I think that a lot of us are shying away from an obvious truth, that the kind of blatant racial prejudice we are witnessing in Ferguson, Missouri, has everything to do with stupidity.

I’m talking about low intelligence, lack of mental ability, cognitive rigidity. The Ferguson racists may be a lot of other things—hateful, insecure—but let’s not sugar-coat what most fair-minded thinkers believe in their hearts: A person of intelligence cannot embrace such authoritarian and racist views.

Intelligence is a scientific concept, something scientists can measure, and have for a long time. And interestingly, this connection between stupidity and prejudice once seemed obvious to social scientists as well. Early theorists suggested a link between low mental ability and prejudicial thinking, and gathered some strongly suggestive evidence to support that view. But there were some knotty methodological and statistical problems that hampered this early line of study, not to mention a huge wave of political correctness, and it was largely abandoned.

But not entirely. A small cadre of psychological scientists have continued over the years to explore the controversial connection between low intelligence and prejudice, and at this point they have overcome most of the methodological barricades, allowing them to rigorously analyze and answer this important societal question. Two of these researchers—Kristof Dhont of Ghent University, Belgium, and Gordon Hodson of Brock University, in Canada—have been studying the idea and synthesizing the work of others, and they summarize the fruits of this ongoing project in a forthcoming issue of the journal Current Directions in Psychological Science. The short answer is yes—there is a clear, predictable and causal link between low intelligence and prejudice, including racism.

Let’s not stop there, however. It’s important, when dealing with such a controversial topic, to get down into the evidentiary weeds a bit. One of the problems plaguing the early research was that the results were confounded by other possible causes, like financial status and class and education. That is, it could have been these things, and not intelligence per se, that led to prejudice. Scientists had trouble sorting all this out. Scientists also didn’t have longitudinal data—data gathered on the same subjects over time—so they could not address the important issue of cause and effect. Plus their study samples were not representative of the population. But scientists have over time solved these problems, and the key finding has held up: Empirical evidence has consistently linked low intelligence with prejudice.

Importantly, scientists have measured intelligence in a variety of ways, and the main conclusion always holds up. In one study of white children, for example, some were less able to see that a short wide glass holds the same amount of water as a taller skinnier glass. This ability is known as “conservation” in the jargon of the field, and it’s widely considered an important mental ability. In this study, the kids who lacked this ability also held more negative views of black children. Other researchers conducted an ambitious meta-analysis—a statistical aggregation of findings from many studies—and this also documented a link between cognitive style and ability, on the one hand, and authoritarian attitudes on the other.

Longitudinal studies provide some of the most convincing evidence. One such study looked at general intelligence in 10- and 11-year-old kids, and then re-studied those kids as adults two decades later—and found a clear connection between low intelligence and subsequent racism and sexism. Similarly, higher intelligence in childhood has been shown to predict less racism in adulthood. These analyses strongly suggest that low intelligence actually leads to hateful attitudes later on.

This is just a sampling of the accruing evidence on this point, all of which points to another puzzling question: Why? Why would verbal ability and math skills and other cognitive assets translate, over the years, into such hateful attitudes?

Dhont and Hodson believe they have an answer to this, again one based on rigorous abundant evidence. Their theory is that right-wing ideologies attract people with lower mental abilities because they minimize the complexity of the world. Right-wing ideologies offer well-structured and ordered views of society, views that preserve traditions and norms, so they are especially attractive to those who are threatened by change and want to avoid uncertainty and ambiguity. Conversely, smart people are more capable of grasping a world of nuance, fluidity and relativity.

The empirical evidence supports this link, too. Low intelligence and “low effort thinking” are strongly linked to right-wing attitudes, including authoritarianism and conservative politics. And again, there appears to be a demonstrable causal link: Studies have found, for example, that children with poor mental skills grow up to be strongly right-wing adults.

There is a final link in the chain of causality, according to Dhont and Hodson. Considerable evidence shows that conservative ideology predicts all sorts of prejudice—against ethnic and racial minorities, the disadvantaged, any outgroup. Indeed, right wingers are much more likely to see outgroups as a threat to traditional values and social order, resulting in heightened prejudice. Dhont and Hodson tested and confirmed this mediation model: Lower childhood intelligence clearly predicts right-wing ideology and attitude, which in turn predicts prejudice in adulthood.

The scientists elaborate on this idea in the Current Directions article: Intelligence and thinking determine how people assess threats in the world. Those with lower ability—reasoning skills, processing speed, and so forth—prefer simple and predictable answers, because that is what they are capable of processing. Any uncertainty is threatening, and they respond to such threats by trying to preserve what is familiar and safe, the status quo. These conservative reactions are basic and normal—they reduce anxiety—but over time they harden into more stable and pervasive world views, which include stereotypical thinking, avoidance, prejudicial attitudes and over discrimination.

The weight of evidence is hard to ignore, yet according to these scientists, it is conspicuously absent from contemporary theories of prejudice. They believe that it’s time for psychological scientists to stop ignoring the evidence—that in fact the field will benefit from open discussion of these controversial findings. The country might as well, and the events in Ferguson may well trigger that discussion.

Follow Wray Herbert’s reporting on psychological science in The Huffington Post and on Twitter at @wrayherbert.