What researchers now can tell us with increasing certainty is just how the brain adapts physically to this threatening environment-how abuse, poverty, neglect or sensory deprivation can reset the brain's chemistry in ways that make some genetically vulnerable children more prone to violence.

Scientists also have found that aggression genes, those that raise a person's propensity for violence, may be passed on to new generations. Some researchers believe that the increase in female criminal violence since the 1950s may be an early sign of how the genes of violence already are building up in the population.

At the University of Illinois Medical School on Chicago's West Side, researchers are examining the blood of children for low serotonin levels. They know from an earlier study that these children are likely to grow up to be troublemakers and they want to find out why.