Genetics (AQA A-Level Psychology): Revision Notes
Genetics
Genetic explanation of offending behaviour refers to a biological theory suggesting that genes inherited from ancestors form the foundation of an individual's criminal behaviour. This approach examines whether criminal tendencies can be passed down through generations via genetic inheritance.
Twin studies
Twin studies examine the concordance rates (similarity levels) between twins to determine whether criminal behaviour has a genetic component. Researchers compare monozygotic (MZ) twins, who share 100% of their genes, with dizygotic (DZ) twins, who share approximately 50% of their genes.
The logic behind twin studies is that if criminal behaviour has a genetic component, MZ twins should show higher concordance rates than DZ twins since they share more genetic material.
Key research findings
Research Finding: Christiansen (1977)
Studied 3,586 twin pairs in Denmark:
- MZ twins: 35% concordance rate for criminal behaviour
- DZ twins: 13% concordance rate for criminal behaviour
Research Finding: Raine (1993)
Conducted a review of 13 twin studies:
- MZ twins: 52% concordance rate for criminal behaviour
- DZ twins: 21% concordance rate for criminal behaviour
The consistently higher concordance rates in MZ twins compared to DZ twins suggests that genetic factors may contribute to criminal behaviour, since MZ twins share more genetic material.
Family studies
The Cambridge Study in Delinquent Development (Farrington, 1996) tracked 411 males from 400 families between ages 8-32 using interviews, and from ages 10-40 using crime records. The research revealed several important patterns:
Cambridge Study Key Findings:
Family clustering patterns:
- 64% of families contained at least one convicted individual
- Just 6% of families accounted for 50% of all convictions recorded
- When one family member had convictions, other family members were strongly likely to have convictions too
Generational transmission:
- Approximately 75% of convicted fathers and convicted mothers had convicted children
- About 75% of families with convicted daughters also had convicted sons
- Older siblings' convictions were more strongly related to younger siblings' convictions than the reverse
These findings suggest that offending behaviour clusters within families and passes from one generation to the next, indicating a possible genetic component to criminal behaviour.
Adoption studies
Adoption studies provide a method to separate genetic influences from environmental factors by comparing adopted children's behaviour with both their biological and adoptive parents. If adopted children's behaviour resembles their biological parents more than their adoptive parents, this suggests genetic influence.
Joseph (2001) reviewed adoption studies examining criminality and found no evidence supporting a genetic basis for any form of criminal or anti-social behaviour. This finding was consistent across twin and family studies as well.
However, Rhee and Waldman (2002) conducted a meta-analysis of 51 twin and adoption studies and discovered that both shared genetic factors and shared environmental influences accounted for 59% of criminal behaviour. This suggests that both genetic and environmental factors contribute substantially to criminality.
Mixed Evidence from Adoption Studies
The research shows contradictory findings - some studies find no genetic influence while others suggest substantial genetic and environmental contributions to criminal behaviour.
Evaluation of genetic studies
Research findings indicate that family factors influence offending behaviour, but these results only demonstrate that criminal behaviour runs in families rather than proving genetic transmission. Studies cannot definitively show whether results occur due to genetic inheritance, social learning, or other environmental influences.
Key Methodological Limitations:
- The stress experienced during adoption could contribute to offending behaviour in adopted children
- Prenatal stress can affect foetal development, meaning environmental influences cannot be completely controlled
- MZ twins typically receive more similar treatment than DZ twins, which could account for increased concordance rates through environmental rather than genetic factors
Twin studies show higher concordance rates when twins are genetically more similar, which could suggest genetic transmission. However, MZ twins typically receive more similar treatment than DZ twins, which could account for increased concordance rates through environmental rather than genetic factors.
Neural explanation
Neural explanations of offending behaviour focus on how abnormally functioning brain physiology and biochemistry may form the basis of an individual's criminal behaviour.
Biochemistry
Three key neurotransmitters are implicated in offending behaviour: noradrenaline, serotonin, and dopamine.
Noradrenaline forms part of the fight-or-flight response and helps individuals respond to threatening situations. Research indicates that elevated levels link to violence and aggression, making it relatively straightforward to explain some crimes as resulting from chemical imbalances.
Serotonin regulates mood and impulse control. When levels are low, this contributes to criminal behaviour as reduced impulse control occurs. In particularly emotional situations, individuals with low serotonin levels may react impulsively due to impaired capacity to restrain themselves.
Dopamine connects to offending behaviour through its association with addiction and substance abuse, which increases crime likelihood. Dopaminergic activity in the brain's limbic system creates pleasurable experiences, and higher activity levels generate stronger pleasure feelings, making addiction more probable.
Each neurotransmitter affects different aspects of behaviour that could lead to criminal activity - noradrenaline affects aggression, serotonin affects impulse control, and dopamine affects addiction potential.
Research evidence
Research Finding: Higley et al. (1996)
- Testosterone levels correlated positively with aggressiveness but not impulsivity
- Serotonin levels correlated negatively with impulsive behaviour and extreme aggression (but not general aggression)
- Results suggest biochemical levels may influence offender behaviour
Krakowski (2003) reported that although serotonin linked to lack of impulse control and violence, establishing causation proved difficult due to individual differences and social behavioural contexts. For instance, violent events occurring in crowds might prompt different reactions compared to individual situations, even with identical serotonin levels.
Brunner (1993) examined effects of the MAOA gene, which affects neurotransmitter levels in individuals with the shortened gene version. This genetic variation connects to aggressive behaviour and violent crime.
Key Points to Remember:
- Twin studies show higher concordance rates for criminal behaviour in MZ twins (sharing 100% genes) compared to DZ twins (sharing 50% genes), suggesting genetic influence
- Family studies demonstrate that criminal behaviour clusters within families across generations, though this could result from genetic or environmental factors
- Adoption studies provide mixed evidence, with some research finding no genetic influence while other studies suggest both genetic and environmental factors contribute to criminality
- Neural explanations focus on neurotransmitters like noradrenaline, serotonin, and dopamine, which influence aggression, impulse control, and addiction-related behaviours
- Methodological limitations make it challenging to separate genetic influences from environmental factors, and research cannot definitively prove genetic causation of criminal behaviour