麻豆传媒

It鈥檚 been called the 鈥渨arrior gene鈥� 鈥� a mutation that seems to make people more aggressive. Now researchers report that people with this gene may not be aggressive, just better at spotting their own interests.

Previous research has found that people with MAOA-L, a gene that controls signalling chemicals in the brain, can be more aggressive. But there is enormous controversy about this, as the gene鈥檚 effects seem to vary with people鈥檚 backgrounds.

and colleagues at the California Institute of Technology in Pasadena have now found that people with MAOA-L 鈥渏ust make better choices鈥�, says Frydman. 鈥淭his isn鈥檛 the same as aggression.鈥�

Raising the stakes

Variants of the gene MAOA produce less or more of an enzyme that degrades several signalling chemicals, known as neurotransmitters. People with MAOA-L, which results in less of the enzyme, sometimes show more aggression or impulsivity 鈥� but not always.

To try to dissect these differences, Frydman gave 83 male volunteers 140 hypothetical choices. With 3聽minutes for each choice, the men had to decide whether they preferred a sure thing, say being given $2, or a risky option, for example a 50:50 chance of gaining $10 or losing $5.

Previous research has shown that these choices can be used to reveal each person鈥檚 overall aversion to risk. The team found this did not differ in people with or without MAOA-L.

But the calculation also allowed them to look at how often each person took the risky option that would also do them the most good. At every level of risk aversion among the participants, 鈥渢he MAOA-L carriers were better at choosing what 鈥� for them 鈥� was the more beneficial option鈥�.

The results are consistent with previous research, says Frydman, but his team could distinguish for the first time between the two components of each decision: deciding how much each option was worth , then comparing them. The MAOA-L carriers were better at the second part.

Pay attention

This edge may look like aggression or impulsivity in some situations, but may simply reflect more focused attention, thinks Frydman. 鈥淚f two gamblers are counting cards, and one is making a lot of bets, it may look like he鈥檚 more aggressive or impulsive. But you don鈥檛 know what cards he鈥檚 counting 鈥� he may just be responding to good opportunities.鈥�

鈥淧revious studies that have associated MAOA-L with aggression or impulsivity might have to be interpreted carefully,鈥� says , who heads the lab where Frydman works. 鈥淭he key question is whether, in the context of the lives of the subjects, these decisions were optimal or not.鈥�

In a of the University of Edinburgh, UK, found that MAOA-L carriers were more aggressive, but only after a large provocation and without apparent impulsiveness. 鈥淭hat could be explained by this new work,鈥� he says, because his subjects seemed to be acting in strategic self-interest, the very thing Frydman鈥檚 MAOA-L carriers were good at. This also suggests how such behaviour 鈥� and the gene that shapes it 鈥� could be selected by evolution.

The implications go beyond the so-called 鈥渨arrior gene鈥�. As gene sequencing gets cheaper, says Frydman, there will be more efforts to link genes to behaviour. To do that accurately, researchers will need to define the components of behaviour as carefully as they do the DNA.

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