Disgust is one of the seven basic emotions that cause people to produce a characteristic facial expression.

Disgust is an emotion that makes you want to avoid eating things that are likely to be harmful or even to touch things that might be infested or contaminated. The classic disgust expression makes sense: it would serve to encourage one to spit out something disgusting and to block bad smells from entering the nose.

What kinds of things arouse a feeling of disgust? Spoiled food and things associated with sickness, injury, death, or contamination. The contamination can be physical or moral. This sense of moral disgust gives rise to ideas of spiritual impurity and drives a need for ritual purification. Disgust can be directed at things that are physically unclean, but they can also be directed at things that are merely strange or foreign. For an animal, this kind of emotional response can have survival value: it could discourage the animal from eating an unfamiliar food that could be poisonous.

Appropriate feelings of disgust can help promote the individual’s health and survival by encouraging that person to avoid things that pose a threat of physical contamination or contagion. Unfortunately, inappropriate feelings of disgust play an important role in many psychological disorders, such as phobias and obsessive-compulsive disorder.

Disgust is the basic emotion that allows one to feel moral outrage. The sense of moral outrage is a powerful emotion that can lead people to do good or bad things. When people feel solidarity with all of humankind, the sense of moral outrage can inspire them to do great things, such as taking part in movements such as the movement to abolish slavery or the civil rights movement. In the following video, an actor portrays William Wilberforce, giving a famous speech against the slave trade to the British Parliament. Notice how he appeals to people’s sense of their common humanity with the victims of the slave trade:

Notice, in contrast, how this Nazi propaganda film was explicitly aimed at undermining that sense of shared humanity:

Unfortunately, in people who lack this sense of solidarity, feelings of disgust can end up provoking racist violence. The problem is not unique to Europe. Notice how the promoters of the Rwandan genocide referred to the Tutsi as cockroaches. I take it as a serious warning sign whenever I hear people referring to some other human beings as vermin.