I N 2015, AFTER the Supreme Court had affirmed the constitutionality of same-sex marriage, Jeremy Frimer of the University of Winnipeg asked 200 randomly selected Americans to take part in a simple experiment. Having established who was for and who was against gay marriage, he told them they had been entered into a lottery to win $10. He then asked those in favour to read and respond to eight arguments against their view. They were allowed instead to read and reply to eight arguments in favour, but in that case, the value of their lottery prize would be reduced to $7. Those against same-sex marriage were offered the same trade-off: they could keep their $10 ticket if they read eight arguments in favour, but the prize was lower if they chose to read arguments against. Almost two-thirds (on both sides) gave up the chance of winning a little extra to avoid being exposed to the other point of view. People look for, remember and in this case are willing to forgo money for information that confirms their pre-existing beliefs.

On November 27th President Trump dismissed a 1,650-page National Climate Assessment in which 13 federal agencies gave warning about the costs and dangers of global warming. “People like myself, we have very high levels of intelligence,” he told the Washington Post, modestly, “but we’re not necessarily such believers.” The president is speaking for his core supporters, too. According to the Pew Research Centre, only 15% of conservative Republicans trust scientists to give full and accurate information about the causes of climate change, compared with 70% of liberal Democrats. Most explanations for the extent of climate denial in America focus on the political influence and campaign contributions of energy companies. But as Mr Frimer’s experiment suggests, psychological explanations also suggest that people are willing to dismiss or deny facts and opinions that run counter to their beliefs.

Such behaviour might seem short-sighted and self-defeating. But in a book of 2017, “The Enigma of Reason”, two cognitive scientists, Hugo Mercier and Dan Sperber, argue that reasoning did not evolve “to help individuals achieve greater knowledge and make better decisions”. Rather, they say, it evolved to improve the ability of ancestral hunter-gatherers to co-operate in small groups. As they put it: “What reason does…is help us justify our beliefs and actions to others…and evaluate the justifications and arguments that others address to us.” In other words, a lot of reasoning is devoted to affirming your group’s identity and your position within it.

Several recent studies suggest that what was useful on the plains of Africa is common in contemporary America. A study in 2013 by Dan Kahan of Yale University asked 1,110 people a question about how effective a skin cream was in reducing a rash. The question required some simple mathematics to solve. Unsurprisingly, the most numerate were most likely to solve the problem correctly. Then Mr Kahan gave the group the question in a politicised form, asking how effective banning handguns was in reducing crime (the underlying mathematics was the same). This time, the most numerate people did not necessarily get the right answer. Rather, Republicans who were good at maths were more likely to conclude that banning guns was ineffective, whereas Democrats said the opposite.

Such thinking informs attitudes to climate change especially. In an earlier study, Mr Kahan asked people to rate their scientific knowledge, partisan affiliation and other characteristics, along with their level of climate concern. You might have expected those with greatest scientific knowledge to be most concerned about climate risks; but the most reliable predictor of concern was people’s worldview. Those who favoured less regimented forms of social organisation were most concerned about it, regardless of scientific knowledge. For those whose basic views were more hierarchical, greater scientific knowledge made them less concerned about the climate, not more. People were using their skills to reinforce the opinions of their group, rather than to establish facts.

They are not necessarily doing this out of bloody-mindedness. It seems that giving consideration to the other sides’ point of view hurts—literally. In another study Mr Frimer asked people who had voted in the 2012 presidential election whether they were interested in hearing why voters had backed the other side. Over a third of Obama voters and more than half of Romney voters compared the experience of listening to the other side’s voters to having a tooth pulled. (Mr Frimer did a related study in Canada before the 2015 election, with similar results, suggesting the findings are not unique to the United States.)

A study in 2016 by Jonas Kaplan of the University of Southern California suggested that such responses are hard-wired in the brain. Mr Kaplan asked 40 liberal voters to get into f MRI scanners while they read various statements, including those that supported liberal political orthodoxy (abortion should be legal) and those that challenged it (ten times more people are murdered with kitchen knives each year than are killed by guns). The opinions that challenged liberal positions prompted a greater flow of blood to a part of the brain which is associated with basic beliefs and a sense of personal identity. If this is true, it is not surprising that, when challenged, people are reluctant to admit the other side might have a point.

Sometimes people refuse point-blank to admit awkward facts, as with climate change. And sometimes they may concede and dismiss them. Brendan Nyhan of the University of Michigan and Ethan Porter of George Washington University ran an online study during America’s presidential debates in 2016, asking 1,500 people to rate the candidates’ statements for accuracy. In some cases, when Mr Trump made a misleading claim, they sent out corrections to it, but only to half the group. Those who got the correction lowered their opinion of Mr Trump’s accuracy, compared with those who did not. But this made no difference to their opinions overall. Mr Trump had the same favourability ratings among those who got the corrections as among those who did not. Alas, dear Economist readers, accurate information does not always seem to have much of an effect (but we will keep trying anyway).

Sources

“Liberals and Conservatives are Similarly Motivated to Avoid Exposure to One Another’s Opinions”. By Jeremy Frimer, Linda J. Skitka and Matt Motyl. Journal of Experimental Social Psychology, 72, 1-12 (2017)

The Enigma of Reason. By Hugo Mercier and Dan Sperber. Allen Lane, £25, Harvard University Press, $29.95. 416 pages

“Motivated Numeracy and Enlightened Self-Government”. By Dan M. Kahan, Ellen Peters, Erica Dawson and Paul Slovic. Behavioural Public Policy, 1, 54-86 (2013). Also available as Yale Law School, Public Law Working Paper No. 307

“The Polarising Ompact of Science Literacy and Numeracy on Perceived Climate Change Risks”. By Dan M. Kahan, Ellen Peters, Maggie Witlin, Paul Slovic, Lisa Larrimore Ouellette, Donald Braman and Gregory Mandel. Nature Climate Change 2, 732-735 (2012)

“Neural Correlates of Maintaining One’s Political Beliefs in the Face of Counterevidence”. Jonas T. Kaplan, Sarah I. Gimbell and Sam Harris, Nature Scientific Reports, December 2016

“Taking Corrections Literally But Not Seriously? The Effects of Information on Factual Beliefs and Candidate Favorability”. By Brendan Nyhan, Jason Reifler, Ethan Porter and Thomas J. Wood