Book Excerpt from COVID-19

In Chapter 8, author Debora MacKenzie recounts an unfortunate history of baselessly blaming disease outbreaks on groups perceived as outsiders.

Debora MacKenzie

Besides our biological immune system, psychological research has recently found evidence that humans have a “behavioral immune system”— a tendency to avoid people who may be carrying disease. Besides avoiding obviously ill people, psychologists think humans universally tend to conform to our own “in-group” and avoid people who are different from us, because originally, we were trying to avoid infection.

This was actually a risk during our early evolution. When we were wandering hunter- gatherers and encountered another wandering tribe, the strangers might have encountered different diseases and be carrying germs to which they had acquired resistance, but we had not. This was especially true because some aspects of disease resistance are genetic, and we would have shared fewer genes with another wandering tribe than we do now with fellow city dwellers. The disease risks that separated populations may pose to each other were confirmed with a vengeance when most of the native people of the Americas died of European diseases after Columbus arrived. Europeans got syphilis back.


There is evidence the behavioral immune system underlies tribalism and xenophobia. People with stronger disgust responses to descriptions and pictures of things that might pose a disease risk, like dead cats or rotten food, tend to be more xenophobic and politically conservative, as are people from places with more pathogens, now or historically.

Researchers have focused on “authoritarian personality,” a set of personality characteristics, partly determined by genes, which include a desire for order, obedience, conformity, and cohesion within the in-group with which the person identifies. Having those characteristics made it more likely that a person would vote for Donald Trump in the US, or Brexit in Britain, in 2016, more than any other variable measured.

Cambridge psychologist Leor Zmigrod has discovered that people who live in US states and cities with a higher prevalence of diseases you catch from humans—but not diseases you get from animals, like Lyme disease—are more likely to have authoritarian personalities and to have voted for Donald Trump. States with more pathogens also tended to have more laws that restrict minorities, such as LGBTQ people. No other variable, such as education or life expectancy, correlated as well.

Other research has found that activating the behavioral immune system, either with a real disease outbreak or with disgusting images or mentions of disease, shifts people’s political attitudes in an authoritarian direction. Canadian psychologist Mark Schaller, who coined the term “behavioral immune system,” found that in 2014, Americans were more likely to tell pollsters they would vote Republican after the appearance of Ebola cases in the US, especially in places with a heightened interest in the disease as reflected by Google searches for “Ebola.” The same went for conservative voting intentions among Canadians.

This fits with a history of sometimes violent xenophobia and hostility to strangers after epidemics. European cities slaughtered Jews and gypsies during the Black Death of 1347. In 1793, Philadelphia blamed a yellow fever outbreak on traveling actors. White North Americans have blamed cholera on Irish immigrants, AIDS on Haitians, plague on Chinese immigrants—Honolulu burned its Chinatown—and SARS and COVID-19 on ethnic Chinese. The Centre for Economic Policy Research says the 1918 flu pandemic led to greater mistrust of governments. As a presidential candidate, Donald Trump blamed Latin American immigrants for “tremendous infectious disease.” All the claims were groundless.

A lot of psychological researchers are now collecting data on the political impact of COVID-19, Schaller told me. “If COVID-19 elevates the allure of authoritarian ideologies, the effects could be long-lasting,” says Zmigrod, as she finds those ideologies are more common in places that merely had more infectious disease in the past than in places that didn’t. That could be especially true if COVID-19 doesn’t quite leave but continues to circulate.

This impulse toward division is troubling when the world needs greater collaboration, not less, to defeat the shared risk of disease. The least likely prospect for cooperation now seems to be between the US and China, with their respective leaders trading barbs and blaming the other for the virus. Yet the need is great. In February, Shi Zhengli, Kevin Olival, and 21 other emerging disease researchers made a detailed case for the US and China to work “synergistically” on research into pandemic threats. Only better understanding of disease ecology, they wrote, “can avert the increasing numbers of catastrophes in waiting.”

Excerpted from COVID-19: The Pandemic That Never Should Have Happened and How to Stop the Next One by Debora MacKenzie. Copyright Debora MacKenzie, 2020. All rights reserved.