According to a study published in the American Journal of Political Science, entitled “Fear and Loathing Across Party Lines,” the intense feelings of loyalty or pride that people have for their political affiliation—and, by extension, the negative feelings they have toward those they see as their opponents—has intensified over the past few decades.

This phenomenon has become so powerful a predictor of behavior, even outside the realm of politics, that the researchers who did the study say that political affiliation now has more influence on what people do and how they behave than race does.

How is this related to the rise of fake news? Because the researchers argue that this powerful desire to be seen as a member of a specific group or tribe influences the way we behave online in a variety of ways, including the news we share on social networks like Facebook. In many cases it’s a way to of signify membership in a group, rather than a desire to share information.

Get Data Sheet, Fortune’s technology newsletter.

Sean Westwood, one of the political scientists who conducted the study, says that party affiliation used to be just one of many attributes people gave when asked about themselves in interviews. Now, it has become a core element of our identity, along with things like gender or ethnicity—people even say they select partners based on political affiliation to a much greater extent than they used to in the past.

This drive to confirm our existing biases affects the news we choose to consume and share, he says. So if a Trump supporter sees a story that references a scandal involving Hillary Clinton—however dubious the story may seem—that person is likely to share it anyway, in order to show their loyalty to the Trump camp and their dislike of the opposition.

“You want to show that you’re a good member of your tribe,” Westwood told the New York Times recently. “You want to show others that Republicans are bad or Democrats are bad, and your tribe is good. Social media provides a unique opportunity to publicly declare to the world what your beliefs are and how willing you are to denigrate the opposition and reinforce your own political candidates.”

Another term for this is “confirmation bias,” which is what sociologists call the desire to believe things that confirm the views we already have about people. The way Facebook is designed tends to exacerbate this problem, because the stories we see come from friends and family members—many of whom we instinctively trust—and the social network is structured in such a way that the emotion a story triggers is more important than whether it is true, since it makes people more likely to click and share.

The result of all these factors, combined with the filtering algorithms that Facebook and other platforms use, can be an intensification of the so-called “filter bubble,” in which we are only exposed to content that fits our preconceived biases or beliefs.

These are all of Trump’s potential conflicts of interest:

In his final address as president, Barack Obama talked about the impact that this phenomenon can have on the American people. “For too many of us it’s become safer to retreat into our own bubbles… surrounded by people who look like us and share the same political outlook and never challenge our assumptions,” he said.

The problem, President Obama added, is that this “splintering of our media into a channel for every taste,” can increase the divisions that already exist in society, whether based on race or political affiliation or class. “Increasingly, we become so secure in our bubbles that we start accepting only information, whether it’s true or not, that fits our opinions,” he said.

And this political tribalism tends to feed on itself, Westwood told the Times. Politicians become increasingly strident and their messages more divisive, in order to appeal to their tribes, and that reinforces the prejudices or behavior of the group. “I don’t think things are going to get better,” the researcher said. “I think this is the new normal.”