There's no gentle way to put it: People who give in to racism and prejudice may simply be dumb, according to a new study that is bound to stir public controversy.

The research finds that children with low intelligence are more likely to hold prejudiced attitudes as adults. These findings point to a vicious cycle, according to lead researcher Gordon Hodson, a psychologist at Brock University in Ontario. Low-intelligence adults tend to gravitate toward socially conservative ideologies, the study found. Those ideologies, in turn, stress hierarchy and resistance to change, attitudes that can contribute to prejudice, Hodson wrote in an email to LiveScience.

"Prejudice is extremely complex and multifaceted, making it critical that any factors contributing to bias are uncovered and understood," he said.

Controversy ahead

The findings combine three hot-button topics.

"They've pulled off the trifecta of controversial topics," said Brian Nosek, a social and cognitive psychologist at the University of Virginia who was not involved in the study. "When one selects intelligence, political ideology and racism and looks at any of the relationships between those three variables, it's bound to upset somebody."

Polling data and social and political science research do show that prejudice is more common in those who hold right-wing ideals that those of other political persuasions, Nosek told LiveScience. [7 Thoughts That Are Bad For You]

"The unique contribution here is trying to make some progress on the most challenging aspect of this," Nosek said, referring to the new study. "It's not that a relationship like that exists, but why it exists."

Brains and bias

Earlier studies have found links between low levels of education and higher levels of prejudice, Hodson said, so studying intelligence seemed a logical next step. The researchers turned to two studies of citizens in the United Kingdom, one that has followed babies since their births in March 1958, and another that did the same for babies born in April 1970. The children in the studies had their intelligence assessed at age 10 or 11; as adults ages 30 or 33, their levels of social conservatism and racism were measured. [Life's Extremes: Democrat vs. Republican]

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In the first study, verbal and nonverbal intelligence was measured using tests that asked people to find similarities and differences between words, shapes and symbols. The second study measured cognitive abilities in four ways, including number recall, shape-drawing tasks, defining words and identifying patterns and similarities among words. Average IQ is set at 100.

Social conservatives were defined as people who agreed with a laundry list of statements such as "Family life suffers if mum is working full-time," and "Schools should teach children to obey authority." Attitudes toward other races were captured by measuring agreement with statements such as "I wouldn't mind working with people from other races." (These questions measured overt prejudiced attitudes, but most people, no matter how egalitarian, do hold unconscious racial biases; Hodson's work can't speak to this "underground" racism.)

As suspected, low intelligence in childhood corresponded with racism in adulthood. But the factor that explained the relationship between these two variables was political: When researchers included social conservatism in the analysis, those ideologies accounted for much of the link between brains and bias.

People with lower cognitive abilities also had less contact with people of other races.

"This finding is consistent with recent research demonstrating that intergroup contact is mentally challenging and cognitively draining, and consistent with findings that contact reduces prejudice," said Hodson, who along with his colleagues published these results online Jan. 5 in the journal Psychological Science.

A study of averages

Hodson was quick to note that the despite the link found between low intelligence and social conservatism, the researchers aren't implying that all liberals are brilliant and all conservatives stupid. The research is a study of averages over large groups, he said.

"There are multiple examples of very bright conservatives and not-so-bright liberals, and many examples of very principled conservatives and very intolerant liberals," Hodson said.

Nosek gave another example to illustrate the dangers of taking the findings too literally.

"We can say definitively men are taller than women on average," he said. "But you can't say if you take a random man and you take a random woman that the man is going to be taller. There's plenty of overlap."

Nonetheless, there is reason to believe that strict right-wing ideology might appeal to those who have trouble grasping the complexity of the world.

"Socially conservative ideologies tend to offer structure and order," Hodson said, explaining why these beliefs might draw those with low intelligence. "Unfortunately, many of these features can also contribute to prejudice."

In another study, this one in the United States, Hodson and Busseri compared 254 people with the same amount of education but different levels of ability in abstract reasoning. They found that what applies to racism may also apply to homophobia. People who were poorer at abstract reasoning were more likely to exhibit prejudice against gays. As in the U.K. citizens, a lack of contact with gays and more acceptance of right-wing authoritarianism explained the link. [5 Myths About Gay People Debunked]

Simple viewpoints

Hodson and Busseri's explanation of their findings is reasonable, Nosek said, but it is correlational. That means the researchers didn't conclusively prove that the low intelligence caused the later prejudice. To do that, you'd have to somehow randomly assign otherwise identical people to be smart or dumb, liberal or conservative. Those sorts of studies obviously aren't possible.

The researchers controlled for factors such as education and socioeconomic status, making their case stronger, Nosek said. But there are other possible explanations that fit the data. For example, Nosek said, a study of left-wing liberals with stereotypically naïve views like "every kid is a genius in his or her own way," might find that people who hold these attitudes are also less bright. In other words, it might not be a particular ideology that is linked to stupidity, but extremist views in general.

"My speculation is that it's not as simple as their model presents it," Nosek said. "I think that lower cognitive capacity can lead to multiple simple ways to represent the world, and one of those can be embodied in a right-wing ideology where 'People I don't know are threats' and 'The world is a dangerous place'. ... Another simple way would be to just assume everybody is wonderful."

Prejudice is of particular interest because understanding the roots of racism and bias could help eliminate them, Hodson said. For example, he said, many anti-prejudice programs encourage participants to see things from another group's point of view. That mental exercise may be too taxing for people of low IQ.

"There may be cognitive limits in the ability to take the perspective of others, particularly foreigners," Hodson said. "Much of the present research literature suggests that our prejudices are primarily emotional in origin rather than cognitive. These two pieces of information suggest that it might be particularly fruitful for researchers to consider strategies to change feelings toward outgroups," rather than thoughts.

You can follow LiveScience senior writer Stephanie Pappas on Twitter @sipappas. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.