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Do chimpanzees care about fairness? The jury’s out

A stranger gets a pot of money and offers you a share of it. If you accept the offer, both of you walk away with your proposed shares. If you reject, you both leave with nothing.

This is the ultimatum game—a classic psychological experiment used to study fair play. If both players behave completely selfishly, the proposer might offer as little as possible, while the responder should accept any offer as long as it’s not zero. That way, both of them walk away with something. In practice, responders typically reject any offers less than 20 percent. They care enough about fairness to do themselves out of money in order to punish unfair partners. Meanwhile, proposers from industrialised countries, who are wary of social norms and the potential for punishment, tend to offer between 40 and 50 percent of the pot.

But what about chimpanzees? Do our closest relatives also share our attitudes to equality? Darby Proctor from Georgia State University thinks so. She modified the ultimatum game so that chimps and human children could play it in the same way. In both cases, when proposers needed to cooperate with responders, they became more likely to offer an equal split, rather than trying to hog the rewards for themselves. The conclusion: “humans and chimpanzees show similar preferences regarding reward division, suggesting a long evolutionary history to the human sense of fairness.”

But her study has prompted stern criticism from scientists who have also tested chimps at the ultimatum game and found the opposite. In their studies, our fellow apes did not make fair offers and accepted anything as long as it was greater than zero.

This debate reflects a growing divide between scientists who study chimpanzees, but it is more than an academic spat. It speaks to a fundamental question about our evolution: is our sense of fairness a uniquely human trait, or one that we share with our closest kin?

Old male chimp, by Prabir Kumar Bhattacharyya

The experiments

Keith Jensen, Josep Call and Michael Tomasello were the first to play the ultimatum game with chimps. In their experiments, two chimps sat in adjacent cages, facing a contraption with two sliding trays. Each tray contained one dish on the proposer’s side and another on the responder’s side, and the two dishes carried varying numbers of raisins. The proposer made an offer by using a rope to pull one of the two trays half-way over. The responder could accept this offer by pulling the tray the rest of the way, allowing them both to eat their respective raisins. Alternatively, they could reject the offer by doing nothing, leaving both animals unfed.

The team found that the proposers were likely to choose the tray that gave them the most raisins, and the responders tended to accept any offer, no matter how unbalanced. They wrote that “in this context, one of humans’ closest living relatives… does not share the human sensitivity to fairness.” And in a second study, the team found that our other close relatives—the bonobos—behaved in a similar way.

But Proctor was unimpressed by the team’s set-up. She felt that the “complex mechanical apparatus” was unlike anything that humans use when we play ultimatum games, and may have been too complicated for the chimps to understand. And while humans usually play for money, which is exchanged for other rewards, the chimps were playing for food, which is immediately rewarding.

In her version of the ultimatum game, two chimps play for tokens that are exchanged for six bananas laid out in front of them. A human experimenter offers two tokens to the proposer chimp, one signifying an equal banana split and the other signifying an unequal 5:1 divide. The proposer picks one token and passes it to a responder in an adjoining cage. They can drop the token to reject the offer, or pass it back to the experimenter to accept.

Proctor played the game with three pairs of chimps, one of which swapped roles as proposer and responder. She found that two of the proposers chose the equal-split token more often than expected by chance. And all four of them chose that token more often in the ultimatum game than in a straight preference test, when their choice dictated their reward irrespective of what a responder did. Proctor concluded that when chimps need to cooperate to get a reward—that is, when the proposer depends on the responder—they change their behaviour to favour the fairer option. Young children, aged two to seven, behaved in the same way.

Margot, an orphaned chimpanzee from a sanctuary in Cameroon. By Daniel Bergin

So what does that mean?

The obvious criticism is that Proctor’s study only included six chimps, and only the two animals who played both roles offered the equal token more often than expected by chance. Proctor admits that the numbers were small, but says that these were the only chimps that passed her rigorous pre-tests and clearly understood the nature of the game.

But Jensen disputes Proctor’s claim. He is glad that another team tried to replicate his results, since “one can only conclude so much from one or two studies,” but says that Proctor’s experiment was no ultimatum game. The most important aspect of the ultimatum game is not what the proposer does, but how the responder reacts,” he says. The proposer’s offers are strategic rather than a sign of fairness—they’re a reaction to what the responder might do. It’s the responder’s ability to reject unequal offers that drives fairness in the game.

And among Proctor’s chimps, no responder ever refused an offer, even the many unfair ones. That’s even less rejection than in Jensen’s study. “Not rejecting unfair offers is puzzling if chimps are really playing the ultimatum game,” says Call. “I see that as a fatal flaw,” adds Jensen. At best, it confirms his original experiment by showing that the responders are insensitive to unfairness and only motivated by getting bananas. At worst, it shows that they didn’t understand the task.

Proctor counters that she did extensive tests to be as sure as possible that the chimps understood what the tokens meant. She admits that she did not explicitly train the chimps that they could refuse offers, but says, “This actually makes our results more striking. Without experiencing a refusal, proposers changed their behaviour to be more equitable. They may be responding to the potential for refusals as do adult humans.”

Jensen doesn’t buy it. “There isn’t the tiniest shred of evidence that proposers understood that responder could reject their offers, and no demonstration that responders understood anything of the possible consequences of their choices,” he says.

David Rand, a psychologist from Harvard University who has used the ultimatum game in human studies, agrees with Jensen’s criticisms. While Proctor’s set-up does look like an ultimatum game, “it looks like maybe the chimps didn’t understand the game structure,” he says.

Jensen thinks that this confusion arose because Proctor’s task is not as simple as she claims. Unlike human ultimatum games, where players interact with each other, Proctor’s chimps spent as much time exchanging tokens with humans. “Passing a token is just an intermediate step to getting food from experimenters, something they are highly trained to do,” says Jensen. He doubts that this set-up, which involved tokens exchanging hands three times, is truly simpler than his tray-pulling machine.

The verdict

As Proctor notes, there are many reasons to suspect that chimps care about equality. They help one another, share food, and cooperate extensively to hunt, fight, patrol, defend, and more. But it’s difficult to interpret wild anecdotal behaviour, which is why experiments are valuable.

None of the existing studies is perfect. In all the chimp ultimatum games, the animals could only reject offers passively, by not pulling a tray or not handing over a token; in human games, rejection is an active choice. In the chimp games, the animals could see each other, and played multiple rounds with the same partners; in human games, partners usually play single rounds anonymously to stop social dynamics and reputations from clouding the results.

Given these shared weaknesses, Proctor’s team is right that Jensen’s studies don’t prove that chimps are insensitive to fairness even though they support that hypothesis. After all, absence of evidence is not evidence for absence. But equally, the problems in Proctor’s study prevent it from confirming that chimps are sensitive to fairness. Until more research is done, we’re at an impasse.

Reference:  Proctor, Williamson, de Waal & Brosnan. 2013. Chimpanzees play the ultimatum game. PNAS http://dx.doi.org/10.1073/pnas.1220806110

Note: This study was “contributed” to PNAS by co-author Frans de Waal, a publishing route where members of the National Academy of Sciences can nominate their own peer-reviewers. I try to avoid papers that use this track but did most of the reporting before I noticed, so here’s the piece anyway.

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Quick intuitive decisions foster more charity and cooperation than slow calculated ones

Our lives are governed by both fast and slow – by quick, intuitive decisions based on our gut feelings; and by deliberate, ponderous ones based on careful reflection. How do these varying speeds affect our choices? Consider the many situations when we must put our own self-interest against the public good, from giving to charity to paying out taxes. Are we naturally prone to selfishness, behaving altruistically only through slow acts of self-control? Or do we intuitively reveal our better angels, giving way to self-interest as we take time to think?

According to David Rand from Harvard University, it’s the latter. Through a series of experiments, he has found that, on average, people behave more selflessly if they make decisions quickly and intuitively. If they take time to weigh things up, cooperation gives way to selfishness. The title of his paper – “Spontaneous giving and calculated greed” – says it all.


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Will we ever have a fool-proof lie detector?

Here’s the fourth piece from my new BBC column

In The Truth Machine, a science-fiction novel published in 1996, scientists invent a device that can detect lies with perfect accuracy. It abolishes crime, changes the world, and generally saves humanity from self-destruction. Which is nice.

Could such a machine ever be a reality? Not if our current technology is anything to go by. The polygraph has been around for almost a century, with wired-up offenders and twitching needles becoming a staple of criminal investigations. But there is no solid evidence that the signs it looks for – faster heart rates, shallower breaths and moist skin – can accurately indicate whether someone is telling a lie. Underpinned by fluffy theory and backed by a weak and stagnant evidence base, this lie-detection device is unlikely to get any better.

Inside the brain

Abandoning the polygraph, some scientists have turned to brain scanners. Two technologies have dominated the field. The first uses electronic sensors on a person’s scalp to measure an electrical signal, or “brainwave”, called the P300, which appears when we recognise something. By looking for this signal, you could potentially tell if someone is hiding knowledge about something they are already familiar with, like a murder weapon. This is certainly useful, but it is a long way from an all-purpose lie-detection method, and two of the key figures in the field have been arguing about how effective this is for many years.

The second technique is functional magnetic resonance imaging (fMRI), affectionately known as blobology for the colourful pictures it produces. It shows the location of firing neurons in an indirect manner, by tracking the blood flow that supplies them with nutrients and oxygen. Several fMRI studies have shown that some parts of the brain are consistently more active when people tell untruths rather than truths, particularly areas at the very front that help us to suppress unwanted actions. Successful lying, it seems, is mainly about repressing the urge to be honest.


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The spread of disorder – a repost in wake of London’s riot cleanup

Yesterday, I watched as hundreds of Londoners took to the streets in a heroic attempt to clean up the mess caused by rioters and looters the night before. Looking at pictures of large crowds getting off trains with cleaning equipment in hand and marching down streets with brooms held aloft, I’ve rarely felt so proud of my city.

The clean-up operation was a great move – a positive note in an otherwise depressing week and a chance for a beleagured capital to come together and reclaim its sense of community. But the act of cleaning away the preceding day’s damage was also important. To explain why, I’m reposting this piece from a few years back about a Dutch study which showed that signs of disorder only breed more disorder. To clarify, this is in no way an attempt to explain the psychology of the riots themselves; it simply suggests another reason why the clean-up operation was a smart move.


Imagine walking through a neighbourhood and seeing graffiti, litter, and shopping trolleys strewn about the place. Are these problems to be solved, or petty annoyances that can be ignored in the light of more serious offences? A new study suggests that the former is right – even the most trivial of transgressions can spread and spiral because their very presence stimulates more of the same behaviour. Through a series of stunning real-world experiments, Kees Keizer and colleagues from the University of Groningen have shown that disorder breeds more disorder. The mere presence of graffiti, for example, can double the number of people who litter and steal.

Their study provides strong support for the controversial Broken Windows Theory, which suggests that signs of petty crimes, like broken windows, serve as a trigger for yet more criminal behaviour. It follows that fixing small problems can prevent the build-up of bigger ones and the gradual decay of a neighbourhood. The idea was first proposed in a magazine article published in 1982, but soon became the basis of many a social policy.

It inspired Rudy Guiliani’s Quality of Life Campaign in New York, which focused attention on seemingly trivial fixes such as removing graffiti, clearing signs of vandalism and sweeping the streets. The campaign seemed to work, which motivated other cities to try the same tactics. But despite its popularity, the Broken Windows Theory still divides opinion, for it lacks the backing of hard evidence, it’s plagued by woolly definitions of “disorder” and critics have questioned its role in New York’s drop in crime. These are fairly hefty shortcomings for a concept that is so central to anti-crime measures and Keiser wanted to address them once and for all.

To do so, he took to the streets of Groningen and watched unknowing passers-by in real-life situations as they reacted to signs of disorder. The recurring question was this: would people exposed to inappropriate behaviour behave in a similar way themselves?

He began in an alleyway in a local shopping district, where bicycles are commonly parked and where a conspicuous red sign warned against graffiti. He attached a flyer from a fictional sportswear shop to the handlebars of parked bicycles and watched what people did as they returned to their rides. Under normal circumstances (picture on the left), most people took the flyer with them and just 33% littered by throwing it on the ground. But that all changed when Keiser covered the wall with graffiti (picture on the right). With this innocuous difference, the proportion of litterers doubled and 69% discarded their flyers on the street.


Keiser explains this behaviour in terms of “social norms” – the rules that separate appropriate behaviours from inappropriate ones. Problems arise when our view of what is common (in this case, graffiti) fails to mesh with our understanding of what society expects (as epitomised by the “No Graffiti” sign). Graffiti is frowned upon, but the covered walls send a message that it is common and therefore, more acceptable. Keizer calls this the Cialdini effect.

Fence.jpgTo see how far its influence would extend, he set up a temporary fence in front of a car park. He attached two signs to the fence, one banning people from locking their bicycles to it, and another saying that entry was forbidden and asking people to use a detour some distance away. When he placed four bicycles a metre away, just 27% of people disobeyed the detour sign and squeezed through the gap in the fence. But when the bikes were locked to the fence, in blatant disregard of the first sign, 82% of people ignored the detour sign too. With one rule broken, the other followed suit.

A third related study took place in a supermarket car park, where prominent stickers asked shoppers to return their carts to the main building. Keizer plastered various cars with the same flyer from the first study. If the garage was clear of carts, just 30% of shoppers littered with the flyer, but if four unreturned shopping carts were left lying about, 58% did so. Again, when people saw that one rule was broken, they felt less strongly about following another.


Together, these three experiments show that signs of disregarded rules can spread to affect commonly held behaviours (“don’t litter”) as well as specific requests from third parties (“don’t enter” or “return trolleys”).

Signs of disorder don’t even need to be seen to have such influences – they can be heard too. In the Netherlands, most people know that setting off fireworks in the weeks before New Year’s Eve is illegal and carries a small fine. Keiser found that he could trigger people to litter more frequently by giving them audible evidence that this law had been flouted. Again, he attached a flyer to bicycles parked near a train station. Under normal circumstances, 52% of cyclists littered but if they heard the sound of fireworks let off by Keiser at a nearby location, that figure grew to 80%.

Letterbox.jpgFor his final and most dramatic demonstration, Keiser showed that the mere presence of graffiti can even turn people into thieves. He wedged an envelope into the slot of a mailbox, with a 5 Euro note showing in the transparent window. If the mailbox and the ground around it were clean, just 13% of passers-by stole the envelope. If the mailbox was covered in graffiti, or if the ground around it was covered in litter, the proportion of thieves doubled to 27% and 25% respectively.

Keiser thinks that it’s unlikely that people inferred a reduced police presence by the presence of litter or graffiti – certainly, litter is generally tolerated by the police in Groningen. Instead, he thinks that one transgression was actually fostering another. This isn’t a simple case of imitation – littering doesn’t just beget littering. Keiser’s idea is that seeing the breakdown of one social norm makes it easier to ignore others, by weakening our general resolve to act appropriately and strengthening our temptations to act in our own self-interest.

All in all, the suite of experiments, all in a realistic setting, provide powerful evidence that the Broken Windows Theory is valid and all of Keiser’s results were statistically significant. Small, petty signs of disorder can indeed turn people away from the straight and narrow. His message to police and policy-makers is stark – it is worth spending time on small and seemingly trivial interventions, to prevent disorder from spreading and escalating.

Reference: Keizer, K., Lindenberg, S., & Steg, L. (2008). The Spreading of Disorder Science, 322 (5908), 1681-1685 DOI: 10.1126/science.1161405

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Power breed hypocrisy – powerful people judge others more harshly but cheat more themselves

MPsLast year, the UK press was abuzz with the so-called “expenses scandal”. In a time when the county was gripped by recession, we were told that Members of Parliament (MPs) were claiming for all sorts of ridiculous luxuries, all at the taxpayer’s expense. The revelations dominated the news, but the idea that people in positions of power often behave hypocritically isn’t new. It is said, after all, that power corrupts. Now, Joris Lammers from Tilburg University has found solid evidence for this.

Through five compelling experiments, Lammers has shown that powerful people are more likely to behave immorally but paradoxically less likely to tolerate immorality in other people. Even thinking about the feeling of power can trigger these double standards.

To begin with, Lammers asked 61 students to remember a time when they either felt powerful or powerless. Those that reminded themselves of power were more likely to frown on cheating; compared to the powerless group, they thought that overclaiming on travel expenses was less acceptable. However, they were also more likely to cheat. Lammers gave the recruits the chance to decide how many lottery tickets they would receive by privately rolling two dice. Those who were primed with power were more likely to lie about their scores to wangle extra tickets.

To explore this hypocrisy further, Lammers did three further experiments where he manipulated a volunteer’s feelings of power and then gave them a common moral dilemma. All of these involved acts that are technically illegal but that many people take part in, such as speeding or tax-dodging. Their job was to say either whether they would be okay with doing it themselves, or whether they would think it acceptable if someone else did it.


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Fake and counterfeit goods promote unethical behaviour

SunglassesAdorning yourself in fake goods, be it a replica Gucci handbag or knock-off Armani sunglasses, makes a statement. It says that you want to feel, or be seen as, wealthier than you actually are. It signals an aspiration towards a richer lifestyle. Of course, such products can’t actually change a person’s status, but a new study suggests that they can change people’s behaviour, and for the worse.

Francesca Gino from the University of North Carolina has shown that counterfeit products actually make people behave more dishonestly. They cheat more in tests and they judge others as unethical with greater abandon. Even worse, they’re completely unaware of this impact. This effect is heavily ironic. People often buy fake goods to look good to other people. But Gino’s study shows that these products can affect our moral choices precisely because they make us look worse to ourselves. As she writes, “Feeling like a fraud makes people more likely to commit fraud.”

In her first experiment, Gino told volunteers that they were going to wear a pair of real of fake designer sunglasses while doing certain tasks. Their job was to test out the glasses. In reality, all the eyewear on offer was real and each cost a princely $300. But even though everyone had the same shades, the volunteers who thought they were wearing the fake ones were more likely to cheat in the tests.


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When is attempted murder more acceptable than harming someone by accident?

Attempted_murderDan, a scientist working on dangerous viruses, is giving a visitor a tour of his lab. Before this happens, all test tubes containing disease-causing agents must be sealed in a chamber with a flick of a switch. Unfortunately, the switch broke recently and it hasn’t been repaired yet. Entering the room means certain death. Dan knows this but still, he bids the visitor to enter. The inevitable happens; they become sick and they die.

Would you consider Dan’s actions to be immoral? What if, in a parallel universe, the visitor miraculously survived? Does that change your views of Dan’s deeds? What if Dan didn’t know about the broken switch? For most of us, the answers are clear. If Dan knew about the broken switch, he was wrong to send in the visitor to potential death, regardless of whether they actually perished. But bizarrely, not everyone would see it that way.

Liane Young from MIT found that people with brain damage in an area called the ventromedial prefrontal cortex (VMPC) are unusually likely to brush off failed attempts at harming other people. They frowned upon actual murder with the usual severity but compared to normal people, they were twice as likely to think that attempted murder was morally permissible. Young thinks that the VMPC is vital for our ability to deduce respond emotionally to the intentions of other people, an important skill when it comes to making moral judgments.


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Clean smells promote generosity and fair play; dark rooms and sunglasses promote deceit and selfishness

The English language is full of metaphors linking moral purity to both physical cleanliness and brightness. We speak of “clean consciences”, “pure thoughts” and “dirty thieves”. We’re suspicious of “shady behaviour” and we use light and darkness to symbolise good and evil. But there is more to these metaphors than we might imagine. The mere scent of a clean-smelling room can take people down a virtuous road, compelling them to choose generosity over greed and charity over apathy. Meanwhile, the darkness of a dimmed room or a pair of sunglasses can compel people towards selfishness and cheating.

These new results are the latest from psychologist Chen-Bo Zhong. Back in 2006, he showed that people who brought back memories of past wrong-doings were more likely to think of words related to cleaning, or to physically crave cleaning products. He called this the “Lady Macbeth effect”. Subsequently, another group found that it works the other way too. People judge moral transgressions more leniently if they had previously washed their hands or if they had been primed with words related to cleanliness, like ‘pure’ or ‘immaculate’.

Now, Zhong, together with Katie Liljenquist and Adam Galinsky, have expanded on these studies by showing that clean smells can make people behave more virtuously. They ushered 28 volunteers into a room that was either unscented or that had been lightly sprayed with a citrus air freshener. In either case, they had to play a trust game, where a “sender” has a pot of money and chooses how much they want to invest with a “receiver”. The investment is tripled and the receiver decides how much to give back.

The volunteers were all told that they had been randomly chosen as receivers. Their anonymous partner had invested their entire $4 pot with them, which had been tripled to $12. Their job was to decide how much to give back. On average, they returned a measly $2.81in the unscented rooms but a more equitable $5.33 in the scented ones. The single spray of citrus nearly doubled their tendency to reciprocate.

In a second experiment, the trio again ushered 99 students into either a scented or unscented room. They were given a pack of miscellaneous tasks, including a flyer requesting volunteers for a charity called Habitat for Humanity. Those in the citrus-scented rooms were more likely to be interested in volunteering, and almost four times more willing to donate money to the cause.


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Will vs. Grace – are people honest because they resist temptation or because they don’t feel it?

Blogging on Peer-Reviewed ResearchIn a world where the temptation to lie, deceive and cheat is both strong and profitable, what compels some people to choose the straight and narrow path? According to a new brain-scanning study, honest moral decisions depend more on the absence of temptation in the first place than on people wilfully resisting these lures.

Joshua Greene and Joseph Paxton and Harvard University came to this conclusion by using a technique called functional magnetic resonance imaging (fMRI) to study the brain activity of people who were given a chance to lie. The volunteers were trying to predict the outcomes of coin-flips for money and they could walk away with more cash by lying about their accuracy.

The task allowed Greene and Paxton to test two competing (and wonderfully named) explanations for honest behaviour. The first -the “Will” hypothesis – suggests that we behave morally by exerting control over the desire to cheat. The second – the “Grace” hypothesis – says that honesty is more a passive process than an active one, fuelled by an absence of temptation rather than the presence of willpower. It follows on from a growing body of psychological studies, which suggest that much of our behaviour is governed by unconscious, automatic processes.

Many studies (and several awful popular science articles) have tried to place brain-scanning technology in the role of fancy lie detectors but in almost all of these cases, people are told to lie rather than doing so spontaneously. Greene and Paxton were much more interested in what happens in a person’s brain when they make the choice to lie.

They recruited 35 people and asked them to predict the result of computerised coin-flips while sitting in an fMRI scanner. They were paid in proportion to their accuracy. In some ‘No-Opportunity trials’, they had to make their predictions beforehand, giving them no room for cheating. In other ‘Opportunity trials’, they simply had say whether they had guessed correctly after the fact, opening the door to dishonesty.

To cover up the somewhat transparent nature of the experiment, Greene and Paxton fibbed themselves. They told the recruits that they were taking part in a study of psychic ability, where the idea was that people were more clairvoyant if their predictions were private and motivated by money. Under this ruse, the very nature of the “study” meant that people had the opportunity to lie, but were expected not to.


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Our moral thermostat – why being good can give people license to misbehave

Blogging on Peer-Reviewed ResearchWhat happens when you remember a good deed, or think of yourself as a stand-up citizen? You might think that your shining self-image would reinforce the value of selflessness and make you more likely to behave morally in the future. But a new study disagrees.

Shoulderangeldevil.jpgThrough three psychological experiments, Sonya Sachdeva from Northwestern University found that people who are primed to think well of themselves behave less altruistically than those whose moral identity is threatened. They donate less to charity and they become less likely to make decisions for the good of the environment.

Sachdeva suggests that the choice to behave morally is a balancing act between the desire to do good and the costs of doing so – be they time, effort or (in the case of giving to charities) actual financial costs. The point at which these balance is set by our own sense of self-worth. Tip the scales by threatening our saintly personas and we become more likely to behave selflessly to cleanse our tarnished perception. Do the opposite, and our bolstered moral identity slackens our commitment, giving us a license to act immorally. Having established our persona as a do-gooder, we feel less impetus to bear the costs of future moral actions.

It’s a fascinating idea. It implies both that we have a sort of moral thermostat, and that it’s possible for us to feel “too moral”. Rather than a black-and-white world of heroes and villains, Sachdeva paints a picture of a world full of “saintly sinners and sinning saints”.


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A bad taste in your mouth – moral outrage has origins in physical disgust

Blogging on Peer-Reviewed ResearchBoth objects and behaviour can be described as disgusting. The term could equally apply to someone who cheats other people out of money as it could to the sight of rancid food or the taste of sour milk. That’s not just a linguistic quirk. Some scientists believe that the revulsion we feel towards immoral behaviour isn’t based on our vaunted mental abilities, but on ancient impulses that evolved to put us off toxic or infectious foods.

It seems that your facial muscles agree. Hanah Chapman from the University of Toronto has found that both physical and moral disgust cause the levator labii muscles, which run from your eyes to your mouth, to contract. The result: you wrinkle your nose and you purse your lips. Nasty tastes, gross photos and foul play all cause the same physical reaction and the same subjective emotions. When people say that moral transgressions “leave a bad taste in your mouth”, it’s more than just a pretty metaphor.

Chapman began by studying disgust in its more primitive forms – reactions to foul tastes. She recruited 27 volunteers and recorded the electrical activity in their levator labii muscles as they drank small vials of various liquids. If the concoctions were unpleasantly salty, sour or bitter, this group of muscles contracted more strongly than if the liquids were sweet or flavourless. These reactions were a good measure of their subjective opinions – the more distasteful they found the drinks, the more strongly their muscles contracted.


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Clean thoughts can soften moral judgments

Blogging on Peer-Reviewed ResearchThroughout our language, the vocabulary of physical cleanliness is also used to describe moral cleanliness. We describe saints as pure and thieves as dirty; consciences can be clean and sins can be washed away. But more and more, psychological studies tell us that these concepts are entwined in a very real way. The act of cleaning, or even just thinking about the concept of cleanliness, can influence a person’s moral compass, swinging it towards a less judgmental direction.

This isn’t the first time that I’ve blogged about this. Two years ago, Chen-Bo Zhong and Katie Liljenquist found that volunteers who dredged up a past misdeed were more likely to think of words related to cleaning or show a physical preference for cleaning products. This “Lady Macbeth effect” is reminiscent of the infamous Shakespearean character and her failed attempts to wash her hands of spilt blood.

Simone Schnall and colleagues from the University of Plymouth have expanded on Zhong and LIllenquist’s study by showing that the effect works in the opposite direction. Not only can feelings of moral muck trigger a desire for physical cleanliness, cleanliness can also change how seriously people view a moral transgression.

They asked 40 volunteers to a rearrange 40 sets of four words into sentences. Through this word-game, they ‘primed’ 20 of the volunteers with thoughts of cleanliness by interspersing half of their sets with cleaning-related words, such as pure, washed, clean, immaculate or pristine. The other 20 volunteers only saw unconnected neutral words in all of their sets.



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The Lady Macbeth effect – how physical cleanliness affects moral cleanliness


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“Out, damn spot! Out I say!” In Macbeth’s fifth act, Lady Macbeth’s role in the treacherous murder of Duncan takes its toll, and she begins obsessively washing her hands to alleviate her guilty conscience. Now, some four centuries after Shakespeare penned his play, scientists have found that physical and moral cleanliness are just as inextricably linked as he suggested.

lmac.jpgThe link between bodily cleanliness and moral purity is evident throughout the world’s cultures. Cleansing ceremonies are common in religions. Christians and Sikhs literally wash away their sins through baptism, while the act of wudu sees Muslims prepare for worship by cleaning their bodies. Our language too reveals hints of an overlap – a ‘clean conscience’ is free of guilt, while ‘dirty’ is a word for thieves and traitors.

Chen-Bo Zhong from the University of Toronto and Katie Liljenquist from Northwestern University have now revealed the strong links between unblemished hands and stain-free hearts in a series of clever psychological experiments.

They asked two groups of people to remember a good or bad deed from their past. Afterwards, the volunteers solved a simple word puzzle by filling in the missing letters in three incomplete words: W_ _H, SH_ _ER and S_ _P. Remarkably, those who remembered unethical deeds thought of cleaning-related words, like shower, wash and soap, about 60% more often than other words that could equally have fit, like wish, shaker and step. Those who remembered ethical actions showed no such preference.