Genes affect bullying behaviour

What makes some children more vulnerable to being bullied by peers than others? Heritability plays a major role in school bullying, even more so than the school and home environment. This also goes for the behaviour of bullies. Some bullies are victims themselves, and this too has a genetic basis. This is shown by scientists from the Netherlands Twin Register of Vrije Universiteit Amsterdam. The study is published today in the scientific journal Behavior Genetics.

09/10/2019 | 2:08 PM

1 in 3
The researchers asked the primary school teachers of over 8,000 twin children whether they had bullied or had been bullied over the past few months. It was found that 1 in 3 children had been involved: 1 in 4 as bully, 1 in 4 as victim, and 1 in 7 were both bullies and victims of bullying. This is the first study to unravel the causes of differences between children in bullying behaviour, including the relationship between engaging in bullying and being targeted as victim.

How can something that happens to you be heritable?
People who work with children can typically identify the children who are at risk of being bullied, such as an insecure child who’s overweight and wears glasses. From previous twin research, we know that these traits are also heritable. So the genetically increased risk for being victimized runs partly through other traits.

What’s next?
"The conclusion that engagement in bullying is substantially influenced by genes does not mean that there is nothing to be done," says Sabine Veldkamp, ​​who will obtain her PhD on this topic on 18th September. "So we cannot say: ‘oh well, it's just in their DNA’. On the other hand, it is not the case that children with a genetically increased risk of being victimized cannot be helped," says Veldkamp. 

How has this been studied?
With twins we can study whether behaviour is heritable. Identical twins have the same DNA, while fraternal twins share on average 50% of their DNA. The researchers saw that identical twins were more similar to each other in their involvement in bullying than fraternal twins, which must be due to the influence of genes. Two thirds of differences between children in bullying (or being bullied) are due to genetic differences. A child whose parents, brothers or sisters have been the victim of bullying, is at increased risk of being bullied him or herself. After all, the child shares half of his genes with each of them.

Better together?
It also turned out that twin children are not involved in bullying any more or less than non-twin children. Moreover, it was striking that girl-girl twins are bullied slightly less if they attend the same rather than separate classrooms. Some schools have a set policy of separating twins, but the decision about classroom sharing can best be made in consultation with the parents.

Read the publication here in Behavior Genetics.