In today’s era, one can barely scroll through the television guide without coming across some sort of crime show. Anything from Law & Order, Criminal Minds or Bones, represents society’s fascination with crime, and more specifically murder. An even more explicit element many of these shows focus on is serial killers and the horrific aftermath they leave in their wake. What exactly, from neurological and physiological perspectives, separates this thankfully very small segment of people from the rest of the general population?
Although television shows seem to suggest that serial killings are commonplace, they are in fact relatively rare. There are actually limited legal definitions of what defines a serial killer, but the frequently used definition categorizes a serial killer as a person who has committed three or more killings in the span of about a month. The elements that “make” someone a serial killer, whether environmental or biological, bring us back to the age old nature versus nurture question. Current theory finds a combination of sociological, psychological, and environmental factors that influence what is already physiologically present in the person’s anatomy . Studies and ongoing research show that neurological differences in brain structure, and biological differences in hormones and genes influence what actions a person takes, including the actions of becoming a serial killer.
Through advances in brain imaging technology, researchers have been able to identify notable differences in the brain activity and brain structure in serial killers and non-serial killers. For example, studies show that the prefrontal cortex of a serial killer is typically less developed when compared to that of the control group of non-serial killers . The prefrontal cortex, located behind the eyes and forehead, carries out many supervisory functions within the brain; it regulates impulse control externally and the limbic system internally. The limbic system, located within the temporal lobe, is often studied when analyzing violent crimes. Individuals with a lesser controlled limbic system, including serial killers, have more angry, violent, and primal tendencies, as well as lower self-control mechanisms in regards to fear and rage . Damage or underdevelopment to the brain can be from birth or during one’s life through a traumatic brain accident. In fact, a significant proportion of those on death row have suffered from head/brain trauma and 70% of these people with trauma have developed greater aggressive tendencies .
Understandably, individuals with damaged limbic systems exhibit a loss of emotion and oftentimes anti-social tendencies. The inability to process emotions is a characteristic hallmark of psychopaths; however, being a psychopath and being a killer is not mutually exclusively. Defining a person in such terms is a complex psychological and biological undertaking. Scientists theorize that environmental factors and childhood upbringing can play an influential role in the development of a psychopath yet there are many exceptions. For example, Charles Manson grew up in an abusive household while Jeffry Dahmer grew up in a supportive, healthy environment, however both men proved capable of horrific crimes .
Beyond the brain, other aspects of a serial killer’s biological makeup also influence their violent tendencies. A common myth with respect to male serial killers’ DNA is that they possess an extra Y chromosome that leads them to exhibit more aggressive behavior . However, scientific studies have disproved this theory. Nonetheless, it is interesting to note that nine out of ten serial killers in the United States are male. A hypothesized explanation for the gender discrepancy may be linked to hormones. Males typically have higher levels of testosterone, an aggression-related hormone. Abnormally high levels of testosterone are relatively common in men, but the combination of high testosterone and low serotonin levels are more exclusively common among serial killers. Serotonin is a neurotransmitter that contributes to our overall sense of happiness and positive feelings towards life. Furthermore, levels of other neurotransmitters, dopamine and norepinephrine, are also usually higher in serial killers. Both dopamine and norepinephrine contribute to aggressive behavior and impulsivity. In addition, it is common for serial killers to display lower levels gamma-aminobutryic acid (GABA), a hormone known to inhibit aggression.
Another common myth is that a hereditary “serial killer gene” is passed from generation to generation. Scientific research indicates that no such “serial killer” gene exists; however geneticists have not ruled out multiple mutated genes as an explanation. It is understood that individuals may have genetic dispositions towards violence and that external factors such as an abusive childhood, can trigger violent episodes. Genetic explanations for serial killers’ behaviors is still being explored, and many research efforts are focused on the monoamine oxidase A gene, which regulates levels of serotonin the brain .
As advancements in scientific understanding and technology continue, the link between science and law becomes more pertinent. Understanding the biology of a serial killer comes in line with the growth of a subsector of law known as “neurolaw” . Should we factor in these studies and biological distinctions when considering serial killers cases and their retribution for such actions? Should we feel empathy for those who have predisposed tendencies? Say we have someone who suffers from negative neurological, biological and sociological factors, and he goes on to commit acts of a serial killer – should the legal system treat him any differently than you or me? These are some of the questions the cross section and the growing field of neurolaw hopes to be able to answer .
Science will continue to provide us a better insight into the biological differences of serial killers. It cannot tell us everything (yet!) about what shapes these people into killers nor how, or if, neurolaw can become applicable.
References Brogaard, Berit. “The Making of a Serial Killer.” Psychology Today. Last modified December 7, 2012.  Adams, Tim. “A Murderer’s Brain Vs. A Normal Brain.” Business Insider. Last modified May 12 2013.  Scott, Shirley. “What Makes Serial Killers Tick?” Chapters 15-16. Crime Library. Accessed December 12 2014  Hagerty, Barbara. “A Neuroscientist Uncovers a Dark Secret.” National Public Radio. Last modified June 29 2010.  Taylor, Matthew. “Psychopaths: Born evil or with a diseased brain?” BBC News Health. Last modified November 14 2011.