With the long-time debate as to whether nature or nurture controls behavior, a recent research finally provides answers that may put the argument -- at least as far as violent behavior is concerned -- to rest. Researchers from the Universite de Montreal in Canada said that genes, together with environmental factors, could also trigger antisocial behavior.
In a study participated by a group of 1,337 high school students (17 and 18 years old) in Vastmanland, in Sweden, the respondents provided saliva samples and completed questionnaires addressing delinquency, family conflict, experiences of sexual abuse, and the quality of their relationship with their parents.
The study found three (3) genes that seem to have "control" over antisocial tendencies, mixed with the influence of experiences and the (violent) environment one is in. The same three genes may also produce shy children if they were brought up in a caring environment.
"Evidence is accumulating to show that the effects of variants of many genes that are common in the population depend on environmental factors. Further, these genetic variants affect each other," Sheilagh Hodgins of the University of Montreal said.
"We found that the three genetic variants interacted with each other and with family conflict and sexual abuse to increase the likelihood of delinquency, and with a positive parent-child relationship to decrease the risk of delinquency. Among carriers of the low activity variants of all three genes, those exposed to family conflict or sexual abuse or both reported high levels of delinquency while those who reported a positive and warm relationship with their parents reported little or no delinquency," she added.
The Monoamine oxidase A (MAOA) gene is a key enzyme in the catabolism and helps to generate energy from molecules the breaking down of complex materials. Researchers found that less-active variations of the genes often led to antisocial behavior in males. Roughly 25 percent of males exhibited the variant. Among women, the high activity variant of the MAOA gene, along with adversity in childhood, resulted in increased antisocial behavior.
A second gene, neurotrophic factor (BDNF), was also found to influence antisocial activities. This section of genetic code normally directs neuronal plasticity, changes in brains caused by injury or environmental damage. Previous research has shown that carriers exposed to aggressive peers displayed aggressive behavior.
"The low expressing variants of BDNF are carried by approximately 30 per cent of individuals and some previous studies had shown that this variant was associated with aggressive behaviour if carriers were exposed to aggressive peers," Hodgins said.
The third gene is a serotonin transporter called 5-HTTLPR. Approximately 20 per cent of individuals carry the low-activity variant of the gene. The study found that, among those with the low-activity variant, exposure to adversity in childhood led to antisocial and aggressive behavior.
"Among carriers of the low activity variants of all three genes, those exposed to family conflict or sexual abuse or both reported high levels of delinquency while those who reported a positive and warm relationship with their parents reported little or no delinquency," Hodgins said.
"These findings add to those from other studies to show that genes affect the brain, and thereby behavior, by altering sensitivity to the environment," she said.
