Why are some men more aggressive than others?

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Why are some men confrontational or break objects in fits of anger, while others appear to be more in control under similar circumstances?

A variation in a gene involved in the activity of the brain chemical serotonin, which is known to play an important role in regulating emotions and impulses, may cause some men to have problems controlling their anger. Yet, this appears to be true only for men raised in certain environments, in particular under adverse circumstances.

Studies have shown that some people with psychiatric disorders and those imprisoned for an impulse-related crime are either deficient in serotonin or exhibit poor regulation of the brain chemical.

In previous studies, researchers also found that men carrying one form of the monoamine oxidase-A (MAOA) gene responsible for inactivating serotonin were more likely to be violent and antisocial than men with a different form of the gene. However, the negative behavior was seen only among men who were abused in childhood.
In other findings, differences in the serotonin 2A receptor, another serotonin gene, were also associated with a higher level of aggressiveness in men. Again, increased aggression was only apparent among men whose fathers had not completed high school. The subjects' educational level did not appear to be related to their behavior.

In another study, Dr. Stephen Suomi, of the National Institute of Child Health and Human Development, studied the association of genetics, the environment and aggression in monkeys.

Up to 10 percent of wild rhesus monkeys exhibit impulsive behavior or extreme aggression under mild stress conditions. Researchers have found that these monkeys are also deficient in the breakdown and use of serotonin.

Suomi found that laboratory monkeys with a gene that blocks serotonin were also more impulsive and aggressive, but only those who failed to develop secure attachment relationships with their mothers. In contrast, monkeys that experienced "maternal buffering" via secure attachment relationships did not exhibit these characteristics.

The study findings imply that even though a child may have a genetically related increased susceptibility for conduct problems, affectionate and loving parents can negate this increased susceptibility, Manuck said. "We can't change our genes, but perhaps we can change our rearing environment."