A Connection Between Genes, the Environment, and Violence

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It is common knowledge that physical traits, such as hair or eye color, are genetically inherited from one’s biological parents. Many people also know that certain disorders are caused by genetic abnormalities or occur more frequently in individuals who are genetically susceptible, as is the case in breast and colorectal cancers. There is somewhat less knowledge and more disagreement about how genes influence mental, emotional, and social factors – specifically in this case, the propensity for violence.

Over twenty years of research has shown that there are links between genetics and aggressive behaviors. For instance, deficient activity of a gene called monoamine oxidase A (MAOA) is known to increase the risk of violence in individuals who have experienced some type of childhood trauma. Minor differences in genotype can alter the expression of MAOA and moderate the effects of environmental exposures such as trauma in youth (Caspi et al., 2002). In addition to MAOA, at least four other genes have been found to be associated with antisocial behaviors such as violence (Ferguson & Beaver, 2009). While this association has been widely studied, the biology behind it was largely unknown – until recently.

In a study published a few weeks ago, behavioral geneticists from Switzerland looked at underlying neurological mechanisms related to aggression using rats as an animal model. They found that among rats psychological trauma during early life led to measurable changes in brain function and increased violent acts during adulthood. Furthermore, this study generated many new questions for future research, particularly about anti-depressants potentially reversing negative effects of trauma.

It is important to note that genes alone do not cause someone to be overly aggressive; as indicated, environment is also a key factor. Environment is a broad term that refers not only to physical surroundings but also to social interactions, which in this case mainly include childhood traumatic events. Examples of childhood trauma include witnessing violence or experiencing sexual assault. Both earlier research and the recent rat study suggest that exposure to trauma is more likely to lead to an increase in aggressive and antisocial behaviors if the individual is also genetically susceptible. This means that a specific subset of the population is at greater risk for violence, which presents a unique but challenging opportunity for violence prevention.