Chapter Summaries for The Moral Animal by Robert Wright

Of course, any summary will misrepresent the original author's work to some degree. I've inevitably put more emphasis on the parts I find more interesting, and may have unintentionally skewed Wright's intent. Where I've consciously added my own notes, such as the comparison to the book Sex At Dawn, I've made that clear. Also, I added some pictures that don't appear in the book, because a wall of text is harder to read than a wall of text interspersed with pictures of furry animals.

So far, I've summarized parts one and two. I hope to get to the final two parts sometime.

Introduction: Darwin and Us

The standard social science model regarded humans as "blank slates". Human nature was thought to be highly malleable, and culture was the biggest determinant of a person's personality, values and desires. Since about 1960, there's a new paradigm. Large parts of human nature - e.g. status-seeking, desire to gossip, a sense of justice, guilt - have genetic causes; they are shared across all cultures.

An understanding of human nature informed by evolutionary biology has significant impact on our daily lives. It might help us achieve our goals, choose our goals, and to understand what our innate sense of morality is telling us and why.

This book will examine Darwin himself as a test case for the explanatory power of evolutionary biology.



The society in which Darwin grew up - Victorian England - encouraged self-restraint, even self-denial, particularly around sex.

After an unenthusiastic foray into studying medicine, Darwin intended a career in the clergy, at his father's suggestion. At the time, theology and zoology were closely linked, because studying plants and animals was studying God's ingenious creations. In preparation, Darwin studied at Cambridge, and then encountered the opportunity to be a naturalist on the HMS Beagle. What he saw on the voyage convinced him that evolution had occurred; two years after his return he understood its mechanism of natural selection.

Wright gives an explanation of how natural selection works.

Consider the speed of evolution. Australopithecines, who had ape-sized brains, lived a few million years ago - 100,000-200,000 generations. Wolves became chihuahuas and all the other breeds we know today in about 5,000 generations.

The rapid evolutionary pressure on human brains was caused by intra-species competition - we grew big brains to manage politics.

Darwin was probably a virgin when he set sail at the age of 23, and after five years on an all-male ship, was probably a virgin on his return. Marriage and prostitutes were the main sources of sex in Victorian England, era of the Madonna-whore dichotomy. A woman could be a potential wife, eligible for love, or a slut or whore, suitable for lust - a dichotomy that exists to some extent today.

"I should say that the majority of women (happily for them) are not very much troubled with sexual feeling of any kind. What men are habitually, women are only exceptionally...the best mothers, wives, and managers of households, know little or nothing of sexual indulgences. Love of home, children, and domestic duties, are the only passions they feel." - Dr. Acton


Darwin observed that, as a generalization, males chase and females choose, in any species. He saw that female choosiness leads to "sexual selection", where traits not obviously related to survival are selected for. Sexual selection can be considered in two categories. One is intra-male competition, where males evolve to be bigger and stronger than each other in order to defeat sexual rivals, which leads to the enormous size of elephant seals and to the presence of stag horns. The other is female choice, which leads to cumbersome peacock tails and colorful puffy necks on some lizards. Darwin didn't accurately explain the reason for female choosiness, however. It is because more resources are required for eggs and pregnancy (especially in mammals) than for sperm. With favorable circumstances, a male can have hundreds of children each year, while a female is limited to about one. So males might have a disposition towards quantity while females might have a disposition towards quality. This wasn't properly explained until the mid-twentieth century.

Male green anole lizard with throat sac inflated for courtship display

Good scientific theories make predictions. It is a sensitive point that the science of evolution struggles slightly with this, since the experiment started billions of years before science was invented. Evolution makes predictions like "males are more eager for sex than females" but the reason we have predictions like this is from noticing the pattern first and then coming up the explanation. But the theory makes further predictions beyond the ones that led us to the hypothesis in the first place. In species where the male makes an unusually great parental investment (such as a species of bird where the male warms the eggs, or the pipefish where the male takes the eggs into his bloodstream for nutrients), females typically take a more active role.

Among apes, a variety of sexual behaviors are seen. Orangutan females stay in their home range, while orangutan males wander in search of them, settling long enough to monopolize one or a few for the duration of the pregnancy. Male gorillas and chimpanzees strive to be the leader of their pack (the chimpanzee hierarchy is longer and more fluid), and the alpha male gets all or most of the access to the females. Bonobos are somewhat similar to chimpanzees, except that sexual contact has taken on social bonding purposes in addition to reproduction, and homosexual contact is common. Gibbons pair-bond much more than most apes, and in one gibbon species, males carry the infants around. Among all this variation, the basic theme remains: males are more eager for sex, females more passive.

Chapter 3: MEN AND WOMEN

Human male parental investment (MPI) is much higher than that of chimpanzee or bonobo males, who don't seem to be aware of which children are theirs. The reasons are several: because humans walk upright, narrower pelvises are optimal, but heads are bigger than ever, so human women give birth prematurely relative to other apes. So, human babies are helpless tiger bait for a relatively long time and they need protection. And when you live in the savannah, protecting children is more difficult than it was in the trees. Relative to other apes, humans ate more meat due to the possibility of hunting. This easy source of nutrients lowered the cost of MPI. Finally, humans are capable of much more training than other apes, so return on educational investment is higher.


Being a high-MPI species, men are designed for treachery. The optimal strategy for men is a "mixed strategy" - invest a lot in a few children, but take opportunities for investment-less flings when they arise. Evolution favored men who persuaded women that they'd invest in their offspring; so evolution favored women who could spot sincere men from liars; so evolution favored men who deluded themselves into thinking their love was everlasting when it was actually ephemeral, because the most persuasive liar is the one who believes his lies.

Other consequences of being a high-MPI species are that women tend to seek wealthy, ambitious, industrious males with high social status for long-term partnership. Particular devotion to the woman is particularly attractive, because abandonment is a possibility and - polygyny being common in the ancestral environment - a second wife and family, attracting resources away from the first wife's children, is also a possibility.

In a low-MPI species, there is little competition between females. One female won't monopolize a male's parental investment at the expense of another. Human females have evolved to compete with other females for male investment, though the combat is different from the violent forms of male competition.

Males may be relatively unselective about sexual partners, but will be very selective about long-term partners. Age matters; the younger a female is, the more children she can bear until she's no longer fertile. Across all 37 cultures in one study, males preferred younger mates and females preferred older mates. Men look for signs of sexual fidelity in women. Studies have shown the men are more distressed at sexual infidelity (which could lead to him investing years into children that aren't his) while women are more distressed by emotional infidelity (which could lead to a man leaving her for another). (But since The Moral Animal was published in 1995, the evolutionary explanation of this has been challenged and some people argue that it's cultural.)

The incentive for females to have multiple sexual partners includes resource extraction (her partners give her gifts), some level of investment in her children by multiple men, or to trick a devoted but not especially strong or attractive man support the children of another male. Unusually among animals, female fertility is not obvious on sight, a curious adaptation that would be explained by the success of treacherous strategies. It might be relatively easy for a male to defend a female from rivals for a short time each month, but if he can't tell when she's ovulating, he can't be sure to be vigilant at the right time. This theory predicts that women might change their behavior towards seeking short-term partners when ovulating, and the prediction is accurate: a study showed that women wear more make-up and jewellery at bars when ovulating. Another study showed that women cheat more often when they're ovulating. (Update: as of 2014, you might have heard that these kinds of studies fail to replicate. A 2014 meta-analysis examined the failed replications, and some successful ones, and said "The strength of women's preference shift proved to be statistically significant, although "small" to "medium" in size, relative to most findings in the field". Meta-analyses are supposed to settle questions like this, but I'm still doubtful. Meta-analyses can get small-but-significant effect sizes even when studying psychic powers.)

Evolution favored women who persuaded men that they'd have sex only with them; so evolution favored men who could spot sincere women from liars; so evolution favored women who deluded themselves into thinking they would be faithful when they'd actually stray at the right opportunity, because the most persuasive liar is the one who believes her lies.

This is the evolutionary explanation for the Madonna-whore dichotomy. If a woman is promiscuous, a man might reasonably (if unconsciously) conclude that she might be promiscuous during marriage. So he might consider her a candidate for sex but not for a relationship. If, during courtship, a woman withholds sex, she might be expected to withhold sex from rivals after marriage.

Most of the time, a particular mutation is strictly better or worse, so it will either spread throughout the population or it will die with its host. But there is also frequency-dependent selection. The males of the bluegill sunfish can adopt one of two different strategies - build nests for females to lay eggs in and then fertilize them, or sneakily fertilize the nests of other males. The more industrious nest-builders there are, the greater the benefit of being a sneaky thief, but the more thieves there are, the fewer opportunities there are per thief. So an equilibrium is maintained of about one fifth of the population being thieves.

There is a similar mechanic present in human reproductive strategies - Madonna, whore, cad, dad. Tendencies to various strategies are genetic, and also it appears we are designed to examine our environment and choose the best strategy accordingly.

Male gorillas are much heavier and stronger than female gorillas

There are implications for public policy, if we think public policy should encourage a particular reproductive style. There are numerous problems associated with fatherless children, which presumably come from women choosing short-term reproductive strategies. Some research (perhaps tentatively) shows that poverty leads to women choosing short-term reproductive styles, so one could argue that evolutionary biology has public policy implications favoring effective anti-poverty programs.

Over time, it tends to be in the male's interest to desert his wife, particularly if he rises in status and wealth. He could, theoretically, find a female with twenty-five more years of fertility ahead of her. But a middle-aged woman past her fertile prime has no strong evolutionary impulse to leave her husband. When that happens, it could be a reflection of the husband's neglect or disaffection. Men are much more likely than women to remarry after a divorce.

Sexual dimorphism correlates with polygyny across many species. Male gorillas, who gain access to all females in their group if they are the strongest male, weigh twice as much as females. Male gibbons, who pair-bond monogamously, are about the same size as female gibbons. Humans are much less dimorphic than gorillas, somewhat less than chimpanzees, and significantly more than gibbons. The anatomical observations predict that we are a somewhat polygynous species...assuming that the obvious anatomical differences tell the whole story. Mental competition between males has been unusually important relative to physical competition in humans.

980 of the 1,154 past or present societies for which anthropologists have data have allowed males to have more than one wife. But among those, 43% have only "occasional" polygyny, and even when polygyny is common, it is only for a few unusually wealthy or high-ranking men. Most societies may have been polygynous, but most marriages have been (meant to be) monogamous.

Wright observes that when a married man falls in love with a younger woman, contemporary monogamo-centric cultures demand that he divorce his wife and abandon his former family. He suggests that polygyny handles this situation better.


Men like having multiple wives, but modern societies, with their history of patriarchical leadership, mostly demand monogamy. Something, it appears, has gone horribly wrong.

When men mostly have the same economic means, polygyny is a bad deal for a woman. Why take half the resources of a man when you could get all the resources of an equally wealthy man? In cases like these, monogamy is "ecologically imposed". Anthropological studies provide evidence: monogamous societies are usually "nonstratified". But there are about 70 societies, including the modern industrial ones, that are both stratified and monogamous. In these societies, monogamy is "socially imposed". But why?

Perhaps the society is non-stratified within economic classes. Upper-class women might never meet low-income men in a mating context, so she can focus her search on the eligible upper-class men. And polygyny may lurk beneath the surface; some women choose to be mistresses.

Only 7% of societies on record have socially imposed monogamy, but they make up 77% of the societies that have dowries - payments from the bride's family to the groom's family. This suggests that the dowry is the product of a market disequilibrium - a payment in lieu of the opportunity for multiple wives. Presumably, if polygyny were legalized, the market would clear, and dowries would disappear.

Polygyny creates winners and losers. For every man with two wives, there is a man with no wives. So polygyny is no overall advantage for men; it is an advantage for attractive men and a disadvantage for unattractive men. Rather than socially imposed monogamy being an egalitarian victory for women, it may be unfortunate. If there are any women with poor, unattractive husbands who would rather be the second wife of rich, attractive husbands, then they are worse off. And every time a man takes an extra wife, that's an extra competitor taken from the dating pool, leaving a favorable ratio of many men competing for a smaller pool of women, enabling the remaining women to marry the more attractive of the men.

So perhaps socially-imposed monogamy occurred as part of a general disbursement of political power. One-man-one-vote-one-wife. And monogamous societies tend to be more peaceful and stable. Sexually frustrated men are dangerous and prone to crime.

Contemporary Western society is not monogamous, as it used to be. It is a society of serial monogamy, which involves the pernicious effects of polygyny (dangerously sexless men) without the benefits (stable loving families). Divorce rates have dramatically increased. There are many attractive men gaining an unequal share of women, so there are many men without any.


Emma Wedgwood

Darwin, coming from a family of status and wealth, was always going to be considered a good prospect for marriage. But when Darwin returned from his voyage on the HMS Beagle, he had earned fame as a naturalist who had made many original discoveries. He wasn't sure he wanted to marry, and he wrote a pros/cons list to aid with the decision. He feared the loss of time, the family obligations, and the temptation towards fatness and idleness. But he chose marriage: "it is intolerable to think of spending ones whole life, like a neuter bee, working, working, & nothing after all...picture to yourself a nice soft wife on a sofa with good fire, & books & music perhaps."

Darwin proposed to Emma Wedgwood, his cousin, whom he had known since childhood. She was a year older than him, and not particularly beautiful. With Darwin's high status, why didn't he choose a young and beautiful wife?

It seems that our opinion of our own social status is heavily influenced by our adolescence. Darwin's success came in his twenties and later, but he didn't spend his adolescence as an alpha male. He seems to have underestimated his marriageability. Wright points out that a low opinion of oneself can be adaptive; it prevented Darwin from marrying the kind of stunning woman who would draw attention from world-class philanderers and cheat on him.

Emma said yes, and Darwin proclaimed his devotion in elaborate, articulate love letters. He wanted a wedding sooner rather than later, while Emma wanted a longer engagement. Males are eager, women are selective, and Emma may have been subconsciously motivated to prolong the engagement to check the seriousness of Darwin's devotion, and to avoid flicking his Madonna->whore switch.

Before the wedding, she wrote: "You need not fear my own dear Charles that I shall not be quite as happy as you are & I shall always look upon the event of the 29th as a most happy one on my part though perhaps not so great or so good as you do."

A few months after the wedding, she wrote: "I cannot tell him how happy he makes me and how dearly I love him and thank him for all his affection which makes the happiness of my life more and more every day."

If it is harder to drag men to the altar today than it used to be, one reason is that they don't have to stop there on the way to the bedroom.

Female sexual desire decreases during pregnancy and breast-feeding. Since a Victorian-era woman might spend a large proportion of her married life pregnant, Acton's dismissal of female sexual arousal from Chapter One might not be quite as misguided as it first appears. "I should say that the majority of women (happily for them) are not very much troubled with sexual feeling of any kind. What men are habitually, women are only exceptionally...the best mothers, wives, and managers of households, know little or nothing of sexual indulgences. Love of home, children, and domestic duties, are the only passions they feel."

Darwin's marriage to Emma Wedgewood was, by all accounts, an idyllic, loving marriage. It was very different from the marriage of his contemporary, Charles Dickens. After two decades and ten children, Dickens was a famous writer, commanding the attention of many young women, while his wife had aged and her fertile years were in the past. Dickens wrote to a friend, "I believe that no two people were ever created with such an impossibility of interest, sympathy, confidence, sentiment, tender union of any kind between them, as there is between my wife and me."

Darwin and Dickens rose to greater fame and fortune after marriage. Darwin's marriage was happy; Dickens' was not. What accounts for the difference?


Starting shortly before his marriage, Darwin's health declined and he struggled with illness for the rest of his life. This decreased his marriage marketability. The chaste engagement secured Emma her Madonna status in Darwin's mind. Darwin lived two hours away from London, away from temptation. They had ten children, keeping Darwin focused on the investments he'd made. "We can now roughly sketch a Charles Darwin plan for marital bliss: have a chaste courtship, marry an angel, move to the country not long after the wedding, have tons of kids, and sink into a deeply debilitating illness."

More practically, if you decide to get married, prepare for the initial ardor to fade, and the marriage will then "live or die on respect, practical compatibility, simple affection, and (these days, especially) determination". When ardor fades, beware your impulse to blame it on marrying the wrong person, and beware your hope to get it right next time. Divorce statistics, Wright says, support Samuel Johnson's characterization of a man's decision to remarry as "the triumph of hope over experience."

Easy divorce, widespread contraception, and relaxed sexual morality have made sex accessible for many men, relative to Victorian times. This may be bad for women's long-term interests in marriage. Divorce has an unequal financial impact on men and women, because men typically orient their lives for a career while women may have invested time in child-rearing. Wright suggests that this inequality be legally rectified.

Early feminists asserted that there were no differences between the sexes. This encouraged girls to indulge their sexual desires and ignore any visceral wariness. It encouraged men to sleep around without worrying about emotional fall-out.

The modern full-time housewife mother, spending her days at home alone with children, is in an unnatural state. Child-rearing used to be a job for the extended family. The modern life of career-oriented men - going to work each day in the company of similar people and returning to wife and children in the evening - is more natural, being similar to the lifestyle of a hunter. To improve happiness and mental health, people should consider how to match their lifestyles to the lives they evolved to lead.

Wright suggests that women seeking long-term commitments should avoid sex too early with men. He suggests two months of courtship before sex, maybe more, and predicts (this is 1995) that society will move towards a custom of long courtship times before sex (though doesn't predict a return to the Victorian extreme). He carefully notes that this is self-help advice, not moral advice.

A return to Victorian morality is impossible and though it has some benefits relative to serial monogamy, it had large and peculiar costs. People were trapped in awful marriages; even married sex was tainted by guilt, especially for women; Victorian men probably weren't very good at sex; women were valued primarily for marriage, not on the same terms as men. Maybe there are other social systems that could sustain monogamous marriage, but they are likely to have large costs too. But compare it to the modern world "featuring, among other things: lots of fatherless children; lots of embittered women; lots of complaints about date rape and sexual harassment; and the frequent sight of lonely men renting X-rated videotapes while lonely women abound."

Much of our sexual morality is, on close inspection, suspiciously self-interested. A varied coalition of interest groups team up against female promiscuity: there are males seeking long-term partners who won't cheat; parents of young, pretty girls who demand they "save" themselves so as to be good targets for male parental investment; these daughters themselves, threatened by the competition who give freely what they are trying to charge a high price for; and married women who fear an atmosphere of promiscuity could distract a man from his investment in his marriage and his children.

There is relative tolerance for male philandering.

Note on Part One: this narrative of human sexuality is criticized in the 2010 book Sex At Dawn by Christopher Ryan, Ph.D. and Cacilda Jetha, M.D. I've read the online excerpts, and I'm not highly impressed with their rigor and tone (e.g. they use lots of rhetorical questions to imply their point without actually stating it; and it appears to me that they don't just want to refute the opposing theory but also to lower the status of their opponents, which is an epistemically questionable motivation) but their thesis seems to be that pre-agricultural humans were likely to have been not monogamous, not even polygynous, but orgiastic. Some of the offered arguments (from here and here) include:

(Personally I suspect you could explain facts like these with other plausible consistent theories, but I don't have a Ph.D. so maybe listen to those other guys.)


Chapter 7: FAMILIES

Darwin spent more than a decade pondering an apparent contradiction to natural selection - organisms such as ants and bees, whose members are mostly sterile. How could a mutation for sterility enhance fitness?

Consider a ground squirrel that, upon sighting a predator, delivers an alarm call, which attracts the predator's attention and brings sudden death. How could a mutation for a suicidal alarm call enhance fitness?

If you look at fitness from a gene's point of view, rather than an organism's point of view, the behavior of ants and bees and squirrels makes sense. Genes expressed in sterile worker ants are transmitted by the queen; genes expressed in heroic squirrels are carried on by siblings. The same mechanism explains human altruism, and it explains why we are more altruistic to those we are more closely related to.

It was once common to speak of maximizing fitness, but now evolutionary biologists speak of "inclusive fitness" - a measure that includes not just the fitness of a particular organism, but of a gene's expression in siblings, cousins and so on.

Consider the slime mold, an organism on the blurry edge between single-celled organisms and multi-celled organisms. Slime-mold cells reproduce asexually, so they are all identical twins. From the point of view of the gene, the life of one cell is as valuable as the life of another. So some cells devote themselves instead to buffering fertile fellow cells from harsh conditions. Human bodies can be seen the same way. Only our sex cells - sperm and eggs - get to make copies of themselves for posterity. The rest of the cells in the body devote themselves to giving the sex cells their best chance.

Siblings share half their genes (i.e. half of the genes currently undergoing fitness tests in the gene pool). This will lead to some altruism or love, but not to the extent of the selfless ants or slime mold cells. It even leads to a frustrating conflict: a child will regard herself as twice as valuable as a sibling (the sibling having only half the relevant genes) but the parent will value them both equally. Hence, human parents teach children to share with their siblings, and the children resist this advice.

A caribou calf will continue to suckle long after milk has ceased to be essential to its survival, even though this prevents the mother from conceiving another calf that will share some of its genes. The time will come when the nutritional rewards from suckling are so marginal that the genetic interest favors another calf over milk. But the mother, valuing the two offspring equally, reaches that point sooner. Conflict over weaning is a regular part of mammalian life. The conflict can last for several weeks and become intense, as infants shriek for milk and even strike their mother.

Children lie, exaggerate and throw temper tantrums to gain resources from parents. Tantrums are a behavior shared among humans, chimpanzees, bonobos and other primates. Fitter parents can distinguish genuine cries for help from resource-stealing tricks.

Parents lie, exaggerate and indoctrinate their children to share resources with siblings, aunts, uncles and other relatives of the parents. Fitter children can distinguish useful advice from resource-stealing tricks.

Evolutionary biologist Robert Trivers: "One is not permitted to assume that parents who attempt to impart such virtues as responsibility, decency, honesty, trustworthiness, generosity, and self-denial are merely providing the offspring with useful information on appropriate behavior in the local culture, for all such virtues are likely to affect the amount of altruistic and egoistic behavior impinging on the parent's kin, and parent and offspring are expected to view such behavior differently."

Females can almost always find a male willing to provide genes, if not much parental investment. Males face a more uncertain future, but the rewards are correspondingly greater; a very fit man could have many more children than the fittest woman. Thus, for a poor low-status family, daughters are more valuable; they have a good chance of passing on genes. Sons are relatively less valuable, as a man with no resources is likely to die childless. The opposite is true of rich, high-status families: rich, high-status sons might have many more children than rich, high-status daughters.

Does reality match this cynical observation? It does:

Florida pack rat mothers, if fed poorly, will force sons off the teat, even letting them starve to death, while daughters nurse freely. In other species, even the birth ratio of males to females is affected, with mothers in the most auspicious condition having mostly sons and less advantaged mothers having mostly daughters.


A study of North American families found pronounced differences in how indulgent the parents of different social classes are of boys and girls. More than half of the daughters born to low-income women were breast-fed, while fewer than half of the sons were; around 60 percent of the daughters born to affluent women were breast-fed, and nearly 90 percent of the sons. And, more dramatically, low-income women, on average, had another child within 3.5 years of the birth of a son and within 4.3 years of the birth of a daughter. In other words: in the contest over how soon to create a sibling, low-income mothers are inclined to let a daughter win; they wait longer to produce a competing target for investment. For affluent women, the opposite was true: daughters had a rival sibling within 3.2 years of birth, sons within 3.9 years. Presumably few if any mothers in the study knew how social status can affect the reproductive success of males and females (or, strictly speaking, how it would have done so in the environment of our evolution). This is another reminder that natural selection tends to work underground, by shaping human feelings, not by making humans conscious of its logic.

Wright also notes that female infanticide, common in 19th century India and China, was most intensively practiced among the upper classes.

Studies show that when a child dies, the intensity of a parent's grief increases according to the number of fertile years they would have had left in the ancestral environment, plus the resources already expended on the child. Thus, an adolescent, who has been the target for years of investment and is about to become fertile, is the saddest death. A baby, yet to absorb many resources, or a 40-year-old past her fertile prime, are less sad. This was shown in Darwin's life. He lost two children under the age of two, and one at the age of ten. He was much, much more grief-stricken about losing the ten-year-old.


Darwin was appalled at the preliterate societies he visited. He wrote that primitive man "delights to torture his enemies, offers up bloody sacrifices, practises infanticide without remorse...I could not have believed how wide was the difference, between savage and civilized man. It is greater than between a wild and domesticated animal."

But he noticed some elements of a common human nature: "The American aborigines, Negroes and Europeans are as different from each other in mind as any three races that can be named; yet I was incessantly struck, whilst living with the Fuegians on board the 'Beagle' with the many little traits of character, shewing how similar their minds were to ours and so it was with a full-blooded negro with whom I happened once to be intimate."

Roots of human morality can be seen in the social instincts of animals. Chimpanzees make friends; cows surround and stare at their dying fellows; crows feed blind compatriots. But how did humans get such a complex moral instinct, particularly one so wide in scope that people will, in some circumstances, help complete strangers?

Darwin succumbed to the trap of group selectionism, an idea that has foiled many biologists since. He wrote: "there can be no doubt that a tribe including many members who, from possessing in a high degree the spirit of patriotism, fidelity, obedience, courage, and sympathy, were always ready to give aid to each other and to sacrifice themselves for the common good, would be victorious over most other tribes; and this would be natural selection."

The problem is that a gene for unusually altruistic or heroic behavior would harm its individual host while it benefits the tribe. Before it can compete in inter-tribe competition, it must first succeed in intra-tribe competition. In modern times, group selectionism is widely regarded as a trap.

Chapter 9: FRIENDS

Wright explains game theory and the Prisoner's Dilemma. The Prisoner's Dilemma where the two prisoners can't communicate is somewhat similar to the situation of two animals who can't speak, and therefore can't communicate. They might benefit from cooperation, but how can they organize that, when cheating is also possible?

Humans have many opportunities for positive-sum interactions. Two cavemen might be able to cooperate to hunt an animal too powerful to be killed by one man. A human might specialize in hide-splicing and another in spear-crafting, and they might gain from trade. Or they might share information, which can be radically positive-sum since information is not consumed, but copied. Information sharing - that is, gossiping - can be very beneficial.

Knowing where a great stock of food has been found, or where someone encountered a poisonous snake, can be a matter of life or death. And knowing who is sleeping with whom, who is angry at whom, who cheated whom, and so on, can inform social maneuvering for sex and other vital resources. Indeed, the sorts of gossip that people in all cultures have an apparently inherent thirst for -- tales of triumph, tragedy, bonanza, misfortune, extraordinary fidelity, wretched betrayal, and so on -- match up well with the sorts of information conducive to fitness.

We can test the theory that cooperative behavior succeeds where exploitative behavior fails. In the 1970s, political scientist Robert Axelrod set up a simulated environment on a computer where different programs could compete in an iterated prisoner's dilemma. He invited experts in game theory to submit programs for competition. The winner was very simple, just five lines long. Called TIT FOR TAT, it began each interaction by cooperating, and in subsequent interactions it repeated its opponent's previous move. If a TIT FOR TAT program finds itself in a community of TIT FOR TAT programs - or programs that are cooperative for any other reason - then they all live in cooperative harmony. If TIT FOR TAT finds itself in an environment of cheaters, it quickly cuts its losses and avoids exploitation after the first interaction.

Axelrod began his simulation with all the submitted programs in equal proportion. After each program had 200 encounters with each other program, he added up their scores and restarted the simulation with the programs represented according to their score in the previous generation. Thus the fittest programs had more offspring, and TIT FOR TAT dominated the later generations, just as a beneficial mutation becomes fixated in a gene pool.

Mutations for reciprocal altruism in humans and other animals succeed for the same reason that TIT FOR TAT succeeded in the simulated environment. Reciprocal altruism enables positive-sum interactions. In humans, reciprocal altruism is conducted through emotions like gratitude, duty, compassion, sympathy and guilt. Reciprocal altruism is likely an extension of altruism towards kin. Parents and older siblings might deduce who they are related to from observing birth, but a younger sibling doesn't have that information, and could induce who is related from observing those who are altruistic. In an environment where altruism from kin is reciprocated, a wider scope of compassion is an easy parameter for evolution to tweak.

We are more likely to help someone in great need than someone in mild need. Emotionally, it is because we pity or empathize more with one who suffers more or is more vulnerable. Evolution has carefully designed our pity to direct it towards those who will owe us the most, like an investment advisor directing resources to the most promising investment.

When someone cheats us, we feel moral indignation, and are likely to tell others of the grievance. Grievances constitute a large proportion of gossip. Our reputation-ruining power can disincentivize others from cheating us, and it can help others to evaluate who is likely to cheat in the future. Small grievances can turn into bloody feuds. We might be willing to risk a small chance of death in order to send a powerful signal that cheating us will have terrible consequences.

Studies show that guilt increases in proportion to the likelihood that we'll be caught. This is an example of the predictive power of evolutionary psychology. If guilt were a beacon for moral guidance, its intensity should not depend on whether the crime is likely to be discovered. But if guilt is a way to keep everyone happy with your level of reciprocation, then whether the crime is public knowledge is relevant.


Darwin was a very decent man, and had an unusually active conscience. His morality didn't just extend as far as his society demanded, but further: he castigated a man for ill-treating a horse, and agonized over brutal treatment of slaves in Brazil.

Guilt is a cerebral emotion - not like the physicality of sex or hunger. This helps us believe we've accessed some higher truth - truly, as Wright puts it, a shameless ploy on the part of evolution.

All over the world, people feel guilt. But some much more or much less than others. Why? Darwin himself attributes his morality to his father and sister Caroline, who would frequently chide him when he was a child.

As the TIT FOR TAT simulation showed, mutual cooperation can be the optimal strategy in some environments. But in the history of human evolution, sometimes it was advantageous to exploit nice people. The heritability of conscientiousness is between 0.3 to 0.4, which leaves a lot of room for environment to play a role. Evolution appears to have given humans a malleable conscience - powerful when conditions favor cooperation and niceness, or weak when conditions favor exploitation and cheating.

All children practice deception - it is spontaneous and universal. This tendency leads children to learn to lie well, and to learn which lies will be judged harshly and which lies won't.

Through positive reinforcement (for undetected and fruitful lies) and negative reinforcement (for lies that peers uncover, or through the reprimand of kin) we learn what we can and can't get away with, and what our kin do and don't consider judicious deceit.

Victorian England was famously moral - a society where character and integrity were highly regarded. Why was this the case then, and not so much now? In the Victorian era, people lived in smaller communities, such as Darwin's home village of Shrewsbury, where they would interact with the same people repeatedly and gossip about the interactions. In modern times, we are much more likely to interact with strangers we'll never see again. A reputation for integrity may be less advantageous now. This theory predicts that if one's adolescence is filled with strangers and untrustworthy people, it may stifle a conscience for life.

From an early age, the conscience of many poor children, the very capacity for sympathy and guilt, is hemmed in by the environment, and as they grow up it settles somewhat firmly into this cramped form. The source of this cramping presumably goes well beyond urban anonymity. Many people in the inner city face limited opportunities for "legitimate" cooperation with the wider world. And the males, risk-prone by virtue of their gender to begin with, don't have the long life expectancies that so many people take for granted. Martin Daly and Margo Wilson have argued that the "short time horizons" for which criminals are famous may be "an adaptive response to predictive information about one's prospects for longevity and eventual success."

Darwin's conscience led him to virtue that couldn't possibly have been any advantage to him, like planting gardens for Fuegian Indians, or bringing a farmer to trial for letting some sheep starve to death. We must remember that organisms are not fitness maximizers, but adaption executers. The adaptions may or may not be executed in the environment they were designed for.

Update 2020-8-15: These chapter summaries were written in 2010 and I always intended to finish the summaries of the rest of the book. People sometimes still write to me, awaiting the final chapters. This project is still technically on my to-do list, but it's been ten years so outside view says it probably won't be soon.