Toddler Aggression Linked to Genetic Factors

It turns out that aggression in toddlers may not just be due to their environment. Researchers have discovered that the development of physical aggression is strongly associated with genetic factors instead. The findings reveal that when it comes to behavior, a lot of it has to do with genes.

Over the past 25 years, researchers have believed that physical aggression has been highly influenced by the social environment. More specifically, they thought that the onset and development of physical aggression is mainly determined by accumulated exposure to aggressive role models and the media. Yet it appears that this may not be the case.

"The gene-environment analyses revealed that early genetic factors were pervasive in accounting for developmental trends, explaining most of the stability and change in physical aggression," said Eric Lacourse, one of the researchers, in a news release. "However, it should be mphasized that these genetic associations do not imply that the early trajectories of physical aggression are set and unchangeable. Genetic factors can always interact with other factors from the environment in the causal chain explaining any behavior."

In this latest study, the scientists tested three general patterns regarding the developmental roles of genetic and environmental factors in physical aggression. First, the most consensual and general point of view is that both sources of influence are ubiquitous and involved in the stability of physical aggression. Second, a "genetic set point" model suggests a single set of genetic factors could account for the level of physical aggression across time. Third, a pattern labeled "genetic maturation" states that new sources of genetic and environmental influences with age.

So what did the researchers find? The scientists conducted a twin study with 667 pairs of twins. The mothers of these twins were asked to rate their physical aggression by reporting behavior such as biting, kicking and fighting.

"The results of the gene-environment analyses provided some support for the genetic set-point hypotheses, but mostly for the genetic maturation hypotheses," said Lacourse in a news release. "Genetic factors always explained a substantial part of individual differences in physical aggression. More generally, the limited role of shared environmental factors in physical aggression clashes with the results of studies of singletons in which many family or parent level factors were found to predict developmental trajectories of physical aggression during preschool."

The findings reveal a little bit more about physical aggression in toddlers. More specifically, it reveals how genetics have more of a role to play than previously thought. Even so, the environment can still play a role in impacting behavior.

The findings are published in the journal Psychological Medicine.