Is There a Genetic Variable that Affects How Violent Individuals Behave? The Attempted Determination of the Aggression Gene
by Carolyn A. Skibinski

A large Dutch family, comprised of many male children, are prone to unprovoked, violent outbursts: one male raped his sister and was subsequently placed into a mental institution, only to attempt murder on a warden; another was criticized by his employer, then attempted to run him over with a car; a third male, who was an arsonist, forced his sister to undress at knifepoint (1). Is there a genetic variable that affects how these, and other violent individuals, behave? I will attempt to demonstrate why many scientists believe that there is a genetic variable in individuals such as these.

Many scientists believe that a mutation exists on a certain gene that causes aggressive behavior. At the University Hospital in Nijmegen, the aforementioned Dutch family was examined. It had been found that there may be a mutation in the gene encoding the enzyme Monoamine Oxidase (MAOA). This seemed significant because the enzyme encoded by this particular gene helped to break down several neurotransmitter substances that, if built up, could cause a person to act excessively, if not violently. These substances are utilized during the "fight-or-flight" response and could conceivably cause a problem, prompting the individual to be "on guard" at all times. The affected individuals in this family were all males, indicating the disorder was (perhaps) carried on the X chromosome, and this has, in fact, been determined to be true (2).

Another study conducted in Finland analyzed men who acted on impulse and were unable to control their behavior. The researchers determined the men possessed a neurotransmitter substance deficiency, particularly in the messenger serotonin (3). A lack of the substance serotonin as well as nonadrenaline have been linked to aggressive behavior: some violent prone individuals did not effectively break down these substances (4).

A study at the Center for Neurobiology and Behavior at Columbia University attempted to determine the behavior of mice lacking the 5-HT(1B) receptor, a serotonin receptor. It was known that 5-HT(1) agonists which are called serenics due to their anti-aggressive properties mimic this receptor-inactive phenotype. Mutant mice were generated by homologous recombination in the embryonic stem cells lacking both copies of the gene that encodes the 5-HT(1B) receptor. Mutant mice and wild type mice were separately placed into a situation with an intruder and the mutant mice attacked the intruder much quicker and at a higher incidence than the wild type mice. Mutant mice were more aggressive and more impulsive then the wild type, thus the 5-HT(1B) receptors may be activated in response to environmental changes. In humans, a homologous receptor of 5-HT(1B) is also a serotonin receptor. If an individual had a reduced level of serotonin, the 5-HT(1B) receptors may not be thoroughly utilized, resulting in the same phenotype as that of serenic mice (5).

In conclusion, many scientists postulate that there may be a genetic foundation as to how violent people behave. This is demonstrated in the study of the large Dutch family and the MAOA mutation, the Finland study of violent behavior as related to serotonin deficiency, and the Columbia University study of the 5-HT(1B) receptor and how this is applicable to humans. As controversial as it may seem, individuals may eventually be able to use the genetic theory of the aggression gene as a defense or as an excuse for behavior: this is destined to have much significance in society.


References
1. The bad seed: amid controversy, scientists hunt for the "aggression" gene. by Jeff Goldberg v17 Omni Feb '95 p16(1)
2. Evidence found for a possible "aggression" gene. by Virginia Morell v260 Science June 18 '93 p1722(2)
3. Born to raise Hell? (genetic predispositions) (Column) by Dennis Overbye v143 Time Feb 21 '94 p76(1)
4. The genetics of bad behavior. (research on the links between violence and heredity) by Geoffrey Cowley v122 Newsweek Nov 1 '93 p57(1)
5. Enhanced aggressive behavior in mice lacking 5-HT(1B) receptor. (serotonin) by Frederic Saudou, Djamel Ait Amara, Andree Dierich, Marianne LeMeur, Sylvie Ramboz, Louis Segu, Marie-Christine Buhot and Rene Hen v265 Science Sept 23 '94 p1874 (4)