Throughout history, all sorts of violence has troubled our human culture. According to recent research, violence and physiology (our body not our mind) may be more tightly linked than initially thought. The tendency to be violent is (so it seems) written right into our DNA.

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It’s obvious to most of us that violence can be a cause of physiological stress and trauma. But it’s also possible that our physiological characteristics are sometimes the source of violence. In other words, our bodies make us do it. But how, and why?
Well, to start with I started looking at what is violence? I looked at definitions in dictionaries and also the World Health Organization, or WHO. According to them:
Violence is the intentional use of physical force or power, threatened or actual, against oneself, another person, or against a group or community that either results in or has a high likelihood of resulting in injury, death, psychological harm, maldevelopment, or deprivation. source
The article PDF from WHO focuses on psychology and physiology, and to aim to identify what attributes predispose an individual to violent behaviour. I wanted to glean out the physiological aspects and there’s not a lot of research about that which is easily available, but there is some.
Many reports, trials and tests consider social and psychological factors – an abused child is likely to abuse people in adult life etc. However, not everyone exposed to risk factors exhibits violence. And not every violent offender has history rife with environmental risk. So how do we explain this? Is there a deeply rooted, physiological component to violent inclinations as opposed to external factors? I.E. can it be nature not nurture? Well, the answer appears to be YES.

STREET FIGHT (source)
To determine what accounts for different outcomes between people who went through similar social lifetimes, I wanted to look at the neurological and physiological research, but I’m no scientists so this was tough going.
However, I came up with this...
On the physiological side of things, scientists have examined the differences in nervous systems between individuals to investigate violent behaviour. Neurological studies indicate that all of our nervous systems can widely differ in how they process, recall, and react to events, information, and situations (tell me something I didn’t know). So, how we are wired can heavily influence our reactions to certain HORMONAL reactions within our bodies. I guess the now infamous women who suffer from menstrual hormone imbalance can be a good example. Normally pleasant, well adjusted females turn into violent raging bulls (not all of us but some do).
So, this is hormonal violence. A kicking would still hurt though, regardless of cause. However, it can work the other way. The nervous system can trigger the hormone rush that excites us to a frenzy, and in some cases this manifests as a violent act. (see below for more on that)
But this was new to me
According to a recent study published in The International Journal of Epidemiology, a person’s resting heart rate may affect their inclination towards violence, especially in young subjects.
Joseph Murray, an academic at the University of Cambridge, worked on a study which measured the resting heart rate of 3,000 male and female children, monitoring them from early childhood to young adulthood.
His team found that men (age 18/19) with a lower resting heart rate averaging around 59-65 beats per minute were between one-and-a-half-times and two-times more likely to have committed violent acts, even after controlling for several other (environmental) variables. Women with a lower resting heart rate were twice as likely to have committed violent crimes than women with a higher resting heart rate.
Some suggestions were that lower resting heart rate causes either displeasure, fearlessness, or under – stimulation, all of which may result in either anti-social behaviour or “thrill chasing”.
From my point of view that would link into my knowledge of the ‘fight or flight’ and adrenaline rush syndrome I have posted about previously. If the body ‘feels’ it’s unhappy or at risk, maybe a mild flash of the fight or flight response kicks in and thus stimulates the aggression, as there’s nothing to actually fight. This could then result in non-psychological, but very physical violence as the person ‘let’s off steam’ into the face of the nearest poor soul who gets in the way.
The nervous reaction
Scientists also believe that neurological factors relate to aggressive behaviours. Of the neurotransmitters known to scientists, four are thought to relate in some way to aggression in either animals or humans. These are dopamine, norepinephrine, serotonin, and GABA.
Research has shown that animals may be “rewarded” by the brain following violent acts with a rush of dopamine, the chemical which causes pleasure. That has also been suggested in people who self-harm. They hurt themselves and get a rush of the good stuff, making them feel a little better. Even though we consider ourselves ‘evolved’ above animal status I wonder if our bodies do not.
Serotonin is a specific neurotransmitter heavily studied in connection with aggression and violence. Interestingly, a body of research shows that in many nonhuman animal species, individuals prone to repeated aggressive or violent behaviour undergo marked changes in brain activity related to serotonin.
There’s a lot of research out there and I would be here for weeks writing about it all, so I’ve posted some links at the end.
The thing is, that in looking at the subject from a variety of angles, from the fight or flight reflex, to the fact that we may or may not have evolved hands (and faces) to specifically cope with better punching, through to the fact that various pain/pleasure hormones are related to a committed act of violence, I feel there’s so much more to this than the way we’re brought up. There’s a lot less research that has focused on the somewhat controversial topic of hereditary predisposition, but what research exists does suggests that nervous system and neurological factors may impact predisposition to aggression.
In other words, some people may ‘have to be violent’ as it’s in their DNA. If they are not well taught to fit in socially and express anger and frustration etc. in acceptable ways, or the urge to be violent outweighs the need for acceptable behaviour, then the person ‘has’ to act.
Human beings are complex creatures and so consideration between environment AND physiology should be accounted for. A wholistic view rather that a simple "he was beaten as a child, so he will beat his child" psychological attitude.
Next, I might look at why children that have tantrums hit out, and why some don’t.
References
http://www.who.int/violenceprevention/approach/definition/en/
https://www.nap.edu/read/1861/chapter/7#103
https://en.oxforddictionaries.com
https://www.simplypsychology.org/stress-biology.html
https://digest.bps.org.uk/2016/03/07/this-one-physiological-measure-has-a-surprisingly-strong-link-with-mens-and-womens-propensity-for-violence/
https://geneticliteracyproject.org/2016/07/29/does-the-human-warrior-gene-make-violent-criminals-and-what-should-society-do/