A research recently suggested the sons and brothers of convicted sex offenders are prone to get convicted of sex crimes, because sex offence may be written in their genes. Unfortunately, no matter how interesting the finding is, it is unlikely to help prevent sex crimes or catch offenders.


DNA of 21,566 men convicted of sex offences in Sweden between 1973 and 2009, was analyzed and results showed that sons and brothers of convicted sex offenders were four to five times more likely to be convicted of sex crimes than men in the general population. Furthermore, the research concluded that in mere 2% of cases, it’s possible to explain this familial connection via shared environmental factors, like social or environmental aspects of their upbringing that siblings would have experienced together.

While shared genetics were a factor in 40% of cases, 58% of cases stemmed from environmental factors not shared between family members but which influenced the offending individual uniquely. It was also found that genetic factors were stronger for child molestation (46%) than for adult rape (19%). The study just makes an estimate of the heritability of sexual offending, and cannot for sure pinpoint the genes that might be involved.

Nature Vs Nurture

This behaviour is inherited directly by the children from their parents.. Surely, genetic material from both parents is passed on, nonetheless, genetic traits are developed through interaction between genes and the environment. The percentages mentioned above show that the largest proportion of cases involved a large, rag bag of environmental factors, whether shared or specific to that individual, that are by far the greatest influence on behaviour than inherited genes.

Setting genetic and environmental factors apart – or nature and nurture – of course is useful as a model but makes no sense because research has shown that gene development is affected by the environment. Opinions regarding genes influencing behaviour, nonetheless, differ.

Some accept scientific evidence, that sex offenders are biologically different from other people and could perhaps be prevented from offending. Others are worried about the stigmatisation of family members defined as “at risk”, but still unlikely to offend themselves. Just 2.5% of brothers or sons of convicted sex offenders were also convicted so the preventative programmes aimed at at-risk families, advised by the researchers, would primarily target the innocent.

A Genetic Defence

A genotype dubbed the “criminal” or “warrior” gene, has been identified; it has in certain cases been used successfully by defence teams in mitigation pleas to avoid the death penalty in the US, or reduce the length of sentences in the US and Italy.

Still it sounds odd that a convicted murderer, who is at increased risk of offending and therefore perhaps more dangerous to the public in the future, would be treated more leniently. Sex offenders, specially child molesters, are perhaps even more stigmatised than other violent criminals so probably a genetic defence would not work in their favour.

What is evident is that finding genetic influences on behaviour has no effect on legal responsibility. Legal responsibility is not determined on the basis of someone being fully autonomous, or on an abstract notion of free will. Definitely there are various genetic, biological and environmental factors that affect behaviour, and it may be harder for all sorts of reasons for some people to refrain from criminal acts than others.

Nevertheless, a research that demonstrates genetic link in 40% of cases – does not tell us that sex offenders “can’t help it” or are different from “normal” people. Around a third of Caucasian men have the “warrior gene”, but those who are not ill- treated in childhood are actually less likely to be violent than the rest of the population.