When you think about why people commit crimes, do you think of nature or nurture? We typically view criminal behaviour as a product of the environment or one's poor choices, but is there a genetic component to it as well? If so, the implications for our justice system can be quite severe, so it's important to assess the different genetic explanations of offending behaviour to truly explore what makes a criminal.
- We are going to explore the various genetic explanations in psychology for offending behaviours. First, we will provide a genetic explanation definition.
- Next, we will discuss studies that support genetic explanations of offending behaviour, including the Christiansen (1977 twin study) and Mednick et al. (1984) adoption study summary.
Then, we will outline how genetics link to neural explanations of offending behaviour.
- Moving along, we will explore how the environment can interact with biological explanations of offending behaviour.
Finally, we will evaluate the genetic explanation of psychology.
Fig. 1 - Genetic explanations of offending behaviour investigate what genes are associated with offending.
Genetic Explanation Definition
Genetic explanations investigate the heritability and genetic correlates of offending behaviour. We can investigate the degree to which genes contribute to a trait or behaviour by calculating heritability estimates.
Genes consist of DNA (deoxyribonucleic acid) strands. DNA provides instructions for general physical characteristics (e.g., height) and the process that occurs within an organism (e.g. neurotransmitter activity), which can affect psychological traits.
Family studies, including twin and adoption studies, investigate whether genetic similarity is associated with a similarity in behaviour.
If a behaviour is more common among people with similar genes (family members) than people with less genetic similarity, it indicates the behaviour has a high heritability.
However, heritability estimates only tell us how differences in genes account for differences in behaviour on a population level. Just because a trait is highly heritable in the population doesn't necessarily mean we can predict how much genes influence a trait in any specific individual.
Christiansen (1977): Twin Study
One way of studying heritability is by conducting twin studies. Twin studies compare how similar monozygotic and dizygotic twins are on a particular trait. If a trait is heritable, we expect to see a greater similarity among monozygotic twin pairs.
In the late 70s, Karl Christiansen launched a large-scale study of 3,586 twin pairs in Denmark. The aim of the study was to investigate the heritability of criminal behaviour.
- He compared the concordance rates of criminal behaviour among monozygotic (who share 100% of their genes) and dizygotic twins (who share 50% of their genes).
Concordance rates refer to the probability of both twins sharing the same trait.
Let's say that the concordance rate for extraversion is 60%, then, if one twin was extroverted, there would be a 60% chance that the other would be as well.
Christiansen found higher concordance rates of criminal behaviour among monozygotic twin pairs compared to dizygotic twin pairs. This suggests that there is an element of heritability to criminal behaviour. However, the concordance rates are relatively low, suggesting that genes are not enough when it comes to offending.
Concordance rates found in Christiansen's 1977 twin study of criminal behaviour |
|---|
Gender of twins | Level of genetic similarity |
Monozygotic (100%) | Dizygotic (50%) |
| Males | 35% | 13% |
| Females | 21% | 8% |
Fig. 2 - One way of studying heritability is by conducting twin studies.Grove (1990): Study of Twins Reared Apart
Grove (1990) also wanted to investigate the genetic contribution to offending behaviour. To fulfil this aim, he conducted a study of twins who have been separated shortly after birth and grew up in different environments.
- Grove (1990) recruited 32 monozygotic twin pairs that grew up separately for his study.
- The twins were assessed through tests and interviews in terms of alcohol problems, drug problems and symptoms related to antisocial behaviour in childhood and adulthood.
Grove found significant positive correlations between genetic influences and symptoms of childhood antisocial behaviour (0.28) and adulthood antisocial behaviour (0.41).
These results indicate similarity in terms of antisocial behaviour among the twins. However, the correlations are low to moderate, even though the twins shared 100% of the same genes; this again indicates a significant contribution of environmental factors as well.
Monozygotic twins are not only identical when it comes to their genes, but also share a similar environment growing up. By studying identical twins reared apart, Grove (1990) wanted to investigate if their similarities remain even if they don't share their environment.
Mednick et al. (1984) Adoption Study Summary
Mednick et al. (1984) investigated the heritability of offending behaviour using an adoption study design.
Adoption studies look at how similar the adoptees are to their biological versus adoptive families. If they remain similar to their biological family on a particular trait despite growing up with the adoptive family, this indicates a contribution of genetic factors to the trait.
They screened 14,427 Danish adoptees to see if they had at least one court conviction and looked at whether their adoptive or biological parents also had any convictions. Those under 15 were excluded.
Percentage of adoptees with prior convictions in relation to their biological or adoptive parents' criminal records. |
|---|
Biological parents | Adoptive parents |
with prior convictions | without prior convictions |
with prior convictions | 24.5% (sons) | 20% (sons) |
without prior convictions | 14.7% | 13.5% |
The study's results suggest that genetic factors may influence criminality, as there was a greater similarity in criminal behaviour between adoptees and their biological families (particularly in sons and biological fathers) compared to their adoptive families.
However, we cannot rule out environmental factors.
Fig. 3 - Mednick et al. (1984) showed that adoptees (sons) are more likely to offend if their biological father has a criminal record.
Neural Explanations of Offending Behaviour
Neural explanations describe behaviour in terms of abnormalities within the brain and the nervous system. One way in which genetics could potentially influence offending behaviour is by causing abnormal monoamine metabolism. One genetic abnormality affecting serotonin metabolism is the MAOA gene.
Monoamines include many neurotransmitters that facilitate communication between brain areas.
Brunner et al. (1993) conducted a family study to investigate the effect of the MAOA gene on behaviour. The researchers studied five males within a Dutch family, the members of which had borderline mental retardation and behavioural problems.
The participants had a rare genetic condition, which only affects males and manifests as an inability to control aggressive behaviours. The researchers hypothesised that males in this family had a MAO-A enzyme deficiency due to an abnormal MAOA gene.
MAO-A enzyme breaks down monoamines like serotonin.
The researchers studied the cells of affected males and found negligible amounts of MAO-A activity, which indicated that the metabolism of monoamines in this population was abnormal. This was supported by a decreased concentration of 5-HIAA (a serotonin metabolite) in the participants' urine samples.
It was concluded that the genetic abnormality in the males was linked to their inability to control their aggression.
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.
Role of the Environment in Biological Explanations of Offending Behaviour
Genes can also influence behaviour indirectly through one's environment. Plomin and Asbury (2005) conducted a review that highlighted that, just as environmental research needs to consider the influence of genetics, genetics research needs to consider the role of the environment.
Let's consider the example of the MAOA gene; while a shorter variation of this gene is independently linked to violent behaviour, it can also interact with one's nurture.
Adverse childhood experiences were found to affect violence only in individuals with a shorter version of this gene (Reif et al., 2007).
There are several ways through which genes can impact our nurture: these include the passive, the reactive and the active way.
- Passive way: Biological parents often create the child's early environment.
- Reactive way: The child's temperament, which develops due to genetics, can influence how others react to them.
- Active way: Temperament can also impact the person's choices for themselves.
The appropriate conjunction between the words nature and nurture is not versus but and. (Plomin & Asbury, 2005, p.86)
Genetic Explanation: Psychology Evaluation
One strength of the genetic explanation of offending behaviour is that it is based on scientific studies and supported by empirical evidence. However, the quality of methodologies varies, and it might be difficult to separate the influence of genetics and other influences.
One criticism of adoption research is that it doesn't control whether the twins actually shared a similar environment growing up. This is important as many adoptees remain in contact with their biological families or are selectively placed in adoptive families that are similar to their biological ones.
The genetic explanation of offending behaviour can be considered to be biologically reductionistic. It looks at aggression as caused by a biological abnormality and doesn't necessarily acknowledge how this may interact with the environment and what other social and environmental factors are related to offending behaviour.
Moreover, the extreme side of this explanation promotes biological determinism. It takes away from people's ability to make free choices about their behaviour and assumes that a genetic predisposition is bound to cause offending.
There are also important social implications to taking that deterministic position. Punishing people will be considered unethical if they offend due to their biology. After all, they were biologically predetermined to commit crimes and had no choice.
Genetic Explanations of Offending Behaviour - Key takeaways
Genetic explanations investigate the heritability and genetic correlates of offending behaviour.
The heritability of offending behaviour is supported by Christiansen's (1977) and Grove's (1990) twin studies and Mednick et al.'s (1984) adoption study.
Genetics are involved in causing neural vulnerabilities to violence and aggression.
The environment also plays an important role in affecting offending behaviour and can interact with one's genetic predispositions to offending.
The genetic explanation of offending behaviour has empirical support. However, it can be considered reductionist and deterministic.
References
- Plomin, R., & Asbury, K. (2005). Nature and Nurture: Genetic and Environmental Influences on Behavior. Annals of the American Academy of Political and Social Science, 600, 86–98. https://doi.org/10.1177/0002716205277184
- Reif, A., Rösler, M., Freitag, C. et al. Nature and Nurture Predispose to Violent Behavior: Serotonergic Genes and Adverse Childhood Environment. Neuropsychopharmacol 32, 2375–2383 (2007). https://doi.org/10.1038/sj.npp.1301359
Explanations 
Exams 
Magazine 
