If you’ve spent much time thinking about the political divide in the United States, you’ve hopefully noted how bloody weird it is. Somehow, just about every topic that people want to argue about splits into two camps. If you visualize the vast array of topics you could have an opinion about as a switchboard full of toggles, it seems improbable that so many people in each camp should have nearly identical switchboards, but they do. This can even extend to factual issues, like science—one camp typically does not accept that climate change is real and human-caused.

How in the world do we end up with these opinion sets? And why does something like climate change start an inter-camp argument, while other things like the physics behind airplane design enjoy universal acceptance?

One obvious way to explain these opinions is to look for underlying principles that connect them. Maybe it’s ideologically consistent to oppose both tax increases and extensive government oversight of pesticide products. But can you really draw a straight line from small-government philosophy to immigration attitudes? Or military funding?

Politics and hit songs

A new study by a Cornell team led by Michael Macy approaches these questions with inspiration from an experiment involving, of all things, downloading indie music. That study set up separate “worlds” in which participants checked out new music with the aid of information about which songs other people in their experimental world were choosing. It showed that the songs that were “hits” weren’t always the same—there was a significant role for chance, as a song that got trending early in the experiment had a leg up.

To see if this sort of “accident of history” model could apply to political divisions, the researchers set up a similar experiment. A total of over 4,500 online participants were split into two experiments where each had an equal number of self-identified Democrats and Republicans. The researchers then created ten separate “worlds” in each experiment.

For the first experiment, all the participants were asked whether they agreed with 20 different statements that had been chosen to plausibly be politically controversial, but not actively subjects of argument today. Topics included things like cryptocurrency, a proposal to switch to licensed professional jurors, and gene-editing. In two of the ten experimental worlds, people simply saw these statements and were asked, “As a [Democrat/Republican], do you agree or disagree with this statement?”

The other eight worlds are where it got fun. After the first person had responded to these statements, every other participant would also see whether Republicans or Democrats were more likely to agree with the statement, with that statistic updated following each response. After everyone finished the survey, you could see which statements ended up being Republican positions, and which ended up being Democratic ones.

Compared to the two worlds without information about how others were responding, the eight “social influence” worlds were significantly more polarized. And among those eight worlds—just like the indie music experiment—different positions became Republican or Democrat “hits” in different worlds.

Who needs consistency?

Using the results from the two non-social worlds, you could pretty accurately predict some of the positions in the other worlds, and there was apparently some inherent ideological consistency in these items. But overall, the early responses (the trend-setters) in each world were a far better predictor of the final scores. Once a few responses moved the average away from the middle, a topic’s fate would more or less be sealed through what’s known as an “opinion cascade.” In order to flip the stat from one party to the other, you’d need an increasingly long run of people to ignore the social cue and vote the other way.

The team’s second experiment was quite similar but produced slightly different results. The setup was the same, except that instead of asking participants “As a Democrat, do you agree?”, they were asked to predict which party would be more likely to agree if there were a separate, real-world survey. Additionally, in between seeing the results from previous participants and giving their answer, they were also asked whether their party’s stance on the topic was likely to be based on principles, historical precedent, or popularity with the party’s base.

This fairly subtle change (along with the promise of a $100 prize for the top predictor) apparently got people’s brains working differently. In this version of the experiment, social influence was a little less important, and a significant number of people voted contrary to the trend. The final results turned out more similar to the outcome of the two worlds in which there was no social information provided. Still, the early responses in the social worlds was still the best predictor of how each one would end up.

Obviously, these experiments aren’t exactly like the real world, where political leaders can try to steer their parties. Still, it’s another way to show that some political beliefs aren’t inviolable principles—some are likely just the result of a historical accident reinforced by a potent form of tribal peer pressure. And in the early days of an issue, people are particularly susceptible to tribal cues as they form an opinion.

The researchers suggest that knowing this could make you more tolerant of opposing opinions. But given the ardor with which we tell ourselves stories that fortify our opinions and choices, that may require some decidedly Herculean introspection.

Science Advances, 2019. DOI: 10.1126/sciadv.aax0754 (About DOIs).