REVIEWS The New Synthesis in Moral Psychology Jonathan Haidt People are selfish, yet morally motivated. Morality is universal, yet culturally variable. Such apparent contradictions are dissolving as research from many disciplines converges on a few shared principles, including the importance of moral intuitions, the socially functional (rather than truth-seeking) nature of moral thinking, and the coevolution of moral minds with cultural practices and institutions that create diverse moral communities. I propose a fourth principle to guide future research: Morality is about more than harm and fairness. More research is needed on the collective and religious parts of the moral domain, such as loyalty, authority, and spiritual purity. I Department of Psychology, University of Virginia, Charlottesville, VA 22904, USA. E-mail: haidt@virginia.edu 998 emotion and the “emotive centers” of the brain. A quantitative analysis of the publication database in psychology shows that research on morality and emotion grew steadily in the 1980s and 1990s (relative to other topics), and then grew very rapidly in the past 5 years (fig. S1). In this Review, I suggest that the key factor that catalyzed the new synthesis was the “affective revolution” of the 1980s—the increase in research on emotion that followed the “cognitive revolution” of the 1960s and 1970s. I describe three principles, each more than 100 years old, that were revived during the affective revolution. Each principle links together insights from several fields, particularly social psychology, neuroscience, and evolutionary theory. I conclude with a fourth principle that I believe will be the next step in the synthesis. Principle 1: Intuitive Primacy (but Not Dictatorship) Kohlberg thought of children as budding moral philosophers, and he studied their reasoning as they struggled with moral dilemmas (e.g., Should a man steal a drug to save his wife’s life?). But in recent years, the importance of moral reasoning has been questioned as social psychologists have increasingly embraced a version of the “affective primacy” principle, articulated in the 1890s by Wilhelm Wundt and greatly expanded in 1980 by Robert Zajonc (2). Zajonc reviewed evidence that the human mind is composed of an ancient, automatic, and very fast affective system and a phylogenetically newer, slower, and motivationally weaker cognitive system. Zajonc’s basic point was that brains are always and automatically evaluating everything they perceive, and that higher-level human thinking is preceded, permeated, and influenced by affective reactions (simple feelings of like and dislike) which push us gently (or not so gently) toward approach or avoidance. Evolutionary approaches to morality generally suggest affective primacy. Most propose that the building blocks of human morality are emotional (3, 4) (e.g., sympathy in response to suffering, anger at nonreciprocators, affection for kin and allies) and that some early forms of these 18 MAY 2007 VOL 316 SCIENCE www.sciencemag.org Downloaded from https://www.science.org at University of Guelph on September 11, 2023 f you ever become a contestant on an unusually erudite quiz show, and you are asked to explain human behavior in two seconds or less, you might want to say “self-interest.” After all, economic models that assume only a motive for self-interest perform reasonably well. However, if you have time to give a more nuanced answer, you should also discuss the moral motives addressed in Table 1. Try answering those questions now. If your total for column B is higher than your total for column A, then congratulations, you are Homo moralis, not Homo economicus. You have social motivations beyond direct self-interest, and the latest research in moral psychology can help explain why. In 1975, E. O. Wilson (1) predicted that ethics would soon be incorporated into the “new synthesis” of sociobiology. Two psychological theories of his day were ethical behaviorism (values are learned by reinforcement) and the cognitive-developmental theory of Lawrence Kohlberg (social experiences help children construct an increasingly adequate understanding of justice). Wilson believed that these two theories would soon merge with research on the hypothalamic-limbic system, which he thought supported the moral emotions, to provide a comprehensive account of the origins and mechanisms of morality. As it turned out, Wilson got the ingredients wrong. Ethical behaviorism faded with behaviorism. Kohlberg’s approach did grow to dominate moral psychology for the next 15 years, but because Kohlberg focused on conscious verbal reasoning, Kohlbergian psychology forged its interdisciplinary links with philosophy and education, rather than with biology as Wilson had hoped. And finally, the hypothalamus was found to play little role in moral judgment. Despite these errors in detail, Wilson got the big picture right. The synthesis began in the 1990s with a new set of ingredients, and it has transformed the study of morality today. Wilson was also right that the key link between the social and natural sciences was the study of building blocks were already in place before the hominid line split off from that of Pan 5 to 7 million years ago (5). Language and the ability to engage in conscious moral reasoning came much later, perhaps only in the past 100 thousand years, so it is implausible that the neural mechanisms that control human judgment and behavior were suddenly rewired to hand control of the organism over to this new deliberative faculty. Social-psychological research strongly supports Zajonc’s claims about the speed and ubiquity of affective reactions (6). However, many have objected to the contrast of “affect” and “cognition,” which seems to imply that affective reactions don’t involve information processing or computation of any kind. Zajonc did not say that, but to avoid ambiguity I have drawn on the work of Bargh (7) to argue that the most useful contrast for moral psychology is between two kinds of cognition: moral intuition and moral reasoning (8). Moral intuition refers to fast, automatic, and (usually) affect-laden processes in which an evaluative feeling of good-bad or like-dislike (about the actions or character of a person) appears in consciousness without any awareness of having gone through steps of search, weighing evidence, or inferring a conclusion. Moral reasoning, in contrast, is a controlled and “cooler” (less affective) process; it is conscious mental activity that consists of transforming information about people and their actions in order to reach a moral judgment or decision. My attempt to illustrate the new synthesis in moral psychology is the Social Intuitionist Model (8), which begins with the intuitive primacy principle. When we think about sticking a pin into a child’s hand, or we hear a story about a person slapping her father, most of us have an automatic intuitive reaction that includes a flash of negative affect. We often engage in conscious verbal reasoning too, but this controlled process can occur only after the first automatic process has run, and it is often influenced by the initial moral intuition. Moral reasoning, when it occurs, is usually a post-hoc process in which we search for evidence to support our initial intuitive reaction. Evidence that this sequence of events is the standard or default sequence comes from studies indicating that (i) people have nearly instant implicit reactions to scenes or stories of moral violations (9); (ii) affective reactions are usually good predictors of moral judgments and behaviors (10, 11); (iii) manipulating emotional reactions, such as through hypnosis, can alter moral judgments (12); and (iv) people can sometimes be “morally dumbfounded”—they can know intuitively that something is wrong, even when they cannot explain why (8, 13). Furthermore, studies of everyday reasoning (14) demonstrate that people generally begin reasoning by setting out to confirm their initial hypothesis. They rarely seek disconfirming evidence, and are quite good at finding support for whatever they want to believe (15). REVIEWS www.sciencemag.org SCIENCE VOL 316 18 MAY 2007 Downloaded from https://www.science.org at University of Guelph on September 11, 2023 The importance of affect-laden Table 1. What’s your price? Write in the minimum amount that someone would have to pay you (anonymously and intuitions is a central theme of secretly) to convince you to do these 10 actions. For each one, assume there will be no social, legal, or material neuroscientific work on morality. consequences to you afterward. Homo economicus would prefer the option in column B to the option in column A for action Damasio (16) found that patients 1 and would be more or less indifferent to the other four pairs. In contrast, a person with moral motives would (on average) who had sustained damage to cer- require a larger payment to engage in the actions in column B and would feel dirty or degraded for engaging in some of tain areas of the prefrontal cortex these actions for personal enrichment. These particular actions were generated to dramatize moral motives, but they also retained their “cognitive” abilities illustrate the five-foundations theory of intuitive ethics (41, 42). by most measures, including IQ and How much money would it take to get you to… explicit knowledge of right and Column A Column B Moral wrong, but they showed massive category emotional deficits, and these deficits crippled their judgment and 1) Harm/ Stick a pin into your palm. Stick a pin into the palm of a child you decision-making. They lost the care don’t know. ability to feel the normal flashes of $___ $___ affect that the rest of us feel when 2) Fairness/ Accept a plasma screen television that a Accept a plasma screen television that a we simply hear the words “slap reciprocity friend of yours wants to give you. You friend of yours wants to give you. You your father.” They lost the ability to know that your friend bought the TV a know that your friend got the television a use their bodies—or, at least, to inyear ago from a thief who had stolen it year ago when the company that made it tegrate input from brain areas that from a wealthy family. sent it, by mistake and at no charge, to map bodily reactions—to feel what your friend. they would actually feel if they were $___ $___ in a given situation. Later studies of 3) Ingroup/ Say something slightly bad about your Say something slightly bad about your moral judgment have confirmed the loyalty nation (which you don’t believe to be nation (which you don’t believe to be importance of areas of the medial true) while calling in, anonymously, to true) while calling in, anonymously, to a prefrontal cortex, including ventroa talk-radio show in a foreign nation. talk-radio show in your nation. medial prefrontal cortex and the $___ $___ medial frontal gyrus (17, 18). These 4) Authority/ Slap your father in the face (with his Slap a friend in the face (with his/her areas appear to be crucial for inrespect permission) as part of a comedy skit. permission) as part of a comedy skit. tegrating affect (including expec$___ $___ tations of reward and punishment) 5) Purity/ Attend a performance art piece in Attend a performance art piece in which into decisions and plans. Other sanctity which the actors act like animals for 30 the actors act like idiots for 30 min, areas that show up frequently in min, including crawling around including failing to solve simple functional magnetic resonance imnaked and urinating on stage. problems and falling down repeatedly on aging studies include the amygdala stage. and the frontal insula (9, 11, 16). $___ $___ These areas seem to be involved in Total for column A: $___ Total for column B: $___ sounding a kind of alarm, and for then “tilting the pinball machine,” as it were, to push subsequent processing in a We can reframe a situation and see a new angle “intuitive scientists” who analyze the evidence or consequence, thereby triggering a second of everyday experience to construct internal particular direction. Affective reactions push, but they do not flash of intuition that may compete with the representations of reality. In the past 15 years, absolutely force. We can all think of times when first. And we can talk with people who raise however, many researchers have rediscovered we deliberated about a decision and went against new arguments, which then trigger in us new William James’ pragmatist dictum that “thinking our first (often selfish) impulse, or when we flashes of intuition followed by various kinds of is for doing.” According to this view, moral changed our minds about a person. Greene et al. reasoning. The social intuitionist model includes reasoning is not like that of an idealized scientist (19) caught the brain in action overriding its separate paths for each of these three ways of or judge seeking the truth, which is often useful; initial intuitive response. They created a class of changing one’s mind, but it says that the first rather, moral reasoning is like that of a lawyer or difficult dilemmas, for example: Would you two paths are rarely used, and that most moral politician seeking whatever is useful, whether or smother your own baby if it was the only way change happens as a result of social interaction. not it is true. One thing that is always useful is an to keep her from crying and giving away your Other people often influence us, in part by hiding place to the enemy soldiers looking for presenting the counterevidence we rarely seek explanation of what you just did. People in all you, who would then kill the whole group of you out ourselves. Some researchers believe, how- societies gossip, and the ability to track reputahiding in the basement? Subjects were slow to ever, that private, conscious verbal reasoning is tions and burnish one’s own is crucial in most respond to cases like these and, along the way, either the ultimate authority or at least a fre- recent accounts of the evolution of human exhibited increased activity in the anterior cingu- quent contributor to our moral judgments and morality (22, 23). The first rule of life in a dense late cortex, a brain region that responds to inter- decisions (19–21). There are at present no data web of gossip is: Be careful what you do. The nal conflict. Some subjects said “yes” to cases on how people revise their initial judgments in second rule is: What you do matters less than like these, and they exhibited increased activity in everyday life (outside the lab), but we can look what people think you did, so you’d better be the dorsolateral prefrontal cortex, suggesting that more closely at research on reasoning in general. able to frame your actions in a positive light. You’d better be a good “intuitive politician” (24). they were doing additional processing and What role is reasoning fit to play? From this social-functionalist perspective, it is overriding their initial flash of horror. not surprising that people are generally more There are at least three ways we can override Principle 2: (Moral) Thinking Is for accurate in their predictions of what others will our immediate intuitive responses. We can use (Social) Doing conscious verbal reasoning, such as considering During the cognitive revolution, many psychol- do than in their (morally rosier) predictions about the costs and benefits of each course of action. ogists adopted the metaphor that people are what they themselves will do (25), and it is not 999 REVIEWS 1000 was “designed” to work with affect, not free of it, and in daily life the environment usually obliges by triggering some affective response. But how did humans, and only humans, develop these gossipy communities in the first place? How relevant to moral judgment? (1=never, 6 =always) principle, I suggest, is the insight of the sociologist Emile Durkheim (30) that morality binds and builds; it constrains individuals and ties them to each other to create groups that are emergent entities with new properties. A moral community has a set of shared norms Principle 3: Morality Binds and Builds about how members ought to behave, combined Nearly every treatise on the evolution of morality with means for imposing costs on violators and/or covers two processes: kin selection (genes for channeling benefits to cooperators. A big step in altruism can evolve if altruism is targeted at kin) modeling the evolution of such communities is and reciprocal altruism (genes for altruism can the extension of reciprocal altruism by “indirect reciprocity” (31) in which virtue pays by improving one’s reputation, which 6 elicits later cooperation from others. Reputation is a powerful force for strengthening and enlarging moral communities (as users of ebay.com 5 know). When repeated-play behavioral economics games allow players to know each others’ reputations, cooperation rates skyrocket (29). Evolu4 tionary models show that indirect reciprocity can solve the problem of free-riders (which doomed simpler models of altruism) in moderately large 3 groups (32), as long as people have access to information about reputations Harm (e.g., gossip) and can then engage in Fairness low-cost punishment such as shunning. 2 However the process began, early Ingroup humans sometimes found ways to Authority solve the free-rider problem and to live Purity in larger cooperative groups. In so 1 doing, they may have stepped through a major transition in evolutionary Liberal Moderate Conservative history (33). From prokaryotes to Very Slightly Slightly Very eukaryotes, from single-celled orgaliberal liberal conservative conservative nisms to plants and animals, and from Politics individual animals to hives, colonies, Fig. 1. Liberal versus conservative moral foundations. and cooperative groups, the simple Responses to 15 questions about which considerations are rules of Darwinian evolution never relevant to deciding “whether something is right or wrong.” change, but the complex game of life Those who described themselves as “very liberal” gave the changes when radically new kinds of highest relevance ratings to questions related to the Harm/ players take the field. Ant colonies are Care and Fairness/Reciprocity foundations and gave the lowest a kind of super-organism whose prolifratings to questions about the Ingroup/Loyalty, Authority/ eration has altered the ecology of our Respect, and Purity/Sanctity foundations. The more conservative the participant, the more the first two foundations planet. Ant colonies compete with each decrease in relevance and the last three increase [n = 2811; other, and group selection therefore data aggregated from two web surveys, partially reported in shaped ant behavior and made ants (41)]. All respondents were citizens of the United States. Data extraordinarily cooperative within their for 476 citizens of the United Kingdom show a similar pattern. colonies. However, biologists have long resisted the idea that group seThe survey can be taken at www.yourmorals.org. lection contributed to human altruism because human groups do not restrict breeding evolve if altruism and vengeance are targeted at to a single queen or breeding pair. Genes related those who do and don’t return favors, respective- to altruism for the good of the group are therely). But several researchers have noted that these fore vulnerable to replacement by genes related two processes cannot explain the extraordinary to more selfish free-riding strategies. Human degree to which people cooperate with strangers group selection was essentially declared offthey’ll never meet again and sacrifice for large limits in 1966 (34). In the following decades, however, several groups composed of nonkin (23, 29). There must have been additional processes at work, and the theorists realized that human groups engage in study of these processes—especially those that cultural practices that modify the circumstances unite cultural and evolutionary thinking —is an under which genes are selected. Just as a exciting part of the new synthesis. The unifying modified gene for adult lactose tolerance evolved 18 MAY 2007 VOL 316 SCIENCE www.sciencemag.org Downloaded from https://www.science.org at University of Guelph on September 11, 2023 surprising that people so readily invent and confidently tell stories to explain their own behaviors (26). Such “confabulations” are often reported in neuroscientific work; when brain damage or surgery creates bizarre behaviors or beliefs, the patient rarely says “Gosh, why did I do that?” Rather, the patient’s “interpreter module” (27) struggles heroically to weave a story that is then offered confidently to others. Moral reasoning is often like the press secretary for a secretive administration—constantly generating the most persuasive arguments it can muster for policies whose true origins and goals are unknown (8, 28). The third rule of life in a web of gossip is: Be prepared for other people’s attempts to deceive and manipulate you. The press secretary’s pronouncements usually contain some useful information, so we attend to them, but we don’t take them at face value. We easily switch into “intuitive prosecutor” mode (24), using our reasoning capacities to challenge people’s excuses and to seek out—or fabricate—evidence against people we don’t like. Thalia Wheatley and I (12) recently created prosecutorial moral confabulations by giving hypnotizable subjects a post-hypnotic suggestion that they would feel a flash of disgust whenever they read a previously neutral word (“take” for half the subjects; “often” for the others). We then embedded one of those two words in six short stories about moral violations (e.g., accepting bribes or eating one’s dead pet dog) and found that stories that included the disgust-enhanced word were condemned more harshly than those that had no such flash. To test the limiting condition of this effect, we included one story with no wrongdoing, about Dan, a student council president, who organizes faculty-student discussions. The story included one of two versions of this sentence: “He [tries to take]/[often picks] topics that appeal to both professors and students in order to stimulate discussion.” We expected that subjects who felt a flash of disgust while reading this sentence would condemn Dan (intuitive primacy), search for a justification (post-hoc reasoning), fail to find one, and then be forced to override their hypnotically induced gut feeling using controlled processes. Most did. But to our surprise, one third of the subjects in the hypnotic disgust condition (and none in the other) said that Dan’s action was wrong to some degree, and a few came up with the sort of post-hoc confabulations that Gazzaniga reported in some split-brain patients, such as “Dan is a popularity-seeking snob” or “It just seems like he’s up to something.” They invented reasons to make sense of their otherwise inexplicable feeling of disgust. When we engage in moral reasoning, we are using relatively new cognitive machinery that was shaped by the adaptive pressures of life in a reputation-obsessed community. We are capable of using this machinery dispassionately, such as when we consider abstract problems with no personal ramifications. But the machinery itself REVIEWS sciousness, our emotions, and our motor movements with those of other people. Principle 4: Morality Is About More Than Harm and Fairness If I asked you to define morality, you’d probably say it has something to do with how people ought to treat each other. Nearly every research program in moral psychology has focused on one of two aspects of interpersonal treatment: (i) harm, care, and altruism (people are vulnerable and often need protection) or (ii) fairness, reciprocity, and justice (people have rights to certain resources or kinds of treatment). These two topics bear a striking match to the two evolutionary mechanisms of kin selection (which presumably made us sensitive to the suffering and needs of close kin) and reciprocal altruism (which presumably made us exquisitely sensitive to who deserves what). However, if group selection did reshape human morality, then there might be a kind of tribal overlay (23)—a coevolved set of cultural practices and moral intuitions—that are not about how to treat other individuals but about how to be a part of a group, especially a group that is competing with other groups. In my cross-cultural research, I have found that the moral domain of educated Westerners is narrower—more focused on harm and fairness— than it is elsewhere. Extending a theory from cultural psychologist Richard Shweder (40), Jesse Graham, Craig Joseph, and I have suggested that there are five psychological foundations, each with a separate evolutionary origin, upon which human cultures construct their moral communities (41, 42). In addition to the harm and fairness foundations, there are also widespread intuitions about ingroup-outgroup dynamics and the importance of loyalty; there are intuitions about authority and the importance of respect and obedience; and there are intuitions about bodily and spiritual purity and the importance of living in a sanctified rather than a carnal way. And it’s not just members of traditional societies who draw on all five foundations; even within Western societies, we consistently find an ideological effect in which religious and cultural conservatives value and rely upon all five foundations, whereas liberals value and rely upon the harm and fairness foundations primarily (Fig. 1 and Table 1). Research on morality beyond harm and fairness is in its infancy; there is much to be learned. We know what parts of the brain are active when people judge stories about runaway trolleys and unfair divisions of money. But what happens when people judge stories about treason, disrespect, or gluttony? We know how children develop an ethos of caring and of justice. But what about the development of patriotism, respect for tradition, and a sense of sacredness? There is some research on these questions, but it is not yet part of the new synthesis, which has focused on issues related to harm and fairness. www.sciencemag.org SCIENCE VOL 316 In conclusion, if the host of that erudite quiz show were to allow you 60 seconds to explain human behavior, you might consider saying the following: People are self-interested, but they also care about how they (and others) treat people, and how they (and others) participate in groups. These moral motives are implemented in large part by a variety of affect-laden intuitions that arise quickly and automatically and then influence controlled processes such as moral reasoning. Moral reasoning can correct and override moral intuition, though it is more commonly performed in the service of social goals as people navigate their gossipy worlds. Yet even though morality is partly a game of selfpromotion, people do sincerely want peace, decency, and cooperation to prevail within their groups. And because morality may be as much a product of cultural evolution as genetic evolution, it can change substantially in a generation or two. For example, as technological advances make us more aware of the fate of people in faraway lands, our concerns expand and we increasingly want peace, decency, and cooperation to prevail in other groups, and in the human group as well. References and Notes 1. E. O. Wilson, Sociobiology (Harvard Univ. Press, Cambridge, MA, 1975). 2. R. B. Zajonc, Am. Psychol. 35, 151 (1980). 3. R. L. Trivers, Q. Rev. Biol. 46, 35 (1971). 4. M. Hauser, Moral Minds: How Nature Designed our Universal Sense of Right and Wrong (HarperCollins, New York, 2006). 5. J. C. Flack, F. B. M. de Waal, in Evolutionary Origins of Morality, L. D. Katz, Ed. (Imprint Academic, Thorverton, UK, 2000), pp. 1–29. 6. R. H. Fazio, D. M. Sanbonmatsu, M. C. Powell, F. R. Kardes, J. Pers. Soc. Psychol. 50, 229 (1986). 7. J. A. Bargh, T. L. Chartrand, Am. Psychol. 54, 462 (1999). 8. J. Haidt, Psychol. Rev. 108, 814 (2001). 9. Q. Luo et al., Neuroimage 30, 1449 (2006). 10. C. D. Batson, Adv. Exp. Soc. Psych. 20, 65 (1987). 11. A. G. Sanfey, J. K. Rilling, J. A. Aronson, L. E. Nystrom, J. D. Cohen, Science 300, 1755 (2003). 12. T. Wheatley, J. Haidt, Psychol. Sci. 16, 780 (2005). 13. F. Cushman, L. Young, M. Hauser, Psychol. Sci. 17, 1082 (2006). 14. D. Kuhn, The Skills of Argument (Cambridge Univ. Press, Cambridge, 1991). 15. Z. Kunda, Psychol. Bull. 108, 480 (1990). 16. A. Damasio, Looking for Spinoza (Harcourt, Orlando, FL, 2003). 17. J. D. Greene, R. B. Sommerville, L. E. Nystrom, J. M. Darley, J. D. Cohen, Science 293, 2105 (2001). 18. J. Greene, J. Haidt, Trends Cogn. Sci. 6, 517 (2002). 19. J. D. Greene, L. E. Nystrom, A. D. Engell, J. M. Darley, J. D. Cohen, Neuron 44, 389 (2004). 20. D. A. Pizarro, P. Bloom, Psychol. Rev. 110, 193 (2003). 21. E. Turiel, in Handbook of Child Psychology, W. Damon, Ed. (Wiley, New York, ed. 6, 2006). 22. R. Dunbar, Grooming, Gossip, and the Evolution of Language (Harvard Univ. Press, Cambridge, MA, 1996). 23. P. J. Richerson, R. Boyd, Not by Genes Alone: How Culture Transformed Human Evolution (Univ. of Chicago Press, Chicago, IL, 2005). 24. P. E. Tetlock, Psychol. Rev. 109, 451 (2002). 25. N. Epley, D. Dunning, J. Pers. Soc. Psychol. 79, 861 (2000). 26. R. E. Nisbett, T. D. Wilson, Psychol. Rev. 84, 231 (1977). 27. M. S. Gazzaniga, The Social Brain (Basic Books, New York, 1985). 18 MAY 2007 Downloaded from https://www.science.org at University of Guelph on September 11, 2023 in tandem with cultural practices of raising dairy cows, so modified genes for moral motives may have evolved in tandem with cultural practices and institutions that rewarded group-beneficial behaviors and punished selfishness. Psychological mechanisms that promote uniformity within groups and maintain differences across groups create conditions in which group selection can occur, both for cultural traits and for genes (23, 35). Even if groups vary little or not at all genetically, groups that develop norms, practices, and institutions that elicit more group-beneficial behavior can grow, attract new members, and replace less cooperative groups. Furthermore, preagricultural human groups may have engaged in warfare often enough that group selection altered gene frequencies as well as cultural practices (36). Modified genes for extreme group solidarity during times of conflict may have evolved in tandem with cultural practices that led to greater success in war. Humans attain their extreme group solidarity by forming moral communities within which selfishness is punished and virtue rewarded. Durkheim believed that gods played a crucial role in the formation of such communities. He saw religion as “a unified system of beliefs and practices relative to sacred things, that is to say, things set apart and forbidden—beliefs and practices which unite into one single moral community called a church, all those who adhere to them” (30). D. S. Wilson (35) has argued that the coevolution of religions and religious minds created conditions in which multilevel group selection operated, transforming the older morality of small groups into a more tribal form that could unite larger populations. As with ants, group selection greatly increased cooperation within the group, but in part for the adaptive purpose of success in conflict between groups. Whatever the origins of religiosity, nearly all religions have culturally evolved complexes of practices, stories, and norms that work together to suppress the self and connect people to something beyond the self. Newberg (37) found that religious experiences often involve decreased activity in brain areas that maintain maps of the self’s boundaries and position, consistent with widespread reports that mystical experiences involve feelings of merging with God or the universe. Studies of ritual, particularly those involving the sort of synchronized motor movements common in religious rites, indicate that such rituals serve to bind participants together in what is often reported to be an ecstatic state of union (38). Recent work on mirror neurons indicates that, whereas such neurons exist in other primates, they are much more numerous in human beings, and they serve to synchronize our feelings and movements with those of others around us (39). Whether people use their mirror neurons to feel another’s pain, enjoy a synchronized dance, or bow in unison toward Mecca, it is clear that we are prepared, neurologically, psychologically, and culturally, to link our con- 1001 REVIEWS 28. T. D. Wilson, Strangers to Ourselves: Discovering the Adaptive Unconscious (Belknap Press, Cambridge, MA, 2002). 29. E. Fehr, J. Henrich, in Genetic and Cultural Evolution of Cooperation, P. Hammerstein, Ed. (MIT Press, Cambridge, MA, 2003). 30. E. Durkheim, The Elementary Forms of the Religious Life (1915; reprint, The Free Press, New York, 1965). 31. M. A. Nowak, K. Sigmund, Nature 437, 1291 (2005). 32. K. Panchanathan, R. Boyd, Nature 432, 499 (2004). 33. J. Maynard Smith, E. Szathmary, The Major Transitions in Evolution (Oxford Univ. Press, Oxford, UK, 1997). 34. G. C. Williams, Adaptation and Natural Selection: A Critique of Some Current Evolutionary Thought (Princeton Univ. Press, Princeton, NJ, 1966). 35. D. S. Wilson, Darwin’s Cathedral: Evolution, Religion, and the Nature of Society (Univ. of Chicago Press, Chicago, IL, 2002). 36. S. Bowles, Science 314, 1569 (2006). 37. A. Newberg, E. D’Aquili, V. Rause, Why God Won’t Go Away: Brain Science and the Biology of Belief (Ballantine, New York, 2001). 38. W. H. McNeill, Keeping Together in Time: Dance and Drill in Human History (Harvard Univ. Press, Cambridge, MA, 1995). 39. V. Gallese, C. Keysers, G. Rizzolatti, Trends Cogn. Sci. 8, 396 (2004). 40. R. A. Shweder, N. C. Much, M. Mahapatra, L. Park, in Supporting Online Material www.sciencemag.org/cgi/content/full/316/5827/998/DC1 Figs. S1 and S2 References 10.1126/science.1137651 2) Images that typically evoke emotionally “positive” and “negative” responses were presented on a computer screen. Experimental participants were asked to indicate when a picture appeared by quickly moving a lever. Some participants were instructed to push a lever away from their body, whereas others were told to pull a lever toward their body. Participants who pushed the lever away responded to negative images faster than to positive images, whereas participants who pulled the lever toward themselves responded faster to positive images (2). 3) Under the guise of studying the quality of different headphones, participants were induced either to nod in agreement or to shake their heads in disagreement. While they were “testing” their headphones with one of these two movements, the experimenter placed a pen on the table in front of them. Later, a different experimenter offered the participants the pen that had been placed on the table earlier or a novel pen. Individuals who were nodding their heads preferred the old pen, whereas participants who had been shaking their heads preferred the new one (3). All of these studies show that there is a reciprocal relationship between the bodily expression of emotion and the way in which emotional information is attended to and interpreted (Fig. 1). Charles Darwin himself defined attitude as a collection of motor behaviors (especially posture) that conveys an organism’s emotional response toward an object (4). Thus, Fig. 1. Two ways in which facial expression has been manipulated in behavioral experiments. (Top) In order to manipulate contraction of the brow muscle in a simulation of negative affect, researchers have affixed golf tees to the inside of participants’ eyebrows (42). Participants in whom negative emotion was induced were instructed to bring the ends of the golf tees together, as in the right panel. [Photo credit: Psychology Press]. (Bottom) In other research, participants either held a pen between the lips to inhibit smiling, as in the left panel, or else held the pen between the teeth to facilitate smiling (39). Paula M. Niedenthal* ere is a thought experiment: A man goes into a bar to tell a new joke. Two people are already in the bar. One is smiling and one is frowning. Who is more likely to “get” the punch line and appreciate his joke? Here is another: Two women are walking over a bridge. One is afraid of heights, so her heart pounds and her hands tremble. The other is not afraid at all. On the other side of the bridge, they encounter a man. Which of the two women is more likely to believe that she has just met the man of her dreams? You probably guessed that the first person of the pair described in each problem was the right answer. Now consider the following experimental findings: 1) While adopting either a conventional working posture or one of two so-called ergonomic postures, in which the back was straight and the shoulders were held high and back or in which the shoulders and head were slumped, experimental participants learned that they had succeeded on an achievement test completed earlier. Those who received the good news in the slumped posture felt less proud and reported being in a worse mood than participants in the upright or working posture (1). H Centre National de la Recherche Scientifique (CNRS) and University of Clermont-Ferrand, France. E-mail: niedenthal@ wisc.edu *Present address: Laboratoire de Psychologie Sociale et Cognitive, Université Blaise Pascal, 34 Avenue Carnot, 63037 Clermont-Ferrand, France. 18 MAY 2007 VOL 316 SCIENCE www.sciencemag.org Downloaded from https://www.science.org at University of Guelph on September 11, 2023 Recent theories of embodied cognition suggest new ways to look at how we process emotional information. The theories suggest that perceiving and thinking about emotion involve perceptual, somatovisceral, and motoric reexperiencing (collectively referred to as “embodiment”) of the relevant emotion in one’s self. The embodiment of emotion, when induced in human participants by manipulations of facial expression and posture in the laboratory, causally affects how emotional information is processed. Congruence between the recipient’s bodily expression of emotion and the sender’s emotional tone of language, for instance, facilitates comprehension of the communication, whereas incongruence can impair comprehension. Taken all together, recent findings provide a scientific account of the familiar contention that “when you’re smiling, the whole world smiles with you.” it would not have come as any surprise to him that the human body is involved in the acquisition and use of attitudes and preferences. Indeed, one speculates that Darwin would be satisfied to learn that research reveals that (i) when individuals adopt emotion-specific postures, they report experiencing the associated emotions; (ii) when individuals adopt facial expressions or make emotional gestures, their preferences and attitudes are influenced; and (iii) when individuals’ motor movements are inhibited, interference in the experience of emotion and processing of emotional information is observed (5). The causal relationship between embodying emotions, feeling emotional states, Embodying Emotion 1002 Morality and Health, A. Brandt, P. Rozin, Eds. (Routledge, New York, 1997), pp. 119–169. 41. J. Haidt, J. Graham, Soc. Justice Res., in press. 42. J. Haidt, C. Joseph, in The Innate Mind, P. Carruthers, S. Laurence, S. Stich, Eds. (Oxford Univ. Press, New York, in press), vol. 3. 43. I thank D. Batson, R. Boyd, D. Fessler, J. Graham, J. Greene, M. Hauser, D. Wegner, D. Willingham, and D. S. Wilson for helpful comments and corrections. The New Synthesis in Moral Psychology Jonathan Haidt Science, 316 (5827), . DOI: 10.1126/science.1137651 Use of this article is subject to the Terms of service Science (ISSN 1095-9203) is published by the American Association for the Advancement of Science. 1200 New York Avenue NW, Washington, DC 20005. The title Science is a registered trademark of AAAS. American Association for the Advancement of Science Downloaded from https://www.science.org at University of Guelph on September 11, 2023 View the article online https://www.science.org/doi/10.1126/science.1137651 Permissions https://www.science.org/help/reprints-and-permissions Chapter 1 The Role of Visions One of the curious things about political opinions is how often the same people line up on opposite sides of different issues. The issues themselves may have no intrinsic connection with each other. They may range from military spending to drug laws to monetary policy to education. Yet the same familiar faces can be found glaring at each other from opposite sides of the political fence, again and again. It happens too often to be coincidence and it is too uncontrolled to be a plot. A closer look at the arguments on both sides often shows that they are reasoning from fundamentally different premises. These different premises—often implicit—are what provide the consistency behind the repeated opposition of individuals and groups on numerous, unrelated issues. They have different visions of how the world works. It would be good to be able to say that we should dispense with visions entirely, and deal only with reality. But that may be the most utopian vision of all. Reality is far too complex to be comprehended by any given mind. Visions are like maps that guide us through a tangle of bewildering complexities. Like maps, visions have to leave out many concrete features in order to enable us to focus on a few key paths to our goals. Visions are indispensable—but dangerous, precisely to the extent that we confuse them with reality itself. What has been deliberately neglected may not in fact turn out to be negligible in its effect on the results. That has to be tested against evidence. A vision has been described as a “pre-analytic cognitive act.”1 It is what we sense or feel before we have constructed any systematic reasoning that could be called a theory, much less deduced any specific consequences as hypotheses to be tested against evidence. A vision is our sense of how the world works. For example, primitive man’s sense of why leaves move may have been that some spirit moves them, and his sense of why tides rise or volcanoes erupt may have run along similar lines. Newton had a very different vision of how the world works and Einstein still another. For social phenomena, Rousseau had a very different vision of human causation from that of Edmund Burke. Visions are the foundations on which theories are built. The final structure depends not only on the foundation, but also on how carefully and consistently the framework of theory is constructed and how well buttressed it is with hard facts. Visions are very subjective, but well-constructed theories have clear implications, and facts can test and measure their objective validity. The world learned at Hiroshima that Einstein’s vision of physics was not just Einstein’s vision. Logic is an essential ingredient in the process of turning a vision into a theory, just as empirical evidence is then essential for determining the validity of that theory. But it is the initial vision which is crucial for our glimpse of insight into the way the world works. In Pareto’s words: Logic is useful for proof but almost never for making discoveries. A man receives certain impressions; under their influence he states—without being able to say either how or why, and if he attempts to do so he deceives himself—a proposition, which can be verified experimentally….2 Visions are all, to some extent, simplistic—though that is a term usually reserved for other people’s visions, not our own. The ever-changing kaleidoscope of raw reality would defeat the human mind by its complexity, except for the mind’s ability to abstract, to pick out parts and think of them as the whole. This is nowhere more necessary than in social visions and social theory, dealing with the complex and often subconscious interactions of millions of human beings. No matter what vision we build on, it will never account for “every sparrow’s fall.” Social visions especially must leave many important phenomena unexplained, or explained only in ad hoc fashion, or by inconsistent assumptions that derive from more than one vision. The purest vision may not be the basis of the most impressive theories, much less the most valid ones. Yet purer visions may be more revealing as to unspoken premises than are the more complex theories. For purposes of understanding the role of visions, William Godwin’s Enquiry Concerning Political Justice (1793) may tell us more than Marx’s Capital. Indeed, we may understand more of Marx’s Capital after we have seen how similar premises worked out in the less complicated model of William Godwin. Likewise, the vision of social causation underlying the theories of the Physiocrats was in its essentials very much like the vision elaborated in a more complex and sophisticated way by Adam Smith and still later (and still more so) by Milton Friedman. A vision, as the term is used here, is not a dream, a hope, a prophecy, or a moral imperative, though any of these things may ultimately derive from some particular vision. Here a vision is a sense of causation. It is more like a hunch or a “gut feeling” than it is like an exercise in logic or factual verification. These things come later, and feed on the raw material provided by the vision. If causation proceeds as our vision conceives it to, then certain other consequences follow, and theory is the working out of what those consequences are. Evidence is fact that discriminates between one theory and another. Facts do not “speak for themselves.” They speak for or against competing theories. Facts divorced from theory or visions are mere isolated curiosities. Ultimately there are as many visions as there are human beings, if not more, and more than one vision may be consistent with a given fact. Theories can be devastated by facts but they can never be proved to be correct by facts. Facts force us to discard some theories—or else to torture our minds trying to reconcile the irreconcilable—but they can never put the final imprimatur of ultimate truth on a given theory. What empirical verification can do is to reveal which of the competing theories currently being considered is more consistent with what is known factually. Some other theory may come along tomorrow that is still more consistent with the facts, or explains those facts with fewer, clearer, or more manageable assumptions—or a new theory may fit both this and other empirical phenomena hitherto explained by a separate theory. Social visions are important in a number of ways. The most obvious is that policies based on a certain vision of the world have consequences that spread through society and reverberate across the years, or even across generations or centuries. Visions set the agenda for both thought and action. Visions fill in the necessarily large gaps in individual knowledge. Thus, for example, an individual may act in one way in some area in which he has great knowledge, but in just the opposite way elsewhere, where he is relying on a vision he has never tested empirically. A doctor may be a conservative on medical issues and a liberal on social and political issues, or vice versa. The political battles of the day are a potpourri of special interests, mass emotions, personality clashes, corruption, and numerous other factors. Yet the enduring historic trends have a certain consistency that reflects certain visions. Often special interests prevail to the extent that they can mobilize support from the general public’s responsiveness to visions which can be invoked for or against a given policy. From the standpoint of personal motivation, ideas may be simply the chips with which special interests, demagogues, and opportunists of various sorts play the political game. But from a broader perspective of history, these individuals and organizations can be viewed as simply carriers of ideas, much as bees inadvertently carry pollen—playing a vital role in the grand scheme of nature while pursuing a much narrower individual purpose. The role of rationally articulated ideas may be quite modest in its effect on a given election, a legislative vote, or an action of a head of state. Yet the atmosphere in which such decisions take place may be dominated by a particular vision—or by a particular conflict of visions. Where intellectuals have played a role in history, it has not been so much by whispering words of advice into the ears of political overlords as by contributing to the vast and powerful currents of conceptions and misconceptions that sweep human action along. The effects of visions do not depend upon their being articulated, or even on decision-makers’ being aware of them. “Practical” decision-makers often disdain theories and visions, being too busy to examine the ultimate basis on which they are acting. However, the object here will be precisely to examine the underlying social visions whose conflicts have shaped our times and may well shape times to come. Chapter 2 Constrained and Unconstrained Visions At the core of every moral code there is a picture of human nature, a map of the universe, and a version of history. To human nature (of the sort conceived), in a universe (of the kind imagined), after a history (so understood), the rules of the code apply. -Walter Lippmann 1 Social visions differ in their basic conceptions of the nature of man. A creature from another galaxy who sought information about human beings from reading William Godwin’s Enquiry Concerning Political Justice in 1793 would hardly recognize man, as he appears there, as the same being who was described in The Federalist Papers just five years earlier. The contrast would be only slightly less if he compared man as he appeared in Thomas Paine and in Edmund Burke, or today in John Kenneth Galbraith and in Friedrich A. Hayek. Even the speculative pre-history of man as a wild creature in nature differs drastically between the free, innocent being conceived by Jean-Jacques Rousseau and the brutal participant in the bloody war of each against all conceived by Thomas Hobbes. The capacities and limitations of man are implicitly seen in radically different terms by those whose explicit philosophical, political, or social theories are built on different visions. Man’s moral and mental natures are seen so differently that their respective concepts of knowledge and of institutions necessarily differ as well. Social causation itself is conceived differently, both as to mechanics and results. Time and its ancillary phenomena—traditions, contracts, economic speculation, for example—are also viewed quite differently in theories based on different visions. The abstractions which are part of all theories tend to be viewed as more real by followers of some visions than by followers of opposing visions. Finally, those who believe in some visions view themselves in a very different moral role from the way that followers of other visions view themselves. The ramifications of these conflicting visions extend into economic, judicial, military, philosophical, and political decisions. Rather than attempt the impossible task of following all these ramifications in each of the myriad of social visions, the discussion here will group these visions into two broad categories—the constrained vision and the unconstrained vision. These will be abstractions of convenience, recognizing that there are degrees in both visions, that a continuum has been dichotomized, that in the real world there are often elements of each inconsistently grafted on to the other, and innumerable combinations and permutations. With all these caveats, it is now possible to turn to an outline of the two visions, and specifics on the nature of man, the nature of knowledge, and the nature of social processes, as seen in constrained and unconstrained visions. THE NATURE OF MAN The Constrained Vision Adam Smith provided a picture of man which may help make concrete the nature of a constrained vision. Writing as a philosopher in 1759, nearly twenty years before he became famous as an economist, Smith said in his Theory of Moral Sentiments: Let us suppose that the great empire of China, with all its myriads of inhabitants, was suddenly swallowed up by an earthquake, and let us consider how a man of humanity in Europe, who had no sort of connection with that part of the world, would react upon receiving intelligence of this dreadful calamity. He would, I imagine, first of all express very strongly his sorrow for the misfortune of that unhappy people, he would make many melancholy reflections upon the precariousness of human life, and the vanity of all the labours of man, which could thus be annihilated in a moment. He would, too, perhaps, if he was a man of speculation, enter into many reasonings concerning the effects which this disaster might produce upon the commerce of Europe, and the trade and business of the world in general. And when all this fine philosophy was over, when all these humane sentiments had been once fairly expressed, he would pursue his business or his pleasure, take his repose or his diversion, with the same ease and tranquility as if no such accident had happened. The most frivolous disaster which could befall himself would occasion a more real disturbance. If he was to lose his little finger tomorrow, he would not sleep to-night; but, provided he never saw them, he would snore with the most profound security over the ruin of a hundred million of his brethren. . . .2 The moral limitations of man in general, and his egocentricity in particular, were neither lamented by Smith nor regarded as things to be changed. They were treated as inherent facts of life, the basic constraint in his vision. The fundamental moral and social challenge was to make the best of the possibilities which existed within that constraint, rather than dissipate energies in an attempt to change human nature—an attempt that Smith treated as both vain and pointless. For example, if it were somehow possible to make the European feel poignantly the full pain of those who suffered in China, this state of mind would be “perfectly useless,” according to Smith, except to make him “miserable”,3 without being of any benefit to the Chinese. Smith said: “Nature, it seems, when she loaded us with our own sorrows, thought that they were enough, and therefore did not command us to take any further share in those of others, than what was necessary to prompt us to relieve them.”4 Instead of regarding man’s nature as something that could or should be changed, Smith attempted to determine how the moral and social benefits desired could be produced in the most efficient way, within that constraint. Smith approached the production and distribution of moral behavior in much the same way he would later approach the production and distribution of material goods. Although he was a professor of moral philosophy, his thought processes were already those of an economist. However, the constrained vision is by no means limited to economists. Smith’s contemporary in politics, Edmund Burke, perhaps best summarized the constrained vision from a political perspective when he spoke of “a radical infirmity in all human contrivances,”5 an infirmity inherent in the fundamental nature of things. Similar views were expressed by Alexander Hamilton in The Federalist Papers: It is the lot of all human institutions, even those of the most perfect kind, to have defects as well as excellencies—ill as well as good propensities. This results from the imperfection of the Institutor, Man.6 Returning to Adam Smith’s example, a society cannot function humanely, if at all, when each person acts as if his little finger is more important than the lives of a hundred million other human beings. But the crucial word here is act. We cannot “prefer ourselves so shamelessly and blindly to others” when we act, Adam Smith said,7 even if that is the spontaneous or natural inclination of our feelings. In practice, people on many occasions “sacrifice their own interests to the greater interests of others,” according to Smith,8 but this was due to such intervening factors as devotion to moral principles, to concepts of honor and nobility, rather than to loving one’s neighbor as oneself.9 Through such artificial devices, man could be persuaded to do for his own self-image or inner needs what he would not do for the good of his fellow man. In short, such concepts were seen by Smith as the most efficient way to get the moral job done at the lowest psychic cost. Despite the fact that this was a moral question, Smith’s answer was essentially economic—a system of moral incentives, a set of trade-offs rather than a real solution by changing man. One of the hallmarks of the constrained vision is that it deals in trade-offs rather than solutions. In his later classic work, The Wealth of Nations, Smith went further. Economic benefits to society were largely unintended by individuals, but emerged systemically from the interactions of the marketplace, under the pressures of competition and the incentives of individual gain.10 Moral sentiments were necessary only for shaping the general framework of laws within which this systemic process could go on. This was yet another way in which man, with all the limitations conceived by Smith, could be induced to produce benefits for others, for reasons ultimately reducible to self-interest. It was not an atomistic theory that individual self-interests added up to the interest of society. On the contrary, the functioning of the economy and society required each individual to do things for other people; it was simply the motivation behind these acts—whether moral or economic—which was ultimately selfcentered. In both his moral and his economic analyses, Smith relied on incentives rather than dispositions to get the job done. The Unconstrained Vision Perhaps no other eighteenth-century book presents such a contrast to the vision of man in Adam Smith as William Godwin’s Enquiry Concerning Political Justice, a work as remarkable for its fate as for its contents. An immediate success upon its publication in England in 1793, within a decade it encountered the chilling effect of British hostile reactions to ideas popularly associated with the French Revolution, especially after France became an enemy in war. By the time two decades of warfare between the two countries were ended at Waterloo, Godwin and his work had been relegated to the periphery of intellectual life, and he was subsequently best known for his influence on Shelley. Yet no work from the eighteenth-century “age of reason” so clearly, so consistently, and so systematically elaborated the unconstrained vision of man as did Godwin’s treatise. Where in Adam Smith moral and socially beneficial behavior could be evoked from man only by incentives, in William Godwin man’s understanding and disposition were capable of intentionally creating social benefits. Godwin regarded the intention to benefit others as being “of the essence of virtue,”11 and virtue in turn as being the road to human happiness. Unintentional social benefits were treated by Godwin as scarcely worthy of notice.12 His was the unconstrained vision of human nature, in which man was capable of directly feeling other people’s needs as more important than his own, and therefore of consistently acting impartially, even when his own interests or those of his family were involved.13 This was not meant as an empirical generalization about the way most people currently behaved. It was meant as a statement of the underlying nature of human potential. Conceding current egocentric behavior did not imply that it was a permanent feature of human nature, as human nature was conceived in the unconstrained vision. Godwin said: “Men are capable, no doubt, of preferring an inferior interest of their own to a superior interest of others; but this preference arises from a combination of circumstances and is not the necessary and invariable law of our nature.”14 Godwin referred to “men as they hereafter may be made,”15 in contrast to Burke’s view: “We cannot change the Nature of things and of men—but must act upon them the best we can.”16 Socially contrived incentives were disdained by Godwin as unworthy and unnecessary expedients, when it was possible to achieve directly what Smith’s incentives were designed to achieve indirectly: “If a thousand men are to be benefited, I ought to recollect that I am only an atom in the comparison, and to reason accordingly.”17 Unlike Smith, who regarded human selfishness as a given, Godwin regarded it as being promoted by the very system of rewards used to cope with it. The real solution toward which efforts should be bent was to have people do what is right because it is right, not because of psychic or economic payments— that is, not because someone “has annexed to it a great weight of self interest.”18 Having an unconstrained vision of the yet untapped moral potential of human beings, Godwin was not preoccupied like Smith with what is the most immediately effective incentive under the current state of things. The real goal was the long-run development of a higher sense of social duty. To the extent that immediately effective incentives retarded that long-run development, their benefits were ephemeral or illusory. The “hope of reward” and “fear of punishment” were, in Godwin’s vision, “wrong in themselves” and “inimical to the improvement of the mind.”19 In this, Godwin was seconded by another contemporary exemplar of the unconstrained vision, the Marquis de Condorcet, who rejected the whole idea of “turning prejudices and vices to good account rather than trying to dispel or repress them.” Such “mistakes” Condorcet traced to his adversaries’ vision of human nature —their confusing “the natural man” and his potential with existing man, “corrupted by prejudices, artificial passions and social customs.”20 TRADE-OFFS VERSUS SOLUTIONS Prudence—the careful weighing of trade-offs—is seen in very different terms within the constrained and the unconstrained visions. In the constrained vision, where trade-offs are all that we can hope for, prudence is among the highest duties. Edmund Burke called it “the first of all virtues.”21 “Nothing is good,” Burke said, “but in proportion and with reference”22—in short, as a trade-off. By contrast, in the unconstrained vision, where moral improvement has no fixed limit, prudence is of a lower order of importance. Godwin had little use for “those moralists”—quite conceivably meaning Smith—“who think only of stimulating men to good deeds by considerations of frigid prudence and mercenary selfinterests,” instead of seeking to stimulate the “generous and magnanimous sentiment of our natures.”23 Implicit in the unconstrained vision is the notion that the potential is very different from the actual, and that means exist to improve human nature toward its potential, or that such means can be evolved or discovered, so that man will do the right thing for the right reason, rather than for ulterior psychic or economic rewards. Condorcet expressed a similar vision when he declared that man can eventually “fulfill by a natural inclination the same duties which today cost him effort and sacrifice.”24 Thus a solution can supersede mere trade-offs. Man is, in short, “perfectible”—meaning continually improvable rather than capable of actually reaching absolute perfection. “We can come nearer and nearer,” according to Godwin,25 though one “cannot prescribe limits” to this process.26 It is sufficient for his purpose that men are “eminently capable of justice and virtue”27—not only isolated individuals, but “the whole species.”28 Efforts must be made to “wake the sleeping virtues of mankind.”29 Rewarding existing behavior patterns was seen as antithetical to this goal. Here, too, Condorcet reached similar conclusions. The “perfectibility of man,” he said, was “truly indefinite.”30 “The progress of the human mind” was a recurring theme in Condorcet.31 He acknowledged that there were “limits of man’s intelligence,”32 that no one believed it possible for man to know “all the facts of nature” or to “attain the ultimate means of precision” in their measurement or analysis.33 But while there was ultimately a limit to man’s mental capability, according to Condorcet, no one could specify what it was. He was indignant that Locke “dared to set a limit to human understanding.”34 As a devotee of mathematics, Condorcet conceived perfectibility as a never-ending asymptotic approach to a mathematical limit.35 While use of the word “perfectibility” has faded away over the centuries, the concept has survived, largely intact, to the present time. The notion that “the human being is highly plastic material”36 is still central among many contemporary thinkers who share the unconstrained vision. The concept of “solution” remains central to this vision. A solution is achieved when it is no longer necessary to make a trade-off, even if the development of that solution entailed costs now past. The goal of achieving a solution is in fact what justifies the initial sacrifices or transitional conditions which might otherwise be considered unacceptable. Condorcet, for example, anticipated the eventual “reconciliation, the identification, of the interests of each with the interests of all”—at which point, “the path of virtue is no longer arduous.”37 Man could act under the influence of a socially beneficial disposition, rather than simply in response to ulterior incentives. SOCIAL MORALITY AND SOCIAL CAUSATION Human actions were dichotomized by Godwin into the beneficial and the harmful, and each of these in turn was dichotomized into the intentional and the unintentional. The intentional creation of benefits was called “virtue,”38 the intentional creation of harm was “vice”,39 and the unintentional creation of harm was “negligence,” a subspecies of vice.40 These definitions can be represented schematically: BENEFICIAL HARMFUL Virtue Vice INTENTIONAL Negligence UNINTENTIONAL The missing category was unintentional benefit. It was precisely this missing category in Godwin that was central to Adam Smith’s whole vision, particularly as it unfolded in his classic work The Wealth of Nations. The economic benefits to society produced by the capitalist, were, according to Smith, “no part of his intention.”41 The capitalist’s intentions were characterized by Smith as “mean rapacity”42 and capitalists as a group were referred to as people who “seldom meet together, even for merriment or diversion, but the conversation ends in a conspiracy against the public, or in some contrivance to raise prices.”43 Yet, despite his repeatedly negative depictions of capitalists,44 unrivaled among economists until Karl Marx, Adam Smith nevertheless became the patron saint of laissez-faire capitalism. Intentions, which were crucial in the unconstrained vision of Godwin, were irrelevant in the constrained vision of Smith. What mattered to Smith were the systemic characteristics of a competitive economy, which he saw as producing social benefits from unsavory individual intentions. While Adam Smith and William Godwin have been cited as especially clear and straightforward writers espousing opposing visions, each is part of a vast tradition that continues powerful and contending for domination today. Even among their contemporaries, Smith and Godwin each had many intellectual compatriots with similar visions, differently expressed and differing in details and degree. Edmund Burke’s Reflections on the Revolution in France in 1790 was perhaps the most ringing polemical application of the constrained vision. Thomas Paine’s equally polemical reply, The Rights of Man (1791), anticipated in many ways the more systematic unfolding of the unconstrained vision by Godwin two years later. Godwin credited Rousseau with being “the first to teach that the imperfections of government were the only perennial source of the vices of mankind.”45 Rousseau was certainly the most famous of those who argued on the basis of a human nature not inherently constrained to its existing limitations, but narrowed and corrupted by social institutions—a vision also found in Condorcet and in Baron D’Holbach, among others of that era. In the nineteenth century, John Stuart Mill said that the “present wretched education” and “wretched social arrangements” were “the only real hindrance” to attaining general happiness among human beings.46 Mill’s most ringing rhetoric reflected the unconstrained vision, though his eclecticism in many areas caused him to include devastating provisos more consonant with the constrained vision.47 Much of nineteenth-century and twentieth-century liberalism (in the American sense) builds upon these foundations, modified and varying in degree, and applied to areas as disparate as education, war, and criminal justice. Marxism, as we shall see, was a special hybrid, applying a constrained vision to much of the past and an unconstrained vision to much of the future. When Harold Laski said that “dissatisfaction” was an “expression of serious ill in the body politic,”48 he was expressing the essence of the unconstrained vision, in which neither man nor nature have such inherent constraints as to disappoint our hopes, so that existing institutions, traditions, or rulers must be responsible for dissatisfaction. Conversely, when Malthus attributed human misery to “laws inherent in the nature of man, and absolutely independent of all human regulations,”49 he was expressing one of the most extreme forms of the constrained vision, encompassing inherent constraints in both nature and man. Godwin’s reply to Malthus, not surprisingly, applied the unconstrained vision to both nature and man: “Men are born into the world, in every country where the cultivation of the earth is practised, with the natural faculty in each man of producing more food than he can consume, a faculty which cannot be controlled but by the injurious exclusions of human institution.”50 Given the unconstrained possibilities of man and nature, poverty or other sources of dissatisfaction could only be a result of evil intentions or blindness to solutions readily achievable by changing existing institutions. By contrast, Burke considered complaints about our times and rulers to be part of “the general infirmities of human nature,” and that “true political sagacity” was required to separate these perennial complaints from real indicators of a special malaise.51 Hobbes went even further, arguing that it was precisely when men are “at ease” that they are most troublesome politically.52 The constraints of nature are themselves important largely through the constraints of human nature. The inherent natural constraint of the need for food, for example, becomes a practical social problem only insofar as human beings multiply to the point where subsistence becomes difficult to achieve for a growing population. Thus this central constraint of nature in Malthus becomes socially important only because of Malthus’ highly constrained vision of human nature, which he saw as inevitably behaving in such a way as to populate the earth to that point. But Godwin, who readily conceded the natural constraint, had a very different vision of human nature, which would not needlessly overpopulate. Therefore, the possibility of a geometrical increase in people was of no concern to Godwin because “possible men do not eat, though real men do.”53 Malthus, on the other hand, saw overpopulation not as an abstract possibility in the future but as a concrete reality already manifested. According to Malthus, “the period when the number of men surpass their means of subsistence has long since arrived . . . has existed ever since we have had any histories of mankind, does exist at present, and will for ever continue to exist.”54 It would be hard to conceive of a more absolute statement of a constrained vision. Where Malthus and Godwin differed was not over a natural fact—the need for food—but over behavioral theories based on very different visions of human nature. Most followers of the unconstrained vision likewise acknowledge death, for example, as an inherent constraint of nature (though Godwin and Condorcet did not rule out an eventual conquest of death), but simply do not treat this as a constraint on the social development of mankind, which lives on despite the deaths of individuals. The great evils of the world—war, poverty, and crime, for example—are seen in completely different terms by those with the constrained and the unconstrained visions. If human options are not inherently constrained, then the presence of such repugnant and disastrous phenomena virtually cries out for explanation—and for solutions. But if the limitations and passions of man himself are at the heart of these painful phenomena, then what requires explanation are the ways in which they have been avoided or minimized. While believers in the unconstrained vision seek the special causes of war, poverty, and crime, believers in the constrained vision seek the special causes of peace, wealth, or a law-abiding society. In the unconstrained vision, there are no intractable reasons for social evils and therefore no reason why they cannot be solved, with sufficient moral commitment. But in the constrained vision, whatever artifices or strategies restrain or ameliorate inherent human evils will themselves have costs, some in the form of other social ills created by these civilizing institutions, so that all that is possible is a prudent trade-off. The two great revolutions in the eighteenth century—in France and in America—can be viewed as applications of these differing visions, though with all the reservations necessary whenever the flesh and blood of complex historical events are compared to skeletal theoretical models. The underlying premises of the French Revolution more clearly reflected the unconstrained vision of man which prevailed among its leaders. The intellectual foundations of the American Revolution were more mixed, including men like Thomas Paine and Thomas Jefferson, whose thinking was similar in many ways to that in France, but also including as a dominant influence on the Constitution, the classic constrained vision of man expressed in The Federalist Papers. Where Robespierre looked forward to the end of revolutionary bloodshed, “when all people will have become equally devoted to their country and its laws,”55 Alexander Hamilton in The Federalist Papers regarded the idea of individual actions “unbiased by considerations not connected with the public good” as a prospect “more ardently to be wished than seriously to be expected.”56 Robespierre sought a solution, Hamilton a trade-off. The Constitution of the United States, with its elaborate checks and balances, clearly reflected the view that no one was ever to be completely trusted with power. This was in sharp contrast to the French Revolution, which gave sweeping powers, including the power of life and death, to those who spoke in the name of “the people,” expressing the Rousseauean “general will.” Even when bitterly disappointed with particular leaders, who were then deposed and executed, believers in this vision did not substantially change their political systems or beliefs, viewing the evil as localized in individuals who had betrayed the revolution. The writers of The Federalist Papers were quite conscious of the vision of man that underlay the Constitution of checks and balances which they espoused: It may be a reflection on human nature that such devices should be necessary to control the abuses of government. But what is government itself but the greatest of all reflections on human nature?57 To the Federalists, the evil was inherent in man, and institutions were simply ways of trying to cope with it. Adam Smith likewise saw government as “an imperfect remedy” for the deficiency of “wisdom and virtue” in man.58 The Federalist Papers said: Why has government been instituted at all? Because the passions of men will not conform to the dictates of reason and justice without constraint.59 To those without this constrained vision of man, the whole elaborate system of constitutional checks and balances was a needless complication and impediment. Condorcet condemned such “counterweights” for creating an “overcomplicated” political machine “to weigh upon the people.”60 He saw no need for society to be “jostled between opposing powers”61 or held back by the “inertia” of constitutional checks and balances.62 The constrained vision is a tragic vision of the human condition. The unconstrained vision is a moral vision of human intentions, which are viewed as ultimately decisive. The unconstrained vision promotes pursuit of the highest ideals and the best solutions. By contrast, the constrained vision sees the best as the enemy of the good—a vain attempt to reach the unattainable being seen as not only futile but often counterproductive, while the same efforts could have produced a more viable and beneficial trade-off. Adam Smith applied this reasoning not only to economics but also to morality and politics: The prudent reformer, according to Smith, will respect “the confirmed habits and prejudices of the people,” and when he cannot establish what is right, “he will not disdain to ameliorate the wrong.” His goal is not to create the ideal but to “establish the best that the people can bear.”63 But Condorcet, expressing the unconstrained vision, rejected any notion that laws should “change with the temperature and adapt to the forms of government, to the practices that superstition has consecrated, and even to the stupidities adopted by each people. . . .”64 Thus he found the French Revolution superior to the American Revolution, for “the principles from which the constitution and laws of France were derived were purer” and allowed “the people to exercise their sovereign right” without constraint.65 Related to this is the question whether the institutions of one society can be transferred to another, or particular blueprints for better societies be applied to very different countries. Jeremy Bentham was noted for producing both specific reforms and general principles intended to apply in very different societies. Yet to Hamilton, “What may be good at Philadelphia may be bad at Paris and ridiculous at Petersburgh.”66 Each of these conclusions is consistent with the respective vision from which it came. While the constrained vision sees human nature as essentially unchanged across the ages and around the world, the particular cultural expressions of human needs peculiar to specific societies are not seen as being readily and beneficially changeable by forcible intervention. By contrast, those with the unconstrained vision tend to view human nature as beneficially changeable and social customs as expendable holdovers from the past. Ideals are weighed against the cost of achieving them, in the constrained vision. But in the unconstrained vision, every closer approximation to the ideal should be preferred. Costs are regrettable, but by no means decisive. Thomas Jefferson’s reply to those who turned against the French Revolution, because of the innocent people it had killed, exemplified this point: My own affections have been deeply wounded by some of the martyrs to this cause, but rather than it should have failed, I would have seen half the earth desolated.67 Belief in the irrelevance of process costs in the pursuit of social justice could hardly have been expressed more clearly or categorically. Yet, in the end, Jefferson too turned against the French Revolution, as its human cost increased beyond what he could continue to accept. Jefferson was not completely or irrevocably committed to the unconstrained vision. The relative importance of process costs has continued, over the centuries, to distinguish the constrained and the unconstrained visions. Modern defenders of legal technicalities which allow criminals to escape punishment who declare, “That is the price we pay for freedom,” or defenders of revolutions who say, “You can’t make omelettes without breaking eggs,” are contemporary exemplars of an unconstrained vision which has historically treated process costs as secondary. At the other end of the philosophical spectrum are those who in essence repeat Adam Smith’s view of process costs: “The peace and order of society is of more importance than even the relief of the miserable.”68 The continuing battle between ideals and the costs of achieving them is only one part of the ongoing conflict of visions. SUMMARY AND IMPLICATIONS Visions rest ultimately on some sense of the nature of man—not simply his existing practices but his ultimate potential and ultimate limitations. Those who see the potentialities of human nature as extending far beyond what is currently manifested have a social vision quite different from those who see human beings as tragically limited creatures whose selfish and dangerous impulses can be contained only by social contrivances which themselves produce unhappy side effects. William Godwin and Adam Smith are two of the clearest and most consistent exemplars of these respective social visions—the unconstrained and the constrained. Yet they are neither the first nor the last in these two long traditions of social thought. When Rousseau said that man “is born free” but “is everywhere in chains,”69 he expressed the essence of the unconstrained vision, in which the fundamental problem is not nature or man but institutions. According to Rousseau, “men are not naturally enemies.”70 The diametrically opposite vision was presented in Hobbes’ Leviathan, where the armed power of political institutions was all that prevented the war of each against all71 that would otherwise exist among men in their natural state, where life would be “solitary, poore, nasty, brutish, and short.”72 While the unconstrained vision of Condorcet led him to seek a society in which man’s “natural inclination” would coincide with the social good,73 Hayek’s constrained vision led to the conclusion that the “indispensable rules of the free society require from us much that is unpleasant”74—that is, man’s nature inherently could not coincide with the social good but must be deliberately subordinated to it, despite the unpleasantness which this entailed. Given the wider capabilities of man in the unconstrained vision, the intentions which guide those capabilities are especially important. Words and concepts which revolve around intention —“sincerity,” “commitment,” “dedication”—have been central to discussions within the framework of the unconstrained vision for centuries, and the policies sought by this vision have often been described in terms of their intended goals: “Liberty, equality, fraternity,” “ending the exploitation of man by man,” or “social justice,” for example. But in the constrained vision, where man’s ability to directly consummate his intentions is very limited, intentions mean far less. Burke referred to “the Beneficial effects of human faults” and to “the ill consequences attending the most undoubted Virtues.”75 Adam Smith’s entire economic doctrine of laissez-faire implicitly assumed the same lack of correspondence between intention and effect, for the systemic benefits of capitalism were no part of the intention of capitalists. In the constrained vision, social processes are described not in terms of intentions or ultimate goals, but in terms of the systemic characteristics deemed necessary to contribute to those goals —“property rights,” “free enterprise,” or “strict construction” of the Constitution, for example. It is not merely that there are different goals in the two visions but, more fundamentally, that the goals relate to different things. The unconstrained vision speaks directly in terms of desired results, the constrained vision in terms of process characteristics considered conducive to desired results, but not directly or without many unhappy side effects, which are accepted as part of a trade-off. With all the complex differences among social thinkers as of a given time, and still more so over time, it is nevertheless possible to recognize certain key assumptions about human nature and about social causation which permit some to be grouped together as belonging to the constrained vision and others as belonging to the unconstrained vision. Although these groupings do not encompass all social theorists, they cover many important figures and enduring ideological conflicts of the past two centuries. Running through the tradition of the unconstrained vision is the conviction that foolish or immoral choices explain the evils of the world—and that wiser or more moral and humane social policies are the solution. William Godwin’s elaboration of this unconstrained vision in his Enquiry Concerning Political Justice drew upon and systematized such ideas found among numerous eighteenth-century thinkers—Jean-Jacques Rousseau, Voltaire, Condorcet, Thomas Paine, and Holbach being notable examples. This general approach was carried forth in the nineteenth century, in their very different ways, by Saint-Simon, Robert Owen, and by George Bernard Shaw and other Fabians. Its twentiethcentury echoes are found in political theorists such as Harold Laski, in economists like Thorstein Veblen and John Kenneth Galbraith, and in the law with a whole school of advocates of judicial activism, epitomized by Ronald Dworkin in theory and Earl Warren in practice. By contrast, the constrained vision sees the evils of the world as deriving from the limited and unhappy choices available, given the inherent moral and intellectual limitations of human beings. For amelioration of these evils and the promotion of progress, they rely on the systemic characteristics of certain social processes such as moral traditions, the marketplace, or families. They conceive of these processes as evolved rather than designed—and rely on these general patterns of social interaction rather than on specific policy designed to directly produce particular results for particular individuals or groups. This constrained view of human capacities found in Adam Smith is also found in a long series of other social thinkers, ranging from Thomas Hobbes in the seventeenth century, through Edmund Burke and the authors of The Federalist Papers among Smith’s contemporaries, through such twentieth-century figures as Oliver Wendell Holmes in law, Milton Friedman in economics, and Friedrich A. Hayek in general social theory. Not all social thinkers fit this schematic dichotomy. John Stuart Mill and Karl Marx, for example, do not fit, for very different reasons, as will be noted in Chapter 5. Others take midway positions between the two visions, or convert from one to the other. However, the conflict of visions is no less real because everyone has not chosen sides or irrevocably committed themselves. Despite necessary caveats, it remains an important and remarkable phenomenon that how human nature is conceived at the outset is highly correlated with the whole conception of knowledge, morality, power, time, rationality, war, freedom, and law which defines a social vision. These correlations will be explored in the chapters that follow. Because various beliefs, theories, and systems of social thought are spread across a continuum (perhaps even a multi-dimensional continuum), it might in one sense be more appropriate to refer to less constrained visions and more constrained visions instead of the dichotomy used here. However, the dichotomy is not only more convenient but also captures an important distinction. Virtually no one believes that man is 100 percent unconstrained and virtually no one believes that man is 100 percent constrained. What puts a given thinker in the tradition of one vision rather than the other is not simply whether he refers more to man’s constraints or to his untapped potential but whether, or to what extent, constraints are built into the very structure and operation of a particular theory. Those whose theories incorporate these constraints as a central feature have a constrained vision; those whose theories do not make these constraints an integral or central part of the analysis have an unconstrained vision. Every vision, by definition, leaves something out—indeed, leaves most things out. The dichotomy between constrained and unconstrained visions is based on whether or not inherent limitations of man are among the key elements included in the vision. The dichotomy is justified in yet another sense. These different ways of conceiving man and the world lead not merely to different conclusions but to sharply divergent, often diametrically opposed, conclusions on issues ranging from justice to war. There are not merely differences of visions but conflicts of visions. Review Feature Review Human cooperation David G. Rand1 and Martin A. Nowak2 1 Department of Psychology, Department of Economics, Program in Cognitive Science, School of Management, Yale University, New Haven, CT, USA 2 Program for Evolutionary Dynamics, Department of Mathematics, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA Why should you help a competitor? Why should you contribute to the public good if free riders reap the benefits of your generosity? Cooperation in a competitive world is a conundrum. Natural selection opposes the evolution of cooperation unless specific mechanisms are at work. Five such mechanisms have been proposed: direct reciprocity, indirect reciprocity, spatial selection, multilevel selection, and kin selection. Here we discuss empirical evidence from laboratory experiments and field studies of human interactions for each mechanism. We also consider cooperation in one-shot, anonymous interactions for which no mechanisms are apparent. We argue that this behavior reflects the overgeneralization of cooperative strategies learned in the context of direct and indirect reciprocity: we show that automatic, intuitive responses favor cooperative strategies that reciprocate. The challenge of cooperation In a cooperative (or social) dilemma, there is tension between what is good for the individual and what is good for the population. The population does best if individuals cooperate, but for each individual there is a temptation to defect. A simple definition of cooperation is that one individual pays a cost for another to receive a benefit. Cost and benefit are measured in terms of reproductive success, where reproduction can be cultural or genetic. Box 1 provides a more detailed definition based on game theory. Among cooperative dilemmas, the one most challenging for cooperation is the prisoner’s dilemma (PD; see Glossary), in which two players choose between cooperating and defecting; cooperation maximizes social welfare, but defection maximizes one’s own payoff regardless of the other’s choice. In a well-mixed population in which each individual is equally likely to interact and compete with every other individual, natural selection favors defection in the PD: why should you reduce your own fitness to increase that of a competitor in the struggle for survival? Defectors always out-earn cooperators, and in a population that contains both cooperators and defectors, the latter have higher fitness. Selection therefore reduces the abundance of cooperators until the population consists entirely of defectors. For cooperation to arise, a mechanism for the evolution of cooperation is needed. Such a mechanism is an interaction structure that can cause cooperation to be favored over Corresponding author: Nowak, M.A. (martin_nowak@harvard.edu). 1364-6613/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tics.2013.06.003 defection [1]. These interaction structures specify how the individuals of a population interact to receive payoffs, and how they compete for reproduction. Previous work has identified five such mechanisms for the evolution of cooperation (Figure 1): direct reciprocity, indirect reciprocity, spatial selection, multilevel selection, and kin selection. It is important to distinguish between interaction patterns that are mechanisms for the evolution of cooperation and behaviors that require an evolutionary explanation (such as strong reciprocity, upstream reciprocity, and parochial altruism; Box 2). In this article, we build a bridge between theoretical work that has proposed these mechanisms and experimental work exploring how and when people actually cooperate. First we present evidence from experiments that implement each mechanism in the laboratory. Next we discuss why cooperation arises in some experimental settings in which no mechanisms are apparent. Finally, we consider the cognitive underpinnings of human cooperation. We show Glossary Evolutionary dynamics: mathematical formalization of the process of evolution whereby a population changes over time. Natural selection operates such that genotypes (or strategies) with higher fitness tend to become more common, whereas lower-fitness genotypes tend to die out. Mutation (re)introduces variation into the population. This process can also represent cultural evolution and social learning, in which people imitate those with higher payoffs and sometimes experiment with novel strategies. Evolutionary game theory: combination of game theory and evolutionary dynamics. There is a population of agents, each of whom has a strategy. These agents interact with each other and earn payoffs. Payoff is translated into fitness, and the frequency of strategies in the population changes over time accordingly: higher-payoff strategies tend to become more common, whereas lower-payoff strategies tend to die out. Game theory: mathematical formalization of social interaction and strategic behavior. A given interaction is represented by (i) a set of players, (ii) the choices available to each player, and (iii) the payoff earned by each player depending on both her choice and the choices of the other players. The prisoner’s dilemma is one such game that describes the problem of cooperation. Mechanism for the evolution of cooperation: interaction structure that can cause natural selection to favor cooperation over defection. The mechanism specifies how the individuals of a population interact to receive payoffs, and how they compete for reproduction. Prisoner’s dilemma: game involving two players, each of whom chooses between cooperation or defection. If both players cooperate, they earn more than if both defect. However, the highest payoff is earned by a defector whose partner cooperates, whereas the lowest payoff is earned by a cooperator whose partner defects. It is individually optimal to defect (regardless of the partner’s choice) but socially optimal to cooperate. Box 1 provides further details. Public goods game: prisoner’s dilemma with more than two players. In the public goods game, each player chooses how much money to keep for herself and how much to contribute to an account that benefits all group members. Trends in Cognitive Sciences, August 2013, Vol. 17, No. 8 413 Review Trends in Cognitive Sciences August 2013, Vol. 17, No. 8 Box 1. Defining cooperation Consider a game between two strategies, C and D, and the following payoff matrix (indicating the row player’s payoff): C D C R S D T P When does it make sense to call strategy C cooperation and strategy D defection? The following definition [163,164] is useful. The game is a cooperative dilemma if (i) two cooperators obtain a higher payoff than two defectors, R > P yet (ii) there is an incentive to defect. This incentive can arise in three different ways: (a) if T > R then it is better to defect when playing against a cooperator; (b) if P > S then it is better to defect when playing against a defector; and (c) if T > S then it is better to be the defector in an encounter between a cooperator and a defector. If at least one of these three conditions holds, then we have a cooperative dilemma. If none holds, then there is no dilemma and C is simply better than D. If all three conditions hold, we have a prisoner’s dilemma, T > R > P > S [6,48]. The prisoner’s dilemma is the most stringent cooperative dilemma. Here defectors dominate over cooperators. In a well-mixed population, natural selection always favors defectors over cooperators. For cooperation to arise in the prisoner’s dilemma, we need a mechanism for the evolution of cooperation. Cooperative dilemmas that are not the prisoner’s dilemma could be called relaxed cooperative dilemmas. In these games it is possible to evolve some level of cooperation even if no mechanism is at work. One such example is the snowdrift game, given by T > R > S > P. Here we find a stable equilibrium between cooperators and defectors, even in a well-mixed population. If 2R > T + S, then the total payoff for the population is maximized if everyone cooperates; otherwise a mixed population achieves the highest total payoff. This is possible even for the prisoner’s dilemma. The above definition can be generalized to more than two people (n-person games). We denote by Pi and Qi the payoffs for cooperators and defectors, respectively, in groups that contain i cooperators and n–i defectors. For the game to be a cooperative dilemma, we require that (i) an all-cooperator group obtains a higher payoff then an alldefector group, Pn > Q0, yet (ii) there is some incentive to defect. The incentive to defect can take the following form: (a) Pi < Qi–1 for i = 1, . . ., n and (b) Pi < Qi for i = 1, . . ., n 1. Condition (a) means that an individual can increase his payoff by switching from cooperation to defection. Condition (b) means that in any mixed group, defectors have a higher payoff than cooperators. If only some of these incentives hold, than we have a relaxed cooperative dilemma. In this case some evolution of cooperation is possible even without a specific mechanism. However, a mechanism would typically enhance the evolution of cooperation by increasing the equilibrium abundance of cooperators, increasing the fixation probability of cooperators or reducing the invasion barrier that needs to be overcome. The volunteer’s dilemma is an example of a relaxed situation [165]. If all incentives hold, we have the n-person equivalent of a prisoner’s dilemma, called the public …
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