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Where Does Violence Come From?The mystery behind MAOA genes
Jee You-seon  |
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승인 2013.10.09  15:18:47
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IN 1991, Stephen Mobley was convicted of armed robbery and murdering a restaurant manager. At first sight, the incident looked like any other case of homicidal burglary. Yet, Mobley’s case received much more attention than other similar cases. One reason was due to Mobley’s refusal to apologize for his heinous crime. Instead, he bragged about it to everyone around him. However, what really grabbed people’s attention was the fact that he had a fault in one of his genes called MAOA genes. This incident provided a case study for scientists studying the abnormalities in MAOA genes that relate to a person’s propensity to violence. Various studies on MAOA genes have been conducted, revealing their many different aspects.

What is MAOA?

The ‘violence gene’ was discovered in the late 1980s by a Dutch genetics scholar named Han Brunner. A Dutch woman visited Brunner, searching for an answer as to why all men in her family, generation after generation, exhibited impulsive, violent behavior. After some testing and research, Brunner found a common genetic characteristic in all males of the family - they all had a rare genetic disorder which prevented MAOA genes from functioning properly. Through further research, Brunner also found out that the abnormality in the MAOA genes had been passed down through the generations, causing men in the household to carry the mutated violence genes.
MAOA genes produce an enzyme called monoamine oxidase-A, which breaks down molecules called neurotransmitters that carry signals between nerve cells and help control one’s mood. When humans confront external threats, a neurotransmitter called adrenaline is released into the body. At the same time, serotonin, another neurotransmitter which is known to make people happy, is released into the brain. If all the serotonin is not broken down immediately, however, it loses its original function and operates in a completely different way, by making the person irritated and angry. MAOA genes, which help dissolve serotonin, are thus helpful in getting rid of the excess serotonins and returning the elevated emotions to normal. However, dysfunctional MAOA genes cannot control the level of serotonin, causing an emotional explosion.

Contrasting men and women

It is not a coincidence that only the men in the Dutch family displayed violent behavior. Through further research, it was found out that the fault in MAOA genes only affects men. MAOA genes are located in the X-chromosome. Recall from biology class that when a baby is created, the baby receives a pair of sex chromosomes, one from each parent. During this process, females are only capable of passing down the X-chromosome. Males, on the other hand, can pass down both the X-chromosome and the Y-chromosome. The chromosome the fetus receives from the father is what determines the sex of the fetus. If the fetus receives two X-chromosomes, one from the father and the other from the mother, the fetus is a girl. In contrast, if the fetus receives one X-chromosome from the mother and one Y-chromosome from the father, the fetus is a boy. Thus, men only have one X-chromosome and when the violence gene is present, the gene will have full effect. On the other hand, as women inherit two X-chromosomes, they are more likely to have at least one normally functioning MAOA gene, meaning that they are not affected by the presence of a single MAOA gene. Though they may be carriers, having one faulty MAOA gene does not affect women in the same manner as one faulty MAOA gene affects men. As for women with two dysfunctional MAOA genes, further study needs to be done to understand how they are affected.
Researchers at the University of South Florida, Columbia University, and the New York State Psychiatry Institute have added the “happiness gene” as an additional nickname to the MAOA gene. The research revealed that the neurotransmitters that MAOA genes break down are the same type of neurotransmitters that chemicals in anti-depressants break down. Thus, basically, MAOA genes operate in the same way that anti-depressants do. However, this effect of MAOA genes, where they make people happy, only works on women. Though more research needs to be done, many scientists believe that testosterone is the most plausible explanation for men not receiving any benefit from normally functioning MAOA genes. Studies show that males tend to feel happier before adolescence because, before puberty, the level of testosterone, which possibly interferes with the happiness gene, is lower.

Nature vs. Nurture

Though dysfunctional MAOA genes are often referred to as the violence genes by the media, having a fault in these genes does not necessarily mean that the man is violent. Rose McDermott from Brown University conducted an experiment on men from various backgrounds, in which some were martial arts fighters, some were former gang members, and one was a Buddhist monk. In the experiment, the participants were each paired up online with a paid actor to take a vocabulary test together. Upon completion of the test, the actor followed the directions and did not equally divide the money he earned together with the participant. Then, the participant was told that he received less money than his partner, in which case he was given the choice to use the remaining money to punish the anonymous partner. Participants with faulty MAOA genes generally reacted in a more aggressive manner, where some even clearly expressed their intention by saying that they wanted to “make him pay” and to “make him hurt.” However, there were others, like the monk, who chose to forgive the supposed thief. Though the monk had the same genetic mutations in MAOA genes, McDermott later revealed that the monk had made a conscious choice to forgive the actor. McDermott, thus, drew the conclusion that gene variants cannot be the sole factor in explaining violent behavior.
As conscious efforts can work to cancel out the violence genes, childhood trauma is one of the factors that enact the potential of the abnormality in the genes. According to McDermott, traumas as a child, such as child abuse, sexual abuse, neglect and alcoholism in the family, can trigger the violence gene to make the person more aggressive and violent. Researchers at the Ecole Polytechnique Federale de Lausanne (EPFL) of Switzerland conducted an experiment with rats and found out that childhood traumas permanently alter brains by causing long-term modification in MAOA genes to influence them to become aggressive.

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The discovery of MAOA genes revealed that violence feeds on itself to create more violence, where aggression is passed down generation after generation. Children who have grown up in violent environments with faulty MAOA genes became aggressive adults and in turn, created a new violent setting for their children to grow up in. However, we should always remember that the vicious cycle can end. Although it is not easy, anyone can overcome a genetic weakness through conscientious efforts, which in turn, will help break the cycle.


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