Scienceline has a 5-minute podcast about a new theory on the origins of disgust. Most scientists think there are four categories of disgust:
1. Core disgust: protects the body from contamination ("dirt, mold, and sick people").
2. Interpersonal disgust: protects the soul and social order ("promiscuous sex").
3. Moral disgust: protects society ("stealing or cheating")
4. Animal reminder disgust: protects the soul from recognizing the body's animal nature. ("Death, wounds, corpses, sexuality").
But Joshua Tybur, a psychologist at the University of New Mexico doesn't think these categories are correct, at least not from an evolutionary standpoint.
"It's difficult to think of natural selection actually encouraging the evolution of these kinds of terror-management, anxiety-reducing kind of activities," he says. To test his hunch,Tybur asked volunteers to write down lists of things that disgusted them. He collated the results and ended up with 105 things that disgusted people, such as seeing mold on leftovers in the refrigerator, touching a stranger's feet, hearing two strangers having sex, touching a dead body, seeing someone's bone sticking out of their leg, stealing from a neighbor, and a student cheating.
Tybur eliminated items that everyone found disgusting, such as eating someone else's vomit, along with extremely specific things that disgusted only one person surveyed. That narrowed down the number of disgusting items from 105 things to 58 "uniquely gross" things. Tyler presented this reduced set of disgusting things to a new group of people and asked to rank how disgusting the things were from 0 (not all disgusting) to 6 (extremely disgusting).
He found that disgust comes in three, not four, varieties: moral disgust, sexual disgust, and pathogen disgust. His conclusion: "Whereas traditional models have suggested that disgust serves to protect the self or neutralize reminders of our animal nature, an evolutionary perspective suggests that disgust functions to solve 3 qualitatively different adaptive problems related to pathogen avoidance, mate choice, and social interaction."
Here's a link to a paper Tybur coauthored, titled: Microbes, Making, and Morality: Individual Differences in Three Functional Domains of Disgust