The Nurture Assumption: Why Children Turn Out the Way They Do by Judith Rich Harris

Here are some highlights:

* Generalization 1: Parents who do a good job of managing their lives, and who get along well with others, tend to have children who are also good at managing their lives and getting along with others. Parents who have problems managing their lives, their homes, or their personal relationships tend to have children who also have problems.

Generalization 2: Children who are treated with affection and respect tend to do better at managing their lives and their personal relationships than children who are treated harshly.

* A foxhound does not behave like a poodle; the two breeds have different personalities. Someone who believed in nurture might point out that the foxhound was reared in a kennel with dozens of other dogs, whereas the poodle was reared in a city apartment and sleeps in its owner’s bed. Someone who believed in nature would scoff and say, “You can’t make a foxhound into a poodle by rearing it in an apartment and spoiling it rotten.”

This experiment could be done: you could rear a pack of poodles in a kennel, give each foxhound a doting owner and a lease on an apartment, and observe the results. What you’d find is that the nature and nurture advocates were both right: you can’t make a foxhound into a poodle, but a foxhound reared in an apartment will behave differently from one reared in a kennel.6 That experiment involves separating the effects of heredity (the genes that determine whether a puppy is born a foxhound or a poodle) from the effects of environment.

The problem with socialization socialization studies of the type I’ve described is that the effects of heredity and environment are not separated; nor are they separable. Every (or nearly every) parent-and-child pair who participate in a socialization study are biological relatives; they are as much alike in terms of their DNA as two poodles from the same litter. Not only do the parents provide the child’s genes; they also provide the child’s environment. The kind of environment they provide—the kind of parents they are—is, in part, a function of their genes.7 There is no way to distinguish the effects of the genes they provide from the effects of the environment…

* Although we can’t switch human babies around for the sake of science, sometimes they are switched around for other reasons. An adopted child has two sets of parents: one provides the child’s genes, the other provides the environment. Studying adopted children is one of the methods used by researchers in the field of behavioral genetics. The stated purpose of their research is to separate the effects of heredity from those of the environment.

* A large number of human characteristics have now been studied with behavioral genetic methods. The results are clear and consistent: overall, heredity accounts for roughly 50 percent of the variation in the samples of people who have been tested, environmental influences for the other 50 percent.

* Child-rearing is not something a parent does to a child: it is something the parent and the child do together.

* A while ago I was in my front yard with my dog. A mother and her two children—a girl of about five and a boy of about seven—walked by in the street. My dog, who was trained not to go into the street, ran to the curb and started barking at them. The two children reacted in very different ways. The girl veered straight toward the dog, asking, “Can I pet him?” despite the fact that the dog was behaving in an unfriendly manner. Her mother said quickly, “No, Audrey, I don’t think the dog wants you to pet him.” Meanwhile, the boy had retreated to the other side of the street and was standing there looking scared, unwilling to walk past the barking dog even though the entire width of the street was between them. “Come on, Mark,” his mother said, “the dog won’t hurt you.” (I was holding the dog’s collar by then.) It took a minute before Mark got up the courage to rejoin his mother, who was waiting for him with her impatience carefully concealed under a good deal of genuine sympathy. As the three went down the street I could hear Audrey making fun of Mark. I didn’t catch her words but the tune (it’s called the “nyah-nyah song”) was unmistakable.

I was sorry for Mark but I identified more strongly with his mother: I, too, reared a pair of very different children. My older daughter hardly ever wanted to do anything that her father and I didn’t want her to do. My younger daughter often did. Raising the first was easy; raising the second was, um, interesting. My Uncle Ben, who had no children of his own, was fond of his grandnieces and often gave me advice on how to rear them. I remember a conversation I had with him when my daughters were about eight and twelve. I was complaining to him about the behavior of my younger child and Uncle Ben (who knew I hadn’t had these problems with my older one) asked, “Well, do you treat them both the same?”

Do I treat them both the same? I didn’t know what to say. How can you treat two children both the same when they aren’t the same—when they do different things and say different things, have different personalities and different abilities? Could the mother of Mark and Audrey treat them both the same?

* Babies with autism don’t look their parents in the eye, don’t smile at them, don’t seem glad to see them. It is difficult to feel enthusiastic about a baby who isn’t enthusiastic about you. It is difficult to interact with a child who won’t look at you.

Autism is caused by an abnormality in brain development, due primarily to genetic factors. The mothers’ apparent coldness was not the cause of their children’s atypical behavior—it was a reaction to it.

* Generalization 2 said that children who are hugged are more likely to be nice, children who are spanked are more likely to be unpleasant. Turn that statement around and you get one that is equally plausible: nice children are more likely to be hugged, unpleasant children are more likely to be spanked.

* Tales of the eerie resemblances between identical twins separated early in life and reared in different homes have made their way into the popular press and the popular imagination. There was the story of the two Jims—both bit their nails, enjoyed woodworking, drove the same model Chevrolet, smoked Salems, and drank Miller Lite; they named their sons James Alan and James Allan. There was the story in my local newspaper, accompanied by a photo of two men with the same face, both wearing fire helmets—reunited because both had become volunteer firefighters. There was the story of Jack Yufe and Oskar Stöhr, one reared in Trinidad by his Jewish father, the other in Germany by his Catholic grandmother. When reunited, they were both wearing rectangular wire-frame glasses, short mustaches, and blue two-pocket shirts with epaulets; both were in the habit of reading magazines back to front and flushing toilets before using them; both liked to startle people by sneezing in elevators. And there was the story of Amy and Beth, adopted into different homes—Amy a rejected child, Beth doted upon—both girls suffering from the same unusual combination of cognitive and personality deficits.1

These true stories of reared-apart identical twins are a testimony to the power of the genes. They suggest that genes can cause striking similarities in personality characteristics, even in the face of substantial differences in rearing environments.

* Among the twins who came to Minneapolis to be tested were a pair known as the Giggle Twins. Although these women had been reared in separate homes, and both twins described their adoptive parents as dour and undemonstrative, both were inordinately prone to laughter. In fact, neither had ever met anyone who laughed as much as she did until the day she was reunited with her identical twin.

* The data showed that growing up in the same home, being reared by the same parents, had little or no effect on the adult personalities of siblings. Reared-together siblings are alike in personality only to the degree that they are alike genetically. The genes they share can entirely account account for any resemblances between them; there are no leftover similarities for the shared environment to explain.8 For some psychological characteristics, notably intelligence, there is evidence of a transient effect of the home environment during childhood—the IQ scores of preadolescent adoptive siblings show a modest correlation. But by late adolescence all nongenetic resemblances have faded away. For IQ as for personality, the correlation between adult adoptees reared in the same home hovers around zero.

* Study after study shows the same thing: almost all the similarities between adult siblings can be attributed to their shared genes. There are very few similarities that can be attributed to the environment they shared in childhood.

* When differences in parents’ behavior to their different children are discussed, often the first issue that comes to mind is the birth order of the children. It is frequently assumed that parents systematically treat their firstborn child differently from laterborn children…. In an important sense such differences are not relevant. This is because individual differences in personality and psychopathology in the general population—the differences in outcome that we are trying to explain—are not clearly linked to the birth order of the individuals. Although this evidence goes against many widely held and cherished beliefs, the judgment of those who have looked carefully at a large number of studies is that birth order plays only a bit-part in the drama of sibling differences…. If there are no systematic differences in personality according to birth order, then any differences in parental behavior that are associated with birth order cannot be very significant for later developmental outcome.

* It’s not that good parenting produces good children, it’s that good children produce good parenting.

* Chinese Americans, for example, tend to use the Too Hard parenting style—the style Baumrind called Authoritarian—not because their kids are difficult, but because that’s the style favored by their culture. Among Asian and African Americans, therefore, parents who use a Too Hard child-rearing style should not be more likely to have problem kids. Again, this is exactly what the researchers find.27 What they find, in fact, is that Asian-American parents are the most likely of all American parents to use the Too Hard style and the least likely to use the Just Right style, and yet in many ways Asian-American children are the most competent and successful of all American children.

* The patterns of behavior that are acquired in sibling relationships neither help us nor hinder us in our dealings with other people. They leave no permanent marks on our character.

* At home there are birth order effects, no question about it, and I believe that is why it’s so hard to shake people’s faith in them. If you see people with their parents or their siblings, you do see the differences you expect to see. The oldest does seem more serious, responsible, and bossy. The youngest does behave in a more carefree fashion. But that’s how they act when they’re together. These patterns of behavior are not like albatrosses that we have to drag along with us wherever we go, all through our lives. We don’t even drag them to nursery school.

* In a 1997 review, a developmentalist asked the question, “Do infants suffer long-term detriments from early nonmaternal care?” The studies she reviewed, she concluded, “have demonstrated that the answer is ‘no.’” Even the variation in quality among day-care centers makes less difference than you might think: “The surprising conclusion from the research literature is that variation in quality of care, measured by experts, proves to have little or no impact on most children’s development.”

* Researchers in California studied a sample of unconventional families over a period of many years. Some of the parents were hippies and lived on communes; others had “open marriages”; still others were unmarried women with good jobs who made the decision to become single parents. The children of these parents were as bright, as healthy, and as well adjusted as children who lived in more conventional families.

* Research done in the past quarter century has turned up no consistent differences between only children and children with one or two siblings.

* William James: “Properly speaking, a man has as many social selves as there are individuals who recognize him and carry an image of him in
their mind…. But as the individuals who carry the images fall naturally into classes, we may practically say that he has as many different social selves as there are distinct groups of persons about whose opinion he cares. He generally shows a different side of himself to each of these different groups. Many a youth who is demure enough before his parents and teachers, swears and swaggers like a pirate among his “tough” young friends. We do not show ourselves to our children as to our club-companions, to our customers as to the laborers we employ, employ, to our own masters and employers as to our intimate friends. From this there results what practically is a division of the man into several selves; and this may be a discordant splitting, as where one is afraid to let one set of his acquaintances know him as he is elsewhere; or it may be a perfectly harmonious division of labor, as where one tender to his children is stern to the soldiers or prisoners under his command.”

* Code-switching is sort of like having two separate storage tanks in the mind, each containing what was learned in a particular social context. According to Paul Kolers, a psycholinguist who studied bilingual adults, access to a given tank may require switching to the language used in that context. As an example, he mentioned a colleague of his who had moved from France to the United States at the age of twelve. This man does his arithmetic in French, his calculus in English.

* “Many bilingual people,” reported Kolers, “say that they think differently and respond with different emotions to the same experience in their two languages.”

* Parents belong in the home; when they come out of the home it makes their children nervous. Aside from the embarrassment, it makes it harder for children to know which context they’re in, which rules they’re supposed to follow.

* If you never go home again, the personality you acquired there may be lost forever.

* Most people do go home again. And the moment they walk in the door and hear their mother’s voice from the kitchen—“Is that you, dear?”—the old personality they thought they had outgrown comes back to haunt them.

* Socialization research has demonstrated one thing clearly and irrefutably: a parent’s behavior toward a child affects how the child behaves in the presence of the parent or in contexts that are associated with the parent.

* Socially, chimpanzees are a lot like us: they have our faults as well as our virtues. Like humans, they divide the world into “us” and “them.”16 Even a familiar animal may be attacked if it is no longer one of “us” and has become one of “them.”

* In the absence of a common enemy, or of a common goal that can be achieved only if everyone pulls together, groups tend to fall apart into a collection of individuals or smaller groups.

* Children are born with certain characteristics. Their genes predispose them to develop a certain kind of personality. But the environment can change them. Not “nurture”—not the environment their parents provide—but the outside-the-home environment, the environment they share with their peers.

* Despite repeated assertions that the quality of social competence with peers is determined by the prior quality of infant–mother attachment relationships, there is actually little empirical support for this hypothesis.

* friendship (or lack thereof) leaves no permanent marks on the personality, whereas identification with a group, and acceptance or rejection by the group, do have lasting effects. Researchers have studied the long-term effects of grade-school friendships (or lack thereof), and the long-term effects of peer acceptance or rejection. They found that peer acceptance or rejection was associated with “overall life status adjustment” in adulthood; having or not having a friend in grade school was not.

* I believe high or low status in the peer group has permanent effects on the personality. Children who are unpopular with their peers tend to have low self-esteem,88 and I think the feelings of insecurity never go away entirely—they last a lifetime. You have been tried by a jury of your peers and you have been found wanting.

* If he discovers he is not the toughest boy in the room, there are plenty of other niches in the fourth-grade classroom he can try out for. Class clown, for example. Middle childhood is when children get typecast into roles that might last them the rest of their lives. They choose these roles themselves or get nominated for them—or forced into them—by others. When it happens, the characteristics a child starts out with tend to become exaggerated. The funny child gets funnier, the brainy child gets brainier. Humor and intellect have become their specialties.

* The world that children share with their peers is what shapes their behavior and modifies the characteristics they were born with, and hence determines the sort of people they will be when they grow up.

* Kids are often forced into social categories they would rather not belong to. No one chooses to be a nerd. In fact, in the typical American high school, no one chooses to be a brain. The kids pinned with that label are those who are not athletic or popular enough to get into one of the groups that have higher status. Among most European-American and African-American adolescents, braininess is not considered an asset.20 You might be able to get away with it, but only if you have other assets that are valued by your peers.

* The personality shaped and polished in our childhood and adolescent peer groups is the one we take with us to the grave.

* Moving is rough on kids. Kids who have been moved around a lot—whether or not they have a father—are more likely to be rejected by their peers; they have more behavioral problems and more academic problems than those who have stayed put.28 McLanahan and Sandefur found that changes of residence could account for more than half of the increased risk of high school dropout, teen births, and idleness among adolescents being reared without their fathers.

Changes of residence jeopardize a kid’s standing in the peer group and interfere with socialization because it’s difficult to adapt to group norms when the norms keep changing.

* Heredity, not their experiences in their childhood home, is what makes the children of divorce more likely to fail in their own marriages.

* Don’t look for a divorce gene. Look instead for traits that increase the risk of almost any kind of unfavorable outcome in life. Traits that make people harder to get along with—aggressiveness, insensitivity to the feelings of others. Traits that increase the chances they will make unwise choices—impulsiveness, a tendency to be easily bored. Does this list sound familiar? Yes, it is similar to the list of characteristics that are often
found in criminals. The same traits that make some kids good candidates for Fagin’s school also lower their chances of a happy marriage. In childhood, individuals with these traits may be diagnosed with what psychiatrists call “conduct disorder.” The adult form is called “antisocial personality disorder” and research has shown that it can be inherited.

* A group of researchers at the University of Georgia discovered that what predicted conduct disorder in children was not parental divorce but parental personality: parents with antisocial personality disorder were more likely to have children with conduct disorder.

* Divorce is bad for children in several ways. First, it comes with a heavy financial penalty: the children of divorced parents usually experience a severe decline in standard of living. Their financial status will determine where they live, and where they live will make a difference. Second, it’s bad for the children because they often have to move to a new residence. Sometimes they have to move several times. Third, it increases the risk that they will suffer physical abuse. Children living in homes with stepparents are far more likely to be abused than those living with two biological parents.40 Fourth, it’s bad for them because it disrupts their personal relationships.

* With little children, parents have almost complete control over who their friends are, at least when they are not in school. But once they turn ten, all bets are off.

* Self-esteem in general—the kind that travels well—is a function of one’s status in one’s group. School-age children are aware of how they compare with their classmates and how they are regarded by them. Low status in the peer group, if it continues for long, leaves permanent marks on the personality. And it can sure wreck a kid’s childhood.

About Luke Ford

I've written five books (see My work has been followed by the New York Times, the Los Angeles Times, and 60 Minutes. I teach Alexander Technique in Beverly Hills (
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