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Additional research published in Discover Magazine on genetic research has revealed that a specific stretch of DNA along a chromosome, if mutated, may produce violent behavior. The study of a family in which ten men over five generations displayed violent behavior has led geneticists to form specific causal links. It was noted that all violent family members were male, and the trait seemed to be passed from mother to son, suggesting that the trait for aggressive behavior may be carried one the single X chromosome of males. These same researchers found that all living males who were violent had the same genetic marker and so did some of the women in the family, who would be carriers of the defect. The non-violent men in the family were not found to have the genetic marker. Researchers suspect one gene that codes for the enzyme monoamine oxidase A (MAOA) may be malfunctioning.
Further research on the biological causes of violent behavior has pointed less to a genetic link and more to brain damage that has occurred to the fetus or postnatal infant. As Adrian Raine notes in the Journal of Biological Psychiatry, murderers' brains show a significantly lower rate of glucose uptake than a healthy brain. The study, conducted by Raine and colleagues at USC and the University of California at Irvine, used positron emission tomography to scan the brains of 41 murderers who had pleaded not guilty due to reasons of insanity. This was followed by a scan of 41 brains of control subjects matched for known mental disorders, as well as for age and gender. The study showed that the murderers, on average, showed significantly lower rates of glucose uptake in three areas of the brain -- the prefrontal cortex, the corpus callosum and the posterior cortex. Their rates were four, 18 and four percentage points lower, respectively, than the rates measured in control subjects performing the same tasks. As noted by Raine, "Poor functioning of these limbic area helps explain why violent offenders fail to learn from experience and are less able to regulate their emotions."
This research demonstrates a link between brain damage and criminal violence, eliminating the possibility that mental disorders alone predispose criminals to violence."
