Nature vs Nurture of a Criminal Mind: Is Criminal Behaviour Influenced by Environmental Causes or Genes?

Nature vs Nurture of a Criminal Mind:  Is Criminal Behaviour Influenced by Environmental Causes or Genes?
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Background to the Case

Abdelmalek Bayout confessed to the murder of Walter Felipe Novoa Perez in 2007 and was sentenced to 9 years and 2 months in prison. But at the Court of Appeal in Trieste in May 2007 the judge dropped a year from his sentence because a psychiatric report had concluded that his genetic makeup means that he is prone to violent behaviour if provoked.

Abnormalities were found in five genes that have been linked to violent behaviour. One of these genes encodes an enzyme called MAOA –metabolizing enzyme monoamine oxidase A. Previous research has associated low levels of MAOA expression with aggression and criminal conduct in boys raised in abusive environments.

Criminal Behaviour Influenced by Environmental Causes and Genes

If there are genes for criminality, is it morally right to lock someone up because their DNA compels them to commit crimes? Should they be offered corrective therapy rather than punishment? It’s the age old debate – is it nature or nurture that makes someone a criminal? Are they just the product of their environment or totally at the mercy of their genes? The truth probably lies somewhere in between. It always seems, to me at least, that it is too simplistic to pin cause down to one and exclude the other when looking for an explanation of some behavioural traits. From a number of twins, family, adoption studies and lab work the evidence points to an interaction between genes and the environment.

Which one plays the most important role in determining the behaviour of an individual? The jury is still out on that one.

But let us, for the sake of this article imagine there are genes for criminal behaviour, however that behaviour is defined - whether it is violence, stealing, or a tendency for tax evasion. So are we justified in punishing someone with ‘criminal genes’? I think the answer is straightforward - yes. You may disagree with me, but here are my reasons.

There is nothing in the scientific literature that says that genes diminish a person’s responsibility for their own behaviour or for how a person makes choices in their life.

If a person does possess a ‘criminal gene’ or marker, this will be a predisposition to behave in such a way. He or she would be inclined to act in a criminal way, not compelled to. This is no different from someone who grows up in an environment that might increase their chances of becoming a criminal. A person from an unfortunate background or someone with a genetic marker for criminality may find it more difficult than the general population to keep on the right side of the law, but neither is bound to behave in a criminal fashion.

Prison cell by Andrew Bardwell - image released under Creative Commons Attribution 3.0 License

As society does not absolve a criminal from responsibility for his crimes because of his upbringing, why should someone with a ‘gene for criminality’ be treated any differently?

Then there is this wonderful quote by University College London geneticist Prof Steve Jones: “90% of all murders are committed by people with a Y chromosome — males. Should we always give males a shorter sentence? I have low MAOA activity but I don’t go around attacking people.”


Any discussion about the genetics of negative behavioural traits raises the horrid spectre of eugenics. If criminal genes are discovered should they be weeded out of the gene pool by limiting the reproductive capacity of people with those genes? Of course not. As discussed above, if there is evidence that links genes to criminality it does not mean that a person will develop criminal behaviour.

A person with a genetic predisposition to lung cancer or heart disease can sometimes avoid contracting these conditions by managing their environment and lifestyle. In the same way a person who may be found to have a genetic predisposition to criminal behaviour could also learn to avoid the stressors that would “tip them over the edge.” Phenotype does not always follow genotype.

So what help could be given to individuals who are identified as having factors that might make them susceptible to developing criminal behaviour? Well, some experts have proposed that education and environment enrichment programs should be designed and developed to treat those who are in need. Not only will the individual benefit, but so will society in the long run.


Lighter sentence for murderer with ‘bad genes’ Nature News Published online 30 October 2009 | Nature | doi:10.1038/news.2009.1050