Contempt can be seen as a biological metaphor for disgust. 

The emotion program of disgust is another good example of protection of the organism’s integrity. Disgust is triggered from a small region of the anterior insular cortex when certain stimuli are present, for instance, the sight of decomposing food or body waste, as well as tastes or odors from decomposing organic matter. The sight of body-boundary violations, as in a wound with blood, also causes disgust. The actions that constitute disgust include a typical facial expression and, for example, the rapid expulsion of the potentially offending food. As a result the subject will not ingest a potentially toxic food and other subjects may also be alerted to the potential danger.

In the social emotion of contempt there is a rejection of certain behaviors or ideas rather than an expulsion of toxic substances or their tell-tale signs. 

Significantly, we refer to actions that cause moral revulsion as “disgusting,” and the repertoire of facial expressions that accompanies a contemptuous judgment is similar to that of disgust. 

- Antonio Damasio 

Neural Basis of Emotion