Consider some of the many things that Donald Trump has called “disgusting”: breastfeeding, sweating, menstruation, and people going to the bathroom. In this way, the new U.S. President is not so different from the rest of us—across cultures, people report finding body products disgusting, and for good reason. Throughout evolutionary history, other people have been the biggest threat of infection and bodily fluids are one of the main vehicles that bacteria and viruses use to get from one person to another. We are the descendants of people who successfully avoided disease by being disgusted by signs of contamination. As one particularly “germaphobic” descendent said about a sweating Senator: "It's disgusting. We need somebody that doesn't have whatever it is that he's got."
Yet Trump—and his opponents—have also expressed a great deal of disgust for things that seem to have no relevance to disease—dishonest journalists, crooked politicians, and Trump himself. This reflects one of the most interesting questions in the psychology of disgust: Why would an emotion that originally evolved to protect us from infectious disease come to be involved in morality? The most prominent answer has been that people like dishonest journalists or sexist presidents are seen as “social contaminants,” and when we detect metaphorical impurity, the same emotion is activated as when real physical contaminants are encountered.
But a research paper published recently in Social Psychological and Personality Science by myself and Roger Giner-Sorolla offers an alternative explanation for disgust’s involvement in morality. The key idea is that it might not be what a person feels that leads them to express disgust, but rather what they seek to communicate. The language and facial expression of disgust are "borrowed" for use in the moral domain because they communicate useful information, even though the expresser doesn’t necessarily feel any nausea or contamination. The expression is useful because the meaning is instantly apparent—the person has encountered something highly offensive that they want to avoid.
Further, disgust assumes agreement. If a person looks disgusted after tasting some food, you do not need to try it yourself to know whether you too will find it unpalatable. Likewise, if disgust is expressed regarding a person’s behavior, then it encourages others to see the behavior as offensive in principle. To say something is “disgusting” is to make a statement about that thing, like calling it loveable or ugly, and you assume others will share your basic reaction.
Inside we might feel something different, like anger. But expressed anger conveys different information. It is typically a response to something that has affected us personally, like when someone has harmed us or hindered our goals. “Angering” is not such a common word, and people are more likely to say they, themselves, are “angry.” “I’m angry” implies that it’s me, not the target of my emotion, that’s responsible for the feeling. If Trump were to express anger about dishonest journalists, then instead of assuming he’s condemning them out of principle, we are more likely to think “what have they done to affect him personally?”
In our research, we showed experimentally that disgust does indeed communicate different information from anger. We asked participants to read a scenario in which they imagined being nearby when a colleague at work expressed either disgust or anger after being told about a wrongdoing. They then had to judge what had motivated the colleague to feel that way about the wrongdoing. If the colleague expressed anger, participants thought that her feelings were more likely to be motivated by self-concern. But if the colleague expressed disgust, participants thought she was more likely to have been motivated by a concern about immoral behaviour. This evidence confirmed that an expression of disgust does communicate different information about moral motives than anger does. Even without feeling disgust, then, it could be useful to express disgust when condemning someone if we want to give the impression that we are motivated by principle, not self-interest.
But this evidence alone was not enough to show that people deliberately express disgust in order to show that they are motivated by moral concerns, so we turned things around and asked people about the emotional strategy they would themselves use. This time, participants imagined they were talking to a colleague about another person who had done something wrong and they were trying to convey that they were either mainly concerned that the wrongdoing had been immoral, or that that the wrongdoing had harmed them personally. As we expected, when the participant aimed to show that their condemnation was motivated by moral concerns, they were more likely to choose disgust. A further study showed that even in a situation where most people would naturally feel angry, they were relatively more likely to choose to show disgust when they wanted to look morally motivated.
Given these findings, it is easier to see why someone would want to express disgust even if they do not actually feel that exact emotion. When Trump expresses disgust about dishonest journalists, then, it might be because he wants the audience to share in a moral, principled, condemnation. Just expressing anger would not serve him so well because his audience would be likely to think he was more concerned about what the press had done to him personally.
Our social signalling perspective on moral disgust nicely reflects a wider debate in the emotion literature about whether facial expressions are automatic readouts of what a person feels inside, or are instead tools used by people to convey information about their motives and intentions. Some emotion scientists (perhaps most prominently Paul Ekman) emphasise the view that facial expressions are automatically tied to feelings. Of course expressions can tell us what a person feels—someone’s expression of fear when we jump out at them unexpectedly tells us that we probably succeeded in making them feel scared.
But social interactions are often more subtle and require us to strategically display expressions, lest they betray a feeling that would be unhelpful to show. An angry chimp would not be well served by automatically revealing feelings aroused by the actions of a larger chimp. Indeed, it was the strategic displays of animals that led Alan Fridlund to strongly advocate the behavioural ecology view of facial expressions as social tools.
If you encounter someone whom you are not overjoyed to see, yet with whom you wish to maintain cordial relations, you are apt to display a polite smile, even though you don’t feel joyful. The polite smile is not an expression of an inner feeling but a way of communicating information about your intentions, in this case, that you will act in a friendly and cooperative way. Similarly, if you are angry that some journalists have maligned you, you could express disgust as a tool to help show that your condemnation is actually motivated by a moral and principled concern about the honesty of the press. So the frequent expression of disgust in political and public discourse may not reflect widespread concerns about physical or metaphorical impurity so much as the ostentatious signaling of moral superiority.