At the end of most years, I’m typically asked to write about the best psychology papers of the past twelve months. This year, though, is not your typical year. And so, instead of the usual “best of,” I’ve decided to create a list of classic psychology papers and findings that can explain not just the rise of Donald Trump in the U.S. but also the rising polarization and extremism that seem to have permeated the world. To do this, I solicited the opinion of many leading psychologists, asking them to nominate a paper or two, with a brief explanation for their choice. (Then I nominated some stories myself.) And so, as 2016 draws to a close, here’s a partial collection of the insights that psychology can bring to bear on what the year has brought about, arranged in chronological order.

Charles Lord, Lee Ross, and Mark Lepper’s “Biased Assimilation and Attitude Polarization”

In 1979, a team from Stanford University—Charles Lord, Lee Ross, and Mark Lepper—published a paper that made sense of a common, and seemingly irrational, phenomenon: that the beliefs we hold already affect how we process and assimilate new information. In other words, we don’t learn rationally, taking in information and then making a studied judgment. Instead, the very way we learn is influenced from the onset by what we know and who we are. In the original study, Lord and his colleagues asked people to read a series of studies that seemed to either support or reject the idea that capital punishment deters crime. The participants, it turned out, rated studies confirming their original beliefs as more methodologically rigorous—and those that went against them as shoddy.

This process, which is a form of what’s called confirmation bias, can help explain why Trump supporters remain supportive no matter what evidence one puts to them—and why Trump’s opponents are unlikely to be convinced of his worth even if he ends up doing something actually positive. The two groups simply process information differently. “The confirmation bias is not specific to Donald Trump. It’s something we are all susceptible to,” the Columbia University psychologist Daniel Ames, one of several scholars to nominate this paper, said. “But Trump appears to be an especially public and risky illustration of it in many domains.” (Ames and his colleague Alice Lee recently showed a similar effect with beliefs about torture.)

A closely related paper by Ross, Lepper, and Robert Vallone, from 1985, found that the polarization effect was particularly powerful among strong partisans. When looking at perceptions of the 1982 Beirut massacre, they found that more extreme partisans saw the facts as more biased, and recalled the media coverage of the massacre differently. They saw more negative references to their side, and they predicted that nonpartisans would be swayed more negatively against them as a result—thus increasing their perception of being assaulted and solidifying their opinions. The more knowledge of the issue they had, the greater their perception of bias. American politics has grown only more partisan since the eighties, and this finding can help explain some of the backlash among Trump supporters to press outlets that reported critically on him.

Dan Kahan’s “Cultural Cognition”

Over the last decade, Dan Kahan, a psychologist at Yale University, has been studying a phenomenon he calls “cultural cognition,” or how values shape perception of risk and policy beliefs. One of his insights is that people often engage in something called “identity-protective cognition.” They process information in a way that protects their idea of themselves. Incongruous information is discarded, and supporting information is eagerly retained. Our memory actually ends up skewed: we are better able to process and recall the facts that we are motivated to process and recall, while conveniently forgetting those that we would prefer weren’t true. The Harvard psychologist Steven Pinker, one of several to nominate Kahan for this list, said that his theory is best called “political and intellectual tribalism.” Like seeks like, and like affirms like—and people gravitate to the intellectually similar others, even when all of their actions should rightly set off alarm bells.

Trump, Pinker said, won over pretty much the entire Republican Party, and all those who felt alienated from the left, by declaring himself to be opposed to the “establishment” and political correctness. And this all happened, Pinker wrote to me, “despite his obvious temperamental unsuitability for the responsibilities of the Presidency, his opposition to free trade and open borders (which should have, but did not, poison him with the libertarian right), his libertine and irreligious lifestyle (which should have, but did not, poison him with evangelicals), his sympathies with Putin’s Russia (which should have, but did not, poison him with patriots), and his hostility to American military and political alliances with democracies (which should have, but did not, poison him with neoconservatives).”

Karen Stenner’s “The Authoritarian Dynamic”

Research published a decade ago by Karen Stenner provides insight into a psychological trait known as authoritarianism: the desire for strong order and control. Most people aren’t authoritarian as such, Stenner finds. Instead, most of us are usually capable of fairly high tolerance. It’s only when we feel we are under threat—especially what Stenner calls “normative threat,” or a threat to the perceived integrity of the moral order—that we suddenly shut down our openness and begin to ask for greater force and authoritarian power. People want to protect their way of life, and when they think it’s in danger they start grasping for more extreme-seeming alternatives. In 2005, Stenner offered a prediction that seems clairvoyant now. In response to the increasing tolerance in Western societies, she wrote, an authoritarian backlash was all but inevitable:

[T]he increasing license allowed by those evolving cultures generates the very conditions guaranteed to goad latent authoritarians to sudden and intense, perhaps violent, and almost certainly unexpected, expressions of intolerance. . . . The kind of intolerance that springs from aberrant individual psychology, rather than the disinterested absorption of pervasive cultural norms, is bound to be more passionate and irrational, less predictable, less amenable to persuasion, and more aggravated than educated by the cultural promotion of tolerance.

John Tooby and Leda Cosmide’s “Groups in Mind: The Coalitional Roots of War and Morality”

In 2010, John Tooby and Leda Cosmides, scholars at the University of California, Santa Barbara, best known for their work in evolutionary psychology, published a paper on the use of outrage to help mobilize coalitions. Their main claim is that humans, like other animals, are predisposed to coalition-building: in order to best protect ourselves, we coöperate with those we see as within our coalition, and we fight those we see as outside it. One of the ways coalitions can be galvanized to action, the authors showed, is by uniting them against a perceived outrage—and this dynamic played out repeatedly in the Trump campaign, both with Trump supporters and the opposition. Play up the outrage factor and suddenly groups bond together like never before—and prepare to attack like never before.