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April 9, 2015

"Reality check: Is sex crime genetic?"

ImagesThe question in the title of this post is the headline of this interesting new Science piece that a helpful reader sent my way.  Here are excerpts:

A splashy headline appeared on the websites of many U.K. newspapers this morning, claiming that men whose brothers or fathers have been convicted of a sex offense are “five times more likely to commit sex crimes than the average male” and that this increased risk of committing rape or molesting a child “may run in a family’s male genes.”  The study, published online today in the International Journal of Epidemiology, analyzed data from 21,566 male sex offenders convicted in Sweden between 1973 and 2009 and concluded that genetics may account for at least 40% of the likelihood of committing a sex crime. (Women, who commit less than 1% of Sweden’s sexual offenses, were omitted from the analysis.) The scientists have suggested that the new research could be used to help identify potential offenders and target high-risk families for early intervention efforts.

But independent experts — and even the researchers who led the work, to a certain degree — warn that the study has some serious limitations. Here are a few reasons to take its conclusions, and the headlines, with a generous dash of salt.

Alternate explanations: Most studies point to early life experiences, such as childhood abuse, as the most important risk factor for becoming a perpetrator of abuse in adulthood. The new study, however, did not include any detail about the convicted sex criminals’ early life exposure to abuse.  Instead, by comparing fathers with sons, and full brothers and half-brothers reared together or apart, the scientists attempted to tease out the relative contributions of shared environment and shared genes to the risk of sexual offending....

Data on sexual crimes are tricky to obtain and parse: It’s extremely difficult to collect sufficient data about sexual offenders and their families to detect statistically robust patterns.  Sweden is unusual because its nationwide Multi-Generation Register allows researchers to mine not only anonymized criminal records, but also to link them with offenders’ family records as well.  Even with access to a nationwide database, Seena Fazel, of the University of Oxford in the United Kingdom, and colleagues had to include a very diverse range of offenses, from rape to possession of child pornography and indecent exposure, to maintain a large sample size.

The team did do some analysis by type of offense, separating rape from child molestation, for example.  But some researchers worry that attributing a genetic basis to such a wide swath of behaviors is premature.  There are also problems with relying on conviction records: Many more sexual crimes are committed than reported, and the proportion of those that go to trial is even smaller.

In addition, families with one member who has been convicted of a sexual offense are likely to be under much higher scrutiny by social services and law enforcement, leading to potential detection bias that artificially enhances the perception that sex crimes run in families, says Cathy Spatz Widom, a psychologist at the City University of New York who studies the intergenerational transmission of physical and sexual abuse.  In a recent study, for example, Widom found that parents with a formal record of being abused as children were 2.5 times more likely to be reported to Child Protective Services for abusing their own children than parents in a control group who admitted to abusing their children, or whose kids said they had been mistreated.

The absolute risk of becoming a sex offender is very low: One of the study’s more dramatic-sounding findings is that brothers and fathers of sex offenders are four to five times as likely as men in the general population to commit sex crimes themselves. That statistic seems pretty striking until you look at the low prevalence of sex offense convictions in Sweden overall....

In summary, there’s no doubt that some families are at a higher risk for abuse and criminal behaviors, including sexual offenses.  But we’re a long way from pinning down genes that can explain why a person commits rape or any other sex crime.

April 9, 2015 at 10:23 PM | Permalink


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A few years ago, you could ask a child or adolescent sex predator, where did you learn how to do that? Many replied, it was done to them, and they were doing the same to others.

Today? It is almost unanimous. From watching adult porn, often in school. True of even 10 year olds.

Posted by: Supremacy Claus | Apr 10, 2015 1:24:51 AM

This is typical of Science. They change their findings and everyone goes with it for a while, then something comes up to prove science wrong and doubt comes in. Then science with all it's 100% brilliance comes back with "yet another explanation" that they will go with for the next run.

Posted by: Book38 | Apr 10, 2015 10:09:03 AM

"There are also problems with relying on conviction records: Many more sexual crimes are committed than reported, and the proportion of those that go to trial is even smaller."

This is not a minor problem but the qualification that swallows the results. Effective sexual criminals don't get caught the same way that effective fraudsters don't get caught. So there is a huge problem with what researchers call systemic risk--that the characteristics between those who get caught and those who don't get caught vary in some statistically meaningful way. The problem with systemic risk is that it is difficult to study and in the case of criminals next to impossible.

In my view these studies do more harm than good. They inflate the researcher's resume without actually offering any actionable intelligence.

Posted by: Daniel | Apr 10, 2015 2:16:53 PM

In 1987, the black juvenile rape arrest rate was 74.3 per 100,000; In 2012 it was 15.4, down almost 80%. It isn't genetics, it's lead poisoning.

Posted by: Rick Nevin | Apr 10, 2015 3:27:49 PM

I agree with Daniel.


Rick. I acknowledged the lead level theory as a major factor in the downward trend of crime, after seeing a longitudinal study showing higher lead levels in criminals. I could not fully accept correlations made from macro statistics, without an individual link. Now, I can.

But surely, a sophisticate like you has adopted the cluster theory of catastrophes, where multiple factors come together in a place and time to produce a catastrophe, or some other major, widespread effect. My disagreement remains that the lead level is the sole or even the strongest factor.

Here is an alternative for your consideration, not yet studied, but self evident. You put millions in prison. They cannot spawn super-predators with their crack whores. So the fecundity of the criminal has been diminished. Release them now. They begin the spawning again, the results in crime rate will take place 16 years later, when the spawn becomes an adolescent.

The other consequence of the Great Release will the end to the current lawyer unemployment. That effect fully explains the strange advocacy of emptying the prisons when the crime rate is so low. If I am a diabetic doing very well on insulin, my doctor says, stop the insulin. Both diabetes and criminality are lifelong chronic conditions. So stopping insulin and stopping Incarceration Nation have the same effect of relapse.

Posted by: Supremacy Claus | Apr 10, 2015 7:28:52 PM

The jean theory is correct. If you are a parent do not let your male child wear blue jeans. Or baseball caps backwards. A capsbackwards guy in blue jeans is a likely suspect. The detectives who investigate these crimes know these things. Now the notion that somehow forty kids with the jeans still on in a swimming pool will accelerate the process is all arse backwards. The jean pool theory is all hogwash. But, to be safe, keep the kids outta the pool unless they are in a swim suit.

Posted by: Liberty1st | Apr 12, 2015 8:04:56 PM

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