battle

The 2002 film Minority Report imagined a world in which violent crime could be predicted before it occurs. In that movie, like the Philip K. Dick short story on which it’s based, suspects were singled out for aggressions they hadn’t committed yet. One of the neuroscientists behind the new discovery of 40 aggression-related genes, Yanli Zhang-James, Ph.D., said she was constantly thinking of the dystopian film and others like it while conducting her research.

“What I feared was that people were going to say, ‘Oh, you have this gene, you’re predicted to be aggressive’. That’s not what we’re trying to report at all,” Zhang-James, the first author on the new Molecular Psychiatry paper and a researcher at the Institute For Human Performance at the State University of New York, tells Inverse.

Zhang-James says her team’s paper had far more important implications.

After the team identified 40 genes that appeared again and again in genetic research on aggression, their review of the functions of those genes revealed that those genes were, in themselves, nothing special. “These functions are so general,” she says.

It turns out that the same genes that play a role in aggression are also involved in basic cell behaviors, like creating proteins involved in cell communication. Some of those genes are also involved in regulating one another.

“Some genes are likely to function as important nodes of the genic networks prone to a violent behaviour, and those would be probably related to other genes which play a minor role”, said study co-author and University of Barcelona biologist Noèlia Fernàndez Castillo, Ph.D. in a statement published Monday. In short, genes that may present a risk factor for aggression are innate parts of being human.

University of Barcelona neurogeneticist and co-author Bru Cormand, Ph.D. explained in the statement that “aggressive behaviour is a present feature over the biological evolution since it has some benefits for the survival of species (accessing resources, breeding, etc.).”

White-footed Mouse, _2016-03-08-11.46
Mice carrying the MAOA gene -- also known as the "warrior gene" -- have been shown to be more aggressive.

The field of behavioral genetics, which attempts to link genes to traits like intelligence, often stokes controversy. The literature on aggression-related genes is far from perfect, Zhang-James admits, but her team’s goal was to perform a meta-analysis, taking everything scientists have found and using that to create a “ranking” of the 40 genes most likely to lead to aggressive behavior in specific social environments.

To do so, the team used evidence from human-based genome-wide association studies and from mouse-based studies, which looked at the behavior of mice missing certain key genes. If a gene was linked to aggression in both lines of evidence — they devised a conversion formula to compare the function of mouse genes to human ones — it was ranked higher on the list.

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The top three genes associated with aggressive behavior. MAOA, the "warrior gene" tops the list 

The gene that topped the list is MAOA, famously called “the warrior gene,”, which is the closest scientists have come to finding a causal relationship between genetics and aggression. It made headlines after a notorious study conducted in 2014 on 798 Finnish prisoners reported that an estimated 9 percent of violent crime in Finland was attributed to the MAOA genotype — regardless of environmental factors, like maltreatment.

Part of the reason the field of behavioral genetics is so controversial is because social factors aren’t always taken into account when trying to explain bad behavior, and the oversimplification of the relationship between genes and loosely-defined traits is often compounded by the media. For example, a 2009 PNAS study from Brown University, showing that people with the warrior gene mutation were more likely to administer punishing amounts of hot sauce to people who took money from them, sparked heated discussion about the potential for discrimination that arises from linking genetics and criminality. There have been many more studies like this, focused mainly on the warrior gene. In 2013, Nature News referred to the field in general as “taboo genetics”.

But there’s reason to believe that the attitudes surrounding behavioral genetics are shifting slightly. Researchers are more interested in pinpointing genetic components in aggression, so long as it’s acknowledged that the primary risk factors remain environmental. If we can establish that it’s the social environment that drives genetic dispositions towards behavior and not the other way around, Zhang-James says, then we can integrate genetics into the equation.

“When exposed to some social environments, some people are resistant. They don’t become aggressive. Others become extremely violent. That’s where the genetic background comes in.” She says.