It is typically thought that bullying behavior in children does not arise until they are older. However, researchers from Cardiff University in Wales found that some of these aggressive tendencies can be seen in children as young as 1 year old as they are developing their motor skills. And, the Association for Psychological Science reports, the source of these violent habits at such a young age might stem from the baby’s mother.

The study, which was published in Psychological Science, studied babies whose mothers had risk factors for violence in children, such as being clinically depressed during their pregnancy, smoking or having a history of conduct problems. The babies were put in a play atmosphere filled with toys and books, a situation where there was the option for them to turn aggressive on the other infants. As the researchers surveyed the infants, bullying tendencies were dramatically apparent among some of the children within 20 minutes.

The researchers found that babies who were most likely to show bullying tendencies had mothers who were depressed during pregnancy or had a history of conduct problems.