Sex offending: the role of genetic factors

silhouetteBy Eloise Godden​

Relatives of men who have been convicted of sex crimes are more likely to commit a sexual offence due to a genetic tendency. This provides new directions for targeting preventative therapy to vulnerable families.

In the large-scale study by the University of Oxford and the Karolinska Institutet in Sweden, it was calculated that men with a brother convicted of a sexual offence were five times more likely to also assault and sons were four times more likely, compared to the general male population.

More than 21,000 Swedish convicts were studied and the crimes included rape, child molestation, sexual harassment and possession of child pornography. Having a brother convicted of a sexual offence raised the risk of a man committing a similar offence from 0.5% to 2.3%. Brothers were significantly more likely to offend than half-brothers, even if half-brothers shared the same upbringing, concluding that this does indeed arise from genetics.

“We are definitely not saying that we have found a gene for sexual offending, or anything of the kind,” said Professor Seena Fazel from the University of Oxford. The scientists strongly emphasised they were not condemning brothers of sexual offenders, rather identifying new areas for preventative therapy. Current therapies only target relapsing offenders.

Evidence resides in the case of half-brothers, the study suggests. Maternal half-brothers of sexual offenders, who commonly lived in the same childhood environment, were compared to paternal half-brothers who tended to have separate upbringings. Predictions assumed there would be a difference between the groups but analysis revealed that the likelihood was almost identical between them.

From this, the scientists concluded that 40% of sexual offending risk can be attributed to a genetic background, with the remainder linked with environmental factors. Personal factors such as upbringing, wealth, education, abuse as a child and medical complications during birth all contribute.

Possible limitations of the study have been highlighted: a focus on men convicted of sexual offences as opposed to the 80% of sexual crimes that go unreported or are not prosecuted, and whether the nature of Swedish reportings and attitudes to sex crimes make it applicable for other countries. Additionally, sexual offences occur at a low rate and therefore small ‘risk’, raising questions over whether a five-fold increase is statistically significant.

men with a brother convicted of a sexual offence were five times more likely to also assault compared to the general male population

“Importantly, this does not imply that sons or brothers of sex offenders inevitably become offenders too,” stressed Niklas Langstrom, who is Professor of Psychiatric Epidemiology at the Karolinska Institute. “Preventive treatment for families at risk could possibly reduce the number of future victims.”

The direction of therapy would address boundary setting, managing relationships, conflict resolution and many other areas linked to sexual crime. Professor Langstrom continued, “It’s important that it does not become a public thing, where not only has your father committed a sexual offence, but you’re forced to attend mandatory courses.”

Concerns arise over whether the study reduces the responsibility of sex offenders. Dr Rajan Darjee, a forensic psychiatrist in Edinburgh, said that offending is not an inevitability, “it just emphasises that genes are an important part of a complicated jigsaw.”

A Finnish study in 2014 suggested that 5-10% of violent crime could be a result of two genes. Although there are no ‘genes for rape’, sexual offence is incorporated in the broad spectrum of extreme violent behaviour, which is thought to have an inherited link. These two genes modify the way the brain functions in many different ways. The Independent newspaper, which leads on the story, explains that countless individuals with the specific gene variants are not violent, demonstrating that it’s a predisposition that can be influenced and controlled, not an assurance.

Genes inherently affect brain development and this underpins psychological workings of the brain. In the realm of behaviour, it’s hard to pinpoint genes to specific traits because the brain is such a complex organ and there is such a heavy bias from environmental roots.

Dr Darjee continued, “We should not interpret the findings of this study to indicate that any male relative of a sexual offender is going to commit a sexual offence so they should be put under special restrictions. We cannot know who will or will not commit sexual offences in this way.”

Can we place any value on genetic links to behaviour, and furthermore, should we? As there are genetic links to committing sex offending, surely there are genetic roots in every type of behaviour imaginable. After all, genes determine brain development. Separation of genetic inheritability from environmental factors is impossible and unlikely to become clearer in the future. Therefore genetic influence should not be considered in cases of sexual assault but it can open the door for preventative measures.

Photograph: Nicolas Alejandro on flickr

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