You can think of human psychology as a series of overlapping mental programs. One program identifies faces as individuals we recognize. Another is working memory, which allows us to make quick calculations in our heads. These programs were coded by evolution and help us survive every day; they are the sources of our ingenuity and our compassion. They are everything we are.

These mental programs — etched in all of us — are also the sources of horror and pain.

Nour Kteily is a psychologist at Northwestern University whose research is about understanding one of the darkest, most ancient, and most disturbing mental programs encoded into our minds: dehumanization, the ability to see fellow men and women as less than human.

Psychologists are no strangers to this subject. But the prevailing wisdom has been that most people are not willing to admit to having prejudice against others.

Kteily suspected otherwise. And so he and his colleagues created a new way to measure people’s levels of blatant dehumanization of other groups. It’s not subtle.

In Kteily’s studies, participants — typically groups of mostly white Americans — are shown this (scientifically inaccurate) image of a human ancestor slowly learning how to stand on two legs and become fully human. And then they are told to rate members of different groups — such as Muslims, Americans, and Swedes — on how evolved they are on a scale of 0 to 100.

Many people in these studies give members of other groups a perfect score, 100, fully human. But many others give others scores putting them closer to animals.

“We have this incredible capacity for cooperation; it’s what makes us human in many ways,” Kteily says. “And yet we have this capacity for othering.”

And that conclusion is opening a Pandora’s box of revelations about the new wave of intolerance toward Muslims and immigrants in America under President Donald Trump — and what it could bring about.

“Dehumanization doesn’t only occur in wartime,” says Nick Haslam, a psychologist who is the world’s current leading expert on the topic. “It’s happening right here, right now. And every day, good people who don’t see themselves as being prejudiced bigots are nevertheless falling prey to it.”

Dehumanization is a mental loophole that lets us harm other people

Thousands of years ago, humans would have felt a pang of anxiety when they saw the silhouette of a foreign tribe marching over a hill. We still have that anxiety inside of us today. Often “people’s spontaneous, knee-jerk reactions to other people who are dramatically different from them is negative,” says Susan Fiske, a psychologist at Princeton University and a leading expert on prejudice. This is especially true when we have quick, minimal exposure to them — as we do today via the media. These thin slices activate the us-versus-them conflict encoded in our minds since the dawn of humanity.

Look back at some of the most tragic episodes in human history and you will find words and images that stripped people of their basic human traits. In the Nazi era, the film The Eternal Jew depicted Jews as rats. During the Rwandan genocide, Hutu officials called Tutsis “cockroaches” that needed to be cleared out.

In the wake of World War II, psychologists wanted to understand how the genocide had happened. And we got Stanley Milgram’s infamous electroshock experiment, which showed how quickly people cave to authority. There was also Philip Zimbardo’s “prison experiment,” which showed how easily people in positions of power can abuse others. At Stanford, Albert Bandura, showed that when participants overhear an experimenter call another study subject “an animal,” they’re more likely to give that subject a painful shock. If you think of murder and torture as universally taboo, then dehumanization of the “other” is a psychological loophole that can justify them.

From these experiments, and those that followed, it became clear that “it’s extremely easy to turn down someone’s ability to see someone else in their full humanity,” says Adam Waytz, a psychologist at Northwestern University who studies how people think about minds and collaborates with Kteily. Even children as young as 5 years old see the world in terms of us versus them.

Fiske at Princeton has studied how immigrants and refugees are uniformly discriminated against the world over. She’s conducted neuroscience research that shows when we dehumanize others, the regions of our brain associated with disgust turn on and the regions associated with empathy turn off. What’s shocking about Kteily’s results from the “Ascent of Man” experiment, she says, is that “people are willing to admit that they have relative scales of humanity in their heads.”

Kteily grew up in Lebanon, a country with a front-row seat to the Israeli-Palestinian conflict. Where he’s from, it’s not uncommon for people to compare members of another group to animals or to lower life forms. Suicide bombers killing civilians at cafes and soldiers being aggressive toward children, he says, are a constant reminder “of what happens when you really don’t care if the other side lives or dies.”

And even though Americans don’t like to talk about it, Kteily had a hunch that they too were just as capable of blatant dehumanization.

With the “Ascent of Man” tool, Kteily and collaborators Emile Bruneau, Adam Waytz, and Sarah Cotterill found that on average, Americans rate other Americans as being highly evolved, with an average score in the 90s. But disturbingly, many also rated Muslims, Mexican immigrants, and Arabs as less evolved.

“We typically see scores that average 75, 76,” for Muslims, Kteily says. “Which I think is a lot on a scale that’s so extreme.” And about a quarter of study participants will rate Muslims on a score of 60 or below.

This shows that perception of “otherness” is like a dial in our minds that can be turned on. That would be troubling enough, if the research also didn’t make two predictions about dehumanization’s power to make the world a more hostile place.

Dehumanization is correlated with support for policies such as a “Muslim ban”

In the months since Donald Trump was elected president, it’s become shockingly commonplace for Americans to blatantly dehumanize Muslims and Mexican immigrants — and then use violence against them. Hate crimes against Muslims in the US are at their highest levels since 2001. In the 1970s, Bandura predicted that dehumanization leads to increased aggression. Today, Kteily and colleagues find something similar: Willingness to dehumanize on the “Ascent of Man” scale predicts aggressive attitudes toward the Muslim world.

People who dehumanize are more likely to blame Muslims as a whole for the actions of a few perpetrators. They are more likely to support policies restricting the immigration of Arabs to the United States. People who dehumanize low-status or marginalized groups score higher on a measure called “social dominance orientation,” meaning that they favor inequality among groups in society, with some groups dominating others.

It goes on: People who dehumanize are more likely to agree with statements such as, “Muslims are a potential cancer to this country,” and, “The attacks on San Bernardino prove it: Muslims are a threat to people from this country.”

And , in a study, blatant dehumanization of Muslims and Mexican immigrants was strongly correlated with Trump support — even when compared with support for other Republican candidates. The data is “consistent with the idea that support for some of the Republican candidates (and Trump in particular) comes not despite their dehumanizing rhetoric but in part because of it,” Kteily and Bruneau conclude in the journal Personality and Social Psychology Bulletin.

(Interestingly, their study found that dehumanization was negatively correlated with support for Bernie Sanders. That is, the more people dehumanized, the less likely they were to support Sanders. There was no correlation in either direction for Hillary Clinton.)

Dehumanizing policies can kick-start a cycle of retribution and hostility

During the Republican presidential primary, Kteily and Bruneau surveyed 200 Muslims in the US, and asked them to respond to statements such as, “Donald Trump sees people from Muslim backgrounds as sub-human,” and, “Donald Trump thinks of people from Muslim background as animal-like.”

On average, the Muslims in the sample “felt strongly disliked and dehumanized by both Trump and non-Muslim Americans more broadly.” On a scale of 1 to 7, with 1 indicating that Muslims did not feel dehumanized at all and 7 meaning they felt it intensely, the group average was 5.66, well beyond the halfway mark. (Similar results were found in a concurrent study of Latino Americans.)

This survey wasn’t designed to be nationally representative of all the Muslims living in America. Instead, it was designed to figure out what happens inside the mind of someone who feels dehumanized.

“And the consequences were big,” Bruneau explains. The more Muslims felt dehumanized by Trump, the more they dehumanized Trump. The more they felt dehumanized, the less likely they were to say they’d report suspicious activities in their communities.

The research predicts a vicious cycle. Trump’s policy and rhetoric gin up fear and dehumanize Muslim Americans. That provokes a more violent response from certain individuals in the Muslim community. Trump responds. And suddenly the whole country is a more hostile, less safe place for everyone, the researchers conclude in a paper that was recently published in the journal Personality and Social Psychology Bulletin.

“We want to be careful to say that any backlash that we might expect isn’t unique to minority groups. In fact, some of our earlier work showed that Americans, too, who think they are dehumanized by Muslims are more likely to dehumanize Muslims,” Kteily says. “We think of this working both ways.”

Ben Herzig, a clinical psychologist in the Boston area who specializes in treating people from the Muslim community, says some of his patients are responding by withdrawing.

“When members of a marginalized group are dehumanized, their tendency is ... to retreat into familiar circles where they know they will be accepted by people like themselves,” Herzig says.

Dehumanizing rhetoric against Muslims is becoming more acceptable in the Trump era

As Vox’s Zack Beauchamp has written, Trump’s top adviser, Steve Bannon, is a devotee of a right-wing worldview known as “counter-jihad.” Counter-jihadists, Beauchamp explains, “argue that a correct reading of Islamic scripture shows that violence is intrinsic to Islam — that the religious doctrine itself, properly understood, commands Muslims to kill subjugate unbelievers.”

Counter-jihad lumps all 1.3 billion Muslims together into one malicious group of people less capable of compassion and cooperation. And it suggests that Muslims are unable to separate themselves from their group as individual thinkers.

Dalia Mogahed, the director of research at Institute for Social Policy and Understanding, a nonprofit that studies Islamophobia, says dehumanizing rhetoric against Muslims is becoming more acceptable to Americans in the Trump era.

“What we have in this era that’s unique is the legitimizing of those perspectives with laws, with people in [positions] of authority,” she says. “It’s given license and legitimacy to these perspective. they’re not perspectives that people have to hide or sugar coat, or qualify in any way.” And as she points out “it isn’t just on the right.” Bill Maher, a liberal pundit, routinely calls Islam a violent religion.

“I’m hearing dehumanizing language that I’ve never heard before,” says Mogahed, who has conducted polling on the intersection of Islam and society for most of her career. And it was especially acute during the presidential election. Ben Carson compared Muslims to dogs. Trump told an apocryphal story of soldiers killing terrorists with bullets dipped in pig’s blood (as if Muslims were creatures that needed to be killed by supernatural means). Donald Trump Jr., compared Syrian refugees to a bowl of Skittles.

There are signs that anti-Islamic sentiment is getting stronger. A January 2016 poll conducted by Mogahed’s group found more than half of Muslim Americans experienced discrimination in the previous year. Reports of hate crimes against Muslims in the US are at their highest levels since 2001. In the past seven weeks, there have been four mosque burnings across America.

It’s hard to draw a direct line from Trump to these incidents. But it’s plausible that he is emboldening people with these feelings, and helping to change norms around talking about members of other racial and ethnic groups.

Meanwhile, Trump still has in place a temporary ban on refugees. He just signed a new ban on issuing visa to travelers from six Muslim-majority countries. In his address to a joint session of Congress on February 28, he invited families of people killed by “illegal immigrants,” furthering the misconception that undocumented immigrants are more dangerous than other people.

If Trump can stoke perceptions of threat, he can stoke dehumanization. Kteily and his co-authors ran the “Ascent of Man” scale before, during, and after the Boston Marathon bombing in 2013. After the attack, blatant dehumanization of Muslims jumped up significantly.

Support for seeking vengeance and conducting drone strikes in Muslim countries grew too. Kteily found that people who dehumanized were more likely to support the statement, “Muslims bombed Boston. We as a planet need to wipe them off this world. Every one of them.”

It’s unlikely we’re on the verge of a horrific genocide. But we also can’t kid ourselves. Inside us all is the same mental machinery that fueled the atrocities of the past century. “We think others to death and then invent the battle-axe or the ballistic missiles with which to actually kill them,” writes the philosopher Sam Keen. Turning on dehumanization won’t immediately lead to massacre, but it does make it easier to make life marginally worse for the marginalized.

We can stop the cycle of dehumanization. But it’s far from easy.

As we’ve seen, the vicious cycles of dehumanization and retaliation can spin — without end — for centuries.

So how to break the cycle?

Part of the reason some Americans dehumanize Muslims is because they think Muslims dehumanize us. But this assumption is wrong.

In the book she wrote with John L. Esposito, Who Speaks For Islam? What a billion Muslims really think, Mogahed lay out data from 50,000 interviews from Muslims around the world. And she finds that the Muslim world does hold a lot of admiration for American values. “It’s not that Muslims have positive opinions of the United States. They don’t. But they actually love and admire our freedom.”

In a study, Kteily and Bruneau created a fake Boston Globe article that highlighted Mogahed’s research. When mostly white participants read that Muslims actually admired Americans, they didn’t dehumanize them as much on the Ascent scale.

This intervention is also remarkably simple. If you take one point away from this article, make it this: Muslims don’t despise America. In many ways, they admire it.

It also helps to get white Americans to think through their hypocrisy. In a study under review, Bruneau finds that when white people are asked questions such as, “Are all Christians responsible for the actions of the Westboro Baptist Church?” they begin to see the folly of blaming all Muslims for a single act of terror. “The hypocrisy is totally unconscious for people,” Bruneau explains. (The point isn’t to call people hypocrites, but rather to have them come to the realization on their own.)

Overall, the experts I spoke to all said that the No. 1 way to combat dehumanization is also, frustratingly, one of the hardest to accomplish: simply getting to know people who are different from us.

It’s hard because we have many opportunities — via the news and social media — to get the thin-slice exposure to unfamiliar groups that activates the us-versus-them program in our brains. And we have so few opportunities to do the hard work of breaking through those first impressions and getting to know the human soul inside.

“I don’t agree with the idea that multicultural societies have to be a powder keg,” Kteily says.

Just as we have the mental capacity to dehumanize, we’re equipped with the mental programs that forge trust and understanding. It’s up to us to turn them on.

Further Reading: Understanding human psychology in the age of Trump