The nature of nurturing

A new study finds that how parents treat a child can shape which of his genes turn on.

Since people, not to mention families, are so infernally complicated, consider the rat. As soon as their wriggly little pups are born, rat mothers lick and groom them, but like mothers of other species they vary in getting every one of their offspring’s hairs in place. Pups whose mothers treat them like living lollipops grow up different from pups of less devoted mothers: particular genes in the pups brains are turned on “high”. These brain genes play a pivotal role in behavior. With genes turned up full blast, the rats churn out fewer stress hormones and, as adults, are more resistant to stress. These rats don’t startle as easily, are less fearful in the face of novel situations and braver when they have to explore an open field. In rats whose mothers did not lick them so much, the brain genes are not turned up so high (though they are very much present), and the pups grow up to be jumpy, angst-ridden and stressed-out. All because of how much Mom licked and groomed them.

Thanks to the experiments like these, the age-old nature-nurture controversy – is the person we become shaped more by the genes we inherit from our parents, or by our life experiences? – is growing up. Now the consensus is that we are shaped by both nature and nurture, also known as heredity and environment. An ambitious study of 720 pairs of adolescents with different degrees of genetic relatedness (from identical twins to step-siblings) reconciles nature and nurture by explaining how genetic tendencies are encouraged, or stifled, by specific parental responses. “Biology is not destiny”, psychologist David Reiss of George Washington University writes in the new book “the Relationship Code”, which describes his 12-year old study. “Many genetic factors, powerful as they may be in psychological development, exert their influence only through the good offices of their family.” And that means that how parents raise their children actually does matter.

To understand why, take a trait like shyness, which seems to be partly heritable. But it is not heritable the way, say, eye color is. If parents pamper and overprotect a shy toddler, she will probably remain shy; if they encourage, even force, her into spending time with other tykes, she has a good chance of overcoming it. Exactly how these different parental responses encourage or suppress, at the molecular level, genes that predispose for shyness remains a great unknown. But the general message is clear: gene expression is not foreordained. To have any effect, genes must be turned on. Whether, and how strongly, genes that underlie complex behaviors are turned on depends on the interaction and relationships a child has with the important people in his or her life.

Any new parent can see that children are born with innate temperaments. These traits - cuddly or cold, cranky or calm – “cause their parents… to respond to them in a certain way”, says Reiss. If a baby is unresponsive, most parents show her less affection; if the child is a holy terror, most parents scream, punish, hit or otherwise lash out. These very responses determine whether the gene underlying the trait is expressed or silenced, turned up or turned down. Genetic factors initiate a sequence of influences on development, but certain social processes are critical for the expression of these genetic influences.

With a problem kid, who is perpetually disobeying, acting out, threatening, hitting, parents typically meet threat with threat, violence with violence and coercion with coercion. That is likely to exaggerate the child’s innate proclivities and even increase the chances that will become seriously antisocial and even criminal. Kids with difficult temperament can be managed and set on a good course, or their innate tendencies can be magnified by the family and catapulted into conduct disorder. This is a concrete, testable model of how genes and environment interact.

A highly verbal toddler will likely elicit hour after hour of reading from her parents; that probably stimulates her innate cognitive tendencies. Later, she also develops self-confidence in her academic abilities, seeks out challenges and gains a reputation as a studious, bright kid.

Figuring out which environments turn up a gene and which turn it down is like trying to match the right soil to a delicate flower, only harder. Still, scientists have identified some links. Besides intellectual achievement, genetic factors seem to influence the first stirring of sociability and antisocial behavior. These glimmerings typically evoke parental responses that reinforce the nascent trait. A child with a difficult temperament – irritability, aggressiveness – brings on parents’ harsh discipline, verbal abuse, hostility and relentless criticism. That seems to exacerbate the child’s innate bad side, which only makes parents even more negative, on and on in a vicious cycle, until the adolescent loses all sense of responsibility and academic focus. Heritable characteristics of the child shape the level of parental hostility toward that child. Parent hostility then intensifies the child’s characteristics, making antisocial behavior more likely. But a social baby brings out a mother’s affection and encouragement, which reinforce those initial tendencies toward sociability.

If this explanation of how children develop is correct, it offers hope that with appropriate parenting, a child’s sociability sense of responsibility and cognitive development will bloom, and his tendency to antisocial behavior, academic failure and emotional problems plummet.

Reading and reading to a child who shows little interest, cuddling a baby who doesn’t cuddle back – won’t come easy. But it can happen.

Bill Chleeve

/ From Newsweek, Dec 12, 2001/

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