We're all capable of committing violence. The person who truly cannot commit violence is quite rare, and likely learned it. Some aspects of behavior depend on interactions in the brain between genetic and environmental factors.

And so, it is said, an individual may be more vulnerable to developing violent behaviors if they have predisposing factors and then undergo stress, abuse, or other triggers, especially early in life.  Neurobiologists have also documented numerous examples of sex differences in the human brain, including differences in brain regions and circuits relevant to violent behavior. 

A new paper in Violence and Gender describes the complex and flexible biological mechanisms in the brain that lead to the development of behaviors. These include interconnected neural networks, multiple genes, and chemical signals such as hormones and neurotransmitters, which can be modified by environmental factors. Brain structure, function, and connectivity can all differ between men and women, affecting how they may change on exposure to stressful or abusive triggers.

Girls can be plenty violent. They just have different triggers. Image link:Buzzhanga.com

The results: there isn't a lot of difference except when it comes to the positive effects of parenting. Male MAOA knockout mice, for example, are unusually aggressive, have higher levels of norepinephrine and serotonin, and display aberrations in brain development, but in human kids, results in different genders has been inconsistent. The detrimental effect of childhood maltreatment on girls with the MAOA-L genotype was less while positive environmental influences, such as the support of a nurturing parent, have been shown to moderate the effect of childhood stressors in MAOA-L girls.

But there's no magic bullet and the studies finding correlation are observational. So don't read too much into it. Girls can easily be violent, there is no female brain any more than there is a Republican one or an organic food one.

"This holistic view of the origin of violence means that reducing violence will not be a simple fix because it does not have a single origin or cause," says Editor-in-Chief of Violence and Gender Mary Ellen O'Toole, PhD, Forensic Behavioral Consultant, and Senior FBI Profiler/Criminal Investigator Analyst (ret.). "The temptation to delineate a male and female brain must be resisted because there is overlap between the two. With more research will come greater insight and knowledge about the biological and environmental causes of violence. With more knowledge will come answers; answers will lead to solutions, and with solutions will come prevention."

Citation: Debra Niehoff, 'Not Hardwired: The Complex Neurobiology of Sex Differences in Violence', Violence and Gender  February 5, 2014  doi:10.1089/vio.2013.0001