Human vomit, festering wounds, food crawling with flies ...... The sight of these scenes makes us subconsciously nauseous and move far away. These are reactions that people take for granted, and few people think about why humans feel disgusted. Recent scientific studies have found that the reason for nausea in humans is an evolutionary act of self-preservation, protecting ourselves from parasites.

The reasons we find disgust are easy to understand, but why we are so repulsed by disgust is a complex question. To date, however, there has been little attempt to fully link the source of disgust to the source of infectious disease.

Looking back through human history, there is a long history of dealing with parasites; malaria, bloodsuckers, plague ...... in the days when medicine was not advanced, these were deadly enough. Not only humans, but all free living animals on earth are threatened from parasites and pathogens, and over a long period of evolution, these animals evolve behavioral countermeasures accordingly as a way that can help avoid parasites.