Monoamine oxidase A gene (MAOA) has earned the nickname “warrior gene” because it has been linked to aggression in observational and survey-based studies. However, no controlled experimental studies have tested whether the warrior gene actually drives behavioral manifestations of these tendencies. We report an experiment, synthesizing work in psychology and behavioral economics, which demonstrates that aggression occurs with greater intensity and frequency as provocation is experimentally manipulated upwards, especially among low activity MAOA (MAOA-L) subjects. In this study, subjects paid to punish those they believed had taken money from them by administering varying amounts of unpleasantly hot (spicy) sauce to their opponent. There is some evidence of a main effect for genotype and some evidence for a gene by environment interaction, such that MAOA is less associated with the occurrence of aggression in a low provocation condition, but significantly predicts such behavior in a high provocation situation. This new evidence for genetic influences on aggression and punishment behavior complicates characterizations of humans as “altruistic” punishers and supports theories of cooperation that propose mixed strategies in the population. It also suggests important implications for the role of individual variance in genetic factors contributing to everyday behaviors and decisions.
Regularly readers know we’ve talked about MAOA in the past, it’s one of those big-effect genes which keeps popping up in behavior genetic studies. It definitely increases my confidence in the reality of past associations to see it produce results in experimental situations which match our predictions. Along with the dopamine receptor loci this is likely a keeper. The issue of mixed strategies is something I’ve been mentioning periodically, the idea of evolutionary game theory has been around for nearly two generations, and frequency dependent selection is over a century old. But I think far too often people who are interested in the intersection between biology and behavior start conversations which assume that these are minor or trivial dynamics. At a certain point if “transient” states are more common than periods when there is an ESS, you need to reorient your frame. Human environments (that is, cultures) change a lot. Sometimes that change is exogenous (consider shifting climate), but in many cases instability in the background parameters upon which an ESS is conditional might result in periodic shifts in state.* Peter Turchin‘s work to some extent describes this on the macro-level, while Martin Nowak has developed models on a smaller scale. The main unfortunate byproduct of accepting this relatively more complex explanatory framework is that it makes glib assertions about natural selection on behavioral traits more difficult.
Here’s the ScienceDaily summary.
* Basically, if you figure out an “unbeatable” strategy at winning a game, you are screwed when the rules change.
Labels: Behavior Genetics