How the Behavioral Immune System Influences Attitudes Toward Immigration

As the refugee crisis unfolded in Europe, the leader of Poland’s anti-immigrant Law and Justice party, Jaroslaw Kaczynski, warned that letting in people fleeing war-torn countries in the Middle East would bring diseases and parasites to Poland. Marine Le Pen, head of the far-right National Front party, raised similar alarm about “non-European diseases,” which she linked to the influx of migrants. In the United States, Donald Trump released a statement early in his presidential campaign that claimed immigration from Mexico meant that “tremendous infectious disease is pouring across the border.”

The dangerous and questionable claim that immigrants threaten public health is not new. In political rhetoric, individuals from unfamiliar and marginalized groups have often been compared to both vectors of disease and to vermin. Recent research conducted by Lene Aarøe, Michael Bang Petersen, and me offers some insight into why this connection between concerns about disease and opposition to immigration exist as well as why it resonates more with some people than others.

The answer lies in how humans evolved to fight and avoid the invisible pathogens that infect and, potentially, kill us. As most elementary school kids can tell you (in similar terms, at least), humans possess an immune system that fights pathogens that enter the body.

A number of peer-reviewed studies suggest there’s a psychological component to our immune system as well. It’s what psychologists are calling the “behavioral immune system.” Because our physical immune system cannot successfully defeat every pathogen we may encounter, the role of the behavioral immune system is to motivate us to avoid pathogens in the first place.


Now, the whole concept of pathogens is new to people. Our ancestors had little to no understanding that invisible germs are our mortal enemies. Consequently, the behavioral immune system operates through perceptions of pathogen threats, and it does so largely outside of our conscious awareness. The human mind is designed to detect superficial signs of dangerous pathogens, such as rashes or putrid smells, and use feelings of disgust to motivate people to avoid the people or things that exhibit these signs.

The behavioral immune system is also designed to err on the side of avoiding perceived threats. So, different can sometimes be unconsciously perceived as dangerous. Because infectious diseases can cause rashes, this approach served our ancestors well, since they could not know whether a rash was infectious or not. Unfortunately, it means that the behavioral immune system sometimes tags innocuous differences as harmful. Harmless birthmarks, for instance, can trigger disgust and concerns about infection. So can physical disabilities and obesity.

Our ancestors lived in small, ethnically homogenous tribes. Large and heterogeneous societies are relatively new in human history, so differences in skin color and unfamiliar cultural practices can be mistakenly interpreted as harbingers of infectious disease.

This may partly explain the anti-immigrant attitudes of political leaders like Kaczynski, Le Pen, and Trump. It’s certainly what their language exploits. And while this language is sick, it does resonate strongly with some people. Our work offers some insights into the type of person who is most likely to view unfamiliar others as a threat who should be kept out of the country (and segregated from the native population if they do enter the country). By implication, it also partly explains why xenophobic language resonates with some people but not everyone.

In our research, we use the fact that people’s behavioral immune system varies in how sensitive it is to perceived pathogen threats to demonstrate how it acts as an unconscious motivator of anti-immigration attitudes for some individuals. People who have a more sensitive behavioral immune system feel disgust more easily. Everyday experience, such as touching money and public restrooms can make individuals with a highly sensitive behavioral immune system feel uneasy and disgusted.

In our research, we found that the more sensitive a person is to disgust, the more likely they are to oppose immigration.

Across four separate studies, conducted in Denmark and the United States, we found that the more sensitive a person is to disgust, the more likely they are to oppose immigration. The influence of disgust sensitivity remains even after we account for education, ideology, demographics, and personality variables. We also observe the effects of disgust sensitivity using an array of measures, including several accepted self-report and physiological measures. In short, we offer comprehensive evidence that behavioral immune system sensitivity is associated with anti-immigrant attitudes.

In order to test whether the behavioral immune system influences immigration attitudes outside of conscious awareness, we conducted an experiment. In one of the U.S. studies, we selected at random half of our subjects to read a story about a janitor cleaning up vomit and for the other half to read the same story but with a pleasant ending where the janitor cleans his hands. After reading the story, subjects answered a questionnaire that asked about immigration. In the disgusting version of the story, we observed the same association between disgust sensitivity and opposition to immigration. However, in the version of the story where the janitor cleans his hands, the positive correlation between disgust sensitivity and anti-immigration attitudes practically vanishes.

Why would a simple story affect the activation of the behavioral immune system? In the disgusting version, the story heightened concerns about pathogens, and in the clean-hands version it allayed those concerns. With those concerns addressed, individuals high in disgust sensitivity had less of a need to oppose immigration as a protective measure. Keep in mind that our story said nothing about immigration. We strongly doubt that our subjects made a conscious connection between the story and their attitudes about immigration, but their unconscious mind appears to have made a connection between pathogen risk and the need to keep out unfamiliar others.

To end on a positive note, I should emphasize that our research does not conclude that the behavioral immune system inexorably leads to anti-immigration attitudes. We see a good bit of variance, in fact. Some people who are easily disgusted support immigration. Moreover, once people come into contact with people who are different from them and get to know them, the behavioral immune system will likely stop categorizing these individuals as a potential threat. The trick, of course, is motivating people to make social connection they may initially be leery to make. Our research offers a place to start.