Smell that? If so, it might mean you're Republican.
The ability to sniff out androstenone -- our ancestors may have used it as a clue to identify dominant males -- tends to be stronger among conservatives than liberals.
Likewise, the degree to which certain images -- someone vomiting, stool in a toilet, a guy eating worms -- turn your stomach can help predict your outlook on same-sex marriage.
"People feel politics in their gut," said Kevin B. Smith, who is marrying physiology and political science in his research at the University of Nebraska.
Increasingly, scientists believe that where we land on the political spectrum isn't just the result of growing up in a union home or an evangelical home or a shopkeeper's home. Some factors that make us more revolutionary or reactionary come naturally.
And as you venture to the left or right in your political outlook, biology tends to keep you there.
Consider what happens when a researcher tells people about a self-contradiction by their politician of choice, and then adds a justification for that contradiction. Subjects' brains subsequently seen through a functional magnetic resonance imager, or fMRI, show little activity in the part of the brain that reasons. But its emotional centers buzz.
"Partisans twirl the cognitive kaleidoscope until they get the conclusions they want," Emory University psychologist Drew Westen said in a press release about the research.
Other studies suggest simply seeing a picture of a candidate's face will stir the brain in different ways depending on whether you've decided to vote for or against her.
At Yale, researchers found that how college Democrats and Republicans viewed welfare proposals turned not on whether the schemes were too generous or too miserly. Rather, judgments fixed more keenly on whether the young partisans thought the plans came from their camp or the opposition.
"Our brains are really uncomfortable with uncertainty," said Jerrold Post, the director of political psychology at George Washington University. "So we seek out things that reinforce our beliefs, not what challenges them."
Our brains know whom we like and don't like, and our brains don't like stuff that would challenge that.
"People really only want to focus on the facts that fit their point of view," said Richard Vatz, a Towson University professor of rhetoric and political communication.
He authored "The Only Authentic Book of Persuasion" and is an increasingly lonely voice dismissing mounting studies that suggest biology influences politics. Vatz contends the way we view politics is largely about spin. We sort out political conflict based on the context in which it's presented to us, he said, not based on predispositions built into our brains.
Others, however, point to experiments and studies showing a tendency toward being conservative or liberal much the same way genetics make some people more susceptible to addiction or depression.
Take one simple study conducted by David Amodio, a professor of psychology and neural science at New York University. He asked test subjects to hit the space bar on a keyboard every time an "m" flashed on a screen and to do nothing when a "w" appeared. The "m" appeared 80 percent of the time, so there was a tendency to hit the space bar even when the "w" showed up.
Liberals tended to show greater accuracy. Take the results how you like, that liberals are more responsive to changes in the environment, or hold weaker convictions. That conservatives are more respectful of tradition, or more reflexive. But it was evidence of differences even when all the personalities and jingoism are stripped away.
"Patterns of brain activity relate to people's political orientation," Amodio said.
No one denies the influence of a political environment. Growing up with Democratic parents in a Democratic neighborhood in a Democratic state dramatically increases the odds of becoming a Democrat. But studies show identical twins, whose genes match each other exactly, grow to have more similar political views than fraternal twins.
"Nobody's saying there's a gene to be pro-choice or anti-abortion," said Smith, the Nebraska researcher. But, "genes influence your sensory and processing architecture."
His study with the gag-worthy pictures didn't show a correlation across the liberal-to-conservative spectrum. Instead, it related only to how people view sex-related issues.
From an evolutionary standpoint, Smith said, people revolted by the images would have a survival advantage. Fecal matter, after all, is best avoided. But those who were less disgusted, he said, may be demonstrating a greater ability to act with reason than with instinct.
In a book released this spring, "The Righteous Mind," psychologist Jonathan Haidt argued the differences between Republicans and Democrats revolve principally around six moral values.
His research, Haidt said in an interview, found that people from both parties place high values on fairness, compassion and liberty. (They do, however, see them differently. Republicans view liberty as escape from government oppression, while Democrats worry about corporate oppression.)
Yet Haidt said Republicans put far more stock in three other values -- loyalty, authority and sanctity -- that barely register with Democrats.
"Democrats commit sacrilege" -- he points to the debate over requiring some institutions to provide birth control -- "and they don't realize it," he said.
So all this conditioning and chemistry, nurture and nature, drives people to polarized extremes. How, then, are voters to open their minds?
"Get to know people on the other side," Haidt suggested. "You'll hear people say, 'He's a conservative' or 'He's a liberal ... but he's actually really nice.' "
