In the early 1990s, geneticist Dr. Han Brunner studied a Dutch family whose male relatives were prone to violence. He discovered that the MAO-A gene, a gene crucial to managing anger, was inactive in the male relations.

The MAO-A gene controls the production of monoamine oxidases (MAOs) enzymes that break down neurotransmitters, serotonin, dopamine, and adrenalin, and are capable of affecting mood.  The MAO-A gene acts as a mop to clean up the serotonin, bringing us back to normal. A mutation in this gene, as seen in the males in the Dutch family, cannot control serotonin levels, and this results in violent behaviour.

The MAO-A gene is present in all of us, carried on the X chromosome, giving women two copies and men one. The second copy in women is believed to result in increased happiness, but the one copy in men has very different results.

The genetic mutation is surprisingly common – 1 in 3 men carry a shortened, less active version of the gene, considered as the cause of anti-social behaviour in Caucasian men if they suffered childhood abuse, and responsible for violent behaviour in some males.

“Warrior gene”

In 1993 when the gene was first studied by Dr. Brunner, the MAO-A mutation and it’s related behaviours became known as the “criminal gene”.

“That was picked up by the media to be called a “criminal gene,” and even the senior author on the paper publicly stated… that it was ridiculous to call it that,” explains Jonathan Beckwith, professor of Microbiology and Molecular Genetics at Harvard Medical School.

“When the media presents these findings in a dramatic way, there are at least hints from the scientists themselves that it should be taken that way. That’s not always the case, though sometimes scientists who produce the work become quite dismayed at its interpretation by the media,” he says. (Source.)

Time passed. The “criminal gene” became the “aggression gene”, and in 2004, through misquotes and miscommunications, the genetic mutation got a new title, the “warrior gene”.

The name derived from testing a very small sample of Maori men from New Zealand, a tribe with a history of warfare.  Unfortunately, the press got a hold of it and the Maoris became known as genetically predisposed to violence and criminal acts, but there is no direct evidence to support this. (See this article from the New Zealand Medical Journal for more information.)

The choice of the term “warrior gene” has huge implications because “warrior” conjures a strongman who can stoically protect and provide for his people. It seems to me that naming a genetic mutation associated with violent behaviour after an appealing masculine archetype is to glorify it. And this can be dangerous.

Born to Rage

National Geographic produced a documentary in 2010 about the “warrior gene”, hosted by Henry Rollins, front man for the American punk band, Black Flag. Henry believes he carries the “warrior gene” because his anger is always simmering just below the surface.

The doc focuses on men from diverse backgrounds and their genetic makeup, testing to see who carries the mutated MAO-A gene. Bikers, Buddhist monks, ex-gang members, mixed martial arts (MMA) athletes, and a Navy Seal participated in the program.

Some of the guys self-identified as warriors and expected to carry the mutation, even boasted about it. A flash of disappointment crossed their faces when they heard the news that they’re genes are normal.

The bikers’ DNA results were split right down the middle – the quiet ones carried the shortened gene. One described himself as “battling a demon”, another “in constant anger”, like Henry.

Shortened gene carriers from violent backgrounds often turn violent themselves, as seen in the two ex-gang members, initiated into gang life at the age of 10, and becoming two of the most feared “enforcers” in Los Angeles.

However, violence is not always the outcome of this combination. The Buddhist monks, all from violent or difficult backgrounds carry the mutation, but dedicate their lives to peace and enlightenment.

All MMA fighters, men in their 20s, expected to carry the gene because they are in top physical condition and know how to fight. Through their training, these are fighters are in physical and emotional control of themselves, and do not fly into the sudden “warrior gene” rage. None of them carried  the shortened gene.

A MAO-A gene  mutation isn’t always associated with violence – the Navy Seal, a man from supportive parents and a good education carried the shortened gene. He channels his internal aggression into a productive use as a successful entrepreneur. He maintains that he overcame the negative effects of the shortened gene through his military training, where he learned to “control the fuse and the anger”.

Henry’s parents divorced when he was young and I understand that his mom’s boyfriend beat him and mentally abused him. Kids beat him up in the school yard. He described himself as a “nervous kid” until the day he snapped and became what he feared. Almost 50 at the time of filming, Henry says he’s still aggressive.

Find out Henry’s DNA results in the 45 minute documentary.


MAO-A is only one of thousands of genes expressed in the brain with the potential to affect behavior.The MAO-A gene is not an explanation for violence, but it does move us closer to understanding what drives violence in some men, and further understanding of the gene will tailor rehabilitation programs to individuals.

It will also alter the law.

A really interesting paper from the National Judicial College of Australia examines the MAO-A gene as evidence in sentencing. The author states that there is not enough scientific understanding of the gene for it to play a part in criminal proceedings, and warns about the moral issues of testing all males for the gene mutation and the possibility of racial profiling because of a man’s ethnic heritage.

The argument over using genetic determinism as a legal defense continues to rage (this paper focuses on genetic determinism and the law). Through our understanding of the MAO-A gene, we will come to understand ourselves better, but we must be careful not to treat the violence associated with the mutation as an excuse, and shirk off responsibility for our actions.

Violence is a choice.

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