To get a sense of how Ebola might be affecting the national electorate, it's worth considering how a simple bottle of hand sanitizer affected students at Cornell University.

In their 2012 paper "Dirty Liberals! Reminders of Physical Cleanliness Influence Moral and Political Attitudes," Erik Helzer and David Pizarro stopped 52 Cornell students in a campus hallway and asked them to take a short survey. But there was a catch. Half the students were asked "step over to the wall to complete the questionnaire." The other half were asked to "step over to the hand-sanitizer dispenser to complete the questionnaire."

the simple reminder of hand sanitizer changed students' self-reported politics

The results were startling: the simple reminder of hand sanitizer — which is, itself, a reminder that disease is everywhere, and you need to be protecting yourself — changed students' self-reported politics. On average, students in the control group rated themselves a 4.93 on a scale where 1 was extremely conservative and 7 was extremely liberal. But students who were cued to think about the hand sanitizer rated themselves, on average, a 4.30 — and the difference held on fiscal, social, and moral issues.

The mere nearness of some hand sanitizer was able "to shift participants' responses toward the conservative end of the political spectrum," Helzer and Pizarro concluded.

The behavioral immune system

The researchers weren't just following up on a hunch. They were building on a rich and unnerving body of evidence that suggests some of our political beliefs run deeper than mere partisanship — they're evolutionary Jedi mind tricks that help us avoid infectious diseases.

The theory, at its core, is this: for most of humanity's history, infectious diseases were the single most profound threat to the survival of the species; they likely killed more humans than "all wars, noninfectious diseases, and natural disasters put together." But humanity fought back on two fronts. The first was the development of highly tuned immune systems. But the second was the development of behavioral responses — like the feeling of disgust when you smell rotted meat, or the shiver of fear you get when you see a rat — that helped us avoid carriers of infection.

Mark Schaller, an evolutionary psychologist at the University of British Columbia, calls this the "behavioral immune system," and once researchers began looking for it, they found it everywhere. People are disgusted by yellowish liquids that look like pus but unbothered by bluish liquids with the same texture. Women have stronger disgust responses when they're pregnant — and thus vulnerable to infection — than when they're not. Societies tend to be more xenophobic when they're in areas with higher risks of infectious disease.

Xenophobia is a completely rational response to the threat of disease

Xenophobia, in particular, is a completely rational response to the threat of disease: a group's immune system might be tuned against local pathogens but helpless against foreign agents, and foreigners may not be schooled in the local norms and behaviors that protect against infection. As such, it makes a lot of sense for groups who are more vulnerable to disease outbreaks to fear foreigners.

Researchers tested this by looking at whether people exhibited more xenophobia when they felt subjectively more vulnerable to infection. They did. In one experiment, Schaller — working alongside coauthors Jason Faulkner, Jason Park, and Leslie Duncan — showed some people a series of pictures that focused on how easily bacteria could be transmitted in modern life and other people pictures showing how easily accidents could happen. The subjects cued to think about disease showed much more prejudice and fear toward immigrants they perceived as particularly foreign than did the subjects cued to think about accidents.

It's not just xenophobia, and it's not just in labs. There have been a number of studies looking at whether high rates of infectious disease risk correlate with different kinds of governments and social behaviors in the real world. They do, and powerfully. As Ethan Watters writes in an overview of the evidence, researchers have found "severe pathogen stress leads to high levels of civil and ethnic warfare, increased rates of homicide and child maltreatment, patriarchal family structures, and social restrictions regarding women's sexual behavior."

How Ebola could twist American politics

The claim here is radical and discomfiting: many of our cherished political beliefs and even cultural and religious practices are, on some level, a faux-rational rebranding of behaviors and attitudes developed to protect against disease. And the reemergence of infectious disease threats can trigger the reemergence of some of these latent beliefs and behaviors.

Which brings us to Ebola, a threat that seems custom-designed to activate our worst instincts. It's an infectious disease, of course, and a particularly scary one at that. It comes from West Africa, and so it lights up the part of our evolutionary hardwiring that connects disease to foreigners. And we're hearing about it all day, every day. If the gentle, neutral mention of hand sanitizer can change someone's politics, what will the constant storm of Ebola coverage do?

If the gentle, neutral mention of hand sanitizer can change someone's politics, what will the constant storm of Ebola coverage do?

From the evolutionary perspective, what the American people want the government to do in response Ebola has been exactly what you would expect: there's been nearly instant pressure to shut down the borders and to quarantine anyone who has been anywhere near the foreigners. These ideas are wildly popular: a recent NPR poll found that 77 percent of Americans supported a travel ban.

As that poll suggests, this isn't really about Democrats and Republicans. When researchers say that infectious disease threats tend to increase traits associated with conservatism, they're talking about traits that run far deeper than party affiliation, and that can live in both parties simultaneously. What an infectious disease threat can do is shift the terms of the entire political system — both Democrats and Republicans will become a bit more closed to outsiders and mistrustful of change than they were before. These instincts long predate the invention of political parties.

You can see it with the travel ban. As modern as a travel ban sounds — it's about airplanes, after all — it is, in its way, an example of our most ancient reactions to infectious diseases: to draw a clear line delineating who is "us" and who is "them" and then make sure the line doesn't get crossed. The problem is, in the modern world, these instincts, which really did work for a very long time, can be counterproductive. "These kinds of reactions may have been adaptive in the past," says Schaller, "but in the current environment, there can be some really negative outcomes from these actions."

Travel bans, for instance, can lead to people hide their contact with Ebola victims, and thus spread the disease in ways we can't trace. They can also make it harder to get health workers and medical supplies to West Africa, where they're desperately needed if we're going to stop the Ebola outbreak. Quarantines effectively criminalize the health workers trying to stop Ebola in West Africa and might lead to fewer health workers willing to help victims.

For most of human history our only defense against disease was to hide from it, and to shun outsiders who might bring new diseases to our tribes. But recent events have proven that we can't hide from Ebola. A regional disease can turn into a global epidemic in an instant. The only way to stop Ebola in America is to stop it in West Africa. And that means our ancient instinct to close our borders won't work. Our only option is to fight Ebola together.