In the experiment, subjects sat in a brain scanner while being shown a mix of images. Some of them were downright nasty, showing filth, rot, and decay. Others were neutral or pleasant -- like landscape shots, or pictures of babies. The researchers noted the neural response to each.
Afterward, the study subjects took a political survey that asked them about their thoughts on issues, such as having prayer in public schools and same-sex marriage legalization.
The researchers, led by Virginia Tech professor Read Montague, found that patterns of brain activity after viewing the gross images could be grouped together based on political leanings. In other words, conservatives reacted one way to the images (at least on a neurological level) and liberals reacted another way.
When asked to rate the disgusting pictures, one group wasn't more grossed out than the other. But the subconscious reactions varied enough for the researchers to tell conservatives and liberals apart.
Montague, who is looking into the heritable nature of political ideology, was looking for a way to identify these leanings on a brain scan.
"But the results were almost too good to be true," he said. "Even with just one picture, we were able to predict their score on the political survey with 94 percent accuracy." And when they used multiple pictures to give them more data, the accuracy shot up.
It might sound wild, but this is in line with some previous studies on political ideology. A 2012 study from Cornell found that the mere mention of hand sanitizer made students more conservative, suggesting that germaphobia can make us less liberal-minded for a time.
An evolutionary bias against disgusting things makes a lot of sense -- avoiding rotting corpses and dirty toilets keeps us from getting sick. But it seems that being reminded of this deeply ingrained fear can also make us fear "the other," leading to xenophobia and other more conservative philosophies, studies say. Again, when you think back to our early evolutionary history, this makes sense -- people lived in tiny, close communities, and outsiders could bring in unfamiliar and dangerous infections.
But when infection and death are on everyone's minds -- as they are now, in the midst of the Ebola crisis -- it's important to make sure conscious logic has as much sway on your vote as outdated evolutionary instincts do.