Disgust

Overview
Disgust is an emotion that is typically associated with things that are perceived as unclean, inedible, or infectious. In The Expression of the Emotions in Man and Animals, Charles Darwin wrote that disgust refers to something revolting. Primarily in relation to the sense of taste, as actually perceived or vividly imagined; and secondarily to anything which causes a similar feeling, through the sense of smell, touch, and even of eyesight. Disgust is one of the basic emotions of Robert Plutchik's theory of emotions. Disgust invokes a characteristic facial expression, one of Paul Ekman's six universal facial expressions of emotion. It is also associated with a fall in heart rate, in contrast, for example, to fear or anger.

Disgust may be further subdivided into physical disgust, associated with physical or metaphorical uncleanness, and moral disgust, a similar feeling related to courses of action.

Origins and development
Disgust is thought to have its origins in (and in some cases to be identical to) instinctive reactions that evolved as part of natural selection for behavior which tended to prevent food poisoning, or exposure to danger of infection. Disgust is frequently associated with waste products such as feces or urine, secretions from the human body (such as mucus), and with decomposing flesh, and insects, such as maggots, associated with it.

As in other human instinctual drives, disgust has an instinctual and a socially constructed aspect. Psychologist Paul Rozin has studied the development of feelings of disgust in children.

Jonathan Haidt is a researcher whose work involves exploring the relationship between disgust and various traditional concepts of morality. His theory of social intuitionism seeks to explain the apparently irrational and visceral reactions to violations of the moral order.

Disgust and shame
Martha Nussbaum, a leading American philosopher, wrote a book published in 2004 entitled Hiding From Humanity: Disgust, Shame, and the Law which examines the relationship of disgust and shame to a society's laws.

A recent study found that women and children were more sensitive to disgust than men. Researchers attempted to explain this finding in evolutionary terms. While some find wisdom in adhering to one's feelings of disgust, some scientists have asserted that "reactions of disgust are often built upon prejudices that should be challenged and rebutted."

Brain structures
Functional MRI experiments have revealed that the anterior insula in the brain is particularly active when experiencing disgust, when being exposed to offensive tastes, and when viewing facial expressions of disgust.

Huntington's disease
Many patients suffering from Huntington's disease, a genetically transmitted progressive neurodegenerative disease, are unable to recognize expressions of disgust in others and also don't show reactions of disgust to foul odors or tastes. The inability to recognize disgust in others appears in carriers of the Huntington gene before other symptoms appear.