Osborn & West (1979) found that 40% of sons of criminal fathers were criminal, compared to only 13% who had non-criminal fathers. This is consistent with most family studies, but the evidence is insufficient to ‘prove’ the heritability of criminal behaviour. Family studies have numerous methodological problems; for instance, it is impossible to separate genetic and environmental contributions to behaviour (Raine 1993). Most researches tend to investigate twin and adoption studies, when seeking a biological answer for criminality.
Twin studies seek explanations in the belief that, as monozygotic (MZ) twins share an identical genetic make up (compared with 50% in dizygotic (DZ) twins); genetics are the cause of criminality because they share the same environment.
Therefore they will be similar in criminal behaviour compared to DZ twins. Lange (1931) studied criminal behaviour finding a mean behavioural similarity of 75% in MZ twins to 24% in DZ twins. However the sample sizes were small and similarity was determined by appearance alone, and therefore may not be accurate.
Research in later years overcomes this problem by using DNA and other genetic techniques to identify MZ and DZ twins.
Furthermore, twins are not a common phenomena and are not, therefore, representative of the population as a whole. It could also be argued that whilst twin studies show high heritability for criminology, they mention nothing about the wide variety of parenting styles and the influence of education. Adoption studies suggest if adopted children are more similar to biological parents than adopted parents in terms of criminal behaviour, this provides strong evidence for genetic endowment.
Alternately, if adopted children are more similar to adopted parents, this provides a strong case for environmental influences. Studies have shown that criminal biological parents lead to a high frequency of criminal offspring (more so when both parents are criminals). Bohman, Clongier, Sigvardsson & Knornig (1982) investigated the relationship between environment and genetic factors using cross fostering analysis of petty crime. The result showed, when both factors were present criminality was 40% compared to 12% for genetic factors alone and 6.7% for environmental alone.
It could be argued therefore, the interaction of environment and genes accounts for the higher numbers of criminal behaviour. In adoption studies, factors such as socioeconomic status of the adoptive home, time spent by the individual in foster care, criminality in adoptive home and knowledge of the biological parents must all be taken into consideration (Cadoret 1978). Whilst contemporary theory has moved away from the notion of a single ‘criminal gene’ towards polygenetic considerations, the 1950’s and 1960’s saw the emergence of an explanation for violet crime in terms of an individual, identifiable genetic abnormality – the XYY chromosome.
The association between the XYY syndrome and crime came from studies that suggested that XYY males had a disproportionate inclination to violent offences. Owen (1972) reviewed the evidence and suggested otherwise, describing a number of shortcomings with the research: including difficulties with the identification of the extra Y chromosome; the fact that the rate of XYY males in criminal populations is not radically different from non-criminal populations; poorly controlled measures of aggression and violence; and that sexual rather than violent offences appear to be more frequent with XYY males.
However, another review by Jarvik et al. (1973) favoured the view that XYY males are over-represented in criminal populations compared to non-criminal populations. A study by Witkin (1976) involved testing over 4000 men for the presence of the extra Y chromosome. Only twelve cases were identified: whilst these twelve men were more likely to involved in crime than might be predicted on the basis of chance alone, this was not found to be violent crime. The data provided strong support for the relationship between criminal behaviour and the extra Y chromosome.
However, the link specifically with violent crime remains unsubstantiated Furthermore, there are individuals with XYY syndrome that are not criminals, and the vast majority of criminals do not have any chromosomal abnormalities at all. Other theories regarding criminality focus more on the social influences of behaviour. It could be argued that a major determinant of violent or aggressive behaviour is social learning (Bandura, 1974; 1977; 1989). Social learning theory argues individuals learn through modelling, that is, copying the behaviour of others.
However, how or what an individual learns varies according socio-cultural background, as their models will differ in each context (Sternberg, 1995). Oatley (1993, in Sternberg, 1995) posits that individualistic cultures will experience more criminal behaviour than collective cultures, perhaps due to the informal social controls of these cultures. Sternberg (1995) further argues that given social learning is an important factor with regards to criminality and violent behaviour, careful attention should be paid to the kind of models individuals present to each other.
Another form of social learning can be explained through the theory differential association (Sutherland, 1939; 1947, Sutherland & Cressey, 1970; 1974). Although differential association theory is frequently defined as a sociological theory, differential association theory has clear links with social learning theory. Differential association theory not only describes the necessary social conditions to produce crime, but also attempts to explain the processes by which the individual becomes criminal.
Thus, ‘crime’ is seen as political, defined by those with the power to do so: however, while some people behave in accordance with these definitions, others act outside them. Differential association theory suggests that some individuals are ‘criminal’ in their preferred ‘definitions’ of acceptable behaviour that are seen as deviant by the lawmakers. Sutherland suggests there are various ways in which an individual acquires their favourable definitions of crime.
Differential association theory is an attempt to explain crime in terms of social learning and proposes that through contact with other people who hold favourable definitions towards crime, similar definitions are learned. It is important to note that the theory does not propose that the learning has to occur through association with criminals, but rather with people who hold definitions favourable to crime. For example, parents who tell their children it is wrong to steal might, however, show examples of dishonesty such as not informing a shop assistant if they receive too much change in error.