6
Seldon’s Solution
Game theory, culture, and human nature

Self-interest speaks all sorts of languages and plays all sorts of roles.

—La Rochefoucauld

You don’t need to know about game theory to understand the ultimatum game. You just need to be a movie fan.

Decades before economists invented the ultimatum game,1 something very much like it appeared in the 1941 movie The Maltese Falcon. The scene is private detective Sam Spade’s apartment. Spade (played by Humphrey Bogart) has just made a deal with the criminal Kasper Gutman (Sydney Greenstreet). Spade will collect $1,000 from Gutman and then presumably will share some of it with Brigid O’Shaughnessy (Mary Astor), the film’s femme fatale.

“I’d like to give you a word of advice,” Gutman whispers to Spade. “I daresay you’re going to give her some money, but if you don’t give her as much as she thinks she ought to have, my word of advice is, be careful.” Gutman knew that people react negatively to the perception of being treated unfairly. He could have predicted the outcome of ultimatum games without game theory or brain scanners, because he was an astute student of human nature.

So why bother with game theory? If you can figure out human nature just by observing how people behave, whether in the real world or the lab, perhaps game theory is nothing more than



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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature 6 Seldon’s Solution Game theory, culture, and human nature Self-interest speaks all sorts of languages and plays all sorts of roles. —La Rochefoucauld You don’t need to know about game theory to understand the ultimatum game. You just need to be a movie fan. Decades before economists invented the ultimatum game,1 something very much like it appeared in the 1941 movie The Maltese Falcon. The scene is private detective Sam Spade’s apartment. Spade (played by Humphrey Bogart) has just made a deal with the criminal Kasper Gutman (Sydney Greenstreet). Spade will collect $1,000 from Gutman and then presumably will share some of it with Brigid O’Shaughnessy (Mary Astor), the film’s femme fatale. “I’d like to give you a word of advice,” Gutman whispers to Spade. “I daresay you’re going to give her some money, but if you don’t give her as much as she thinks she ought to have, my word of advice is, be careful.” Gutman knew that people react negatively to the perception of being treated unfairly. He could have predicted the outcome of ultimatum games without game theory or brain scanners, because he was an astute student of human nature. So why bother with game theory? If you can figure out human nature just by observing how people behave, whether in the real world or the lab, perhaps game theory is nothing more than

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature superfluous mathematics. Besides, when game theory math incorporates the economists’ belief in selfish rationality, it doesn’t even predict human behavior correctly. Actually, though, game theory provides a more sophisticated and quantitative tool for describing human nature than the intuition of criminals. Looked at in the right way, the ultimatum game does not disprove game theory, but expands it. Fairness, trust, and other social conditions do affect how people play games and make economic choices. But that just means that the standard economic notion of self-interest is too restrictive—life is more than money. Game theory’s math doesn’t really tell you what people want, but rather how people should behave in order to achieve what they want. As economist Jörgen Weibull observes, reports of game theory’s death have been exaggerated. “It has many times been claimed that certain game-theoretic solutions—such as Nash equilibrium … —have been violated in laboratory experiments,” Weibull writes. “While it may well be true that human subjects do not behave according to these solutions in many situations, few experiments actually provide evidence for this.”2 Early experiments with tests such as the ultimatum game merely assumed that people wanted to maximize their money—which they often failed to do when playing the game. Such tests do not disprove game theory, though; instead, they suggest that something is wrong with the experimenter’s assumptions. Later versions of the ultimatum game attempted to include things like fairness, or, more generally, test how a player’s social preferences (that is, concerns for others) influence game decisions. Such factors as altruism and spite, Weibull notes, affect the outcome that players prefer to reach, and they make their choices accordingly. “Indeed, several laboratory experiments have convincingly— though perhaps not surprisingly for the non-economist—shown that human subjects’ preferences are not driven only by the resulting material consequences to the subject.”3 In some cases, social context (say, the norms of a person’s peer group) dictates choices that appear inconsistent with both personal self-interest and con-

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature cern for the welfare of others. “Further analysis of preferences of this type seems highly relevant for our understanding of many social behaviors,” Weibull observes.4 THE NATURE OF HUMAN NATURE By getting a grip on the nuances of social preferences, game theory enhances its prospects for forging a science of human behavior, a Code of Nature for predicting social phenomena. But there might be a flaw in that plan. It presumes that there is such a thing as “human nature” to begin with for game theory to describe. At first glance, experiments such as those using the ultimatum game do seem to provide evidence for a consistent human nature. After all, when economists play the ultimatum game with college students, the results come out pretty much the same, whether in Los Angeles, Pittsburgh, or even Tokyo. And of course, one wellknown battalion of social scientists argues strongly that there most definitely is a universal human nature. They are devotees of a discipline known as evolutionary psychology, a widely publicized field contending that human behavior today reflects the genetic selection imposed on the species during the early days of human evolution. Human nature, this notion implies, is a common heritage of the race, shaping the way people instinctively respond to situations today, based on how they behaved in order to survive in hunter-gatherer times. A typical advocate of this view is Harvard psychologist Steven Pinker, who argued his beliefs with considerable passion in a book called The Blank Slate. Viewing the brain as blank at birth, to be shaped totally by experience, is nonsense, he insisted. General features of human nature have been programmed by evolution and stored on a genetic hard drive that guides the brain’s development. As a result, human nature today derives from the era of early human evolution. “The study of humans from an evolutionary perspective has shown that many psychological faculties (such as our hunger for fatty food, for social status, and for risky sexual liaisons) are better adapted to the evolutionary demands of our ancestral

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature environment than to the actual demands of the current environment,” Pinker wrote.5 In other words, people today are just hunter-gatherers wearing suits. On the surface, it might seem that it would be a good thing for game theory—and the rest of the human sciences—if this idea is right. If the Code of Nature is inscribed into the human genetic endowment, that should improve the prospects for deciphering the rules governing human nature and then predicting human behavior. After all, the concept that a Code of Nature exists might be interpreted to mean that there is some universal behavioral program to which all members of the human species conform. Yet with all due respect to much of the intelligent research that has been done in the field of evolutionary psychology, some of the conclusions that have been drawn from it rest on rather shaky ground. And it turns out that rather than bolstering evolutionary psychology, game theory helps to show why it breaks down. Furthermore, the way game theory does it has much in common with the way that Asimov’s fictional hero Hari Seldon found the solution to formulating his physics of society, or psychohistory. COMPARING CULTURES In Prelude to Foundation, the first prequel to Asimov’s Foundation Trilogy, a young Hari Seldon delivers a talk at a mathematics conference on the planet Trantor, capital world of the Galactic Empire. Seldon’s talk describes his idea of predicting the future via the math of psychohistory, a science that he had just begun to develop. Naturally the emperor receives word of this talk (in the galactic future, politicians pay more attention to science than they do today) and invited Seldon to an audience. “What I have done,” Seldon told the emperor, “is to show that, in studying human society, it is possible … to predict the future, not in full detail, of course, but in broad sweeps; not with certainty, but with calculable probabilities.”6 But the emperor was dismayed to learn that Seldon couldn’t

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature actually predict the future just yet, that he merely had the germ of an idea about how to do so if the mathematics could be properly developed. Seldon, in fact, was skeptical that he would ever succeed. “In studying society, we put human beings in the place of subatomic particles, but now there is the added factor of the human mind,” Seldon explained. “To take into account the various attitudes and impulses of mind adds so much complexity that there lacks time to take care of all of it.”7 In fact, Seldon pointed out, an effective psychohistory capable of predicting the galactic future would have to account for the interacting human variables on 25 million planets, each containing more than a billion free-thinking minds. “However theoretically possible a psychohistorical analysis may be, it is not likely that it can be done in any practical sense,” he admitted.8 By displeasing the emperor with such pessimism, Seldon soon found himself a fugitive, roaming from one sector to another on the planet Trantor—the urban sector of the Imperial capital, a university town, a farming region, an impoverished mining center. By the end of the book Seldon realized that Trantor was a microcosm of the galaxy, home to hundreds of societies each with their own mores and customs. That was his solution to achieving a science of psychohistory! He didn’t have to analyze 25 million worlds; he could understand the variations in human behavior by using Trantor itself as a laboratory. Toward the end of the 20th century, Earth-bound anthropologists independently arrived at a similar scheme for analyzing human social behavior. By playing the ultimatum game (and some variants) in small, isolated societies around the planet, those scientists have found that human nature isn’t so universal after all. College students in postindustrial society, it turns out, are not perfectly representative of the entire human race. This worldwide game-playing project began after anthropologist Joe Henrich, then a graduate student at UCLA, tried out the ultimatum game with the Machiguenga farmers of eastern Peru in 1996. The rules were the same as with college students: One player

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature is given a sum of money and must offer a share of it to the second player. The second player may either accept the offer (and the first player keeps the rest) or the second player may reject the offer, in which case all the money is returned and neither player gets anything. By the time Henrich tried the game in Peru, it had been widely played with college students, who usually make offers averaging more than 40 percent of the pot. Such offers are routinely accepted. Sometimes lower amounts would be offered, but they would usually be rejected. Among the Machiguenga, though, Henrich observed that lower amounts were routinely offered—and usually accepted. “We both expected the Machiguenga to do the same as everybody else,” UCLA anthropologist Robert Boyd told me. “It was so surprisingly different that I didn’t know what to expect anymore.”9 Could it be that the Machiguenga actually understood the rational-choice rules of game theory, while everybody else in the world let emotions diminish their payoffs? Or would other isolated cultures behave in the same way? Soon Henrich, Boyd, and others acquired funding from the MacArthur Foundation, and later the National Science Foundation, to repeat the games in 15 smallscale societies on four continents. The results were utterly baffling. From Fiji to Kenya, Mongolia to New Guinea, people played the ultimatum game not just the way college students did, or the way economic theory dictated, but any way they darn well pleased. In some cultures, like the Machiguenga, low offers were typical and were often accepted. But in other cultures, low offers were frequently made but typically rejected. In a few cultures the offers would sometimes be extra generous—even more than half. But in some societies such generous offers were likely to be refused. Among other groups, rejections almost never occurred, regardless of the size of the offer.10 “It really makes you rethink the nature of human sociality,” Henrich, now at Emory University in Atlanta, told me. “There’s a lot of variation in human sociality. Whatever your theory is about human behavior, you have to account for that variation.”11

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature CULTURAL DIVERSITY This cross-cultural game theory research clearly shows that people in many cultures do not play economic games in the selfish way that traditional economic textbooks envision. And it appears that the differences in behavior are indeed rooted in culture-specific aspects of the group’s daily life. Individual differences among the members of a group—such as sex, age, education, and even personal wealth—did not affect the likelihood of rejecting an offer very much. Such choices apparently depend not so much on individual idiosyncrasies as on the sorts of economic activity a society engages in. In particular, average offers seemed to reflect a society’s amount of commerce with other groups. More experience participating in markets, the research suggested, produces not cutthroat competition, but a greater sense of fairness. The stingy Machiguenga, for instance, are economically detached from most of the world—in fact, they hardly ever interact with anyone outside their own families. So their market-based economic activity is very limited, and their behavior is selfish. In cultures with more “market integration,” such as the cattle-trading Orma in Kenya, ultimatum game offers are generally higher, averaging 44 percent of the pot and often are as much as half. Orma average offers are similar to those found with American college students. But sometimes students make low offers, and the Orma rarely do. College students find their low offers are usually rejected, but in some societies any offer is accepted, no matter how low. Among the Torguud Mongols of western Mongolia, for example, a low offer is rarely refused. Even so, Torguud offers averaged between 30 and 40 percent—despite the fact that the offerer would surely get more by offering less. Apparently the local Mongolian culture values fairness more than money. At the same time, inflicting punishment (by rejecting an offer) is not highly regarded there, either. In society after society, the anthropologists discovered different ways in which cultural considerations dictated unselfish behavior. Among the Aché of Paraguay, for example, hunters often leave

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature the day’s game on the outskirts of their village. Members of the tribe then retrieve it for sharing among the villagers. When playing the ultimatum game, the Aché typically make high offers, often more than half. So do the whale-hunting Lamalera of Indonesia, who carefully and fairly divide up the meat from killed whales. In other societies, though, the cultural influences play out differently. In Tanzania, the Hadza share meat, but they complain about it and try to get away without sharing when they can. Nonsharers, though, risk ostracism, social scorn, and negative gossip. It makes sense, then, that when playing the ultimatum game, the Hadza make low offers, with high rejection rates. On the other hand, high offers do not always signify a culture imbued with altruism. The Au and Gnau of Papua New Guinea often offer more than half the money, but such generosity is frequently rebuffed. The reason, it seems, is that among the Au and Gnau accepting a gift implies an obligation to reciprocate in the future. And an excessively large offer may be interpreted as an insult. Colin Camerer, one of the economists collaborating with the anthropologists in the cross-cultural games, observes that this result is just another twist in the cultural influence on economic behavior. “Offering too much money, rather than being extremely generous, is actually being kind of mean—it’s demeaning,” Camerer explained to me. “So the money is turned down because they don’t want to be insulted, and they don’t want to be in debt.”12 The surprising results of the cross-cultural game theory experiments showed that the games were not necessarily measuring what the scientists thought they were. Rather than purely testing economic behavior, the games actually tapped into patterns of cultural practice. Players apparently tried to figure out how the game related to their real-world life and then behaved accordingly. For instance, the Orma quickly recognized a similarity between real life and a variant of the ultimatum experiment, the public goods game (which we encountered in Chapters 3 and 4). In that game the experimenter (Jean Ensminger of Caltech) offered each

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature of four Orma some money from which they could contribute to a community pot and keep the rest. Ensminger would then double the pot and divide it equally among the four players. When she described the game to her Kenyan assistants, they quickly replied that it was just like harambee—a practice of soliciting contributions for community projects. “That really changed our thinking a lot about what was going on when people are in an experiment,” Camerer told me in one of our conversations at Caltech. “In game theory, the bias we inherited was the mathematician’s bias.” In other words, the initial belief was that “when you present the game, it’s like a smart kid sitting down to play Monopoly or poker…. They read the rules, figure out what to do—they treat it as like a logic problem. But these subjects treat it as like analogical reasoning—what is this like in my life?”13 So what the game theory experiments have shown is that life differs in different cultures, and economic behavior reflects those differences in cultural life. Game theory has consequently illuminated the interplay of culture and economic behavior, showing that humankind does not subscribe to a one-size-fits-all mentality. Human culture is not monolithic—it’s like a mixed strategy in game theory. In an intriguing way, this diversity in cultural behavior around the world parallels the multiplicity of versions of “human nature” found within various academic disciplines. When I visited Boyd in his office—on the third floor of Haines Hall on the UCLA campus—our discussion turned to that problem in pursuing the general notion of human nature and the basic principles of human behavior. Boyd lamented the academic world’s fragmented and inconsistent view of how people tick. “We have this weird, I think untenable, situation in the social sciences,” he said. “You go over to Bunch Hall and the economists tell the students one thing. And the students come over here to sociology, one floor down, and they get told no, that’s all wrong, this is right. And they come up here, and we anthropologists tell them all kinds of different things…. And then they go to the

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature psychology department and they get told something different again. This is not OK. It’s not acceptable that the economists are happy with their world and the sociologists are happy with their world, and this persists in an institution which is supposed to be about getting at the truth.”14 Perhaps the rise of game theory as a social science tool, though, will help change that situation. In particular, merging the abstract math of game theory with the real-world immersion of anthropologists and other social scientists has begun to show how disparate views of human nature may be drawn closer to how life really works. “Somehow in the last 20 years there’s been this emergence,” Boyd said, “of people who are interested in doing mathematical theory like game theory, but building it on psychologically real people.” GAMES, GENES, AND HUMAN NATURE The fairness displayed in many societies and the variety of behaviors among them are hard to reconcile with the view that human psychology is universally programmed by the evolutionary past. A hard-line interpretation of evolutionary psychology would predict similar behavior everywhere. The game experiment project argues otherwise, posing a conundrum for evolutionary psychologists. “I think that if it had turned out that everywhere in the world people were … ruthlessly selfish, they would have said, ‘See, I told you so,’” said Boyd. “And when it didn’t turn out that way … that’s not a comfortable fact for them. It’s some fairly strong evidence on the other side of the scale.” He pointed out, though, that evolution remains important to human psychology. “No educated person should doubt that our psychology is the product of evolution— that’s a given,” Boyd said. “The question is, how did it work?” And as Camerer pointed out, evolutionary psychologists can always retreat to the fallback position that the ancestral environment programmed people to be different. But in that case the original claim about a single “human nature” is substantially softened. “I

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature think the hard story about cultural universality, you can reject,” Camerer said.15 It’s important to perceive, I think, that these are not the knee-jerk reactions against “genetic determinism” expressed by some enemies of evolutionary psychology and its intellectual predecessor, sociobiology. These are evidence-driven conclusions about evolutionary psychology’s limitations. While evolutionary psychology has benefited from a surge of often favorable publicity over the last decade or so, more and more thoughtful critiques (as opposed to vitriolic polemics) have begun to appear. One of the more interesting critiques comes from philosopher David Buller, of Northern Illinois University in Dekalb, who critically assessed the methodological rigor underlying several of evolutionary psychology’s claimed “successes” and found that the evidence for them was actually ambiguous. In a book published in 2005 and in a paper published the same year in Trends in Cognitive Sciences, Buller distinguished the mere study of evolution’s relationship to psychology—evolutionary psychology with a lowercase e and p—from Evolutionary Psychology, the paradigm based on the “doctrine of a universal human nature” and the “assumption that the adaptational architecture of the mind is massively modular.” “Evolutionary Psychologists argue that our psychological adaptations are ‘modules,’ or special-purpose ‘minicomputers,’ each of which evolved during the Pleistocene to solve a problem of survival or reproduction faced by our hunter-gatherer ancestors,” Buller wrote.16 He contends that many of the “discoveries” claimed by evolutionary psychologists crumble under critical analysis. Evolutionary psychologists say their work explains sex differences in jealousy, an innate ability to detect “cheating” (as when someone fails to perform an obligation incurred in return for receiving some benefit), and a tendency of parents to abuse stepchildren more than their own genetic offspring. But however plausible the Evolutionary Psychology explanations might be, Buller says, the actual evidence underlying them suffers from a number of defects. In some

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature cases the data on which the claims are based may be biased or incomplete, and sometimes the research methods are not rigorous enough to exclude alternative explanations for the findings. Buller argues, for example, how results of a card-choosing task, designed to illustrate the brain’s “cheating detector” module, could also be explained by a nonmodular brain just acting logically. “Although the Evolutionary Psychology paradigm is a bold and innovative explanatory framework, I believe it has failed to provide an accurate understanding of human psychology from an evolutionary perspective,” he wrote.17 Buller’s criticisms reflect the latest stage of a long-running controversy about the role of genes and evolution in shaping human culture and patterns of behavior, an issue commonly framed as a battle of nature versus nurture—genes versus environment. The Evolutionary Psychology view ascribes enormous power to the role of genetic endowment in directing human behavior; many scientists, philosophers, and scholars of other stripes find the belief in the dictatorial determinism of genetic power to be particularly distasteful. In any case, objections such as Buller’s—whether they turn out to be well founded or not—should not be regarded as support for the extreme view (sometimes still expressed, surprisingly) that rejects any role for genes in behavior—or more precisely, in differences among humans in their behavior. Without genes, of course, there is no behavior—because there would be no brain, and no body, to begin with. The real question is whether variations in individual genetic makeup contribute to the wide variety of behavioral tendencies found among people and cultures. In recent years, the most thoughtful investigators of this issue have tended to agree that genes do matter, to some degree or another. Anyone who says that genes don’t matter at all has clearly not been paying attention to modern molecular genetics research, particularly in neuroscience. And modern neuroscience does even provide some evidence for modularity in many brain functions, as Evolutionary Psychologists argue. But the latest neuroscience also undercuts the Evolutionary Psychology paradigm in a major way by showing

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature how flexible the brain is. A brain hardwired for certain behaviors ought to be, in fact, hardwired. But the human brain actually exhibits remarkable flexibility (the technical term is plasticity) for adapting its tendencies in the wake of experience. “One of the surprises of the last few years is the fact that we’re learning that the brain is hardwired for change,” says Ira Black, of the Robert Wood Johnson Medical School in New Jersey. “We’ve learned that the environment is capable of accessing genes and altering their activity within the brain.”18 Heredity does wire some predispositions into the brain, to be sure, but it’s a mistake to believe that experience must somehow defy the brain’s genetic hardwiring. It is actually the brain’s genetic wiring that creates the capacity to change with experience. “You are flexible because of your genes, not in spite of them,” declare neuroscientists Terrence Sejnowski and Steven Quartz in their book Liars, Lovers, and Heroes. “Your experiences with the world alter your brain’s structure, chemistry, and genetic expression, often profoundly, throughout your life.”19 So most experts would agree that genes are important, and genetic variation can influence propensities toward different kinds of behavior. On the other hand, genes are not so all-powerfully important as some gene-power dogmatists contend. Even animals, often portrayed as mere “gene machines” responding to stimuli with programmed responses, actually exhibit a lot of variability in their behavior that cannot be ascribed to genetic variations. A few years back I ran across a study that put this issue in particularly sharp perspective, having to do with an especially simple behavioral response in mice. For years, scientists have annoyed mice by dipping their tails into a cup of hot water (typically about 120 degrees Fahrenheit). The idea is to test a mouse’s reaction to pain. Sure enough, the mice do not like having their tails dipped into hot water; as soon as you put the tail in, the mouse will jerk it out. But not all mice behave in exactly the same way—at least, not all pull their tails out as rapidly as others. Experimenters have found that some mice react, on average, in a second or less; others might

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature take three or four. Some mice are simply more sensitive to pain than others. Since the environmental conditions are apparently just the same, it is tempting to conclude that differences in this simple behavior reflect some difference in the mice’s genes. It’s an easy enough question to check: Since the experiments are performed on different genetic strains of mice, all you need to do is compare the results for the different strains to see if some genetic profiles corresponded with slower (or faster) tail-jerk reactions than others. As it turns out, Jeffrey Mogil of McGill University in Montreal and collaborators at the University of Illinois had been dipping mouse tails in hot water for more than a decade and had accumulated plenty of data with which to perform such an analysis. And that analysis did confirm the relevance of genetic differences. Keep the environmental conditions constant (the water temperature should be precisely 49 degrees Celsius, for example) and some genetic strains, on average, do flip their tails out of the water faster than others. Upon further review, though, it became clear that genes were not the only things that mattered, and a constant water temperature was not the only environmental factor to consider. After reviewing the scores of more than 8,000 irritated mice, Mogil’s team found that all sorts of things influence reaction speed. Are the mice kept in a crowded cage, or do they have room to roam? Was it the first mouse out of the cage, or the second? Is it morning, afternoon, or night? Did anybody remember to measure the humidity? And who was holding the mouse at the time? “A factor even more important than the mouse genotype was the experimenter performing the test,” Mogil and colleagues wrote in their paper.20 In other words, genes aren’t even as important as which researcher is handling the mouse. In fact, a computerized cross-check of all the factors found that genetic differences accounted for only 27 percent of the variation in tail-test reaction speed. Environmental influences were responsible for 42 percent of the performance differences, with 19 percent attributed to interactions between environment and genes.

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature (That just means that certain conditions influenced some genetic strains but not others.) Mogil and collaborators concluded that the laboratory environment plays an important role in the way mice behave, either masking or exaggerating the effects under genetic control. And since tail-flipping is such a simple behavior—basically a spinal cord reflex—it’s unlikely that the environment’s influence in this case is a fluke. More complicated behaviors would probably be even more susceptible to environmental effects, the researchers observed. Results such as these strike me as similar to findings about how humans play economic games in different ways. Genes, environment, and culture interact to produce a multiplicity of behaviors in mice, and in people. The human race has adopted a mixed strategy for surviving in the world, with a diverse blend of behavioral types. It shouldn’t be surprising that cultures differ around the world as well, that the planet is populated by a “mixed strategy” of cultures, rooted in a mixture of influences on how behavior evolves. A MIXED HUMAN NATURE So what of human nature, and game theory’s ability to describe it? There is a human nature, but it is not the simplistic consistent human nature described by extreme evolutionary psychologists. It is the mixed human nature that, on reflection, should be obvious in a world ruled by game theory. Evolution, after all, is game theory’s ultimate experiment, where the payoff is survival. As we’ve seen, evolutionary game theory does not predict that a single behavioral strategy will win the game. That would be like a society populated by all hawks or all doves—an unstable situation, far from Nash equilibrium. Game theory’s rules induce instead a multiplicity of strategies, leading to a diverse menagerie of species practicing different sorts of behaviors to survive and reproduce. Seen through the lens of game theory, evolution’s role in human psychology is still important, but it operates more subtly than

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A Beautiful Math: John Nash, Game Theory, and the Modern Quest for a Code of Nature hard-line evolutionary psychologists have suggested. Game theory guarantees that evolution will produce a diversity of species, a mixture of behaviors, and in the case of the human race, a multiplicity of cultures. So it seems to me that game theory has itself answered the question about why it doesn’t seem to work, at least as it was originally formulated. Nash’s original game theory math was construed and interpreted a little too narrowly. Applied solely to economics, it predicted behavior that was often at odds with what people really did. But that was because the math originated and operated in an abstract realm of assumptions and calculations. Now, by playing games around the world with real people enmeshed in their own cultural milieus, scientists have shown how that purely mathematical approach to economics and behavior can be modified by real-world considerations. “My goal is to get the mathematicians to loosen their grip on game theory and get away from thinking about a game … that’s purely of mathematical interest,” Camerer told me. Instead, he said, playing games can be thought of as something “like an X-ray about a thing that’s happening in the world.”21 Viewed in this way, game theory becomes even more powerful. It becomes a tool for grappling with the complexity of human behavior and understanding the innumerable interactions that drive human history. It’s just the sort of thing Hari Seldon was looking for to produce a science of society. Of course, Asimov’s character had many real-life predecessors who sought a similar science of society. In fact, the statistical physics that Asimov cited as the inspiration for psychohistory owed its own inspiration to the pioneers who applied statistics to people—especially an astronomer turned sociologist named Adolphe Quetelet.