IQ has nothing to do with aggressive behaviour.

Unfortunately for those who wish to deny IQ (sometimes known as ‘G’ for general intelligence) is real, the data and the science continue to pile up against such beliefs. In fact, studies repeatedly confirm the reality of IQ and the connections between a variety of both positive and negative life outcomes and intelligence. Not only do studies of the general population support the reality of IQ, but even studies specifically conducted inside prison systems confirm those claims.

For example, studies consistently reflect the fact that chronic or repeat criminal offenders have a lower average IQ than non-offenders. This is true among both juvenile repeat offenders (who average about 92) and adult repeat offenders (who average about 85). IQ tests are normed for a populace to 100. Every few years the tests are re-normed due to IQ drift, which tends to be upwards (commonly referred to as the ‘Flynn effect’). The 15 point difference between the norm for the general population and that of chronic offending adults is known as 1 standard deviation.

More evidence comes from a study conducted in the Texas prison system which found that more than 20% of criminal offenders had an IQ below 80. IQ’s at such a level begin to seriously impede a person’s chances at life success and it is thought that a life of crime then becomes an alternative (dangerous and risky) path for such persons. Additionally, those who have IQ scores around 80 and below have significant problems in balancing short-term vs long-term desires. This is sometimes referred to as the ability to delay gratification and is related to time-preference (‘I want what I want and I want it now by any means necessary’ vs ‘I want X but will work slowly, methodically, and legally or morally to attain it’).

This is not, however, to say that those of moderate to high IQ do not commit crimes. The presumption here is that those of higher IQ tend to commit crimes which they are able to conceal or are harder to detect for a host of reasons. Still yet, chronic offenders do tend to be involved in far more physical crimes: burglary, assault and battery, car-jacking, drunk-driving accidents, homicides, and the like. Much of this is supported in the study linked below:

http://criminal-justice.iresearchnet.com/crime/intelligence-and-crime/3/