Nature, Nurture, Murder?

It has been found in many studies that male children who abused or experience violence are more likely to be violent when they grow up – but not all male children who experience violence whilst growing up turn out to be violent people. Some may ask, well what about alcohol abuse or drug abuse? Finances, education, or up-bringing? While all of these environmental factors have been linked to aggressive behavior, behaviorists are having a difficult timing creating strong correlations between aggressive/ violent behavior and environment alone. This has forced geneticists to ask the question that many had been hoping to avoid – is there a gene for violent behavior?

Stephen King begins his (very well-known) article Why We Crave Horror Movies with a very bold claim, “I think that we’re all mentally ill…”. He goes on to explain that he believes that insanity is a spectrum of control that spans from mumbling unintelligibly to yourself (when you’re frustrated) to cutting off people’s faces and wearing them as your own (a reference to The Texas Chainsaw Massacre); From nervous ticks to serial murder, we all possess insanity and different levels of controlling it (the action the we display outwardly is the portion that we struggle to suppress). He breaks down emotions into two categories, civilized emotions and anticivilization emotions. The former is accepted and positively rewarded by society (love, kindness, loyalty, etc.) and the latter are punished and suppressed. However, this does not make them go away – and like all of your other emotions (similar to muscles) they need to be exercised in order to stay toned. King argues that watching horror films is a way to exercise that emotion. It allows our brain the freedom to think about and experience these things that society tells us not. He relates it to feeding the alligators to keep them from coming out of the water. It is a way to live out our darkest desires without actually having to commit any act – and for most of us, that method works. But there are those on the more extreme end of the spectrum that don’t get release from viewing but instead feel a drive to experience first-hand the horrible things our anticivilization emotions demand.

What may come to you as a shock is that science (for the most part) agrees with this seemingly outlandish notion. Daniel Weinberger, a neuroscientist at John Hopkins University, was quoted in an article saying, “everyone’s genome has a different level of risk for different disorders. Everyone’s got something.” The possibility of a gene being responsible for aggressive behavior was brought to the table by two separate cases – a Dutch family with a long history of passed-down extreme aggression and violence within the family unit (which began in 1978 but wasn’t concluded until 1993) and the murder trial for Bradley Waldroup (in 2006). A common link, scientists found, lies in a variation on a gene on the X chromosome that codes for the enzyme monoamine oxidase-A (MAO-A).


 The MAO-A gene (known as the “Warrior gene”) produces MAO-A protein. The job of this protein is to break down crucial neurotransmitters, such as dopamine, serotonin, epinephrine, and norepinephrine. These chemicals are potent and if they are not broken down, they will build up in the brain and cause a loss of impulse control and an increase in aggression/rage and violence.


L-MAOA (or MAOA-L) means that the person (whose blood has been tested) has lower levels of MAOA. MAOA-H means that the person has a higher amount of MAOA proteins (enough to be able to properly break-down the proper amount of neurotransmitters in proportion to how much their body is producing). Studies have linked L-MAOA a significant increase in the possibility of that individual developing Anti-Social Personality Disorder (ASPD), which is a very serious mental health condition that results in the individual being very manipulative and often violates the rights or exploits other people. Studies have also shown that people with mental illnesses are as high as two to three times more likely to be violent. There is a high possibility that the violence exhibited by people with mental illness is due to the fact that they have L-MAOA and thus do not make enough enzymes to break-down all of the neurotransmitters they are creating. However, this is not to say that all people who suffer from mental illness are violent nor is it to say that everyone with L-MAOA will subsequently suffer a mental illness and/ or become violent.

In fact, it is estimated that a very large portion of the population has L-MAOA (but no concrete numbers can be found yet, as this is relatively new research). Much like the genes and proteins for cancer, a large number of people have L-MAOA that is “inactive” and requires and certain environment to “activate” them. L-MAOA (as previously stated) is a variation of a gene found on the X chromosome – which means both male and females carry the variation. However, because females have two X chromosomes, if one of them has a variation, the other chromosome will compensate for this variation or defect, which results in no behavior change (or ‘normal’ function) for females whose second chromosome is capable for compensating the defective one. Even though the variation is compensated in most females, it can still be passed down to their offspring. Males, having only one X chromosome, do not have a way of compensating for the defect, and thus a change in behavior can be observed.

Even though the variation is more easily observed in males, not all males who have L-MAOA exhibit extremely aggressive and/or violent behaviors. Like I mentioned earlier, it depends on the environment, whether or not these genes become ‘activated’. Environment can range from upbringing (abuse during childhood being one of the most common denominators), alcohol/ substance abuse (both during pregnancy – maternal abuse – or by the individual), increased levels of testosterone, education quality and level, financial support, ect.  Nature and nurture work together in terms of effect on human behavior, and this is no exception. Neither environment nor genetics can be the sole source of aggressive and violent behavior, but they work together and fill in each other’s missing link.

L-MAOA isn’t the only gene that may be working towards violent behavior. Researchers in Germany discovered that homicidal behaviors are linked to a variation in another dopamine regulating protein called Catechol-O-Methyltransferase (COMT). Finnish researchers found that many of the prisoners who are incarcerated for serious crimes had variations in genes that code for CDH13, protein that assists in brain-cell signifying. Other prison research, conducted by Kent Kiehl, involving scans of the limbic and paralimbic cortex of psychopaths showed that inmates have a smaller amygdala region (which is the brain region responsible for empathy and emotion), as well as less grey matter in these brain regions. He says that psychopaths have different brains, and this is caused by “at least 50 percent genetics”.

Since a request in 1978 by a concerned Dutch woman demanding a test be made on her family to examine why the past 200 years of family members had very violent histories, researchers and scientists have been working on honing in on genes that cause violent behavior. The fact that there may be a biological cause for aggression is a concern to many. What if science is able to pin-point a gene that is responsible for violent behavior? Will we create a screening test for it? And if we do, what will do with/ to the people who test positive for the defective gene? Will there be a sure way to control the environment of those who test positive to ensure that they don’t “snap”? What even is an ideal environment, does it exist?

This is a huge grey area in ethics and morals; unless scientists are able to also create a solution to whatever the defect may end up being, that is. Even then, do they have the right to test children for the ‘murder gene’? Or would the solution just end up being a vaccination that we give to everyone regardless of whether or not they have L or M-MAOA? The more I start to ponder the possibilities of outcomes that could arise from this continued research, the more the novel The Giver is starting to seem like a potential reality. Scientists who are working on this are still very far away from being able to produce concrete findings, but every day is another day closer to finding out if such a gene exists and leaves more people wondering, ‘are you a potential violent, psychopath, murderer? Am I?’

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7 thoughts on “Nature, Nurture, Murder?

  1. This was a super interesting post to read. I liked how you started it off with Stephen King’s quote and then went on to explain how you interpreted it and related it back to the class. I found it super interesting when you discussed how everyone’s genome has a different level of risk for different disorders and the idea that everyone has something. Super interesting and makes me question a lot about not only other people and their behavior, but myself as well! great post!

    Liked by 1 person

    1. Thank you! I feel the same way about the way I view myself and other people, haha. I really love the Stephen King article – it’s very short and I would suggest reading it (if you haven’t already). I’m glad that you found this interesting and that it got you thinking!

      Liked by 1 person

  2. I agree with Kaleigh- the quote from Weinberger is really interesting. I think adding the image from the Aggression and MAOA page that illustrates the sequential difference between low and high MAOA might add some clarity to the underlying genetics of aggression. It might also help to mention that the enzyme deaminates neurotransmitters since the amine groups in each are circled in the image you used. This is a thought-provoking post, great job!

    Liked by 1 person

    1. I really like those images, and I’m glad that you also liked them and found they they were helpful!
      Thank you for the suggestion! I actually didn’t know that about the enzyme (the research I did only mentioned it very briefly). I will definitely do more research on that aspect and put in a small paragraph about that.
      Thank you for reading my post and for your suggestion, I’m glad you liked it!

      Liked by 1 person

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