Do serial killers have an extra chromosome?

There is no such thing as a “killer gene”, but research is revealing genetic tendencies towards violent behaviour.

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Face of a serial killer. Photo Credit: Curtis John via Flickr [BY-ND-2.0], 2009.

It’s a slippery, discreet mutation, after all we don’t see entire families of serial killers

Parents of children, who have grown up to be serial killers, have reported that their child was markedly different from their other non-violent siblings. Ted Bundy, an American serial killer, kidnapper and rapist, at the tender age of three slipped butcher knives under the covers of his auntie’s bed. “He just stood there are grinned” she reported as he watched on and she repeatedly cut herself trying to get up. Nine-year-old Jesse Pomeroy from Charlestown Massachusetts, sexually tortured seven boys at his school. Three years later he murdered a four-year-old boy, decapitating his head with a blunt kitchen knife. These gruesome and unethical crimes got me thinking about the kind of influences that trigger one to kill. Are serial killers inherently evil, reflections of their environment or unfortunate victims of gene malfunctions?


 Cropped image of blood in water. Photo credit: Peter Almay via Flickr [BY-NC-SA-2.0], 2009.

Nature vs. Nurture; bad seeds blossom in bad environments

Environment alone cannot explain deranged behaviour as too many abused and neglected children grow up to be law-abiding citizens. Yoon-Mi Hur and Thomas Bouchard, a professor of phycology conducted a study in 1997, examining the behaviour of 57 pairs of identical twins, 49 pairs of fraternal twins and 90 non-twins who had all been raised in separate households. They evaluated the extent to which heredity influences perceptions of childhood family environment using the Family Environment Scale and Block Environmental Questionnaire. The study revealed a strong link between impulsivity and sensation-seeking behaviour, attributed almost entirely to genetic factors. Both sensation-seeking traits and impulsivity have been found to be higher in drug abusers, delinquents, and serial killers.

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Nature vs. Nurture. Photo credit: Frank DeFreitas via Flickr [BY-NC-ND-2.0], 2012.

Chromosomal abnormalities in serial killers 

According to Dr Helen Morrison, an American forensic psychologist and writer, chromosome abnormality in serial killers begins to express itself during puberty. Serial killer, Bobby Joe Long has an extra X chromosome, causing him to produce excess amount of oestrogen. During puberty his breasts began to develop causing him a lot of embarrassment and anger. Bobby channelled this anger into raping over 50 women over a thirty-year time period. His crimes escalated killing 10 women over a 10-week period in 1983.

Conversely, serial killer Richard Speck’s had an extra Y chromosome, which his lawyers argued was the cause of his violent crimes. The court found that while an extra Y chromosome seems like a logical explanation for mutant-aggressive behaviour, there is not much evidence that links the X or Y chromosome to the deviant behaviour of serial killers.

Gosavi Gajbe conducted a study looking at the role of chromosomes in criminality. He examined the chromosomes of 140 murders and looked for any abnormalities that may have influenced them to commit their crimes. The study revealed that there was a definite association between the both variables but he concluded that further studies needed to be completed on more recent cases before conclusions could be made.                                                                                                                                                                                                   pic4

 Cropped image of the inheritance of an extra chromosome.Photo Credit: Paul Studios via Flickr [BY-CC-2.0], 2012.

The thrill of the kill, is the nervous system to blame?  

Studies by Newman et al. have revealed that the nervous system of serial killers is considerably different to an average person. Serial killers feel less fear and anxiety. A study was conducted where a group of sociopaths and a group of healthy individuals were provided with four levers and were asked to identify which lever turned a light on. One of the levers gave an electric shock. While both groups identified which lever supplied the electric shock, the sociopaths took much longer to avoid the punishment. This need for higher levels of stimulations makes psychopaths seek more dangerous situations, which had led scientist to believe that it could partly explain their thrill to kill.

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Nervous System. Photo Credit: Paul Walker via Flickr [CC-BY-SA-2.0], 2011.

Causes for killing 

One cannot explicitly conclude that chromosome abnormalities are the reason for why people commit such malicious crimes. Further research needs to be conducted to come to a definitive answer. I personally think it’s a combination of genetic factors and the environment one is brought up in. However, it’s hard to believe that some people cannot be inherently evil after reading some of the gruesome acts they have committed.

What do you think? Are serial killers inherently evil, reflections of their environment, unfortunate victims of gene malfunctions or is there a more complex formula that incorporates all of the above?

10 Responses to “Do serial killers have an extra chromosome?”

  1. avukovic says:

    Thank you for taking the time to read my post. I love you last line ” Just because someone may be genetically predisposed to such behaviour, does it mean they actually fulfil that?” Research/history has shown that there are many people who have either been brought up in bad environments or who have chromosomal abnormalities who are still functioning members of society. So I guess to answer that question, currently research is suggesting that no, people who are genetically predisposed to serial killer behaviour will not necessarily commit such crimes. I think there is a lot more research to be done in this area as there are a lot of gaps in knowledge. I am so glad you enjoyed the post 🙂

  2. jrowland says:

    Really interesting post. I’m a little like @georginao. I find it really interesting reading those real life crime stuff and wondering about the psychology behind it. Immediately regretting it as I can never sleep afterwards! As much as I don’t like the idea, I’m inclined to think that some people are inherently evil, if you can have people that are inherently good. Research like this into the genetics of serial killers makes me wonder about how people with some psychological issues may be treated in the future. Will there be ‘serial killer’ tests? Just because someone may be genetically predisposed to such behaviour, does it mean they actually fulfil that?

  3. avukovic says:

    I know exactly what you mean. I actually do the same thing. I love watching scary movies that are based on true stories, it makes it that bit creepier. I don’t know how psychologists do it. I could never be in the same room as someone who has killed so many people. Thank you for taking the time to read my post Im glad you enjoyed it 🙂

  4. georginao says:

    I’ve got such a morbid fascination with serial killers – its so bizarre. I’ll watch a movie about a serial killer based on a true story, then look up the real picture of the person and read all about them. Even though as I’m reading it makes me so horrified and really upset, I can’t stop reading (or hiring movies about serial killers!).
    Can you imagine how tough a psychologist who interviews them would have to be? But so necessary for us to learn more about how this happens.

  5. avukovic says:

    Thank you for taking the time to read my post. There have been a lot of mixed views online debating that exact question your asking. You see there are functioning members of society who also have an extra Y or X chromosome who have no become serial killers. Therefore, one cannot say that all people who possess this additional chromosome will kill. I think people kill for a whole number of reasons, I also think that there are varying degrees of serial killers. I think that your genes as well as your environment both play a part. Again reading some of the cases and hearing about children as young as 3 killing makes you think that perhaps they are inherently evil. Some signs to look for in a child to determine whether they may develop violent behaviour is the killing of animals. Many studies have found a correlation between children hurting animals and developing into adults that hurt humans. In terms of preventative measures I think bringing children up in a safe, loving, alcohol and abuse free environment, where they are taught to care and be responsible for animals is a great way to try and reduce the possibility of them harming animals. But then I am no expert. What are your thoughts? I am so glad you enjoyed the read 🙂

  6. vdrs says:

    Wow, interesting read- a little creepy too haha. I found it interesting that an extra Y or X chromosome might have something to do with serial killer behaviour. Do you think it might be because of the problems associated with these chromosomes anger is creative and these behaviours are a result of that anger or is it actually much more direct than that, i.e. you have the mutation, youre prone to exhibiting this behaviour? Strange that some started showing signs at such a young age, reminds me of the movie “we need to talk about kevin”. Do you know if there are any signs that a child could potentially develop such violent behaviour? and if so are there preventative measures?

  7. avukovic says:

    Thanks so much for taking the time to read my post. I definitely agree with you there are varying degrees of serial killers, some are definitely more evil then others. I really like your logic behind why you think they are all inherently evil as well as reflections of their environment.

    I wanted to add more about Klineflelter syndrome, there is plenty of research out about it, but my blog post was already exceeding 700 words. It is very interesting though, and thank you for bringing that up, very relevant. I am so glad you enjoyed my post.

  8. pmulcahy says:

    I think that like all things serial killers come on a sliding scale. Some are more evil than others. But I do think they are all inherently evil, as well as a reflection of their environment. And if you accept that some people are inherently evil, as in they cannot change who they are and this is not a result of their environment, I cannot think of a cause excepts genetics. So gene malfunctions are the same as their inherent evilness.

    Loved the article too. Found it very engaging.

    1 thing, somehow through a haze of alcohol, I remembered something from 1st year biology. Having an XXY (+the other 44 chromosomes) karyotype is called Klinefelter syndrome, but XYY does not have a name other than XYY syndrome.

  9. avukovic says:

    Thanks Jessica for taking the time to read my post. I know what you mean about those images of the scary pictures i felt the same way when i first looked at them. Thank you for the great feedback, I am so glad you enjoyed it 🙂

  10. Jessica Breadsell says:

    wow loved your post!!! Especially since when I first read it I accidentally clicked on the first image and got a full page scary face picture which set my nerves off!
    I really enjoyed how you presented the evidence then talked about your personal opinion, I felt this flowed really well and helps us make our own conclusions about the evidence. I agree with you that its probably a combination of both. Thanks for the post!