Top Quotes: “How The Mind Works” — Steven Pinker

“Perhaps pregnancy sickness protects women against eating or digesting foods with toxins that might harm the developing fetus. Your local Happy Carrot Health Food Store notwithstanding, there is nothing particularly healthy about natural foods. Your cabbage, a Darwinian creature, has no more desire to be eaten than you do, and since it can’t very well defend itself through behavior, it resorts to chemical warfare. Most plants have evolved dozens of toxins in their tissues: insecticides, insect repellents, irritants, paralytics, poisons, and other sand to throw in herbivores’ gears. Herbivores have in turn evolved countermeasures, such as a liver to detoxify the poisons and the taste sensation we call bitterness to deter any further desire to ingest them. But the usual defenses may not be enough to protect a tiny embryo.

So far this may not sound much better than the barf-up-your-baby theory, but Profet synthesized hundreds of studies, done independently of each other and of her hypothesis, that support it. She meticulously documented that (1) plant toxins in dosages that adults tolerate can cause birth defects and induce abortion when ingested by pregnant women; (2) pregnancy sickness begins at the point when the embryo’s organ systems are being laid down and the embryo is most vulnerable to teratogens (birth defect-inducing chemicals) but is growing slowly and has only a modest need for nutrients; (3) pregnancy sickness wanes at the stage when the embryo’s organ systems are nearly complete and its biggest need is for nutrients to allow it to grow; (4) women with pregnancy sickness selectively avoid bitter, pungent, highly flavored, and novel foods, which are in fact the ones most likely to contain toxins; (5) women’s sense of smell becomes hypersensitive during the window of pregnancy sickness and less sensitive than usual thereafter; (6) foraging peoples (including, presumably, our ancestors) are at even higher risk of ingesting plant toxins, because they eat wild plants rather than domesticated crops bred for palatability; (7) pregnancy sickness is universal across human cultures; (8) women with more severe pregnancy sickness are less likely to miscarry; (9) women with more severe pregnancy sickness are less likely to bear babies with birth defects.”

“The first whale evolved in something like ten million years from its common ancestor with its closest living relatives, ungulates such as cows and pigs.”

“The final word on the political non-implications of group differences must go to Gloria Steinem: “There are really not many jobs that actually require a penis or a vagina, and all the other occupations should be open to everyone.””

“A linguist friend of mine who studies the Wari in the Amazon rainforest learned that their language has a term for edible things, which includes anyone who isn’t a Wari.”

“The people of early civilizations, including the Greeks of Homer and the Hebrews of the Old Testament, were unconscious. Dennett is sympathetic to the claim; he believes that consciousness “is largely a product of cultural evolution that gets imparted to brains in early training” and that it is “a huge complex of memes,” meme being Dawkins’ term for a contagious feature of culture, such as a catchy jingle or the latest fashion craze.

Something about the topic of consciousness makes people, like the White Queen in Through the Looking Class, believe six impossible things before breakfast. Could most animals really be unconscious — sleepwalkers, zombies, automata, out cold? Hath not a dog senses, affections, passions? If you prick them, do they not feel pain? And was Moses really unable to taste salt or see red or enjoy sex? Do children learn to become conscious in the same way that they learn to wear baseball caps turned around?”

“The white peppered moth gave way in nineteenth-century Manchester to a dark mutant form after industrial soot covered the lichen on which the moth rested, making the white form conspicuous to birds. When air pollution laws lightened the lichen in the 1950s, the then-rare white form reasserted itself.”

“The seminal ducts in men do not lead directly from the testicles to the penis but snake up into the body and pass over the ureter before coming back down. That is because the testes of our reptilian ancestors were inside their bodies. The bodies of mammals are too hot for the production of sperm, so the testes gradually descended into a scrotum. Like a gardener who snags a hose around a tree, natural selection did not have the foresight to plan the shortest route.”

“Small cold-blooded animals like insects struggle to regulate their temperature. Their high ratio of surface area to volume makes them heat up and cool down quickly. (That is why there are no bugs outside in cold months; winter is the best insecticide.) Perhaps the incipient wings of insects first evolved as adjustable solar panels, which soak up the sun’s energy when it is colder out and dissipate heat when it’s warmer. Using thermodynamic and aerodynamic analyses, Kingsolver and Kohl showed that proto-wings too small for flight are effective heat exchangers. The larger they grow, the more effective they become at heat regulation, though they reach a point of diminishing returns. That point is in the range of sizes in which the panels could serve as effective wings. Beyond that point, they become more and more useful for flying as they grow larger and larger, up to their present size. Natural selection could have pushed for bigger wings throughout the range from no wings to current wings, with a gradual change of function in the middle sizes.”

“Birds are not bom with this knowledge, not because it is unthinkable that it could be innate, but because if it were innate it would soon be obsolete. The earth’s axis of rotation, and hence the celestial pole (the point in the sky corresponding to north), wobbles in a 27,000-year cycle called the precession of the equinoxes. The cycle is rapid in an evolutionary timetable, and the birds have responded by evolving a special algorithm for learning where the celestial pole is in the night sky. It all happens while they are still in the nest and cannot fly. The nestlings gaze up at the night sky for hours, watching the slow rotation of the constellations. They find the point around which the stars appear to move, and record its position with respect to several nearby constellations, acquiring the information imparted to me by the Cub Scout manual. Months later they can use any of these constellations to maintain a constant heading say, keeping north behind them while flying south, or flying into the celestial pole the next spring to return north.

Honeybees perform a dance that tells their hivemates the direction and distance of a food source with respect to the sun. As if that weren’t impressive enough, the bees have evolved a variety of calibrations and backup systems to deal with the engineering complexities of solar navigation. The dancer uses an internal clock to compensate for the movement of the sun between the time she discovered the source and the time she passes on the information. If it’s cloudy, the other bees estimate the direction using the polarization of light in the sky.”

“Only so much solar energy falls on a patch of ground, and if the biomass it supports is locked up in wood it is not available to make animals. But grass is like the legendary self-replenishing goblet, growing back as soon as it is grazed. Grasslands can feed vast herds of herbivores, who in turn feed carnivores.”

“One kind of evidence is that the mitochondrial DNA (mDNA) of everyone on the planet (which is inherited only from one’s mother) can be traced back to an African woman living sometime in that period 100,000 years ago. (The claim is controversial, but the evidence is growing.)”

“According to their scenario, which is based on the remarkable sameness of genes across modern human populations, around 65,000 years ago our ancestors dwindled to a mere ten thousand people, perhaps because of a global cooling triggered by a volcano in Sumatra. The human race was as endangered as mountain gorillas are today. The population then exploded in Africa and spun off small bands that moved to other corners of the world, possibly mating now andagain with other early humans in their path. Many geneticists believe that evolution is especially rapid when scattered populations exchange occasional migrants. Natural selection can quickly adapt each group to local conditions, so one or more can cope with any new challenge that arises, and their handy genes will then be imported by the neighbors. Perhaps this period saw a final flowering in the evolution of the human mind.”

“A different technique, the anaglyph, overlays the two images on one surface and uses clever tricks so that each eye sees only the image intended for it. A familiar example is the notorious red-and-green cardboard eyeglasses associated with the 3-D movie craze of the early 1950s. The left eye’s image is projected in red and the right eye’s image is projected in green onto a single white screen. The left eye peers at the screen through a green filter, which makes the white background look green and the green lines intended for the other eye invisible; the red lines intended for the left eye stand out as black. Similarly, the red filter over the right eye makes the background red, the red lines invisible, and the green lines black. Each eye gets its own image, and the Sludge Monsters from Alpha Centauri rise out of the screen.”

“An easy way to experience the wallpaper effect is to stare at a tile wall a few inches away, too close to focus and converge on comfortably. (Many men rediscover the effect as they stand at a urinal.) The tiles in front of each eye easily fuse, creating the surreal impression of a very large tile wall a great distance away. The wall bows outward, and as the head moves from side to side the wall rocks in the opposite direction. Both would have to happen in the world if the wall were really at that distance while projecting the current retinal image. The brain creates those illusions in its headlong attempt to keep the geometry of the whole hallucination consistent.”

“Unfortunately, a given amount of light reflecting off a patch could have come from a dark surface angled toward the light or from a light surface angled away. So there is no foolproof way to recover a surface’s angle from the light it reflects without making additional assumptions.

A first assumption is that surface lightness is uniform: the world is made of plaster. When surfaces are unevenly pigmented, the assumption is violated, and our shading analyzer should be fooled. It is. Paintings and photographs are the most obvious example. A less obvious one is countershading in animal camouflage. The hides of many animals lighten from back to belly in a gradient that cancels out the effects of light on their 3-D shapes. This flattens the animal, making it harder to detect by the assumption-making, shape-from-shading analyzer in the brain of a predator. Makeup is another example. When applied in sub-Tammy Faye Bakker amounts, pigment on the skin can fool the beholder into seeing the flesh and bone as having a more ideal shape. Dark blush on the sides of the nose makes them look as if they are at a shallower angle to the light, which makes the nose appear narrower. White powder on the upper lip works the other way: the lip seems to intercept the light source head-on as if it were fuller, bestowing that desirable pouty look.”

“Why. on earth — or space — should a mismatch between vision and gravity or inertia lead, of all things, to nausea? What does up-and-down have to do with the gut? The psychologist Michel Treisman has come up with a plausible though still unproven explanation. Animals vomit to expel toxins they have eaten before the toxins do further harm. Many naturally occurring toxins act on the nervous system. This raises the problem faced by Ingrid Bergman in Notorious: how do you know when you have been poisoned? Your judgment would be addled, but that would affect your judgment about whether your judgment has been addled! More generally, how could a malfunction detector distinguish between the brain’s malfunctioning and its accurately registering an unusual situation? (Old bumper sticker: “The world is experiencing technical difficulties. Do not adjust your mind.”) Gravity, of course, is the most stable, predictable feature of the world. If two parts of the brain have different opinions about it, chances are that one or both is malfunctioning or that the signals they are getting have been delayed or garbled. The rule would be: if you think gravity is acting up, you’ve been poisoned; jettison the rest of the poison, now.”

“The geon theory says that at the highest levels of perception the mind “sees” objects and parts as idealized geometric solids. That would explain a curious and long-noted fact about human visual aesthetics. Anyone who has been to a figure-drawing class or a nude beach quickly learns that real human bodies do not live up to our sweet imaginations. Most of us look better in clothes. In his history of fashion, the art historian Quentin Bell gives an explanation that could have come right out of the geon theory:

If we wrap an object in some kind of envelope, so that the eyes infer rather than see the object that is enclosed, the inferred or imagined form is likely to be more perfect than it would appear if it were uncovered. Thus a square box covered with brown paper will be imagined as a perfect square. Unless the mind is given some very strong clue it is unlikely to visualize holes, dents, cracks, or other accidental qualities. In the same way, if we cast a drapery over a thigh, a leg, an arm or a breast, the imagination supposes a perfectly formed member; it does not and usually cannot envisage the irregularities and the imperfections which experience should lead us to expect.

… We know what [a body] is probably like from experience, and yet we are willing to suspend our disbelief in favour of the fictions of [the person’s] wardrobe. Indeed I think that we are ready to go further in the way of self-deception. When we slip on our best jacket and see our deplorably unimpressive shoulders artfully magnified and idealised we do, for a moment, rise in our own esteem.

Geons are not good for everything. Many natural objects, such as mountains and trees, have complicated fractal shapes, but geons turn them into pyramids and lollipops. And though geons can be built into a passable generic human face, like a snowman or Mr. Potato Head, it is almost impossible to build a model of a particular face — John’s face, your grandmother’s face that is different enough from other faces not to confuse them, but stable enough across smiles, frowns, weight gains, and aging to identify that person every time.”

“None of us is good at remembering how to begin. Left and right shoes look so alike that children must be taught tricks to distinguish them, like placing the shoes side by side and sizing up the gap. Which way is Abraham Lincoln facing on the American one-cent piece? There is only a fifty percent chance you will get the answer right, the same as if you had answered by flipping the penny. What about Whistler’s famous painting, Arrangement in Black and Gray: The Artist’s Mother? Even the English language likes to collapse left and right: beside and next to denote side-by-side without specifying who’s on the left, but there is no word like bebove or aneath that denotes up-and-down without specifying who’s on top. Our obliviousness to left-and-right stands in stark contrast to our hypersensitivity to up-and-down and front-and-back. Apparently the human mind does not have a preexisting label for the third dimension of its object-centered reference frame. When it sees a hand, it can align the wrist-fingertip axis with “down-up,” and the back-palm axis with “backward-forward,” but the direction of the pinkie-thumb axis is up for grabs. The mind calls it, say, “thumb-ward,” and the left and right hands become mental synonyms. Our indecisiveness about left and right needs an explanation, because a geometer would say they are no different from up and down or front and back.

The explanation is that mirror-image confusions come naturally to a bilaterally symmetrical animal. A perfectly symmetrical creature is logically incapable of telling left from right (unless it could react to the decay of cobalt 60!). Natural selection had little incentive to build animals asymmetrically so that they could mentally represent shapes differently from their reflections. Actually, this puts it backwards: natural selection had every incentive to build animals symmetrically so that they would not represent shapes differently from their reflections. In the intermediate-sized world in which animals spend their days (bigger than subatomic particles and organic molecules, smaller than a weather front), left and right make no difference. Objects from dandelions to mountains have tops that differ conspicuously from their bottoms, and most things that move have fronts that differ conspicuously from their behinds. But no natural object has a left side that differs nonrandomly from its right, making its mirror-image version behave differently. If a predator comes from the right, next time it might come from the left. Anything learned from the first encounter should generalize to the mirror-image version. Another way of putting it is that if you took a photographic slide of any natural scene, it would be obvious if someone had turned it upside down, but you wouldn’t notice if someone had flipped it left-to-right, unless the scene contained a human-made object like a car or writing.”

“Donald Symons notes that reactivating a visual experience may well have benefits, but it also has costs: the risk of confusing imagination with reality. Within moments of awakening from a dream, our memory for its plot is wiped out, presumably to avoid contaminating autobiographical memory with bizarre confabulations. Similarly, our voluntary, waking mental images might be hobbled to keep them from becoming hallucinations or false memories.”

“It is not only science that can suffer under the thumb of those in power. The anthropologist Donald Brown was puzzled to learn that over the millennia the Hindus of India produced virtually no histories, while the neighboring Chinese had produced libraries full. He suspected that the potentates of a hereditary caste society realized that no good could come from a scholar nosing around in records of the past where he might stumble upon evidence undermining their claims to have descended from heroes and gods. Brown looked at twenty-five civilizations and compared the ones organized by hereditary castes with the others. None of the caste societies had developed a tradition of writing accurate depictions of the past; instead of history they had myth and legend.”

“Fish do not occupy one branch in the tree of life. One of their kind, a lungfish, begot the amphibians, whose descendants embrace the reptiles, whose descendants embrace the birds and the mammals. There is no definition that picks out all and only the fish, no branch of the tree of life that includes salmon and lungfish but excludes lizards and cows. Taxonomists fiercely debate what to do with categories like fish that are obvious to any child but have no scientific definition because they are neither species nor clades. Some insist that there is no such thing as a fish; it is merely a layperson’s stereotype. Others try to rehabilitate everyday categories like fish using computer algorithms that sort creatures into clusters sharing properties. Still others wonder what the fuss is about; they see categories like families and orders as matters of convenience and taste — which similarities are important for the discussion at hand.”

“Murderous rampages by disgruntled postal workers are so common (a dozen incidents in a dozen years) that a slang term for losing one’s temper is “going postal.” But running amok is not unique to America, to Western nations, or even to modern societies. Amok is a Malay word for the homicidal sprees occasionally undertaken by lonely Indochinese men who have suffered a loss of love, a loss of money, or a loss of face. The syndrome has been described in a culture even more remote from the West: the stone-age foragers of Papa New Guinea.”

“Here is the key to why we have emotions. An animal cannot pursue all its goals at once. If an animal is both hungry and thirsty, it should not stand halfway between a berry bush and a lake.”

“Homo sapiens is adapted to two habitats. One is the African savanna, in which most of our evolution took place. For an omnivore like our ancestors, the savanna is a hospitable place compared with other ecosystems. Deserts have little biomass because they have little water. Temperate forests lock up much of their biomass in wood. Rainforests or, as they used to be called, jungles, place it high in the canopy, relegating omnivores on the ground to being scavengers who gather the bits that fall from above. But the savanna grasslands dotted with clumps of trees — is rich in biomass, much of it in the flesh of large animals, because grass replenishes itself quickly when grazed. And most of the biomass is conveniently placed a meter or two from the ground. Savannas also offer expansive views, so predators, water, and paths can be spotted from afar. Its trees provide shade and an escape from carnivores.

Our second-choice habitat is the rest of the world.”

“Our love of flowers, which we don’t eat except in salads in overpriced res-taurants, needs an explanation. People are intuitive botanists, and a flower is a rich source of data. Plants blend into a sea of green and often can be identified only by their flowers. Flowers are harbingers of growth, marking the site of future fruit, nuts, or tubers for creatures smart enough to remember them.”

“Disgust deters people from eating certain things, or, if it’s too late, makes them spit or vomit them out. The facial expression says it all: the nose is wrinkled, constricting the nostrils, and the mouth is opened and the tongue pushed forward as if to squeegee offending material out.

Disgusting things come from animals. They include whole animals, parts of animals (particularly parts of carnivores and scavengers), and body products, especially viscous substances like mucus and pus and, most of all, feces, universally considered disgusting. Decaying animals and their parts are particularly revolting. In contrast, plants are sometimes distasteful, but distaste is different from disgust.”

“The anthropologist Elizabeth Cashdan has documented that children’s willingness to try new foods plummets after the third birthday. Third, if children had to learn what to avoid, then all animals would be palatable except for the few that are proscribed. But as Rozin himself points out, all animals are disgusting except for a few that are permitted. No child has to be taught to revile greasy grimy gopher guts or mutilated monkey meat.

Cashdan has a better idea. The first two years, she proposes, are a sensitive period for learning about food. During those years mothers control children’s food intake and children eat whatever they are permitted. Then their tastes spontaneously shrink, and they stomach only the foods they were given during the sensitive period. Those distastes can last to adulthood, though adults occasionally overcome them from a variety of motives: to dine with others, to appear macho or sophisticated, to seek thrills, or to avert starvation when familiar fare is scarce.”

“Social threats lead to shyness and gestures of appeasement. People really do faint at the sight of blood, because their blood pressure drops, presumably a response that would minimize the further loss of one’s own blood.”

“A crime is a gamble whose payoff is immediate and whose possible cost comes later. They attributed the discounting to low intelligence. The psychologists Martin Daly and Margo Wilson have a different explanation. In the American inner cities, life expectancy for young males is low, and they know it. (In Hoop Dreams, the documentary about aspiring basketball players in a Chicago ghetto, there is an arresting scene in which the mother of one of the boys rejoices that he is alive on his eighteenth birthday.) Moreover, the social order and long-term ownership rights which would guarantee that investments are repaid are tenuous. These are precisely the circumstances in which steeply discounting the future taking risks, consuming rather than investing is adaptive.”

“A social smile is executed by circuits in the cerebral cortex that are under voluntary control; a smile of pleasure is executed by circuits in the limbic system and other brain systems and is involuntary. Anger, fear, and sadness, too, recruit muscles that can’t be controlled voluntarily, and the genuine expressions are hard to fake, though we can pantomime an approximation. Actors must simulate facial expressions for a living, but many cannot avoid a mannered look. Some great actors, like Laurence Olivier, are highly coordinated athletes who have doggedly learned to control every muscle. Others learn method acting, inspired by Konstantin Stanislavsky, in which actors make themselves feel an emotion by remembering or imagining a charged experience, and the expression pops on the face reflexively.”

“Incredible as it may seem, many of us used to believe this treacle. A leading idea of the 1960s and 70s was that mistrust, jealousy, competitiveness, greed, and manipulation were social institutions due for reform. Some people thought they were unnecessary evils, like slavery or the denial of the vote to women. Others thought they were hidebound traditions whose inefficiency had gone unnoticed, as with the genius who figured out that toll bridges could charge a dollar to the traffic going one way instead of fifty cents to the traffic going both ways.”

“The most extreme examples of kin-directed altruism are found among social insects like ants and bees, in which the workers give their all to the colony. They are permanently sterile and defend the colony with kamikaze tactics like blowing up to spray noxious chemicals on an invader or stinging it with a barbed stinger that pulls the insect’s body apart when dislodged. Such dedication comes largely from an unusual genetic system which makes them more closely related to their sisters than they would be to their offspring. By defending the colony they help their mothers make sisters instead of making offspring of their own.”

“In one study of emotionally healthy middle-class families in the United States, only half of the stepfathers and a quarter of the stepmothers claimed to have “parental feeling” toward their step-children, and fewer still claimed to “love” them.”

“These intrigues have spawned two of the modern myths of kinship: that in traditional societies, people have no voice in whom they marry, and that kinship has nothing to do with genetic relatedness. The grain of truth in the first myth is that parents everywhere wield as much power as they can to influence whom their children marry. Children do not, however, passively accept their parents’ choice. People everywhere have powerful emotions about whom they want to marry — that is, romantic love and engagements are often fierce battles of wills between parents and children. Even when parents have the final say, the children lobby day and night to make their feelings known, and the feelings almost always enter into the decision. The plot of Sholem Aleichem’s Tevye’s Daughters (adapted into the musical Fiddler on the Roof) unfolds on this battlefield, and similar plots are found across the world. When children elope, it is a catastrophe for their parents. The business deal or strategic opportunity of a lifetime may have just been frittered away. Worse, if the parents had pledged the child years before — which often happens, because children are born at different times and the second half of an exchange must wait until a child reaches marriageable age — the parents are now in default and at the mercy of the loan sharks. Or the parents may have mortgaged themselves to the eyeballs to buy a spouse for the departed child. Defaults on marriage agreements are a leading cause of feuding and warfare in traditional societies. With the stakes so high, it is no wonder that the parents’ generation always teaches that romantic love is frivolous or does not exist at all.”

“A gene that made a child murder his newborn sister would have a fifty percent chance of destroying a copy of itself, and in most species that cost outweighs the benefit of having one’s mother’s milk all to oneself. (In some species, like spotted hyenas and some birds of prey, the costs don’t outweigh the benefits, and siblings do murder one another.) A gene that made a fifteen-year-old want to nurse would foreclose an opportunity for his mother to manufacture new copies of that gene inside viable siblings. Either cost would exceed twice the benefit, so most organisms have their siblings’ interests at heart, though discounted relative to their own.”

“Though enlightened parents try mightily never to play favorites, they don’t always succeed. In one study, fully two-thirds of British and American mothers confessed to loving one of their children more.”

“In some parts of China, brides used to move into their in-laws’ homes, giving rise to frictions that you can well imagine. Parents hit on the brilliant idea of adopting a bride for their son when she was still a child, guaranteeing that she would forever be under her mother-in-law’s thumb. What they did not realize was that the arrangement mimicked the psychological cues to siblinghood. When the couple grew up, they found each other unsexy, and compared with conventional couples, their marriages were unhappy, unfaithful, unfecund, and short. In parts of Lebanon, paternal parallel cousins grow up together as if they were siblings. Parents pressure the cousins into marrying, but the couples are sexually apathetic, relatively childless, and prone to divorce. Unconventional childrearing arrangements have been found to have the same outcome on all continents, and various alternative explanations can be ruled out.

Conversely, people who do commit incest often have not grown up together. A study of sibling incest offenders in Chicago found that the only ones who had contemplated marriage were those who had been raised apart. Fathers who sexually abuse their daughters tend to have spent less time with them when they were small. Stepfathers who have had as much contact with their young stepdaughters as biological fathers do are no more likely to abuse them.”

“Germs are small, and they evolve diabolical tricks for infiltrating and hijacking the machinery of the cells, for skimming off its raw materials, and for passing themselves off as the body’s own tissues to escape the surveillance of the immune system. The body responds with better security systems, but the germs have a built-in advantage: there are more of them and they can breed millions of times faster, which makes them evolve faster. They can evolve substantially within the lifetime of a host. Whatever molecular locks the body has evolved, the pathogens can evolve keys to open them.

Now, if an organism is asexual, once the pathogens crack the safe of its body they also have cracked the safes of its children and siblings. Sexual reproduction is a way of changing the locks once a generation. By swapping half the genes out for a different half, an organism gives its offspring a head start in the race against the local germs. Its molecular locks have a different combination of pins, so the germs have to start evolving new keys from scratch.”

“The mitochondria, has its own genes, the famous mitochondrial DNA which is so useful in dating evolutionary splits. Like all genes, the ones in mitochondria are selected to replicate ruthlessly. And that is why a cell formed by fusing two equal cells faces trouble. The mitochondria of one parent and the mitochondria of the other parent wage a ferocious war for survival inside it. Mitochondria from each parent will murder their counterparts from the other, leaving the fused cell dangerously underpowered. The genes for the rest of the cell (the ones in the nucleus) suffer from the crippling of the cell, so they evolve a way of heading off the internecine warfare. In each pair of parents, one “agrees” to unilateral disarmament. It contributes a cell that provides no metabolic machinery, just naked DNA for the new nucleus. The species reproduces by fusing a big cell that contains a half-set of genes plus all the necessary machinery with a small cell that contains a half-set of genes and nothing else. The big cell is called an egg and the small cell is called a sperm.”

“Female elephant seals, for example, congregate on beach strips which a male can easily patrol. A single male can monopolize the group, and males fight bloody battles for this jackpot. Bigger fighters are better fighters, so the males have evolved to be four times the size of the females.”

“In a study of homosexuals in San Francisco before the AIDS epidemic, twenty-eight percent of gay men reported having had more than a thousand sex partners, and seventy-five percent reported having had more than a hundred. No gay woman reported a thousand partners, and only two percent reported as many as a hundred.”

“Leaders have outlawed polygyny when they needed less powerful men as allies and when they needed their subjects to fight an enemy instead of fighting one another. Early Christianity appealed to poor men partly because the promise of monogamy kept them in the marriage game, and in societies since, egalitarianism and monogamy go together as naturally as despotism and polygyny.

Even today, inequality has allowed a kind of polygyny to flourish. Wealthy men support a wife and a mistress, or divorce their wives at twenty-year intervals and pay them alimony and child support while marrying younger women. The journalist Robert Wright has speculated that easy divorce and remarriage, like overt polygyny, increases violence. Women of childbearing age are monopolized by well-to-do men, and the shortage of potential wives trickles down to the lower strata, forcing the poorest young men into desperate competition.”

“Throughout the English-speaking world, the common law recognizes three circumstances that reduce murder to manslaughter: self-defense, the defense of close relatives, and sexual contact self-defense, with the man’s wife.”

“The word for “leader” in most foraging societies is “big man,” and in fact the leaders usually are big men. In the United States, taller men are hired more, are promoted more, earn more ($600 per inch in annual salary), and are elected president more: the taller candidate won twenty of the twenty-four elections between 1904 and 1996. A glance at the personal ads shows that women want taller men. As in other species whose males compete, the human male is bigger than the female, and has evolved ways of appearing bigger still, like a low voice and a beard (which makes the head look bigger and has evolved separately in lions and monkeys). Leonid Brezhnev claimed that he got to the top because of his eyebrows! Men everywhere exaggerate the size of their heads (with hats, helmets, headdresses, and crowns), their shoulders (with pads, boards, epaulettes, and feathers), and, in some societies, their penises (with impressive codpieces and sheaths, sometimes a yard long).”

“Biologists since Darwin had been puzzled by displays like the peacock’s tail, which impresses the peahen but consumes nutrients, hinders movement, and attracts predators. The biologist Amotz Zahavi proposed that the displays evolved because they were handicaps. Only the healthiest animals could afford them, and females choose the healthiest birds to mate with. Theoretical biologists. were initially skeptical, but one of them, Alan Grafen, later proved that the theory was sound.”

“When the class structure loosens, or sumptuous goods (or good imitations) become widely available, the upper middle class can emulate the upper class, the middle class can emulate the upper middle class, and so on down the ladder. The upper class cannot very well stand by as they begin to resemble the hoi polloi; they must adopt a new look. But then the look is emulated once again by the upper middle class and begins to trickle down again, prompting the upper class to leap to yet a different look, and so on. The result is fashion. The chaotic cycles of style, in which the chic look of one decade becomes dowdy or slutty, nerdy or foppish in the next, have been explained as a conspiracy of clothing makers, an expression of nationalism, a reflection of the economy, and much else. But Quentin Bell, in his classic analysis of fashion, On Human Finery, showed that only one explanation works: people follow the rule, “Try to look like the people above you; if you’re at the top, try to look different from the people below you.”

Once again animals discovered the trick first. The other dandies of the animal kingdom, butterflies, did not evolve their colors to impress the females. Some species evolved to be poisonous or distasteful, and warned their predators with gaudy colors. Other poisonous kinds copied the colors, taking advantage of the fear already sown. But then some nonpoisonous butterflies copied the colors, too, enjoying the protection while avoiding the expense of making themselves distasteful. When the mimics become too plentiful, the colors no longer conveyed information and no longer deterred the predators. The distasteful butterflies evolved new colors, which were then mimicked by the palatable ones, and so on.”

“In foraging societies, men go to war to get or keep women — not necessarily as a conscious goal of the warriors (though often it is exactly that), but as the ultimate payoff that allowed a willingness to fight to evolve. Access to women is the limiting factor on males’ reproductive success. Having two wives can double a man’s children, having three wives can triple it, and so on. For a man who is not at death’s door, no other resource has as much impact on evolutionary fitness. The most common spoils of tribal warfare are women. Raiders kill the men, abduct the nubile women, gang-rape them, and allocate them as wives.”

“War, or aggression by a coalition of individuals, is rare in the animal kingdom. You would think that the second-, third-, and fourth-strongest elephant seals would gang up, kill the strongest male, and divide his harem among them, but they never do. Aside from the social insects, whose unusual genetic system makes them a special case, only humans, chimpanzees, dolphins, and perhaps bonobos join up in groups of four or more to attack other males. These are some of the largest-brained species, hinting that war may require sophisticated mental machinery.”

“Laughter is contagious. The psychologist Robert Provine, who has documented the ethology of laughter in humans, found that people laugh thirty times more often when they are with other people than when they are alone. Even when people laugh alone, they are often imagining they are with others: they are reading others’ words, hearing their voices on the radio, or watching them on television.”

“The Bible contains instructions for genocide, rape, and the destruction of families, and even the Ten Commandments, read in context, prohibit murder, lying, and theft only within the tribe, not against outsiders.”