Thursday, 27 September 2007

Switching the parents around

Judith Rich Harris: "In a 1995 paper in Psychological Review, I proposed a new theory of child development, based on the idea that children's personalities are shaped, not by their parents, but by the environment they encounter outside the home. This proposition, I said, doesn't imply that children can get along without parents. What it does imply is "that children would develop into the same sort of adults if we left them in their homes, their schools, their neighbourhoods, and their cultural or subcultural groups, but switched all the parents around."

It was a thought experiment - I wasn't suggesting that parents should actually be switched around. What I was saying was that, given a child's genetic makeup, and given the child's environment outside the home, the environment provided by the parents inside the home would not have any noticeable impact on the child's adult personality.

The experiment is an important one but it cannot be done, and not only for practical and ethical reasons. For one thing, there's no control group. We'd need two identical universes so that we could switch the parents around in one and leave them in place in the other. Then we could compare the children in the two universes. We'd have to compare them one by one, because my prediction wasn't about group averages - it was about individual differences. But that wouldn't work either, because we already know that two children with identical genes and essentially identical outside-the-home environments - namely, reared-together identical twins - don't end up with the same adult personalities. (The personality differences between reared-together identical twins is a mystery I address in my 2006 book, No Two Alike.)

There are ways to work around these problems and show that, given a child's genetic makeup, and given the child's outside-the-home environment, the environment provided by the parents inside the home makes no noticeable difference in the long run. But it involves putting together evidence from many different sources. This evidence already exists. For example, evidence exists that identical twins reared by different parents are (on average) as similar in personality as those reared by the same parents, and that adoptive siblings reared by the same parents are as dissimilar as those reared by different parents. Evidence exists that children reared by immigrant parents have the personality characteristics of the country they were reared in, rather than those of their parents' native land. Evidence exists that environmental differences within the family, such as those associated with birth order, leave no long-term marks on children's personalities. Even in childhood, firstborns do not behave differently from laterborns when they are outside the home, playing with their agemates.

Is it less convincing to put together many little bits of evidence (as I did in The Nurture Assumption and No Two Alike) than to point to a single grand experiment that proves one's thesis conclusively? It certainly requires more patience from one's audience. But sometimes the piecemeal approach is all that is possible."

--
Judith Rich Harris is the author of The Nurture Assumption and No Two Alike. She is an independent investigator and theoretician.

18 comments:

  1. Your conclusion that home environment has no influence on personality is ridiculous. Twins raised separately may appear similar, but I suspect that the upbringing of twins is generally similar, too -- show me some data regarding one twin in a loving household and the other in an abusive, sexualized, or extremely neglectful setting and I'll be a little more open. Only a very little more, though, because you still succumb to the error of assuming that home life has no impact on what you call the "outside the home" environment. Good parents control their kids' external experiences to any degree possible; bad parents don't. So to say that the "outside the home" environment has an impact on personality is equivalent to saying that the home life does; they are certainly not isolated from one another.

    Your approach is worse than "piecemeal" -- it is specious.

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  2. Doodaddy: How much of Harris' work have you actually read? You might find that several of your objections have already been answered (for instance, Harris admits that abusive situations will obviously have an abnormally large effect on a child's development).

    (I have a brief summary of The Nurture Assumption up at my website. While I don't really buy the idea that switching parents would have no effect on the children, I do accept that the effect may be smaller than is commonly thought.)

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  3. I've only read the abstract above. When the summary is so obviously flawed, why would I waste time with the methodology?

    I come from a science background, where you can't talk your way out of conclusions. As I said, even as presented, the "experiment" has no control (and no way of control) and assumes that two of the variables ("home environment" and "environment outside the home") are independent, when a one-day observation of any family will demonstrate very clearly that they are closely linked.

    The fact that any serious consideration is given to the above is a fairly clear demonstration of why social science has a bad name.

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  4. The Nurture Assumption has something to say in terms of the manner in which too much emphasis can be placed on the role of parents alone. However, the idea that factors outwith the home completely outweigh the role of parents is no more than an idea. The difference in outcomes between looked after children and adopted children is one of many indicators that suggest the likely significance of the developmental influence of parents and different types of parenting.

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  5. rafting4:43 pm

    Plato ('s Republic) has already suggested/implied this line of thought!

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  6. Anonymous6:43 pm

    Doodaddy, I assure you that if you're making remarks like this one:

    "I come from a science background, where you can't talk your way out of conclusions."

    then your so-called "science background" didn't take. Scientists talk themselves out of their conclusions all the time. It's the DATA that you can't talk yourself out of.

    Some data exist to support her conclusion (e.g., genetically identical twins who are raised in normal-but-different homes generally turn out fairly similar). This may or may not be powerful enough to support her conclusion in the eyes of other people, but the data is still real, even if you disagree with the conclusions she draws from it.

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  7. Pretty straightforward, do a twin study where the parents kept one and put the other up for adoption.

    There are lots of other separated at birth twin studies out there ...

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  8. Doodaddy is positively religious in his "suspicions", strawman attack, lack of any evidence, and certainty in the right. By all means, don't bother to actually read what you disagree with. Less mess, to be sure.

    Stephen, twin studies stop short of demonstrating what parents don't have influence over. They support JRH, but her thought experiment would add to it. Hence, not really straightforward, unfortunately.

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  9. Kristen M3:21 am

    This is a new idea on the subject of nurture for me. But it is just that, an idea. To say that children are more influenced by their “outside of the home” surroundings is impossible to prove and has very little evidence to even support the idea. Though twins born from the same mother and raised in separate houses/countries often carry similar traits, another set of twins separated at birth could carry very different traits as well. Also it is also hard to argue the opposing side of this argument, that children’s home-life directly affects their adult personality traits, because 2 children born and raised in the same family/household may later have very different adult personalities. By arguing that nurture directly determines the physical and behavioral traits of humans, we are arguing that it is the upbringing AND personal experiences (including those outside the home) that influence personality traits in people. So we must consider that it is all aspects of one’s childhood that determine their adult personalities.

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  10. Anonymous12:57 am

    "The personality differences between reared-together identical twins is a mystery" perhaps only insofar as it tends to torpedo from the git-go the author's idea that environment and especially interpersonal dynamics are wholly irrelevant to how a given genetic pattern turns out.

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  11. James6:40 pm

    “This is a new idea on the subject of nurture for me. But it is just that, an idea. To say that children are more influenced by their “outside of the home” surroundings is impossible to prove and has very little evidence to even support the idea.”

    There is actually a lot of evidence, covered in The Nurture Assumption and in No Two Alike.

    “Though twins born from the same mother and raised in separate houses/countries often carry similar traits, another set of twins separated at birth could carry very different traits as well.”

    Studies looking into the traits of reared-apart twins find that overall there is a 50% concordance in their traits. Incidentally, reared-together twins also show the same 50% concordance in their personality traits.

    “Also it is also hard to argue the opposing side of this argument, that children’s home-life directly affects their adult personality traits, because 2 children born and raised in the same family/household may later have very different adult personalities.”

    It is precisely this sort of discrepancy between conventional wisdom and reality that inspired Harris to investigate the supposed importance of the home environment and subsequently develop her theory, as she recounts in The Nurture Assumption.

    “By arguing that nurture directly determines the physical and behavioral traits of humans, we are arguing that it is the upbringing AND personal experiences (including those outside the home) that influence personality traits in people. So we must consider that it is all aspects of one’s childhood that determine their adult personalities.”

    It is clear that the environment has an effect on an individual’s development since people raised in the American South speak with a “twang” and often like country music. Fortunately, there are ways to separate the contribution of each of these potential influences. One large contributor is found to be heredity, which accounts for roughly half of the variance in adult personality traits. The question then becomes what factors account for the non-genetic variance, the half assumed to be attributable the “environment.” Unfortunately, failure to appreciate the effect of heredity has made studying the environment more difficult. But such controls can be taken into account and when they do, it is found that the home environment is far less important than is (sadly not was) commonly believed.

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  12. James6:41 pm

    Forgot to credit quotes to Kristen M in my previous post.

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  13. James6:44 pm

    anonymous said:
    ""The personality differences between reared-together identical twins is a mystery" perhaps only insofar as it tends to torpedo from the git-go the author's idea that environment and especially interpersonal dynamics are wholly irrelevant to how a given genetic pattern turns out." (emphasis added)

    Harris has never made any such claim in any of her works.

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  14. Hi, in regard to the passage above I agree and disagree. In my opinion, i think that the way chidren are affected isnt only by their enviroment, i think that their lifestyle is an important part of how they develop. Another thing that can affect them is how they are nurtured. Enviroment can change how your child is personality wise but i don't think it can hurt them in developing.

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  15. If I understand her argument correctly, then abuse in the home should only affect the child’s home life and relationship with its parents. Because of “code switching” we have one personality at home and a different one with our peers. As with immigrant children, who speak their parent’s language at home but perfectly master their schoolfriends’ accents and dialect. She makes a lot of Cinderella, an abused skivvy at home but a princess in the outside world. Grudgingly, she does make some exceptions: “Only the super bad parents that beat or abuse their children have lasting impact.”

    Now this vague language should be sounding alarm bells. What is robust parenting to one is abuse to another. And there are plenty of studies that satisfactorily demonstrate the corrosive effect of early stress on the developing brain. Martin Teicher has shown with brain scans how verbal and emotional attacks can be much worse than beating and seriously impair the developing brain.
    In fact, there are very many studies clearly demonstrating the importance of a stable home life and parental support in children’s success. It’s hard not to conclude she has cherry picked the evidence to suit her thesis.

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  16. Anonymous7:28 am

    Do not believe in psychological experiments, they are always influenced by the certain idea. Besides who needs to impovise the cituations which excist all around - collect & document the cases, tons of them, then organize the observations by categories. Every family can feed a valuable material.
    Using my own observations for some years,I came to conclusion that, besides the twins, the siblings in the family grow up into very different characters.Parents establsh certain habits & skills but not the brain construction & biochemistry which makes the personality.
    I am
    very impresed by Antonio Damasio book: Looking for Spinosa.Joy,Sorrow, and the feeling brain,
    investigating the neurobiological foundatios of human life.His innovative research gives the best answers to the big question- what it is that influences humain brain.
    I'd love to read Judith Harris works too.

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  17. Anonymous6:53 pm

    One important thing that I think people miss is that these debates are about *personality* i.e. enduring traits such as the Big Five.

    Arguing that personality isn't affected by homelife is not the same as arguing that people are not affected by homelife in any way whatsoever.

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  18. Hi,

    Having come to the end of my PhD studies I can offer support to Harris in a sense that I observed children change drastically during the first year of schooling.
    I investigated ethnographically the transition from home to school for 4 year olds in the UK. Now I know that I didn't control the home environment nor did I control the school environment. All I wish to add to the matter is that you would honestly be surprised how much impact 'outside the home' environments really have on our children, even at the age of 4!

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