Nature vs. Nurture: The Role of Genetics and Environment
The question of whether a serial killer is destined to be a serial killer from birth, or whether an individual's experiences in their early life lead them to kill is an age-old question. For many psychological disorders, a combination of both provides the best explanation. For example, abnormalities in brain development within areas of the brain important for impulse control, aggression, or empathy can predispose an individual to be more susceptible to the effects of a chaotic, violent, or abusive childhood. When these factors occur together, it may raise the risk that an individual will be a violent and repetitive offender. In a classic but controversial study conducted by Stanley Milgram in the 1960s, research participants from the general public were led to believe that they were "teaching" another participant (who was actually an actor involved in the study) to memorize a list of word pairs. Each time the actor made a "mistake," the participant was required to administer what they believed was an electric shock. With each additional mistake, the participant was required to administer increasingly intense electric shocks to the actor. Even though the actor was not actually receiving electric shocks, he behaved as though he did, becoming increasingly panicked and afraid, pleading to stop, and even saying that he had a heart condition. Whenever the research participants indicated any sort of objection or hesitation, the experimenter in charge of the study would demand they continue. The results of the study indicated that a surprisingly high proportion of research participants (65%) were willing to inflict the maximum amount of "electric shock" even though they believed they were causing the actor serious and potentially fatal harm. Though it has come under intense criticism for its ethical shortcomings, this study (now known as the Milgram Obedience Study) is an example of how ostensibly "normal" people from the public can be made to inflict intense and repeated pain on a vulnerable person, at least under a particular set of conditions.
Neuroanatomy of Serial Killers
There has been intense interest from the public and scientific community in advanced brain imaging techniques such as magnetic resonance imaging (MRI) being used to search for differences in brain anatomy between normal individuals and serial killers. Again, this body of research is severely limited by the relative scarcity of serial killers that make it difficult to draw broad conclusions. One theory involving neuroanatomy and serial killers suggests that serial killers have underdeveloped or underactivated neural structures that are responsible for inhibition. In one study (Kiehl, Smith, Hare, & Liddle, 2000) measured the brain's electrical activity through electrodes placed on the scalp (also known as electroencephalogram, or EEG) among participants with schizophrenia, psychopathy, and normal controls as they performed a computer task requiring them to quickly decide whether or not to press a button depending on a shape flashed on the screen. They found that when participants had to stop themselves (or inhibit) from pressing the button, normal controls displayed strong electrical activity in the frontal lobes, while participants with psychopathy displayed virtually no increased electrical activity in the frontal lobes. Though there are many potential reasons for this finding, it is consistent with the notion that differences in frontal lobe abnormalities may play a role in the difficulty psychopaths have in inhibiting behaviors.
While researchers have learned much about serial killers over the past several decades, much more research needs to be done before anyone is able to make confident predictions about such extreme violence. So far, this research has been challenged by low sample sizes (many studies are single-person case studies) along with problems attributing specific experiences or traits uniquely to serial killers. For example, while many serial killers experienced trauma or abuse during childhood, the vast majority of individuals with these experiences do not go on to commit repetitive and violent crimes. However, future advances in brain imaging, medical tests, and other methods may help us to make more confident predictions.