Judith Rich Harris: 1938 - 2018

Judith Rich Harris: 1938 - 2018

Judith Rich Harris [1.9.19]

It was in the 1990s that I received a phone call from Steven Pinker who wanted to make the world aware of the work of Judith Rich Harris, an unheralded psychologist who was advocating a revolutionary idea which she discussed in her 1999 Edge interview, “Children don't do things half way: children don’t compromise,” in which she said “How the parents rear the child has no long-term effects on the child's personality, intelligence, or mental health.”  

From the very early days of Edge, Judith Rich Harris was the gift that kept giving. Beginning in 1998, with her response to “What Questions Are You Asking Yourself” through “The Last Question” in 2016, she exemplified the role of the Third Culture intellectual: “those scientists and other thinkers in the empirical world who, through their work and expository writing, are taking the place of the traditional intellectual in rendering visible the deeper meanings of our lives, redefining who and what we are.”

Her subsequent Edge essays over the years focused on subjects as varied as natural selection, parenting styles, the effect of genes on human behavior, twin studies, the survival of friendship, beauty as truth, among others are evidence of a keen intellect and a fearless thinker determined to advance science-based thinking as well as her own controversial ideas.

In this special 16,000-word edition of Edge, dedicated to the memory of Judith Rich Harris, we take a deep dive into her ideas.



Judith Rich Harris Remembered by Steven Pinker

Children Don't Do Things Half Way: Children Don’t CompromiseA Talk with Judith Rich Harris [June 28, 1999]

— "What Are The Questions You're Asking Yourself?" (1998)
— "What is Today's most Unreported Story?" (2000)
— "What Questions Have Disappeared?" (2001)
— "What's your Question?" (2002)
— "What Are The Pressing Scientific Issues For The Nation and the World, and What Is Your Advice On How I Can Begin to Deal with Them?" (2003)
— "What's Your Law?" (2004)
— "What Do You Believe Is True Even Though You Cannot Prove It?" (2005)
— "What Is Your Dangerous Idea?" (2006)
— "What Have You Changed Your Mind About?" (2008)
— "How Is The Internet Changing The Way You Think? " (2010)
— "What Is Your Favorite Deep, Elegant, Or Beautiful Explanation?" (2012)
— "What Do You Consider The Most Interesting Recent [Scientific] News?" (2016)
— "What Is The Last Question?" (2018)


“We are in considerable doubt that you will develop into our professional stereotype of what an experimental psychologist should be." When the Harvard psychology department kicked Judith Rich Harris out of their PhD program in 1960, they could not have known how true the words in their expulsion letter would turn out to be.

Harris, an active Edge contributor for twenty years, and a charter member (and exemplar) of The Third Culture, died this week at the age of 80. After leaving Harvard, she wrote textbooks in child psychology until she could no longer believe what she was writing. The epiphany came when she was reiterating the conventional wisdom that adolescents were attempting to attain mature adult status and realized, “If teenagers wanted to be like adults they wouldn’t be shoplifting nail polish from drugstores or hanging off overpasses to spray I LOVE YOU LIƨA on the arch. If they really aspired to ‘mature status’ they would be doing boring adult things like sorting the laundry and figuring out their income taxes. Teenagers aren’t trying to be like adults: they are trying to distinguish themselves from adults!”

Harris expanded this insight into a radical new theory of socialization—that children’s personalities are shaped by genes and peers, not parents—which she laid out in a 1995 article in the flagship journal Psychological Review and a 1998 bestseller, The Nurture Assumption. Her case began with a finding that was common knowledge among behavioral geneticists but unknown to most psychologists or to the public: that the similarities between parents and their biological children can be explained by their shared genes (siblings reared apart grow up no more different than siblings reared together, and adopted siblings are not similar to each other at all). It was bolstered by findings on the minimal effects of big differences in upbringing, such as first born versus later-born, day care versus having a stay-at-home mom," and heterosexual versus homosexual parents. It got a third shot of support from the immigrant experience—children of immigrants melt into their peer groups. In the past 20 years, these findings have held up (see, in particular, Robert Plomin’s 2015 review in Perspectives in Psychological Science “The top ten replicated findings from behavioral genetics”).

Harris’s theory got wide attention. Her article won the George Miller Prize from the American Psychological Association, proof, she wrote, that the gods have a sense of humor: the letter kicking her out of graduate school had been signed by the Acting Chair of the department at the time, who was none other than George Miller. Her book, The Nurture Assumption, became a best seller, made the covers of leading mainstream magazines, and caused a sensation in the news media.

She was a big influence on a number of social scientists, including me. I featured her ideas in the “Children” chapter of The Blank Slate (which I dedicated to her, together with three others). That chapter was the most commented-upon discussion in the hundreds of reviews and interviews.

Harris defied the stereotype of an experimental psychologist in other ways. Stricken with an autoimmune disorder, she was a physical shut-in but a prolific correspondent. Her lack of conventional credentials led the press to note that the field of developmental psychology had been upended by “a grandmother from New Jersey.” She was a clear-eyed, unsentimental observer of human behavior, an irreverent challenger of alpha males and other blowhards, and the wielder of a Voltairean wit. In The Nurture Assumption, she reproduced the famous poem by Philip Larkin:

They fuck you up, your mum and dad.
They may not mean to, but they do.
They fill you with the faults they had
And add some extra, just for you.

And commented:

Poor old Mum and Dad: publicly accused by their son, the poet, and never given a chance to reply to his charges. They shall have one now, if I may take the liberty of speaking for them:

How sharper than a serpent’s tooth
To hear your child make such a fuss.
It isn’t fair — it’s not the truth —
He’s fucked up, yes, but not by us.

Harris repeatedly had to deal with the misunderstanding, “So you’re saying it doesn’t matter how I treat my children.” She reminded her readers that parenting is a moral responsibility: “We may not hold their tomorrows in our hands but we surely hold their todays, and we have the power to make their todays very miserable.” It is also a human relationship: “If you don’t think the moral imperative is a good enough reason to be nice to your kid, try this one: Be nice to your kid when he’s young so that he will be nice to you when you’re old.” And she ended her book with a reply to the charge that she was absolving parents of responsibility for their children’s lives, by reminding them of the responsibility they have for their own lives: “As for what’s wrong with you: Don’t blame it on your parents.”


A Talk with Judith Rich Harris 

[June 28, 1999]

JOHN BROCKMAN: You are frequently accused of being an extremist. Are you an extremist?

JUDITH RICH HARRIS: Well, I'm prone to making statements like this one: How the parents rear the child has no long-term effects on the child's personality, intelligence, or mental health. I guess you could call that an extreme statement. But I prefer to think of myself as a defender of the null hypothesis.

The null hypothesis is the hypothesis that a putative "cause" has no effect, and it's supposed to be the starting point for scientific inquiry. For instance, when a new drug is being tested, the researchers are expected to start out with the hypothesis that the drug is no better than a placebo. If they find that the patients who received the drug are more likely to recover than the ones who got the placebo, then they can reject the null hypothesis at some level of confidence, some probability level.

This comes as a surprise to most people, but psychologists have still not managed to collect evidence of a sort that would enable them to reject the null hypothesis of zero parental influence. In the absence of such evidence, the only scientifically sound position is the one I've taken.

BROCKMAN: But you can't prove that parents have zero influence, can you?

HARRIS: No. But why should I have to? Shouldn't the burden of proof be on the people who claim that parents do have an effect? Shouldn't the burden of proof be on the people who claim that their treatment—the style of child-rearing they recommend—works the way they say it will?

The problem is that the null hypothesis of zero parental influence hasn't been treated as the starting point, due to a pervasive pattern of thought I call "the nurture assumption." To say, "We will assume that parents do have an effect until you prove that they don't" is a demonstration of the nurture assumption in action. It's an a priori bias based on faith rather than evidence.

BROCKMAN: But some people are saying that there is evidence—plenty of evidence—of parental influence, and that for some reason you have chosen to ignore it.

HARRIS: On the contrary, I've haven't ignored it at all. I've looked at it closely and found it to be worthless. The evidence they're talking about is hopelessly confounded and is contradicted by other evidence.

Let me give you an example. Many studies have shown that verbal, literate parents tend to have verbal, literate kids. Parents who talk to their kids a lot tend to have kids with an above-average vocabulary. Parents who read to their kids tend to have kids who become good readers. This evidence comes packaged with a moral: If you want your kid to get into Harvard, you'd better start drilling him 18 years before his application is due.

The trouble is, the evidence is ambiguous. It's clear that children resemble their biological parents; what isn't clear is why. Is it the environment the parents provided, or is it the genes they provided? Just knowing there's a correlation isn't enough—we have to tease apart the effects of the genes from the effects of the home environment. One way to do it is by looking at adopted kids. And what we find is that the correlation disappears. The adopted child reared in a let's-read-a book-together home ends up no smarter, on the average, than the one reared in a don't-bother-me-I'm-watching-TV home. As far as Harvard is concerned, it doesn't make a dime's worth of difference whether the kid grew up listening to Mozart or Muzak.

In general, studies that provide a way of controlling for the effects of the genes by looking at twins, siblings, or adopted children show that the home environment has little or no effect on intelligence or personality. They show that the similarities between parents and their biological children, or between two biological siblings reared in the same home, are almost entirely a function of their shared genes. Eliminate the effect of the shared genes and you've eliminated all, or nearly all, of the similarity.

BROCKMAN: You mean all that matters is having the right genes?

HARRIS: No, it's not just genes. The environment definitely matters too. In fact, for personality (which is what I'm mainly interested in), only about half the variation from one person to another can be attributed to the genes. More precisely, about half the reliable variance in measured personality characteristics—the variance that remains after measurement error is subtracted—can be attributed to differences in genes.

BROCKMAN: What do developmental psychologists have to say about the power of the genes?

HARRIS: That's a curious thing, actually. Nowadays most of them are quite willing to admit that children are born with predispositions to develop in a certain way, and they're even willing to admit that these predispositions have a genetic basis. But it doesn't seem to have dawned on them that children get their genes from their parents. They still haven't acknowledged the fact that whatever genetic predispositions the children have, there's a good chance the parents have them too. A child who was born timid has a better-than-average chance of being reared by a timid parent. A child who was born aggressive has a better-than-average chance of being reared by an aggressive parent. And the parents' genes are going to influence how they rear their kids. Timid parents are likely to be wimpier in their child-rearing methods; aggressive parents will be quicker to punish; affable parents will dole out more affection and praise. So everything's correlated: the parents' characteristics, the children's characteristics, and the parents' style of child-rearing. We haven't a hope of untangling this mess unless we have some way of factoring out genetic effects.

BROCKMAN: How? By studying twins or adopted children?

HARRIS: That's one way—using the methods of behavioral genetics. And when the behavioral geneticists used these methods, they found something very surprising and puzzling, and it didn't have to do with genes, it had to do with the environment. What they found, in study after study, was that the environment shared by two kids reared in the same home could account for no more than 5 percent of the variance in personality characteristics. Heredity accounts for about half, so the other half must be due to the environment. But it isn't the homeenvironment—at least, it isn't the environment shared by siblings who grow up in the same home.

The reason this is surprising is that the environment shared by siblings includes most of the things that are generally thought to have important effects on a child's development. The parents may have a happy or unhappy marriage or no marriage at all; the mother may stay home or go to work; the parents may spend their free time reading books or watching TV or going to a gambling casino. All these things are part of the shared environment: all the children in the family experience them in common, and if they're twins they experience them at the same age. But once we control for heredity by looking at twins or adopted children, we find that the shared environment has little or no effect.

BROCKMAN: But most kids aren't twins and aren't adopted.

HARRIS: The problem is that if you don't use these methods, any environmental factor that you look at is likely to reflect genetic variation too. The parents who spend their time reading books are likely to differ in personality from the ones who opt for the gambling casino, and personality is partly genetic. So if their kids turn out differently, you can't tell if it's because of the environment the parents provided or the genes they provided.

One thing we can do, though, is to look at environmental factors that are less likely to reflect genetic variations in personality. For example, the home environment of the only child is very different from that of the child with siblings. All the affection, all the criticism, all the hopes and dreams that would normally be divided among two or three kids gets piled on this one poor kid. And yet researchers have been unable to find any consistent differences between only children and children with siblings. They've spent a lot of time looking for them, and published studies often do report minor differences—it's hard to get something published if there are no significant effects—but it's a different difference in each study. There's no overall tendency for the only child to be more neurotic or selfish, or less friendly or popular, than the child with siblings.

BROCKMAN: Aren't you giving me proof that parents have zero influence?

HARRIS: I'm giving you proof that, in the ways parents are usually thought to have influence, they have little or no influence on the outcomes that have been measured so far. But I can't prove that they have zero influence.

For one thing, there's that 5 percent I mentioned. A typical behavioral genetic study shows that about 5 percent of the variation in adult personality can be attributed to the environment shared by siblings who grew up in the same home. But one of the weaknesses of the behavioral genetic method is that it can't distinguish between the shared home environment and the environment that siblings share outside the home. Siblings who grow up in the same home also live in the same neighborhood and go to the same schools. If they're twins they probably belong to the same peer group. I attribute the 5 percent to experiences shared by siblings outside the home, and, with the methods currently available, there's no way to prove that I'm wrong. On the other hand, I have no way to rule out the possibility that some or all of that 5 percent is due to shared experiences at home.

Second, researchers haven't looked at all the possible ways that parents could conceivably influence their kids. Perhaps there are subtle effects that their measuring instruments have missed. I must say, though, that they've been looking for them for an awfully long time.

Third, the data we have don't cover the entire range of families. They cover a wide range, but the same kinds of families that slip through the net of the census takers are also likely to missed by researchers. I can't rule out the possibility that a home environment could be bad enough to inflict permanent damage on a child's personality or mental health.

And fourth, it's possible that parents influence their children in ways that are completely unsystematic and unpredictable. What the behavioral genetic results show is that children raised in the same family don't turn out alike, except to the degree that they share genes. But why should they turn out alike when everybody knows that parents don't treat their children alike? Maybe parents treat their children differently in a completely random fashion—eeny, meeny, miney, mo—and maybe these random differences have important effects.

BROCKMAN: Why random?

HARRIS: Random in the sense that the parents aren't just reacting to pre-existing differences in the children themselves—differences the children were born with. We know that parents do react to genetic differences between their children—for example, that a child with a troublesome disposition will be treated more harshly than one who was born agreeable. The problem is that these differences in parental behavior can't explain what we're trying to explain: the differences in personality, not caused by differences in genes, between two people who grew up in the same household. These unexplained differences turn up in adoptive siblings, in ordinary biological siblings, and in identical twins reared together, and we need an explanation that will work for all three kinds of sibling pairs. We need an explanation for the personality differences between identical twins reared in the same household, and we can't blame them on the parents' response to genetic differences between the twins, because there aren't any genetic differences between the twins. The vague but popular idea that it must be an "interaction" between heredity and environment won't work either. If there isn't any genetic difference, an interaction between heredity and environment can't produce a difference. It has to be a difference in environment, which puts us back to where we started.

BROCKMAN: Maybe the parents are reacting to differences between the twins that aren't genetic. Identical twins aren't necessarily exactly alike when they're born. One can be larger or healthier than the other.

HARRIS: Sure. And there's no question that parents act differently toward a healthy child and a sick one, or to a larger child and a smaller one. But if these differences in parental behavior had long-term effects, we would have known about them a long time ago, because they would have turned up in birth order studies. There's no question that parents treat older children differently from younger ones, and firstborns differently from laterborns. These are systematic differences in parental behavior, not random ones, so if they had important effects it would be easy to detect them.

BROCKMAN: You mean, because parents tend to favor firstborns?

HARRIS: No, I mean parents are more demanding with firstborns. Firstborns are given more responsibility; more is expected of them; they tend to be punished more harshly for mistakes. Parents are more tolerant of laterborns.

BROCKMAN: But doesn't the firstborn get more attention?

HARRIS: Only till the second child arrives. Once another baby is born and the parents are taking care of both children at the same time, it's the younger one who gets the lion's share of attention and affection. This is true the world around: parents pay more attention and are more indulgent towards the youngest and smallest of their offspring. The firstborn may end up with the title or the farm, but it's the laterborn who gets the kisses.

Of course, this is going to vary from one family to another—an adorable 3-year -old might get more affection than a whiny or unattractive baby. But the trend is clear. In the studies I cited in my book, at least half of the parents questioned admitted that they gave more affection to one child than the other, and more than 80 percent of these parents favored the younger child.

You'd expect favoritism of this magnitude to lead to sizable birth order effects, if differences in parental treatment had important effects on children's personalities. You'd expect birth order to account for a noticeable amount of the unexplained variation in personality. But it doesn't. If birth order effects on personality exist at all, they must be very small and fragile, because big, well-done studies more often than not fail to find them.

However, there's an interesting exception to that rule. Significant birth order effects usually do turn up when personality is judged in a family context—for example, when parents are asked to judge the personalities of their children, or people are asked to compare themselves to their siblings.

BROCKMAN: What's wrong with that method?

HARRIS: Nothing, if you want to know how people behave in the presence of their parents and their siblings. The trouble is, it doesn't tell you how they function in the world they inhabit as adults, which is what we would like to explain.

BROCKMAN: But isn't there a carryover from one to the other?

HARRIS: That's what most people believe: that what you learn at home in the early years forms a template for your future. That your early relationships set a pattern you are constrained to follow, at least to some extent, for the rest of your life.

BROCKMAN: And you don't think it's true?

HARRIS: No. I believe that children learn separately how to behave in each of their environments and with each of the important people in their lives. The learning device that humans come equipped with doesn't operate on the principle that what worked in one context will work equally well in another. The baby who learns that his mother will pick him up and feed him when he cries can't assume that his cries will have the same effect on his father or his sister or the kids at the day-care center. It would be foolish of him to make that assumption, and he doesn't. The human mind is very good at making fine distinctions and at storing things in separate bins.

BROCKMAN: What kind of evidence do you have for that?

HARRIS: There's quite a lot of evidence. Researchers have looked to see whether children who are dominated by older siblings at home are more likely to be dominated by their peers at school, and the answer is no, they aren't. Similarly, children who fight all the time with their siblings are not more likely to have stormy relationships with their peers. A baby who behaves in a somber, subdued fashion with his depressed mother will behave normally with a caregiver who is not depressed. A baby who has learned to kick her left foot in order to jiggle a mobile hanging over her crib will stare up at the mobile cluelessly if the crib is moved to another room. A child who is a troublemaker at home may be well-behaved in school, or vice versa.

BROCKMAN: On the other hand, there are children who are troublemakers wherever they go.

HARRIS: Yes, that's true. I'm not saying that an individual's behavior in one situation is uncorrelated with that individual's behavior in a different situation: I'm saying that what the individual learned in one situation doesn't carry over to a different situation. Learning isn't the only thing that determines behavior: behavior is influenced by genetic factors as well, and our genome goes with us wherever we go. What we learned at home we can leave at home, but what we were born with we always have with us. The timid child tends to behave in a timid fashion in every environment. It was recently demonstrated that this consistency of behavior is due almost entirely to the genetic component of timidity.

The other reason why there is sometimes a correlation between behavior in different environments is that there is a good deal of similarity in the environments themselves. Many of the behaviors children learn at home—speaking English, saying please and thank you, not taking things that don't belong to them—work equally well outside the home. Most of the attitudes and values that people think they got from their parents—"Be honest," "Trust in God," "Work hard," whatever—are the values of the society as a whole, or of the subculture they grew up in. You might have learned these things at home to begin with, but the reason you took them with you, the reason you kept them, is that they agreed with what you encountered outside the home.

BROCKMAN: Fair enough. But you were telling me what was wrong with some kinds of birth order studies.

HARRIS: Right. We were talking about what happens when you have people make personality judgments of their siblings, or of themselves relative to their siblings. What you get when you use these methods is a picture of how people behave with, or how they feel about, the members of the family they grew up in.

I don't doubt that birth order influences how siblings think and feel about each other and about their parents, and how they behave in the family setting. What I doubt is that people drag these effects along with them wherever they go. The kid who's bossed around by his older sister at home might find that he's the largest and strongest kid in his nursery school classroom. It wouldn't make sense for him to behave the same way with his classmates as he does with his sister, and he doesn't behave the same way. This is true even at nursery-school age.

The idea that learned behavior is specific to the situation in which it is learned may be the most important idea in my book, because it resolves so many discrepancies in the research data, and so many discrepancies between the data and people's everyday observations. It explains why you do find birth order effects if you ask people to compare themselves to their siblings, but you don't find them if you give people a neutral kind of test—a test free of family associations.

It also explains why most people believe in birth order effects. You aren't likely to know someone's birth order unless you've seen them in the context of their family. When people think about birth order, they think about the families they know well: their own brothers and sisters, other relatives, the kids next door. But these are people they've seen mainly in a family context, behaving the way they behave with their siblings and parents. Try guessing the birth order of people you know fairly well but haven't seen in a family setting. I'll bet you do no better than chance!

The idea of context-specific learning can also explain why people believe so strongly in parental influence. After all, when you see a parent and a child together you can see that the parent is influencing the child! You cansee the child responding to the parent's praise or criticism or method of discipline or lack thereof. What you're less likely to see is that this child will behave differently in environments that aren't associated with the parent. Or, if you do notice that the child behaves differently, the nurture assumption causes you to believe that the way the child behaves with the parent must somehow be more important or more lasting.

BROCKMAN: Whereas just the opposite is the case?

HARRIS: Well, the way children behave outside their parents' home is certainly more lasting, because that's where they're going to spend their adult lives. But I'm not saying that the way they behave at home is unimportant. This is one of the ways that parents do have an influence: they can determine, to a large extent, how their children will behave at home. But they can't determine how their children will behave when they're not at home. It maylook as though they can, but I believe the correlations that we notice are due mainly to genetic effects. Children carry their genes along with them wherever they go, and they got their genes from their parents. If an aggressive parent has an aggressive child, you can't conclude that the child learned to be aggressive from the parent until you've eliminated genetic effects.

BROCKMAN: How does this idea resolve discrepancies in the research data?

HARRIS: A couple of years ago, two articles appeared in the same issue of Archives of Pediatrics and Adolescent Medicine. The first got into all the newspapers: the researchers reported that children who were spanked by their parents became more aggressive. The second went unnoticed: the researchers reported that children who were spanked by their parents did not become more aggressive. It turned out that the two groups of researchers were measuring different things: the first group looked at how the children behaved at home, the second at how they behaved at school. Spanking at home apparently makes kids act up more at home (or maybe kids who act up at home get more spankings), but it doesn't make the child more aggressive outside the home. The widely quoted conclusion of the first group of researchers—that if parents stopped hitting their kids it could "reduce the level of violence in American society"—was nothing but hot air.

BROCKMAN: I take it you don't think spanking makes kids more violent?

HARRIS: I used to but I don't anymore. Look, in the early part of this century, American parents routinely spanked their kids. They considered it their duty to spank a kid if the kid did something wrong. That's where we got the expression, "This is going to hurt me more than it's going to hurt you." What the parent meant by this bizarre statement was, "I don't really want to spank you, but the experts tell me I'm supposed to." In those days, the advice-givers didn't warn parents against damaging their child's self-esteem—they warned against "spoiling" the child. Too much attention and affection were thought to be bad for kids. 

The know-it-all tone of voice hasn't changed a bit, but the current crop of advice givers are giving advice that is almost the exact opposite of what parents were being told two or three generations ago. Since a large number of parents actually listen to the advice, kids today are being raised very differently from the way their grandparents were raised. They're getting more praise and kisses, fewer smacks and scoldings. Now ask yourself this: Are children today less aggressive than they were two or three generations ago? Are they nicer? Are they happier? The answer is no. Rates of violence, of depression, and of suicide have gone up, not down.

BROCKMAN: So why haven't the advice-givers noticed that their advice is not having the predicted effects?

HARRIS: Good question. I suppose they'd say, if pressed, either that parents aren't following their recommendations carefully enough, or that changes in the culture as a whole have outweighed the changes in parenting styles. But shouldn't the culture as a whole have become more benevolent if parenting styles have become more benevolent?

Another example of a change that hasn't had the expected effect is the switch to androgynous child-rearing. Middle-class parents are giving their children unisex names and dressing them in unisex clothing. They're giving dolls to their sons and construction sets to their daughters. But the children are as sexist as ever. Grade-school kids still prefer to play with others of their own sex. They still get a kick out of insulting the opposite sex. Boys are still boyish and girls are still girlish, especially in places where there are lots of kids, such as school playgrounds.

BROCKMAN: Do you think these differences are innate?

HARRIS: Only in part. There's undoubtedly an innate component—the same sex differences are found in every culture. But a lot of the behavioral differences between girls and boys are the result of group socialization. Group socialization is my theory of how kids learn how to behave when they're not at home. How they learn how to behave in public.

BROCKMAN: How do they learn how to behave?

HARRIS: It's a very complex task—as complex as learning the language. Here are some of the problems kids have to deal with. First, they find out pretty early that behaviors that were acceptable at home, such as displays of emotion, are not acceptable outside the home. Second, the consequences of behaving correctly or incorrectly are also different inside the home and outside. Children don't get patted on the head when they do the right thing in school or on the playground: the usual result of doing the right thing is that nothing at all happens. On the other hand, if they do the wrong thing, the consequences can be much more serious outside the home. At home, children can cry or wet their pants or say something dumb, and nothing terrible is likely to happen, whereas if they do these things at school they might be laughed at or picked on or given an unflattering label that could stick to them for years.

So children know that they have to learn how to behave in public, and they want to avoid making mistakes. The safest way is to observe how others behave, but now there's another problem: which others do you observe? In every society, proper behavior depends on what sort of person you are—whether you're a kid or a grownup, a male or a female, a landowner or a peasant. These are called "social categories," and before children can figure out how to behave, they have to figure out what social categories are available in their society and which one they belong in.

This turns out to be surprisingly easy for them—as easy as learning the language. The fact that people (like most things in the natural world) come in continua rather than convenient clumps doesn't faze them: they don't hesitate to draw the lines, even though they might have trouble deciding where to put a particular individual. I once saw a 6-year-old go up to a 14-year-old and ask him, "Are you a kid or a grownup?"

It's a kind of concept formation and it starts early. By the time they're 2, children have acquired mental categories for grownups and kids, men and women, girls and boys. They know which ones they belong in, and they're already showing a preference for their own social category. Kids are attracted to other children, even at an age when they're wary of strange adults. When they have a choice, most little girls prefer to play with girls, most little boys prefer boys. (If they don't have a choice, they'll choose a child of the other sex over an adult, because the age category usually takes precedence over the gender category.) By kindergarten age, girls and boys are splitting up into sex-segregated groups whenever they have the chance—whenever there are enough kids to form separate groups and whenever there isn't an adult insisting that they play together.

One of the things that happen when people split up into groups is that the different groups develop contrasting behaviors and attitudes. You can see this happening in the sex-segregated groups of grade-school kids. It's on the playground where boys act most boyish and girls act most girlish. Boys act tough—they hide their weaknesses and vie with each other for dominance. Girls don't have to hide their weaknesses—they use them as tokens of good faith. You show me yours and I'll show you mine and we'll be friends forever . . . or at least until Wednesday.

Timid girls often remain timid, but timid boys tend to become less timid as they get older—a change that is usually attributed to socialization by the parents. Our culture frowns on timid boys, the story goes, so parents teach their sons not to be timid. But the idea that it's the parents is contradicted by the evidence from behavioral genetics. It's not the parents: it's the peer group! A timid boy has a rough time of it in the boys' peer group. He's going to be picked on until he learns to master his timidity.

BROCKMAN: So it's "peer pressure"?

HARRIS: In this case, yes. But I don't like to use that term because in most cases it's misleading. Pressure isn't usually necessary, and the impetus comes from the child doing the conforming, not from the group. Tailoring your behavior to that of the other members of your group is something that people of all ages do automatically, usually without even realizing that they're doing it.

BROCKMAN: One of the criticisms I've heard of your theory is that kids generally associate with other kids who are similar to themselves—for example, good students hang around with other good students. So the kids who belong to the same group were already similar—it's not that they're conforming to the group.

HARRIS: Yes, it's true: kids who belong to the same group were similar to each other to begin with. That's not a valid criticism of my theory—it's one of the premisesof my theory. Children identify with a group because they see that it consists of people like themselves. But once they've identified with it, three things happen. They become even more like their groupmates in some ways, less like them in other ways, and the differences between groups get wider.

The first effect is called assimilation. It's how socialization occurs—how children acquire the behaviors and attitudes of their culture. It's how the children of immigrants end up with the language and accent of their peers, not the language or accent of their parents.

The second is differentiation within the group. I think this is where most of the nongenetic variation in personality comes from. The members of a group don't act as a group all the time—sometimes they act as individuals. They vie with each other for dominance. They choose or are chosen for various roles and niches within the group—"group clown," for instance. These roles can be very stable—the dominant members tend to remain on top and those on the bottom tend to remain at the bottom—and I believe they have permanent effects on the personality.

The third thing that happens is called the group contrast effect. When kids split up into two groups—girls versus boys, jocks versus nerds—the differences between groups become exaggerated. The girls become more girlish. The nerds become nerdier. The kids who pride themselves on being weird or bad (these are often kids who were rejected by other groups) become weirder and badder. There's also likely to be hostility between groups, especially at times when group identification is salient, even though individual members of different groups might be friends with each other at other times.

BROCKMAN: Do you have evidence that these things have an effect on personality?

HARRIS: Not as much as I'd like to have. In fact, my theory of personality development is still largely untested. I said at the beginning of The Nurture Assumption that I had two purposes in writing the book: to dissuade my readers of the notion that a child's personality is shaped or modified by the child's parents, and to present an alternative view of how the child's personality is shaped. But I should have said something about the scientific status of these two purposes. In regard to the first, the evidence is abundant and solid and I'm not saying anything original. I've just put all the evidence together and stated the conclusions more forcefully. The evidence indicates that children are socialized, and their personalities are shaped, by their experiences outside their parents' home. So now the challenge is to specify how this happens, and that's my second purpose. What I've done is to propose a new theory of how children are socialized and how their personalities are shaped. But I don't claim to have proved this theory, because the right kind of research hasn't yet been done. I've had to hunt around for bits and pieces of evidence, some of it anecdotal. I think the theory is promising and I hope it's going to be proven right, but it's early days yet.

BROCKMAN: How does your theory account for the personality differences between identical twins raised together?

HARRIS: Within-group differentiation. Identical twins raised together usually belong to the same peer group, and a group that contains a pair of identical twins is going to find some way of distinguishing between them. They might be typecast in different ways: one might be regarded as the cautious one, the other as the one who'll do anything on a dare. Or they might differ in social status: questions and suggestions from the other members of the group will be addressed to one twin rather than the other.

BROCKMAN: But doesn't the same sort of thing happen at home?

HARRIS: Yes. People find their own niches within their group and also within their family, and in both cases it affects the way they behave in that context. But the behaviors children acquire in the family don't have lasting effects, whereas the behaviors they acquire outside the home do.

BROCKMAN: Why do you think that is?

HARRIS: It seems to be a built-in bias. It starts very early—by nursery-school age. Kids start dropping the accent they acquired at home and picking up the accent of their peers at an age when they're still spending more time with their parents than with their peers. It's not simply that they adapt readily to their two different language environments—it's that they favor one over the other, right from the beginning. They bring the language or accent of the nursery school home with them, they don't bring the language or accent of the home to school (unless, of course, it's being used there, too).

Simon Baron-Cohen made an interesting observation about accents in his review of my book in the journal Nature. He said that my theory had helped make sense of a study he did years ago, involving children with autism and their non-autistic siblings. These were the children of immigrants—one or both of the parents spoke a language other than English. Baron-Cohen found that the non-autistic children rapidly acquired the accent of their peers, but the autistic children generally retained the accent of one of the parents (the mother, in most cases). Children with autism have something wrong with the part of the brain responsible for social development. Studying these children has helped us appreciate aspects of normal development that might otherwise have gone unnoticed.

BROCKMAN: Why do you think normal children are biased toward what they learn outside the home?

HARRIS: I think it's an evolved adaptation. Humans were designed by evolution to become members of a group, and to strive to become valued members of their group, because that's what it took to make a go of it during most of our evolutionary history. As Robert Trivers has pointed out, in the long run it would be counterproductive for children to allow themselves to be molded by their parents, because parents have their own agenda and it doesn't necessarily coincide with the child's. Anyway, if nature wanted to turn children into little replicas of their parents, there's a much easier way to do it. It's called heredity.

BROCKMAN: What does your theory say about the transmission of culture?

HARRIS: That the usual view of cultural transmission—that the culture is passed down from the parents to the child—is inadequate and misleading.

Let me show you how it really works, using language as an example of a social behavior that is part of a culture. I like to use language because it's free of the genetic complications that plague other sorts of social behavior. If a person behaves in a cold or affectionate or aggressive manner, her behavior could be partly genetic, but we know that she didn't inherit her language or accent from her parents.

In the usual situation, the parents speak the same language as their neighbors. Let's say we're talking about an American family and their language is English. The child learns English at home and when she gets to nursery school she finds that everyone there speaks English too. No problem. She may be tentative about using it at first—she has to make sure it's going to work—but there's no need for her to acquire a new language or accent because her peers are using the same language and accent. She simply goes on speaking the way she learned to speak at home.

That's the usual situation, and it's the one that psychologists and anthropologists have in mind when they construct their theories. But if the child's parents are immigrants who speak English poorly or not at all, the child who grows up in a neighborhood where everyone speaks English will nonetheless become an English speaker, even if English was not the first language she learned and even if she goes on speaking her parents' language at home. She'll learn English from her peers, and she'll speak it the same way they do—without the foreign accent of her parents—and quite soon it will begin to supplant her parents' language. It will become her primary language, the language she'll think in as an adult.

BROCKMAN: But sometimes the children of immigrants do end up with an accent.

HARRIS: That happens either because they were too old when their parents made the move—puberty generally puts an end to the ability to learn a new language without an accent—or because they grew up in a neighborhood where there were a lot of immigrants from the same country. A child who grows up in a Mexican-American neighborhood, for instance, will learn to speak English but she may always speak it with a Mexican accent, because that's how everyone in the neighborhood speaks it. That's how her peers speak it.

BROCKMAN: How do you know that it's the way the peers speak it that matters? How do you know it's not the grownups?

HARRIS: There's an interesting story that Derek Bickerton tells, of the children of people who immigrated to Hawaii around the turn of the 19th century. The parents came to work on the sugar plantations and they came from all over the world—the Philippines, Puerto Rico, China, and so on. They had no language in common, so a pidgin language developed among them—a sort of skeletal language that permits people to communicate the bare essentials but that is inadequate for complicated ideas.

The children of these people got together and found that they too had no language in common—nothing but the pidgin, and that wasn't good enough. So they created a language! Out of the mouths of babes came a full-fledged language called a creole! This was a language they couldn't have learned from any of the adults they knew, because none of the adults could speak it. And it became their "native language," the language they brought with them to adulthood. Bickerton studied these people when they were middle-aged or older, and he found that an immigrant's child of a given age used the same version of creole as the others of the same age—it was the language they had used in their childhood peer groups. The language evolved over time, but the people who learned a certain version of it in childhood continued to speak that version all their lives. No trace of the language of their parents was detectable in their speech—the language of their parents was forgotten.

BROCKMAN: So what do your observations of language tell us about the transmission of culture?

HARRIS: I think other aspects of a culture are transmitted the same way as language. In developed societies the parents start the process at home, so the kids come out of the house already knowing something. But whether they keep what they learned at home will depend on what they find when they get outside. And they don't have to learn anything at home, and they'll still be okay. There are many societies where the parents hardly talk to their babies at all, and the babies don't learn the language until they graduate from their mothers' arms into the local play group. They learn the language, and they learn how to behave, from the older children in the play group. 

BROCKMAN: So memes spread from one child to another, rather than from parent to child?

HARRIS: Not entirely, because anything that has an effect on the majority of kids in the peer group can affect the entire group. Even though parents may not have much influence as individuals, they can have a great deal of power if they get together. Hebrew used to be a dead language—a language used only for ceremonial purposes. A bunch of grownups got together and decided to make Hebrew the language of their new country, and they taught their kids to speak Hebrew. The kids found that their peers spoke Hebrew too, and Hebrew became their "native language," even though it wasn't the native language of their parents. It worked because the parents who decided to do it lived in one place and their children played together and went to school together. It wouldn't work if only one family in a neighborhood decided to do it. So parents who want to have an influence on their kids should get together with other like-minded parents and send their kids to the same school. That's the way the Amish do it, and the Hasidic Jews. In fact, it's what middle-class parents do when they move to "nice" neighborhoods so their kids can go to "nice" schools.

BROCKMAN: Does this tell us anything about memes?

HARRIS: The idea of memes is that bits of culture tend to reproduce themselves like genes. Successful bits of culture are passed on, unsuccessful ones die out. The trouble with this theory is that it doesn't take account of the human tendency to split up into separate groups that become culturally distinct. Memes spread freely within a group, but between groups there's a motivation to reject the memes of the other group and do something different. A meme can give rise to a similar meme, but under slightly different circumstances it can engender an anti-meme. I don't think the meme theory can account for that.

BROCKMAN: Give me an example.

HARRIS: They worship many gods, so we will worship only one. They say, an eye for an eye; we say, turn the other cheek. They eat cows, we don't. They hold their forks that way, we hold our forks this way. They say "tomahto," we say "tomato."

When Europeans got to the interior of New Guinea, they found the people split up into groups that each spoke a different language—almost a thousand different languages, most of them mutually unintelligible. That's not just the accumulation of random variations: something was driving these languages apart and keeping them apart. It was the fact that the people didn't want to speak the same language as their enemies! A village would split up into two smaller villages, they would go to war against each other, and then the inhabitants of Village A would find ways of distinguishing themselves from the inhabitants of Village B. Different hairstyles, different designs on the pots, different words.

You can see the same thing happening between contrasting groups within a single society. Developed societies have a special age group for people who are no longer children but are not yet adults, and this group becomes a source of social change. In societies that have only two age groups, children and adults, a culture can go along virtually unchanged for generation after generation, but as soon as there's a special age group for teenagers, things start to happen. The teenagers look for ways of demonstrating their fealty to their own age group—ways of showing that they're different from adults. They use weird forms of adornment that adults find unacceptable, and they invent new words or use old words in new ways. If people didn't keep graduating out of the teenage group and taking their vocabulary with them, eventually they would create a whole new language and the adults wouldn't be able to understand them. Which, of course, is just what they're after!

BROCKMAN: What makes you think that what's true of language is true of culture in general? Doesn't language have its own module in the brain?

HARRIS: Lots of things have their own module. Language is just one of the many things that babies need to learn in order to become acceptable members of their society. It's complicated, yes, but so are the other things they have to learn. I don't see any essential difference between learning a custom that is called "language" and learning the other behaviors and skills of the culture.

Let me end this discussion by coming back to the question you asked me at the beginning: am I an extremist? The children of immigrants who speak English with a heavy accent, if they grow up in a neighborhood of native-born Americans, end up speaking English with no foreign accent at all. They don't end up with something in between what they learned from their parents and what they learned from their peers: they end up, pure and simple, with the language of their peers. That's why I am an extremist: because children don't do things half way. Children don't compromise.

Judith Rich Harris Answers 
the Edge Annual Question

"What questions are you asking yourself?" (1998)


"How can we reconcile our desire for fairness and equity with the brutal fact that people are not all alike?"


"What is today's most important unreported story?" (2000)


What stories are most likely to go unreported? Those that have to do with things that happen so gradually that they aren't noticed, or happen so commonly that they aren't news, and those that have politically incorrect implications.

A story that has gone unreported for all three reasons is the gradual and pervasive change in parenting styles that has occurred in this country since the 1940s, and the consequences (or lack of consequences) of that change.

In the early part of this century, parents didn't worry about shoring up their children's self-esteem or sense of autonomy, and they didn't feel called upon to provide them with "unconditional love." They worried that their children might become spoiled, self-centered, or disobedient. In those days, spankings were administered routinely, often with a weapon such as a belt or a ruler. Kisses were exchanged once a day, at bedtime. Declarations of parental love were made once a lifetime, from the deathbed.

The gradual but dramatic change in parenting styles over the past 50 years occurred mainly because more and more parents were listening to the advice of the "experts," and the experts' advice gradually changed. Nowadays parents are told that spankings will make their children more aggressive, that criticism will destroy their self-esteem, and that children who feel loved will be kinder and more loving to others. As a result of this advice, most parents today are administering far fewer spankings and reprimands, and far more physical affection and praise, than their grandparents did.

But that's only half the story. The other half is the results, or lack of results, of this change in parenting styles. Are today's children less aggressive, kinder, more self-confident, or happier than the children of two generations ago? If anything, the opposite is true. Rates of childhood depression and suicide, for example, have gone up, not down. And certainly there has been no decline in aggressiveness.

The implications, whatever they are, are bound to be politically incorrect. Perhaps the "experts" don't know what they're talking about. Perhaps parenting styles are less important than people have been led to believe. Perhaps human nature is more robust than most people give it credit for—perhaps children are designed to resist whatever their parents do to them. It's possible that being hit by a parent doesn't make children want to go right out and hit their playmates, any more than being kissed by a parent makes them want to go right out and kiss their playmates. It's even possible (dare I suggest it?) that those parents who are still doling out a lot of punishment have aggressive kids because aggressiveness is, in part, passed on genetically.

But now I'm getting into a story that has been reported.


"What Questions Have Disappeared?" (2001)


This question bit the dust after a brief but busy life; it is entirely a second-half-of the-20th-century question. Had it been asked before the 20th century, it would have been phrased differently: "heredity" instead of "genes." But it wasn't asked back then, because the answer was obvious to everyone. Unfortunately, the answer everyone gave—yes!—was based on erroneous reasoning about ambiguous evidence: the difference in behavior between the pauper and the prince was attributed entirely to heredity. The fact that the two had been reared in very different circumstances, and hence had had very different experiences, was overlooked. 

Around the middle of the 20th century, it became politically incorrect and academically unpopular to use the word "heredity"; if the topic came up at all, a euphemism, "nature," was used in its place. The fact that the pauper and the prince had been reared in very different circumstances now came to the fore, and the behavioral differences between them was now attributed entirely to the differences in their experiences. The observation that the prince had many of the same quirks as the king was now blamed entirely on his upbringing. Unfortunately, this answer, too, was based on erroneous reasoning about ambiguous evidence. 

That children tend to resemble their biological parents is ambiguous evidence; the fact that such evidence is plentiful—agreeable parents tend to have agreeable kids, aggressive parents tend to have aggressive kids, and so on—does not make it any less ambiguous. The problem is that most kids are reared by their biological parents. The parents have provided both the genes and the home environment, so the kids' heredity and environment are correlated. The prince has inherited not only his father's genes but also his father's palace, his father's footmen, and his father's Lord High Executioner (no reference to living political figures is intended). 

To disambiguate the evidence, special techniques are required—ways of teasing apart heredity and environment by controlling the one and varying the other. Such techniques didn't begin to be widely used until the 1970s; their results didn't become widely known and widely accepted until the 1990s. By then so much evidence had piled up that the conclusion (which should have been obvious all along) was incontrovertible: yes, genes do influence human behavior, and so do the experiences children have while growing up. 

(I should point out, in response to David Deutsch's contribution to the World Question Center, that no one study, and no one method, can provide an answer to a question of this sort. In the case of genetic influences on behavior, we have converging evidence—studies using a variety of methods all led to the same conclusion and even agreed pretty well on the quantitative details.)

Though the question has been answered, it has left behind a cloud of confusion that might not disappear for some time. The biases of the second half of the 20th century persist: when "dysfunctional" parents are found to have dysfunctional kids, the tendency is still to blame the environment provided by the parents and to overlook the fact that the parents also provided the genes. 

Some would argue that this bias makes sense. After all, they say, we knowhow the environment influences behavior. How the genes influence behavior is still a mystery—a question for the 21st century to solve. But they are wrong. They know much less than they think they know about how the environment influences behavior. 

The 21st century has two important questions to answer. How do genes influence human behavior? How is human behavior influenced by the experiences a child has while growing up?


"What’s Your Question?" (2002)


This question needs to be asked because of the widely held conviction that we already know the answer to it. We don't. Okay, we know half of the answer: one of the reasons why people differ from each other is that they have different genes. That's the easy half.

The hard half is the part that isn't genetic. Even people who have identical genes, like Freeman Dyson's twin grandsons (see his question), differ in personality. I am not asking about the feeling each twin has of being "me": George and Donald could be identical in personality, and yet each could have a sense of me-ness.

But if George and Donald are like most identical twins, they aren't identical in personality. Identical twins are more alike than fraternal twins or ordinary siblings, but less alike than you would expect. One might be more meticulous than the other, or more outgoing, or more emotional. The weird thing is that the degree of similarity is the same, whether twins are reared together or apart. George and Donald, according to their grandfather, "not only have the same genes but also have the same environment and upbringing." And yet they are no more alike in personality than twins reared by two different sets of parents in two different homes.

We know that something other than genes is responsible for some of the variation in human personality, but we are amazingly ignorant about what it is and how it works. Well-designed research has repeatedly failed to confirm commonly held beliefs about which aspects of a child's environment are important. The evidence indicates that neither those aspects of the environment that siblings have in common (such as the presence or absence of a caring father) nor those that supposedly widen the differences between siblings (such as parental favoritism or competition between siblings) can be responsible for the non-genetic variation in personality. Nor can the vague idea of an "interaction" between genes and environment save the day. George and Donald have the same genes, so how can an interaction between genes and environment explain their differences?

Only two hypotheses are compatible with the existing data. One, which I proposed in my book The Nurture Assumption, is that the crucial experiences that shape personality are those that children have outside their home. Unfortunately, there is as yet insufficient evidence to support (or disconfirm) this hypothesis.

The remaining possibility is that the unexplained va riation in personality is random. Even for reared-together twins, there are minor, random differences in their experiences. I find it implausible, however, that minor, random differences in experiences could be so potent, given the ineffectiveness of substantial, systematic differences. If randomness affects personality, the way it probably works is through biological means—not genetic but biological. The human genome is smallish and the human brain is vast; the genome couldn't possibly contain precise specifications for every neuron and synapse. Identical twins don't have identical brains for the same reason that they don't have identical freckles or fingerprints.

If these random physical differences in the brain are responsible for some or all of the personality differences between identical twins, they must also be responsible for some or all of the non-genetic variation in personality among the rest of us. "All" is highly unlikely; "some" is almost certainly true. What remains in doubt is not whether, but how much.

The bottom line is that scientists will probably never be able to predict human behavior with anything close to certainty. Next question: Is this discouraging news or cause for celebration?


"What Are The Pressing Scientific Issues For The
and the World, and What Is Your Advice
On How I Can Begin to Deal with Them?"
A hypothetical question from the President
of the United States of America (2003)


I respectfully decline your invitation to compete for the job of science adviser. I just don't think we could work together successfully. For one thing, you're a morning type and a jogger, and I'm not. For another, I somehow don't think we have compatible views of what science is and how it works.

You're an upbeat sort of guy, and would no doubt expect your science advisor to bring you lots of good news about how science is going to solve all the world's problems. But to tell the truth, I'm a little discouraged right now about science's ability to solve all the world's problems.

You see, in my view the source of the world's problems is people. It's people who make wars, commit crimes, mess up the environment, spend too much, spend too little, whatever. So in order to solve the world's problems, we need to understand people. The science of understanding people is called "psychology." But psychology isn't taken seriously, because most folks think they already understand people—who needs science?

What's worse, this attitude is common not just among non-experts like (begging your pardon) yourself: it's common even among psychologists. They all have their own pet theories of what makes people tick, and if the evidence doesn't happen to agree with their theories—well, to hell with the evidence.

Do you see the dilemma? We need a science of human behavior—a science of the human mind—that would tell us (among other things) why people won't believe the evidence that science produces. But if such a science produced interesting and novel results, nobody would believe them! So what's the point?

Maybe you should look for a science advisor in some other field ... um, botany? No, too controversial. Dermatology?

Thanks anyway, and good luck!

Judith Rich Harris
Author, The Nurture Assumption


"What's Your Law?" (2004)


Good things go together. Miller's Iron Law of Iniquity—" in practice, every good trait correlates positively with every other good trait"—is true, and follows from Harris's First Law.


Bad things go together, too.


People think they know why good things go together, and why bad things go together, but they are wrong.


"What Do You Believe Is True Even Though You Cannot Prove It?" (2005)


I believe, though I cannot prove it, that three—not two—selection processes were involved in human evolution.

The first two are familiar: natural selection, which selects for fitness, and sexual selection, which selects for sexiness.

The third process selects for beauty, but not sexual beauty—not adult beauty. The ones doing the selecting weren't potential mates: they were parents. Parental selection, I call it.

What gave me the idea was a passage from a book titled Nisa: The Life and Words of a !Kung Woman, by the anthropologist Marjorie Shostak. Nisa was about fifty years old when she recounted to Shostak, in remarkable detail, the story of her life as a member of a hunter-gatherer group.

One of the incidents described by Nisa occurred when she was a child. She had a brother named Kumsa, about four years younger than herself. When Kumsa was around three, and still nursing, their mother realized she was pregnant again. She explained to Nisa that she was planning to "kill"—that is, abandon at birth—the new baby, so that Kumsa could continue to nurse. But when the baby was born, Nisa's mother had a change of heart. "I don't want to kill her," she told Nisa. "This little girl is too beautiful. See how lovely and fair her skin is?"

Standards of beauty differ in some respects among human societies; the !Kung are lighter-skinned than most Africans and perhaps they pride themselves on this feature. But Nisa's story provides a insight into two practices that used to be widespread and that I believe played an important role in human evolution: the abandonment of newborns that arrived at inopportune times (this practice has been documented in many human societies by anthropologists), and the use of aesthetic criteria to tip the scales in doubtful cases.

Coupled with sexual selection, parental selection could have produced certain kinds of evolutionary changes very quickly, even if the heartbreaking decision of whether to rear or abandon a newborn was made in only a small percentage of births. The characteristics that could be affected by parental selection would have to be apparent even in a newborn baby. Two such characteristics are skin color and hairiness.

Parental selection can help to explain how the Europeans, who are descended from Africans, developed white skin over such a short period of time. In Africa, a cultural preference for light skin (such as Nisa's mother expressed) would have been counteracted by other factors that made light skin impractical. But in less sunny Europe, light skin may actually have increased fitness, which means that all three selection processes might have worked together to produce the rapid change in skin color.

Parental selection coupled with sexual selection can also account for our hairlessness. In this case, I very much doubt that fitness played a role; other mammals of similar size—leopards, lions, zebras, gazelle, baboons, chimpanzees, and gorillas—get along fine with fur in Africa, where the change to hairlessness presumably took place. I believe (though I cannot prove it) that the transition to hairlessness took place quickly, over a short evolutionary time period, and involved only Homo sapiens or its immediate precursor.

It was a cultural thing. Our ancestors thought of themselves as "people" and thought of fur-bearing creatures as "animals," just as we do. A baby born too hairy would have been distinctly less appealing to its parents.

If I am right that the transition to hairlessness occurred very late in the sequence of evolutionary changes that led to us, then this can explain two of the mysteries of paleoanthropology: the survival of the Neanderthals in Ice Age Europe, and their disappearance about 30,000 years ago.

I believe, though I cannot prove it, that Neanderthals were covered with a heavy coat of fur, and that Homo erectus, their ancestor, was as hairy as the modern chimpanzee. A naked Neanderthal could never have made it through the Ice Age. Sure, he had fire, but a blazing hearth couldn't keep him from freezing when he was out on a hunt. Nor could a deerskin slung over his shoulders, and there is no evidence that Neanderthals could sew. They lived mostly on game, so they had to go out to hunt often, no matter how rotten the weather. And the game didn't hang around conveniently close to the entrance to their cozy cave.

The Neanderthals disappeared when Homo sapiens, who by then had learned the art of sewing, took over Europe and Asia. This new species, descended from a southern branch of Homo erectus, was unique among primates in being hairless. In their view, anything with fur on it could be classified as "animal"—or, to put it more bluntly, game. Neanderthal disappeared in Europe for the same reason the woolly mammoth disappeared there: the ancestors of the modern Europeans ate them. In Africa today, hungry humans eat the meat of chimpanzees and gorillas.

At present, I admit, there is insufficient evidence either to confirm or disconfirm these suppositions. However, evidence to support my belief in the furriness of Neanderthals may someday be found. Everything we currently know about this species comes from hard stuff like rocks and bones. But softer things, such as fur, can be preserved in glaciers, and the glaciers are melting. Someday a hiker may come across the well-preserved corpse of a furry Neanderthal.

People think they know why good things go together, and why bad things go together, but they are wrong.


"What Is Your Dangerous Idea?" (2006)


Is it dangerous to claim that parents have no power at all (other than genetic) to shape their child's personality, intelligence, or the way he or she behaves outside the family home? More to the point, is this claim false? Was I wrong when I proposed that parents' power to do these things by environmental means is zero, nada, zilch?

A confession: When I first made this proposal ten years ago, I didn't fully believe it myself. I took an extreme position, the null hypothesis of zero parental influence, for the sake of scientific clarity. Making myself an easy target, I invited the establishment—research psychologists in the academic world—to shoot me down. I didn't think it would be all that difficult for them to do so. It was clear by then that there weren't any big effects of parenting, but I thought there must be modest effects that I would ultimately have to acknowledge.

The establishment's failure to shoot me down has been nothing short of astonishing. One developmental psychologist even admitted, one year ago on this very website, that researchers hadn't yet found proof that "parents do shape their children," but she was still convinced that they will eventually find it, if they just keep searching long enough.

Her comrades in arms have been less forthright. "There are dozens of studies that show the influence of parents on children!" they kept saying, but then they'd somehow forget to name them—perhaps because these studies were among the ones I had already demolished (by showing that they lacked the necessary controls or the proper statistical analyses). Or they'd claim to have newer research that provided an airtight case for parental influence, but again there was a catch: the work had never been published in a peer-reviewed journal. When I investigated, I could find no evidence that the research in question had actually been done or, if done, that it had produced the results that were claimed for it. At most, it appeared to consist of preliminary work, with too little data to be meaningful (or publishable).

Vaporware, I call it. Some of the vaporware has achieved mythic status. You may have heard of Stephen Suomi's experiment with nervous baby monkeys, supposedly showing that those reared by "nurturant" adoptive monkey mothers turn into calm, socially confident adults. Or of Jerome Kagan's research with nervous baby humans, supposedly showing that those reared by "overprotective" (that is, nurturant) human mothers are more likely to remain fearful.

Researchers like these might well see my ideas as dangerous. But is the notion of zero parental influence dangerous in any other sense? So it is alleged. Here's what Frank Farley, former president of the American Psychological Association, told a journalist in 1998:

[Harris's] thesis is absurd on its face, but consider what might happen if parents believe this stuff! Will it free some to mistreat their kids, since "it doesn't matter"? Will it tell parents who are tired after a long day that they needn't bother even paying any attention to their kid since "it doesn't matter"?

Farley seems to be saying that the only reason parents are nice to their children is because they think it will make the children turn out better! And that if parents believed that they had no influence at all on how their kids turn out, they are likely to abuse or neglect them.

Which, it seems to me, is absurd on its face. Most chimpanzee mothers are nice to their babies and take good care of them. Do chimpanzees think they're going to influence how their offspring turn out? Doesn't Frank Farley know anything at all about evolutionary biology and evolutionary psychology?

My idea is viewed as dangerous by the powers that be, but I don't think it's dangerous at all. On the contrary: if people accepted it, it would be a breath of fresh air. Family life, for parents and children alike, would improve. Look what's happening now as a result of the faith, obligatory in our culture, in the power of parents to mold their children's fragile psyches. Parents are exhausting themselves in their efforts to meet their children's every demand, not realizing that evolution designed offspring—nonhuman animals as well as humans—to demand more than they really need. Family life has become phony, because parents are convinced that children need constant reassurances of their love, so if they don't happen to feel very loving at a particular time or towards a particular child, they fake it. Praise is delivered by the bushel, which devalues its worth. Children have become the masters of the home.

And what has all this sacrifice and effort on the part of parents bought them? Zilch. There are no indications that children today are happier, more self-confident, less aggressive, or in better mental health than they were sixty years ago, when I was a child—when homes were run by and for adults, when physical punishment was used routinely, when fathers were generally unavailable, when praise was a rare and precious commodity, and when explicit expressions of parental love were reserved for the deathbed.

Is my idea dangerous? I've never condoned child abuse or neglect; I've never believed that parents don't matter. The relationship between a parent and a child is an important one, but it's important in the same way as the relationship between married partners. A good relationship is one in which each party cares about the other and derives happiness from making the other happy. A good relationship is not one in which one party's central goal is to modify the other's personality.

I think what's really dangerous—perhaps a better word is tragic—is the establishment's idea of the all-powerful, and hence all-blamable, parent.


"What Are You Optimistic About?" (2007)


I am optimistic about human relationships—in particular, about friendship. Perhaps you have heard gloomy predictions about friendship: it's dying out, people no longer have friends they can confide in, loneliness is on the rise.

But friendship isn't dying out: it's just changing, adapting to the changes in the world. People are discovering different ways of getting together. It may be harder to find a bowling partner, but it's easier to find someone to chat with because there are many more ways to chat.

When I was a child, people with chronic illnesses were described as "shut-ins." Now a person can be shut in without being shut out. I have friends whom I know only through e-mail conversations but who are as dear to me as my college roommate and dearer by far than my next-door neighbor.

The desire to form and maintain relationships is one of the built-ins of human nature. Primates are social animals, and humans are the most social of all. An extravagant amount of mental capacity is devoted to relationships. We can recognize at a glance the faces of thousands of different people and, with equal ease, remember whether or not we like them. With a bit more effort, we can dredge up other useful information about most of them: their names or professions or where we met them. Throughout our lives we collect and store information about specific individuals, so that—just in case we ever run into them again—we will know how to act. We even store information about people we have never met and whose faces we have never seen.

Collecting people information is something we do without training and with no reward other than the enjoyment we get from doing it. We don't need a nudge from the conscious mind, telling us that the information may come in handy someday. But in fact it may come in handy. People we have never met before may be important to us in the future. They may become our trading partners or employers. They may become our lovers or our rivals.

Or they may simply become our friends. Wednesday


"What Have You Changed Your Mind About?" (2008)


Anyone who has taken a course in introductory psychology has heard the story of how the behaviorist John B. Watson produced "conditioned fear" of a white rat—or was it a white rabbit?—in an unfortunate infant called Little Albert, and how Albert "generalized" that fear to other white, furry things (including, in some accounts, his mother's coat). It was a vividly convincing story and, like my fellow students, I saw no reason to doubt it. Nor did I see any reason, until many years later, to read Watson's original account of the experiment, published in 1920. What a mess! You could find better methodology at a high school science fair. Not surprisingly—at least it doesn't surprise me now—Watson's experiment has not stood up well to attempts to replicate it. But the failures to replicate are seldom mentioned in the introductory textbooks.

The idea of generalization is a very basic one in psychology. Psychologists of every stripe take it for granted that learned responses—behaviors, emotions, expectations, and so on—generalize readily and automatically to other stimuli of the same general type. It is assumed, for example, that once the baby has learned that his mother is dependable and his brother is aggressive, he will expect other adults to be dependable and other children to be aggressive.

I now believe that generalization is the exception, not the rule. Careful research has shown that babies arrive in the world with a bias against generalizing. This is true for learned motor skills and it is also true for expectations about people. Babies are born with the desire to learn about the beings who populate their world and the ability to store information about each individual separately. They do not expect all adults to behave like their mother or all children to behave like their siblings. Children who quarrel incessantly with their brothers and sisters generally get along much better with their peers. A firstborn who is accustomed to dominating his younger siblings at home is no more likely than a laterborn to try to dominate his schoolmates on the playground. A boy's relationship with his father does not form the template for his later relationship with his boss.

I am not, of course, the only one in the world who has given up the belief in ubiquitous generalization, but if we formed a club, we could probably hold meetings in my kitchen. Confirmation bias—the tendency to notice things that support one's assumptions and to ignore or explain away anything that doesn't fit—keeps most people faithful to what they learned in intro psych. They observe that the child who is agreeable or timid or conscientious at home tends, to a certain extent, to behave in a similar manner outside the home, and they interpret this correlation as evidence that the child learns patterns of behavior at home which she then carries along with her to other situations.

The mistake they are making is to ignore the effects of genes. Studies using advanced methods of data analysis have shown that the similarities in behavior from one context to another are due chiefly to genetic influences. Our inborn predispositions to behave in certain ways go with us wherever we go, but learned behaviors are tailored to the situation. The fact that genetic predispositions tend to show up early is the reason why some psychologists also make the mistake of attributing too much importance to early experiences.

What changed my mind about these things was the realization that if I tossed out the assumption about generalization, some hitherto puzzling findings about human behavior suddenly made more sense. I was 56 years old at the time but fairly new to the field of child development, and I had no stake in maintaining the status quo. It is a luxury to have the freedom to change one's mind.


"How Is The Internet Changing The Way You Think? " (2010)


The Internet dispenses information the way a ketchup bottle dispenses ketchup. At first there was too little; now there is too much.

In between, there was a halcyon interval of just-enoughness. For me, it lasted about ten years.

They were the best years of my life.


"What Is Your Favorite Deep, Elegant, Or Beautiful Explanation?" (2012)


"Beauty is truth, truth beauty," said John Keats. But what did he know? Keats was a poet, not a scientist.

In the world that scientists inhabit, truth is not always beautiful or elegant, though it may be deep. In fact, it's my impression that the deeper an explanation goes, the less likely it is to be beautiful or elegant.

Some years ago, the psychologist B. F. Skinner proposed an elegant explanation of "the behavior of organisms," based on the idea that rewarding a response—he called it reinforcement—increases the probability that the same response will occur again in the future. The theory failed, not because it was false (reinforcement generally does increase the probability of a response) but because it was too simple. It ignored innate components of behavior. It couldn't even handle all learned behavior. Much behavior is acquired or shaped through experience, but not necessarily by means of reinforcement. Organisms learn different things in different ways.

The theory of the modular mind is another way of explaining behavior—in particular, human behavior. The idea is that the human mind is made up of a number of specialized components, often called modules, working more or less independently. These modules collect different kinds of information from the environment and process it in different ways. They issue different commands—occasionally, conflicting commands. It's not an elegant theory; on the contrary, it's the sort of thing that would make Occam whip out his razor. But we shouldn’t judge theories by asking them to compete in a beauty pageant. We should ask whether they can explain more, or explain better, than previous theories were able to do.

The modular theory can explain, for example, the curious effects of brain injuries. Some abilities may be lost while others are spared, with the pattern differing from one patient to another.

More to the point, the modular theory can explain some of the puzzles of everyday life. Consider intergroup conflict. The Montagues and the Capulets hated each other; yet Romeo (a Montague) fell in love with Juliet (a Capulet). How can you love a member of a group, yet go on hating that group? The answer is that two separate mental modules are involved. One deals with groupness (identification with one's group and hostility toward other groups), the other specializes in personal relationships. Both modules collect information about people, but they do different things with the data. The groupness module draws category lines and computes averages within categories; the result is called a stereotype. The relationship module collects and stores detailed information about specific individuals. It takes pleasure in collecting this information, which is why we love to gossip, read novels and biographies, and watch political candidates unravel on our TV screens. No one has to give us food or money to get us to do these things, or even administer a pat on the back, because collecting the data is its own reward.

The theory of the modular mind is not beautiful or elegant. But not being a poet, I prize truth above beauty.


"What Do You Consider The Most Interesting Recent [Scientific] News?" (2016)


The topic itself is not new. For decades, there have been rumors about famous historical scientists like Newton, Kepler, and Mendel. The charge was that their research results were too good to be true. They must have faked the data, or at least prettied it up a bit. But Newton, Kepler, and Mendel nonetheless retained their seats in the Science Hall of Fame. The usual reaction of those who heard the rumors was a shrug. So what? They were right, weren't they?

What's new is that nowadays everyone seems to be doing it, and they're not always right. In fact, according to John Ioannidis, they're not even right most of the time. 

John Ioannidis is the author of a paper titled "Why Most Published Research Findings Are False," which appeared in a medical journal in 2005. Nowadays this paper is described as "seminal" and "famous," but at first it received little attention outside the field of medicine, and even medical researchers didn't seem to be losing any sleep over it. 

Then people in my own field, psychology, began to voice similar doubts. In 2011, the journal Psychological Science published a paper titled "False-positive psychology: Undisclosed flexibility in data collection and analysis allows presenting anything as significant." In 2012, the same journal published a paper on "the prevalence of questionable research practices." In an anonymous survey of more than 2000 psychologists, 53 percent admitted that they had failed to report all of a study's dependent measures, 38 percent had decided to exclude data after calculating the effect it would have on the outcome, and 16 percent had stopped collecting data earlier than planned because they had gotten the results they were looking for.                                    

The final punch landed in August, 2015. The news was published first in the journal Science and quickly announced to the world by the New York Times, under a title that was surely facetious: "Psychologists welcome analysis casting doubt on their work." The article itself painted a more realistic picture. "The field of psychology sustained a damaging blow," it began. "A new analysis found that only 36 percent of findings from almost 100 studies in the top three psychology journals held up when the original experiments were rigorously redone." On average, effects found in the replications were only half the magnitude of those reported in the original publications.

Why have things gone so badly awry in psychological and medical research? And what can be done to put them right again?

I think there are two reasons for the decline of truth and the rise of truthiness in scientific research. First, research is no longer something people do for fun, because they're curious. It has become something that people are required to do, if they want a career in the academic world. Whether they enjoy it or not, whether they are good at it or not, they've got to turn out papers every few months or their career is down the tubes. The rewards for publishing have become too great, relative to the rewards for doing other things, such as teaching. People are doing research for the wrong reasons: not to satisfy their curiosity but to satisfy their ambitions. 

There are too many journals publishing too many papers. Most of what's in them is useless, boring, or wrong. 

The solution is to stop rewarding people on the basis of how much they publish. Surely the tenure committees at great universities could come up with other criteria on which to base their decisions!

The second thing that has gone awry is the vetting of research papers. Most journals send out submitted manuscripts for review. The reviewers are unpaid experts in the same field, who are expected to read the manuscript carefully, make judgments about the importance of the results and the validity of the procedures, and put aside any thoughts of how the publication of this paper might affect their own prospects. It's a hard job that has gotten harder over the years, as research has become more specialized and data analysis more complex. I propose that this job should be performed by paid experts—accredited specialists in the analysis of research. Perhaps this could provide an alternative path into academia for people who don't particularly enjoy the nitty-gritty of doing research but who love ferreting out the flaws and virtues in the research of others.        

In Woody Allen's movie "Sleeper," set 200 years in the future, a scientist explains that people used to think that wheat germ was healthy and that steak, cream pie, and hot fudge were unhealthy—"precisely the opposite of what we now know to be true." It's a joke that hits too close to home. Bad science gives science a bad name. 

Whether wheat germ is or isn't good for people is a minor matter. But whether people believe in scientific research or scoff at it is of crucial importance to the future of our planet and its inhabitants.


"What Is The Last Question" (2018)


How could one last question possibly be enough?