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Review of "No Two Alike"

By Judith Rich Harris
WW Norton, 2006
Review by John D. Mullen, PhD on Mar 8th 2006
No Two Alike

Children are different from each other both when they are young and after they mature.  Why is that?  There was a time when no one hesitated with the answer; they're different because they were reared differently.  Some were spanked, some were not.  Some received authoritarian parenting, some permissive, some authoritative.  Some were toilet trained early and harshly, some were left to cry in the crib and some were cuddled, and so it went.  Anyone reading this review knows this story and knows that the emphasis was on parenting and genes were not a part of the account. 

Behavioral genetics, by studying identical twins, fraternal twins, other siblings and adopted children altered that account in the late twentieth century.  It showed convincingly that genetic variance accounts for a good deal of trait variance, leading to the (oversimplified) formulation:  trait (phenotypic) variance = genotypic variance + environmental variance.  While this seems vaguely like common sense, the admission of genotype as an important factor in human development placed almost the entire corpus of developmental research under suspicion for not controlling for genes.  Agreed, children whose parents read to them regularly become better readers.  But with genes in play the correlation no longer implies that reading to children causes them to become better readers.  Thousand of dissertations, scholarly articles and parenting paperbacks need to be cast into the flames of discarded paradigms.  But behavioral genetics went further.  It failed to detect any significant parenting effects from within the environmental realm of the causation of traits (The exception is pathologically abusive parenting.)

Questions lingered.  If environmental variance accounts for roughly half of phenotypic personality variance, why are siblings raised at home so different?  They seem to share half the genotype and the entire environment.  Even more curiously, why are identical twins reared together so different when they share all of their genes and all of the environment?  Why were the Iranian conjoined twins Laleh and Ladan so different when their genes and environments seemed all but identical?  No Two Alike, this wonderful new book by Judith Rich Harris, takes on this most difficult of questions.  While behavioral genetics has established that genes have an important role in the development of human differences, it is Judith Harris who seeks to uncover the complicated and subtle mechanisms through which the environment in its broadest senses leaves its marks.

In developmental psychology when Robert Plomin of Kings College, London speaks, people listen.  In 2001 Plomin, et. al. provided a comprehensive review of the literature in an article, "Why are children in the same family so different", Canadian Journal of Psychiatry, 46, 225-233.  Where "non-shared" environment denotes factors that make people different, they wrote, "We also need to consider the gloomy prospect that chance contributes to non-shared environment in terms of random noise, ..."  They had failed to detect any systematic factors that separate out children, leaving the possibility that they become different as a result of chance events.  These singular events are not literally by chance, of course, but they and their effects are unpredictable.  One sibling finds himself in the sights of a bully and is frequently frightened, another loses control of his bowels in gym class and gains the long-lasting nickname "shitty", a third has counseling from a charismatic therapist and devotes herself to psychology.  These singular events alone do not alter lives.  They create what Plomin, et. al. refer to as a, "... subtle interplay of a concatenation of events."  They set something in motion that gains momentum.  As Kierkegaard has a character say in Either/Or, "The smallest of causes can bring about the greatest of effects."  The prospect of admitting these events into the picture is "gloomy" and the events are "noise" because just as noise grates upon the ear, singular events grate on a scientist's penchant for regularity.

Judith Harris shook the field of socialization research in 1998 with her impressive and hugely popular The Nurture Assumption where she argued (1) that genes are a big part of human developmental variation, (2) the effects of diverse parenting practices are restricted to the home, and (3) environmental effects come largely from peer socialization.  In No Two Alike she seeks to fill in the account of how the variation in the environment contributes to differences among people.

Harris is an unusual figure in academic psychology.  She has no Ph.D. and no academic appointment.  She's a reformed textbook writer from New Jersey who has become a leading developmental theoretician.  Harris delights in retelling the story of her ignominious exile from graduate study at Harvard at the hands of Chairman George A. Miller and her redemption in 1998 when the she received from the American Psychological Association the George A. Miller Award for her 1995 paper, "Where is the Child's Environment", Psychological Review, 102, 458-489.  And Harris, a devotee of mystery writing, is a great storyteller, relating exchanges with researchers who have tried to obscure the details of their work under the glare of Harris' keen eye.  I can think of no rival to Judith Harris' ability to spot confounds in research and to suggest alternative conclusions that are more consistent with the data than the researcher's own.  Let me illustrate:

Harris is not a researcher, at least in the sense that she does not run subjects, have a laboratory or seek research funds.  As a result she must rely upon the data of others to support her critiques and the ideas she promotes.  This places a heavy burden to be certain that first, the research she sights is methodologically adequate to the conclusions drawn and second, that what is reported, even widely reported, was actually what was done.  On this matter, had Harris been canine she would have been a bloodhound-bulldog cross.  Two examples:

First, Harris long ago concluded that, within the realm of the non-pathologically abusive, parenting styles have little effect outside the home.  This was argued in The Nurture Assumption and is argued again in No Two Alike, and God help the researcher who reports data to the contrary.  Following The Nurture Assumption Harris was invited to a conference on parenting sponsored by the National Institute of Child Health and Human Development (NICHD).  One of the organizers reported to Harris, "I had to fight to get you on the program" (53).  Harris' only ally present was David Rowe whose The Limits of Family Influence (1994) preceded Harris' 1998 work.  The conference papers were published as an important anthology, J. G. Borkowski, et. al., Parenting and the child's world: influences on academic, intellectual and social-emotional development. (2002).  Harris provides an amusing account of the conference and a very clear description of the issues involved.  Socialization theorists, who for decades had ignored genetic contributions to personality traits in favor of parenting effects, have now admitted the former into their conversations.  But they continue to reject the behavioral genetic evidence against parenting effects beyond the home.  Their new claim is that parenting effects are mediated through the genes, through gene-environment interactions, so that in the same family one child may flourish under harsh discipline while another withers.  They contend as well that these parenting effects are cancelled out in the behavioral genetic analysis, explaining why no parenting effects turn up despite their existence.  Of course if this were true, then using parenting research to formulate child-rearing advice would be impossible since the same recommendations could have opposite effects upon two children.  But Harris denies that it is true in the sense proposed.  She agrees that the effects of parenting will be mediated through the genes of the child, but that differences as great as to cancel each other out, so-called "crossover effects", are very rare anywhere in nature.  She argues that genetic mediation tends to have "sensitivity effects" where the consequences of an environmental variable run in the same direction though to greater or lesser extents. 

One paper at the conference caught Harris' attention as a serious challenge to her claim that parenting styles do not have consequences beyond the home.  Stephen Suomi does research on Rhesus monkeys at NICHD.  He reported his study that employed two genetic strains of monkeys, one bred to be nervous or "high-reactive" the other to be calm or "low-reactive.'  The monkeys of both groups were reared by adoptive monkey mothers who were either good or bad mothers.  The "low-reactives" turned out okay regardless of having good or bad mothers but the "high-reactives" with bad mothers were social failures while the ones with good mothers were okay.  And the effects of the different mothering persisted even after they left their mothers.  Even with qualifiers about human-monkey differences, this tended to disconfirm Harris' viewpoint and she needed to be convinced, "What surprised me was not that monkeys with good foster mothers did well while they were with their mothers, but that the effects of good mothering persisted ...(61)."  And Harris found Suomi's research sited again in an article by prominent developmentalists six months later.  Since Suomi had been sketchy about his research in the conference talk, Harris found the location of its full description from the references in the developmentalists' article.  It was in a chapter that Suomi contributed to an anthology, but upon checking Harris found no reference to the cross-fostered monkeys.  A call to the first author of the developmentalists' article led to another of the authors who reported that her source was a phone call from Suomi.  Suomi reported by email to Harris that the study involves thirty-six cross fostered monkeys, eighteen of each strain but nothing of the results.  He promised a monograph in 2000.  A literature search turned up a study with fewer than eight monkeys, meaning that a maximum of four were "high-reactives" and a maximum of two of those would be raised by bad foster mothers.  A later book chapter reported a "recent" study, but gave no data and no N.  When it came time for Suomi's conference presentation to appear in print in 2002 there was no mention of cross-fostered monkeys.

The second example of Harris' doggedness (no pun here) involves the revered Harvard developmentalist, Jerome Kagan.  As it happens, Kagan and Harris have several good reasons to think of each other as kindred spirits.  His research from the 1960s pinpointed shyness as a genetic trait.  His study of Guatemalan children emphasized the flexibility of child development at a time when parents were being warned, in this case by John Bowlby, that leaving a child with Grammy even for a fortnight could have serious later implications.  And he has been a persistent critic of early experience theories.  But alas, Kagan and Harris drifted into an adversarial relationship following The Nurture Assumption, after Kagan accused Harris of ignoring research that disagreed with her positions.  A point in question was a claim of Kagan's to have measured children at four months and at school age.  He reports finding that fearful children whose parents (over)protected them were still timid while those whose parents pushed them to try new things were not.  These are parenting effects beyond the home and on a trait with a strong genetic base.  Newsweek duly reported these results in its article on Harris.  She wanted to know the truth.  It turns out that what Kagan had published, in a chapter of a book in 1994, was a preliminary report of a study done by one of his Harvard doctoral students.  Harris found that the retests were done, not at "school age" as Newsweek had reported but at 21 months.  Three years later the graduate student published results that reported retests at four and a half years but eliminated any reference to child-rearing style for that group. 

Finally, Harris notes somewhat scornfully that Suomi's cross-fostered monkeys and Kagan's once-timid babies continue to get press, rather like academic urban legends, and the above-mentioned lead developmentalist is still teaching his students about Suomi's findings.  She tells a third story about the persistent efforts of a lawyer, Frederic Townsend, to track down the data on which Frank Sullaway drew his amazing conclusions about birth order effects in his Born to Rebel (1996).  It is a story of insult, threats of lawsuit, obfuscation within the scientific community and missing data. 

Harris is persistent not only concerning whether research has been done as reported but whether the methodological assumptions of the research hold water.  She criticizes Kagan-type research for assuming that any changes that take place between time-one and the retest at time-two cannot be caused by genes.  This assumption seems reasonable since one's genotype does not change over time.  But Harris points out that many genes switch on, and thus turn their effects on, at different times in the developmental process.  One does not conclude that male pattern baldness is not genetic simply because hair loss begins post adolescence.  Her second objection is that such research neglects the well-documented phenomenon of child-to-parent effects, that parents alter their behaviors as a result of the child's behaviors.  The child who loves to be read to gets read to and the child who is a hellion as early as his descent through the birth canal receives harsh discipline.  That these children turn out to be great readers and car thieves cannot be automatically attributed to parenting styles.     

I'll give two more examples of Harris' expertise at methodological critique.  Intervention studies are the closest that developmental psychologists can get to controlled experiments and the best way to skirt the correlation-causation problem.  This research randomly selects an experimental and a control group from a population, gives the experimental group parenting training, and then measures the behavior of the children of both groups.  Harris' interest is in the extra-home child behaviors since she denies that parenting styles affect it.  Philip and Carolyn Cowan from UC Berkeley do this research as well as anyone and were good enough to supply Harris with their most recent study.  They concluded that if you improve parent-to-parent and parent-to-child interactions with a four-month program the child's school performance improves.  But Harris was unable find any comparison between the school performance of the children of the experimental and control groups.  When asked, Cowan responded that they were reporting only on the children of the parents who improved as a result of the intervention, the others dropped into the control groups.  Harris says, "Hmm.  So the parents who improved as a result of the intervention had kids who did better in Kindergarten (132)."  Just another correlation study.  Cowan directed Harris to studies by Marion Forgatch who works with David DeGarmo.   In an article in a peer reviewed journal (Harris, despite being outside the academy, has great respect for the peer review process.) Forgatch and DeGarmo created experimental and control groups, administered an intervention to the experimental group that sought to reduce "coercive parenting" among single mothers of young sons and did follow-up reminder calls to the mothers.  They reported that mothers became less coercive and that, "improved parenting correlated significantly with improvements in teacher-reported school adjustment (133)."  The statistic that was missing from the Cowans' study, comparisons between control and experimental groups, was provided in this one.  There were no significant differences in school behaviors between the two groups.

I have taken some time with issues of both academic sociology and research methodology to show how complex it is either to establish parent-to-child effects outside the home or to undermine ideas about them that have been so long and so widely disseminated.  And I wanted as well to give a glimpse at who this person Judith Harris is who has so shaken the establishment in developmental psychology.

Of course it is easier to critique than to build.  But Harris is not only a critic.  In the hubbub surrounding The Nurture Assumption it was largely lost that the book contained a revised socialization theory, one that focused upon the effects of peer culture in the way that previous researchers has emphasized the family.  No Two Alike contains a theory about how it is that this system works.  How, over and above our genotype, does environment shape who we are?   Harris takes as her challenge the most difficult case.  How does environment cause identical twins to have such different personalities?  Her theory is ingenious, subtle and original. 

Harris seems to believe that her theory is wedded to evolutionary psychology and to the theory of the "modular mind".  I don't think that it is.  It can be clearly and completely stated independently of both of these and that it is stronger for its independence.  If evolutionary psychology were simply be the idea that we will have a better understanding of mind and behavior as evolutionary scientists learn more, it would be both true and innocuous.  But its proponents, like Judith Harris' friend Harvard's Stephen Pinker, think of it as more, as an actual methodology, one that includes "reverse engineering".  This in general means asking about some existing but unexamined entity what it must be like, what its components must be, to be able to perform the function that it does.  (Interestingly, a priori approaches to this type of question resembles the transcendental inquiries found in Immanuel Kant's Critique of Pure Reason.)  In cognitive science this involves a conceptual mapping of the mind into functional systems and sub-systems without an initial commitment to any specific physical realization.  This mapping leads to the idea of a modular mind, one separated out by evolution into distinct systems with relatively narrow jobs to do.  The idea was developed for lower order cognitive activities in Jerry Fodor's The Modularity of Mind, MIT Press (1983).  Ironically Fodor is a strong critic of Pinker's wider use of modularity in Pinker's How the Mind Works, Norton (1999).  See Fodor's The Mind Doesn't Work That Way, MIT Press. (2000).  I mention that Harris's work is stronger for being independent of all this because first, she doesn't need it and second, it's philosophically contentious.  As Fodor mentions somewhere, we knew a lot about what hands and fingers were for long before we knew anything about their evolution.

So how do identical twins raised in the same household become so different?  By extension, how do any siblings become different.  It's not parenting style.  It's not birth order.  Harris' story proceeds something like the following.  Every person's personality behavioral traits are influenced, by three "systems" or dispositions (this is beyond any genotypic influences).  They are the relationship system, the socialization system, and the status system.  I will describe each.

The Relationship System:  It is certainly true that we collect and store data about the individuals that we meet.  Harris compares this to the "mental lexicon" by which we store words and their meanings, here Harris takes her lead from Pinker.  Our "people lexicon" allows us to distinguish and recognize people as individuals, not as class members, e.g., as my friend Antonia, not as an example of Italian, women, communist.  This involves things like face-recognition, but we are able to take its cues from other things as well.  People who are close to identical twins have no trouble distinguishing them even if they don't know how they do it.  While the relationship system is a cognitive skill it is also a motivational device.  People are driven to collect information about other people, and we don't need evolutionary speculation to seek agreement on the existence of this intrinsic motivation.  The relationship system guides our behavior by supplying information about this or that individual. 

The Socialization System:  Having identified individuals we must act in ways that are appropriate to who they are.  This system of instructions is the socialization system which tends to make people of the same group more alike.  Harris has a theory about how socialization works.  She notes studies that show that judgments of facial attractiveness tend to regress to the mean.  Show a person a group of facial photos of strangers and they tend to prefer the one that has been artificially blended from the others.  On a conceptual level this blending creates prototypes that define categories.  Children have a motivation to categorize according to these prototypes and to self-categorize in relation to others.  Thus a young person will categorize herself as girl or African-American or American or New Yorker, etc. depending upon which prototype she is dealing with, and she will switch behaviors accordingly.  Socialization is self-motivated and takes place as the adjustment of one's behaviors to the expectations of the central tendencies of a category. 

The Status System:  Humans everywhere compete with fellow group members.  No reward system or external reinforcers are necessary.  The outcomes of that competition constitute status.  Harris relates studies that show that people react separately to social acceptance and social status.  Bullies can fail at acceptance but succeed at status and so can have adequate self-esteem.  Children by age six or seven have an idea, through pairwise competitions, of their status in their groups.  For boys, who's strongest, fastest, toughest, etc.  Harris believes that self-acceptance derives from the status system (that portion that is not genetic) and, interestingly, that it is adolescent status that is determining.  She argues this on the basis that adolescents that were tall relative to their peers make more money than those peers when they are adults, regardless of their adult height.  The idea is that the earlier height-generated status conveyed a self-confidence that translated into later "status-conferring" positions.  The most conceptually complicated part of determining one's own status is being able to read what other's consider my status to be.  This is a matter of picking up on sometimes subtle clues involving the eye contact, posture, speech, etc. of others.  It is this system that shapes one's personality.

Genes have at least two types of effects upon personality.  There are direct affects where a child is born with a certain level of aggressiveness, openness to change or shyness.  And there are indirect effects, for example, one's size, attractiveness or intelligence affects the status others give to one, a status that is read from others and internalized.  But identical twins have identical genotypes and so these factors do not come into play.  Recall that Harris began the book promising to explain the very different personalities of Lalah and Ladan, the identical, conjoined Iranian twins.  In this case the entire personality difference must be explained by the three systems, particularly by the status system.  How is it that others formed different idea of the status positions of Lalah and Ladan, ideas that were read off from these others by each of the twins?  Here Harris needs to fall back on singular (random) events.  She seems a bit embarrassed by this and is quick to note, "The incidents may be random but their consequences are not (231)."  An unusual and impressively correct answer on a teacher's question can cause others to view you as "smart", a belief that gains momentum in the eyes of others, is read from them into your self-categorization, creating a confidence in academic matters that reinforces others' status judgments, etc.  This is Plomin's "gloomy prospect", and its appearance is somewhat of a disappointment, almost as if an implicit understanding about the rules of the game has been breached.   I think of Lucretius' first century BCE cosmology in which all atoms fall naturally in a straight line toward the center of the universe.  But to explain how a cosmos of colliding atoms arose from this it was necessary for one of them to swerve, ever-so-slightly.  This swerve, a dues ex machima if there ever was one, did not itself fall within the principles of Epicurean physics, but it explained the origins of the motions that did.  Paraphrasing Harris, the swerve may have been random but its consequences were not.  And later, in response to Einstein's 1926 letter to Max Born where he assured us that, "God does not play dice with the universe," Nils Bohr is reported to have said that Einstein should, "Stop trying to tell God what he can do with his dice."  Researchers will likely seek the disappearance of the singular event as a factor in the origins of personality differences at which time Bohr's God will need to decide if they get their way.

This is a very important book.  The community of academic psychologists would do well to get over its arms-length response to this outsider, Judith Harris, and to her sometimes quirkiness.  Her theoretical ideas about the environmental mechanisms of personal individuation deserve the kind of rigorous investigation and testing that is the hallmark of good science.           



© 2006 John D. Mullen


Link: Review by John Mullen of Judith Rich Harris' The Nurture Assumption: Why Children Turn Out the Way They Do

John D. Mullen is professor of Philosophy at Dowling College in Oakdale, New York.  He has written a widely read text, Kierkegaard's Philosophy: Self-deception and cowardice in the present age, Hard Thinking: A Reintroduction of logic to everyday life, and co-authored with Byron M. Roth, Decision Making: Its logic and practice.

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