The Nature of Nurture: Parents or Peers?
a Slate dialogue
Judith Rich Harris and Jerome Kagan
Message #1: Oct. 28, 1998
From: Judith Rich Harris
To: Jerome Kagan
You wouldn't know it from the way it has been depicted in the
media, but my book The Nurture Assumption covers a diversity of
topics. I talk about how cultures are passed on and what makes them
change, and why girls and boys behave differently in some
circumstances, and how adolescents turn into adults and lose their
annoying ways, and why humans have such a strong tendency to
identify with a group and to hate the members of other groups, and
why the "me" that looks out at the world from behind my eyes still
feels 20 even though the eyes are 60 years old. But none of this
gets mentioned in the media storm surrounding my book. All the
attention is focused on one idea, which journalists insist on
overstating as "Parents Don't Matter."
Yes, I'm the terrible grandmother from New Jersey -- the gadfly
who has taken on the academic establishment and has been ferociously
attacked by some of its members (few of whom have actually read the
book). I'm the one who says that parents have no power to mold their
child's personality -- that parents have no important long-term
effects on the way their children behave when they're not at home.
And I should tell you right off, Jerry, I'm not here to repent of my
sins. My head is bloody but unbowed.
In your attacks on me on National Public Radio and in the
Boston Globe, you accused me of ignoring all the evidence that
indicates that parents do have important long-term effects on their
children. You implied that I must be ignorant of that evidence. But
I've spent almost 20 years studying it. As a writer of textbooks in
developmental psychology (the senior author of a text that went
through three editions), I spent many years telling credulous
college students about that evidence. I told them about your work,
But now I've looked more closely at the evidence -- looked at
it under a microscope, to turn one of your metaphors around -- and
I've seen that it is full of holes. It isn't just that there is
ample evidence against the nurture assumption, it's that the
evidence supporting the nurture assumption is so embarrassingly
weak. If it weren't for the fact that researchers take the idea of
parental influence as a "given," they would never accept evidence of
this sort as proof of anything. Yes, there is an awful lot of it,
but no matter how high you pile it, horse manure never turns into
Developmental psychology rests upon data that come almost
entirely in the form of correlations, and correlations are
ambiguous. Epidemiology has the same problem. When epidemiologists
find a correlation between exercise and good health, they like to
think it shows that exercising causes good health. They know there
is a possibility that the connection works the other way -- that
healthy people may be more likely to exercise -- but they assume that
at least some of the correlation must be due to what they're looking
for: an effect of exercise on health.
But assuming just isn't good enough. Ambiguous results must
be backed up with evidence from other kinds of studies. When all
you've got is correlations, you have to home in on the truth from
different directions, using a variety of techniques.
In developmental psychology, all you've got is correlations.
And when I look at other kinds of studies, they do not back up your
interpretation of the correlations. Take, for example, the
correlation you mentioned in the Boston Globe: "that the best
predictor of a child's verbal talent is the frequency with which the
parents talk and read to the child."
It is perfectly true that talkative, bookish parents tend to
have children who score high on vocabulary tests. But this is an
ambiguous result, because correlations don't come with labels
saying, "X caused Y." Parents and children tend to be alike partly
for biological reasons -- children inherit some of their
characteristics from their parents. Although most developmental
psychologists admit this, they nevertheless make the assumption that
some of the correlation between verbal parents and verbal children
must be due to what the children learned at home.
The problem is, if we do a different kind of study -- look at
adopted children, for example -- we find no support for this
assumption. On the contrary. By the time they reach late
adolescence, adopted children do not resemble their adoptive parents
in any measure of intelligence. The adolescent reared by talkative
adoptive parents is no more verbal, on the average, than the one
reared by taciturn parents.
The problem with your evidence, Jerry, is that a whole bunch
of causes and effects are tangled together, and the methods of
developmental psychology provide no way to tease them apart. Before
you can conclude that the parents are influencing the children, you
have to separate parental influence from other possible explanations
of your results. Children resemble, for genetic reasons, their
biological parents. Parents are more likely to read to children who
want to be read to. Children and parents are usually members of the
same culture or subculture, and the culture influences both the
parents and the kids.
Like you, I believe that kids are influenced by their
culture. But you assume they get their culture from their parents,
and that's an assumption I don't buy. I hope to take this up with
you in the next round of our debate.
Message #2: Oct. 29, 1998
From: Jerome Kagan
To: Judith Rich Harris
This reply to your essay deals directly with your claim that
parents have no power to mold their child's personality and that
they exert no important long-term effects on the child.
First, let us clear up the meaning of correlations.
Astrophysics deals only with correlations, yet it has been able to
infer deep principles. Moreover, watch out or you will be damaging
your argument. Your claim that parents have little effect is based
on correlations, albeit low ones. If correlations are no basis for
inferring anything important then you, too, are on weak
I begin the rebuttal with the August 1998 issue of Child
Development, our premier journal. The National Institute of Child
Health and Human Development research group reports the results of a
study of over 1,000 children from 10 different cities who were
exposed to very different forms of surrogate care, along with
children raised only at home. When the children were assessed at age
3, there was very little effect of form of surrogate care, while
family influences were the major cause of variation among the
children. The authors wrote, "What transpires in the family appears
to be more important in explaining children's early social and
emotional development than ... quality, quantity or stability of
type of care."
You claim that the reason children of parents who talk
frequently to their child are more verbal is attributable to genes.
However, this argument is vitiated by a study published in Science
in 1978. Schiff, et al., studied working-class children who were
adopted early into upper-middle-class homes and compared the
intellectual talents of these adopted children with that of their
siblings who remained with their working-class parents. The adopted
children had significantly higher intelligence scores than the
nonadopted children who were genetically related to them. The
differences in cognitive skills had to be due to the family
practices and not to genes. (See Schiff, et al., Science, 1978, 200:
Perhaps the most serious source of vulnerability in your
position comes from the fact that children from different cultures
behave very differently even before peers have had a chance to have
a serious effect. The work of the Whitings has proved this point to
the satisfaction of most scientists. I trust that you will not claim
that rural Mexican children are more nurturant and less aggressive
than New England children because of heredity.
A third flaw in your argument comes from studies of young
children orphaned by war -- World War II and the Korean War. These
children were adopted by nurturant families and years later their
intense anxiety and retarded cognitive abilities were muted in a
serious way. There is no other way to account for this result
without attributing power to family practices. (See Rathbun, et al.,
American Journal of Orthopsychiatry, 1958, 28: 408-415; Winick, et
al., Science, 1975, 190: 1173-1175.)
Finally, I believe you ignore one of the most important
influences on children; namely, the identification with the parents.
I could find no reference in your book to any study that dealt with
this process. A child with an incompetent, unemployed, impulsive
parent is ashamed of that parent and his or her image of self is
affected by that shame. On the other hand, the child with a
competent, talented, reflective parent feels a certain pride that
has a benevolent effect on personality development. Most memoirs
ascribe extraordinary power to these processes. (See J.S. Mill; C.
Darwin; F. McCourt.)
I know of no culture that claims that parental character and
practices have a minimal effect on children. I take that universal
fact to mean that a truth is contained there. The fact that your
review of the literature led you to a very different conclusion
suggests that your review was selective, indifferent to data that
were not consistent with your position (see Schiff, for example),
and perhaps colored by the a priori bias you arrived at for reasons
that remain obscure.
Message #3: Nov. 3, 1998
From: Judith Rich Harris
To: Jerome Kagan
Let me begin with your assertion that I reviewed the
literature selectively on the basis of my a priori bias.
Five years ago, my bias was the same as yours: I too was a
believer in the nurture assumption. Up to that point I had focused
on the literature of developmental psychology. The change in my
thinking came after I read more widely in psychology and
anthropology, in preparation for writing another textbook. It gave
me a bird's-eye view of the field. Sometimes things can be seen from
a middle distance that aren't visible from close up. I've noticed
that psychologists who are not focused on a single area but who are
able to see the bigger picture -- writers of introductory textbooks,
for instance -- tend to be more receptive to my ideas.
Yes, there are behavioral differences between Mexican
children and New England children. No, I wasn't going to claim that
they are due to heredity. But surely you're not implying that you
would object to such a claim, in view of the fact that you've
attributed the behavioral differences between Chinese babies and
Irish babies to differences in heredity!
You're way ahead of most developmentalists, Jerry, in your
willingness to admit that genes play a role in how children behave.
But even developmentalists who are willing to admit it are strangely
reluctant to admit that, since children inherit their genes from
their parents, genes can produce resemblances between children and
That study you mentioned from the August 1998 issue of Child
Development? There are hundreds like it. The method provides no way
of controlling for the effects of heredity. When researchers do use
the appropriate controls, heredity is always found to make a
contribution. Therefore it is scientifically indefensible to go on
doing research that provides no way of controlling for these
effects. The study also provided no way of separating the effects of
the parents' child-rearing style on the child from the effects of
the child on the parents' child-rearing style, even though we know
that the parents' behavior is partly a response to the child's
Nevertheless, this study did produce an interesting result:
No differences were found between children who entered day care in
early infancy and those who spent their first three years at home.
Which brings me to what you said about correlations. I never claimed
that correlations are "no basis for inferring anything important": I
said they are ambiguous. If you find that two things tend to go
together, you don't know what caused that correlation. You need
additional information to explain it. But if you discover that two
things are not correlated, you've learned something. If the amount
of time children are cared for by people other than their parents is
unrelated to the children's behavior and adjustment, that tells us
something important, doesn't it? Doesn't it tell us that a lot of
the advice being given to parents is hogwash?
The differences between adopted children reared in
middle-class homes and those reared in working-class homes do show
up in studies that control for heredity (see Capron and Duyme in
Nature, Aug. 17, 1989). But you were going well beyond the data
when you said, "The differences in cognitive skills had to be due to the
family practices and not to genes." There is a third alternative you
haven't considered: They could be cultural differences, like the
difference between the Mexican kids and the ones from New England.
When children reared by middle-class parents live in
middle-class neighborhoods and go to middle-class schools -- which is
almost always the case -- you can't tell whether the effect on their
cognitive skills is due to the home environment or to the
environment outside the home. The problem is that the two
environments match. You have to look at cases where they don't match
to see what's really going on. You have to look at cases where the
parents' culture differs from that of most of the other families in
I describe many such cases in my book. The children of
immigrants: They adopt the language and culture of their peers. The
hearing children of deaf parents: They adopt the language and social
behavior of the hearing culture, not those of the deaf culture. Kids
from fatherless, low-income families who live in middle-class
neighborhoods are as unaggressive as their middle-class peers,
whereas kids from similar families living in low-income
neighborhoods are highly aggressive (see Child Development, April
1995). When there is a cultural discrepancy between the home and the
neighborhood, the child starts out with the home culture and ends up
with the neighborhood culture. But in most cases there is no
discrepancy between them, and no need to change. Almost all your
data come from those uninformative cases.
The idea that parents have important and lasting effects on
their children -- is it universal? No. See Chapter 5 of my book. But
even if it were universal, would that make it true? Didn't everyone
used to believe that the Earth was flat?
One of our problems is that you seem to think of the study of
children as art or literature, and I think of it as a science. You
talk about what people say in their autobiographies and what they
tell pollsters who ask, "Do parents matter?" I happen not to believe
that we can answer scientific questions by means of public opinion
Message #4: Nov. 9, 1998
From: Jerome Kagan
To: Judith Rich Harris
Your last reply makes two points. The first is that a child's
heredity always makes a contribution to his or her behavior and
mood. The second claim is that similar neighborhoods usually produce
similar psychological profiles because of interactions with peers.
Both of these claims are broad and remain premises rather than
proven facts once one specifies particular profiles. Each is an idea
to be tested empirically. I now deal with each of the claims in turn.
The bold proposition that heredity always makes a
contribution to a child's psychological profile is as general and,
therefore, as empty of significant meaning as the statement that
environments always make a contribution to a child's profile.
Therefore, your demand that all investigators who study the role of
the environment must control for a child's heredity invites the
equally reasonable suggestion that all investigators who study the
role of heredity must measure the child's environments. As you know,
behavioral geneticists do not do so. No report describing the
influence of heredity on any psychological trait, whether it be IQ
or a personality characteristic, has directly measured the
psychological environments of the subjects over the first dozen
years of life. The complex influences of the environment are
inferred from an equation called the heritability equation. But
these inferences are not accurate for, as you know, the equation
that estimates the heritability of a trait contains terms not only
for genes and environment but also for the interaction of genes with
environment and the influence of all the background genes possessed
by a particular individual. This process is given the technical name
epistasis. Neither of the latter two influences is awarded a
reasonable value in the current heritability equations.
Thus, we have a situation in which the equation that
estimates the heritability of a trait has four separate terms:
genes, environment, interaction of genes and environment, and
epistasis, but the latter three are never directly measured, leaving
us with unknowns for three of the four terms. For that reason, all
current estimates of the heritability of any psychological trait
must be suspect.
Equally relevant is the fact that most studies of the
heritability of personality traits in children are based on parental
report, and in adults on information from self-report using
questionnaires. In the few cases where actual observations of
children were made, a paradoxical result occurred. When mothers
describe their children's degree of shyness on a questionnaire,
estimates of the heritability of shyness increase with age. However,
when actual observations of children are made, estimates of the
heritability of shyness go down with age. Every conclusion
concerning the magnitude of heredity's influence is limited in
significance for it depends always on the source of the evidence.
One finding on fruit flies should motivate reflection among
those who claim that genes exert profound influences on personality.
A pair of alleles in fruit flies produce abnormal wings in offspring
if the two parents possess the genes for this anatomical anomaly.
But this result only occurs if the flies are reared in a laboratory
where the temperature is about 20 degrees Centigrade. If the
temperature of the laboratory is raised by only 10 degrees, the
offspring develop almost normal wings. If a difference of 10 degrees
in room temperature can influence a significant anatomical feature
of a fruit fly, surely children's personality traits, which are
controlled by a much larger number of genes, must be influenced, in
a major way, by the environments in which they are reared. (See W.J.
Keaton and J.L. Gould, 1993, Biological Science.) Listen to a
leading behavioral biologist, Gilbert Gottlieb who writes in the
recent edition of the Handbook of Child Psychology, "When
there is heredity-environment interaction, the degree of apparent
heritability of some characteristic depends on the specific rearing
This means that every study you cite and interpret as showing
the influence of genes is seriously dependent on the rearing
environments of the individuals. The vast majority of studies of the
heritability of personality are conducted on middle-class, white
children and adolescents, and we have no idea of the magnitude of
heritability of any trait in other groups, for example, economically
disadvantaged Vietnamese immigrant children or children from elite
families living in Kuwait. Your book is written as if you do not
appreciate that the heritability of any trait can never be a fixed
quality; it is always at the mercy of the rearing environment.
Finally, the estimates of heritability you quote assume that
the effects of genes and environments are additive. For readers who
are not familiar with this idea, it means that the distribution of a
particular trait, say children's verbal ability, can be predicted by
assuming that the influence of the genes for verbal skill are added
to the influence of environmental supports for verbal ability.
This assumption raises a serious problem because most
biological characteristics are not additive. For example, the
electroencephalogram profiles of identical and fraternal twins are
best explained as the result of an interaction among the person's
genes (epistasis) rather than by assuming that genetic and
environmental forces combine additively. (See J.C. Christian, et
al., 1996, Psychophysiology, 33: 584-591.) Even the simpler
phenomena we call "size of a snowfall" is not predicted very well by
adding the influence of the temperature to the influence of
Thus, your evaluation of the power of genes to influence a
child's personality is permissive and not sufficiently
Your second claim is that neighborhoods play an important
role in children's development. I found this conclusion surprising
for I know of no study that has shown, for example, that half of
children living in the same neighborhood are essentially similar in
their perceptual, memorial, and verbal abilities or in the
constellation of personality traits. Consider as a thought
experiment a single block on East 75th Street in Manhattan, where
children from different cultural backgrounds live in the same small
area. If you sampled 100, 15-year-olds on that block, you would find
extraordinary variability in any psychological trait you decided to
There is a study that supports this hypothetical thought
experiment. Most of Warsaw was destroyed by bombs during World War
II. When the city was rebuilt after the war, authorities decided
that families with different educational and vocational backgrounds
should live in the same apartment houses so that their children
would play on the same playgrounds and attend the same schools. Your
position suggests that these children should be very similar in
their abilities. But the data revealed a great deal of variability
in cognitive qualities, and this variability could be attributed to
the values of their families. The children's intellectual talents
were a function of their family's influence, not of the peers with
whom they interacted everyday.
You state on Page 317 of your book that we do not know why
children who are abused by their parents often grow up with
psychological problems. You note correctly that this outcome could
be due to parental treatment, parental personality, genes, or peers.
Your conclusion is correct not only for the outcomes of abuse but
also for every trait and talent that psychologists study. We simply
do not know the differential contribution of the varied influences
that can affect a particular profile. The proper posture to this
frustrating state of affairs is reflection and reserve, and not your
opening statement in the preface that claims boldly that you wished
to dissuade readers of the notion that a child's psychological
profile is shaped by parents. It is hard for me to understand how
you can be so certain of the minimal influence of parents when you
acknowledge on Page 317 that scientists don't know why parental
abuse is likely to produce problems in adolescence. Let me be clear:
No one, whether a scientist or an educated citizen, understands the
complex ways in which genes, prenatal effects, family practices,
parental personality, children's interpretations of their
environments, historical era, size of city and, yes, even peers come
together to produce any psychological trait. Under these conditions,
every scholar should resist temptation to cry, "Fire!"
Message #5: Nov. 18, 1998
From: Judith Rich Harris
To: Jerome Kagan
OK, you've made your point -- I'm sorry I accused you of being
unscientific. But is this the place to talk about epistasis and the
wing anomalies of fruit flies? Why don't we save the technicalities
for a specialized journal, where I'd be happy to go on debating you
till the last fruit fly wears out its telomeres.
Better still, I could find you a behavioral geneticist to
argue with. This is not my quarrel. My interest is not primarily in
heredity. I'm interested in the environment -- in how the child's
environment shapes the child. It was you, not I, who wrote an entire
book on inborn differences in temperament. "Thus," you said in it,
"inhibited and uninhibited behaviors are heritable" (Galen's
Prophecy, Page 168). The reason I didn't bother explaining that
heritability depends upon the population measured is that it's not
relevant: My book is not about heritability.
Heredity concerns me mainly in a negative way: I want to
control or eliminate its effects, the better to judge the effects
of the environment. My point was that the studies you use to support
your position, including the one from the August 1998 issue of Child
Development that you mentioned in your first posting, use methods
that cannot disentangle the effects of heredity and environment.
You don't have to take my word for it: The authors of that study
admitted it themselves! (See Page 1,168 of that article.)
Nor is it enough to disentangle genetic effects from
environmental ones: We also need to disentangle environmental
influences from each other. That often isn't done either. You
needled me for admitting, on Page 317 of my book, that we don't
know why children who are abused by their parents grow up with
psychological problems. But the reason we don't know is that
researchers haven't done the work: They haven't separated the
effects of parental abuse from other environmental factors. For
example, children who are physically abused by their parents are
often treated badly by their peers as well, because risk factors
that increase the chances that a child will become a victim in the
home -- slow development, a difficult disposition -- also increase the
chances that he or she will become a victim on the playground. When
this unfortunate individual ends up with psychological problems,
psychologists assume that the parental abuse was to blame. No one
has bothered to find out whether being picked on or rejected by
peers might actually be a better predictor. It's simply taken for
granted that what happens at home must matter more.
What really disappoints me is the evidence that, even though
you've been attacking my book for two months now, you still haven't
looked at more than a few odd pages here and there. People who've
read the book tell me they found it very interesting -- even fun.
The Nurture Assumption is about how evolution shaped the human mind
and how the child's mind, as a result of that evolutionary history, is
predisposed to conceptually divide people into categories -- male/female,
kid/grown-up, good reader/bad reader -- and to put the self into one
of the categories. "Self-categorization," Australian social
psychologist John Turner calls it. Children identify not with their
parents but with a group of people they see as being "like me."
Under ordinary conditions they don't see a grown-up as being "like
me" because grown-ups are in a different social category, with
different rules of behavior. Identification with a parent is real
but comes much later -- it doesn't happen until the offspring can
plausibly be included in the same social category as the parent. The
embarrassment children feel when their parents don't measure up is
not due to identification, at least not in the sense you mean. It's
the same embarrassment they feel when they have to go to school
carrying a Mickey Mouse lunchbox when everyone else has a Lion King
I never said that peer groups homogenize their members.
Groups make their members more alike in some ways but also act to
widen the differences among them. Of course living in the same
neighborhood doesn't turn children into little clones -- neither does
living in the same family!
My theory of child development is new, speculative, and
largely untested. But it does a good job of explaining a lot of
annoying little things that don't fit into traditional theories.
It explains why only children, who bear the full brunt of their
parents' attention, do not differ in personality from children with
siblings. Why generations of upper-class British boys, reared by
nannies and sent to boarding schools at the age of 8, turned out so
much like their fathers. Why girls and boys behave as differently in
egalitarian societies as in sexist ones, and why these differences
show up in some situations and not in others. Why well-behaved
children become rebels in their teens and then solid citizens in
adulthood. And why the children of immigrants end up with the
language and accent of their peers, not of their parents -- and not
something in between, either.
Yes, my theory is still speculative: It has not been proved.
But what you are attacking me for is not my theory. What you are
attacking me for -- the assertion that parents have little or no
long-term influence on the personality, intelligence, or mental
health of their children -- is not new, is not mine, and is not
speculative. It is firmly grounded in evidence. The evidence is of
many different kinds and has been accumulating for nearly 20 years.
It indicates that, across a wide range of households, variations
from one household to another -- including variations in how the
parents rear their children -- have no measurable effects on how the
children turn out.
I am by no means the first to point out the implications of
these findings -- see David C. Rowe's excellent book, The Limits of
Family Influence -- nor will I be the last. David Cohen, a University
of Texas professor with a background in clinical psychology, is
currently putting the finishing touches on a book called Stranger
in the Nest: Do Parents Really Shape Their Child's Personality,
Intelligence, or Character?
Stopping me -- telling people that I don't know what I'm
talking about -- will not help your cause. This is not a leak that can
be plugged: It's the beginning of a deluge. I know this must be
upsetting to someone who has put in 45 years laboring under what has
turned out to be a false premise. I don't blame you for being mad at
me. But killing the messenger will not stop the message.
What I'm really shouting is not "Fire!" -- it's "Hey, the
emperor isn't wearing any clothes!" If that message sounds to you
like "Fire!" it's not surprising. After all, Jerry, you're one of
Message #6: Nov. 21, 1998
From: Jerome Kagan
To: Judith Rich Harris
I was a bit saddened by the ad hominem tone of your last
reply. I accepted the invitation from Slate because I believed you
came to a mistaken conclusion, despite honest intentions.
I have only three brief points to make in this final reply.
First, I continue to believe that you selected the evidence and
ignored the data inconsistent with your premise. Each year's
literature provides ample support for the effect of family experience.
The November 1998 issue of Developmental Psychology has
two papers (Pages 1,233 to 1,245 and 1,450 to 1,458) pointing to the
significant influence of parental behavior on children and youth.
Second, you argued that peers play a major role in sculpting
significant personality traits (e.g., introversion, sociability,
impulsivity, conscientiousness, and others). I know of no study that
has shown this claim to be true. Peers influence dress code, musical
tastes, and dialect but not major personality profiles. And as I
indicated in an early reply, peers do not exert power until the
child is 6 or 7 years old.
Finally, you acknowledge on Page 361 of your book a premise
held by a majority of developmental scholars; namely, most of the
information children process and store is unconscious. The problem
for you is that almost all the studies you cite did not measure
these unconscious structures, which include the shame and pride
children carry with them because of the emotional identification
with parents. You write, "The bond between parent and child lasts a
lifetime." You add, to my surprise, the suggestion that readers not
blame their parents for their personality profile. I agree. But it
does not follow from a restraint on ascribing blame to family that
the family had no influence. Of course, adults should not blame
their parents because, in most cases, parents did the best they
could. The ethical imperative to accept oneself is independent of
the scientific fact that families sculpt part of the adult profile.
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