THE NURTURE ASSUMPTION: Why Children Turn Out the Way They Do. By Judith Rich Harris. Free Press. 462 pp. $26.

When I was in the hospital after my son was born in 1982, I could hear the hungry babies crying as they were being wheeled from the nursery to their mothers. But none of those wailing babies were ever ushered in to me. When James was brought in, he was invariably calm and collected, a self-possessed tiny person who seemed to bear little resemblance to my high-strung husband or myself. (We were both sure that we would have been loudly demanding our every meal.) He was his own man from day one.

I was so intrigued by the early signs of an infant's uniqueness that I soon wrote an article for McCall's titled "Babies Are Born Different." I reported the growing evidence that infants are not blank tablets on which parents inscribe their future personalities. They come premixed: shy or assertive, sensitive or thick-skinned, amiable or irritable. As most observant mothers know, kids are themselves, and a parent's influence is exerted by trying to work with a child's innate temperament, not by trying (futilely) to create a temperament to order.

This was widely known more than fifteen years ago. The importance of heredity in shaping human personality is no longer breaking news. The only debate is over degree: According to Judith Rich Harris, heredity accounts for about 50 percent of the variation in personality traits, while environment counts for the other half. Since genes are a given, the interesting question is what is going on in the environment that shapes human personality.

In The Nurture Assumption: Why Children Turn Out the Way They Do, Harris takes the extreme position that parental nurturing is not a significant part of a child's formative environment. She argues that the way parents treat their children has no lasting influence on their behavior or character or development.

This shocking assertion has enabled Harris to achieve the remarkable feat of attracting attention in the midst of the biggest sex scandal in American history. Her message has been heard above the din--but only because she and possibly her editors have framed it in the most sensational terms. The uproar over this book is a case of one down-market media controversy out-shouting another: Monicagate's "What should we tell our children?" interrupted by The Nurture Assumption's "Who gives a damn what you tell them? It doesn't matter."

Harris and President Clinton even share one salient characteristic: slipperiness. The politician offers an elastic definition of sex; the writer of textbooks in child psychology offers an elusive definition of nurturing. Buried in the fine print of The Nurture Assumption are so many caveats that the book's thesis virtually evaporates. Apparently Harris believes that parents don't matter, with these exceptions: (1) early relationships--up to the age of 4--are essential for brain development and normal social development, including the ability to form close relationships; (2) babies need familiar caregivers--parents or parent substitutes--in order to develop normally; (3) parents determine their child's neighborhood and peer group, and thereby permanently affect their future; (4) parents have the power to make childhood happy or miserable; and (5) parents inhabit our conscious minds, our thoughts and our memories all our lives. Oh, and providing a proper diet and healthcare are "not the sort of things this book is about."

In short, everything I thought I could and should do for my child turns out to be important after all. No parent should take this book, or the commentary on it, as a license to stop tracking.

These little details aside, The Nurture Assumption does make some valuable contributions to the endless squabbles over proper child- rearing. Harris is most persuasive in her careful demolition of the kinds of dumb studies that find correlations between such things as broccoli-eating and good health, or divorce and troubled children. This type of research can tell us nothing about causality. And she convincingly argues that socialization studies by Diana Baumrind and her followers on the effects of different child-rearing methods on development are largely worthless. This research indicates that parents who do a good job of managing their lives and getting along with others tend to have children who manage their lives well. Parents with problems in these areas tend to have kids with problems. Studies also consistently show that children who are treated with affection and respect have better personal relationships than children who are treated harshly.

But what does this prove? As Harris points out, it is entirely possible that "good" parents pass desirable traits on to their children and "bad" parents hand down undesirable characteristics. If so, heredity and not parental behavior can explain variance in outcomes. She also takes note of "child-to-parent" effects: the possibility that a pleasant or pretty child elicits benign treatment, and a difficult or homely child brings out a caregiver's worst qualities. A child, in other words, can produce a child-rearing approach, rather than simply being subjected to it.

Harris's heroes are the behavioral geneticists--such as Robert Plomin-- whose studies have shown that there are no predictable similarities between siblings raised in the same home, and incredible similarities between identical twins reared in very different homes. This is the work that has persuaded her that the "nurture assumption"--that parental nurturing is the most important part of a child's environment--is wrong. As she puts it, "There is evidence that parents cannot modify the personality their child was born with, at least not in ways that can be detected after the child grows up."

What does affect a child's personality and development, then, apart from his or her genes? What in a child's environment does matter, if parents don't? Harris's answer: peers. She calls this "group socialization theory"--the idea that children learn how to behave by identifying with a peer group and taking on its attitudes, behavior, speech and so on. The theory predicts "that children would develop into the same sort of adults if we left their lives outside the home unchanged--left them in their schools and their neighborhoods--but switched all the parents around."

Harris's argument rests so heavily on language-learning that her book might be more accurately titled The Primacy of Peers: How Language Acquisition Occurs in Children. Young children of deaf and immigrant parents quickly become fluent in the language of their peers, not of their parents, Harris points out. She also has fun with the story of a small boy whose parents in the thirties raised him with a chimpanzee "sister" for several months, in an experiment to see how human the chimp could become. The experiment ended abruptly after it became clear that the 19-month-old human was coming to resemble a chimp. (He had a vocabulary of three English words, and demanded food by grunting.)

Harris has told interviewers that one of her motives in downgrading parents' influence was to relieve the guilt and anxiety of parents who are not perfect, or whose children turn out less than perfectly. This is indeed a valuable contribution in an age when mothers, in particular, are blamed for neglect if they so much as work outside the home for a living. She summarizes studies that have punctured the burdensome myths that daycare is detrimental, that maternal employment or an unconventional family structure has any particular impact on child development and that divorce invariably damages children. She points out that the famous study of children of divorce by clinical psychologist Judith Wallerstein is "useless" because all of the families Wallerstein looked at were getting divorced and had sought counseling. Wallerstein had no control group and no way to screen out her professional biases. A massive and properly controlled study of children of divorce in Britain found only a slight difference between those children and children of intact families, a difference that could be accounted for by heredity, Harris points out. Fatherlessness has virtually no detectable ill effects, she writes, and why should it? For most of our history as a species, we had no way of even knowing who our fathers were.

A heightened awareness of the importance of peer groups could also lead to more effective social policy. If peers are what matters most to a child, then divorce arrangements that force children to leave a familiar group need to be re-examined. On the other hand, if the peer group is delinquent, then the best way to set a child straight is to move him into a new, law-abiding neighborhood. If teenagers tend to split into competing peer groups that negatively stereotype many kids--the nerds, the jocks, etc.--then educators need to devise ways to unify their classes.

But if parents can't be blamed for much of anything, then they can't claim any credit either. Unfortunately, The Nurture Assumption is symptomatic of a culture that utterly fails to recognize, respect or reward the difficult and essential work of raising children. Even if Harris is right that reasonably conscientious parents are essentially interchangeable, this does not mean that they are unnecessary. Peer groups are hardly likely to provide the steady guidance that young children, in particular, need. Harris's assertions could undermine support for the many promising early intervention programs that help at-risk children precisely by providing the consistent care that is normally supplied by a capable parent (the Perry Preschool Project in Michigan was one such example). Tellingly, her book makes no mention of such programs.

Harris ignores the economic value of a parent's work as well. Productive individuals in a dynamic capitalistic system have to be literate, well trained, self-starting and adaptable to change. Such people do not spring spontaneously from the soil or the playground; they have to be carefully cultivated, by relatively well-educated adults.

There is some evidence that the development of more intensive child- rearing practices has been essential to the rise of dynamic capitalism. Certainly, as capitalism has progressed, the role of mothers in child- rearing has actually intensified. Raising a child equipped to thrive in the modern economy is too important a task to be left to a slightly older sibling, a tired grandmother, a poorly educated babysitter or the neighborhood gang. Mothers have become so crucial to the process of raising productive individuals that economic development experts, including Treasury official Lawrence Summers, the former chief economist of the World Bank, are now convinced that the most efficient way to stimulate economic growth is to educate and empower mothers.

The omission of this critical economic piece of the child-rearing puzzle is a major fault. But there are other, deeper problems with Harris's thesis as well. I can't help thinking about the stories of young men brought down on the battlefield. Fallen among their comrades, members of one of the tightest peer groups ever invented, the wounded warriors cry out not for their buddies but for their mothers.