David Ropeik is an instructor at Harvard and author of "How Risky Is It, Really? Why Our Fears Don’t Always Match the Facts."

An aedes aegypti mosquito is photographed through a microscope at the Fiocruz institute in Recife, Brazil. (Felipe Dana/AP)

There is a serious disease outbreak in Brazil right now. And then there is the Great Zika Freakout, the part of this outbreak that is offering some interesting lessons about the emotional nature of risk perception and how our fears so often don’t match the facts.

You wouldn’t know it from the World Health Organization’s declaration of a global public health emergency, or all the dramatic news coverage, but while the microcephaly risk from Zika is real, at this point it’s lower than you might expect, given the alarms.

The rate of confirmed microcephaly cases (641) out of total births in Brazil (roughly 3 million) is about 2 in 10,000. While that does make it a real public health concern, it’s hardly the imminent danger many might assume.

But as the West Nile virus scare reminded us in 1999-2000, even when the probabilities are low, new risks scare us more than those that have been around a while. As the excessive fears of childhood vaccines illustrate, we are super-sensitive to any risk to kids. And as countless examples teach, when we can’t escape 24/7 alarmist news coverage of the risk du jour (shark attacks, childhood abductions, rare but frightening mass shootings), that elevated awareness magnifies our sense of danger, too. The Zika Freakout may not match the numbers, but psychologically it makes sense.

It’s also demonstrating how readily we abandon critical thinking and believe even the wildest claims when those claims fit our values and beliefs. One example: On a Reddit board devoted to conspiracy theories, someone suggested that genetically modified mosquitoes being tested in Brazil to control mosquito populations caused the Zika/microcephaly outbreak. (The modified bugs breed offspring that die, so the population crashes.) Despite such an overtly questionable source, and numerous glaring inaccuracies that were quickly reported by responsible journalists, the “genetic modifications cause Zika” notion quickly spread. Within days of that Reddit post, the theory was repeated by the environmental journal the Ecologist, London’s Daily Mail newspaper, the anti-GM and anti-West Russian government (they also blamed Bill Gates directly) and anti-GM websites.

The viral spread of the theory demonstrates how readily our fears are informed more by underlying emotions and values than careful evidence-based thinking.

Those underlying values in this case are clear. A link between Zika and genetic modification taps a widely held sentiment that human technology and behavior are fouling up the natural world (a view I generally share). Some who feel this value most passionately blame humans for almost anything that goes amiss in nature, concocting a set of facts that fit those beliefs. It’s automatic, the environmentalist version of, “If you only have a hammer, everything looks like a nail.”

A new theory of what caused the Zika outbreak also rises from those beliefs. Anti-GM advocates in Argentina now blame an industrial pesticide used to control mosquito populations, despite the fact that this particular chemical has been globally approved by health agencies and has been safely used for decades in areas infected by Zika, with no microcephaly outbreak. Along with this claim, advocates warn that “chemical control is contaminating the environment as well as people,” that the use of larvacide to control mosquitoes “is in fact a commercial maneuver from the chemical poisons industry,” and to top it all off, that the larvacide is manufactured by a subsidiary of Monsanto (which is incorrect). Like the purported link between genetic modifications and Zika, such allegations resonate with the values of environmentalists, who accept and spread the claim without skepticism or critical thinking despite the overt bias of the source.

Research suggests that we do this sort of thing — motivated reasoning based more on how we feel than simply what the facts say — for profound reasons. It helps us survive. We uncritically accept claims that support our values because such claims provide evidence of the truth of our beliefs. That helps us argue that our values are the ones that everybody should hold, that society should operate along our guidelines, not according to the values and beliefs of other groups or tribes. We prefer, and feel safer, in a society operating by our rules. And adopting values-based views that are shared by those in the groups we most closely identify with establishes us as loyal members of the group, worthy of the group’s support and protection, a vital goal for social animals like us. These are powerful subconscious influences on cognition, motivations way more powerful than the goal of just objectively figuring stuff out.

This motivated reasoning shapes our views on politics or religion or economics or, well, on pretty much anything, not just how we feel about Zika or other risks. But with risk, this feelings-based system — what researchers Paul Slovic and Melissa Finucane call the Affect Heuristic — has consequences. Some areas in Brazil, threatened not only by Zika but dengue and Chikungunya viruses spread by the same species of mosquito, are holding back on using that larvacide. Many places around the world facing mosquito-born diseases that sicken and kill millions are fighting the use of the genetically modified mosquito that could help protect public health. The values-based fear of these technologies, in denial of robust evidence of their safety and efficacy, is blocking their use. People are getting sick and dying as a result.

We can’t entirely overcome the innately subjective nature of human cognition and become perfectly objective, fact-based, critical thinkers. But we can recognize the dangers from affective thinking that cause us to worry about some things more than we need to, and worry about some things less than we should. We can recognize and take more seriously the risks that these risk misperceptions can create. We can realize that a little more careful thinking, and just a touch of skepticism about the latest scary claim, even if that means letting the evidence push back against our own values just a bit, could help keep us safer. It’s one of the lessons the Zika panic is offering us — if we’re smart enough to listen.