Capítulo 1
The Mind's Inner Workings: A Journey Through Human Psychology
When was the last time you paused to consider the extraordinary machine sitting between your ears? The one that's reading these words right now, constructing meaning from abstract symbols, while simultaneously maintaining your heartbeat, monitoring your surroundings, and perhaps wondering what's for dinner? Paul Bloom's "Psych: The Story of the Human Mind" invites us on a fascinating journey through this remarkable organ and its capabilities. As a Yale professor whose online psychology course has reached over a million students, Bloom brings scholarly rigor to the table while maintaining an accessible approach that resonates with readers from all backgrounds. The book has become a favorite among celebrities like Bill Gates, who praised its "clear explanations of complex ideas," and has been featured on numerous "Best Science Books" lists. Beyond academic circles, it's sparked conversations about consciousness, free will, and human nature across social media platforms, podcasts, and book clubs. In a world increasingly concerned with mental health and understanding behavior, Bloom's exploration of the mind offers both scientific insights and practical wisdom about what makes us uniquely human.
Capítulo 2
The Physical Basis of Mind: Brain Makes Thought
The story of Phineas Gage stands as one of psychology's most dramatic illustrations of the brain-mind connection. In 1848, this railway foreman survived an iron rod shooting through his skull and brain, yet emerged as a different person. Though he retained basic functions like speech and movement, his personality transformed dramatically-from responsible and temperate to impulsive and childlike. Unable to hold down jobs, Gage drifted through life before dying from seizures eleven years later.
Similar cases abound throughout medical literature. Oliver Sacks described a patient named Greg F. who developed an unusual serenity after going blind. His Hare Krishna community interpreted this as spiritual transcendence, but it was actually caused by a tumor "the size of an orange" destroying his visual centers and extending into his frontal and temporal lobes. After surgical removal, Greg remained blind with impaired memory and flat emotions-arguably worse off than Gage had been.
These cases illustrate what Francis Crick called the "Astonishing Hypothesis": that our identities, emotions, and sense of self are "no more than the behavior of nerve cells and molecules." This materialist view contradicts our intuitive dualism-the feeling that mind and body are separate substances. Rene Descartes famously defended dualism by pointing to our unpredictable choices and our ability to doubt our bodies but not our thinking selves ("Cogito ergo sum"). But modern psychology rejects dualism because physical damage to the brain demonstrably changes personality, consciousness, and memory.
The brain's complexity is staggering-often described as "the most complicated thing in the known universe." Despite weighing just three pounds, it contains roughly 86 billion neurons with hundreds of trillions of connections. Each neuron has a cell body with a nucleus, branching dendrites that receive information, and a long axon that transmits electrical signals to other neurons. Information flows from dendrites to cell body to axon, crossing tiny gaps called synapses using chemical neurotransmitters that either excite or inhibit other neurons.
Unlike iron filings mindlessly drawn to a magnet, beings with brains can intelligently navigate obstacles to reach goals. Though it seems paradoxical to use our brains to understand themselves, there's reason for optimism. Just as computers perform intelligence through simple binary operations (0s and 1s), neurons' basic fire/don't-fire dichotomy might similarly generate complex thought. While brains differ significantly from conventional computers-operating in parallel rather than serially and having malleable rather than fixed memory-they are truly "computational" in that they process information.
The brain isn't uniform but contains specialized parts performing different functions-what Noam Chomsky called "mental organs." Modern neuroscience began with natural experiments-studying patients with brain damage. Paul Broca discovered a patient who could only say "tan, tan" due to damage in what's now called Broca's area. Carl Wernicke found patients who spoke fluently but produced gibberish due to damage in another region. The brain has both cortical (surface) and subcortical structures, like a peach with its skin and stone.
Though appearing symmetrical, the brain has important asymmetries. The left hemisphere typically handles language, reason and logic, while the right manages social processes, imagination and music. When the connection between hemispheres is severed (as was done for severe epilepsy), patients sometimes experience "alien hand syndrome" where one hand acts independently of conscious control-even removing clothes the other hand just put on.
While all mental activity happens in the brain, we shouldn't reduce psychology to neuroscience. Different levels of explanation serve different purposes. Some neuroscience findings do matter for psychological theory, however. Research by Naomi Eisenberger shows that social exclusion activates the same brain regions as physical pain, suggesting deep commonalities between social and physical suffering. This explains why drugs like Tylenol might reduce the hurt of loneliness.
Yet there remains what philosopher David Chalmers calls "the hard problem" of consciousness-how physical brain activity creates subjective experience. We know computers can perform complex tasks without feeling anything. So what's missing? What gives a being the capacity to feel? Nobody yet knows.
Capítulo 3
The Mystery of Consciousness: Our Inner Experience
Once dismissed by behaviorists as irrelevant, consciousness has become central to the science of mind. It's both our most certain reality and morally significant-suffering requires consciousness. Yet consciousness presents unique challenges as a fundamentally first-person phenomenon. While we assume others are conscious, we can't know if their experiences match our own. Genetic variations cause differences in sensory experiences, from color-blindness to synesthesia, and philosophical questions arise about whether we experience the same colors even when using the same words.
Scientific research offers insights into consciousness through studies of brain structure and function. EEG oscillations reveal states of consciousness: alpha waves (8-15hz) indicate relaxation, theta waves (below 4hz) correspond to sleep, and beta waves (16-31hz) signal agitation. fMRI studies can determine which image a person consciously perceives when presented with competing visual stimuli by tracking activation in specific brain regions. This technology even allows communication with "locked-in" patients who cannot speak or move-researchers can detect neural activity patterns when patients imagine playing tennis (signaling "yes") versus walking around their house (signaling "no"), enabling basic dialogue through thought alone.
The "hard problem" of consciousness-how physical brains create subjective experience-remains deeply contested. Some philosophers argue consciousness emerges from computational systems regardless of physical substrate, suggesting consciousness could exist in silicon-based life or even be "uploaded" to machines. Others view consciousness as fundamentally biological, comparable to digestion, making the idea of conscious computers as absurd as expecting a simulated rainstorm to produce real water.
Our conscious awareness is remarkably limited. We can't simultaneously perceive competing visual stimuli, as demonstrated by the famous vase-faces illusion where we see either two black faces or a white vase, but never both simultaneously. The "Gorillas in Our Midst" study dramatically illustrates our attentional blindness: roughly half of participants counting basketball passes miss an obvious gorilla walking through the scene. We compensate for these limitations through automaticity-with practice, activities like driving become habitual and unconscious, freeing our conscious mind for other tasks.
Our conscious experience extends beyond perception into our social lives. Experience sampling studies reveal our minds wander nearly half the time, typically leading to less pleasant mental states than when we're focused on the present. The "spotlight effect" demonstrates we dramatically overestimate how much others notice us-students wearing embarrassing Barry Manilow t-shirts consistently overestimated others' awareness of them.
Several mechanisms can diminish our self-focus. Being in crowds, as Gustave Le Bon observed in 1895, can make self-consciousness partially disappear-"An individual in a crowd is a grain of sand amid other grains of sand, which the wind stirs up at will." This loss of self-awareness has mixed effects: it enables the joyful synchronization at concerts or raves, but also facilitates harmful group behaviors like bystander apathy, where diffused responsibility reduces helping behavior.
Access consciousness-having information in one part of our psyche available to other parts-enables crucial functions like language and communication. Yet not everything in our minds is consciously accessible. Robert Trivers proposed an evolutionary advantage to keeping certain information unconscious: it facilitates deception. If you genuinely believe you're in love with someone rather than consciously faking it, your deception becomes more convincing.
Capítulo 4
The Unconscious Mind: Freud's Enduring Insights
Sigmund Freud's reputation has severely declined due to revelations about his character and questionable ethics. Documents showed he altered facts to fit theories, conducted therapies inconsistently with his principles, claimed success in failed treatments, took credit for others' work, and engaged in manipulative behavior. Many of his theories now seem strange and unsupported-from penis envy and castration anxiety to his interpretations of simple behaviors as revealing deep sexual pathologies. Despite these flaws, some core Freudian insights remain valuable, particularly his notion of an unconscious mind at war with itself.
The idea that our unconscious minds control much of our behavior is deeply unsettling-perhaps even more disturbing than materialism. While we believe we understand our own motivations, Freudians suggest our true reasons may be hidden from us. This explains powerful attractions or dislikes without obvious cause, forgotten names at crucial moments, or missed appointments despite conscious intentions. According to Freud, the unconscious reveals itself through dreams, jokes, and Freudian slips-verbal errors that betray our true thoughts. Examples include Donald Trump referring to "she's got a son" about his own child, a neuroscientist implying people with autism aren't human, or the fictional Ross saying "Rachel" during wedding vows to Emily.
Freud conceived the mind as three conflicting processes. The id, present at birth, represents our animal nature seeking immediate gratification according to the pleasure principle. The ego develops next, introducing consciousness and the reality principle-allowing us to either satisfy desires pragmatically or suppress them. Finally, the superego emerges, internalizing moral codes from parents and society. The ego thus serves two masters, caught between animal desires and conscience.
When defense mechanisms fail to properly repress impulses from the id, psychological problems arise. Freud studied hysteria-patients with physical symptoms without physical causes-initially linking it to childhood sexual abuse before later claiming these were fantasies. He developed psychoanalysis or "the talking cure," which aimed to bring repressed traumas to consciousness through techniques like dream interpretation and free association. Unlike modern approaches that address everyday difficulties directly, Freud saw these as mere symptoms of deeper issues.
Freud's theories, while influential, face criticism for being unfalsifiable-they can't be proven wrong regardless of evidence. When tested empirically, Freudian hypotheses about breastfeeding affecting personality, dream content containing sexual imagery, and Freudian slips fail to find support. Despite these shortcomings, Freud remains historically significant, was a gifted writer, and his core insight about the primacy of the unconscious endures as a fundamental psychological principle.
Capítulo 5
The Science of Learning: How Behavior is Shaped
B.F. Skinner, the "American Freud," achieved comparable fame but developed theories opposite to Freud's. While Freud explored rich unconscious dynamics, Skinner rejected internal psychological processes entirely, seeing no fundamental distinction between humans and animals like rats. Behaviorism centers on three radical claims: first, the primacy of learning and rejection of innate differences; second, the absence of meaningful differences between species; and third, antimentalism-the rejection of internal mental states as valid subjects for scientific study.
Classical conditioning, pioneered by Ivan Pavlov, demonstrates how neutral stimuli can become associated with natural responses. Pavlov discovered this while studying digestion in dogs, noticing they would salivate not just to food but to signals predicting food. The process involves three stages: first, an unconditioned stimulus (food) naturally produces an unconditioned response (salivation); second, a neutral stimulus (bell) is repeatedly paired with the unconditioned stimulus; finally, the neutral stimulus alone triggers the response, now called a conditioned response.
Operant conditioning explains how animals learn to act in the world. Edward Thorndike established its foundations by observing cats in puzzle boxes, discovering they solved problems not through reasoning but through trial and error-gradually getting better at hitting the escape lever. This led to his Law of Effect: actions producing satisfying results become more likely to recur, while those causing discomfort diminish. B.F. Skinner expanded this work, showing how behaviors could be shaped through reinforcement.
While consistent reinforcement teaches behaviors quickly, intermittent rewards create more persistent behaviors. When rewards stop after consistent reinforcement, the behavior quickly extinguishes. But when rewards were only occasional, the behavior persists much longer after rewards cease-like a gambler at a slot machine hoping the next pull will pay off. This explains why children whose tantrums are occasionally rewarded with attention will persist longer than those whose tantrums are consistently rewarded then suddenly ignored.
While behaviorism correctly identified conditioning principles that apply to humans, Chomsky's devastating 1959 review of Skinner's "Verbal Behavior" exposed its fundamental emptiness when applied to complex human behavior. Chomsky argued that Skinner's explanations were either trivially true or meaningless-if anything someone says can be attributed to "stimulus control" without specifying what the stimulus actually is, the theory has no explanatory power. Similarly, saying people do things because they find them "reinforcing" is merely rephrasing "people do what they like" without adding any scientific insight.
Despite these fatal theoretical flaws, Skinner's practical insights about learning mechanisms remain valuable in treating phobias and understanding addictive behaviors, like our compulsive social media checking that resembles a rat pressing a lever for intermittent rewards.
Capítulo 6
The Developing Mind: How Children Make Sense of the World
Developmental psychology offers profound insights into fundamental questions about human nature. The study of children's minds reveals not just how these "small creatures" think, but addresses broader questions about human destiny and development. Despite producing fewer colorful brain scans and perhaps suffering from sexism due to its association with childcare, developmental psychology has unique power to satisfy our curiosity about children's strange behaviors and remarkable learning abilities.
The fundamental question of where knowledge comes from-whether inborn or learned-has divided thinkers throughout history. Empiricism, championed by British philosophers like Locke who described the mind as "white paper void of characters," proposes that knowledge comes through environmental exposure. Opposing this is nativism, which argues much knowledge is innate. Though nature and nurture are inseparable-learning requires initial machinery, and innate systems require environmental input to function-some capacities clearly lean toward one side.
Jean Piaget, the preeminent developmental psychologist, began as a child prodigy who published his first scientific article at age ten. Though his ultimate interest was "genetic epistemology"-the development of human knowledge-he studied children as a window into this broader question. Piaget proposed that mental development occurs through schemas (cognitive structures) that evolve through assimilation (applying existing schemas to new situations) and accommodation (modifying schemas to fit new information).
Piaget proposed that children progress through distinct developmental stages. In the preoperational stage (ages two to seven), children begin reasoning, understanding time, and grasping object permanence, but have notable limitations. One is egocentrism-not selfishness, but an inability to understand others' perspectives, demonstrated in the Three Mountains task where children can't grasp that someone on the opposite side would see mountains in reverse order. Another limitation is their failure to understand conservation-they believe spreading candies makes them "more" or pouring water into a taller container increases its volume.
Modern developmental psychology has invented clever methods to explore infant cognition beyond Piaget's techniques. The "pacifier method" uses the Law of Effect-babies suck more to hear sounds they prefer, revealing preferences like mothers' voices over strangers'. Habituation studies leverage babies' tendency to lose interest in familiar stimuli-when they perk up at a green circle after seeing many red ones, it shows they perceive color differences. Looking-time studies exploit surprise-babies stare longer at unexpected events, revealing their understanding of how objects should behave.
These ingenious methods have demonstrated that babies are far more cognitively sophisticated than Piaget believed. In classic studies, five-month-olds show surprise when a screen rotates through a space where a block should be (but was secretly removed), suggesting they expect hidden objects to remain where placed. Based on such findings, Elizabeth Spelke proposed that babies possess an innate system for reasoning about objects that includes four principles: objects are cohesive (connected masses), solid (impermeable), move on continuous paths (don't teleport), and typically move only on contact.
Children are "natural-born essentialists," understanding that categories have deeper properties beyond surface appearances. Even three-year-olds, when shown a robin with a special blood chemical, will assume a different-looking flamingo (same category) shares this property rather than a similar-looking bat (different category). Young children believe removing a dog's insides makes it no longer a dog, while changing its outside appearance doesn't change its identity.
Returning to the fundamental question of whether children and adults think differently, some theorists say no-both empiricists and many nativists believe the basic mental structures remain consistent across development. Others, following Piaget, see radical cognitive change. Susan Carey's influential "child-as-scientist" theory proposes that conceptual change in children mirrors paradigm shifts in scientific thinking, with children developing intuitive theories about the world that transform over time.
Capítulo 7
The Language Instinct: How Humans Master Communication
Language sits at the heart of any successful theory of mind-indeed, behaviorism largely collapsed due to Skinner's failure to explain "verbal behavior." Despite their surface differences-demonstrated when students from diverse backgrounds translate a simple sentence like "The girl thinks that the house is big" into dozens of languages-all natural languages share remarkable expressive power. Languages may structure information differently or contain unique concepts (like Yiddish "nachas" for pride in others' accomplishments), but all can capture the same complex thoughts, making translation possible.
Language's universality likely stems from its innate roots in human nature, as Darwin observed: "Man has an instinctive tendency to speak." Evidence supporting this includes specialized brain regions (Broca's and Wernicke's areas), specific genes linked to language disorders, and even physical adaptations like the lowered larynx-a modification that increases choking risk but enables speech production, suggesting natural selection favored language despite its dangers.
Language consists of several interconnected systems. Phonology deals with language sounds-phonemes that distinguish words (like /p/ versus /b/ in "pat" and "bat"). Languages vary dramatically in phoneme count, from fewer than twelve in Rotokas to over a hundred in Taa, with English having about forty-four. Morphology concerns words and their meaningful units (morphemes). Syntax-the rule system for combining words-gives language its infinite generative power. Through recursive structures, humans can create and understand countless novel sentences.
Language involves both rule-based and associative processes. While brains function partly as association machines-noticing relationships between experiences as emphasized by British Empiricists and behaviorists-language also requires symbolic rule manipulation. Rules give language its communicative power. In English, past tense formation with "-ed" and adjective-before-noun ordering are generative rules we can apply to novel words.
While animals have rich communication systems, they differ fundamentally from human language. Animal systems lack phonology, morphology, syntax, arbitrary names, and recursive structures. Despite numerous attempts to teach language to nonhuman primates, these efforts have largely failed. Animals can develop limited vocabularies but show little evidence of syntax comparable to human language.
Language acquisition begins before birth, with newborns preferring their mother's voice and their native language. Initially, babies can distinguish phonemes from all languages-a capability adults lose as they specialize in their native tongue. Around six months, babies begin babbling, producing language-like sounds-deaf children similarly "babble" with their hands in sign language. By six months, infants recognize some word meanings, looking at corresponding images when words are spoken. First words typically emerge around the first birthday, with remarkable cross-cultural similarities-"Mommy" is usually first, followed by names for people, animals, toys, foods, and social words.
Language learning has a specific window of opportunity-a "critical" or "sensitive" period. Phonology is particularly time-sensitive; learn a language too late and you'll always speak with an accent. Syntax has a longer window, with recent data suggesting successful learning can occur until around age seventeen. Vocabulary acquisition, however, appears exempt from critical period constraints-we continue acquiring new words throughout our entire lives.
Before learning word meanings, children must solve the problem of determining where one word ends and another begins-speech lacks the convenient spaces of written text. Research shows infants accomplish this through statistical learning, tracking which syllables frequently occur together. When hearing a stream like "bidakupadotigolabubidaku," babies notice that "bi" is always followed by "da" then "ku," inferring that "bidaku" is likely a word.
The relationship between language and thought is both fascinating and contested. Thought clearly exists without language-animals think without words, babies reason before speaking, and adults perform complex spatial tasks they can't verbally describe. Language itself can't be the medium of thought because it's ambiguous (like "bat" meaning either animal or baseball equipment) while thoughts are precise. However, language may be most crucial for enabling abstract thought. While we can intuitively grasp the difference between two and three objects, distinguishing between ninety and ninety-one requires symbolic representation.
Capítulo 8
The Perceptual World: How We Construct Reality
Our minds construct representations of reality through a process where sensory information enters our brains, is processed, attended to, and sometimes stored as memories. We rarely experience pure sensation-the raw sensory data entering our brains. Instead, we perceive a preprocessed world, where coffee tastes like a specific brand, loved ones appear beautiful, and spoken language arrives already parsed into meaningful words.
We vastly underestimate the complexity of perception. In 1966, an MIT researcher assigned an undergraduate the seemingly simple task of connecting a computer to a camera so it could "describe what it saw." This summer project exemplifies our naive assumption about perception's simplicity. Despite over fifty years of research, computer vision still struggles to match human perception-no machine can perceive the world as well as a toddler. The problem feels easy because our brains solve it automatically. This "instinct blindness" makes us experience the world as "already parsed into objects, relationships, goals, foods, dangers" rather than appreciating the complex processes involved.
Our visual system performs the remarkable feat of inferring a stable three-dimensional world from constantly changing two-dimensional retinal images. When a dog runs away, its image shrinks on our retina, but we don't perceive the dog as shrinking. When it moves into shade, we don't see its color changing. Somehow, our brain calculates that there's a singular unchanging being moving through space and time. Successful perception coordinates two types of information: bottom-up input (neural firing from light hitting the retina) and top-down information (assumptions about the world).
Gestalt psychologists identified principles that help us organize visual perception. We naturally group objects by proximity (items close together are seen as related), similarity (similar items are grouped together), and good continuation (we perceive smooth, uninterrupted patterns). These principles reflect how objects typically exist in the world. Our visual system also places objects in three-dimensional space using various depth cues. Binocular disparity (the difference between what each eye sees) helps calculate distance. Even with one eye, we use cues like typical size (houses appear smaller than people when far away), interposition (objects blocking others are perceived as closer), and motion parallax (distant objects appear to move more slowly).
Memory underlies everything we know-not just our autobiography but all our skills and knowledge. A complete memory loss would be an obliteration of the self. There are distinct memory systems: autobiographical memory stores personal experiences, semantic memory holds facts like Paris being France's capital, and procedural memory governs skills like walking or driving.
The standard memory model begins with sensory memory-brief storage of visual afterimages or auditory echoes lasting seconds. When attended to, information moves to working memory (often identified with consciousness itself), which has a severely limited capacity of about four "chunks" of information. Long-term memory has virtually unlimited storage capacity (estimated at 2.5 petabytes) and holds everything from vocabulary to life experiences. Information enters long-term memory through depth of processing (thinking deeply about meaning), vivid associations, and consolidation during sleep.
Retrieval follows the compatibility principle-memories return easier in the same context they were acquired, whether physical environment or psychological state. Sometimes memories are irretrievable because they weren't stored properly or have degraded over time. Most importantly, memory isn't a faithful recording but is shaped by expectations and suggestions-explaining why eyewitness testimony can be unreliable and why people can develop false memories of events that never happened.
Capítulo 9
The Emotional Brain: What Drives Human Behavior
Edward Thorndike's 1937 article "Valuations of Certain Pains, Deprivations, and Frustrations" explored human motivation by asking people how much money they would accept to endure various unpleasant experiences. His survey revealed fascinating hierarchies of aversion, from relatively minor discomforts (spitting on a crucifix: $300) to experiences many refused at any price (having an ear cut off or being confined to an apartment for life). The median responses showed people would endure severe pain for an hour for $500, have a front tooth pulled for $5,000, and choke a stray cat to death for $10,000. These responses reveal our complex valuations of physical integrity, sensory abilities, freedom, and social reputation.
What fundamentally drives human behavior? Early theories proposed singular motivations like homeostasis (maintaining the body's internal environment), minimizing prediction error, or simply seeking pleasure and avoiding pain. However, these one-dimensional theories fail to provide comprehensive accounts of human motivation. The reality of human motivation is far more complex, involving multiple drives that evolved for different purposes.
William James rightly scoffed at the notion that humans alone lack instincts when every other creature possesses them. Rather, "man possesses all the impulses that [other animals] have, a great many more besides." These instincts emerged through natural selection-variations in traits influencing reproductive success became more common in subsequent generations. The critical insight is that evolution shaped our minds not for survival alone but for reproduction-we're driven to have sex and care for offspring because these behaviors increased our ancestors' reproductive success, not because they kept individuals alive.
Emotions are fundamental to human motivation, with distinct conscious experiences, physiological responses, and facial expressions. The six basic emotions-anger, disgust, fear, happiness, sadness, and surprise-appear universally, even among congenitally blind people who couldn't have learned them through observation. Yet emotional expression isn't purely universal-cultural "display rules" influence how emotions are shown, with Japanese people less likely to express anger than Canadians. Despite science fiction portrayals like Spock and Data suggesting otherwise, emotions aren't impediments to rational thought but essential for functioning.
Disgust manifests as an unpleasant feeling, often accompanied by nausea, a distinctive facial expression (scrunched nose, closed mouth, tongue pushed forward), and the motivation to avoid the disgusting object. Core disgust is universal-blood, gore, vomit, feces, urine, and rotten flesh disgust people everywhere. However, children aren't born disgust-sensitive; they'll readily touch or eat disgusting things until early childhood when this aversion emerges. Rather than resulting from toilet training, disgust likely evolved as an adaptation to avoid contamination and disease.
The fundamental asymmetry in reproduction creates different optimal strategies for males and females. As Robert Trivers noted, females invest substantially more in offspring-pregnancy, nursing, and years of care-while males need only contribute intercourse. This biological reality means females can have fewer offspring, making each one more valuable, which leads to greater selectivity in mating partners. Human data confirms these evolutionary predictions. In a study across fifty nations, men consistently wanted more sexual partners than women-about twice as many in the next month and triple over the next decade.
Beyond self-serving emotions, our moral emotions drive cooperation despite natural selection favoring gene propagation over group welfare. This creates an evolutionary puzzle: free riders who take benefits without costs should outcompete altruists. Robert Trivers proposed that kindness to non-kin could only evolve alongside mechanisms punishing free riders-either through direct punishment or by shunning those who don't reciprocate. Ironically, our finest instincts-love, gratitude, friendship-depend on our capacity for anger and resentment. Without the appetite for revenge, our cooperative society couldn't exist.
