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Warrior Gene

Should people with a genetic predisposition to aggression be punished for violence? This question became particularly important in the court case of Abdelmalek Bayout, an Algerian male, who was sentenced for stabbing a man to death in Italy in 2007. His initial sentence was reduced by a judge because Abdelmalek had the Warrior Gene, which has been linked to aggression.So, is…

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Warrior Gene

Warrior Gene
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Should people with a genetic predisposition to aggression be punished for violence? This question became particularly important in the court case of Abdelmalek Bayout, an Algerian male, who was sentenced for stabbing a man to death in Italy in 2007. His initial sentence was reduced by a judge because Abdelmalek had the Warrior Gene, which has been linked to aggression.

So, is there any scientific basis for the Warrior Gene to be used as a get-out-of-jail-free card?

  • First, we'll look at the warrior gene definition.
  • Next, we'll introduce the warrior gene theory of aggression.
  • Then, we'll consider the origins and history of the Maori warrior gene.
  • Moving along, we'll briefly explore the case of the warrior gene in females.

  • Finally, we'll evaluate the MAOA Warrior Gene theory of aggression.

Warrior Gene, hands controlling puppets, StudySmarterFig. 1 - The Warrior Gene theory of aggression proposes that genetic factors can predispose us to aggression. Can our genes determine our actions?

Warrior Gene Definition

The warrior gene, also called the MAOA gene, codes for an enzyme that is crucial for breaking down monoamines, including serotonin.

The MAOA gene codes for the production of monoamine oxidase A (MAO-A), which is an enzyme involved in breaking down neurotransmitters after they have been released into the synapse between neurones.

Serotonin is one of the primary neurotransmitters broken down by MAOA, although dopamine and norepinephrine are also affected.

Serotonin is a neurotransmitter which acts as a mood stabiliser.

Many refer to the MAOA gene as the ‘Warrior Gene’ due to its ties with aggression. This is not to say that these ties are factual and proven, and we will assess the studies to determine the validity of their findings.

How does the MAOA Warrior Gene Affect Mood?

Neurotransmitters are fundamental in regulating moods and subsequently behaviours. As MAOs are enzymes that break down these neurotransmitters, any issues with the MAOA gene and its ability to produce these enzymes would affect a person’s mood.

If neurotransmitters are left in the synaptic cleft, it can cause many issues. The neurotransmitter effects are ultimately prolonged, resulting in continued activation of the neurones involved.

For example, acetylcholine is involved in the contraction of muscles. The muscle will continue to contract if acetylcholine is left in the synaptic cleft and is not removed (through reuptake, breakdown or diffusion).

Warrior Gene Theory of Aggression

As MAOA is involved in the production of enzymes that break down neurotransmitters, issues with this gene can result in mood disorders, as seen in the case of Brunner et al. (1993), where Brunner Syndrome was established.

In this study, 28 males in a Dutch family were investigated, as they were showing signs of abnormal behaviour and borderline mental retardation.

These behaviours consisted of impulsive aggression, arson, and attempted rape.

  • Researchers analysed the participants' urine over 24 hours and found a deficiency in the MAOA enzyme activity.
  • In 5 affected males, further investigation revealed a point mutation in the MAOA structural gene (specifically the eighth axon). This changed how this gene coded for enzyme production, which caused issues with the breakdown of neurotransmitters.

If the serotonin cannot be broken down properly, the level of serotonin increases, affecting mood and behaviour. This finding suggests that the MAOA gene mutation is linked to abnormal, aggressive behaviours.

MAOA gene can have various effects on aggression depending on its variation.

  • One variant of the gene, MAOA-L, is linked to low levels of MAOA.
  • Another variant, MAOA-H, is associated with high levels.

So, people with the MAOA-L variant may display high levels of aggression, whereas the MAOA-H variant may display low levels of aggression.

Māori Warrior Gene

The MAOA Warrior Gene was the subject of a New Zealand study conducted by Dr Rod Lea in 2006, which found the ‘warrior gene’ in Māori men, explaining their aggressive behaviours and lifestyles (Lea & Chambers, 2007).

Lea stated that several negative behaviours are associated with a certain variation of the warrior gene.

These behaviours included aggressive behaviours, drinking, smoking, and risk-taking behaviours.

When genotyping 46 unrelated Māori men, researchers found the following:

  • 56% of the Māorimen had this variation of the MAOA gene, almost double that of Caucasian men analysed in a different study.

Further identification of different polymorphisms of the MAOA gene revealed that:

  • 70% of Māori men compared to 40% of non-Māori men had this variation of the MAOA gene.

Warrior Gene, Maori warriors performing, StudySmarterFig. 2 - Lea & Chambers (2007) found a higher prevalence of the Warrior Gene in Māori men compared to Caucasians¹.

Lea reportedly stated to the media (Wellington: The Dominion Post, 2006):

Obviously, this means they are going to be more aggressive and violent and more likely to get involved in risk-taking behaviour like gambling.

This statement is ethically questionable and raises many questions, namely, is it fair to describe all men with this gene as aggressive and violent?

Lea suggested this was due to the nature of the Māori men’s past. They had to engage in many risk-taking behaviours, such as migration and fighting for survival, which has then led to aggressive behaviours in the present, modern-day, and a genetic bottleneck. The study suggests that this genetic variation might have evolved due to natural selection, and continued to be present in Māori men.

According to Lea, the gene was dubbed the Warrior Gene due to the culture of the Māori men, who value their ‘warrior’ traditions, which remain a part of their culture today.

When a specific gene is associated with or labelled as the reason behind a particular abnormality, it brings severe consequences. Anyone with this gene or issues with the gene will automatically be associated with the label. Any stereotypes will be unfairly placed on them.

Warrior Gene in Females

The Warrior gene is found on the X chromosome, which means that it is sex-linked. Due to its location, only males inherit a single copy of this gene and are affected by it. However, females can still be carriers of this gene.

Evaluation of the MAOA Warrior Gene Theory of Aggression

First, let's explore the strengths of the warrior gene theory.

  • Research in favour of the theory: Brunner et al. (1993) found that the presence of a mutation in the MAOA gene was associated with aggressive and violent behaviours, this suggests that the MAOA gene can lead to aggressive behaviours if defective.

  • Caspi et al. (2002) assessed a large sample of male children from birth to adulthood. The study wanted to investigate why some maltreated children develop antisocial behaviour, whilst others don't.

    • They found the MAOA gene was important in moderating the effect of maltreatment.

    • If children had a genotype that expressed high levels of MAOA, they were less likely to develop antisocial behaviours.

    • This suggests genotypes can moderate children’s sensitivity to maltreatment and the development of aggressive behaviours.

  • Associations between the gene and behaviour regulation: As mentioned in the studies above, the MAOA gene is fundamentally linked to mood due to the need to produce enzymes that deal with neurotransmitters. If the gene is affected, it stands to reason that mood and behaviours will be affected, too.

Now, let's explore the weaknesses of the warrior gene theory.

  • Aggression occurs only when provoked: In the study of McDermott et al. (2009) subjects were paid to punish people they believed had taken money from them.

    • People with low activity MAOA genes only behaved aggressively in the lab when provoked.

    • It suggests that the MAOA gene is not explicitly tied to aggression, even in low provocation conditions, but instead, it predicts aggressive behaviours in high provocation situations.

    • This finding suggests that the MAOA gene is only associated with aggression if the subject is provoked.

  • Reductionist: The suggestion that a gene is responsible for violent or aggressive behaviours reduces all the causes of human behaviour down to biology. It ignores the environmental factors that may significantly influence a person’s choices and behaviours. It oversimplifies the nature of behaviour.

  • Deterministic: If a gene controls human behaviour outright, with no room for a person’s free will or choices to decide what they want to do, it can create many issues for society. If a person is more inclined to be violent purely because they have a gene for it, is it fair to treat them similarly to everyone else? Should they be prosecuted for violent behaviour when they are helpless but follow their biological urges?

  • Merriman and Cameron (2007): In their review of the 2006 study, whilst they agree that there is an association between the genetic variant of MAOA and antisocial behaviours in Caucasians, the study has no direct evidence to suggest there is an association for Māori men. Overall, they criticise the warrior gene study, suggesting the conclusions were based on ‘science with insufficient investigative rigour’ in applying new literature and understanding older, relevant literature.

  • Ethical issues: The term warrior gene is ethically problematic, as it reduces a person’s nature to their genetic predispositions, ignoring other aspects of their character and their overall free will to make moral choices. It has connotations that are not fair to place on a whole race of people.


Warrior Gene - Key takeaways

  • We refer to the monoamine oxidase A gene when talking about the MAOA gene. It codes for the production of the enzyme MAOs (monoamine oxidases), involved in breaking down neurotransmitters in the synapses between neurones.
  • Many refer to the MAOA gene as the ‘Warrior Gene’ due to its ties with aggression, linked unjustly to Māori culture.
  • As MAOA is involved in producing enzymes that break down neurotransmitters, issues with this gene can result in mood disorders.
  • The Warrior Gene gained notoriety from a New Zealand study by Dr Rod Lea in 2006, which stated a ‘warrior gene’ existed in the Māori men.
  • Overall, evidence suggests dysfunctions with the gene can lead to aggressive behaviours, as seen in the Brunner et al. (1993) study. However, stating that aggressive behaviours are due to the gene is reductionist and deterministic. The ‘Warrior Gene’ is an unethical term that has been used to unfairly portray the Māori men.


References

  1. Fig. 2 - Maori men by DoD photo by Erin A. Kirk-Cuomo (Released), Public domain, via Wikimedia Commons
  2. Brunner, H. G., Nelen, M., Breakefield, X. O., Ropers, H. H., & van Oost, B. A. (1993). Abnormal behavior associated with a point mutation in the structural gene for monoamine oxidase A. Science (New York, N.Y.), 262(5133), 578–580.
  3. Lea, R., & Chambers, G. (2007). Monoamine oxidase, addiction, and the" warrior" gene hypothesis. The New Zealand Medical Journal (Online), 120(1250).
  4. Maori violence blamed on gene. Wellington: The Dominion Post, 9 August 2006; Section A3.

Frequently Asked Questions about Warrior Gene

The MAOA gene codes for the production of monoamine oxidase A (MAO-A), which is an enzyme involved in breaking down neurotransmitters after they have been released into the synapse between neurons. 

It is suggested that if a person has the ‘warrior gene’, they will be more aggressive and have aggressive traits. It would not be accurate to say they have ‘symptoms’. Lea also suggested that addiction problems (alcohol and nicotine) could be ascribed to the warrior gene.

The warrior gene, evolved as a result of natural selection.

The MAOA gene does exist and is linked to aggressive behaviours. 

Studies suggest that the prevalance of the warrior gene is around 70% in Mãori men and 40% in non-Mãori men.

Final Warrior Gene Quiz

Warrior Gene Quiz - Teste dein Wissen

Question

What is the MAOA gene?

Show answer

Answer

We refer to the monoamine oxidase A gene when talking about the MAOA gene.

Show question

Question

What does the MAOA gene do?

Show answer

Answer

The MAOA gene codes for the production of the enzyme MAO-A (monoamine oxidase A), involved in breaking down neurotransmitters in the synapses between neurones.

Show question

Question

Where is the MAOA gene found?

Show answer

Answer

The gene is found on the X chromosome.

Show question

Question

Why would dysfunction of the MAOA gene affect a person’s mood?

Show answer

Answer

The gene codes for enzymes that break down neurotransmitters such as serotonin. If the gene cannot do this properly, these neurotransmitters are left in the synaptic cleft for longer and affect a person’s mood.

Show question

Question

What study investigated the warrior gene in Maori men?

Show answer

Answer

Lea & Chambers, 2007

Show question

Question

What behaviours are associated with the warrior gene, according to Lea & Chambers (2007)?

Show answer

Answer

Aggressive behaviours, risk-taking, addiction issues.

Show question

Question

How many Mãori men had the MAOA gene variant compared to Caucasian men?

Show answer

Answer

56% of the Mãori men had this variant, almost double that of Caucasian men analysed in a different study.

Show question

Question

What did Brunner et al. (1993) find in their study?

Show answer

Answer

There was a point mutation in the MAOA structural gene (specifically the eighth axon). This changed how this gene coded for the enzyme production, which caused issues with the breakdown of neurotransmitters.

Show question

Question

What did the men in Brunner et al. (1993) show in their behaviours?

Show answer

Answer

The behaviours of the men in Brunner et al. (1993) consisted of impulsive aggression, arson, and attempted rape.

Show question

Question

What did Lea state the Mãori men were more likely to be like?

Show answer

Answer

‘Obviously, this means they are going to be more aggressive and violent and more likely to get involved in risk-taking behaviour like gambling.’

Show question

Question

What reportedly is the cause of the high occurrence of the MAOA (warrior) gene in the Mãori men?

Show answer

Answer

Lea suggested this was due to the nature of the Mãori men’s past; they had to engage in many risk-taking behaviours, such as migration and fighting for survival, which has led to aggressive behaviours in the present, modern-day, and a genetic bottleneck.

Show question

Question

Give a strength of the genetic research on the MAOA gene.

Show answer

Answer

The MAOA gene is fundamentally linked to mood due to producing enzymes that deal with neurotransmitters. Mood and behaviours will also be affected if the gene is affected. This suggests a genetic component to behaviour and moods, particularly aggression, and validates the genetic research on the MAOA gene.

Show question

Question

What did Caspi et al. (2002) find in their study?

Show answer

Answer

They found that the MAOA gene was important in moderating the effect of maltreatment. If children had a genotype that expressed high levels of MAOA, they were less likely to develop antisocial behaviours after suffering maltreatment.

Show question

Question

Give one weakness of the genetic research on the MAOA gene.

Show answer

Answer

McDermott et al. (2009) found in their study that the MAOA gene is not explicitly tied to aggression in low provocation conditions. Instead, it predicts aggressive behaviours in high provocation situations.

Show question

Question

Is the term ‘warrior gene’ unethical?

Show answer

Answer

Yes, the term ‘warrior gene’ is unethical as it has racist overtones that unfairly describe a race of people as aggressive due to their genetic makeup.

Show question

Question

What is one of the primary neurotransmitters broken down by MAOA?

Show answer

Answer

Serotonin 

Show question

Question

What 3 neurotransmitters are affected my MAOA?

Show answer

Answer

  • Serotonin
  • Dopamine
  • Norepinephrine

Show question

Question

What is the function of serotonin?

Show answer

Answer

Serotonin is a neurotransmitter which acts as a mood stabiliser.

Show question

Question

If neurotransmitters are left in the synaptic cleft, it can cause many issues.

Show answer

Answer

True.

Show question

Question

Why is the warrior gene explanation of aggression reductionist?

Show answer

Answer

The suggestion that a gene is responsible for violent or aggressive behaviours reduces all the causes of human behaviour down to biology. It ignores the environmental factors that may significantly influence a person’s choices and behaviours. It oversimplifies the nature of behaviour.

Show question

Question

What was the reason for the aggression in males studied by Brunner et al. (1993)?

Show answer

Answer

MAOA gene mutation, which prevented a proper break down of serotonin in males.

Show question

Question

How is the level of serotonin affected in individuals with lower levels of monoamine oxidase A?

Show answer

Answer

In individuals with lower levels of monoamine oxidase A, serotonin is not broken down properly, which causes the overall levels of serotonin to increase.

Show question

Question

Why does the Warrior gene only affect males?

Show answer

Answer

The Warrior gene is found on the X chromosome, which means that it is sex-linked. Due to its location, only males inherit a single copy of this gene and are affected by it. 

Show question

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