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Genes as One Factor

Researchers from Sweden have reported that sexual offending tends to run in families and that it appears to have primarily genetic, rather than environmental, roots.

As they write in the International Journal of Epidemiology, researchers led by Thomas Frisell from the Karolinska Institutet studied longitudinal Swedish crime and family registers to examine crime rates among fathers and brothers of more than 21,500 men convicted of rape and child molestation between 1973 and 2009. By comparing that to crime rates among the family members of a control set of men, they found that full brothers of convicted sexual offenders are five times more likely to also have committed sexual crimes. Fathers and half-brothers of convicted sexual offenders were also more likely to have committed sexual crimes.

Through a statistical analysis, Frisell and his colleagues found that genetic and non-shared environmental factors were more likely than shared environmental factors to explain this effect. According to their analysis, about 40 percent of the risk is accounted for by genetics.

"This does not imply that sons or brothers of sex offenders inevitably become offenders too," first author Niklas Långström from Karolinska tells the Guardian. "But although sex crime convictions are relatively few overall, our study shows that the family risk increase is substantial."

Co-author Seena Fazel from Oxford University adds that social service interventions — focusing on teaching about boundaries, relationship skills, and anger management — could be targeted at the male relatives of sex offenders, though Fazel and colleagues note it would have to be done with sensitivity so as not to ostracize the relatives of sex offenders.

The Guardian also says that there "is no evidence for a 'sex offending gene'" and that genes related to impulse control and others are likely involved.