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Natural born killers?


THROUGHOUT THE UNITED STATES, the media recount stories of senseless murders. An angry glance or curt response can snap hair-trigger tempers and send bullets flying. Violence is on the rise everywhere, experts say, but particularly among the young. The number of murders committed by children 14 to 17 years old has risen 165 percent since 1985, according to data from the American Association for Advancement of Science. Violent deaths (by either homicide or police intervention) among children 5 to 14 and among young adults 15 to 24 have risen threefold since the 1950s, according to the National Center for Health Statistics. "This generation of youth is far more violent than any other before it," says James Fox, dean of the College of Criminal Justice at Northeastern University. "They have much more deadly weapons in their hands, many more dangerous drugs in their bodies, and above all a much more casual attitude toward violence."

Somehow America's children are learning that violence is an acceptable way to solve problems. Researchers across the country are looking for ways to interrupt that learning process. Most agree that the trend toward more violence cannot be explained simply. A diverse group of factors--violence in the media, poor parenting practices, stresses on the family such as unemployment--produce people with shorter fuses and a bent toward aggressive behavior.

Now some scientists implicate biology as well. Studies of brain chemistry and heart physiology have shown that physical markers may flag children at risk. Because genetic and environmental effects are so tightly intertwined, it's difficult to say whether these markers reflect inherited traits or an adverse childhood, says Columbia researcher Daniel Pine. Animal studies suggest that both scenarios are possible.

Pine and Gail Wasserman, director of the Lowenstein Center, are following a group of 126 New York boys, ages 6 through 10, whose older siblings have had a run-in with the law. The researchers began by giving the boys a full medical workup and interviewing family members to gain insight into parenting practices. Pine and Wasserman then followed up with regular interviews to establish whether the boys were becoming more aggressive or antisocial. The researchers also kept track of biological factors such as heart rate reactivity (a measure of how the heart rate responds to a stress), blood pressure, and levels of the neurotransmitter serotonin.

Preliminary results show a correlation between increases in aggression and bad parenting. Three separate factors appear to be independent predictors of aggression: harsh discipline, low involvement with the child, and poor monitoring of a child's whereabouts.

Biological factors appear to mirror the environmental results. The more aggressive children tend to have more reactive hearts and higher resting blood pressures. With regards to serotonin, Pine says, the results are still too preliminary.

Other research, however, has shown a correlation between low serotonin and aggressive behavior, particularly in adults. Data on children are sparse, but a two-year study conducted by Markus Kruesi, director of the Institute for Juvenile Research at the University of Illinois, Chicago, found that among children diagnosed with disruptive behavior disorders, low serotonin predicted aggression.

Animal studies offer a clue to how both genetics and the environment can affect biology. At the National Institutes of Health,Steve Suomi studies how aggression develops in rhesus monkeys. These monkeys have a well-developed social hierarchy, which most respect. But a small portion of them--those born with low serotonin levels--never develop social skills as they grow up. Impulsive and aggressive, they are inevitably kicked out of the troop into a world where they have little chance of survival, Suomi says.

Aggressive monkeys aren't just born; they also can be made. Monkeys born with normally functioning serotonin systems, but reared badly, can end up both with low serotonin and aggressive tendencies.

None of these researchers claims that low serotonin causes aggressive behavior. "We know it's associated, but is it the cause?" Kruesi asks. "Or is it just something that appears together with aggressive behavior for some other reason, in the same way a scar marks rather than causes an injury?" The biological factors "may be a way station that will help us explain the relation between harsh rearing and antisocial behavior," Wasserman suggests.

Emil Coccaro, however, views serotonin as the culprit, possibly along with other neurotransmitters. In preliminary results from a study of 40 impulsive-aggressive adults, Coccaro has shown that treatment with fluoxetine, a drug that keeps serotonin levels high, can improve behavior.

This is because serotonin modulates the brain's response to external stimuli, says Coccaro, director of the clinical neuroscience research program at the Medical College of Pennsylvania and Hahnemann University. Normally, when something catches the attention of the brain, neurons begin to fire. Serotonin is an inhibitory neurotransmitter that helps attenuate this response, much like the brakes in a car. If the brakes are bad, there's nothing to prevent a crash.

But while biology may offer insight into how aggression develops, it is not the whole answer, cautions Leonard Eron of the Institute for Social Research at the University of Michigan. "Biology is important, but not every youngster born with these kinds of dispositions will turn out to be aggressive. Only a small minority do. The one who turned out to be aggressive learned to behave this way in order to maintain his or her status." Eron's study of upstate New York youth found that exposure to TV violence was an independent predictor of aggressive behavior later in life, whether or not the children were aggressive early on.

A marker that could locate children at higher risk, Eron allows, would be valuable--though "a lot of people might object to that kind of fingering." What society might do with such information is a separate question, with intriguing and perhaps ominous ramifications.

LINDA CARROLL is a free-lance science journalist whose writing has appeared in Medical Tribune, New York Newsday, and Earth. She is a 1992 graduate of the Columbia Graduate School of Journalism and has additional training in geophysics.

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