.3. Biological explanations for criminal behaviour

.3. Biological explanations for criminal behaviour

Study

Aim: Mednick et al. (1984) studied the heritability of criminal behaviour in an adoption study.

Method: Using data from the Danish adoption data bank, which covers the social histories of more than 14,000 children, the criminal conviction rates of male adoptees were compared with those of their biological and adoptive parents.

Results: Twenty per cent of adoptees whose biological parents had convictions but who had been raised by non-criminal parents had convictions. For adoptees whose birth parents were not criminals and who had been raised by non-criminal adoptive parents the rate was 13.5%. Thus biology seems to influence behaviour.

Conclusion: The results are consistent with a modest genetic effect.

Evaluation of the biological explanation

• Although much is known about chromosomes and genetic disorders, no single criminal gene has been identified.

• Twin and adoption study evidence seems to support a genetic component, but does also indicate that the environment may have an influence; even MZ pairs do not show 100% concordance.

• Early twin studies were not well controlled: there was no definitive way to determine whether twin pairs were MZ or DZ, so the researchers often guessed. Twins who were supposedly separated at birth often attended the same school and visited each other regularly.

• Andrews and Bonta (2006) point out that the common criminality of biological parent and adopted child may be a side effect of inherited emotional instability and/or mental illness rather than directly inherited criminality.

• No direct causal link can be established between anomalies in neurological function and criminal behaviour. Evidence from animal studies cannot readily be generalised to explain human behaviour.

• Biological explanations are reductionist, attempting to explain complex offending behaviour at the level of chemicals and cells.

Other neurophysiological anomalies have been noted in psychopaths. Kurland et al. (1963) found that 66% showed spontaneous bursts of rapid brain waves (positive spikes) during sleep. It has also been suggested that APD may be correlated with hemispheric dysfunction. The left hemisphere is usually responsible for language function and the right hemisphere for the understanding and communicating of emotion. Hare and Connolly (1987) suggested that criminals with APD (psychopaths) show an abnormal balance in hemispheric activity, which might explain their inability to use language to regulate their impulsive behaviour and aggressive outbursts. More recently, Raine et al. (2000) have found that people with APD show abnormal brain structure.

In humans, most neurophysiological investigation has been conducted with people diagnosed with antisocial personality disorder (APD). People with APD, sometimes referred to as psychopaths, show no emotion and no feeling for others.

Studies using EEGs of brain activity in the 1950s and 1960s showed that people with APD had abnormal EEG patterns of slow-wave activity, which are typical of brain immaturity.

This led Hare (1970) to propose the maturation retardation hypothesis, which said that the brain of the APD individual is immature and childlike. Characteristics of APD include impulsivity, self-centredness and the inability to delay gratification (all childlike traits). Moffitt (2003) argued that adolescent delinquency may be a result of delayed brain development, although this would not explain persistent life-course offending.

Neurophysiology

Animal research has identified structures in the brain, responsible for control of aggressive behaviour. Even in animals however, aggression usually requires an environmental stimulus, such as the presence of another male. Different regions of the brain have been linked to different types of aggression. For example, Adams (1986) found that lesions to the midbrain of rats stopped offensive aggression but did not affect predatory and defensive aggression.

Chromosomes

Although much is known about chromosomes and genetic disorders, no single criminal gene has been identified. However, there has been an attempt to link criminal behaviour to possession of an extra Y chromosome. The Y chromosome is what determines maleness and is responsible for male sexual development and the male hormone testosterone. You will recall from your AS studies that testosterone has been linked to aggression.

In 1965, Jacobs et al. claimed to have discovered an incidence of the atypical sex chromosome pattern XYY in 1.5% of the prison population, as opposed to the incidence rate of 0.1% in the normal population. There was great excitement that a cause of criminal behaviour had been identified, but this quickly died out when further studies failed to confirm a link. For example, Witkin et al. (1976) found that only 12 men in a sample of over 4,500 had the extra Y chromosome, and none of the XYY males was an offender. The XYY theory of offending is no longer accepted.

Study

Aim: Grove et al. (1990) investigated concordance rates of criminal behaviour in separated in pairs of MZ twins.

Method: Thirty-one sets of MZ twins and one set of triplets were interviewed individually. All the interviewees had been reared apart from shortly after birth. The researchers assessed their behaviour at the average age of 43 years. The interviewers, who were blind to the purpose of the study, scored each interviewee for presence of psychiatric disorders and antisocial personality. Scores for alcohol problems, drug problems, child and adult antisocial behaviour were calculated.

Results: The drug score and both antisocial scores showed significant heritability. The concordance rate for antisocial personality disorder was 29%.

Conclusion: The researchers concluded that these traits had a substantial genetic component.

Genetic Transmission

Twin and adoption studies have been carried out to investigate the heritability of offending behaviour. Concordance rates between identical or monozygotic (MZ) twin pairs and non-identical or dizygotic (DZ) twin pairs are compared. If offending behaviour is genetic, we would expect a greater degree of similarity for that trait between MZ pairs, who share 100% of their genes, than between DZ pairs, who share only 50% of their genes.

Lombroso and Sheldon were forerunners of modern biological psychologists, who look for biological explanations for offending. Three biological explanations are considered here: genetics, chromosomes and neurophysiology. These are not mutually exclusive and offending may be caused by all three. It is quite possible that a behaviour determined initially by genetic inheritance in turn influences neurophysiology.

Adoption studies

Adoption studies involve comparing the criminal futures of adopted children with the criminal history of a) their biological parents and b) their adoptive parents. The method assumes that if there is a greater degree of similarity in the criminal behaviours of adoptees and their biological parents than there is for the adoptees and their adoptive parents, criminality has a genetic component.

The earliest twin study of criminality was carried out by Lange (1929). He found con-cordance rates of 77% for MZ pairs and 12% for DZ pairs. However, early twin studies tended to ignore the fact that MZ twins were usually raised in more similar ways. More recent studues show a difference but it's less vast. The best studies involve MZ twins separate at birth and raised differently.