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NJ-ACT Newsletter, Special Book Review Supplement
March 1999

(published by the New Jersey Association of Cognitive-Behavioral Therapists)

Copyright 1999 by Milton C. Spett.
Posted with the author's permission.

Is It True That Parenting Has No Influence
On Children's Adult Personalities?

A Review of Judith Rich Harris's The Nurture Assumption.

By Milton Spett

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 zero.
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 hypothesis.
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 design. 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 peer group.
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 resolving them."

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.

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