One of the most fascinating things about political ideology is that it's likely much more genetic than most people realize. Of course "nurture" matters, but there's strong evidence that people are also born with certain features and personality traits that predispose them toward leaning liberal, conservative, or libertarian. A new study suggests that unconscious reactions to a single "disgusting image" can reliably predict whether someone identifies as liberal or conservative.

The study, published in the most recent issue of Current Biology, relied on brain scans of people shown a series of gross, pleasant, and neutral images. Researcher P. Read Montague, a Virginia Tech professor and head of the school's Human Neuroimaging Lab, said he was inspired by research showing political affiliation is highly heritable and how one identifies politically has deep connections to biology, especially the way our bodies respond to threats of "contamination" or violence.

The brain scans revealed that, indeed, the way one's neurons fired in response to gross-out imagery was a pretty damn good indication of whether one identified as liberal or conservative. While responses to the pleasant and neutral images were predictive of nothing, responses to an image of a mutilated animal body were split neatly down political lines.

"A single disgusting image was sufficient to predict each subject's political orientation," said Montague. "I haven't seen such clean predictive results in any other functional imaging experiments in our lab or others." The results "suggest that important foundational parts of political attitudes ride on top of preestablished neural responses," he said.

Self-reported responses to the imagery were not an accurate predictor of political persuasion.

"These results provide strong support for the idea that fundamental neural processing differences that emerge under the challenge of emotionally evocative stimuli may serve to structure political beliefs in ways formerly unappreciated," the researchers concluded.

Ronald Bailey has written here previously about research showing political conservatives are more easily grossed out. Other research has shown that those with low sensitivity to disgust tend to be liberals or libertarians.

h/t Mark Sletten