Maggot infestations, rotting carcasses, unidentifiable gunk in the kitchen sink – how much your brain responds to disgusting images could predict whether you are liberal or conservative.

If you don't want to read any further because this is based on functional magnetic resonance imaging and claims that political leaning is a biological trait, here is the short version and you can just rant in the comments: if you are not grossed out, you are a liberal. The authors feel so confident in the result they say they can predict your politics based on a single image with 95 percent to 98 percent accuracy,   

"Disgusting images generate neural responses that are highly predictive of political orientation even when those neural responses don't correspond with an individual's conscious reaction to the images," said lead author Read Montague of the paper in Current Biology, a biophysicist and Virginia Tech Carilion Research Institute professor. "Remarkably, we found that the brain's response to a single disgusting image was enough to predict an individual's political ideology."

In a brain scanner, participants were shown disgusting images, such as dirty toilets or mutilated carcasses, mixed with neutral and pleasant images, such as landscapes and babies. Afterward, the subjects took a standard political ideology inventory, answering questions about how often they discuss politics and whether they agreed or disagreed with hot-button topics such as school prayer and gay marriage. 

The responses to the disgusting images could predict, with 95 percent to 98 percent accuracy, how a person would answer questions on the political survey. That suggests to the authors that political ideologies are mapped onto established neural responses that may have served to protect our ancestors against environmental threats. If so, those neural responses could be passed down family lines, that disgust reactions are inherited.

"We pursued this research because previous work in a twin registry showed that political ideology — literally the degree to which someone is liberal or conservative — was highly heritable, almost as heritable as height," said Montague. 

Conservatives tend to have more magnified responses to disgusting images, but reasons why are speculative. Nonetheless, speculation says that the responses could be a callback to the deep, adverse reactions primitive ancestors needed to avoid contamination and disease. To prevent unsavory consequences, they had to learn to separate the canteen from the latrine. 

So conservatives are less likely to crap where they eat, which may be important for the elections next week that have motivated the latest rash of 'politics is biological' articles this month.

Are we hardwired to respond on instinct alone? Not really. In many familes, children have various heights even though genetics determines height.

"Genetics predetermines height – but not fully," Montague said. "Nutrition, sleep, and starvation can all change someone's ultimate height. But tall people's children tend to be tall, and that's a kind of starting point. If we can begin to understand that some automatic reactions to political issues may be simply that – reactions – then we might take the temperature down a bit in the current boiler of political discourse."

Montague says human behavioral control in spite of biology is a 'behavioral superpower'. 

"People can deny their biological instincts for an idea – think of hunger strikes for political reasons," Montague said. "That requires a high degree of cognitive control, and that's the point."

The takeaway message for Election Day?

"Think, don't just react," Montague said. "But no one needs neuroscience to know that's a good idea."