Twin studies nature vs nurture crime

While Lombroso’s work was influential, it quickly lost popularity. That being said, those who had previously agreed with the concept of atavistic form, later retracted that assertion, but did go on to say that while it may not account for the whole criminal population, it could explain as much as a third of it (Lombroso-Ferrero, 1911).

Much later, research into biological explanations of offending behaviour continued, and contemporary methods such as neuroimaging have helped us to develop scientific ways of classifying offending behaviour.

Twin Studies

Twin studies are a well-known method for identifying a genetic basis of behaviour. By examining monozygotic (identical) twins and dizygotic (non-identical) twins (who share 100% and 50% of their genetic make-up respectively), concordance rates (i.e. percentages to show how many twin pairs share the behaviour under observation) can help to indicate a possible genetic tendency.

Christiansen (1977) examined over 3,500 twin pairs in Denmark and identified concordance rates of criminal behaviour as follows:

The findings are interesting as they indicate a degree of inheritance; however, there are some key points to consider. Firstly, the concordance rates are low, even for monozygotic twins, which indicates that the environment still plays a large part in criminal behaviour. Secondly the difference between male and female twin pairs raises an interesting question about the role of gender in criminal behaviour (see critical thinking section below).

Family Studies

Family studies are another way of investigating genetic links in offending behaviour. Brunner et al. (1993) conducted an analysis of a large family in the Netherlands, a number of which had been responsible for various counts of anti-social and criminal behaviour including attempted rape, exhibitionism and arson. The researchers found that the males had a genetic condition which became later known as “Brunner syndrome” (it is important to note that females only carry this condition, as it only affects the MAOA production gene on the single X chromosome in males). The condition results in lower intelligence levels (the family studied had an average IQ of 85) and causes a deficiency in monoamine oxidase A (MAOA), an enzyme responsible for the metabolism of neurotransmitters such as serotonin (which has links to aggression). The conclusion here is that individuals can inherit genetic conditions which make them prone to offending behaviour.

Exam tip – the Brunner study can be used as an example of both genetic and neural explanations, as both explanations can be used to justify the conclusions drawn by the researchers.

Adoption Studies

Adoption studies – A key criticism raised by research into genetics is that it cannot rule out the effect of the environment. For example, a twin study may find a 68% concordance between monozygotic twins, but if they are raised in the same home environment, then the chances are that they will be treated in a similar way by their parents/siblings and therefore the learning environment that they grow up in is likely to be a factor in their behaviour. Adoption studies attempt to rule this out by looking at children who have been adopted and have therefore been raised by adopted parents where there is no genetic similarity.

Crowe (1972) compared a group of adopted children whose biological mother had a criminal record, to a control group of adopted children whose biological mother did not have a criminal record. It was found that if a biological mother had a criminal record, 50% of the adopted children also had one by the time they were 18. In the control group, only 5% of the adopted children had a criminal record by the time they were 18. This suggests that regardless of the changed environment, children seemed biologically predisposed to criminality.

Evaluation of Genetic Explanations

Twin studies and family studies are seen as problematic since they don’t rule out the impact of the environment. The results could be due to social learning since the twin sets and families concerned are all occupying the same environment. One way around this is to use adoption studies, which enable psychologists to rule out the effects of the environment, since the adoptees are being raised in a different environment from the biological parent concerned. This helps us to see if there is any genetic link, in spite of the shared environment.

Brunner et al.’s (1993) research has been criticised for using a case study method. Case studies are uniquely specific to the small number of individuals involved and therefore lack representativeness. This matters because it is difficult to apply the results beyond the family in question, since the genetic make-up is unique to them.

Biological explanations of offending behaviour provide strong support for the nature side of the nature versus nurture debate.For example, research into families and twins, suggests that there is some genetic basis for behaviour, which has implications for our understanding of offending behaviour. However, supporters of the nurture argument argue that to ignore the influence of external factors such as parenting, culture and social learning, misses crucial elements of explaining offending behaviour and it can therefore be considered reductionist.This is important to consider as while the evidence to support a biological basis for offending behaviour is strong, there are other elements to consider which reduce the effectiveness of the biological findings.

For More Study Notes…

To keep up-to-date with the tutor2u Psychology team, follow us on Twitter@tutor2uPsych, Facebook (AQA) / OCR / Student or subscribe to the Psychology Daily Digest and get new content delivered to your inbox!

How does the nature vs nurture argument describe crime?

How does twin studies explain criminal Behaviour?

What can twins teach us about nature vs nurture?

What did the twin study prove?