Table of Contents
The aims and objectives of this paper is behavioural genetics that are associated with aggression and violent behaviour. In this paper, MAOA gene that is also known the “warrior” is discussed and how it was discovered, and the conclusion reached from it discovery and analysis. Behavioural genetics have an influence on the criminal justice system. There have been cases that involved behavioural genetics as part of the evidence and the sentences for the perpetrators were cut down or some of the cases were dismissed.
The MAOA gene is a gene that is found in the X chromosome and it encodes monoamine oxidase A (MAOA) which is an enzyme that is responsible for breaking down neurotransmitters such as serotonin, dopamine and norepinephrine, (Raine, 2008). When the neurotransmitters are not broken down, there is an excess of the three chemicals in the blood which have an effect on the body and the brain. Having a higher quantity of the neurotransmitters in the body/blood leads to miscommunication between the neurons. This results to aggression and antisocial behaviour. MAOA-L is an allele that is formed by a specific mutation and this produced MAOA knockouts in human beings at low level MAOA.
The first chapter of this paper provides information about behavioural genetics and the history to help understand how genetics work and what happens if they change. Behavioural genetics is not only influencing the criminal law changes, it also explains why each individual behaves the way they behave and the changes either around them or within them that lead them to having certain characteristics. The effect caused by behavioural genetics can result in aggressive or violent behaviour.
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Having an understanding of the aggressive and violent behaviours, new criminal laws can be set, and institutions set up with the necessary skilled personnel and facilities to help those in need. Further research can be done to find out new way medical or other scientific ways to assist those affected and the individuals will understand their actions in relation to one’s genetics.
The second chapter gives an in-depth information of the MAOA gene (warrior gene). Its discovery and how it relates to aggression and violence. The third chapter gives information about the neurogenetic origins of behaviour which is about “2B OR NOT 2B”. This is a human gene known as the “knockout gene”
The third chapter provides information on the impact of behavioural genetics on the criminal law. The final chapter relates to the criminal cases that involved behavioural genetics and how they were dealt with in court. One of the cases will be an Italian court case and the other case will be of Bradley Waldroup which will show how the information obtained from behavioural genetics was not used correctly during the trial.
Introduction to Behavioural Genetics
Behavioural genetics investigates why humans are different; why individuals behave differently and act they act in ways that they act. Behavioural genetics tries to find the link between the genotypes and the differences observed in the human nature. The heredity (nature) and the environment(nurture) theory has been used for years to answer the question of why people are different. The heredity is the transmission of difference characteristics that are passed on from parent to child. This means that heredity plays a major role in why some children turn out the way they are. Behavioural genetics cannot explain why some people are taller than others and why some are intelligent than the next person, however, it deals with the environmental and genetic sources that influence one to be who they are.
For example, behavioural genetics can tell us why some children have delayed speech, but it cannot inform us why humans use language for communication or why boys tend to perform less better than girls on verbal tests. In addition to this, new DNA IS formed when mutations happen during the process of copying DNA. The mutations then lead to the formation of different alleles known as polymorphisms, for example the alleles that were formed in Mendel’s pea plant experiment. A single base mutation can lead to a different amino acid attaching to a different protein. This kind of mutation will change the function of the protein.
The nature and nurture theory was invented by Charles Darwin’s half cousin, Francis Galton basing his theory on the theory of evolution that was created by Charles Darwin. One of Galton’s experiments showed that behavioural traits run within a family therefore it is hereditary. Behavioural genetics topic explores a range of sub topics such as sexuality, intelligence, personality and aggression/violence. Behavioural genetics goes hand in hand with the environmental/ social structure that one spends most of their time around. The development and enforcement of social structures can become an emotionally charged topic, especially when focused around aggressive and violent behaviour (Parens,2004, p. S5).
Studying human behaviour is difficult and not as easy as one can study animal behaviour therefore the adoption and twinning experimental methods are used to see if the nature and nurture theory is valid or how it contributes to behavioural genetics or human behaviour. The adoption theory tries to prove if the child resembles his/her birth parents traits or the environmental traits of the adoptive parents. Twinning method uses twins for comparison, it uses identical and fraternal twins. Identical twins are genetically identical because they are from the same zygote whereas the fraternal twins are from different fertilised eggs therefore they are not genetically identical.
How Do Genes Influence Behaviour?
There are no genes that can be specifically said to be genes for behaviour just as there are no genes that can be said they are genes for a sporty individual. As far as concerned, genes are chemical structures that code for amino acids sequences only.
Gregor Mendel came up with three laws of heredity transmission while he carried out his study in pea plant. The three laws he came up with were; the law of segregation that states that each inherited trait is explained by a gene pair. Parental genes are separated randomly to the sex cells to allow the sex cells to have only one of the genes in the pair therefore the offspring will have only one of the two elements from each parent. The second law was the law of independent assortment that stated that different genes for different traits are sorted separately from each other to avoid one trait being dependent on another trait.
The last law is the law of dominance which states that the dominant gene will be expressed by an organism with alternate genes. Another point that could be added is that if an individual lives in a certain area and it influences a certain trait within them, the family members living with the individual in the area are more likely to have the trait too as the environment is shared meaning that environment plays a role on who an individual is becoming.
Genes to Brain to Antisocial Behaviour
Some genes play an important role in the brain’s functionality therefore if they are altered in any way they affect how the brain functions which will lead to changes in an individual’s behaviour.
Warrior Genes and Other Behavioural Genes
There has been several experiments carried out to try and explain the function of the MAOA and in the models, the mice was used. There were two types that were used, a normal mice and a mutant mice. The results of the experiments showed that the MAOA mutant mice was more aggressive when an intruder mouse was brought into the picture and it reacted to the stress than a normal mice.
Humans have different MAOA gene variants that lead to individual’s having different levels of gene expression. Individuals perceived to be “normal” have the MAO variant that shows high levels of the neuronal MAOA. Some patients have the MAO variant that leads to the absence of functional MAOA. Other people have the variants that contribute to having low levels of MAOA expression in the brain.
Monoamine oxidase A gene (MAOA) and CDH13 are known as human warrior genes. Both genes are associated with aggressive behaviour hence the term. The MAOA is produced by the X chromosome that influences how neurotransmitters like serotonin, norepinephrine and dopamine are broken down.
The serotonin deals with the impulse control and affects sleep, appetite and regulation. The dopamine system is involved in motivation and reward, mood, arousal and other behaviours. The norepinephrine deals with the fight or flight reactions and the autonomic nervous system activity. The breakdown of the neurotransmitters affects one’s mood, feelings and individual’s behaviour.
MAOA is responsible for the metabolism rate of the neurotransmitters and how quickly the metabolism happens making the levels of MAOAs in the brain and other tissues important. MAO enzyme levels found in the brain tissues can have significant effects on an individual’s behaviour varying from panic disorders, to aggression and violence. There is a strong correlation between the MAOA enzyme and an individual’s life experience of abuse/ trauma in their childhood.
DAT1 Gene
DAT1 gene is responsible for transporting dopamine that is encoded by the SLC6A3 gene. These genes monitor the inactivation and active reuptake of dopamine from the synapse. In addition to this, they are responsible for regulating the dopaminergic neurotransmission. Dopamine lasted about 100 times longer in the extracellular space when tested in the homozygous DAT1 null mice. This is a biochemical explanation related to the hyperlocomotion, the hyperdopaminergic phenotype.
For further research by GUO and colleagues, a set of children were examined to look for any extra genetic of aggression and the research showed that DAT1 has a variant known as the DAT1*10R genotype was involved in serious delinquent behaviour. This gene is responsible for limiting duration and level of the dopamine receptor activation hence it controls the synaptic dopamine levels.
DRD2 Gene
The D2 dopamine receptor is coded by the DRD2 gene. The D2 dopamine receptor is a G protein- coupled receptor that is found on the postsynaptic dopaminergic neurons. It is part of the reward-mediating mesocorticolimbic pathways. The DRD2 gene controls the physiologic functions linked to hormone production, locomotion and drug abuse. Researchers, Guo and colleagues, while carrying out their research and experiments, they found out that DRD2 variant was also a risk factor of violent delinquency.
However, this was noticed when the young adults and adolescents had been exposed to some sort of stress like failing at school or experiencing family problems. There are other genes and variants that are associated with aggressive behaviour and these include the likes of the androgen receptor gene and its variants and the catechol-O-methyltransferase gene. These are also responsible for dopamine breaking.
The warrior gene was found within a Dutch family in the 70’s. In the family, the male family members were known to be aggressive and would fight and threaten people. Two of the males were arsonists, one raped his sister and when placed in a mental hospital, he tried to stab the warden with a pitchfork and one of the males tried to run his employer over with a car when he was criticised that his work was not up to standard.
Analysis of their X chromosome were carried out and it was found that the males have the defective MAOA gene which is meant that the gene was not functioning resulting in the neurotransmitters not being broken down leading to having large quantities of unbroken neurotransmitters within the body/ blood. The large quantities of the different chemicals affected them and possibly affected their brains too.
MAOA occurs in apes, ancient monkeys and humans therefore elucidating the impression that the allele was present over 25million years ago in the ancestor of the primates and later favoured by the process of natural selection. It has been reported by other researchers that there is a link between serotonin levels and aggression in humans and animals. Serotonin and aggression have been said to have a link when it comes animals and humans.
Having high levels of noradrenaline and dopamine in animals has been linked with aggression. This is the first genetic effect to be linked with aggressive behaviour. For the results to be verified that the “warrior genes” are linked to aggression/violence, there needs to be another family of criminals or aggressive members tested to see if there is a link. Furthermore, serotonin has a gene called the HTR2B gene and the gene encodes one of the serotonin receptors that is responsible for controlling the peripheral and central physiologic functions of serotonin.
In addition to this, males that have a common polymorphism in the MAOA gene have about 8% reduction of the anterior cingulate, amygdala and orbitofrontal volume. The mentioned brain structures play an important role in emotions and are associated with antisocial behaviour. One of the genes that is associated with antisocial behaviour is results in structural changes to the brain areas that are linked to antisocial behaviour. Changes in the brain lead to cognitive, emotional and behavioural changes.
There is new evidence indicating brain impairments in antisocial groups. This includes evidence relating to the prefrontal cortex that is considered strong (Raine & Yang, 2006). Murderers’ s prefrontal cortex has shown that they have a reduced metabolism rate for glucose in the presence of an activity that is known to activate it. This is also noticed in impulsively violent offenders. The prefrontal cortex can be viewed as the “emergency brake” when one gets overwhelmed by their emotions.
CDH13 which codes for neuronal membrane adhesion protein plays a role in the signalling between cells. This gene alongside MAOA are said to be responsible for extreme violent/ aggressive criminal behaviour.
