White supremacists rally in Charlottesville on Friday. (Evelyn Hockstein for The Washington Post)

Torch-bearing white supremacists shouting racist and anti-Semitic slogans. Protesters and counter protesters colliding with violence and chaos. A car driven by a known Nazi sympathizer mowing down a crowd of activists.

Many Americans responded to this weekend's violence in Charlottesville with disbelieving horror. How could this happen in America, in 2017? “This is not who we are,” said Virginia Sen. Tim Kaine (D).

And yet, this is who we are.

Amid our modern clashes, researchers in psychology, sociology and neurology have been studying the roots of racism. We draw on that research and asked two scientists to explain why people feel and act this way toward each other.

What causes people to be racist?

“In some ways, it’s super simple. People learn to be whatever their society and culture teaches them. We often assume that it takes parents actively teaching their kids, for them to be racist. The truth is that unless parents actively teach kids not to be racists, they will be,” said Jennifer Richeson, a Yale University social psychologist. “This is not the product of some deep-seated, evil heart that is cultivated. It comes from the environment, the air all around us.”

Richeson compares children's instinctive formation of biases to a student at a new school. “When you arrive at a new high school. You are instinctively trying to figure out who’s cool, who’s not, who’s a nerd, who gets beat up? Kids quickly acquire these associations,” she said.

To get a sense of just how pervasive and imperceptibly our environment can affect us, one study at Tufts University found that even with a TV show on mute displaying scenes with no explicit discrimination, the nonverbal body language of black and white actors interacting was enough to cause watchers to test higher for implicit bias afterward.

“An us-them mentality is unfortunately a really basic part of our biology,” said Eric Knowles, a psychology professor at New York University who studies prejudice and politics. “There’s a lot of evidence that people have an ingrained even evolved tendency toward people who are in our so-called 'in group.'”

But how we define those groups, and the tendency to draw divisions along racial lines, is social, not biological, he added. “We can draw those lines in a number of ways that society tells us,” he said. 

A car plowed into crowds at a white nationalist gathering in Charlottesville on Aug. 12, killing one person and injuring 19 others. (The Washington Post)

When does racism drive people to commit violence?

“The most likely predictor of that is exposure to a kind of ideology,” Knowles said. Most if not all people carry implicit biases and unexamined prejudices, he said, and some may harbor feelings of fear or resentment that they don’t express in public.

“But when people come into contact with an organized ideology that valorizes or glorifies an intergroup struggle like a race struggle — that scaffolds from people’s everyday prejudices into something altogether more violent,” he said.

White supremacist groups promote a “siege mentality” among their followers, Knowles said — rhetoric that aims to lend legitimacy to people’s racial and ethnic fears. He pointed to the slogans shouted by participants in the Charlottesville rally: “You will not replace us” and “White Lives Matter.”

“I think that one thing that these violent ideologies are communicating to people, and people are receptive to, especially people who are struggling, is that whites are actually the ones who are being discriminated against in society,” Knowles said.

Charlottesville was hardly the first time this thinking has led to violence. Dylann Roof, who shot and killed nine people at a historic African Methodist Episcopal Church in Charleston, S.C., justified the killing with a hate-filled rant in his journal in which he wrote that he wanted to “take action for my race.”

Knowles has been studying what he calls “everyday racism” for nearly two decades. He said he hasn’t seen significant change in baseline levels of  bias among Americans. Instead, he thinks, more virulent forms of racism are being “unleashed” — particularly by President Trump. He noted the president did not explicitly condemn the hate groups that organized the Charlottesville rally until two days after it was held.

“The fetters are coming off,” Knowles said. “When you have a president who won’t specifically signal out Nazis and white supremacists for opprobrium that communicates something to people with racial resentment. … That’s a powerful message that these feelings you’ve been having, these racial and ethnic fears that are inside of you are, okay to express.”

Can you teach people not to be racists?

“The only way to change bias is to change culture,” Richeson said. “You have to change what is acceptable in society. People today complain about politically correct culture, but what that does is provide a check on people’s outward attitude, which in turn influences how we think about ourselves internally. Everything we’re exposed to gives us messages about who is good and bad.”

Knowles agreed that norms can serve as a check on expression of violent racism. But to challenge the deep-seated prejudices that shape our behavior, to unlearn our implicit biases, “we need contact,” he said.

“It's absolutely the opposite of what white nationalists want, which is a segregated society,” he said. “We need an integrated society, and at the same time need to create as much socioeconomic fairness as we can, so what relationships people have across group lines are egalitarian relationships. … That’s the one thing that can create trust between people on each side of an us-them divide, and the only thing in the long term I would put my money on to reduce prejudices.”

James Alex Fields Jr., 20, is accused of driving his car into a crowd of people protesting a white nationalist rally in Charlottesville. (Elyse Samuels,Sarah Parnass,Whitney Leaming/The Washington Post)

Will racism disappear over time? Aren’t older people more racists and younger generations more progressive?

“It’s a myth that our country will somehow become more progressive. And it’s equally a myth to think that our children will save us,” Richeson said. Most of alt-right activists who sparked violence in Charlottesville, she pointed out, were young white men.

“There's data that shows young groups like millennials are more progressive and egalitarian. But that’s usually on issues like climate change or gay marriage, usually not in their level of implicit bias,” Richeson said.

In fact, Richeson in recent years has been studying how white people react to the fact that America is shifting into a majority minority country (where minorities make up more than 50 percent of the population). In those studies, young white subjects responded just as strongly as older white ones with anxiety and uncertainty, expressing more negative explicit and implicit racial bias in tests.

After reading about the coming demographic change, for example, white subjects, including college students, were more likely to agree with statements like “I would rather work alongside people of my same ethnic origin.”

Richeson said, “Yes, there have been gains in policy like allowing interracial marriage and discrimination laws, but when it comes to our interpersonal biases, it’s simply not true that we just need to wait for the few old racist men left in the South to die off and then we’ll be fine. The rhetoric for racism is still in place. The environment for racism is still there. Unless we change that, we can't lessen racism.”