On smoking: 'The best predictor of whether a teenager will become a smoker is whether her friends smoke. This is a better predictor than whether her parents smoke.'

"Intervention" studies --where a scientist gets a parent to act differently--also undercut Harris. "These show that if you change the behavior of the parents you change the behavior of the kids, with effects outside the home," says John Gottman of the University of Washington. Programs that teach parents how to deal with little monsters produce effects that last for years. "When parents learn how to talk to and listen to kids with the worst aggression and behavior problems, and to deal with the kids' emotions," says Gottman, "the kid becomes less impulsive, less aggressive, and does better in school." Maybe such effects aren't picked up in the studies Harris cites because such motivated--dare we say saintly?--parents are so rare. Gottman studies children at the age of 4, and then at 8. Some have parents who learned to be good "emotion coaches." They're sensitive, they validate the child's emotion ("I understand, sweetie"), they help her verbalize what she's feeling, they patiently involve her in solving the problem ("What should we do?"). Other parents didn't learn these tough skills. The 8-year-olds of emotionally adept parents can focus their attention better and relate better to other kids. "There is a very strong relationship between parenting style and the social competence of their children," says Gottman. Since the parents learned to be emotion coaches, and the kids changed over the years, the result cannot be easily dismissed as genetic (emotionally intelligent parents pass on emotional-IQ genes).

Critics also slam Harris's interpretation of twins studies. From this research she concludes that "parents do not make siblings any more alike than their genes already made them... [P]arenting has no influence." But some of the leaders in the field say their measurements cannot support that. "The sample sizes we use are so small that you can't detect a 10 percent or even a 20 percent effect of the family environment," says Dr. Kenneth Kendler of the Medical College of Virginia. And as Kagan points out, the vast majority of such studies rely on questionnaires to assess personality, recollections of childhood and descriptions of what goes on in the home. "Questionnaires are totally suspect," Kagan says. "The correlation between reality and what people say is just 30 or 40 percent." Such flaws could be why twins studies fail to detect an influence of parents on kids.

Finally, some researchers take issue with Harris's logic. This one is tricky, but crucial. Harris says studies of twins and siblings find no effect of "shared environment." True. But even children who grow up with the same parents do not have an identical environment. The firstborn does not have the same "environment" as her baby brother: she has younger, less experienced parents, and no midget competitors. Also, parents treat children differently, as Harris admits: she monitored Elaine's homework but not Nomi's. Children, through their innate temperament, elicit different behaviors from their parents; thus they do not share this environment called "parents." Parents, then, arguably belong in the category called "unshared environment"--which behavioral genetics suggests accounts for about half the differences among people. And besides, even what seems like an identical parenting style may be received differently by different children . One may conform, the other rebel. That does not mean that parents did not influence what their children became. It means that we are not smart enough to figure out how parents shape their child. Says psychologist Theodore Wachs of Purdue University, "The data do show that the same [parenting] does not have the same effect on kids. But that doesn't mean there is no effect."

In person, Harris backs off a bit from her absolutist stance. "I do think there is something to the possibility that parents determine their child's peer group, and children do learn things at home which they take to the peer group," she told NEWSWEEK. She allows that children can retain many of the values and other lessons parents teach despite peer influences. "If the group doesn't care about plans for the future, then the child can retain those ideas from home," she says. "And if things like an interior life aren't discussed by peers, then that wouldn't be affected by the group either." Might different children experience the same parenting differently, and be influenced by it? Harris pauses a few seconds. "I can't eliminate that as a possibility," she says. As for her own daughter, yes, Elaine was a handful and a heartache. But she is now married, a mother and a nurse in New Jersey--and close to her parents.

If "The Nurture Assumption" acts as a corrective to the hectoring message of so many books on child rearing, then it will have served a noble function. It lands at a time when many parents are terrified that failing to lock eyes with their newborn or not playing Mozart in the nursery or--God forbid--losing it when their kid misbehaves will ruin him for life. One of Harris's "primary motivations for writing the book," she says in an e-mail, was "to lighten the burden of guilt and blame placed on the parents of 'problem' children." Her timing is perfect: millions of baby boomers, having blamed Mom and Dad for all that ails them, can now be absolved of blame for how their own children turn out. Harris is already receiving their thanks. As one mother wrote, "We parents of the difficult children need all the support and understanding we can get." Clearly, the idea that actions have consequences, that behavior matters and that there is such a thing as personal responsibility to those who trust you is fighting for its life. Near the end of "The Nurture Assumption," Harris bemoans the "tendency to carry things to extremes, to push ideas beyond their logical limits." Everyone who cares about children can only hope that readers bring the same skepticism.

— With Erika Check