Violence, though deeply rooted in our evolutionary history, has to be one of the most destructive of human behaviours. For years, researchers have tried to understand what drives us to commit acts of violence. Is it the environment we were raised in? The socioeconomic situation we find ourselves in? Or is it driven by something completely different – something we have no control of – our genes? Or specifically, the so-called ‘warrior gene’?

The story of the warrior gene starts in 1978, when a woman walked into a hospital in the Netherlands, and not because she was worried about herself, but because she was worried about her family. All the men in the family had a history of really terrible violent crimes. There were murders, there were rapes, going back generations and generations. Researchers started gathering DNA samples from the members of her family, and they discovered that all the men who had this history of very violent crime, they had the same genetic change in a gene called MAOA …… or monoamine oxidase A, that completely knocked out the function of the gene, it wasn’t working at all.

We all have two copies of this ‘warrior gene’. It makes a molecule in your brain that breaks down a chemical called serotonin. This is a neurotransmitter, it sends signals between the cells in your brain, and affects your behaviour. So, if this gene isn’t working as well as it could do, it’s thought that perhaps it makes you more impulsive, it makes it harder to control urges.

So, the Dutch study was the first time that this gene, MAOA, had been linked to violent behaviour, but then a study in New Zealand took this further. The Dunedin study followed 1,000 New Zealanders for decades, looking for connections between childhood experiences and violent behaviour later in life.They found that having a variation that just lowers the level of activity of this gene, not knocks it out completely, but just lowers the activity, was associated with a history of violence. But curiously, mostly only in people who also had a very difficult childhood as well. And that caught the eye of researchers in Finland, working with prisoners in a very high-security prison.

We collected a cohort of around 800 prisoners, and about two-thirds of them had conducted at least one violent crime. But, a little bit more than 10% or 15% had committed at least 10 violent crimes, murders, attempted murders, manslaughters. I was sceptical, but what we did find was, indeed, if an individual had two or more violent crimes, then he or she had significantly more of the low activity MAOA.

We know that up to six in ten people are walking around with a low activity version of MAOA, but of course, six out of ten people don’t commit horrific violent crimes. So, obviously we can’t say that if you’ve got this gene variation, you are going to be a violent criminal, genetics doesn’t really work like that.

But this idea that there’s a gene behind violent behaviour, could you use that as a defence in court? You know, “It wasn’t me, guv. It was my genes that made me do it.” Well, it might sound a bit strange, but that is actually what’s happening.

It’s only really been used in two countries, two in an Italian court, and the rest have been in American courts. It’s been used as a way of saying that the person lacked control. I think it’s the sort of evidence that is attempting to be used to dazzle a jury.

In the US, where you have the death penalty for these kinds of incredibly violent crimes, the stakes are obviously, literally, life and death. So, lawyers will try and introduce any kind of evidence they can to argue against the death penalty for their client.

To say that there is a gene, like a time bomb that none of us are aware of, I think is wishful thinking.

So, humans carry different versions of the MAOA gene, and those that reduce the activity of this gene have been linked to increased risk of aggressive behaviour. Some studies also suggest a link between an abusive childhood, the MAOA gene not functioning adequately … …and an increased risk of developing antisocial personality disorder, which may result in committing violent criminal acts.But whilst it can be tempting to paint a simple picture of how genetics influence our behaviour, in reality, it’s an incredibly complex issue.

Everything that happens to us interacts with our genes and influences who we are and how we behave. The fact that we can find a connection between genes and violent behaviour doesn’t mean that we’re going to be heading towards some terrible genetic dystopia … … where little Johnny is locked up because he’s got ‘bad genes’ that might make him do bad things. That simply isn’t how genetics work. We have agency, we have independence, we can make our own free choices about who we are and how we behave.
(End)

• Rooted adjective (verb): having developed from something.
• Destructive (adjective): causing, or able to cause, damage.
• To drive someone (verb): to motivate or cause someone to do something.
• To raise someone (verb): to take care of a person until they are fully grown.
• Socioeconomic (adjective): relating to differences in groups based on financial situation.
• A gene (noun): a part of the DNA in a cell that controls development, behaviour, etc.
• So-called (adjective): said or called by people, but may not be completely accurate.
• A warrior (noun): a brave or experienced soldier or fighter.
• A generation (noun): all the people about the same age within a family.
• To gather something (verb): to collect several things, often from different places.
• A DNA sample (noun): a small piece of a person’s body (e.g. blood) that is taken to analyse.
• To knock out something (phrasal verb): to stop something from working.
• A molecule (noun): a very small group of atoms joined together.
• To break down something (phrasal verb): to divide something into smaller parts.
• A neurotransmitter (noun): a chemical that carries messages between cells in the body.
• Impulsive (adjective): doing things suddenly without any planning or considering the results.
• An urge (noun): a strong desire, need, or wish to desire something.
• To link something (verb): to make a connection between two or more people or things.
• A variation (noun): a change in amount or level, or something that is different from normal.
• Curiously (adverb): in an unusual and interesting way.
• To catch someone’s eye/ the eye of someone (idiom): to get someone’s attention.
• High-security (adjective): carefully protected or guarded.
• A cohort (noun): a group of people who have something in common.
• Manslaughter (noun): the crime of killing a person by accident, without planning to do it.
• Sceptical (adjective): doubting that something is true or useful.
• Indeed (adverb): really or certainly, used to emphasise something.
• To walk around with something (phrase): to have something with you.
• Behind (preposition): responsible for or the cause of something.
• A defence (noun): an argument or explanation you use to show you are not guilty.
• Guv (noun, UK old-fashioned slang): term of address for a man, sir.
• To lack something (verb): to not have enough of something that is needed.
• To dazzle someone (verb): to make someone think something is new and exciting.
• A jury (noun): a group of people in court who decide if a person in a trial is guilty or not.
• The death penalty (noun): the legal punishment of being killed for a crime.
• The stakes (phrase): how serious the situation is, the level of risk or consequences involved.
• A time bomb (noun): a situation that is likely to become difficult to deal with or control.
• Wishful thinking (noun): imagining an unlikely situation like it was possible and may happen.
• Abusive (adjective): using physical violence or emotional cruelty.
• Adequately (adverb): in a way that is enough or satisfactory for a particular purpose.
• Antisocial personality disorder (noun): a condition in which a person behaves in a way which is harmful to others but feels no guilt.
• Tempting (adjective): attractive or something you want to do.
• To paint a (simple) picture of something (idiom): to describe something (in a simple way).
• To head somewhere (verb): to go in a particular direction.
• A dystopia (noun): an imaginary society which is very bad, unfair, and cruel.
• To lock up someone (phrasal verb): to put someone in prison.
• Agency (noun): the ability to take action or choose what action to take.

In this text, there are some interesting examples of subject-verb agreement. Verbs always agree with the subject noun in a sentence: ‘I sometimes read a book.’   ‘She sometimes reads a book.’ However, there are different types of noun and noun phrases in English and it can be difficult to decide if a noun takes a singular or plural verb. Some common difficulties include:

Collective nouns: singular and plural verb choice: some nouns describe a group of people or things, called ‘collective nouns’. With these, you can use a singular or plural verb, depending on whether you see the group as a unit or as separate individuals:

‘The band is recording a new album.’ (It…)   ‘The band are arguing about their new album.’ (They…)

Other nouns like this include: government, staff, audience, board, class, army, orchestra.

*In a relative clause, we use who + plural for the group (collection of individuals), and which + singular (single unit) for the unit:

‘The band, who are all Irish, are here today.’   ‘The band, which is playing next week, is here today.’

Quantities and amounts, portions and mathematics: within context, amounts, distances, weights, quantities, etc. are often considered singular units, even when plural numbers and plural nouns are used:

‘10 minutes was not enough time.’    ‘200 kilometres is too far for one day!’

Expressions with ‘one’ use a singular verb, even if the noun is plural:

‘One of my friends is coming.’   ‘More than one of the players was injured.’

When talking about portions and percentages, the noun after ‘of’ tells us whether the verb is plural or singular:

‘50% of people live in apartments.’   ‘Half of the city was destroyed.’

When discussing maths, the verb can be singular or plural and depends on the phrasing:

‘Sixteen minus six is/are ten.’    ‘Seven and ten are/is seventeen.’ 

Indefinite nouns: indefinite nouns and pronouns take a singular verb:

‘Everyone loves him.’    ‘Somebody is talking.’   ‘Nothing is left.’ 

*When using ‘none (of) ’, the noun after ‘of’ tells us whether the verb is plural or singular:

‘None of my wishes come true!’    ‘None of it makes sense.’

Examples in the text:

• … about two-thirds of them had conducted at least one violent crime: ‘two-thirds of’ is followed by the plural pronoun ‘them’, meaning this portion is considered plural.
• genetics doesn’t really work like that: ‘genetics’ is considered here as a singular unit, a science, and followed by a singular verb form (doesn’t really work …).
• I think it’s the sort of evidence that is attempting to be used to dazzle a jury: ‘evidence’ is a singular uncountable noun (the evidence is..). ‘Jury’ may be singular or plural (the jury is/ are dazzled).
• … like a time bomb that none of us are aware of: ‘none (of)’ is an indefinite pronoun, followed by the plural pronoun ‘us’, meaning the following verb form is plural (are).
• it can be tempting to paint a simple picture of how genetics influence our behaviour: ‘genetics’ is considered here as a plural collection of factors, and followed by a plural verb (genetics influence…).
• Everything that happens to us interacts with our genes: ‘everything’ is an indefinite pronoun and is followed by a singular verb form (everything that happens to us interacts …).

https://www.bbc.co.uk/learningenglish/english/course/towards-advanced/unit-21/session-1

http://englishpodcastscollected.com/new/wp-content/uploads/2025/12/BBC-Ideas-Can-your-genes-make-you-violent.pdf

http://englishpodcastscollected.com/new/wp-content/uploads/2025/12/BBC-Ideas-Can-your-genes-make-you-violent.docx