Aggression biological approach - Genetics

The role of Genes

This theory argues that aggression is carried in the genes. This means that if your parents are aggressive there is a high chance that you will be aggressive too. This is not due to observational 

learning as SLT would predict but due to a ‘genetic gene’ that you
have inherited. In our society we emphasise the role of free will
and opportunity and so theories like this are seen as quite
unpopular as we like to think that individuals can ‘break the cycle’
of aggression that they may have been brought up in. However, if we look to the animal kingdom we can clearly see how aggression does have a genetic element. Certain breeds of dog have been purposefully bred to be aggressive and it is generally accepted that some breeds, regardless of upbringing have an instinct to be aggressive and so may ‘snap’. The Dangerous Dogs Act (1991) has prohibited the ownership and breeding of certain breeds (e.g. Pit Bull Terrier) based on the idea that their aggression is genetic. 

Research Supporting the Role of Genes in Aggressive Behaviour

Stevenson and Goodman (2001) used 828 randomly selected children. They assessed them at age 3 for behaviours such as temper tantrums, bedwetting, poor concentration and an inability to get along with siblings. They also took into account their family and social circumstances.
As adults, 82 were convicted of crimes, 26 of them violent. Those who had committed the violent crimes were the ones who showed the most aggressive behaviours as three year olds.
Why is this relevant? The researchers concluded that aggression must have a genetic basis as there was a similarity in the way the children behaved at age 3 and the way they behaved as adults.
Problems with this study. This study shows a very weak link between genes and aggression, there are many factors other than genes, family and social circumstances that could have led to these results (e.g. getting bullied at school, being in a negative peer group, watching violent films…etc). 

Mednick et al (1984) had a more thorough way of assessing the link between aggression and genetics.
They looked at 14,427 Danish adoptees to see if they showed signs of aggression. They then looked to see if both their biological and adoptive parents showed signs of aggression. The logic behind this is that if aggression is due to genes there should be higher levels of aggression in those adoptees who had aggressive biological parents, whereas if aggression is a result of nurture there should be higher levels of aggression in those adoptees who had aggressive adoptive parents.
They found that:
- 13.5% of adoptees with parents (biological and adoptive) without a criminal conviction had one themselves.
- 14.7% of adoptees with at least one adoptive parent with a criminal conviction had one themselves.
- 20% of adoptees with at least one biological parent with a criminal conviction had one themselves.
- 24.5% of adoptees with at least one biological parent and at least one adoptive parent with a criminal conviction had one themselves

Why is this study relevant? The third percentage is higher than the second percentage. This suggests that criminality (which is often aggressive in nature) has a genetic basis.
Problems with this study. This study also shows that upbringing has an effect on the likelihood of committing a crime (evidenced by the fact that the second percentage is higher than the first percentage). The final finding suggests a clear role for both biology and upbringing. This means that whilst the study offers some support for the genetic theory, it also shows us that the relationship is not that clear cut. It should also be considered that this study looked at criminal convictions but not all criminal convictions are violent in nature. 

The MAOA (monoamine oxidase A) gene has been linked to aggression.
The job of the MAOA gene is to produce enzymes to break down the
neurotrasmitters norepinephrine, dopamine and serotonin.
Norepinephrine is a stress hormone that causes increased blood
pressure and alertness. Dopamine and serotonin are biochemicals
that are involved in regulating mood and alertness. The theory goes
that if these chemicals are not broken down properly, mood and arousal are not being controlled properly and so aggression can result.

The MAOA gene can lead to aggression if it is faulty in some way.
Sometimes the MAOA gene can be mutated. This means that it cannot do its job properly and the neurotransmitters are not broken down properly.
There are also two variants of the gene – MAOA – L (low) and MAOA – H (high). MAOA – L is the low variant. If you have this variant then not as many enzymes are produced to break down the neurotransmitters. Therefore, having the MAOA – L variant makes you at risk for showing aggressive behaviour.

The MAOA gene is passed down on the X chromosome. This means that a faulty MAOA gene will only negatively affect men. This is because if women have a faulty MAOA gene on one X chromosome they will have a functioning one on the other X chromosome to make up for it. Men, on the other hand, only have one X chromosome and so are affected by a faulty MAOA gene. 

Supporting Research

A strength of this theory is that it is supported by the research of Brunner et al (1993). They studied the case of a Dutch family that had a history of violence in its male members. The case came to light after a female member of the family came forward to talk about the horrific acts committed by the male members of her family. One of them had tried to **** his sister, another had tried to run down his boss in his car, and another had made his sisters undress at knifepoint. In addition to this, her grandfather, who was not violent himself, had made a family tree tracing all the men in the family that seemed to be affected by overly aggressive behaviour out of worry for his family. 

The researchers examined 28 members of the family. They found that all of the violent men had a defective MAOA gene but that none of the non aggressive men did. They also found that some women had the defective MAOA gene, which means that whilst they were not adversely affected by it, they had the potential to pass it on. This case study clearly shows a link between a faulty MAOA gene and aggression providing strong evidence for the role of genes in aggression.

This explanation is also supported by the research of Caspi et al (2002).
They carried out a longitudinal study of 1,037 children over 25 years.
They found that those males with a MAOA-L gene were:
-  more than twice as likely to have been diagnosed with a conduct disorder in adolescence
 - and three times more likely to have been convicted of a violent crime by 26 years of age. This study clearly shows a link between MAOA-L and aggression. However, it should be noted that not everyone in the sample who showed aggression had the MAOA-L gene. Equally, not everyone who had the MAOA-L gene went on to show aggressive behaviour. This means that there is clearly more to aggression than a malfunctioning MAOA gene alone

Issues and Debates

A limitation of the genetic explanation of aggression is that it takes the ‘nature’ side of the nature/nurture debate. This means that it ignores the role of environmental factors in explaining aggressive behaviour (such as aggressive role models).  The study by Mednick et al (1984) clearly shows that the role of the environment cannot be ignored. A person is not purely the result of their genes, their upbringing plays a large role in whether they will be aggressive or not.

The genetic explanation is also fairly determinisitic. It implies that if people are aggressive it is because they are victims of their own biology, i.e. they cannot help the aggression. It suggests that if you have a faulty MAOA gene or the MAOA-L variant you WILL be aggressive and there is nothing you can do about it. This is simply not the case, as Caspi et al (2002) showed, not everyone with the MAOA L gene was aggressive.

Finally, as with the other biological explanations this is also socially sensitive as it suggests that people with an aggressive gene are not responsible for their behaviour. This had implications for the legal system. There was a case in Italy whereby a judge cut the sentence of a man who had committed murder on the basis that he had an abnormal MAOA gene.  Such a ruling sets a dangerous precedent as it may lead to defendants not being punished for aggression if faulty genes can be proven and also takes away a sense of justice from the victim or victim’s family.