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]

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.