Politically, Americans are highly divided.
When it comes to issues of race, immigration, national security, public health, and environmental protection, they disagree about how the government should handle things like never before.
Relative to polls in the 1990s, Republicans are now much more likely to say poor people have it easy, while Democrats are less likely to say so. Conservatives are more likely to say that environmental regulations are costing the US too many jobs. Liberals now seem less convinced that peace can be achieved through military strength than they were decades ago.
The Pew Research Center reports that the country's political divisions now far exceed "divisions along basic demographic lines, such as age, education, gender and race." The share of Americans who sit in the middle of the political spectrum is lower, too.
Bots, pundits, and hate groups have taken advantage of these widening differences on social media, in an attempt to drive Americans' opinions even further apart.
But what in the brains of conservative and liberal voters actually drives their belief systems? Scientists have been researching the psychological differences between people with different stances, and there are a few key ways that people on opposite ends of the political spectrum see the world. Here's what the data shows:
SEE ALSO: A Yale psychologist's simple thought experiment temporarily turned conservatives into liberals
Being scared can make you more conservative.
Decades of research have shown that people get more conservative when they feel threatened and afraid.
Threats of terrorism make everyone less liberal — researchers found this was especially true in the months after 9/11. During that time, the US saw a conservative shift, and Americans displayed increased support for military spending and for President George W. Bush.
Americans aren't the only ones whose political leanings are influenced by fear. A 2003 review of research conducted in five countries looked at 22 separate tests of the hypothesis that fear fuels conservative viewpoints and found it was universally true.
A conservative brain is more active in different areas than a liberal one.
Brain scans show that people who self-identify as conservative have larger and more active right amygdalas, an area of the brain that's associated with expressing and processing fear. This aligns with the idea that feeling afraid makes people lean more to the right.
One 2013 study showed conservative brains tend to have more activity in their right amygdalas when they're taking risks than liberals do.
On the other hand, feeling safe and endowed with strength might make you lean a little more liberal than you otherwise would.
Groundbreaking research that Yale psychologists published in 2017 revealed that helping people imagine they're completely safe from harm can make them (temporarily) hold more liberal views on social issues.
The authors of that study said their results suggest that socially conservative views are driven, at least in part, by people's need to feel safe and secure.
That finding didn't hold true for people with economically conservative views, though.
Liberals are less squeamish about looking at yucky stuff like vomit, feces, and blood.
A 2018 study of college students showed that those with more socially conservative views were quicker to physically look away from disgusting images — like pictures of blood, feces, or vomit — than their liberal peers.
The self-reported social conservatives also stared longer at photos of other people reacting in disgust to icky stuff.
This research backs up other studies that have suggested conservatives are more easily grossed out than liberals.
A gut reaction of disgust is, evolutionarily speaking, a good thing for survival, since it helps humans keep some foreign and potentially dangerous secretions at bay. But in our modern world, some research suggests this kind of aversion toward "impure" pathogens may also impact how people see other people who aren't like them, including social "out-groups" like immigrants or foreigners.
Conservatives tend to display more ordered thinking patterns, whereas liberals have more "aha" moments.
A 2016 study at Northwestern University found that when conservative and liberal college students were given word problems to solve, both groups managed to arrive at some correct answers through gradual, analytical analysis.
But when feeling stuck on a problem, liberals were much more likely to draw upon a sudden burst of insight — an 'aha' moment, like a lightbulb turning on in the brain.
This didn't mean that the liberals were any smarter than the conservatives. Rather, it showed that their brains had a tendency to reorganize their thoughts in more flexible ways, while the conservatives tended to take a more step-by-step approach. The researchers suggested this finding may indicate that liberals and conservatives prefer solving problems in different ways.
Lead study author Carola Salvi said the results were consistent with what scientists already knew about the brains of people with different political leanings.
"Conservatives have more structured and persistent cognitive styles,"she said in a statement.
Liberals tend to follow the wandering gaze of others more often, while conservative eyes stay more focused on the original subject they're looking at.
In 2010, researchers at the University of Nebraska tested whether conservatives and liberals physically see the world in different ways. They found that when it comes to matching the gaze of other people, the two groups differ.
The scientists measured this by having individual study participants watch a certain point on a computer screen and wait for a ball to show up in the frame. Then they added a distracting human face on the screen before the ball appeared. The face's eyes would look around. The scientists watched their participants to see if they followed the wandering gaze.
The researchers found that the liberal participants tended to follow the direction of the eyes on the screen. Conservatives, on the other hand, weren't as swayed by their pixelated peers, and kept waiting for the ball.
That finding surprised the study authors.
"We did not expect conservatives to be completely immune to these cues," lead author Michael Dodd said when the study was released.
Holding conservative views seems to make people more resistant to change and help them explain inequality.
A 2003 review of decades of research on conservative people suggested that their social views can help satisfy "psychological needs" to make sense of the world and manage uncertainty and fear.
"People embrace political conservatism (at least in part) because it serves to reduce fear, anxiety, and uncertainty; to avoid change, disruption, and ambiguity; and to explain, order, and justify inequality among groups and individuals,"the researchers said.
Liberal and conservative tastes in music and art are different, too.
Studies from the 1980s showed that conservatives preferred more simple paintings, familiar music, and unambiguous texts and poems, while liberals enjoyed more cubist and abstract art.
Although that research dates back to a drastically different political climate, the findings hold up in more recent studies from 1997, 2010 and 2015. In 2014, Time magazine conducted an online survey and found that conservative readers tended to say they'd rather visit Times Square than the Metropolitan Museum of Art.
The finding fits with other research that indicates conservatives tend to avoid uncertainty and dislike ambiguity more than their liberal counterparts.
Liberals are more likely to describe themselves as compassionate and optimistic, while conservatives are more likely to say they're people of honor and religion.
A 1980 study of US high school students found that conservative students at that time were more likely to describe themselves as "responsible,""organized,""successful," and "ambitious," while liberal students might describe themselves as "loving,""tender," or "mellow."
Surveys suggest that today's adults aren't much different than those 80s kids. A Pew Research Center study from 2014 showed that liberals were more likely than social conservatives to describe themselves as compassionate, trusting, upbeat, and optimistic, while conservatives were more likely to say they were people of honor, duty, religion, and proud to be American.
The self-reports go along with research from 2012 that suggested liberals' top moral concerns tend to be about compassion and fairness, while conservatives are more concerned with loyalty, tradition, respect for authority, and purity.
Conservatives believe they have more self-control.
One 2015 study found that conservative students were often better at focusing their attention on a cognitive task called the Stroop color and word test. The common psychological study tool asks participants to quickly name the correct color of a word that's written on a different color background.
In the study, conservative students seemed to correctly answer the color questions faster than their liberal peers. The researchers think that's because the conservatives were more likely to believe in the concept of self-control.
"What we're finding is that conservatives are more likely to believe they can control their own behavior," psychologist Joshua Clarkson from the University of Cincinnati said when his study was released.
But the conservatives didn't always out-perform the liberals. When they were told that their free will might undermine their own self-control, they performed worse than their liberal peers.
"One could imagine a host of situations where knowing you are responsible for your actions could lead to frustration, anxiety and other negative emotions that could impair self-control," Clarkson said.
Liberals and conservatives extend feelings of compassion to different people.
New research finds that conservatives tend to express compassion to smaller social circles than liberals.
For example, conservative voters were found to be more likely to agree with statements like: "I often have tender, concerned feelings for my family members who are less fortunate than me."
But their responses suggested such feelings did not extend to people from other countries.
Liberals, on the other hand, were more likely to feel that same level of compassion for people around the world, and even to non-human and imaginary subjects like animals and aliens.
"Conservatives self-report more parochialism in that they tend to expend their empathy toward more well-defined, closed social circles like the family whereas liberals self-report more universalism in that they expend their empathy toward more permeable, broader social circles, like the world as a whole," Dr. Adam Waytz, a professor at Northwestern's Kellogg School of Management, told Insider.
Conservatives tend to report feeling greater meaning and a sense of purpose in life than liberals do.
Researchers at the University of Southern California conducted a study in 2018 hinging on the theory that conservatives tend to be more satisfied in life than liberals.
Their findings suggested that theory is true, at least, according to self-reports.
"Finding meaning in life is related to the sense or feeling that things are the way they should be, and that there is a sense of order," study author David Newman, a doctoral candidate at USC Dornsife's Mind and Society Center, said when his study was released. "If life feels chaotic, then that would likely dampen your sense that life is meaningful."
The study complied data on thousands of people in 16 different countries around the world over four decades, and found that conservatives, overall, reported feeling greater meaning and purpose in life.
The study also found greater satisfaction in life was related more closely to social conservatism, rather than economically conservative views.
Research also suggests shared values likely matter more than shared politics when it comes to who we vote for.
For example, Trump supporters may share more in common with the president's personal and professional values than his policies. A survey of 1,825 people conducted on the internet in March 2016 revealed that Trump supporters were more likely to connect with his overall personality and outlook on money than they were to support his politics.
The survey respondents tended to agree with statements like "people who are poor just need to work harder" and "vacations are for weaklings," while disagreeing with statements like "I try to stay out of the spotlight" and "I don't like to gamble."
The study authors said these kinds of personal values were better predictors of support for then-candidate Trump than party affiliations or political ideologies.
"Trump supporters ... seek power over others, are motivated by wealth accumulation, and prefer conformity, hierarchy, and clear-cut rules for behavior," the authors wrote in their paper, published online in the journal Personality and Individual Differences in February 2018.
The researchers think these perceptions of shared values between candidates and constituents probably play into everyone's voting behavior, not just that of Trump's supporters.
One British study found that voters who were aggressive, angry kids were more likely to distrust the government and lean liberal as adults.
A longitudinal study of more than 16,000 people in the UK found that those who were more aggressive as youngsters (when they were 5-7 years old) became more economically liberal and mistrusting of the government as adults in their early 30s.
"Children who showed higher levels of conduct problems — that is, aggression, fighting, stealing from peers — were more likely to be economically left-leaning and distrustful of the political system as adults," study author and psychologist Gary Lewis from the University of London said in a release.
"Some, but not all, of this link was explained by educational attainment and socioeconomic status in adulthood."
Both conservatives and liberals think they're always being fair.
A 2018 study by researchers at Stanford University found liberals and conservatives both think they judge people of all political backgrounds equally for their actions, based on their moral codes.
However, the findings suggested that while liberals and conversations may both think they are applying their judgment equally, they each tend to judge members of their own ideology more favorably than others.
"It seems that most people think that they are applying their moral principles in an even-handed way,"authors Dr. Jan Voelkel and Dr. Mark Brandt told PsyPost."However, our findings suggest that we humans struggle to apply our moral principles equally to our outgroups and ingroups."
Update: This story was originally published in 2018. It has been updated with new research.