THE BIOLOGY OF VIOLENCE

Why Some People Become Dangerous!  Why Awareness Saves Lives!
By Rob Andress, Street Safe Self Defence Training Company

Violence isn’t random, and it isn’t mysterious.
Modern neuroscience has shown something that aligns perfectly with what we teach at Street Safe:

Violence is patterned, predictable, and influenced by identifiable biological factors, but biology is never the whole story.

Yes, there are biological roots: genetics, hormones, and the structure of the brain itself.
But these biological predispositions don’t guarantee violence. Instead, they interact with environment, upbringing, trauma, stress, and personal choices.

Understanding these factors doesn’t excuse

 violent behavior, it helps you recognize danger sooner and protect yourself earlier.

Let’s break it down.

1. Genetic Factors: Biology Loads the Gun, Environment Pulls the Trigger

Researchers have never found a “violence gene.”
But they have found genetic variations that increase the likelihood of aggression, especially when paired with childhood trauma or unstable environments.

The MAOA Gene (The Warrior Gene)                                            The Most Studied Link to Aggression

One of the strongest findings in violence research is the MAOA gene, sometimes called the “warrior gene.”

• People with the low-activity version (MAOA-L) process serotonin and dopamine differently.

• This can lead to poor impulse control, heightened emotional reactivity, and stronger responses to perceived threats.

• But here’s the key:
  MAOA-L alone doesn’t cause violence, but when combined with childhood abuse, neglect, trauma, or early adversity, the risk increases 

• dramatically.

This is called gene environment interaction, and it explains why some children exposed to trauma become calm, functional adults… while others become violent offenders.

Other Genetic Influences

Genes affecting serotonin and dopamine receptors have also been linked to heightened aggression. These chemicals regulate:

• mood

• impulse control

• threat perception

• reward-seeking behavior

When these systems are dysregulated, a person may be more prone to explosive reactions, risk-taking, or violence under stress.

2. Hormones: Chemistry That Fuels

Testosterone, The Best-Known Hormonal Aggression Driver

High testosterone has been consistently associated with:

• increased aggression

• dominance-seeking behaviour

• reduced sensitivity to risk

This doesn’t mean people with high testosterone are violent, but they may be more reactive, more competitive, and more prone to escalate under pressure.

Serotonin & Cortisol: The Brake Pedals

While testosterone may press the gas pedal, serotonin and cortisol act as the brakes.

• Low serotonin is linked to impulsivity and violent outbursts.

• Dysregulated cortisol (the stress hormone) can make a person less responsive to fear a dangerous combination in individuals already predisposed to aggression.

Violence often emerges when the body’s “calming systems” aren’t working properly.

3. Brain Structure & Function: The Hardware of Aggression

A healthy brain regulates emotion, processes threat accurately, and applies impulse control.
But when certain regions are underdeveloped or dysfunctional, violence becomes more likely.

The Prefrontal

 Cortex, The Control Center

This region governs:

• decision-making

• impulse control

• judgment

• long-term planning

Damage, underdevelopment, or dysfunction in the prefrontal cortex is strongly linked to:

• impulsive aggression

• poor self-control

• difficulty evaluating consequences

This is why individuals with prefrontal dysfunction often act first, think later, sometimes with devastating results.

The Amygdala, The Brain’s Alarm System

The amygdala processes:

• fear

• threat

• emotional responses

Research shows:

• Some violent offender

• s have hyperactive amygdala’s, meaning they interpret neutral situations as threats.

• Others show amygdala hypoactivity, leading to underreaction, low fear, and in some cases, psychopathic traits.

Either extreme — too much fear or too little, increases the risk of violent behaviour.

4. Other Biological Factors

Violence isn’t caused

by just one thing. It’s a combination of vulnerabilities and triggers.

Substance Use

Alcohol and drugs alter brain chemistry, reducing inhibition and increasing emotional volatility.
Withdrawal states can also trigger aggression in vulnerable individuals.

Medical Conditions

Certain neurological conditions, especially epilepsy originating in the temporal or frontal lobes  have been linked with aggressive episodes.

Early Life Biological Stressors

The first years of life shape the brain dramatically.
Factors like:

• birth complications

• poor maternal nutrition

• exposure to lead

• early brain injury

…all increase the risk for later aggression and violent behaviour.

Medications

Some prescription medications, particularly certain antidepressants in children can, in rare cases, cause agitation, suicidal ideation, or violent impulses as side effects.

Again, this does not mean medication causes violence,  only that it can influence emotional regulation in sensitive individuals.

5. So What Does All This Mean for Real-World Safety?

Here’s the Street Safe truth:

**Biology creates predisposition.

Life experience shapes behaviour.
Violence emerges when the two collide.**

People with biological vulnerabilities are far more impacted by trauma, instability, and adversity. They escalate faster, react more explosively, and often give early warning signs.

This is why we teach:

• Pattern recognition

• Behaviour over words

• Reading emotional intensity

• Identifying impulsivity and boundary violations

Violence has roots in biology, but it shows up in behaviour long before it becomes physical.

And that is where prevention lives.

Final Word

Understanding the biology of violence doesn’t replace self-defence — it strengthens it.

When you understand:

• how the brain escalates

• how hormones influence behaviour

• how trauma and genetics interact

• how early warning signs emerge

…you become harder to target, quicker to recognize risk, and more capable of controlling your safety.

At Street Safe Self Defence Training Company, our approach is built on one foundational truth:

Safety isn’t instinct, it’s intentional.
Knowledge saves lives. Awareness prevents violence.

Rob Andress is a Violence Prevention Specialist and the operator of Street Safe Self Defence Training Company. recognized as one of Canada’s leaders in modern, reality-based violence prevention and safety education.

Street Safe Self Defence delivers specialized training across Ontario, including high-school violence prevention programs, high-risk corporate safety education, municipal conflict-management training, and practical self-defence instruction rooted in real-world behaviour, not theory.

Street Safe also designed and launched the first program of its kind addressing Intimate Partner Violence (IPV) and sexual assault for Inuit women in Northern Quebec—an initiative built on cultural respect, trauma-informed practice, and community empowerment.

Rob is also the developer of T.R.A.A.C.S — Tactical Risk Awareness & Applied Combative System, a groundbreaking training system created to fill the human-behaviour gap left untouched by traditional Use of Force and IMIM models.

Static, pre-planned training works—until you add the human element. That’s where most systems fail.
T.R.A.A.C.S changes that.

Built for Law Enforcement, Security Specialists, By-Law Officers, and Corporate Protection teams, T.R.A.A.C.S brings the missing piece to modern professional safety training:
a deep understanding of human behaviour under stress.