The Warrior Gene; A genetic predisposition for violence?


In philosophy and psychology, the nature Vs nurture debate is the oldest dispute to be had and still very much rages on.  Most views take an interactionist approach, taking the view that human behaviour is a meeting between genetic predisposition and that potential shaped by experience.  However, there are some basic human behaviours that are so entrenched that they are considered to be almost purely constitutional such as aggression.  Freud believed that aggression was an innate force caused by hydraulic drivers and displacement.   However, modern science allows access to information that allows us to look at he genetic makeup of an individual at a micro level.  MAOA (Monoamine Oxidase A) is protein-coding gene like the other 24,000 genes making up the human experience.  MAOA is an enzyme that metabolises monoamines, such as serotonin, norepinephrine and dopamine. A version is referred to as MAOA-A, also known as ‘The Warrior Gene‘.

Brunner and beyond

‘The story of the warrior gene dates back to the early 1990s, when several groups reported a link between violent aggression and a gene on the X chromosome that encodes for an enzyme called monoamine oxidase A (MAOA), which regulates the function of the neurotransmitters such as dopamine and serotonin. The correlation first emerged from studies of a large Dutch family whose male members were mildly retarded and extremely violent. Two were arsonists, one tried to run over an employer with a car, another raped his sister and tried to stab the warden of a mental hospital with a pitchfork. The men all lacked monoamine oxidase A, suggesting that they possessed a defective version of the MAOA gene.’

                                                                                                                                              Scientific American 

Brunner’s syndrome is isolated to 14 individuals as part of the extension of the same family and therefore, does not give much assistance on our understanding of wider criminality in society, however, it has prompted research into the natural variations in levels of MAOA coupled with childhood experience to give a more generalised account of aggression, anti-social behaviour and criminality.  One key piece of such evidence is that of Moffit and Caspi (2002), as can been seen from the results below the trends for antisocial behaviour becomes elevated with the genetic predisposition of low MAOA activity.  Read the full study here. 


So it seems the Nature Vs Nurture debate for aggression and criminality is still deciding the key factors between the interaction between the two and which exerts the most influence.  Or is the naturally occurring ‘Warrior gene’ an atavistic device acting as a defence for the human race – like human army ants?

Further Reading

Research papers

  • Cary Frydman et al., MAOA-L carriers are better at making optimal financial decisions under risk, Proc. R. Soc. B, (2010)
  • Rose McDermott et al., Monoamine oxidase A gene (MAOA) predicts behavioral aggression following provocation, Proc. Natl Acad. Sci., (2008)
  • Beaver et al., MAOA Genotype is Associated with Gang Membership and Weapon Use, Comprehensive Psychiatry, (2009)