An Otago University study has challenged the idea that depression and anti-social behaviour are primarily influenced by genes.
The study, which has been published in the international journal Psychological Medicine, found parenting practices were linked to child mental health problems, specifically depression and aggression.
Lead by the head of the university's Centre for Research on Children and Families Professor Gordon Harold, the research suggested the parenting environment plays a unique role in children's development.
Professor Harold and colleagues from Cardiff University and University College London compared genetically related and genetically unrelated children born to parents using in-vitro fertilisation.
A thousand British and American families with children aged four to six years took part in the study over a three-year period.
Mothers and fathers completed a questionnaire on aspects of family life including economic circumstances, family relationship experiences and parenting practices, as well as parent and child mental health symptoms.
Parent and child levels of aggression and depression were assessed among genetically related and genetically unrelated parent and child groupings.
"Associations were found between parent and child symptoms of depression and aggression among parents and children who were genetically related, but, crucially, also among parents and children who were not genetically related," Professor Harold said.
"While common genetic factors such as genes passed on from parents to their biologically related children may explain this association in the first of these groupings, they cannot explain associations in the second grouping as parents and children are not genetically related.
"This suggests that the rearing environment children experience may explain why symptoms are passed on from one generation to the next where common genetic factors cannot account for this transmission process.
The study also found that parents who were hostile towards their children promoted increased levels of aggression in children, but not depression.
Neither hostility nor decreased warmth explained the transmission of depressive symptoms from parent to child, suggesting that some other family environmental factors, such as distressed inter-parental relations, may be important in explaining this specific association.
Professor Harold said the study's results could provide greater impetus for social agencies and Government policy to target specific aspects of the home environment early in life so as to promote more positive outcomes for children later.
"While this conclusion might seem obvious, the unique design feature of this study where genetically-related and genetically-unrelated parent-child groupings may be compared allows the study to counter the idea that common genetic influences serve as the predominant influence on children's behavioural problems," he said
"This finding has significant implications for all parents - including those who are not genetically related to their children such as adoptive parents and genetically unrelated parents of IVF children.
"Rather than blame children's behaviour solely on the genes passed on from a biological parent to a child, look at the environments that children live in to understand better why some children develop behavioural problems while other children do not."