biological theories of crime

  • Created by: hwelch17
  • Created on: 17-10-18 13:23


Need to learn:

  • XYY syndrome 
  • brain injury
  • amygdala and aggression
  • personality.
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XXY syndrome (1)

People with 47,XYY syndrome will be:

  • taller than normal 
  • High testosterone levels
  • Powerful bodily build
  • Heightened aggression
  • Propensity for violent crime
  • have severe acne.
  •  47,XYY syndrome people may have reduced intelligence
  • there can be learning difficulties
  • developmental delays in speech and language
  • There can also be difficulties in development of physical skills such as walking

There is no obvious connection with crime and anti-social behaviour in what has been said about XYY syndrome regarding symptoms and characteristics. The link comes only from observations of XYY syndrome people in criminal populations. 

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XXY syndrome (2)

  • Theilgaard (1984)

Looked for a ‘criminal gene' Studied blood samples of over 30,000 men born in the 1940s. Found that XYY males had slightly lower levels of intelligence than average and tended to be more aggressive towards people than normal men. Limited evidence Witkin et al (1976) no direct link between crime and XYY syndrome  Denmark4591 men in the top height distribution (total of 28884 men) and found only 12 cases of XYY. results - No significant difference once background variables were controlled for. They did find lower intelligence in XYY males compared with XY males and they were taller than average. This might have led to their over representation in the prison population because of the social reactions such characteristics might produce Conclusion: it is not the biological differences in having an extra chromosome that led to people being over represented in the prison population

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XXY syndrome (3)

Limitations of XYY syndrome 

- The problem with the term ‘criminal behaviour’. Are we talking violence? Fraud? Shoplifting? The range of crimes is from first degree murder to tax evasion or copyright theft. Will one gene explain these? Genetic theorists struggle to explain why criminal behaviour changes over the lifespan, reaching its peak when individuals are in their 20s and declining in most people after the age of 30. - One problem is that the classification of men into XXY, XY or even XXY patterns has been incorrect in some studies. XYY syndrome tends to lead to men being extra tall and having acne and scars and maybe these were the characteristics that were used to classify the men – however this is not enough to ensure that they were XYY - Even in studies that find XYY does relate to crime, there could be labelling and a self fulfilling prophecy as the cause of the link. This raised the issue of nature and nurture – genetically someone might have XYY syndrome but any effect from the genetic difference can be down to environmental influences.  strengths of XYY If XYY found early (about 25% found before birth) then issues around physical development and behavioural and emotional issues can be addressed early – studies seem to suggest that it is not the XYY chromosome pattern that leads to criminality but there may be an element of labelling and the SFP that can lead someone with the syndrome into crime. It is therefore a strength that by researching the link between XYY and crime, we are able to help prevent it. Lots of research into XYY and deviant behaviour so reviews such as Re and Birkhoff (2015) can show conclusively that a link is not shown.  

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XXY syndrome (3)

Re and Birkhoff (2015) review of the evidence about 47,XYY syndrome and deviance

Reviewed evidence over last 50 years Concluded there is NO link between XYY syndrome and crime They discussed how problems associated with XYY such as problems with impulse control, low tolerance of frustration, aggressiveness, could also be linked to environmental factors such as dysfunctional family.

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Eysenck Personality Theory (1)

Eysenck (1952, 1967, 1982) proposed a theory of personality based on biological factors, arguing that individuals inherit a type of nervous system that affects their ability to learn and adapt to the environment.

Eysenck (1947) found that their behavior could be represented by two dimensions: Introversion / Extroversion (E); Neuroticism / Stability (N). Eysenck called these second-order personality traits.

Each aspect of personality (extraversion, neuroticism and psychoticism) can be traced back to a different biological cause. Personality is dependent on the balance between excitation and inhibition process of the autonomic nervous system (ANS).


Extraverts -  are sociable, crave excitement and change, and become bored easily. They tend to be carefree, optimistic and impulsive. More likely to take risks and be thrill seekers. Eysenck argues that this is because they inherit an under aroused nervous system and so seek stimulation to restore the level of optimum stimulation.

Introverts -  are quiet and reserved. They are already over-aroused and shun sensation and stimulation. Introverts are reserved, plan their actions and control their emotions. They tend to be serious, reliable and pessimistic.

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Eysenck Personality Theory (2)

2. Neuroticism/stability

A person’s level of neuroticism is determined by the reactivity of their sympathetic nervous system. A stable person’s nervous system will generally be less reactive to stressful situations, remaining calm and level headed.

Someone high in neuroticism on the other hand will be much more unstable, and prone to overreacting to stimuli and may be quick to worry, anger or fear. They are overly emotional and find it difficult to calm down once upset. Neurotic individuals have an ANS that responds quickly to stress.

3. Psychoticism/normality

Eysenck (1966) later added a third trait / dimension -Psychoticism – e.g., lacking in empathy, cruel, a loner, aggressive and troublesome. This has been related to high levels of testosterone. The higher the testosterone, the higher the level of psychoticism, with low levels related to more normal balanced behaviour.

- According to Eysenck, the two dimensions of neuroticism (stable vs. unstable) and introversion-extroversion combine to form a variety of personality characteristics.

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Eysenck Personality Theory (3)

Evidence – strength

  • Prison inmates score higher on psychoticism and extroversion as well as on neuroticism (Eysenck and Gudjonsson, 1979).
  • It can explain all crimes (i.e. internet fraud) as the offenders could be said to be looking for excitement
  •  Eysenck’s personality and criminal behaviour theory is one of the most comprehensive theories.
  •  Recognises the interaction between genetics (nature) and the environment (conditioning/nurture).

Evaluation – weakness

  • Extraversion may not lead to criminal behaviour - consider extreme sports, high profile business people, etc - thrill seeking, impulsive etc
  • It’s a questionnaire - Demand characteristics, lie for earlier release
  • Concerns of self preservation and desire to appear ‘tough’
  • Prison experience might have bought out personality that wasn’t there before.
  • Prison experience might have brought about depression
  • Eysenck and Gudjonsson’s study might be a reflection of inmates’ current prison experience, rather than of their offending behaviour that got them into prison in the first place!!!  Prison is not a good place to be if you have a vulnerability to mental illness.
  • However it does not explain why men commit most crimes.
  • It does not explain the socio economic patterns of crime and does not take into account social factors such as poverty and unemployment.
  • It is deterministic (if you have the genes for an ‘underaroused’ brain then you will commit crime) and reductionist as it does not take into account social factors. (see SFP!)
  • Blackburn (1993) therefore concludes that Eysenck’s theory of criminality is not well supported despite the fact that correlates between criminal behaviour and personality traits have been obtained. REMEMBER correlation and causation are NOT THE SAME THING!!
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Prefrontal cortex/limbic system/amygdala

Brain Structures:There are various brain structures that have been implicated in aggression, these include the amygdala, hypothalamus and the frontal lobe. One area of the brain thought to play a key role in aggression is the amygdala. Research has found that direct stimulation of the amygdala in hamsters produces aggressive behaviour and that the amygdala is more active when they are under threat of attack.

Neurotransmitters:Neurotransmitters are chemicals that send messages from one area of the brain to another, research suggests that three neurotransmitters in particular are implicated in aggression. These are serotonin, dopamine and noradrenaline.

Serotonin plays a role in emotions such as impulsive aggression during social decision making by keeping aggressive social responses in check.

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Prefrontal cortex/limbic system/amygdala (2)

Raine (Supporting Research for Neural Mechanisms):

  • Compared the brain structure of 39 males and 2 females who had been charged with committing either murder or manslaughter by matching them with 41 normal individuals based on their *** and age. Participants were asked to complete a 32 minute visual attention task whilst their brain activity was monitored using PET scans. Found significant differeces in amygdala activity, murderers brains were more active on the right whilst the control group had an equal amount of activity on either side.

Scientific Validity (Evaluation of Raine):

  • Praised for having good scientific validity due to the objective scientific measures used e.g. PET scans. This therefore increases the internal validity of the research, providing substantial support for the role of neural mechanisms involved in aggression.
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Prefrontal cortex/limbic system/amygdala (3)

Reductionist (Evaluation of Neural Mechanisms): Some critics have agrued that it is very difficult to isolate presice areas of the brain and theories that do this tend to oversimplify the complex interconectedness of the brain. Similarly, they argue that neurotransmitters alone cannot account for aggressive behaviour as they are part of a wider network. It is widely accepted that there are actually a lot more processes involved in aggression than just the amygdala or serotonin.

Real World Applications (Evaluation of Neural Mechanisms): If aggressive behaviour is a product of imbalanced neurotransmitter levels then it should be possible to treat aggression by administering serotonin increasing drugs. This strategy has been successfully used in aggressive patients suffering from dementia. Therefore the research into neural mechanisms involved in aggression has significant practical applications.

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