Farnam Street helps you make better decisions, innovate, and avoid stupidity.

With over 400,000 monthly readers and more than 93,000 subscribers to our popular weekly digest, we've become an online intellectual hub.

Category Archives: Health

Michael Pollan’s Simple Rules for Eating

What if eating right wasn’t actually all that complicated?

What if you read enough to see patterns develop, to realize that when you stripped away all the confusing bits that maybe the skeleton underneath was actually pretty simple?

This is what happened to author Michael Pollan a few years ago when he started doing research to try and figure out what he should be eating.

Most of the time when I embark on such an investigation, it quickly becomes clear that matters are much more complicated and ambiguous — several shades grayer — than I thought going in. Not this time. The deeper I delved into the confused and confusing thicket of nutritional science, sorting through the long-running fats versus carb wars, the fiber skirmishes and the raging dietary supplement debates, the simpler the picture gradually became. I learned that in fact science knows a lot less about nutrition than you would expect – that in fact nutrition science is, to put it charitably, a very young science. It’s still trying to figure out exactly what happens in your body when you sip a soda, or what is going on deep in the soul of a carrot to make it so good for you, or why in the world you have so many neurons – brain cells! – in your stomach, of all places. It’s a fascinating subject, and someday the field may produce definitive answers to the nutritional questions that concern us, but — as nutritionists themselves will tell you — they’re not there yet. Not even close. Nutrition science, which after all only got started less than two hundred years ago, is today approximately where surgery was in the year 1650 – very promising, and very interesting to watch, but are you ready to let them operate on you? I think I’ll wait awhile.

The diet industry brings in billions and billions of dollars every year and some of the latest internet celebrities are food and fitness models/gurus. Is it any surprise? Our survival and well-being depends very largely on our health and (arguably) ours looks. The diet industry taps directly into one of our basic survival instincts. Food is cultural.

There is good money to be had if you can find the magical thing that will help people lose weight and feel better. Unfortunately, there is also good money to be had in treating people for illnesses that occur from poor diet and lack of exercise. In short, complexity is good for business. (This is a misaligned incentive problem of the highest order.)

… consider first the complexity that now attends this most basic of creaturely activities. Most of us have come to rely on experts of one kind or another to tell us how to eat — doctors and diet books, media accounts of the latest findings in nutritional science, government advisories and food pyramids, the proliferating health claims on food packages. We may not always heed these experts’ advice, but their voices are in our heads every time we order from a menu or wheel down the aisle in the supermarket. Also in our heads today resides an astonishing amount of biochemistry. How odd is it that everybody now has at least a passing acquaintance with words like “antioxidant,” “saturated fat,” “omega-3 fatty acids,” “carbohydrates,” “polyphenols,” “folic acid,” “gluten,” and “probiotics”? It’s gotten to the point where we don’t see foods anymore but instead look right through them to the nutrients (good and bad) they contain, and of course to the calories — all these invisible qualities in our food that properly understood, supposedly hold the secret to eating well.

But for all the scientific and pseudoscientific food baggage we’ve taken on in recent years we still don’t know what we should be eating. Should we worry more about the fats or the carbohydrates? Then what about the “good” fats? Or the “bad” carbohydrates, like high-fructose corn syrup? How much should we be worrying about gluten? What’s the deal with artificial sweeteners? Is it really true that this breakfast cereal will improve my son’s focus at school or that other cereal will protect me from a heart attack? And when did eating a bowl of breakfast cereal become a therapeutic procedure, anyway?

For Pollan, the picture actually got clearer the further he traveled down the rabbit hole.

While his research uncovered the fact the we don’t know a whole lot about nutrition — there’s a lot of pseudoscience here — one obvious fact seems to recur: populations that eat a Western diet are generally less healthy than those who eat more traditional diets.

What does Pollan mean by “more traditional diet”?

These diets run the gamut from ones very high in fat (the Inuit in Greenland subsist largely on seal blubber) to ones high in carbohydrate (Central American Indians subsist largely on maize and beans) to ones very high in protein (Masai tribesmen in Africa subsist chiefly on cattle blood, meat, and milk), to cite three rather extreme examples. But much the same holds true for more mixed traditional diets. What this suggests is that there is no single ideal human diet but that the human omnivore is exquisitely adapted to a wide range of different foods and a variety of different diets. Except, that is, for one: the relatively new (in evolutionary terms) Western diet that most of us now are eating.

Research has shown that moving away from the Western diet can reduce your chances of developing the chronic illnesses it causes. Pollan believes this shift is most easily done by coming up with a set of simple rules to govern how we eat and interact with food. (This idea reminded us a lot of Donald Sull’s work in Simple Rules. More specifically his decision rules which help us to set boundaries, prioritize, and know when to stop an action.)

No one is quite sure which parts of the Western diet are the most destructive. There are a lot of confounding variables here — one type of food or macronutrient is tough to isolate. Gary Taubes thinks it’s the easily digestible carbohydrates. Others disagree. And since we’re not quite sure, Pollan thinks we should stick with a set of heuristics to get as close as we can.

Pollan curated these rules into a book called Food Rules: An Eater’s Manual. Let’s take a closer look at some of our favorites.

Don’t Eat Anything Your Great Grandmother Wouldn’t Recognize as Food

Agriculture has come a long way since your great grandmother was born. Many chemicals have been created to both enhance the flavor of food and to help with its shelf life. While all these additives aren’t necessarily bad for you it’s still smart to avoid them most of the time. So if you think great grandma wouldn’t be able to pronounce or understand most of the words on that box of frozen lasagna you’re holding it’s best to pass it up. Speaking of that frozen entree …

Eat Only Foods That Have Been Cooked by Humans.

Pollan means buying raw ingredients and making the food yourself, rather than buying food pre-cooked and pre-packaged. Corporations use too much junk in cooking your food. This is the biggest predictor of a healthy diet.

Eat All the Junk Food You Want as Long as You Cook It Yourself.

This is an interesting rule because generally we are trying to either remove or go around obstacles and in this instance we are very purposefully adding one. If you have a sweet tooth there is nothing wrong with eating cake on occasion. The key here is to eat those unhealthful foods only occasionally. Taking the time to make the food means that you have to be incredibly motivated to have that cake. (And you’re probably not going to whip up a bag of Oreos or potato chips.)

If You’re Not Hungry Enough to Eat an Apple, Then You’re Probably Not Hungry

This is another obstacle style rule, but it also offers you the opportunity to get better in tune with your hunger. Are you grabbing that candy bar from the vending machine at two o’clock in the afternoon because you are hungry or because you do that same thing at two o’clock every day? There are many reasons why we eat and hunger is only one of them.

Stop Eating Before You’re Full

This probably sounds a bit crazy to the average North American. In our society we eat because we are hungry and we stop because we are full. This is our tradition, but in many other cultures the goal of eating is to simply stop the hunger, which is actually quite different. Try this experiment for yourself. Try to wait until you are hungry for your next meal. You want to be able to feel it. Then as you are eating try to be mindful of the moment you stop feeling hungry. You’ll notice that this moment comes quite a few bites before that full feeling comes.


Food Rules feels like a succinct tool to help you navigate the confusing nutritional landscape. It’s a quick read that is packed with a lot of information. Imitate Bruce Lee and Absorb what is useful, discard what is useless and add what is specifically your own.

Still Interested? The Omnivore’s Dilemma: A Natural History of Four Meals is one of the best food books we’ve ever read.

Why Are No Two People Alike? (Part 2)

(This post is the second in a two-part series on the work of Judith Rich Harris. See the first part here.)

As we concluded Part 1 of our exploration of Judith Rich Harris’s work on human personality, we had begun sketching out her theory by delving into the first of three systems that she believes carry the heavy lifting in determining how our adult personalities are formed.

The first system was the Relationship System, the “people information lexicon” we automatically begin building at birth to recall the details of the people we encounter throughout our lives. This mental Rolodex carries a lot of freight, but it’s only one cog in a larger system. The workings of the Relationship System start to impact us in a broader way as we begin computing statistics about all the people in our lexicon.

This leads us to start developing a second system: the Socialization System, which we use to figure out how we need to act to fit into the groups we’ll need to be a part of to become a member of society.


Recall from Part 1 the definition of Socialization: “Acquiring the social behaviors, customs, language, accent, attitudes, and morals deemed appropriate in a particular society.”

When Harris says “particular society,” she also means “particular group” — we do not, of course, act the same around our parents as we do around our friends, our co-workers, our neighbors, or our own children. Each group has its norms, and we must learn them. Unless we are autistic or otherwise severely mentally challenged, we do just that! We do it by automatically using the information we’ve gathered, which is called implicit knowledge.

As Harris discusses in the book, even patients with severe dementia, Parkinson’s, or amnesia can recall all kinds of implicit or categorical knowledge. She refers to an amnesiac patient named Frederick who couldn’t remember that he’d played golf recently, but nonetheless didn’t forget anything about playing golf in general: He recalled all the mechanical knowledge, the lingo, the customs, and the rules. Just not his last round:

All memories are not alike; nor are all memory disorders. What Frederick had lost was his ability to form new memories of a sort called “episodic” — explicit memories of actual events, which can be consciously recalled and put into words. What he had retained was his semantic memories (factual knowledge, like the meaning of birdie) and his implicit or procedural memories (how to play golf). You may have episodic memories of being taught to play golf by your father, but your knowledge of how to play golf is procedural. Sad to say, you may lose your explicit memories of your father sooner than your implicit memories of how to play golf.

An Alzheimer’s patient may not remember meeting any specific man, but ask him what a man is, and he can describe one just fine. As we’ll see below, the systems are distinct from one another.

Thus, our collection of implicit social knowledge, what many people would call stereotypes but what are simply averages of our experience, end up being extremely useful to us. At an unconscious level, these averages give us the fodder for our “self-socialization” — our maturation into socially functioning individuals.


As we begin developing our categories by averaging out a large amount of information collected by our social intelligence systems, we become eager to figure out which categories we’re in and begin acting appropriately to become a part of that group. The term “peer pressure” is a misnomer — peers needn’t pressure us at all for us to want to become a part of their group. (Harris shows in The Nurture Assumption that even a little girl who only sees other little girls from afar, and does not interact with them, will start acting as they do in hopes of becoming more “little girl-ish.”)

Other species are capable of averaging out information about groups and creating categories, but humans have a unique problem: We all belong to many different categories. We touched on this above — we are at turns many different things — boy, male, student, child, etc. We must learn to navigate each of them uniquely, and we do:

Self-categorizations are exquisitely sensitive to social context and can change at the drop of a hat. Girls and boys in a school lunchroom or playground ordinarily categorize themselves as girls and boys, but the presence of a mean or bossy teacher can cause them to unite in a common cause and to classify themselves simply as children. After the terrorist attacks of September 11, 2011, Democrats and Republicans classified themselves, for a while, simply as Americans.

As that last example illustrates, humans can identify even with groups (such as Democrats and Republicans) composed chiefly of strangers. They can identify with groups even if they don’t know who is in them. The social psychologist Henri Tajfel told some boys, supposedly on the basis of a test, that they were “overestimators” and others that they were “underestimators.” That’s all it took to evoke what Tajfel called “groupness” in the boys. When they were given the opportunity to award monetary payments to other members of the overestimator and underestimator groups (identified by group but not by name), they not only awarded more of the members of their own group: they also made sure to underpay the members of the other group. The boys who participated in this study all went to the same school, but none of them knew which of their classmates were overestimators and which were underestimators. There was no opportunity for the relationship system to put in its two cents.

Social categorization operates independently of the relationship system, just as the system for generating the past tense of a regular verb acts independently of the system for retrieving the past tense of an irregular verb.

As a group-adapted species, like chimpanzees or ants, humans must successfully figure out how to “get along,” and evolution has given us the automatic ability to do so. That’s why the vast majority of people end up similar to the people they grew up around: Those are the people we had to become similar to in order to socialize successfully. As we grow up, we acquire the customs, habits, language, accent, types of goals and aspirations, and lots of other traits of the culture around us, and it continues on as we age, although less dramatically over time.

But of course, we aren’t all brainless zombies, mindlessly mimicking our friends and peers. Human beings are far more complex than that, and this is why we all turn out differently, besides our differing genetics.

The socialization system explains why we become similar to those around us. What explains why we remain quite different? Harris calls it the Status System, and it’s the final piece of the puzzle.

The Status System

The most speculative, and perhaps controversial, aspect of Harris’s theories might be her thoughts on how we compete for status within our self-identified groups. She believes, and the evidence she corrals does support, a theory that this competition for superiority is a major long-term modifier of human personality:

The purpose of this system is the baby’s Job 3: to compete successfully. I’m talking now about competition within the group, classic Darwinian competition. To compete with one’s groupmates is to strive for status; the goal is to be better than one’s groupmates. “Humans everywhere pursue status.” observed the evolutionary psychologist Donald Symons, and for good Darwinian reasons: higher-status individuals have access to more of the world’s goodies.

But in humans, striving for status is a complicated matter. There are no straightforward rules for how to go about it; no single set of tactics is going to work for everyone. The status system’s assignment is to work out a long-term strategy of behavior that is tailor-made for the individual in whose head it resides. 

Mental organs are specialized collectors of data; each is tuned to respond selectively to certain kinds of cues. The relationship system and the socialization system both collect information about other people. The status system has a more difficult job: it specializes in collecting information about the self. One of the important things that children have to learn while they are growing up is what sort of people they are. Are they big or small, strong or weak, pretty or plain? Without this information they would have no basis for deciding whether to try to dominate others or yield without a fight, to make suggestions or follow the suggestions of others, to turn down potential mates in hopes of doing better or take whatever comes along.

During childhood and adolescence, young humans collect information on how they compare with the others who will be their rivals in adulthood. Armed with this information, they make long-term modifications in their behavior. It is the status system that enables them to do this.

Again, these systems are often at odds with each other. We can, at the same time, feel well-accepted by a group in general and feel we have little status within it, and those things may affect us in different ways. A bully who has little group acceptance can nonetheless have perfectly healthy self-esteem due to their status.

We develop our sense of self slowly over a very long gestation period. We figure out if we’re strong compared to most, smart compared to most, funny, quick, good-looking, suave, tall, or svelte, or perhaps the reverse. And we begin tailoring our behavior in a way that plays to our strengths, as a way to compete successfully for attention and status.

One economic study explored the idea, for example, that height had an impact on income for adult males. But once the economists sussed it all out, they figured out that it wasn’t simply tall adults who were better paid: What mattered was their height when they were adolescents. If you became tall late, you weren’t making more money than average.

Cross referencing this with another study on adolescent height and personality traits, Harris figures that because height (and other related traits like strength and athleticism) generally affords some status when you’re young, they can have long-term effects on your personality, including self-assurance and leadership ability. As it is with height, so it goes with other traits — height and income are simply the easiest to measure.


So as we collect information about other specific people and other types of people to feed into our first two engines, the Relationship System and the Socialization System, we also collect information on the way we’re seen by the “generalized other,” which goes into System 3: the Status System. The use of that system enables us to design a personality that fits our particular situation.

This talk of “design” makes it sound more deliberate than it really is. All of this is happening with very little input from the “Head Honcho” upstairs. We can involve our slower, more deliberate “System 2” in the process, but the effect is dwarfed by what’s happening on its own.

Here’s how Harris thinks this whole Status System thing works its magic:

The status system, designed to collect and store information about the self, makes clever use of the features of the relationship system (the system designed to collect information about other people). The activities of the two systems dovetail like this: while your relationship system is gathering information about me and storing it on the page assigned to me in your people-information lexicon, my status system is trying to figure out what you’ve got recorded on that page. You keep the information you’ve learned about me separate–you don’t mix it together with information about other people–but I take that information I’ve gotten about myself from my page in your lexicon and put it together with similar information I’ve gotten from other people’s lexicons. What I need is a picture of myself from the point of view of the “generalized other.”


Unfortunately, this system doesn’t work perfectly–the picture is blurry…The reason we can’t read the page as accurately as we would like (or as accurately as we think we would like) is that the mind in which that page resides doesn’t want us to. It is to my advantage to know that you are thinking about me, but it may be to your advantage to keep me from knowing it.

The picture may be blurry but it’s nuanced and multidimensional. The status system uses this information to work out a long-term strategy of behavior tailored specifically for its owner. Using data collected in childhood and adolesence–How many people can beat me up? How often do other people look at me? Do people trust me to give good advice? — the system shapes and modifies personality in a way that takes account of the individual’s preexisting characteristics and the opportunities afforded by the environment.

From an evolutionary standpoint, this tendency for experience to modify long-term behavioral patterns, the tendency to use the self-knowledge obtained through the “mind-reading mechanism,” has increased the behavioral diversity among humans within our groups. While we do indeed seek to be part of a group, and will sacrifice for the success of that group, we also have deep self-interest. (Some of the most interesting worldly results come when those things are at odds with one another; see suicide bombers and kamikaze warriors.)

This drive to compete successfully and specialize as individuals makes us extremely well suited to live in large groups, something our species does uniquely well. In fact, Harris believes the modification of personality by way of social experience to be a unique human trait.


So that’s it. As human beings develop, they collect vast amounts of social information and use it to form specific relationships and understand the specific details of the people around them, but also average out that information to create categories and groups, and to understand how to act to become part of the groups we think we belong in. We also seek to pursue our self-interest and, by figuring out what other people think about us relative to what they think about everyone else, we select strategies that we think will help us get ahead relative to the other members of our group or category.

The answer to the nature/nurture question is, of course, that both are hugely influential. Our genetics provide the blueprint by which we will interact with the world, and from there the specific course of our interactions and experiences with other people will determine how we turn out.

Harris admits that her theory needs rigorous testing to figure out whether she’s nailed it exactly or more refinement is needed. She suspects the latter will be true. As we dig into the details over time, we’ll figure out more specifically how these systems work and interact, where the lines blur between them, and how their relative effects take a toll on our long-term personality.

Regardless of the work that remains to be done, Harris’s work provides us with tremendous insight into what makes us who we are.


Still Interested? It’s highly recommended that you read both of her books in full: The Nurture Assumption and No Two Alike.

Why Are No Two People Alike? (Part 1)

“My solution to the mystery is that three perpetrators are involved:
three mental systems that go about their business in different ways.
Together, these three can answer the hows, whys, whens, and wheres of personality development.”

 Judith Rich Harris


Becoming Human

What makes us…us? What makes one person open, honest, and enthusiastic, and another ornery and closed-minded? Why do some of us love risk-taking and some not? What causes us to be so alike…and yet so different?

The “nature versus nurture” debate is probably as old as modern humanity. There’s something related to our consciousness which makes us wonder whether our personality is pre-determined or perhaps whether our parents, peers, culture, nation, or experiences are the determining factor.

We still wonder, but thanks to Darwin and all that came after him, we don’t have to speculate as much as we once did. The modern study of behavioral genetics has shown us that the answer is, unequivocally, both. Our genes play an enormous role in how we turn out as children and full-grown adults, and the evidence is unmistakable.

In fact, oddly enough, we can see through carefully done research that about half of personality variation can be explained genetically. Take two identical twins and their personalities will be similar to the extent of their identical genes. This surprises no one.

The surprise is that two identical twins are so damn different! Think about it: They share all of their genetics, they probably grew up in the same house with the same set of parents, with the same books on the wall and the same TV watching habits, went to the same schools at the same time, had similar groups of friends…and yet two completely separate personalities emerge. How?

The Nurture Assumption

Judith Rich Harris may have the best answer, and it’s in her book No Two Alike, an amazing contribution to modern thought. What Harris — a former author of child development textbooks turned super-synthesizing social scientist — wanted to know was: Why do we all turn out with unique personalities? What really drives the differences?

She had begun to answer this in her deeply controversial 1998 book The Nurture AssumptionThat book proposed her group socialization theory, the idea that children are mostly socialized by their peers, not their parents. By socialized, we mean — how do children learn the way to behave and operate within their culture? How to speak the right way, act the right way, play the right way, say the right things, and so on? The idea that parents had the primary influence had become fashionable in the 20th century Western world, thanks to Freud.

But contrary to popular belief, Harris explained, whether identical siblings were raised by the same set of parents or by two different sets, years of research proved they’d be no more or less alike than their genetic connection would predict. Likewise, two siblings put up for adoption end up no less alike, on average, than if they’d been raised in the same home. Identical twins are more alike than regular siblings in general, but the reason is ultra simple: They share more genes!

This meant, Harris explained, that parenting doesn’t have an effect on adult personality which isn’t already explained by genetic factors, any more than Chinese parents can give their child a Chinese accent if they raise him or her in Minnesota. It’s a bit hard to see on the surface, but many traits we think are due to parenting are simply due to the genetics shared between parent and child. Before behavioral genetics showed the genetic component, the two were regularly confounded, making much of the “research” on development worthless.

What does have an effect, besides genetics, is the peer group and culture children the child was raised in. And so besides genetics, it is the groupneighborhood, social group, and subculture of the child that matters, not whether their parents were kind or scolding, attentive or inattentive, soft or hard, or any other style of parent. Just like the child of Chinese immigrants would take on the Minnesota accent, they’d also take on the social behavior of their peers as well. Harris showed that people simply do not depend on direct input from their parents to become successful adults, as hard as it is to believe. (Although parents can have indirect influence in a number of ways, most obviously by moving the child to different areas and cultures.)

For this revelation and investigation into human development, the debunking of what Harris called the Nurture Assumption — that parents can mold the personalities of their children — Charlie Munger said that Ms. Harris “has not lived in vain.”

But that still left a big question: Since group socialization tends to make people more similar to others in their identified group, what accounts for personality differences, even among identical twins hanging in the same social circle? How do we end up with a group of “conforming individualists,” as Harris calls us? Why are some people trustworthy, and some not? Why are some more law-abiding and some less so? Why are some friendly and some mean?


The difficulty in figuring out the answer is illustrated by a story Harris tells about a pair of identical twins:

Conrad and Perry McKinney, age fifty-six, were featured in an article in the Boston Globe titled “Two Lives, Two Paths.” Born and reared in New Hampshire, the twins did everything together in their earlier years. They attended the same schools, sat in the same classrooms. Academically they were average students, but they were troublemakers. Eventually their teachers got fed up with their shenanigans and the twins were separated: Perry was held back in fifth grade, Conrad was promoted to sixth. That, according to the Globe reporter, was where their paths diverged. Conrad went on to graduate from high school; Perry dropped out in eleventh grade. Today, Conrad is a successful businessman–as it happens, he runs a private detective agency. Perry…well, Perry is a homeless alcoholic “who sleeps amid trash under a bridge,” by the Piscataqua River in New Hampshire.

Small changes in circumstance, many of which are random, can have dramatic effects on one’s life, making many experiments totally unethical. We can’t just sort out twins and send some of them to the ghetto and some to Palo Alto and see what happens — we’re reliant on what we can observe in natural experiments.

In No Two Alike, Harris does this by corralling information from a wide variety of sources including developmental psychology, evolutionary psychology, cognitive science, and genetics, dispatching a number of popular red herrings in the search for a theory of why human personality turns out the way it does. By elimination and investigation, the theory she lands on seems not only plausible, but probable.

The Modular Mind

Her theory derives from what modern evolutionary psychologists have come to call the “modular mind” — the idea that the mind is made up of specific, useful, mechanisms to carry out a variety of functions, all put there through a long process of natural selection. Our mental tools allow us to see, hear, taste, feel, learn, speak, and do lots of other things that we need to survive and thrive. Some of these are present in other species and some are not: It depends how highly developed they are. (For example, ants can certainly see and taste, although crudely, but cannot speak or learn non-programmed behavior.)

As Harris sees it, from the perspective of human personality development, it doesn’t all happen in one simple way. Our modular minds have at least three separate but interrelated systems, working at turns separately and together to produce social success — one of the prime goals of a human being. (We are, after all, a highly social species.)

One passage illustrates why this is so important:

“Why,” asked the psychologist William James in 1890, “are we unable to talk to a crowd as we talk to a single friend?” Why do we shrug when we hear of hundreds of people killed in an earthquake but weep when we see a photo of one injured child? Why is it that getting to know and like someone doesn’t necessarily causes us to think well of the group to which he or she belongs–a disjunction revealed by the ineffectiveness of the protest, “Some of my best friends are Jews?”

The answer is that there are multiple systems in the mind for processing information. We have, I propose, two different mental mechanisms designed to process and store information about people. One collects data on individuals, the other on groups or social categories–types or classes of people. Criminal justice and law enforcement are (or should be) based on information processed by the first mechanism; war and bigotry are outcomes of the second. These mechanisms belong to different mental systems.

Besides the two systems that help us learn about others, we have a uniquely human third: A system that helps us learn about ourselves. Let’s take each in turn and see what we can learn and why they matter in the development of unique human personalities.

The Relationship System

Harris calls the Relationship System our “people information lexicon”. It’s how we know how to identify and deal with specific people. As humans, we need to know not just that girls at school tend to be mean if we don’t wear makeup, but that Jane will say something particularly nasty and that Sally will say something particularly nice. The mental system for categorizing the “girls our age at school” isn’t the same as the one that knows the difference between Jane and Sally.

We have a number of “modules” that roll up into a Relationship System: Our ability to recognize faces, voices, and scents; our ability to know what’s a familiar face — one that belongs to someone we know; the ability to put specific names to people and things and recall them, and hundreds more.

Harris uses the analogy of a Rolodex:

We have thousands and thousands of mental storage sites for people-information. Each is associated with a particular individual; each contains (or is linked to) other information we have about that individual. Picture a mental lexicon with a page for each individual you know, with slots for the face, name, and whether he or she is a close relative; plus other information such as occupation, plus memories of the experiences you’ve had with him or her.

There may also be an emotional marker, indicating how you feel about this person. The contents of some slots may be hard to read; other slots may never have been filled in. A page can be set up in the lexicon even if you’ve never set eyes (or ears) on the individual it refers to. You collect and store information on characters you read about in novels or hear about from other people. Folks you’ve never met may have a page in their lexicon for you!

This “lexicon” of information, constantly updated, gives us what we need to deal with individual people and figure out how to interact with them. Although we generalize and categorize people we don’t know, once we do get to know them specifically (even at a distance) we start filling in details and set up a page in the lexicon. We don’t have to be motivated to do this for a specific reason — we just do it automatically.

The evolutionary purpose of the people lexicon is as clear as the evolutionary purpose of pair-bonding: to enable us to behave appropriately toward different individuals, depending on what we have learned about them. To enable us to tailor our behavior to the nature of the relationship we have with each. The baby lifts up its arms to its mother but not to the stranger, even if the stranger is the right age and sex. The child learns to avoid the bully but to seek out other kids in the neighborhood. People stop doing favors for people who never pay them back, unless they are close relatives.


So the relationship system contains many intricately connected parts. There’s a people-information acquisition device that constructs and stores a lexicon of people and provides the motivation to collect the information. There are regulatory mechanisms that make use of the information stored in the lexicon to guide behavior in different domains of social life and that provide their own motivations, the sex drive being an obvious example. Other specialized modules deliver input to the relationship system: they include the face-recognition module, a device that assesses kinship, and the mindreading mechanisms I described in the previous chapter. Whatever you are considering doing with another person–help them, mate with them, engage in trade with them, pick a fight with them–it is extremely useful to have an idea of what their intentions are and what they are thinking about you.

And so it goes. From birth, our lexicon is ready to go, ready to be filled in. We spend a lifetime gossiping, learning, thinking, interacting with, and watching others so that we can have successful relationships with them.

But we also begin to categorize fairly early, based on a deeper analysis of our lexicon. We start putting people into groups — adults, children, teenagers, girls, boys, teachers, students, and a million others, depending on context. Importantly, we also begin to categorize ourselves, and this is where the socialization process occurs.

The Socialization System

Why is it that children “hive off” into groups and seek to differentiate themselves from other groups? The usual high school groups are not uncommon all around the world — they may differ in makeup and interests, but all young (and old) people form some group or another, if given the opportunity.  During this grouping process, the child is socialized:

In the old days, a human’s life, too, depended on remaining a member of the group. But because human groups differ in culture, the behaviors necessary for group membership couldn’t all be built in–much had to be learned. The baby’s Job 2, therefore, is to learn how to behave in a way that is acceptable to the other members of his or her society. This is the process that developmentalists call “socialization.” It consists of acquiring the social behaviors, customs, language, accent, attitudes, and morals deemed appropriate in a particular society. 

Socialization makes children more alike–more similar in behavior to others of their age and gender. Therefore, socialization cannot solve the central mystery of this book: why people (even identical twins reared together) differ in personality and social behavior. But the socialization system is an essential part of the solution, because one of the things I have to explain is why children become both more alike and less alike while they are growing up. The ways in which they become more alike do not consist solely of language and customs. There is evidence that children become more alike even in the sorts of things that are measured on personality tests. 

This process must happen as a child grows up — they must prepare for adulthood outside the home. And to do that, the child must learn what is acceptable in the groups they are a part of, and they will be part of many. A young boy from Texas will be at times a boy, a male, a student, an employee, an American, a Southerner, an athlete, and a child, among many more. These all require somewhat different actions and behaviors. So we start categorizing as best as we can:

The first step for the child is to figure out the social categories that exist in his or her society. This task is equivalent to that of learning other kinds of categories: for example, chairs and fish. Like chairs and fish, categories of people have fuzzy boundaries. Is a three-legged stool a chair? Is a seahorse a fish? Is this person a boy or a man? Traditional societies often provide rites of passage to sharpen the boundaries between age categories, but industrialized societies seem to manage pretty well without them. What we haven’t gotten used to yet is the blurring of the boundary between male and female.

An interesting thing about fuzzy mental categories is that, although they tend to be hazy around the edges, they’re clear at the center. We have an image of what the ideal or prototypical member of each category should be, and it’s somewhere in the middle. When I say “man,” you don’t think of an eighteen-year old or an eighty-year old and you probably don’t picture him wearing a dress. When I say “bird,” you think of a robin or a sparrow, not an ostrich or vulture. The prototypical chair has four legs, a seat, and a back.

We build up all kinds of implicit knowledge about the world, and we do it like the relationship system — automatically and without thought. We categorize people the same way we categorize chairs and birds, though the idea of stereotyping is certainly unpopular. Until we actually have a sheet set up in the lexicon for an individual person, all we can do is categorize them. Once we do start to learn about them specifically, the two systems begin interacting. Let’s say we meet a woman named Susan. At first, we might classify her as “White, middle-aged woman who looks like a mother.” (Again, not purposely — it happens instantly and automatically.)

Once we go on a date with her though, Susan becomes no longer just a member of a category: She becomes Susan. And although we don’t immediately remove the categories, we let her entry in the lexicon begin to develop and dominate our thoughts about her. Sometimes the two systems conflict. (I don’t usually like white middle-aged women, but that Susan is alright!)


Let’s leave it there for now. In Part 2, next week, we’ll explore the rest of Harris’s theory, and tie it all together to try to understand the mystery of human personality.

Gary Taubes and the Exquisite Balancing Act of Getting it Right

Last year, the wonderful Gary Taubes, whose ideas about nutrition we have written about before, gave a commencement address to the students of the Schmid College of Science and Technology at Chapman University in California.

The address is near and dear to our way of thinking, because Taubes raises a difficult and correct truth: In order to pursue new knowledge of the world, we must be confident that our ideas are correct, but because we are very susceptible to fooling ourselves, this tendency will lead us to believe lots of untruth as well. He calls it a tightrope walk: The thin line between being confident in an unpopular or yet unknown piece of knowledge and being a fool who buys into his cherished untruths.

Part of the speech is reprinted below, but be sure to check the whole thing out.

The idea is we’re always going to try to fool ourselves – that’s how our brains are wired — but here’s a way of thinking that will help us minimize the tendency. Another great philosopher of Science, Robert Merton, in the 1960s, put it this way: he said that Aristotle was right when he said “all men by nature desire to know” but then he added, what makes scientists different is they “desire to know that what they know is really so.”

Now here’s the catch: In science, as in life, you have to have faith in yourself and your ideas. You have to make decisions about what you’ll pursue, what you’ll continue pursuing despite times getting very tough, who you’ll do it with, who you’ll stay doing it with even after times get tough, where you’ll do it; why other people should do it with you and keep doing it with you through the tough times. You’ll make these decisions based on the assumption that what you believe is true really is. Without this belief we don’t do anything; it’s what drives us forward and allows us to act decisively. But if we fool ourselves, and we’re the easiest person to fool, we’ll make the wrong decisions – as individuals, as a society.

From this perspective, life becomes a tightrope walk in which you never actually see the rope. But it’s there. And, in all honesty, there’s almost invariably a net, too, so our missteps are rarely as damaging as we fear they’ll be while they’re happening. On this rope, we have to find the balance, time and again, between this need to think critically and skeptically about what we believe, and the need to have faith that what we’re doing and what we believe is right. Faith moves us forward; skeptical critical thinking keeps us balanced.


Still Interested? Check out a few other great commencement speeches or read up on Gary Taubes’ thoughts on Why we Get Fat.

What Predicts a Healthy Diet?

In this brief video, Michael Pollan, the author of perhaps the best food book I’ve ever read, argues that the answer is surprisingly simple and it has nothing to do with calories or nutrients.

When I started learning about nutrition, about which, by the way, much less is known than you might think, I learned that what mattered most about one’s health was not necessarily the nutrients, good or bad, that you were consuming, or staying away from, or even the calorie counts, but what predicted a healthy diet more than anything else is the fact that it was being cooked by a human being and not a corporation. Corporations cook very differently than people do.

Still curious? Check out food as culture and coevolution and artificial selection.

America’s Food Crisis: The Omnivore’s Dilemma

As a follow up to the Michael Pollan food as culture post (on his new book Cooked), a reader passed along a link to this video on Pollan’s 2006 classic The Omnivore’s Dilemma: A Natural History of Four Meals.

The Omnivore’s Dilemma was deservedly called one of the most important food politics books of all time. In the video below, Pollan and other prominent chefs and foodies weigh in on the current state of the American food industry.

The Omnivores’s Dilemma came from Pollan’s realization that Americans didn’t know where their food came from. Pollan wanted to do “a kind of detective story following the food back to the source.” The book explores the state of food in America by examining three different food chains: corn, grass, and the forest.

This book, along with Jonathan Safran Foer’s Eating Animals, changed my relationship with food.