Painted tabletop models of the Republican elephant and the Democratic donkey, right, shown on March 11, 2002, in Washington, D.C. (Jacqueline Roggenbrodt/AP)

Conservatives and liberals do not smell the same to potential mates. According to a study published this month in the American Journal of Political Science, people can literally sniff out ideology — and this may explain why so many couples share political beliefs. Or, as the study’s title says, “Assortative Mating on Ideology Could Operate Through Olfactory Cues.”

Researchers led by Brown University political scientist Rose McDermott found that, to a small but significant degree, people prefer the body odor of those who vote as they do.

Previous studies showed long-term mates are more similar when it comes to politics than anything else besides religion. Researchers set out to determine whether this is a purely socially driven phenomenon, or whether biology plays a role.

To test the link between smell and party affiliation, researchers rounded up 146 people aged 18 to 40 from “a large city in the northeast United States.” They used a seven-point scale to determine where they fell on the political spectrum. They sent 21 of these —10 liberals and 11 conservatives — home with fragrance-free soap and shampoo and a gauze pad taped to their armpit. The subjects were told not to smoke, drink, use deodorant or perfume, have sex, eat fragrant foods, sleep with people or pets or linger near strong odors.

They returned the stinky armpit pads 24 hours later. Then 125 participants sniffed the stinky pads, taking a break between whiffs to cleanse their nasal palate with the aroma of peppermint oil. The sniffers, who never saw the people whose smells they were evaluating, then rated the attractiveness of each armpit sample on a 1 to 5 scale.

The subjects found the smell of those more ideologically similar to themselves more attractive than those with opposing views.

“It appears nature stacks the deck to make politically similar partners more attractive to each other in unconscious ways,” the researchers wrote.

Evolution might explain it. “Parental similarity in values increases the likelihood that such individuals may be able to say together long enough to raise their children successfully into adulthood,” the researchers wrote.

Or, in other words, you’re more likely to raise children with someone you agree with than someone you don’t. And smell tips you off on your chances of long-term relationship success.

The link between smell and political preference may also be related to how parents transfer their preferences for certain smells to their children. “Humans, including mothers, spend most of their time around ideologically similar others,” the researchers wrote. “If social attitudes are linked to odor, as the literature suggests, then one mechanism that odor preferences transfer from parents to children may operate through their mother’s choice of mate. In this way, social processes may drive some of the pathways by which individuals come to prefer those whose ideological ‘smell’ matches their own.”

The researchers pointed out that smell isn’t the whole story when it comes to attraction. Many things including conscious choices and other physical urges can influence who we choose to mate with. Smell likely plays a subtle role by affecting hormones and emotional changes.

And of course, some couples defy this science. Exhibit A: James Carville and Mary Matalin.