Genetic Explanations of Offending Behaviour

Do genes make a person a criminal? There are genetic explanations for crime in psychology that state that criminals have a gene that predisposes them to commit crimes.

Johannes Lange (1930) studied 13 identical (monozygotic, MZ) and 17 non-identical (dizygotic, DZ) twins, one of whom had served time in prison. He found that 10 of the MZ twins but only 2 of the DZ twins had a twin who served time in prison.

More recently, Karl Christiansen (1977 twin study) studied 87 MZ and 147 DZ twins and found a concordance rate of the criminality of 33% for MZ twins but only 12% for DZ twins. This finding supports the view that criminality may have a genetic basis.First, let us clarify some essential terms before we get to the topic at hand.

Diagram showing how genes affect the physical features of an organism, YB - StudySmarter Originals

What are candidate genes?

Candidate genes are genes that scientists believe influence a particular behaviour or trait. The Tihonen et al. (2014) genetic analysis of nearly 900 offenders revealed abnormalities in two genes associated with a violent crime:

• The MAOA gene controls dopamine and serotonin and links to aggressive behaviour.

• CDH13 gene linked to substance abuse and attention deficit disorder.

People with a combination of both genes were 13 times more likely to have a history of violent behaviour.

Diagram showing the effects of the MAOA gene and CDH13, StudySmarter Originals

Diathesis-stress model

Criminality is likely related to environmental factors (we have already seen how the diathesis-stress model is related to schizophrenia). A combination of genetics and a dysfunctional environment may cause criminality.

What are neural explanations of offending behaviour?

There is evidence of neural differences between the brains of criminals and non-criminals. Much of this research has looked at individuals with antisocial personality disorder (APD), a condition characteristic of many convicted criminals.

Prefrontal cortex

Adrian Raine reported several dozen brain imaging studies showing that individuals with APD have decreased activity in the prefrontal cortex (this regulates emotional behaviour). He also found an 11% reduction in grey matter volume in the prefrontal cortex of people with APD compared to controls.

Mirror neurons

Research shows that offenders with APD can show empathy less easily than other people. Keysers et al. (2011) found that criminals showed compassion only when prompted (by an image of someone feeling pain in a film). Such reaction is due to the activation of mirror neurons.APD criminals have a neural empathy ‘switch’ in the brain that can be turned on or off, whereas this switch is permanently on in other people.

Evaluation of genetic explanations of offending behaviour

Are there any problems with the genetic explanation of offending behaviour? Does the notion of a ‘criminal gene’ pose a dilemma? The following overview of the pros and cons might help us answer these questions.

Strengths

• Support for genetics: Mednick et al. (1984) screened 13,000 Danish adoptees to see if they had at least one court conviction.
  • They found that the percentage of adoptees with prior convictions was 13.5% when neither the biological nor adoptive parents had previous convictions. When adoptive parents had convictions, 15% of adoptees had criminal records. When biological parents had convictions, it was 20%. When both biological and adoptive parents had convictions, it was 24.5%. These results suggest genetic factors may influence criminality (adoptive parents – 15% vs biological parents – 20%). However, we cannot rule out environmental factors, as adoptees were most likely to have convictions when both biological and adoptive parents had prior convictions.

Weaknesses

• Twin studies: Early twin studies such as Lange’s decided whether they were MZ or DZ twins based on appearance rather than DNA testing, which reduces their validity. Twins are an unusual sample and may not represent the rest of the population. The fact that most twins grew up in the same environment is an important confounding variable, and their similarities may be due to environmental factors rather than genetic factors.
• Adoption studies: It is difficult to distinguish between genetic and environmental factors because a) many adopted children are adopted late in life (and therefore are already under the environmental influence) and b) many adoptees continue to contact their biological parents.
• Difficult distinction: It is difficult to distinguish between all the things that occur in families; crime, emotional instability, social disadvantage, mental illness, poverty, etc. (Katz et al., 2007). How do we know what causes what
• Criminal gene: In our society, we punish criminals for morally wrong behaviour. But if criminals behave in specific ways because of their genes, could we argue that they are not acting out of free will? And if so, is it ethical to punish them?