The Selfish Gene

Dawkins explores the relationship between parents and offspring:

If there is conflict of interest between parents and children, who share 50 per cent of each others' genes, how much more severe must be the conflict between mates, who are not related to each other? All that they have in common is a 50 per cent genetic shareholding in the same children (106).

Each parent has incentive to care for his or her half of their children’s genes. However, each also has genetic incentive to let the other parent care for children while going off to have more children: “Each partner can therefore be thought of as trying to exploit the other, trying to force the other one to invest more” (107).Genes push individuals to reproduce with as many partners as possible, leaving the partner to raise the children. Males of some species achieve this, although in other species share in child-rearing. This genetic perspective inverts the common viewpoint of sexual relations from cooperative to competitive.

Dawkins describes males and females fundamentally. While humans often associate sex with a set of features such as the penis, breasts, and chromosomes, other animals and plants confuse such notions. The defining difference is that one sex produces smaller and more numerous sex cells (“gametes”) than the other sex. Some primitive species, such as fungi, reproduce through “isogamy” without two different sexes. Two isogametes contribute equal quantities of genes and food to produce a baby. A sperm and an egg contribute equal quantities of genes, but only eggs contribute food.

Because males make smaller sex cells that only need to fertilize, males can afford to make many millions of times more sex cells. This enables males to reproduce with more females at a time. A female has to feed one embryo at a time, severely limiting how many babies she can have. Among isogametes, some sex cells would have been slightly larger than average. These carried more food, improving the survival of offspring.

An arms race produced ever bigger isogametes. This opened the possibility for selfish smaller genes to mate with larger ones, by becoming more mobile: “Natural selection favoured the production of sex cells that were small and that actively sought out big ones to fuse with. So we can think of two divergent sexual 'strategies' evolving” (108). Dawkins describes “honest” large cells competing for food, and exploitative small cells competing for large cells:

Each honest one would 'prefer' to fuse with another honest one. 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 (108).

One male can produce enough sperm to fertilize at least 100 females. On group selection theory, the good of the species would be served by a sex ratio of 100 females to 1 male. The males would be more “expendable” and females more “valuable” (108) to the species. In many animals, only a few males reproduce.

R.A. Fisher explained the sex ratio through the selfish gene. As with determining how many offspring to have, parental genes determine how many of each sex to have. The effective ratio evolves. Mammal eggs can become male or female. Fertilizing sperms determine sex: the Y half produce males, the X half produce females. An evolutionarily stable strategy arises.

In elephant seals, heavily female-producing genes could theoretically evolve. This would serve the good of the species, having many females carry the babies of a few males. However, the genetic payoff for producing males would then far outweigh the payoff for producing females. Each male could produce hundreds of times more genetic copies than each female, so the evolutionarily stable strategies is to produce an even number of males and females.

Genes evolve to invest the same amount for the same expected return. Over evolutionary time, each gene spends approximately half its time in males, half in females. A gene can make use of each of these bodies differently. Males and females have different opportunities. In a couple, the male and female both aim for large numbers of offspring, half male and half female. The less a parent invests per child, the more children: “The obvious way to achieve this desirable state of affairs is to induce your sexual partner to invest more than his or her fair share of resources in each child, leaving you free to have other children with other partners” (111).

Males do not carry children or eggs, so can roam more freely. Females invest more in offspring, making females less likely than males to abandon children and mates: “The female sex is exploited, and the fundamental evolutionary basis for the exploitation is the fact that eggs are larger than sperms” (111).In some species, evolutionary pressure forces mothers to raise offspring alone. In other species, monogamous couples share parenting duties.

An abandoned mother would serve her genetic interests to deceive another male into caring for her child. If the child is not yet born, she could even convince the second man that he is the father: “Natural selection would severely penalize such gullibility in males and indeed would favour males who took active steps to kill any potential step-children as soon as they mated with a new wife” (112).

Male mice emit a chemical that can cause abortions in female mice, if the female smells different than the male’s previous mate. Male lions arriving in a pride sometimes murder the cubs. Instead of killing rival offspring, a male can isolate the female for a period, an “engagement” (112), ensuring that she does not carry any. If a female cannot fool a male into adopting, she could abort a baby. For older children, it could make more sense for her to become a single parent.

Due to genetic logic, it can pay greater dividends to become the parent who deserts offspring first. The second parent would have to decide whether to desert too, which could kill their child. Therefore, the first parent to desert pressures the second into investing in the child. The female advantage is having more mating possibilities: “She has a strong card in her hand. She can refuse to copulate. She is in demand, in a seller's market. This is because she brings the dowry of a large, nutritious egg” (113).

Before sex, a female can bargain: “Once she has copulated she has played her ace—her egg has been committed to the male” (113).The animal version of “driving a hard bargain” could come in two forms. In the “domestic-bliss strategy” (113), the female looks for signs of a domestic, loyal male. By playing hard to get, her incentive for an “engagement”(112), she finds the faithful male. Numerous animals exhibit long engagement periods, and female coyness: “Courtship rituals often include considerable pre-copulation investment by the male. The female may refuse to copulate until the male has built her a nest. Or the male may have to feed her quite substantial amounts of food” (114).

Dawkins suggest that females could compel males to invest enough before sex that it becomes not worthwhile for the male to abandon: “There will be little temptation for him to desert her, if he knows that any future female he approaches will also procrastinate in the same manner before she will get down to business” (114).Importantly, mates make judgments on the basis of expected returns, not on the amount already invested. Therefore, loose females would undermine the incentive for males to commit. Applying the Maynard Smith method of evolutionarily stable strategies, Dawkins shows how a mix of coy and fast females, and faithful and philandering males, spreads genetically to equilibrium.

In monogamous bird species, males often build the nest before mating, and then feed the female, so that their parental investment adds up to more than just sperm. Females could impose any type of cost on males to prove their sincerity. However, genetic advantage accrues for females insisting on costs that improve the survival of her and offspring.

Some insects engage in courtship feeding. In the case of the praying mantis, this can include the male himself being eaten by the female. An unfaithful male could deceive a female into thinking him loyal, propagating his genes at little personal expense. A female who can detect such disloyalty favors her own genes: “One way they can do this is to play especially hard to get when they are courted by a new male, but in successive breeding seasons to be increasingly ready to accept quickly the advances of last year's mate” (117).

Rather than entirely honest or dishonest animals, Dawkins describes the general tendency for each animal to have evolved a small amount of dishonesty, somewhat more in males. In some animals, especially fish, males invest more than females in their children. Sex cells fertilize each other in the water, not in a fish. Therefore, as per Trivers, fish face a “cruel bind” of whether to desert the mate first, with greater punishment for deserting second: “It seems probable that an evolutionary battle will develop over who sheds their sex cells first” (118). However, in fish the mother does not hold the baby. Because male sex cells are more likely to spread out in the water, the male actually has greater incentive to hold onto his sex cells longer. This explains why males in water but not on land care more for their young.

An alternative female behavior, the “he-man strategy” (119), sacrifices fatherly involvement for fatherly genes. Females withhold sex, not for male commitment, but for male quality. Females evolve to detect indications of effective males. In elephant seals and other animals, females figure out the few quality males, who provide the sperm. Females gauge survival ability. Old age does not suffice, because it could show survival but not virility, producing few descendants. Instead, strength or speed would improve her offspring.

As realized by Darwin and later Fisher, in societies where females select males, sexually attractive masculinity itself becomes genetically valuable. Therefore, in addition to selecting muscles as a sign of strength, females also select muscles for their own attractiveness: “Extravagances such as the tails of male birds of paradise may therefore have evolved by a kind of unstable, runaway process” (119).This “sexual selection” (119) produces traits that would otherwise impede natural selection.

An alternative explanation by A. Zahavi has male genes producing traits that accurately reflect their capabilities because of the arms race between show-offs and deception-detectors. According to this theory, males show that they can survive even despite a costly ostentatious feature. Dawkins expresses skepticism over the handicap explanation, noting that mathematical models by biologists including Maynard Smith have failed to calculate it. Male elephant seals who win fights can hold harems. A female can gauge strength effectively by mating with a harem holder. In other species, territory or dominance can indicate attractive male genes.

Animals form mating systems, such as monogamy or polygamy, as a result of conflicting interests between the males and females. The sperm-egg difference generally results in promiscuous males and selective females. In some species, males and females differ significantly, and females go for the “he-man” strategy. Males tend to have brighter colors, and sexually attractive coloring also attracts predators. A compromise results in somewhat bright males, who need to attract mates. Females have few eggs, easily fertilized, and do not need to attract mates, so they remain drab.

Animals generally avoid mating with other species. In some cases, such as a man with a sheep, no embryo is formed, and little is lost. A horse and a donkey can produce a sterile mule, costing precious parental investment, especially from the mother. Females are therefore more selective in mating. Likewise, incestuous mating results in reproductive problems, costing females more than males. Because sex initiators are often older, this theory predicts that father-daughter relations should be more common than brother-sister, and the latter more common than mother-son.

Because of the higher cost of eggs, females can less afford to be promiscuous than males. Each time a male has sex, he gets a chance to reproduce his genes, whereas a female only needs sex once in a long time to reproduce. Dawkins notes that human societies often feature monogamy, with females withholding sex until commitment. Parental investment is large and involves both parents. Mothers often directly care for the children, while fathers earn resources. Some human societies feature more promiscuous males, even harems:

What this astonishing variety suggests is that man's way of life is largely determined by culture rather than by genes. However, it is still possible that human males in general have a tendency towards promiscuity, and females a tendency towards monogamy, as we would predict on evolutionary grounds (124).

Western humans conspicuously reverse the trend in “sexual advertisement,” with showier females: “Women paint their faces and glue on false eyelashes. Apart from special cases, like actors, men do not” (124). A biologist would ordinarily conclude that women compete for sex with men: “What has happened in modern western man? Has the male really become the sought-after sex, the one that is in demand, the sex that can afford to be choosy? If so, why?” (124).

Animals interact not only among immediate mates and offspring, but in larger groups:

Birds flock, insects swarm, fish and whales school, plains-dwelling mammals herd together or hunt in packs. These aggregations usually consist of members of a single species only, but there are exceptions. Zebras often herd together with gnus, and mixed-species flocks of birds are sometimes seen (125).

Animals live in groups so that their genes benefit. For example, hyenas catch enough extra food from pack hunting to outweigh the costs of sharing. Some spiders build communal webs. Emperor penguins huddle to conserve heat. Fish and birds travel in V formations for speed.

W.D. Hamilton theorizes that numerous animals herd to avoid predators. Because predators pose a danger to the nearest prey, each prey animal constantly strives for central, protected positions. This produces the tight-packed herd geometrically. Animals herd for selfish reasons, not out of altruism. In some situations, such as birds sounding warning calls, behavior appears altruistic. Alarm calls evolved to have acoustic profiles making them hard to detect, implying danger to the alarm caller:

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. Obviously, if there is a chance that the flock contains some close relatives, a gene for giving an alarm call can prosper in the gene pool because it has a good chance of being in the bodies of some of the individuals saved (127).

Numerous other explanations have also appeared. Gazelles engage in “stotting” (129), or jumping high while being pursued. One biologist suggested that this requires group selection. Zahavi has proposed a gene selection response claiming that gazelles stot not to signal their comrades, but to signal to the predator enough strength to escape so that the predator pursues a different gazelle. Predators often pursue old, weak prey. Bees who sting predators often die in the process. Social insects generally engage in complex group activity, appearing altruistic. They share food and information and heat, acting as a single organism:

Finally and most importantly, the analogy extends to reproduction. The majority of individuals in a social insect colony are sterile workers. The 'germ line'—the line of immortal gene continuity—flows through the bodies of a minority of individuals, the reproductives. These are the analogues of our own reproductive cells in our testes and ovaries. The sterile workers are the analogy of our liver, muscle, and nerve cells. Kamikaze behaviour and other forms of altruism and cooperation by workers are not astonishing once we accept the fact that they are sterile (129).

A social insect colony generally has one mother. Several classes of sterile insects include small and large workers, soldiers, and specialists, and some males reproduce. An evolutionarily stable strategy for bearing and caring offspring has formed such that social insects have an extremely strong divide between the two functions. One queen bears many offspring, and many related individuals care for them. Some biologists have proposed that the queen chemically manipulates the brood to care for her offspring, or that the sterile workers “farm” (130) reproductive insects to make genetic copies.

The Hymenoptera (including ants and bees) reproduce such that the queen fertilizes her female but not her male offspring with stored sperm. Therefore, males do not have fathers, and males have only one set of genes. Females have two sets of genes and can grow into workers or queens. As a result, queen bees have the same genetic relatedness with offspring as human mothers do with their offspring. However, sisters can have one and a half times the relatedness (sharing three quarters of their genes instead of one half).Because sister insects have more common genes than mother-offspring insects, genes evolve for sisters to assist each other even if at the expense of their mother:

A gene for vicariously making sisters replicates itself more rapidly than a gene for making offspring directly. Hence worker sterility evolved. It is presumably no accident that true sociality, with worker sterility, seems to have evolved no fewer than eleven times independently in the Hymenoptera and only once in the whole of the rest of the animal kingdom, namely in the termites (131).

A brother in the Hymenoptera has one half of the genes from his mother, and only one quarter of the shared genes in a sister. Therefore, while the mother has genetic incentive to produce an equal number of males and females, the sisters have a genetic incentive produce three females for every male. The insects face an intergenerational conflict of interests over which sex to produce.

Scientists tested twenty species of ants and found a three to one ratio of female to male production. This supports the view of worker ants “farming” (131) their mother for sisters. The workers have more strength than the queen.

Some ant species have slaves. The slaves come from another species of ants and gather food and care for the nest. Because the slaves have different genes, they have not evolved to take effective countermeasures against the queen in the intergenerational battle. In the arms race to select the sex of offspring, the queen gets to play against an untrained different species who do not pass on genes in this contest. In fact, the scientists measured these species of slave-making ants and found a one to one sex ratio. The queens won. Other species have their own sex ratios. For example, honey bees invest more in males than in females. This depends on the specifics of how each species reproduces.

Insects, apart from “farming” their mother for genes, farm the land for food. Insects have farmed, for its increased efficiency, since long before humans. Parasol ants harvest leaves which they use as fertilizer for fungi. The fungi convert leaf energy more efficiently than ants could. The fungi get their genes propagated. The ants and fungi appear to have mutual altruism.

Aphids efficiently suck plant sap, excreting sugary liquid. Some ant species drink this liquid, even squeezing it out of aphids. Aphids sometimes even wait for an ant before excreting. The aphids gain protection, and the ants gain food. Different species combine their own strengths, in symbiosis. Mutual cooperation arises in evolutionarily stable strategies. Lichens unite a fungus and an alga so closely that it appears as a single plant.

A human cell contains tiny mitochondria, producing energy. Mitochondria may have started as separate cells, merging symbiotically with humans. Dawkins writes that people likewise contain symbiotic colonies of genes. Viruses, strands of DNA dependent on organisms, could also be “rebel” (136) genes. People then are virus colonies: “Some of them cooperate symbiotically, and travel from body to body in sperms and eggs. These are the conventional 'genes'” (136).

Free-floating DNA in bodies would explain junk DNA, while DNA outside of bodies represent what people now call viruses. Because evolution happens at the genetic level rather than the individual or species level, symbiosis can happen among individuals as well as groups. It occurs when different organisms gain more by cooperation. Mutual benefit can look comparable to one side exploiting the other. Given a time delay, the recipient of a favor could cheat.

Birds, as with some other animals, groom each other, cleaning areas they cannot themselves reach. Species that recognize each other as individuals can practice “reciprocal altruism” (140). Applying evolutionarily stable strategies or comparable game theory math, the gain for grooming other individuals exceeds the cost. Cheaters would overtake a population of groomers, to the point that disease destroys the population. However, a population that remembers individuals and refuses cheaters would both gain the benefits of mutual grooming and resist cheaters.

Trivers describes dozens of species of small fish and shrimps, which survive by cleaning larger fish. The large fish could eat the small animals while they clean its mouth. However, the cleaners have distinct appearances, and mesmerize the larger fish. Some other fish mimic the cleaners, entrancing a larger fish and then eating part of it. The evolutionarily stable strategy for cleaners functions in fixed locations around coral reefs. This way, large fish line up at their favorite spots, like customers at a barber shop, knowing that they can trust these cleaners.

Trivers extends the game theory argument to humans. Emotions may have evolved primarily to detect cheats and appear honest:

Of particular interest are 'subtle cheats' who appear to be reciprocating, but who consistently pay back slightly less than they receive. 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 (140).