People seem inordinately keen to pit nature and nurture as imagined adversaries, but this naive view glosses over the far more interesting interactions between the two. These interactions between genes and environment lie at the heart of a new study by Rose McDermott from Brown University, which elegantly fuses two of my favourite topics – genetic influences on behaviour and the psychology of punishment.
<Regular readers may remember that I've written three previous pieces on punishment. Each was based on a study that used clever psychological games to investigate how people behave when they are given a choice to cooperate with, cheat, or punish their peers.
McDermott reasoned that the way people behave in these games might be influenced by the genes they carry and especially one called monoamine oxidase A (MAOA), which has been linked to aggressive behaviour. Her international team of scientists set out to investigate the effect that different versions of MAOA would have in a real situation, where people believe that they actually have the chance to hurt other people.
MAOA encodes a protein that helps to break down a variety of signalling chemicals in the brain, including dopamine and serotonin. It has been saddled with the tag of “warrior gene” because of its consistent link with aggressive behaviour. A single fault in the gene, which leads to a useless protein, was associated with a pattern of impulsive aggression and violent criminal behaviour among the men of a particular Dutch family. Removing the gene from mice makes them similarly aggressive.
These are all-or-nothing changes, but subtler variations exist. For example, there is a high-activity version of the gene (MAOA-H), which produces lots of enzyme and a low-activity version (MAOA-L), which produces very little. The two versions are separated by changes in the gene’s “promoter region”, which controls how strongly it is activated.
A few years ago, British scientists found that children who had been abused are less likely to develop antisocial problems if they carry the MAOA-H gene than if those who bear the low-activity MAOA-L version. An Italian group has since found the same thing. It is a truly fascinating result for it tells us that the MAOA gene not only affects a person’s behaviour, but also their reactions to other people’s behaviour.
But both studies had a big flaw – they measured aggression by asking people to fill in a questionnaire. Essentially, they relied on people to accurately say how belligerent they are and we all know that many people like to talk big. McDermott wanted to look at actions not claims.
To that end, she recruited 78 male volunteers and sequenced their MAOA gene to see which version they carried (just over a quarter had the low-activity version). The volunteers played out a scenario where they believed that they could actually physically harm another person for taking money that they had earned. Their weapon of retribution? Spicy sauce.