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The relative effect of various influences in the formation of a serial killer
Research Question : To what degree do genetics contribute to the development of psychopathic traits which characterize a serial killer?
Although accounting for only 1% of all murders in a given year in the United States, serial murders cases are usually not clear and the personalities involved in the murder are of great interest to psychologists and in popular culture as people attempt to solve the puzzle of the motivations behind a certain crime. This phenomenon is not exclusive to the United States and has been documented previously in other regions of the world. One of the first books to document violent and sexual crimes committed by such murderers was Psychopathia Sexualis, by Dr. Kraft Ebing, which was published in 1886 and was expanded upon in its following versions. The book was a pioneer as it was one of the first texts written in an academic fashion which discussed sexual practices and how sexual desires outside of the motivation to sire offspring were considered to be a form of perversion as practices done by homosexuals did not provide any biological benefit. It acted as a reference which allowed for legal judgements of sexual criminals as it suggested that their mental state was to blame for the crime and thus must be accounted for.
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Serial killers are defined as people who had committed acts of violence at several, unique times (different from mass murder where multiple people are killed at one particular time). They are more broadly categorized as people that display characteristics of antisocial personality disorder. This classification of personality disorder can be further divided into sociopathy or psychopathy which includes behavioural traits such as lack of empathy, wish to exploit people, absence of guilt and lack of ability to learn from wrong-doings. These types of personalities align with serial killers who are cruel, lack remorse, hindered emotionally, and egocentric. Although not all serial killers are psychopaths and may not display the characteristics, their willingness to kill or sexually abuse someone repeatedly shows the shortage to comprehend the consequences of the crime, egocentricity and cruelty which are traits of antisocial personality disorder. Since the sample size of serial killers is small, it is more efficient and easier to generalize to the population by looking at studies researching the influences causing antisocial behaviour. In addition it allows for standardized psychopathic evaluation tests as well as other quantitative data which can provide empirical results, rather than just case studies on specific serial killers.
Investigations during 20th century provided greater insight into the topic which eventually led to the coining of the term ‘serial killer’ by John E. Douglas and Robert K. Ressler. Working in the Behavioural Science Unit, they lead an FBI investigation in which serial killers were interviewed in order to evaluate the motivation behind the crimes they had perpetrated. Over 2 decades Ressler and Douglas conducted these interviews in order to create a case study for each killer and find a way to profile them in such a way that their behaviour could be used to trace back to them. Through their method, unidentified serial killers were easier to find by analysis of the crime scene which gave insight into the individual’s behaviour. Interrogations of infamous criminals such as Edmund Kemper, Ted Bundy and Charles Manson included relating to the perpetrator in order to make them more comfortable which would cause them to share more details of what led them to commit the crime. This led to the classification of killers based on several criteria including their ‘signature’ which was made up of unique things an offender did at a crime scene in order to fulfill their psychological requirements. Although providing great insight through interviews, the internal and ecological validity of the FBI’s profiling process should be evaluated critically as the interviews were subjective and unstructured which does not provide uniformity outside of the personal setting in turn having weak ecological validity.
In the 21st century, new technology provides a new perspective of biological influences into the profile of a serial killer, while including all of the environmental factors proposed by previous profiling methods. Research into genetics as well as new methods to analyze the activity of the brain allow for scientists to study patterns which may be present with multiple serial killers. From new research correlations between genetics or brain activity patterns and the development of a person into a psychopath can be made, providing the opportunity for other killers to be identified prior to their crimes by means of genetic or neurological testing. In fact, a twin study done at the University of Minnesota shows that psychopathic traits are 60% heritable. Due to this, biological details of criminals can be crucial to prevent them from developing into psychopaths or serial killers by accommodating them in an environment that nurtures their psychological needs.
Although not solely responsible for psycopathy, it can be seen that genetics play a significant role in the development of a criminal. Greater knowledge of what causes the development of psychopaths is also key for juries in the court of law when sentencing psychopathic criminals. Brain scans or genetics may allow for lenient penalties, thus it is important to consider the research question:
To what degree do genetics contribute to the development of a psychopathic profile of a serial killer?
This essay will be discussing an answer to the research question by evaluating the influence from environment/social aspects, genetics, and neuroscience. It will argue that genetics are responsible for the development of psychopathic traits in serial killers to an extent, but basing likelihood of development into a psychopath on exclusively genetics is not accurate or reliable and other influences affecting a person will also be explored throughout this essay. The essay is limited by the amount of factors that can be regarded as only genetics, neuroscience and environmental aspects will be analyzed. Evaluating all the possible influences on a person’s life would include minute and irrelevant details while being difficult as well as time consuming to represent in the essay.
Essential concepts and theories that will be discussed throughout this essay include localization of brain functions, epigenetics, genetics, neuroscience and their relation to human behaviour. Studies that will be used in order to demonstrate these theories will be sourced from academic journals of law, medicine and psychology as well as articles on neuroscience research. It will also include excerpts from lectures by reputable professors.
There are several myths surrounding the characteristics of serial killers due to the influence of popular culture on stereotypes of these criminals. False information can also spread as research which was previously believed to be true in already engraved in human minds and reversing the beliefs due to new research can be of great difficulty. One such phenomenon is the inclusion of an extra Y chromosome in males, also referred to as the XYY syndrome that supposedly causes greater amount of aggression in men. This hypothesis from scientists caused stories of XYY males to be picked up, creating the stereotype of a “supermale” a male with an extra Y chromosome prone to commit violent crimes due to the genetic flaw. This was disproved by a study comparing crimes done by a control group of males and a group of males with XYY syndrome demonstrated that XYY males committed 8.6% of their crimes against people in contrast to 21.9% by the control group. Another myth is that serial killers are exclusively driven by a sexual desire, this is false as the motivation of a serial murder may be a variety of things, including anger, the thrill of murder itself as well as possible financial benefit. A troublesome upbringing or toxic environment is necessary for the development of a serial killer is yet another myth as there have been killers. A study in the Journal of Police and Criminal Psychology (2005) shows that for 50 serial killers that were used as the sample 68% suffered some type of abuse while 32% reported no abuse. This shows that serial killers are likely to have an unstable family environment but it is not a necessity for their development.
Genetics and Epigenetics
Genes are a fundamental physical unit made up of DNA which mainly contain information to instruct for the creation of protein in the human body that code for traits and functions. Genes are passed on through generations by heredity as 50% of each parents’ genes are inherited by the offspring. As they contain information rather than actual instructions for behaviour, they indirectly affect behaviour by encoding molecules that affect brain function. The environment directly affects genes and how they effectively each gene expresses information, therefore having an effect on the behaviour of an organism. The aforementioned phenomenon is due to epigenetics, which can lead to changes in cognition, appearance, and most importantly behaviour. As a consequence it is crucial to consider when discussing both environmental or genetic influences on the development of antisocial behaviour traits. Epigenetics research is limited as most of it has been done during the preliminary stages of life in organisms, and behavioural epigenetics being a subcategory of that is even more restricted in terms of research. Hence, while behavioural epigenetics will be discussed, information is subject to change as adequate research in specific areas is done.
Monozygotic twins or identical twins that share 100% of their genome and dizygotic twins or fraternal twins which share 50% of their genes, both groups are assumed to be exposed to the same environmental conditions in a classical twin study. Twin studies are critical to genetic and behavioural genetic research as a set of twins can be analyzed, yet unlike using a random set of people the variables for twins are very similar making them easy to compare and contrast. Through the comparison of antisocial behaviour traits between monozygotic and dizygotic twins, the variance in their behaviour can be accounted for through heritability (genes), environmental factors which are shared by the genes (making them similar to each other), and environmental factors that are not shared by the twins (making them different from each other). Behavioural genetics research has shown that genetic influences can be blamed for approximately 50% of the development in antisocial traits. Nevertheless, both types of environmental factors, shared and nonshared, also show evident results to satisfy the other 50% of the variance in antisocial behaviour. This will be further discussed in the latter part of this essay.
A study done including a community sample of 780 twin pairs by Wang et al. (2013) analyzed the influence of genetic and environmental factors on antisocial behaviour in the sample. It was found that the type of antisocial behaviour, aggressive or non-aggressive, was important as both types as heritability increased in males as their age increased from 9 to 18, while only non-aggressive antisocial behaviour decreased for females. Such results exihibit that differences in behavioural development between sex should be considered and investigated further. Aggressive and non-aggressive behaviour was also examined by Niv et al. (2013), in which the influences on childhood antisocial behaviour were investigated, data was collected between the ages of 9 and 10 as well as 14 and 15. Through the study it was found that antisocial behavior in the younger children was influenced by 41% genetics, 40% shared environment and 19% non-shared environment. From ages 14-15, 41% of influences on the common antisocial behavior factor were purely due to genetics, while the other influences remained stable across time. Regardless of the data it is important to note that delinquency during childhood or adolescence is a common trait and it is very rare to predict the development of a serial killer just from childhood behaviour.
Research that is more relevant to criminals emphasizes the role of impaired self-control as a key risk factor for antisocial behavior, as stated through a study done by Gottfredson & Hirschi (1990). Following this line of research, Beaver et al. (2013) examined the genetic and environmental stability and change in self-control in 2,412 twin pairs through a correlational study which were measured at three time points being : 1994, 1996, and 1998. The data set was collected from the Child and Young Adult Supplement of the National Longitudinal Survey of Youth 1979. Results showed that genetic factors were responsible for between 74–92% of the stability in self-control and between 78–89% of the variance in self-control. Accordingly, it could be assumed that shared and nonshared environmental factors with the twin pairs accounted for the rest of the stability and difference in levels of self-control. This study although recent, uses data from 1990s and does not explicitly gauge any advancements in genetic research or limitations in the data, in addition cause and effect inferences cannot be made since the study is correlational. Though, it still provides strong evidence for a link between genes and stability in self-control.
An MRI is a brain scanning technique used to produce detailed pictures of the brain so that it can be evaluated and compared to other models, it does this by aligning hydrogen protons in the body. Using this method, a study done by Mayer et al. (2006) discovered that people with the MAOA‐L gene had a greater chance of having a smaller limbic system. The limbic system consists of the hippocampus, amygdala, the nuclei of the anterior thalamus and limbic cortex, these parts of the brain execute processes related to emotion, behaviour and long term memory. Emotional cognition such as fear perception is specifically managed by the amygdala. The team then applied functional MRI, another brain scanning technique measures changes in blood flow, this allows for the analysis of activity patterns in the brain by looking at patterns of blood flow. Through fMRI it was discovered that the MAOA‐L gene displayed heightened responsiveness of the amygdala when participants were asked to perform tasks such as copying facial expressions. The results showed that the MAOA-L group had a lower capability of inhibiting strong emotional impulses. Consequently, it can be seen that genes and neurology are deeply connected, having a major impact on one’s behaviour. The effects on a person’s limbic system as well as amygdala due to the MAOA-L genes shows that people with the gene group have greater susceptibility to behavioural anomalies.
Ahmad Hariri made a statement concerned about the findings of the research done by Mayer et al. (2006). Mr. Hariri is an investigator at the Institute for Genome Sciences & Policy at Duke University and he states, “This is a significant basic science finding linking genes to brain to behaviour,” “But it is not a significant clinical finding in and of itself. Only in as much as this very, very, very subtle bias in the brain tips the balance toward an aggressive response to provocation is this finding even remotely clinically relevant.”, he continued. The limitation of uncertainty arises as it is not accurate to label MAOA-L as the only gene to cause violence or aggression.
The concept of gender differences is present yet again as females are protected from the gene. One way they are protected is through the X chromosome as women with the MAOA‐L variety on one chromosome will likely have a normal allele on the other. Also there is significant evidence that women having defence mechanisms stemming from other genes lowering their exposure to violence. In men, there is some trigger required to activate MAOA‐L gene which leads to violence. Results from an earlier study by Caspi et al. (2002) suggested that this trigger could be persistent maltreatment during childhood, which would align with environmental influences of development. This correlation was portrayed as a chart displaying the variables of antisocial behaviour and maltreatment during childhood, although there is a strong correlation with a large sample size of 442 males evaluated at several time intervals between ages 3 and 21. Cause and effect inferences cannot be made and the quality of operationalizations should be criticized since it was a quasi experiment. This is an example of how epigenetics may function as environmental factors affect genes and hence affect behaviour.
Figure 1 : A graph displaying a standardized score of antisocial behaviour vs. childhood maltreatment for two types of MAOA genes (n represents sample size used for each gene group)
Along with genomic data, information from neuroscience also provides great insight into the biological influences on human behaviour. James Fallon is an Amerian neuroscience professor at the University of California and has had several notable works correlating neurobiology and human behaviour, including one in which he compares his own mind with violent relatives in his family tree. In one of his books, Fallon states that neurotransmitter activity is mainly based on genetics and can affect the brain due to different activity levels of serotonin, dopamine and other neurological circuits that directly influences the brain. The simplified normal distribution in Figure 1 theoretically portrays the effect of genes and the environment on neurotransmitter systems, it shows how genes are the main determining factor, while the smaller range of changes due to the environment can be seen below the charts.
Figure 1 : Activity in neurotransmitter systems represented as simplified normal distributions (Fallon, 2006)
James Fallon also did a blind study of 70 brains from psychopathic murderers, in which he analyzed normal and psychopathic brains to discover any patterns in both groups. Each one of the psychopathic killers was found to have brain damage at the orbital cortex and anterior temporal lobe as can be viewed in Figure 3. It should be also noted that brain damage for each psychopathic killer was not exactly the same, instead there was a pattern and there was brain damage unique to each case.
Figure 3 : An image showing consistency of brain damage with murders (Fallon, 2006) 
Even though Fallon has found patterns in genetics, brain damage, and brain activity patterns there is great importance he places upon timing of the several factors including a person’s association with their environment.
Even though it is rather difficult to quantitatively measure environmental influences due to the amount of variables present in a natural setting, there are many resources that can be explored in order to find a link between certain environmental factors and antisocial behavior or extremely violent behaviour. In a study done by Cotter (2007) on the developmental dynamics that leaed a serial killer to their first act of murder, there were 5 stages discovered that lead to extreme violence :
- Emotional problems
- Adaptation to murder
- Trigger event
- Act of murder
As previously stated in the introduction of this paper, FBI research including the interviews of serial killers in order to find the motive of their crimes found that most perpetrators had a difficult childhood, Ressler et al. (1992)  causing them to be in the initiation stage of the development process. The table in Figure 4 provides insight into the amount of abuse serial killers face compared to the general population, providing evidence for the initiation stage. Despite the fact that the table below provides evidence for links between serial killers and abuse, the information must be looked at critically as abuse may not be reported accurately and the data collected in the study is not from a primary source representing 50 lust serial killers (motivated by sexual desire). Due to being socially isolated because of their environment, they create other paths to fulfill their social necessities. Fantasies are built on top of already egocentric personalities which further justify any abnormal or violent actions, Douglas and Olshaker (1999). Immense drive for dominance is then caused due to a trigger event which can be a crucial moment in life such as a relationship problem. This leads the killer to seek power by committing crimes against vulnerable victims, Ressler and Schachtman (1992).
Figure 4 : A table comparing serial killers to the general population in terms of abuse
The same paper by Cotter (2007) details how genocides are a similar phenomenon, continuously developing until an ideology of extreme violence is considered normal, and being triggered due to a major event such as military defeats in war. It is important to note that usually several risk factors are required in order to have a large emotional impact, according to studies conducted by the University of Minnesota confirmed this hypothesis as five types of risks were assessed over 15 years , Appleyard et al. (2005) and one risk factor was unable to hinder a child’s development compared to a combination of several influences which would cause them emotionally break down eventually.
Figure 5 : A statistical excerpt from a study examining trauma and behavioural health treatments with incarcerated men (N represents sample size). 
The previously indicated correlation between childhood trauma is followed further in this study by Wolff and Shi (2012) as it seeks to test 3 hypotheses, being : if childhood trauma exposure leads to psychopathology in adulthood, different types of trauma have varied impacts, and if incarcerated males who were exposed to trauma required greater amounts of behavioral health treatment compared to other incarcerated males with no reported trauma. From Figure 5 it can be noticed that as trauma exposure, for both children and adults led to a greater amount of treatment for health issues such as depression or anxiety disorder. The same study also reported that trauma exposure during the ages of minority was able to foresee future behavioural health treatment necessities. Sexual trauma prior to adulthood was a major cause of future behavioural health treatment as men with childhood sexual trauma recorded receiving treatment for depression and anxiety and substance abuse while incarcerated 2 times as much and 1.5 times as much respectively. In addition, childhood abandonment was also consistently linked to similar symptoms. Although most of the research did line up with prior research done on similar topics, the researchers state there were contrasting findings reported by Dutton and Hart (1992), the details opposing the previously stated study was that symptoms of agression did not increase due to sexual abuse prior to adulthood. Demographic and criminal history variables were accounted for when evaluating results providing greater validity to the discoveries. A nurturing environment can prevent the development of a serial killer according to James Fallon and from the research presented it can be recognized that environmental influences are also greatly influential to emotional issues and possibly violence.
Despitethe extensive data available for both genetic as well as environmental influences, it is necessary to do further research in conflicting theories such as military theory and compare gender characteristics. Military theory states that experience in an institution such as the army desensitizes murder and thus encourages violent behavioural characteristcs which cause the development of potential serial killers, this link was studied at the Department of Criminology, Indiana University of Pennsylvania (2002).
By thoroughly evaluating the information presented in the studies cited previously in the paper, it can be concluded that both genetics and environment are approximately equally responsible for the development of behavioural traits and thus the formation of serial killers. It can be distinguished that while genetics play a major role in the potential for aggressive or antisocial behaviour, a nurturing environment without multiple risk factors is enough to keep abnormal behaviour at bay. Consequently, there is greater need for genetic and epigenetic research to determine genes other than MAOA that are responsible for violence and the exact effect of the environment on the activity of genes. Heritability and patterns in brain damage are also consistent with psychopathic killers, but from James Fallon’s example, it can be observed that not everyone in the family will become a serial killer due to biological similarities.
With the information currently available, a biosocial model is the best representation of this as it incorporates a variety of processes and risk factors, later outlining the outcome in terms of antisocial behaviour subcategories. By illustrating how various influences both genetic and environmental have approximately equivalent contribution to the development of potential antisocial behaviour, though protected by resilience which may be present biologically or socially such as a supportive environment hence preventing formation of abnormal characteristics.
Figure 6 : A diagram exhibiting the biosocial model of antisocial behavior
 Ressler et al 1992
 James Fallon, Neuroscientist – A Scientist’s Journey Through Psychopathy
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