That’s Disgusting! Thank Goodness
Would you share a toothbrush with the postman? Would you eat a plate of bodily fluids or use a stained towel? Do you like worms and lice?
No? Well, you are not odd. In fact, you share an ancient emotion with almost everybody on the planet. Disgust is such a powerful feeling that it can make you stop what you are doing, even make you physically sick. And it seems that people the world over feel disgust for the same sets of things: bodily fluids; excrement; creatures like lice, rats and cockroaches, and, in certain cases, other people.
I work with a team of researchers at the London School of Hygiene and Tropical Medicine. We theorized that disgust serves a very specific purpose. In the same way that the emotion fear helps us protect ourselves from danger (by avoiding being eaten by large animals, for instance), so the emotion disgust helps stop us from being eaten alive by little animals: the viruses, bacteria and parasites that want a free meal from our bodies.
Why not? It is, after all, readily accepted that humans evolved physical defenses against infection -- like our complex immune system, for instance, and the antibiotics in our tears. It seems reasonable, therefore, that we might have evolved behavioral defenses as well. Human ancestors with a heightened repulsion from saliva, say, or parasites would have been healthier, and thus more likely to pass on their genes. Indeed, Charles Darwin theorized as early as the 19th century that disgust was an evolutionary response to those things that could harm our prospects of survival, although he didn’t say exactly how.
To test the hypothesis, we conducted a study in six separate countries and an international airport to find out what kinds of things disgusted people, and earlier this year we created a follow-up experiment on the BBC’s website (www. bbc.co.uk/science/humanbody/mind /surveys/disgust/).
In the BBC experiment, we began by making pairs of images, set up to look as similar as possible, except that one photo contained a disease threat and the other did not. So, for example, two identical towels appeared on the respondents’ screens, one with a bright blue stain, the other showing a yellow-brown stain. Two pictures of the same person appeared, one looking healthy, the other looking feverish, damp, pink and spotty. The images were mixed up randomly and those logging on were asked to score each picture on a scale of one (not disgusting) to five (very disgusting). The Web experiment response was overwhelming -- crashing the BBC’s Web server -- and could not have been clearer. To date more than 80,000 people from 172 countries have filled in the survey, making it possibly the biggest Web experiment ever.
The findings were exactly as we predicted. A picture of a festering wound was more disgusting than a clean burn, a train full of people more disgusting than an empty one, a louse was more yucky than a wasp. The apparently sick person was twice as disgusting as his healthy counterpart, and the towel stained with bodily fluids was more than twice as revolting as the towel with the blue stain. The pattern held for every region of the world (although, overall, the macho Australians were the least squeamish).
Women were consistently more disgusted than men. This was what we had expected also. Because women have a double genetic burden -- they need to pass their own genes on to the next generation and also to nurture their offspring to ensure that they too survive and reproduce -- women need an even greater ability than men to detect potential signs of disease threats in the environment.
Despite small differences in different regions -- like the yuck-tolerant Australians -- overall, for everyone, everywhere, signs of infection and disease rendered innocent pictures more disgusting.
A final question in the survey asked people who they’d least like to share a toothbrush with. Least acceptable was the postman, followed by the boss at work, the TV weatherman, a sibling, a best friend and then the spouse/partner. Clearly, sharing bodily fluids is something we are prepared to do only with someone very close. This makes sense, as those close to us tend to share our germs and are less likely to infect us with disease. So it looks like disgust may be a very ancient emotion, one that evolved with us to give us an instinct to avoid disease. Think of that next time you see something nasty in the bathroom.
