If you read about the record-breaking “fatberg” lurking under Kingston recently and reacted the same way as me - “Oh my God - a gob of fat in the London sewers as big as a bus - that’s disgusting!” - you’ll probably have had the same reaction that I did: a churning stomach, a curdling sensation in the mouth and a loud exclamation for all to hear.
It may even have put you off your lunch. But why do we feel this way? It seems a completely irrational response. How and why can a printed story about fat in a London sewer reach out from newsprint and grab us by the guts?
Gobbing in your own drink
And here’s another disgusting puzzle: imagine taking a glass of water, spitting a big gob of saliva into it, putting the glass down, then a few minutes later picking the glass up again and trying to drink it. Most people would find that revolting - even if it that shiny goo is their own saliva.
I’ve been trying to figure out the strange power of disgust for many years and have collected various accounts of the disgusting from my studies of hygiene around the world. Disgust is such a visceral emotion, one that can even ruin lives. I’ve been puzzling over their rich, revolting variety, and what cockroaches, off-smelling meat, bad breath, people who look unkempt, sexual fluids, oozing spots and poor hygiene have in common – apart from the fact that most people find them disgusting.
A common pattern of disgust
Looking up an obscure tropical parasite in the index of a textbook of infectious diseases, a pattern jumped out – all the things that people find disgusting were there - and had some connection to infectious disease, parasites and pathogenic microorganisms.
The purpose of disgust, then, it appears is to keep us away from sources of infection: whether they be disease-causing bugs themselves, the animals and insects that carry them, or, most dangerous of all, other people and their emanations – the riskiest source of infectious diseases.
There are some theories, mainly from the US, that disgust is a psychological reaction to a fear of our own mortality. But in the pathogen theory, it’s an emotion that kept our ancestors from getting sick, that may, or may not, be doing the same thing for us now, in our modern world of sewers and newspapers.
Disgust, it turns out, is a lot like fear. If our ancient ancestors had made a habit of cuddling up to lions or poisonous snakes then they would have been unlikely to have become our ancestors. Those ancients who feared lions and snakes would have avoided them and hence had more children, and more grandchildren, and hence would be more likely to be our ancestors. That is why we all have a healthy sense of fear.
Tasting poo is bad
Disgust works in the same way – those ancients that went about tasting poo or embracing stinky, unkempt, parasites-ridden people would have been more likely to catch an infection. But those who happened to have the opposite tendencies, with a healthy squeamishness about bodily emanations and parasitic worms, would have been fitter, healthier and had more descendants. And those descendants would have inherited a healthy sense of disgust.
So it turns out that recoiling from the idea of waste food mixed with poo in the London sewers is not so irrational after all. The last thing we want to do is to touch it or eat it, and the voices of our ancestors in our heads tell us we should stay away – even when all we are responding to is words on a page or a picture on a screen.
We all, of course, have competing motives within us. Sometimes disgust attracts us, for example when we watch movies where humans are parasitised by aliens or as when a child pokes at the cat bowl or the contents of the potty. We all like to play, to learn about things. But parents soon put us right about poo, the disgust face pulled by a mother assures that every child gets potty trained by about the age of two.
Disgust may give you unpleasant sensations and put you off your food, but those responses tell you something. Next time you come across something nasty in your fridge or your bathroom or something revolting in a newspaper, listen to that disgust voice in your head. It’s the voice of your ancestors telling you what to do, and it’s an important message that has been keeping you and your ancestors safe from disease for millennia.