Biological Explanations of Offending Behaviour

• MAOA gene

  Gene located on the X chromosome, low variant causes a deficiency in monoamine oxidase A
• Monoamine oxidase A (MAOA)


  An enzyme that breaks down important neurotransmitters in the brain, including dopamine and noradrenaline which has links to aggression which may lead to offending behaviour
• Variations of the MAOA gene

  • Low activity form (MAOA-L)
  • High activity form
• People with the low activity form (MAOA-L)


  Produce less of the enzyme, have higher levels of neurotransmitters, and have been linked to offending behaviour
• About one-third of men in Western populations have the low-activity form of MAOA
• Criminal behaviour


  Runs in families and is transmitted genetically
• Genetic explanations for crime


  Suggest that (would be) offenders inherit a gene, or combination of genes, that predispose them to commit crime
• Twin studies

  • Identify a genetic basis of behaviour by comparing concordance rates between identical (monozygotic MZ) and non-identical (dizygotic DZ) twins
• Twin studies


  • Lange (1930) found 77% concordance rate for MZ twins and 12% for DZ twins, concluding that genetic factors must play a predominant part in offending behaviour
• MAOA gene


  Gene linked to aggression and offending behaviour
• Research by Brunner et al (1993)


  • Investigated male members of a Dutch family with history of aggressive and violent acts
  • Found males had genetic condition "Brunner syndrome"
  • Condition results in lower intelligence (average IQ 85)
  • Causes deficiency in monoamine oxidase A (MAOA)
  • Results in abnormal levels of neurotransmitters including noradrenaline and dopamine
• The research by Brunner et al offers compelling evidence that individuals can inherit genetic conditions which make them prone to offending behaviour
• Concordance rates

  The rate at which twins show the same behaviour or trait
• Concordance rates of criminal behaviour

  • 33% (MZ)
  • 12% (DZ)
• Concordance rates of criminal behaviour


  Suggests offending may have a genetic component
• Twin studies of criminality

  • Most twins are reared in the same environment, which is a major confounding variable
  • Concordance rates may be due to shared learning experiences rather than genetics
  • Identical twins (MZ) may be more likely to model the criminal behaviour of their twin than non-identical (DZ) twins
• Twin studies of criminality highlight the difficulty of disentangling nature from nurture when explaining offender behaviour
• Diathesis-stress model


  Modern understanding of genetic influence no longer propose that one or even a few genes on their own will determine offending behaviour. Instead, current thinking suggests a diathesis-stress model, whereby a tendency towards criminal behaviour may come about through the combination of genetic predisposition and a psychological factor (i.e. being raised in a dysfunctional environment or having criminal role models).
• Caspi et al. (2002) study

  • Longitudinal study in New Zealand that followed about 1,000 people from when they were babies in the 1970s
  • Assessed antisocial behaviour at age 26
  • Found that a low activity version of MAOA gene ALONE was not a significant predictor of aggression, however low activity version of the MAOA gene, PLUS maltreatment had a significant effect on aggression
• A more appropriate explanation for offending behaviour is to use an interactionist approach by combining genetic factors with environmental factors (maltreatment).
• A criticism of genetic explanations of offending behaviour is that they are biologically deterministic; they are presented as if the genes a person is born with determines (controls) later behaviour
• Stephen Mobley's lawyers' argument


  • Mobley was genetically predisposed to seeking violent solutions to conflict and that his behaviour was outside of his control
• Evidence argues that criminality cannot be 100% explained in terms of genetics and Mobley was sentenced to the death penalty
• Tiihonen et al. study


  • Those with the defective gene were 13 times more likely to have a history of repeated violent behaviour
  • Not everyone with the gene had become an offender
• It is suggested that at the very least it is harder for some men to avoid criminal violence, because of their biology, however we should not forget the role of free will
• Neural explanations for offending behaviour

  Possible differences in brain structure and the bio-chemistry of the body
• Aggression

  • The result of an interaction between a system of brain structures
  • Frequently linked to offending behaviour
• Amygdala


  • Part of the limbic system which processes emotional information
  • Implicated in offending behaviour
  • Aggressive impulses are created in the amygdala in response to a threat in the environment
  • Involved in the stress response, can initiate the process of fight or flight
• Men with lower amygdala volumes were three times more likely to be aggressive, be violent, and to show psychopathic traits than men with more normal-sized amygdala's
• Prefrontal cortex


  • Regulates impulse control and social interactions
  • Damage associated with antisocial behaviour and offending behaviour
  • Responsible for planning behaviour
• Participants with anti-social behaviour and frontal lobe damage showed emotional instability and a failure to consider the consequences of their actions or to adapt their behaviour in response to external cues
• Serotonin

  • Regulates mood and impulse control
  • Low levels implicated in offending behaviour due to more impulsivity
• Noradrenaline


  • Abnormally high levels associated with aggression, violence and criminality
  • High levels associated with the activation of the sympathetic branch of the autonomous nervous system and the fight or flight response
• Research Support


  Research from Raine et al (2000) supports neural explanations of offending behaviour
• Raine's study

  1. Used PET scans

  2. Highlighted areas of brain activity in offenders who had been charged with murder or manslaughter and had pleaded not guilty by reason of insanity

  3. Compared to a matched control group
• Findings of Raine's study

  • Reduced activity for the offender group in areas such as the prefrontal cortex and corpus callosum
  • Abnormalities in the activity of the limbic system, including the amygdala and thalamus
  • Offenders (specifically violent offenders) have abnormal brain function when compared to normal controls
• Structural brain abnormalities found in Raine et al. (1997)


  Could be a cause of offending behaviour or the result of some environmental factor, which in turn makes them more likely to become a criminal
• The relationship between biology and behaviour is complex and further investigation is required
• Research into the role of neural mechanisms on offending behaviour

  • Uses laboratory experiments
  • Uses PET scanning method to highlight areas of brain activity
  • Objective method using scientific measurements
  • Removes extraneous variables
  • Removes subjectivity in measuring emotions
• The rigorous control of the research process meets the criteria of psychology as a science