Monoamine oxidase A ("warrior gene")
Monoamine oxidase A (MAOA), often referred to as the "warrior gene," is an enzyme encoded by a gene located on the X chromosome in humans and some primates. This gene plays a critical role in regulating the levels of several neurotransmitters, including serotonin, dopamine, epinephrine, and norepinephrine, which are vital for mood regulation, emotional responses, and stress management. Research has suggested that individuals with lower levels of the MAOA enzyme may exhibit a predisposition to aggressive behaviors, which led to the gene's nickname. However, scientists caution against oversimplifying the relationship between genetics and behavior, emphasizing that various environmental factors, such as upbringing and personal trauma, also significantly influence aggression and antisocial behavior.
The discovery of the MAOA gene emerged from a study of a Dutch family with a history of violent behavior, revealing a defect in their MAOA enzyme production. Although some studies, particularly in prison populations, have found links between low MAOA levels and violence, findings indicate that not all individuals with the "warrior gene" engage in aggressive behavior. Additionally, factors like childhood experiences and societal influences can shape behavior, suggesting a complex interplay between genetics and environment. The concept of the "warrior gene" has sparked discussions in both scientific and legal contexts, but researchers advocate for a nuanced understanding rather than attributing aggression to a single genetic factor.
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Monoamine oxidase A ("warrior gene")
Monoamine oxidase A, or MAOA, is an enzyme produced on a gene on the X chromosome of humans and some primates. The gene is known as the MAOA gene. MAOA regulates the body's production of several neurotransmitters in the brain. These signals help regulate mood, emotions, and the body's response to stress, among other things. Some researchers believe that when the gene does not produce the correct amount of MAOA, it can predispose the person or animal to aggressive responses to certain stimuli. This has led to the MAOA gene being referred to as the "warrior gene." However, scientists also note that various factors prompt responses and actions and blaming aggressive behavior on a single gene may be too simplistic.
Background
Genes are the part of a cell that contains deoxyribonucleic acid, or DNA. DNA contains the instructions that determine the characteristics of the cell. As a result, they also determine the characteristics of the organism in which they are found. Organisms generally have two copies of each gene. One copy comes from each parent; this is the reason that people have physical traits and characteristics similar to their parents.
Some of these traits are visible, such as hair and eye color, while others are not easily seen, such as a predisposition to certain diseases. One gene that functions in this less visible way is the MAOA gene. Its main function is to make the MAOA enzyme. An enzyme is a catalyst, which means that it helps to produce a chemical reaction.
The MAOA enzyme is responsible for helping the process of oxidizing, or breaking down, a number of key neurotransmitters. Neurotransmitters help pass signals along the nerve fibers in the brain. The neurotransmitters affected by MAOA include serotonin, dopamine, epinephrine, and norepinephrine. Serotonin helps to control appetite, mood, emotions, and sleep, while dopamine is involved in controlling the body's movements. Epinephrine and norepinephrine are essential to controlling how the body reacts to stress. In addition, the MAOA enzyme helps break down other monoamines that are ingested as food. The MAOA gene and its enzyme are also thought to be involved in fetal brain development and in apoptosis, the controlled break down of cells that have fulfilled their purpose.
The existence of the MAOA gene was discovered in 1993 after a Dutch family asked scientists to investigate the reason why so many males in their family had extremely violent behavioral tendencies. These behaviors included arson, attempted murder, and incestuous rape. Research determined that the men were all missing the MAOA enzyme, an indication of a defect in their MAOA gene. In 2004, a journalist writing about the gene for Science magazine dubbed it the "warrior gene" because of its connection to aggression. Researchers have also discovered an allele, or related gene. It is called MAOA-L because it produces lower than normal levels of the MAOA enzyme. It has since been identified in a number of primate species, which some researchers speculate means MAOA and MAOA-L could have first developed millions of years ago in ancestors shared by humans and primates.
Overview
The human body is designed to have different chemicals in a specific balance to control or support a number of functions. When these chemicals are out of balance, problems can result. For instance, low levels of the neurotransmitter serotonin have been associated with depression and related problems. On the other hand, excess amounts of serotonin and other neurotransmitters—including dopamine, epinephrine, and norepinephrine—can also have consequences. For example, too much serotonin is thought to trigger anxious behavior and possibly violence, while too much norepinephrine is thought to prime the body for high stress levels that can lead to overreactions and reduced impulse control. Other problems researchers have connected to excess amounts of these neurotransmitters include sleep and mood disorders, bursts of violence, and an inability to control certain urges, especially in inappropriate circumstances.
Some of the research into the role of the MAOA gene and enzyme was done in Finnish prisons, where a large percent of inmates were found to have low levels of the MAOA enzyme or none at all. Other researchers have investigated the behavior and brain chemistry of other inmates, looking for a link between the warrior gene and criminal behavior. However, studies have also uncovered the fact that some people who have the deviant gene or allele do not have a history of violent, aggressive, or out-of-control behavior. This has led researchers to theorize that other factors besides the MAOA enzyme influence such behavior.
One factor that seems to play a role in the development of antisocial and violent behavior in people with the deviant MAOA gene is their upbringing and their history of trauma. Researchers have found some correlation between violent behavior and childhood abuse and trauma. People raised in stable, loving homes are less likely to develop aggressive or violent tendencies, some research has determined.
Researchers have also pointed out that people can be conditioned to be more accepting of various types of behavior, including those seen as overly aggressive or violent. Some factors that can justify a person's violent or aggressive behavior in their mind include the following:
feeling that one's group is better than the group the aggression is directed at
seeing "others" as a group instead of as individuals
holding prejudices and negative feelings about the character or intelligence of "others"
being under the influence of an authority figure who promotes or encourages aggression
experiencing desensitization through exposure to violent or aggressive scenarios, even virtual ones
The "warrior gene" defense has been used by attorneys to gain leniency for clients accused of violent acts. Still, many researchers remain unconvinced that violent, antisocial, or aggressive behavior can be connected to a single gene or gene mutation. They point to the difficulty of separating the factors that can cause such complex acts and suggest that more study is needed on MAOA.
Bibliography
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