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 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 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 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 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 h
andling 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. (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 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.
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Quetelet's Statistics and Maxwell's Molecules Statistics and society, statistics and physics
The mob has many heads but no brains.
—English proverb
The actions of men … are in reality never inconsistent, but however capricious they may appear only form part of one vast system of universal order.
—Henry Thomas Buckle
When creating the fictional science of psychohistory, more than half a century ago, Isaac Asimov didn't bother to give the details of how the math worked. He simply said you could describe masses of people in the same way you describe masses of molecules. Trained as a chemist, Asimov knew well that the behavior of gases under different conditions could be calculated with precision, even though nobody could possibly know what any one of that gas's atoms or molecules was doing. And so he reasoned that a sufficiently advanced science could do the same thing with people.
"Psychohistory dealt not with man, but man-masses," Asimov wrote.1 "It was the science of mobs; mobs in their billions…. The reaction of one man could be forecast by no known mathematics; the reaction of a billion is something else again." So while any one person could do his or her own thing, society might collectively exhibit patterns of behavior that equations could capture. Psychohistory might not be quite as accurate as the laws governing gases, but that's only because there are many more molecules than people. As one of Asimov's characters explained, "The laws of history are as absolute as the laws of physics, and if the probabilities of error are greater, it is only because history does not deal with as many humans as physics does atoms, so that individual variations count for more."2
Still, psychohistory was fiction, and using math to describe something as complex as society still strikes many people as an overly ambitious goal for real life. On the other hand, in the mid-19th century math seemed similarly useless for physicists pondering the complexities of molecular motion in gases. Gross properties of gases could be observed but not understood without a way to quantify the apparent anarchy of molecular interactions. How could anyone grasp the inner workings of a mass of molecules too numerous to count and too small to be seen? Yet the Scottish physicist James Clerk Maxwell found a way, by using statistics— mathematical descriptions of the average behavior of large groups of molecules.
Calculating such averages provided amazing predictive power. Although you couldn't say exactly what any one molecule was up to, you could predict precisely what a sufficiently large group of molecules would do in certain circumstances. Measuring the temperature of a gas, for instance, tells you something about the average speed of its molecules, and you can calculate the effect of altering the temperature on the gas's pressure. Similar methods were developed to deal with matter in all sorts of situations. Knowing the average amount of energy possessed by molecules of various substances, for instance, allows you to predict whether a chemical reaction will proceed or not—and if so, how far. You can use the statistical approach to describe a substance's magnetic or electric properties, or whether it will snap or stretch when under tension. In Asimov's psychohistory, features of society corresponded to variables like the temperature and pressure of a gas or the ebb and flow of chemical reactions or the fracture of a beam in a building.
While Asimov's vision remains a science fiction dream, it is now closer to reality than probably even he would have thought possible. The statistical approach inaugurated by Maxwell has today become physicists' favorite weapon for invading the social sciences and describing human actions with math. Physicists have applied the statistical approach to analyzing the economy, voting behavior, traffic flow, the spread of disease, the transmission of opinions, and the paths people take when fleeing in panic after somebody shouts Fire! in a crowded theater.
But here's the thing. This isn't a new idea, and physicists didn't have it first. In fact, Maxwell, who was the first to devise the statistical description of molecules, got the idea to use statistics in physics from social scientists applying math to society! So before statistical physicists congratulate themselves for showing the way to explaining the socia
l sciences, they should pause to reflect on the history of their field. As the science journalist Philip Ball has observed, "by seeking to uncover the rules of collective human activities, statistical physicists are aiming to return to their roots."3
In fact, efforts to apply science and math to society have a rich history, extending back several centuries. And that history contains hints of ideas that can, in retrospect, be seen as similar to key aspects of game theory—foreshadowing an eventual convergence of all these fields in the quest for a Code of Nature.
STATISTICS AND SOCIETY
The idea of finding a science of society long predates Asimov. In a sense it goes back to ancient times, of course, resembling at least partially the old notion of a "natural law" of human behavior or a Code of Nature. In early modern times, the idea received renewed impetus from the success of Newtonian physics, stimulating the efforts of Adam Smith and others as described in Chapter 1. Even before Newton, though, the rise of mechanistic physical science inspired several philosophers to consider a similarly rigorous approach to society.
In medieval times, the importance of the mechanical clock to society conditioned scientists to think of the universe in mechanical terms. Descartes, Galileo, and other pioneers of modern science advocated a mechanical, cause-and-effect view of the cosmos that ultimately led to Newton's definitive system of physics, published in his Principia in 1687. It was only natural that the implications of mechanism for life and society attracted the attention of other 17th-century thinkers. One was Thomas Hobbes, whose famous work Leviathan described the state of society that (Hobbes believed) maximized the well-being of all its members. Conveniently for Hobbes, a supporter of the British monarchy, his conclusion was that the people should turn over control of society to an absolute monarch. Otherwise, he argued, a dog-eat-dog mentality of unrestrained human nature would guarantee life to be "nasty, brutish, and short."
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