Bioethics Blogs

Is Sexual Offending Genetic?

Do genes make sex offenders? Are rapists and child molesters driven by biology or environment?

An article published last week in the International Journal of Epidemiology&nbsp;provides compelling evidence for a genetic component to risk of sexual offending.[1] The study found that sons or brothers of convicted sex offenders are 4 to 5 times more likely than randomly selected males to be convicted of a sexual offence. Half-brothers of sex offenders, in contrast, are only twice as likely as controls to be convicted of such offences. The study estimates on this basis that genetic factors contribute about 40% of this variability in risk of offending. Environmental factors shared between siblings, such as parental attitudes, were estimated to contribute only 2% of this variability.

The article predictably has generated significant interest, with The Telegraph, for example, heralding that ‘sex offending is written in DNA of some men.&rsquo; To the casual reader, this might all sound as though sex crimes are biologically preordained, an inevitable consequence of genetic heritage. Before we get carried away, however, it&rsquo;s important to reflect on what the study shows, and what it doesn&rsquo;t.

First, as we&rsquo;ve already noted, only 40% of the increased risk of offending is attributed to genetic factors. 58% of this risk is attributed to unshared or ‘unique&rsquo; environmental factors (and measurement error). This includes pretty much every biological, psychological, and social event outside of the shared home environment, including in the womb, at school, and beyond. Genes grab the headlines, but an equally important story lies in untangling this hugely complex biopsychosocial web of causation.
