The Nurture Assumption by Judith Rich Harris (1998, New
York: The Free Press) is about the transmission of language,
culture, and personality from one generation to the next, but my
review will be limited to the transmission of personality. Harris's
four main points are:
1. Half of adult personality is determined by heredity.
2. The other half of adult personality is determined by the
child's peer group.
3. The percent of adult personality determined by parenting is
zero, zilch, none, nada.
4. Behavior that develops within the family, remains within the
family; it does not generalize to non-family relationships.
Half of adult personality is determined by heredity.
Here Harris is on firm scientific grounds. She cites
behavioral genetic research to support this point, explaining that
some of the effects of heredity are the direct expression of our
genes, and the rest is indirect: people treat us in certain ways due
to our genetic endowment. Cute babies receive more attention and
affection than babies who are cuteness-challenged.
The percent of adult personality determined by parenting is
Harris is so insistent about this point that one gets the
impression she would have made the percent even lower if that were
mathematically possible. Harris correctly rejects most of the
personality development research because it confounds heredity with
parenting. If parents who behave a certain way have children who
behave a certain way, this does not mean that the parental behavior
was the cause of the child's behavior. For example, if strict
parents have rebellious children, this does not mean that parental
strictness caused the children to rebel. It could be that
rebellious children cause their parents to become stricter. Or a
third factor, such as heredity, could have caused both the parental
strictness and the children's rebellion.
In order to study parental behavior as the cause of children's
adult personality, researchers must separate heredity from
parenting. This can be accomplished by studying identical twins who
were adopted and reared in different families. And these studies
support Harris's view: identical twins reared together are no more
similar than identical twins reared apart. In addition, adopted
siblings reared in the same family are no more alike than adopted
siblings reared separately. Finally, researchers have failed to
find any parenting variable that is consistently associated with any
aspect of the child's adult personality.
Failing to find significance does not prove the null
Just because researchers have not yet found any causal relationship
between parenting and children's adult personality, does not mean
that none exists. It is quite possible that the relationship is
just too complex to be detected by the typical research
Research studies tend to look for one parenting variable that is
causally related to one personality variable. But clinicians have
long assumed that a parenting variable, such as strict parenting,
can have different effects on different children. Strict parenting
may have no effect on some children, while causing others to become
either rebellious or compliant. If this is true, strict parents
will have children who are either rebellious or compliant or
neither, and if we measured average compliance among the children of
strict parents, we would find no difference between them and the
children of lenient parents. Harris does consider this possibility,
but dismisses it as "unpredictable" and therefore useless.
This type of complex causal relationship may be unpredictable at
present, but perhaps we just do not understand the mediating
variables which determine whether strict parenting will lead to
rebellious children, compliant children, or neither. Or perhaps
there are five mediating variables whose interaction determines the
relationship between strict parenting and the child's adult
personality. Our current research designs are just not complex
enough to detect five-way interactions.
The other half of adult personality is determined by the child's
Harris calls her theory "group socialization theory."
Her view is that as children grow up, they socialize themselves,
largely in order to conform to their peer group, but somewhat to
maintain their individual role within the peer group. Harris
briefly mentions, but does not emphasize, the fact that children
gravitate toward certain peer groups and away from others. If a
child becomes part of the academic group at his or her school
instead of the athletic or the drug group, this could be due to
either heredity or parental influence. So we do not know to what
extent peer group membership is a cause of personality
characteristics rather than a result of heredity or parental
influence. Harris presents a great deal of anecdotal evidence that
language and culture are transmitted to the child from the child's
peer group, but the amount of research she cites supporting her
theory is zero, zilch, none, nada.
Implications for psychodynamic theory.
Psychodynamic therapists have long assumed that an individual's
personality structure is largely determined by that individual's
childhood relationship with his or her parents, especially the
mother. Many psychodynamic theorists have become rich and famous by
attributing adult personality to toilet training, mother-infant
bonding, infant-parent attachment, good enough mothering, parental
empathy, separation-individuation, etc. Virtually all psychodynamic
therapists accept the "blame the mother" view of adult
neurosis, and the general public has enthusiastically embraced this
concept. Harris convincingly rejects the research purporting to
demonstrate the effects of parenting on adult personality, but I
doubt that her analysis will cause any psychodynamic clinicians to
modify or even re-evaluate their views.
Implications for clinical practice.
From a clinical perspective, it really doesn't matter if parenting
causes adult neurosis. If this belief helps the patient feel less
guilty, no harm is done. If this type of explanation helps patients
feel that their lives make sense, this is all to the good. Many
patients have a deeply ingrained belief that their neurosis was
caused by their parents. There is little value in challenging this
belief so long as we tell our patients "Your parents may be
responsible for causing your problems, but you are responsible for
What parents can do.
Harris maintains that the following endeavors will have no effect
on your child's adult personality: letting your baby cry, not
letting your baby cry, sleeping with your baby, not sleeping with
your baby, reading to your child, building up your child's
self-esteem, not even spending "quality" time with your
child. Although Harris argues that parents have no influence over
their child's personality, language, or culture, she suggests that
there are two steps parents can take to help their children. First
of all, parents can live in a neighborhood and have their child
attend a school where the peer group will be a constructive rather
than a destructive influence. Secondly, parents can have a good
relationship with their children. Harris is a strict believer in
what Walter Mischel called "situation specific behavior."
That is, people behave differently in different situations. Having
a good relationship with your children may not affect their
personality, or increase their self-esteem, or improve their
relationships with anyone else, but at least one part of their lives
will turn out well: their relationship with you.
Summary and conclusions.
Harris reviews the behavioral genetic research indicating that
about half of adult personality is determined by heredity. But what
about the other half? Her major contribution is her demonstration
that there is no research support for any theory suggesting that any
type of parenting is a cause of any aspect of the child's adult
personality. Her second contribution is her theory that the child's
peer group, particularly those peers a little older and a little
higher in status, determine the other half of the child's adult
personality. However, there is no more scientific evidence for
Harris's theory than there is for the theory that parenting is the
critical determinant of adult personality. We just do not know what
determines the other half of adult personality. It could be
parental influence, or peer influence, or an interaction between
parental influence and peer influence, or an interaction between
parental influence and heredity, or an interaction between peer
influence and heredity, or a three-way interaction, or, more likely,
all of the above.
Milton Spett, Ph.D., is a licensed psychologist with a private
practice in Cranford, New Jersey.