Titled "Sexual offending runs in families: A 37-year nationwide study
," the paper was published Thursday in the International Journal of Epidemiology. It was written by five experts from the Karolinska Institute in Stockholm, Sweden, the University of Ottawa in Canada, and Oxford University in the UK. It was based on nationwide Swedish data about 21,566 men convicted of sexual crimes between 1973 and 2009.
One of the authors, Seena Fazel of the Oxford University Department of Psychiatry, said realizing that genetics can increase the risk that someone will commit a sex crime could help governments target those most in need of help.
In an interview with CNN.com, Fazel acknowledged that isolating genetic factors can be difficult. But he said comparisons -- including of half-brothers who grew up in the same environment but had different mothers -- showed that the biological sons of offenders had a higher risk of becoming offenders themselves.
The biological sons of a sex offender were five times more likely than the norm to commit sex offenses, the study found. But their maternal half-brothers were only twice as likely to do so, the paper said.
"There is a genetic component," Fazel said. "It's not insignificant. It hasn't really be shown before in this field."
The study concludes that genetics accounts for 40% of the risk. But Fazel said that was perhaps too precise a figure, and it would be better to think of it as anywhere between 20% and 50%.
Information might help social services help families
Fazel described the study as an incremental step in increasing understanding of the factors that contribute to the risk of sexual crime. And considering that genetics influences people's sexuality in general, he said, the finding should not come as a complete surprise.
"We shouldn't discard the genetic component," he said. "It isn't all about environment."
One use of the information, he said, would be to help social services that might already be attending to a particular family to work more closely with a person at greater risk regarding relationships, boundary setting and problem solving.
He stressed that a genetic predisposition did not by any means indicate that a person was bound to become a sex offender and said the risk of any particular person committing sexual offenses was small.