Parents, take note! Toddlers throw tantrums because of their genes and not because of their upbringing, a new study has found.
Physical aggression in toddlers is strongly linked with genetic factors and to a lesser degree with the environment, according to the study led by Eric Lacourse of the University of Montreal, Canada.
Researchers worked with the parents of identical and non-identical twins to evaluate and compare their behaviour, environment and genetics.
"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," Lacourse said.
"However, it should be emphasised 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 behaviour," he said.
The study, published in the journal Psychological Medicine, involved parents of twins born between April 1995 and December 1998 in Montreal.
Mothers were asked to rate the physical aggression of their twins by reporting behaviour such as hitting, biting, kicking and fighting, at the ages of 20, 32 and 50 months.
Lacourse and his colleagues 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.
A third pattern labelled 'genetic maturation' postulates new sources of genetic and environmental influences with age.
"According to the genetic maturation hypothesis, new environmental contributions to physical aggression could be of short duration in contrast to genetic factors," Lacourse said.
"The results of the gene-environment analyses provided some support for the genetic set-point hypotheses, but mostly for the genetic maturation hypotheses," Lacourse said.
"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," he said.
Our results suggest that the effect of those factors may not be as direct as was previously thought, Lacourse said.
