These protests, which contradict health advice to reduce transmission rates of the virus, come at a time of widely circulated conspiracy theories about the virus, including that it is a hoax (believed by 13% of Americans polled), or that the virus was deliberately created in a Chinese weapons lab (a claim believed by as much as half the population), and that 5G wireless technology somehow spreads the virus. Such theories have been boosted and spread by a handful of prominent conservative politicians and far-right activists, including Republican Senator Tom Cotton. And research shows that even smart people can believe such conspiracy theories, if they’re couched in the right language.

“If you have the kind of hyper-partisanship we have in the United States, it’s like a dry forest and all it’ll take is one match to light it and cause a problem,” says Jay van Bavel, associate professor of psychology at New York University. “That’s what we’ve seen in the last few months in the US, where Trump didn’t take the virus seriously at first, and the right-wing media sphere – Fox News and talk radio – downplayed the threat of the pandemic for a long time to protect his electoral chances. So then you have the recipe for differences in beliefs.”

As polls have shown, as far back as February, Americans’ attitudes to Covid-19 risk are closely tied to voting behaviour, with Republicans showing much less concern about the outbreak.

Tribal culture affects how people see the world more than facts do. Take human-caused climate change, for which there is near-unanimous global scientific consensus. This, too, divides Americans, but in an unlikely way: the more education that Democrats and Republicans have, the more their beliefs in climate change diverge. Of Republicans with only a high school education, 23% report being very worried about climate change. But among college-educated Republicans, that figure was just 8%.

This may seem counter-intuitive, because better-educated Republicans are more likely to be aware of the scientific consensus. But in the realm of public opinion, climate change isn’t a scientific issue, it’s a political one. Climate change science is relatively new and technically complicated, and many Americans adopt the opinions of their tribal leaders: the political elites. Even though better-educated Republicans may have more exposure to information about the science around climate change, they also have more exposure to partisan messages about it, and this matters more.

“We’ve had three years of Americans arguing about different perceptions around facts: say, the size of crowds at Trump’s inauguration versus Obama’s inauguration. It’s easy to laugh that off, because it doesn’t have any consequences. But now we have a virus that imposes enormous risks to people’s health,” van Bavel says. “And the risks have non-partisan consequences because most people have a family member or work with someone who’s from a different political party. If they get exposed to the virus and contract the disease, they put you at risk. So there is a very strong reason to try to figure out a way to solve this.”

Since we have culturally evolved to acquire our knowledge and beliefs primarily through high-fidelity copying of others rather than by invention (by looking at the evidence and deciding for ourselves), we are vulnerable to this problem of copying unreliable models. Worse still, because we have culturally learned to value rational explanations over subjective ones for scientific issues, we can be manipulated into believing the opinions we copy are rational, so it is harder to change them.

Despite our culturally evolved norms for rationality and evidence-based decision making, our biological evolution has not caught up and our cognition continues to be emotionally led. The problem is not necessarily that we use the emotive part of our brain more than the rational in decision making, but that we are self-delusional. Even experts are prone to biases and these mean costly mistakes are made, and irrational prejudices are systemic in organisations where people believe themselves to be non-racist, non-sexist and to hold the positions they do through skill rather than luck.

Often, the main role of reasoning in decision making is actually not to arrive at the decision but to be able to present the decision as something that’s rational. Some psychologists believe we only use reason to retrospectively justify our decisions, and largely rely on unquestioned instincts to make choices. It may be that our unconscious instincts – despite our cognitive biases and prejudices – are more capable of rationality than our logical thought-processing minds. Few of us are able to fully separate our subjective and objective reasoning during decision making – this is one of the promises of artificial intelligence.

Our decision making is influenced by our biology and our social environment. Take the psychological and physiological influence of fear: it’s been shown that people who vote more conservatively tend to have a bigger amygdala, the brain’s fear centre. In one study, the more fear a three- or four-year-old showed during a lab study, the more conservative their political attitude was found to be 20 years later.

The impact of fear is instant: when people with liberal attitudes experienced physical threat, during a study, their political and social attitudes became more conservative, temporarily. Conservative politicians and electioneering exploit this, aiming to raise voters’ fears of immigration by comparing immigrants to germs, for example, which targets our deep, biologically evolved motivations to avoid contamination and disease. In one study, during an H1N1 flu epidemic, researchers reminded people of the dangers of the flu virus and then asked them their attitudes towards immigration, after which they were asked whether they had been vaccinated against flu yet. Those who hadn’t received their anti-flu shot were more likely to be anti-immigration than the ones who felt less threatened.

But in a follow-up study, the researchers offered people a squirt of hand sanitiser straight after the flu warning. The immigration bias went away. Making people feel safe changes their voting decision to more liberal. When researchers asked people to imagine themselves completely invulnerable to any harm, Republican voters became significantly more liberal in social attitudes to issues like abortion and immigration. Reason is suffused with emotion.

The social implications of most decisions are also important factors in decision making. In very partisan situations, people who disobey the social norm by voting against the group majority risk ostracism. In such cases, therefore, it may be more rational for the individual to go against the evidence because we are motivated more by social cohesion and maintaining support networks than being objectively right.

Whatever your political persuasion, the Covid-19 virus will not discriminate as it seeks more lungs to infect. But, because contagion is inherently social, it may well turn out that those populations who continue to socialise undeterred might end up experiencing worse epidemics. In other words, your voting record may well influence your fate.

Needless to say, these overall trends linking political leanings and attitudes towards coronavirus are not the whole story. Rand Paul, junior Senator from Kentucky, for example, has been volunteering in a hospital to help patients during the crisis, including those with coronavirus, after he had the disease himself.

And there are signs things are changing. As Republicans get exposed to people they know affected by the virus, they are taking the threat more seriously – something known as the “reality constraint”. “People’s motivations for partisanship start to get outweighed by the value of being accurate and being healthy for themselves and their family,” says van Bavel.

The most recent poll shows that over 95% of Democrats support social distancing measures, and a large majority of of Republicans do too – over 80% – so the gap is narrowing. Perhaps, then, it is unsurprising that Trump’s approval rating has declined over the same time that approval ratings have risen for state governors who have shown leadership in responding to the virus.

Gaia Vince discusses these ideas in her book TRANSCENDENCE