What is disgust?

We all know the feeling that disgust brings with it, but what exactly is disgust, and why have we evolved it?
17 August 2015

Interview with 

Professor Paul Rozin, University of Pennsylvania


Disgust. We have all experienced it- whether from treading on a slug in the dark or poorealising you have just bitten into an apple crawling with worms. That creeping feeling of your skin, the rising nausea and the desire to distance yourself from whatever it is you have just seen or felt is familiar- you may even be experiencing it now from reading these descriptions. Ginny Smith asked Professor Paul Rozin, who was one of the first researchers to work on disgust, what exactly it is:

Paul - Disgust is a basic emotion, but it actually means two things in English. One is, what the psychologist means, a particular type of negative emotion. But it's also used in English to mean bad. So, you might say anything is disgusting when you want to say it's bad and that produces a problem because when we ask people about disgust, there were both of these usages. Now, we have a word in English, 'gross' which actually means more like what psychologists mean by disgust.

Ginny - What kinds of things evoke that feeling of disgust or grossness?

Paul - The basic idea is the things that are offensive. But in a particular kind of way, the most clear-cut forms of disgust are to rotting things like animal flesh or certain kinds of dirty animals like rats, or dead bodies. But they're all very bodily and some people think that the basic core of that is a system to keep us from acquiring pathogens which are usually carried in animals and more so in decaying animals. But it's extended way beyond that in the way culture uses the term.

Ginny - So, let's go back a step. When we first evolved disgust, where do you think that came from?

Paul - Well, it's pretty clear with the system that it originated from. That's the bitter taste system which is then rats and primates. It's the negative response to bitter taste and the face that infants make to that which is an innate rejection is very similar to the disgust face. So, it looks like that system was co-opting or the term I use is 'pre-adapted', used for another purpose in the course of evolution. The system was already in place, it was a food rejection system, but now, a whole new class of things, that system became used for those. And actually, bitter taste were no longer disgusting. People don't use the term and they don't feel nausea which is the sign of disgust. So, the system was pre-adapted and co-opted from the bitter system, but it's now independent of it.

Ginny - So, that disgust face you mentioned, that's the kind of wrinkled nose, the gaping mouth, maybe even sticking your tongue out that if you think of something disgusting, you'll probably start doing.

Paul - There are a number of faces but they all have to do with rejection of stuff from the mouth and not smelling it. It's the raised upper lip is the most important piece of it, but it also includes the wrinkling of the nose and the gape. So, that system is used in response to all sorts of things which are primarily animal things that we reject. And then through the same process of co-optation or pre-adaptation, it becomes used for other things that are offensive but not having to do with the body. For example, strangers, people you don't like, negative figures like Hitler, and also, for all sorts of sexual things like incest.

Ginny - Now that's really interesting that it could've gone from being something that's physically to protect you against poisons or pathogens to - it's still protective in a way but in a more kind of indirect way. Is that quite unusual?

Paul - It's not unusual. It's a very common process in both biological and cultural evolution. That's something that evolved from one purpose that's used for another. For example, your mouth evolved to eat and breath, but it's used for language. So, the language system co-opted the mouth. You need your teeth and your tongue to speak, but they didn't evolve for that purpose. So, we are constantly re-using things and this is just one example. So, the big issue now is, how do you link the presumed pathogen origin of disgust which may have been biologically or culturally evolved, we don't know, but how do we get from that to other negative things? So, one is to talk about the fact that sexual activity also is a potential way of passing pathogens like sexually transmitted disease. That's one view. My own view with my colleagues, McCauley and Haidt is that that's not really what happened. That the culture discovered that if they can make something disgusting, people wouldn't do it. So, they have this disgust system and they just apply it to other things like incest or evil people which are not related to pathogens at all. They all have the property that we want to get rid of them, we won't want to deal with them.

Ginny - Now, you spent a lot of time studying disgust in the lab. What do you do to people to make them disgusted? What kind of experiments have you done?

Paul - Well first, let me just say, disgust is extremely easy to elicit in people in a laboratory setting, much more so than anger or sadness. But disgust is easy. All we have to do is take out of disgust the object. And we even have to take out an image of disgusting object.

Ginny - Even just talking about something disgusting, I know when I've been planning the show, there have been a few moments I've been talking to people and got that horrible cringing feeling just from talking about something. It's amazingly easy.

Paul - The most indirect thing is that something looks disgusting. But really is that people still show the response. So, we did this in the lab by presenting college students with a piece of chocolate shape to look like a dog doo. They do it with chocolate and there was a piece of the chocolate it was made from right there and most people didn't want to eat it even though they knew it was chocolate because it looked like dog doo. So, there's a powerful sense of disgust that way.

Ginny - You've done all the studies where you've looked at how disgust can get passed on from a disgusting object to another object as well, haven't you?

Paul - We give them a glass of juice that they know was good juice. We pour it out for them from the container and they drink it. And then we drop a cockroach in it. It's a dead cockroach and take it out. So, there's no sign of the cockroach and they won't touch that juice. They hated it. So, it's so powerful that when it touches something, it renders it inedible. Now, if we ask people, "Why didn't you drink the juice?" They'll say "because cockroaches are diseases vectors. You'll never what's in there. You can get something." So we say, "Okay, we'll do it again with a sterilised cockroach. This is a cockroach that is safer than your fork." We dropped that and take it out and they won't drink it because as it plays out now, though it may have originated as a pathogen, it's the whole idea that cockroach-ness entered the juice. When a cockroach touches your juice, its essence passes into the juice and it doesn't matter whether it's carrying microorganisms or not. Hitler's sweater which is a thing that we don't own but we use it in describing it. It's something that people are really offended  by. They won't wear Hitler's sweater even if you'll wash it and do everything you can to it. It isn't the pathogen threat. It's a moral threat. So, that's how disgust is expanded from being just about potential bad consequences of eating to be - it's a sign of immorality and it's a way of labelling them and getting other people to avoid them.


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