Sad to learn of the death of a major influence and dear friend, the brilliant and witty psychologist Judith Rich Harris. Too early for an obit, but the NYT review of her magnum opus may be found here: https://t.co/nrqZyHJqMc 
— Steven Pinker (@sapinker) December 30, 2018 
I discovered her when a reader of this blog recommended her bestselling book The Nurture Assumption: Why Children Turn Out The Way They Do  to me when I was writing The Benedict Option.  The reader said the book would help me understand why it is so important for Ben Op families to find each other. It’s a powerful book; no wonder scientists like Steven Pinker praised it to the skies. Here’s what I said about it in The Benedict Option :
Peer pressure really begins to happen in middle childhood. Psychology researcher Judith Rich Harris, in her classic book The Nurture Assumption, says that kids at that age model their own behavior around their peer group’s. Writes Harris, “The new behaviors become habitual—internalized, if you will—and eventually become part of the public personality. The public personality is the one that a child adopts when he or she is not at home. It is the one that will develop into the adult personality.”
Harris points to the example of immigrants and their children. Study after study shows that no matter how strong the home culture, first-generation offspring almost always conform to the values of the broader culture. “The old culture is lost in a single generation,” she writes. “Cultures are not passed on from parents to children; the children of immigrant parents adopt the culture of their peers.”
On the other hand, says Harris, is that in most cases, it’s not too late for kids who have been exposed to bad influences. Researchers find that damage to a child’s moral core can be repaired if he is taken away from a bad peer group. What’s more, determined parents who run a disciplined home, and who immerse their children in a good peer group, can lay a good foundation, no matter how lax they have been until now.
The bad news about the fragility of culture is also good news, according to Harris: “Cultures can be changed, or formed from scratch, in a single generation.”
From the Education chapter:
A reader of my blog said she sees the same sort of thing watching her daughter navigate from junior high to high school. “There’s nothing like having your twelve-year-old come home from school and start ticking off which of her classmates are bi,” the reader said. “I told my daughter it was statistically impossible for there to be that many bisexual students in her class, and that for most girls—and they were all girls—seventh grade was entirely too early to make pronouncements on their sexuality. In return, I got a lot of babble about gender being fluid and nonbinary.”
The reader called a friend with a daughter in the same class and asked her what was going on. “‘Where have you been?” she laughed. “‘At least a third of these girls are calling themselves bi.’”
Few parents have the presence of mind and strength of character to do what’s necessary to protect their children from forms of disordered sexuality accepted by mainstream American youth culture. For one thing, the power of media to set the terms of what’s considered normal is immense, and it affects adults as well as children. For another, parents are just as susceptible to peer pressure as their children are.
“People rear their children the way their friends and neighbors are doing it, not the way their parents did it,” says psychology researcher Judith Rich Harris, “and this is true not only in media-ridden societies like our own.”
Here’s a link to Malcolm Gladwell’s New Yorker piece on the book.  It’s well worth reading if you want to grasp Harris’s insights and argument. Excerpts:
Not long ago, Anne-Marie Ambert, a sociologist at York University, in Ontario, asked her students to write short autobiographies describing, among other things, the events in their lives which made them most unhappy. Nine per cent identified something that their parents had done, while more than a third pointed to the way they had been treated by peers. Ambert concluded:
There is far more negative treatment by peers than by parents…. In these autobiographies, one reads accounts of students who had been happy and well adjusted, but quite rapidly began deteriorating psychologically, sometimes to the point of becoming physically ill and incompetent in school, after experiences such as being rejected by peers, excluded, talked about, racially discriminated against, laughed at, bullied, sexually harassed, taunted, chased or beaten.
This is Harris’s argument in a nutshell: that whatever our parents do to us is overshadowed, in the long run, by what our peers do to us. In “The Nurture Assumption,”Harris pulls together an extraordinary range of studies and observations to support this idea. Here, for example, is Harris on delinquency. First, she cites a study of juvenile delinquency–vandalism, theft, assault, weapons possession, and so on–among five hundred elementary-school and middle-school boys in Pittsburgh. The study found that African-American boys, many of them from poor, single-parent, “high-risk” families, committed far more delinquent acts than the white kids. That much isn’t surprising. But when the researchers divided up the black boys by neighborhood the effect of coming from a putatively high-risk family disappeared. Black kids who didn’t live in the poorest, underclass neighborhoods–even if they were from poor, single-parent families–were no more delinquent than their white, mostly middle-class peers. At the same time, Harris cites another large study–one that compared the behavior of poor inner-city kids from intact families to the behavior of those living only with their mothers. You’d assume that a child is always better off in a two-parent home, but the research doesn’t bear that out. “Adolescent males in this sample who lived in single-mother households did not differ from youth living in other family constellations in their alcohol and substance use, delinquency, school dropout, or psychological distress,” the study concluded. A child is better off, in other words, living in a troubled family in a good neighborhood than living in a good family in a troubled neighborhood. Peers trump parents.
Gladwell explains that Harris’s insights came in part from raising her two daughters — one the biological child of her and her husband, the other adopted. They were raised in the same household, but turned out very differently. Nomi, the biological daughter, was studious and high-achieving, the other one, Elaine, was not. Here’s Gladwell:
There are a hundred ways of explaining Nomi and Elaine, and there is, of course, something very convenient about the explanation that Harris arrived at: it’s the kind of thing that the mother of a difficult child wants to believe. Harris has constructed a theory that lets herself off the hook for her daughter’s troubled childhood. It should be said, though, that the idea that parents can control the destiny of their children by doing all the right things–by providing children with every lesson and every experience, by buying them the right toys and saying the right words and never spanking or publicly scolding them–is just as self-serving. At least, Harris’s theory calls for neighborhoods, peers, and children themselves to share the blame–and the credit–for how children turn out. The nurture assumption, by contrast, places the blame and the credit squarely on the parent, and has made it possible to demonize all those who fail to measure up to the strictest standards of supposedly optimal parenting.
You can take that insight too far, of course. Again, she’s not saying that parents, and parenting styles, don’t matter at all; rather, she’s saying that in most cases, they matter less than we think. And they matter in ways that are not always obvious to us. For example, last week we had a big discussion here about kids who are addicted to Fortnite , and parents who don’t know what to do about it. Judith Rich Harris would tell those parents that unless they get together and shut down their kids’ access to Fortnite, they’re not going to do much good. The peer culture in which their boys are embedded is far more powerful than their home culture. If the parents want to change the peer culture, they have to figure out a way to get together and do it.
The Nurture Assumption explains why it makes total sense for parents to sacrifice to get their kids into good schools — defining “good” as schools with peer groups that embody pro-social virtues and characteristics. And, come to think of it, it helps explains why the insane rate of rapid-onset gender dysphoria manifesting itself in middle schools and high schools is heavily down to social contagion among peer groups. In fact, if you interpret the book in terms of cultural politics, you will run hard up against a number of left-liberal orthodoxies. As Steve Sailer said in his 1998 review: 
Although she tends to tiptoe around the political implications, her analysis of how young people naturally form peer groups that define themselves by excluding others explains why multicultural education, bilingualism, college-admission quotas, busing, and co-ed boot camps perversely worsen race and sex conflicts.
In fact, read the Gladwell piece , and think about its account of the three little girls on the playground, and contemplate what it reveals about social psychology and the unwisdom of having immigration at a rate faster than can be naturally assimilated. It has nothing to do with race and ethnicity; it’s all about human nature, and how all of us learn to live together in peace. Or fail to. As Sailer avers, it sheds light on why liberalism’s “diversity” do-goodery often makes the problem worse.
I’m not sure that Judith Rich Harris would have been willing to accept that, but she was aware that her work had at least some public policy implications. As she told Scientific American in a 2008 interview: 
I’ve put together a lot of evidence showing that children learn at home how to behave at home (that’s where parents do have power!), and they learn outside the home how to behave outside the home. So if you want to improve the way children behave in school—for instance, by making them more diligent and less disruptive in the classroom—then improving their home environment is not the way to do it. What you need is a school-based intervention. That’s where teachers have power. A talented teacher can influence a whole group of kids.
The teacher’s biggest challenge is to keep this group of kids from splitting up into two opposing factions: one pro-school and pro-learning, the other anti-school and anti-learning. When that happens, the differences between the groups widen: the pro-school group does well, but the anti-school group falls further and further behind. A classroom with 40 kids is more likely to split up into opposing groups than one with 20, which may explain why students tend to do better in smaller classes. But regardless of class size, some teachers have a knack for keeping their classrooms united. Teachers in Asian countries seem to be better at this than Americans, and I suspect this is one of the reasons why Asian kids learn more in school. No doubt there’s a difference in cultures, but maybe we could study how they do it and apply their methods here.
The tendency of kids to split up spontaneously into subgroups also explains the uneven success rate of programs that put children from disadvantaged homes into private or parochial schools. The success of these programs hinges on numbers. If a classroom contains one or two kids who come from a different background, they assimilate and take on the behaviors and attitudes of the others. But if there are five or six, they form a group of their own and retain the behaviors and attitudes they came in with.
One more clip, and I’ll stop. Here’s a lengthy 1999 interview she did with Edge.org.  Excerpt:
JB: 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.
JB: 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.
Anyway, read the book.  It’s challenging, even unsettling — but in a constructive way.