dawkins distinguishes between DNA as replicators, versus bodies as  “vehicles,” that is, survival machines: “Vehicles don't replicate themselves; they work to propagate their replicators. Replicators don't behave, don't perceive the world, don't catch prey or run away from predators; they make vehicles that do all those things” (187).

Biologists can study the replicators or the vehicles. This difference resolves the conflict between evolution of genes versus individuals: “Gene and individual organism are not rivals for the same starring role in the Darwinian drama. They are cast in different, complementary and in many respects equally important roles, the role of replicator and the role of vehicle” (187).

Individuals or groups could act as vehicles for the replicators. Dawkins argues that the individual wins that rivalry. Individual animals have a more coherent exit route for genes than groups. Genes fight for survival. Weapons include phenotypes, such as teeth and claws. Most phenotype effects occur in the same vehicle or body, funneling through sperm and eggs. To explain why genes come and go through individual bodies, Dawkins addresses how replicators grow into survival machines.

Replicators traded in their freedom for residence in groups of cells. Together, the clumps of cells could produce chemicals through complex reactions that an individual cell could not perform alone. Larger groupings of cells formed into organisms. Bigger bodies could eat smaller bodies. Larger organisms also enable cell specialization.

If there are many cells, some can specialize as sensors to detect prey, others as nerves to pass on the message, others as stinging cells to paralyse the prey, muscle cells to move tentacles and catch the prey, secretory cells to dissolve it and yet others to absorb the juices. We must not forget that, at least in modern bodies like our own, the cells are a clone. All contain the same genes, although different genes will be turned on in the different specialist cells. Genes in each cell type are directly benefiting their own copies in the minority of cells specialized for reproduction (190).

Bodies reproduce through a “bottleneck” (190), a narrow passage. Even an organism as big as an elephant starts as a single cell. In its lifecycle, the elephant then reproduces through another fertilized egg. Dawkins describes two hypothetical seaweeds, reproducing either by splitting or seed. The splitting seaweed reproduces by breaking apart, the same as it grows only in separate places. The seeding seaweed releases single cells instead of larger groupings.

Organs become more complex through gradual evolution. Changes accrue through new organisms, rather than directly to older organisms. New organisms start from a single cell. The DNA gets reused, but not the body: “One important thing about a 'bottlenecked' life cycle is that it makes possible the equivalent of going back to the drawing board” (192).

The bottleneck in the lifecycle also introduces a rhythm to reproduction, timing the sequence of embryonic development. This enables the growth of complex organs: “The precision and complexity of an eagle's eye or a swallow's wing couldn't emerge without clockwork rules for what is laid down when” (193). Reproduction through a single cell also unites the new organism in its genes. By contrast, a dividing plant would have mixes of genes with different relatedness. This makes bottleneck organisms better at producing complex organs.

Dawkins notes that viewing organisms as groups of cells has parallels with ideas relating to group selection, parasites sharing reproduction with hosts, and sexually reproducing cells cooperating only through fair reproduction. The bottleneck arguments show how complex organisms evolve as independent vehicles:

Indeed I suspect that the essential, defining feature of an individual organism is that it is a unit that begins and ends with a single-celled bottleneck. If life cycles become bottlenecked, living material seems bound to become boxed into discrete, unitary organisms. And the more that living material is boxed into discrete survival machines, the more will the cells of those survival machines concentrate their efforts on that special class of cells that are destined to ferry their shared genes through the bottleneck into the next generation. The two phenomena, bottlenecked life cycles and discrete organisms, go hand in hand (194).

Summarizing the extended phenotype and selfish gene view, any object in the universe that copies itself (a replicator) forms life. Small particles randomly form replicators. Replicators form numerous copies, and imperfections occur. Among the copies, some fail to replicate and end. Others replicate less effectively. Some replicate more effectively and take over subsequent generations.

Over evolutionary time, replicators become more complex. The survivors often propagate through indirect effects on the environment. Survival depends on environmental conditions, particularly other replicators. Mutually cooperative replicators survive better. Earth life formed into cells, and cells into bodies:

Vehicles that evolved a bottlenecked life cycle prospered, and became more discrete and vehicle-like. This packaging of living material into discrete vehicles became such a salient and dominant feature that, when biologists arrived on the scene and started asking questions about life, their questions were mostly about vehicles—individual organisms. The individual organism came first in the biologist's consciousness, while the replicators—now known as genes—were seen as part of the machinery used by individual organisms. It requires a deliberate mental effort to turn biology the right way up again, and remind ourselves that the replicators come first, in importance as well as in history (195).

Genes act on other bodies and the environment, indicating their independence from organisms. A gene reaches out to a web of distant objects, and an object is reached by a web of distant genes: “The long reach of the gene knows no obvious boundaries. The whole world is criss-crossed with causal arrows joining genes to phenotypic effects, far and near” (196).Most genes and their phenotypes now travel together in bodies. However, theoretically only the genes are necessary for life.