Why kids turn out the way they do

If there is one thing experts on child development agree on, it is that kids learn best when they are allowed to make mistakes and feel the consequences.

So Mom and Dad hold back as their toddler tries again and again to cram a round peg into a square hole. They feel her pain as playmates shun her for being pushy, hoping she'll learn to back off. They let their teen stay up too late before a test, hoping a dismal grade will teach her to get a good night's sleep but believing that ordering her to get to bed right now will not: kids who experience setbacks rather than having them short-circuited by a controlling parent learn not to repeat the dumb behavior.

But not, it seems, all kids. In about 30 percent, the coils of their DNA carry a glitch, one that leaves their brains with few dopamine receptors, molecules that act as docking ports for one of the neurochemicals that carry our thoughts and emotions. A paucity of dopamine receptors is linked to an inability to avoid self-destructive behavior such as illicit drug use. But the effects spill beyond such extremes. Children with the genetic variant are unable to learn from mistakes. No matter how many tests they blow by partying the night before, the lesson just doesn't sink in.

The discovery, reported last December, is part of what is fast becoming the newest frontier in studies of why children turn out as they do. Since the first advice book for American parents appeared in 1811, the child-rearing industry, as well as researchers who have made child development a science, have assumed that, although every child is an individual, there are certain universals. If parents are too take-charge about homework, the child becomes disengaged and eventually gives up; if they are warm and affectionate, kids don't act out. But while most children do respond the way research shows, there have always been "outliers," kids who don't turn out the way experts promise.

After years of ignoring those children, a few scientists now realize that they are telling us something that promises to revolutionize our understanding of child development. In an echo of "personalized medicine" (matching drugs to people's DNA), scientists are finding that how parents treat their children is filtered through the prism of DNA.

Parents may intuit that, as they notice that what worked with one child is failing abysmally with another, but now science is pinpointing exactly what combinations of nature and nurture spell gridlock. It is finally dawning on experts that "individual genetic differences are the 800-pound gorilla of child development," says Jack Shonkoff, director of the Center on the Developing Child at Harvard University. "The promise of genomics is that you will be able to tailor experiences as we tailor drugs."

Research showing that the most scientifically rigorous child-rearing advice can blow up on you couldn't come at a worse time for the millions of American parents who are desperate for direction. They are gobbling up how-to books and DVDs, even hiring coaches and consultants.

More than earlier generations, new parents are panicked that they're going to screw up. That feeling is fed by posts on Web sites such as www.UrbanBaby.com, in which someone, somewhere, can be counted on to flame your every parenting decision.

But for parents who look back in sadness - perplexed that although they did everything "right," their child is not as kind, or intelligent, or self-confident, or well adjusted as the recipes promised - the emerging science offers an explanation, and perhaps an out: with the DNA stacked against you, it wasn't your fault.

One of the strongest and most counterintuitive findings in this nascent field is that children with a sweet temperament, which is under strong genetic control, are the least likely to emulate their parents and absorb the lessons they teach, while fussy kids are the most likely to do so. Fussy children have a hypersensitive nervous system that is keenly attuned to its surroundings - including what Mom and Dad do and say.

In studies that are shaking up textbook dogmas, Jay Belsky of Birkbeck University of London has shown that fussy babies are therefore wired to be more strongly shaped by their parents than mellower children are. It is the fussy baby who, read to night after dutiful night, is likely to develop a love of books; the mellow baby, given the same literary diet, might just as easily grow into a teen who has no interest in reading anything longer than a text message.

Children who go with the flow of new people and new situations are like Teflon: good parenting doesn't stick to them - but neither, necessarily, does bad parenting. "You can get by with sloppier parenting if you have a 'good temperament' kid," Belsky says. Even children who fall between the extremes are generally closer to one than the other.

Although whether you have an easy or a fussy child is obvious, other innate differences that shape whether and how a child will respond to how parents raise them are less apparent.

But since they reflect the presence of a DNA variant, they are all candidates for being pinpointed with a genetic test that will help parents know what to expect.

Consider the gene variant that influences whether children learn from their mistakes. With the misspelled gene, brains have about 30 percent fewer dopamine receptors and less activity in the brain's frontal cortex (the site of higher-order thinking, including monitoring negative feedback) and hippocampus (memory) than do people with the more common form of the gene. In an experiment at the Max Planck Institute for Neurological Research in Germany, people with the misspelling weren't able to avoid choices that they were told over and over were incorrect. Numerous other studies have linked this gene variant to addiction, obesity and compulsive gambling, suggesting that the underlying problem is trouble learning the negative consequences of your actions.

Other DNA variants can protect children from bad parenting. For instance, most girls who are sexually abused are at higher risk for becoming alcoholics, as well as for developing other mental-health problems. But girls who have a "sluggish" version of the gene called MAOA seem to be vaccinated against this effect, reported scientists led by neurogeneticist David Goldman of the National Institute on Alcohol Abuse and Alcoholism last year. And children with a certain form of a gene called DRD4, which stands for dopamine-receptor D4, are Teflon-coated, at little to no risk of becoming emotionally insecure as a result of mothers who are emotionally distant, found a 2007 study.

The discoveries questioning the connection between what parents do and how children turn out has not exactly taken the science of child development by storm. That seems to reflect a culture clash within the field. Most researchers who study child development were trained as psychologists, and - to overgeneralize, but only a little - are uncomfortable with or even suspicious of genetics. Geneticists tend to see behavioral research as squishy, not hard science. That produces a body of scientific literature that is remarkably ignorant of genetics.

Since companies already offer storefront DNA tests, the day is not far off when parents can determine their child's MAOA or DRD4 status, or the presence of any other variant that influences the effect of parenting.

In her best-selling book "I Feel Bad About My Neck," Nora Ephron laments how American society "came to believe in the perfectibility of the child just as it also came to believe in the conflicting theory that virtually everything in human nature was genetic."

Both views - that everything is genetic and that parents can transform a child like a lump of clay - are as wrong as wrong can be.