The Killer Gene: Are Some People Simply Programmed to Kill?

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Supposedly, in the 19th Century, the traits of a criminal were high cheekbones, deep-set eyes and a strong jaw line. These days, such accusations have a more scientific feel, with research suggesting that murderers may be coded for their behaviour at birth; they possess a ‘killer gene’. If true, this could have serious implications for our courts and the application of justice. Who can hold a murderer responsible when their genetics defy willpower and compel them to kill? How do we decide whether certain actions are simply criminal activities, or the outcome of a diseased mind?

The killing of one human being by another in our moral society has been attributed to many factors, in attempts to rationalise such behaviour. Did the individual snap? Were they exposed to violence at a young age? The classic nature vs. nurture debate. Current English law requires ‘mens rea’ (guilty mind)- there must be evidence of intent in murder cases. Diminished responsibility is a partial defence that may, if successful, reduce a murder charge to manslaughter. The burden is on the defendant to prove this on the balance of probabilities.

Genes to die for? A comprehensive family history

Monozygotic twin studies are useful in trying to startling discovery when a fellow prisoner likened answer the nature or nurture debate. Twins raised in different conditions are the perfect study subjects as they share identical genetic information but are exposed to different environmental influences. A study in Denmark showed that a twin was 50% more likely to have a criminal record if their twin was in prison. Irving Gotetsman, who worked on the Danish twin study, believes that ‘Criminals are not born but the odds at the moment of birth of becoming one are not even’

Support for a genetic basis to violence may be found in the case of Jeffry Landrigan, who committed the murder of a friend when he was 20 and killed again, later in life, when he staged an armed robbery. Landrigan had been adopted, and was raised by a caring and successful couple. He was sentenced to death row where he made a startling discovery when a fellow prisoner likened him to a man named Darrell Hill. It turned out that Hill was Landrigan’s biological father who too had committed murder and been sentenced to death. In addition, he learnt that his grandfather had been a violent criminal. Despite all the care from his adopted parents it appears Landrigan had a genetic predisposition to violence and was programmed with the potential to murder.

So what could this genetic connection be? Well, there has been talk of a “warrior” gene that codes for aggressive behaviour. This gene supposedly controls the levels of the enzyme Monoamine oxidase A (MAO-A). Low levels of the enzyme, combined with a history of abuse and neglect during childhood years, correlate with a pattern of more aggressive behaviour- possibly predisposing an individual to becoming a murderer.

MOA-A: Neurotransmitter breakdown

Evidence supporting the “Warrior” gene brings up the nature vs nurture debate yet again, as it is both low levels of the gene (nature) and a hostile childhood (nurture) that appears to predispose to violence- leading some to question whether it is the presence of violence during an individuals upbringing that causes levels of MAO-A to be so low.

The principle of environmental elements altering gene expression is explored in epigenetics- a field of medicine that looks into non-genetic causes of changes of gene expression, bridging the two arms of the nature verses nurture debate. Some epigenetic studies have suggested that a killer’s environment itself may result in the production of lower MAO-A levels. The enzyme is heavily involved in the breakdown of neurotransmitters such as serotonin, and hence influences feelings, emotions and behaviours. Therefore, should an environment cause lower levels of the enzyme, an individual may become more aggressive and violent.

MOA: Prefrontal Cortex

A variant of the MAO-A gene has been associated with an underdeveloped prefrontal cortex. This area of the brain is believed to assist in weighing up conflicting thoughts and in ensuring behaviour is socially acceptable. Damage to the prefrontal cortex (as found in those with this variant) is associated with limited ability to assess situations, leading to acts of violence during which a killer is unable to moderate his or her behaviour.

The Orbital Cortex

In addition to low levels of MAO-A there is an additional ingredient which may further increase the chances of producing a killer. The orbital cortex is an area of the brain that processes the emotions and rewards associated with decision- making and so can also assist in themaking of ethical decisions. The orbital cortex may be malformed congenitally or can become damaged throughout life. This can diminish ethical decision making, impairing an individuals’ ability to distinguish right from wrong.

The resulting limitation on moral reasoning, in combination with a possible predisposition to violence and subsequent lack of its suppression (due to lowered levels of MAO), creates an ideal recipe for a dangerous individual.

The current practise of criminal law does not question the concept of free will and instead attempts to fix blame. This is challenged by the newly evolving field of neuro-law that seeks to explain criminal behaviour and so may allow for a case of insanity. Despite these advances, Landrigan was sentenced to death by lethal injection and the courts overruled his plea that he had inherited a ‘killer gene’.

Psychopaths and Spree killings

More recently on the 14th December 2012, Adam Lanza, aged 20, went on a killing spree in a school in Connecticut. He murdered 20 children and 6 adults before turning the gun on himself. His brother described Lanza, as a bit of a nerd and a ‘loner’ and scientists are currently analysing his DNA to see if there are any clues in his genes that could explain this behaviour.

Lanza is classified as a ‘spree killer’. Spree killers have shown to have a history of depression and an immature brain. They are extremely sensitive to insults, being unable to process and rationalise them, and they crave revenge.

In contrast, psychopaths have difficulties in considering the consequences of their actions. Their brains have been shown to have low levels of density in their paralimbic system, which is the area of the brain responsible for processing emotions such as guilt and remorse. As a result their brains apart to limit the capacity for foresight, possibly explaining their violent actions.

It could be argued that looking for a genetic reason to explain the actions of violent criminals belittles the impact of the environment in forming a killer, and so shifts the responsibility from society for producing such characters. Yet Oxford University neuroscientist Kathleen Taylor believes that searching for a killer gene should never be dismissed saying ‘new knowledge is always useful’.


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