Researchers have found that male relatives of convicted sex offenders are five times more likely to commit a similar crime themselves, and that the risk is influenced heavily by their genes.
The study, led by Niklas Långström, a professor of psychiatric epidemiology at the Karolinska Institute in Sweden, looked at 21,566 records from men who had been convicted of a sexual offence in Sweden between 1973 and 2009. The team chose to focus only on men, since less than 1 percent of convicted sexual offenders during this time were female.
The analysis revealed that 2.5 percent of men who were closely related to a sex offender - so, brothers or sons - ended up being convicted of a similar crime themselves, which is significantly higher than the 0.5 percent of men in the general population who are at some point convicted of a sexual offence.
"Having a father or a brother convicted of a sexual offence increased the odds of being convicted oneself four to five times compared with age-matched control men without a sexually aggressive father or brother," the team writes in the International Journal of Epidemiology. This familial connection when it comes to sex offenders suggested to the researchers that something, either environmental or genetic, or both, was at play.
The team used statistical modelling to analyse the data, and found that genetic factors accounted for 40 percent of the risk, and non-shared environmental factors, such as individual social experiences and challenges, accounted for 58 percent of the risk.
Shared environmental influences, on the other hand, such as the influences of parenting, the place you grow up, and education, accounted for just 2 percent of the risk. In an accompanying analysis, the researchers write, "genetic effects tended to be weaker for rape of an adult (19 percent) than for child molestation (46 percent.)"
The researchers are careful to point out that this in no way means that the sons or brothers of sex offenders will inevitably become sex offenders themselves, nor should we be locking them up or ostracising them. The study is about better understanding who is at risk, so assistance and intervention can be offered to those in high-risk families.
It's also about clearing up long-held misunderstandings related to who is more likely to commit a sexual offence in their lifetime. The 'cycle of abuse' idea in particular, Långström told Hannah Devlin at The Guardian, has probably been given too much weight. Devlin explains:
"To demonstrate this, they considered the case of maternal half-brothers (typically brought up in the same family home) and paternal half-brothers (who normally live with different mothers). If environmental factors were largely responsible, a much higher risk would be expected in maternal half-brothers whose siblings had committed crimes.
But both groups were roughly twice as likely to offend if their half-sibling had previously committed a sexual offence. The link was also about half as strong as for full siblings, again supporting the idea that genetic factors were more powerful."
The more we know about the risks, the more we can intervene and give support to those who need it, which makes studies like this so important.
Source: The Guardian