Criminology: Intellectual History

Studies of twins and adoptees lend general support for the notion that there is a connection between biology and crime. For example, some studies have found that identical twins (who develop from a single fertilized egg and thus have identical genetic heritage) are more likely to have similar criminal records than fraternal twins (who develop from two different fertilized eggs and thus have the same genetic relationship as ordinary siblings). In addition, some studies of adopted children have found that the criminal records of adopted children are similar to the criminal records of their biological parents, regardless of the criminal records of their adopted parents. These studies suggest at least some connection between biological heritage and the tendency to commit crime. On the other hand, it is possible that the increased criminality may instead be due to social conditions. For example, identical twins are physically more similar than fraternal twins, and so they may have more similar social experiences while growing up. These more similar social experiences then may explain the tendency for identical twins to have more similar criminal records than fraternal twins.

Other biological research attempts to identify specific biological factors associated with an increased risk of criminality. For example, recent studies have found that certain neurotransmitter imbalances in the brain such as low seratonin, and certain hormone imbalances such as extra testosterone, are associated with some greater likelihood of committing crime. Other studies have found that criminals tend to have slower reactions in their autonomic nervous systems. While some criminologists infer that these biological conditions increase the tendency to commit crime, other criminologists point out that all of these biological factors can be influenced by the environmental conditions. Thus, it may be that low seratonin and high testosterone increases a person's tendency to commit crime, but it may also be that committing crime tends to lower seratonin levels and increase testosterone levels.

At least some biological conditions result from a person's interaction with the environment. There has been considerable research, for example, on the influence of diet on crime, with some people arguing that excessive sugar intake results in increased aggression in juveniles. Consuming alcohol has a strong relationship with increased aggression in the short run, as does the consumption of certain illegal drugs. Ingesting various toxic substances such as lead tends to result in long-term increases in the tendency to commit crime. In addition, complications during pregnancy or birth and certain types of head injuries increase the risk of crime in the long run. There is, however, a similar problem with inferring that these environmentally based biological conditions cause crime. For example, some other factor such as poverty could cause both crime and the increased tendency to experience complications during pregnancy and birth, to ingest lead and other toxins, and to drink alcohol. If this were the case, then these biological factors would not themselves have any causal impact on crime.

Even if these biological factors are eventually shown to have a direct causal impact on crime, they would not determine absolutely that people with these factors would turn out to be criminal. Rather, the relationship between biological factors and crime is similar to the relationship between being tall and being a basketball player. Most basketball players are tall, but most tall people are not basketball players. Similarly, it may turn out that a fairly large number of criminals have low seratonin or high testosterone, but most people with these biological factors would not be criminals at all.