Criminal Brains: Intelligence and Criminal Behaviours

I believe that one of the questions asked at least once in everyone’s lifetime is: “why people do what they do? Why in the same conditions/situations do people make completely different decisions?”. One aspect of human behaviour, in particular, is very intriguing from my point of view: why people choose or find themselves engaging in criminal behaviours, and other individuals in similar circumstances don’t? This article doesn’t obviously claim to be a philosophical treatise, although someone of you may find it fascinating – I don’t have the competences for doing so. However, as neuroscience student what I can do is try to identify some of the factors that may contribute to render some brains more propense to develop the criminal outcome decision compared to others.

Correlation between IQ and criminal behaviours

One of the factors that seems to critically influence the tendency to engage in criminal activities is intelligence. A study conducted by Jovanovic D. et al in 2012 on 120 inmates (60 murderers and 60 non-murderer), showed a negative correlation between IQ and criminal activity; that is, the average IQ of the total inmate population resulted to be lower than the general population. Specifically the average intelligence of the inmates investigated was 95.7, placing the cognitive abilities of these individuals in the lower average of normal abilities. Interestingly, the overall intelligence of the homicide group of inmates (97.4) showed to be greater compared to the non homicide group (94.04), suggesting that the individuals convicted for murders seemed to be “smarter” than individuals convicted for other crimes such as robbery, theft and fraud – but still in the lower average compared to general population. It is important to note that the overall score of IQ was given by the combination of two aspects of intelligence: verbal and manipulative-non verbal tasks. The fascinating fact is that while the non-verbal tasks remain mainly unchanged between all inmates and the general population, the component of the test responsible for decreasing the overall IQ score of all inmates was verbal abilities. Another study from Gibson et al conducted in 2001 showed that the interaction between family adversity and below average verbal IQ at the age of seven is a predictive indicator of early onset of offending behaviours. Once again, it appears that the defecting aspect of intelligence in individuals with higher risk of engaging earlier in criminal behaviours is the verbal part. An even more interesting finding from this study is that the children with higher family adversity factors (i.e. more serious situations), had also lower verbal IQs; in constrast, children with lower adversity factor had higher verbal IQs,. These results can be interpreted in many way, but the most intuitive one would be that specific adverse life events can have an important impact on the development of natural abilities.

Can Intelligence development be promoted to ultimately prevent crime?

I am convinced that the results above describe may raise a number of questions…The first of them being: “what is this trait of personality, i.e. intelligence, that seems to be influenced by the environment and life events?”. Well, it is very difficult to define intelligence, and today, a univocal definition of it that is accepted by everyone still does not exist. However, a broad picture of what intelligence is can be given by describing it as ‘the entirety of abilities that allow individuals to understand and develop complex concepts, engage in diverse types of abstract reasoning and consequently adapt efficiently to the external environment’ (Neisser et al 1996). The finding of Gibson’s et al study seems to suggest that these abilities can be enhanced or reduced by external factors, to the point where the result of this interaction can be considered as a predictive indicator of early offending. Other studies also show that socioeconomical status may have an important impact on neurocognitive abilities during development, in particular on language skills (Hackman et al 2010). It is important to underline the fact that in all the studies here described one particular aspect of intelligence, verbal reasoning, seems to be mostly affected by external adverse events and is found to be responsible for lowering the IQ scoring in criminal adults. This finding opens a wide range of considerations, for example that it is plausible that some adverse events in life may interfere more with the development of some aspects of intelligence, for example verbal skills but not with – or at a lesser extent to – others, such as manipulative/non-verbal abilities. Furthermore, it is possible to infere from this that the study of intelligence in correlation to criminal behaviours can also be used as a tool not only to understand the “reasons” of criminal outcomes, but also for reaching a clearer insight of how intelligence works and is developed.

At this point it is important to notice that, although the external environment plays a crucial role in the development of these abilities, it is widely known that the heritability of intelligence (i.e. the amount of trait variation that is due to the individual genetic code) can be up to 50% (Deary et al 2009). Unfortunately, the genes responsible for heritability of normal range intelligence haven’t been found yet, but what if one day we could map these genes? Could this variable, in conjunction with other indicators such as detrimental life events, family adversity and socioeconomical status, help us to one day predict even more precisely which individuals have higher risk of engaging in criminal activities? And prevent those events by supporting those individuals?

In conclusion, I believe that in light of these considerations, it is reasonable to state that a more supporting society in respect to disadvantaged situations could eventually promote intelligence development in children and could ultimately represent a less criminal society. And even if this wasn’t the case…why not give it a try?

Author: Cristina Cabassi

Edited by Molly Campbell


  • Deary J. I., Johnson W., Houlihan L.M., 2009, Genetic foundations of human intelligence, Hum Genet, 126:215–232


  • Gibson L.C., Piquero R.A., Tibbets S.G., 2001 The Contribution of Family Adversity and Verbal IQ to Criminal Behavior,I nternational Journal of Offender Therapy and Comparative Criminology, 45(5), 574-592


  • Hackman A.D., Martha J. F., Miachael J.M., 2010, Socioeconomic status and the brain: mechanistic insights from human and animal research, Nat Rev Neurosci; 11(9): 651–659.


  • Jovanovic D., Novakovic M., Salamadić A., Petrovic , Maric s., 2012, Analysis of the relation between intelligence and criminal behavior, Journal of Health Sciences, Vol 2, N. 3,


  • Neisser et al, 1996, Intelligence: Known and Unknowns, American Psychologist, Vol. 5, N. 2, 77-101














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