Aggression is defined as being a behaviour involving anger and resulting in violent behaviour. For a long time, we have been told that aggression happens because of the environment or circumstances that a person experienced during childhood or adolescence. However, there are a number of biological factors that contribute to aggression including genes and the structure of the brain.
Genes
Genes are made of DNA and carry information that determines the traits of a person. One of many genes is the MAOA gene, which encodes an enzyme known as monoamine oxidase A (MAO-A). Such enzyme breaks down serotonin, dopamine and noradrenaline which are hormones that are involved in aggression, emotion and cognition. Low levels of the MAOA gene are linked with an increase of antisocial behaviour and violent delinquency. Serotonin is associated with happiness and optimism and if there are low levels of it in the body, then there is a reduction of control over impulsive behaviour. When there are high levels of dopamine, there would be an increase in the likelihood of feelings of reward when aggression is experienced, which might cause the person to commit the same aggressive acts. If adrenaline is not broken down, individuals may experience hypersensitivity to external stimuli and may perceive threats where there are none.
Brain Structure
A part of the brain associated with aggression is the amygdala which controls emotions, fear and motivation and is located in the temporal lobes. It is also known as the emotional centre of the brain which processes threatening stimuli. When triggered, dopamine and adrenaline are released into the bloodstream and the blood flow is increased, preparing the person to fight against a perceived threat. Damage to the amygdala has been associated with fearlessness and aggression.
The prefrontal cortex is also involved in aggressive behaviour. This area of the brain is responsible for decision making, personality expression, reasoning and maintaining social etiquette. It also delays the gratification of impulses and when damaged, these impulses, which may include aggressive ones, would no longer be controlled and a person may act upon them.
The thalamus which is located above the midbrain and below the cerebral cortex is known as the body’s informational relay station. This means that all of the body’s senses including hearing, taste, sight and touch are processed through here before being sent to the cerebral cortex. Damage to the thalamus might affect the perception of these senses and the intensity of our emotions, which may lead to an aggressive response to certain stimuli.
Another part of the brain that has been linked with aggression is the hypothalamus. The hypothalamus regulates the autonomic nervous system and emotional responses as well as maintaining homeostasis and regulating hormones. If damaged, the responses to emotional circumstances may result in inappropriate responses to perceived threats.
Nature vs Nurture
Although there are biological factors that may increase the aggressiveness of an individual, there are other aspects that should be considered. For example, psychological and socioeconomic influences should be considered as well as things like medications, substance abuse, stress or fear. Although genes and the structure of the brain should not be the only factors that are held responsible for aggression, they do play a role in such behaviour.
Sources:
- https://www.tutor2u.net/psychology/reference/aggression-genetic-factors
- https://www.webmd.com/brain/amygdala-what-to-know
- https://www.nature.com/articles/s41398-024-02870-7
- https://www.jax.org/news-and-insights/jax-blog/2015/december/the-genetics-of-violent-behavior
- https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(04)17622-8/fulltext
- https://my.clevelandclinic.org/health/body/22652-thalamus
- https://www.tutor2u.net/psychology/topics/maoa-gene
