MAOA-L : Warrior Gene or Justice Gene ?
In June 2005, an unpublished study by Dr Rod Lea et al. was presented at the Molecular Biology and Evolution Conference in Auckland, New Zealand, then again a year later at the International Congress of Human Genetics in Brisbane, Australia. It literally send shockwaves to the media around the world. The study claimed to have identified a "Warrior Gene" by studying the indigenous Māori people of New Zealand.
The aim of the study was to determine what caused the Māori to behave more aggressively and violently and to get involved more often in risk-taking behaviour like gambling, compared to New Zealanders of European descent. The gene that they found responsible was MAO-A, encoding the monoamine oxidase A, an enzyme which role is to degrade amine neurostransmitters like adrenaline, noradrenaline, serotonin, and dopamine. Dr Lea's team discovered that people with the low-activity version of the gene (MAOA-L), producing less enzyme, have a higher level of aggression when provoked than those with the high-activity variant (MAOA-H). The explanation is that the level of adrenaline and other hormones and neurotransmitters soar following an aggression, and people producing less MAOA enzyme take longer to regain their composure (normal levels). The results of this study have since been replicated several times by other studies.
The MAOA gene being on the X chromosome, men only have one copy of it and therefore their behaviour is more affected by the variant that they inherited. A key finding was that the MAOA-L associated with antisocial behaviour in men, but only against a background of prior maltreatment. Male carriers of the MAOA-L with a history of child abuse were especially likely to become violent.
A newer study by Cary Frydman et al. from the California Institute of Technology claimed that MAOA-L carriers are better at making optimal financial decisions under risk (review by Nature News and New Scientist).
About one third of people of European descent possess the low-activity version, against 60 to 80% in most Asian populations (Indians, East Asians, Pacific Islanders). Nonetheless, Asian people are not known for being more aggressive, violent or anti-social than Caucasians. If anything East Asian societies are generally more peace-loving, law-abiding and socially harmonious than Western societies.
The well publicised study by Rose McDermott et al. (2008) from Brown University confirmed the link between MAOA-L and aggression following provocation, but added a crucial nuance. They found that MAOA-L carriers punished more readily offenders than MAOA-H carriers.
In other words, the study has linked the low-activity of MAOA with two new essential behavioural strategies :Originally Posted by McDermott et al.
1) altruistic punishment of others for the sake of society and fairness, even if it is costly and not personally beneficial. It means punishing cheaters and free-riders because they deserve it and just can't get away with it.
2) holding long-term grudge against people who have harmed them, broken the rules of society, or committed crimes.
Provocation can therefore be seen in a broader, more general context. It seems that MAOA-L individuals are more likely to take action when somebody is breaking the rules. The study also points out that MAOA-L carriers are less aggressive when not provoked, but much more aggressive when provoked.
This is probably why Asian societies, and particularly East Asian ones (China, Japan...), are more law-abiding, tougher on crime and misdemeanours, and less tolerant of rule breakers in general (and incidentally also why the Koreans and Chinese still hold grudges against Japan for WWII, whereas most Europeans have put it behind them). As the Japanese saying has it, the nail that sticks out is hammered down. This strikes me not as a warring behaviour but as a righter of wrongs or upholder of the law type of behaviour. That's why I think it is more appropriate to dub the MAOA-L as the "Justice Gene" instead of the "Warrior Gene". MAOA-H carriers, on the contrary, have a more laissez-faire approach to cheaters and free-riders, and are less likely to hold long-term personal grudges against people who have wronged them.
I believe that the nickname "Warrior Gene" survived because it is more evocative and serves better the interest of the media. I was dismayed to see that Family Tree DNA abused the credulity of lay people by offering an outrageously priced MAOA test (99$ just to determine the number of repeats in that gene) when it is possible to determine one's variant using the SNP's from a 23andMe, deCODEme or Navigenics test (look for rs6323; the G allele encodes the low-activity form, i.e. MAOA-L).
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