Criminal behaviour biological explanation - genetics

• Notions such as “genes for crime” are nonsense. Still, the following notion is reasonable: There may be partially genetically influenced predispositions for basic behavioural tendencies, such as impulsivity, that in certain experiential contexts make the probability of committing certain crimes higher than for individuals who possess lesser degrees of such behavioural tendencies.”
• A gene is the basic physical and functional unit of heredity. Genes, which are made up of DNA, act as instructions to make molecules called proteins. In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases.
• Every person has two copies of each gene, one inherited from each parent. Most genes are the same in all people, but a small number of genes (less than 1 percent of the total) are slightly different between people.
• Alleles are forms of the same gene with small differences in their sequence of DNA bases. These small differences contribute to each person’s unique physical features.
• Genes determine physical features such as hair and eye colour, but there is increasing evidence that the genes we inherit from our parents can also determine psychological traits such as our personality, abilities, and even what mental illnesses we may suffer from. 

  Any genetic explanation in psychology contributes to the nature-nurture debate.
• Few supporters of an ‘inherited criminality’ claim that there is a specific gene for specific crimes; there is not a ‘murderer’ gene or a ‘burglar’ gene as such. 
• Hollin (1992), for example, suggests that some people inherit a biological predisposition for criminal behaviour, specifically a personality type that makes them more likely to commit crime. It may also be the case that some individuals may inherit a gene that makes them more aggressive, and as such it makes them more likely to demonstrate criminal behaviours.
• Identical twins are also known as monozygotic twins.​​​

  ​​​​Identical twins result from the fertilization of a single egg that splits in two.​​​

  ​​​Identical twins share all of their genes and are always of the same sex.​​
• Non-identical or fraternal twins are also known as dizygotic twins.​​​

  ​​​Non-identical twins are the result of the fertilization of two separate eggs during the same pregnancy.​​

  ​​​​​Non-identical twins share up to half of their genes and may be the same sex or different sexes. ​​
• concordance rates of twins for Criminal behaviour

  Lange (1931)

  MZ - 77

  DZ - 12

  Kranz (1936)

  MZ - 65

  DZ - 53

  Yoshimasu (1965)

  MZ - 50

  DZ - 0

  Christiansen (1977)

  MZ - 60

  DZ - 30
• Twin studies

  One of the earliest twin studies into criminal behaviour was by Rosanoff et al (1934). He studied 97 twin pairs, finding male concordance rates of 22/33 MZ (67%) and 3/23 DZ (13%).
• Raine (1993),reviewed the literature comparing the delinquent behaviour of twins, and it was found that the average concordance rate was higher for MZ twins (52%) than DZ twins (21%). A later meta-analysis by Ishikawa and Raine (2002)  found a concordance rate for criminality of 44% for MZ twins and 21.6% for DZ twins.

  (A01)
• The main limitation with twin studies is that they do not take into account environmental factors. For instance, if one identical twin grows up in an affluent area while the other lives in poverty, this could have a significant impact on their likelihood of committing crimes. Therefore, we cannot say whether any differences between the twins were due to genetic influences or environmental ones.
• Adoption studies involve children being adopted at birth and then followed through life. The aim is to compare the characteristics of adoptees who develop criminal tendencies with those who don’t. This allows researchers to determine how much influence nature has over nurture when it comes to criminal behaviour.
• However, (A03), Dalgard and Kringlen (1976) studied 49 male MZ and 89 same-sex male DZ pairs, finding no statistically significant concordance rate difference using either a “broad” or “strict” definition of crime. The MZ twin concordance rate for broadly defined crime was 22%, and 26% for strictly defined crime. Based on these results and of the more similar environments experienced by identical twins, the authors concluded, “These findings support the view that hereditary factors are of no significant importance in the aetiology (cause) of common crime.”
• Family Studies A01

  The Cambridge Study of Delinquent Development is a study that started in 1962, it aimed to be a prospective longitudinal study of boys, and it started with a sample size of 411 males born in 1953. 

  The sample was drawn from working-class areas of London. Researchers have reported on the results of this group and have assessed numerous factors which may explain the delinquency and criminal behaviour levels seen in the sample.
• One of the most notable findings from the CSDD was reported by Osborn and West (1979) who reported on a survey of 383 of the original 411 males. The boys were aged 24-25 at the time of this research; the fathers were all in their forties. 

  Osborn and West reported on the number of sons who had criminal convictions and found that 40% of sons with ‘criminal fathers’ also had a criminal conviction, compared to only 13% of the sons with ‘non-criminal’ fathers.
• A01

  Similarly, Farrington (2002) investigated the concentration of criminal behaviour in families by looking at three generations of relatives, including parents, grandparents, aunts, uncles and cousins. It was found that if one relative had been arrested, there was a high probability that another relative had also been arrested. The most important relative was the father; if the father had been arrested, there was a high chance of sons being arrested too.
• A03

  While this would initially seem to suggest that genes may play a part, we cannot rule out the effect of the shared environment. Another finding from Farrington was that having a young mother and living in a bad neighbourhood added to the probability of fathers and sons being arrested. This again confuses the issue of genes and environment.
• Adoption Studies

  Mednick (1987) studied over 14,000 adoptees….. A01

  Parents with a  criminal record

  % of sons with a criminal record?

  None

  13.5

  Biological only

  20.0

  Adoptive only

  14.7

  Biological and adoptive

  24.5
• How could we use this data to argue that the environment has an effect? A03

  Interestingly, even when adoptive parents know that their adopted child’s a family history of criminality, this has no effect on their later criminal behaviour (Bohman 1996). 
• Which genes? A01

  If there is a genetic basis for criminal behaviour, then genes should be able to be identified which lead to that behaviour. The gene would have some sort of effect on the body, which would in turn lead to the behaviour such as impulsiveness or aggression that would lead to a higher risk of criminal behaviour. There have been a number of potential genes for criminal behaviour proposed.
• A01

  One gene that is of particular interest is the gene for monoamine oxidase type-A (MAOA), which helps to recycle the neurotransmitter serotonin.
• The gene for monoamine oxidase type-A (MAOA), helps to recycle the neurotransmitter serotonin. Seo et al (2008) proposed that low levels of serotonin may predispose individuals to impulsive and aggressive behaviour. Brunner et al (1993) studied a Dutch family, many of whom were highly aggressive. Their behaviour was linked to a mutation in the MAOA gene, meaning that they had abnormally low levels of serotonin, accounting for their aggressive behaviour.
• Brunner et al (1993) studied a Dutch family, many of whom were highly aggressive. Their behaviour was linked to a mutation in the MAOA gene, meaning that they had abnormally low levels of serotonin. This could possibly account for their aggressive behaviour. 
• This is supported by other studies that have found a link between a mutation in this genes and criminal behaviour (Tiihonen et al, 2015)
• A03 - Simply identifying the gene isnt enough...

  We need to identify exactly what the genes do in the body or brain in order to create the criminal behaviour. As we have seen above, a mutation in the MAOA gene may affect levels of serotonin, altering behaviour. Another possible explanation may be that these genes cause changes in the brain.
• A03

  It might also be the case that these genes cause criminals to inherit a different type of personality, one that predisposes them towards crime.
• A01

  Caspi (2002) used data from the longitudinal Dunedin study that has followed around 1,000 people from when they were babies in the 70’s .  Caspi assessed antisocial behaviour at age 26 and found that 12% of those men with the low MAOA gene had experienced maltreatment but were responsible for 44% of violent convictions.