What is the role of chance in human life? If a book tops the bestseller list, a new product takes over the market, or people suddenly want to stem immigration, might it all be some kind of accident?

Over a decade ago, a celebrated paper by sociologists Matthew Salganik, Peter Dodds, and Duncan Watts tried to answer such questions. They asked: When a song turns out to be a spectacular success, is it because it’s really great, or just because enough people, at an early stage, were seen to like it?

Salganik and his colleagues created a control group in which people could hear and download one or more of dozens of songs by new bands. In the control group, people were not told anything about what anyone else had downloaded or liked, left to make their own independent judgments.

The researchers also created eight other groups, in which people could see how many people had previously downloaded songs in their particular groups. Here was the central question: Would it make a big difference if people could see the downloads of others?

It did. While the worst songs (as established by the control group) never ended up at the top, and while the best songs never ended up at the very bottom, essentially anything else could happen. If a song benefited from a burst of early downloads, it could do really well. If it did not get that benefit, almost any song could fail.

These findings were electrifying. They suggested that success in business and politics can be difficult or even impossible to predict.

In subsequent work, Watts has argued that we are often wrong to attribute success or failure to intrinsic merit or to deep cultural forces. Whether it’s the election of President Donald Trump, the views of the Republican Party on immigration, or the fame of the Mona Lisa, the real reason might be: visible downloads, at just the right time.

A new study provides Watts with a lot of support. Building directly on the music downloads experiment, sociologist Michael Macy of Cornell University and his collaborators asked whether the visible views of other people could suddenly make identifiable political positions popular among Democrats and unpopular among Republicans, or vice versa.

Here’s how the experiment worked. All participants (consisting of thousands of people) were initially asked whether they identified with Republicans or Democrats. They were then divided into 10 groups. In the “independence” groups, participants were asked what they thought about 20 separate issues — without seeing the views of either political party on those issues. In the eight other “influence” groups, participants could see whether Republicans or Democrats were more likely to agree.

The authors carefully selected issues on which people would not be likely to begin with strong convictions along party lines. For example: “Companies should be taxed in the countries where they are headquartered rather than in the countries where their revenues are generated.”

The authors hypothesized that in the influence condition, it would be especially hard to predict where Republicans and Democrats would end up. If the early Republican participants in one group ended up endorsing a position, other Republicans would be more likely to endorse it as well — and Democrats would be more likely to reject it. But if the early Republicans rejected it, other Republicans would reject it as well — and Democrats would endorse.

That’s exactly what happened. Across groups, Democrats and Republicans often flipped positions, depending on what the early voters did. As the researchers put it, “Chance variation in a small number of early movers” can have major effects in tipping large populations — and in getting both Republicans and Democrats to embrace a cluster of views that actually have nothing to do with each other.

These findings help explain how members of both parties flip over short periods of time, and also how issues suddenly, and surprisingly, become polarizing across political lines. Immigration is the most obvious example.

The fundamental point is that the most intense political or cultural divisions may have nothing to do with ideology or core values. Everything may depend on unpredictable social cascades — driven by the fact that some prominent Republicans, or some prominent Democrats, happened to take a particular position at just the right time.

Cass R. Sunstein is a columnist for Bloomberg Opinion, where a version of this piece first appeared. He is the author of “The Cost-Benefit Revolution."