There is a strong difference in juvenile crimes and adult crimes, in the fact that monozygotic twins and dizygotic twins were very similar when looking at juvenile criminality thus not showing any difference between environment and genetic factors causing the behaviour (Lyons et al. 1995). However the study did show that in adulthood crimes, monozygotic twins reassembled each other more than dizygotic twins. Kalat (2003) says that this shows that adults have more power over their environment thus magnifying a genetic predisposition to criminal behaviour.
Ridenour (2000) brought up the fact that birth complications occur much often with twins than with singletons, this being may be a factor confounding the evidence of twin studies, for indeed it has been shown (Rosanoff, Hardy and Plesset 1941) complications at birth are in correlation to criminal behaviour. The last biological factor that would be interesting to study is the hormonal aspect of criminal behaviour. Bernhardt (1997), Brooks and Reddon (1996) found that men with the highest testosterone levels had the most violent behaviours.
They also found that individuals incriminated for violent crimes such as rape and murder had the highest levels of testosterone. Acher supports this theory of testosterone as a correlation to criminal behaviour for indeed he found in 2000 that the men between 15 and 25 were the men most frequently convicted for violent criminals offences this coinciding with the fact that between 15 and 25 men experience the highest levels of testosterone in their life. Another correlation can be made by the fact that testosterone is an essentially male hormone; they are thus incriminated more frequently for violent crimes than women.
Indeed when injecting testosterone into women Van Honk found that their heart beat went up significantly when looking at angry faces (2001). He concluded that testosterone made reactions more vigorous. However Kalat (2003) indicates that the problem with explaining violent criminal behaviours is that "environment stressors could affect hormone levels and violent behaviours independently". Indeed one could imagine a factor inducing criminal behaviour and at the same time inducing the production of higher levels of testosterone.
In conclusion to this first discussion around the possibilities of genetic factors inducing criminality, it is important to say that simply physiology could be at the source of getting involved in violent criminal behaviour or not. Indeed a study by Raine, Reynolds, Verables, Mednick, and Farrington in 1998 showed that boys that were tall for their age at three were more aggressive and more fearless. Indeed these boys when reaching the age of eleven were just as fearless and aggressive even though not being in the higher range for sizes.
This could show a habituation to fearlessness and thus a readiness towards aggressiveness. The major criticism about heritability studies and studies that look into the genetics of behaviour in general, is that the prenatal environment is not taken into account. Indeed prenatal environment is at the fringe of nature and nurture, not precisely in either category. A very interesting study by Bernan, Grekin, Madnick, in 1999, showed a relationship between maternal smoking during pregnancy and the criminal behaviour of the offspring in adulthood.
Moreover Colinger et al. (1982) found that smoking during pregnancy combined with a difficult delivery multiplied the effect of predisposition to criminal behaviour, showing that the two factors in combination showed extremely significant levels of predisposition; whereas individually the factors of smoking and difficult delivery were only slightly significant. However it has been said that "it would be premature to conclude that maternal prenatal smoking can now be included among the established risk factors for later antisocial behaviours.
There is further work to be conducted into underlying mechanisms and the possible confounding effects of genetic factors. Given the ambiguities in the evidence, the most prudent summation of research in this area is that maternal prenatal smoking may affect longer-term behavioural development, but considerable uncertainty still exists about the origins of the relationship" (Fergusson, David 1999). In this discussion one can not put aside exclusive environmental factors that could induces criminal behaviours even if genetic factor clearly lead to some kind of predisposition.
The precursors must be found in the environment surrounding the individual. Indeed Gottfredson and Hirschi's (1990) say that lack of self control is the first factor leading to criminal behaviour. Thus one could think that self control is learnt with the socialisation of the individual, being a main factor for criminality. This would also meant that people less advanced in the socialisation process such as adolescents would have less self control and thus be more open to falling in to criminality.
Thus leading us back to Lyons study (1995) that showed that monozygotic twins and dizygotic twins were very similar when looking at juvenile criminality, showing that whether having the same genes or not the environmental factor is stronger. Conversely Peter Lagrange and Silverman (2003) in a study using data from 2,000 adolescents attending junior and senior high schools in Canada found that self control was an important contributors to criminal behaviour but in an additive way and not an interactive way.
In a more general way it has been shown that general factors of the socialisation of the individual are precursors to criminality, such as peers, education and qualification for adolescents and drug abuse, marital and parenting difficulties for adults (Messer, Maughan, Quinton, Taylor, 2004). In a more critical way Swanston found that child sexual abuse is a risk factor for criminal behaviour (2003), this showing that the differences in experiences lived for each individual are defining, and are correlated to the behaviours developed by each individual.
However a major criticism in the studies looking only into the environmental effects as precursors to criminal behaviour, is that there is no differentiation made between non violent and violent criminal behaviour, two types that we considered very different and that need to be studied independently and not assumed as one type of behaviour. A study by Kerner and Weitekamp in 1997 looking into the correlation between alcohol abuse and criminality shows that environmental factors as well as biological factors go hand in hand when explaining criminal behaviour.
Indeed the findings where that drinking was a typical behaviour of criminals and that the more criminal offences were committed the more the individual was drinking. On the other hand, it has also been found that neither early experiences of socialisation nor imprisonment experiences were sufficient casual conditions for a heavy, alcohol consumption in later life (Kerner and Weitekamp, 1997). In any case significant results showed that less criminality was closely correlated to less alcohol consumption.
A study of this nature shows that an environmental factor at first (being exposed to alcohol) can become a biological factor, (the effect of the alcohol intake) both connected to the behaviour in question. A study about the effect of non treated head injuries at a young age also shows this ambivalence. Leon-Carrion and Ramos in 2003 showed that non treated head injuries could be correlated to violent criminal behaviours in later life. Indeed obtaining the head injury is an environmental factor however the brain damage occurring from it becomes a biological factor both correlated to the criminal behaviour.
What was even more interesting was the fact that this study showed that non treated head injuries could be correlated to violent criminal behaviours in later life whereas academics difficulties could be correlated to non violent criminal behaviours. This last study leads us to our conclusion to the discussion. It seems that the differentiation between non violent criminality and violent criminality is essential, they are two extremely separate behaviours that cannot be treated together.
It would seem that the evidence for genetic predisposition to non violent criminality is quasi inexistent and thus finds all its precursors within the environment of the individual. However strong evidence has been brought up to show the importance of genetic factors when considering violent criminality creating a predisposition to crime going hand in hand with environmental factor, becoming the precursors to the behaviour in question.
As a concluding comment it should be said that biological, psychological and social explanations are closely connected and complementary when it comes to criminal behaviour (Koutouvidis, Minogianni, 2003). Brennan (1997) proposes to look in to personality theories, for "personality is a concept that is an essential feature of any acceptable theory of criminality. Personality provides taxonomy of human behaviour and relates to genetics and biological variables".
rennan, P. A. , Grekin, E. R. , Mednick, S. A., (1999) Maternal smoking during pregnancy and adult male criminal outcomes, Archives of General Psychiatry, vol. 56 (3): 215-219. Fergusson, D. N. , (1999) Prenatal smoking and antisocial behaviour, Archives of General Psychiatry, vol. 56 (3): 223-224. Swanston, H. , et al. (2003) Juvenile crime, aggression and delinquency after sexual abuse: A longitudinal study, British Journal of Criminology, vol. 43 (4): 729-749 Peter, T. , Lagrange, T. , Silverman, R. , (2003) Investigating the interdependence of strain and self-control, Canadian Journal of criminology and criminal justice, vol. 45 (4): 431-464.