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The Roles of Genetics and the Limbic System in Aggression

written by: efrontiers•edited by: Leigh A. Zaykoski•updated: 5/31/2011

There have been several studies that clearly demonstrate the role of genetics and the limbic system in aggression. Although the subject of aggression can be quite complex in human beings, this information will hopefully shed light on the limbic system genetics aggression relationship.

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    Defining Aggression

    Aggression is quite easily defined in animals because of specific stereotyped patterns of violence including killing to mark a territory or to gain food. With humans, however, the definition of aggression can be more complex because of the complication of intent.

    To better understand aggression, psychologists classify aggressive behaviors into one of the following three categories:

    Predatory aggression - stalking and killing of other species

    Social aggression - this is the unprovoked form of aggression directed at another member of the same species. The purpose of such behavior is to establish dominance.

    Defensive aggression – this behavior is set against threatening aggressors.

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    The Role of the Limbic System

    Based on animal clinical trials, the different types of aggression are actually controlled by different subsets in the brain, specifically the limbic system. The limbic system is composed of several interconnected nuclei and cortical structures within the telencephalon and diencephalon. Although the system serves various functions, it is known for functions associated with self-preservation, endocrine, and autonomic functions. The limbic system plays a crucial role in emotional response, arousal, motivation and reinforcing behaviors. Because it is essential to survival, this system is closely connected to the olfactory system in most species of animals.

    The main parts of the limbic system that are important in the study of aggression include the amygdala, limbic cortex, the septum, the pituitary gland and the hypothalamus.

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    Genetics and Aggressive Behaviors

    The link between genetics and aggressive behaviors had been researched since the 1960s. The theory during that time was that men born with an extra Y chromosome will display violent tendencies. This was disproved due the rarity of individuals with an extra Y chromosome. It cannot explain the prevalence of aggression all over the world.

    Despite the failure of the first attempt to correlate genetics to aggressive behavior, the scientific community believes that there is a genetic component behind aggressive behaviors. This is because violent behaviors have the tendency to run in families.

    This can be best explained by determining the brain structures that have control over aggression. According to scientific facts, the amygdala is implicated as the key brain structure behind aggression. Based on the 1939 study of Kluver and Bucy, monkeys who had their temporal lobes removed were found to be very tame, yet manifested little fear. Modern studies later explained that such Kluver-Bucy syndrome can be attributed to the removal of amygdala. Modulation of the amygdala, on the other hand, increases aggression even in humans.

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    Hurdles for Further Research

    Even with the finding that there is a possibility of inheriting a predisposition to violence, there remains hurdles for further research on this subject. The hurdle in studies is to separate the environmental factors from pure genetic influence. Furthermore, many psychologists argue that modeling aggression in the home, as performed for research purposes, is equivalent to promoting violence.

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    Scientists have been quite successful in identifying the role of limbic system genetics on aggression. Despite this knowledge, however, the genetic traits connected to aggression do not directly demonstrate pathological aggression. The scientists remain doubtful regarding the true factors that might contribute to this dangerous type of aggression within the society. This is the more important issue in resolving the problems in criminality and violence. Environmental factors such as exposure to television, internet, and other forms of influences are now being investigates as factors that may shape aggression. With the help of biologists, doctors, psychologist, and sociologists, we are slowly starting to understand the complexity of pathological aggression.

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