Science

Charles Darwin | Sigmund Freud | Brain research | Centre for Chemical Senses | Paul Rozin | Obsessive Compulsive Disorder | Social Induction | Val Curtis | Mary Douglas

Is disgust an instinctive reaction or are we taught to be disgusted? Why does everyone find faeces repellent? Is it an evolutionary mechanism to protect us from germs or do we need to be taught by society that it is disgusting to touch excrement?

Certain things are universally disgusting. Urine and vomit, rats and cockroaches have the same effect on people across the world. Our heart rate slows. We make a 'disgust face'. We wrinkle our noses to close them from the smell and open our mouths slightly, as if about to vomit.

But disgust is not simple. Shit is only shunned by the over-twos. Babies are not repelled by it; they find it fascinating. This suggests that it is not an innate reaction.

Despite the questions that disgust throws up, studies of this most primal of emotions are rare. The first enquiries into it were made just over 100 years ago. But the subject was then forgotten by scientists for decades.

Charles Darwin

Darwin, the British naturalist, first addressed the subject in the 1870s. He believed that what we find disgusting was determined by nature. Disgust was an evolved response to things that might harm our prospects of survival.

However, Darwin classified disgust alongside emotions that imply a value judgement: disdain, contempt and pride. This suggests he believed that disgust is more complex than a simple instinctive reaction.

Smell experiment

Sigmund Freud

Freud, the originator of psychoanalysis, took a different view. Just as Freud's theories of sexuality were based on our relationships with our parents, he thought that our disgust response was also conditioned at an early age. Children internalise their parents' attitude to faeces which is displayed during toilet training, developing a disgust response at this time.

Freud believed that society creates mechanisms to ensure that we control our basest instincts. The development of disgust is one method of social control.

Brain research

Freudian psychoanalysis may have given us indirect insights into the workings of the mind, but these days we have a more direct route. Using MRI brain scans, British researchers have turned up some remarkable new evidence about the nature of disgust.

Dr Mary Phillips carried out brain scans on people while showing them pictures which would disgust them. She found that when we feel disgusted, a part of the brain is stimulated which is much older than the part which deals with rational thought. It is millions of years older than the oldest human civilisations. She concluded that disgust was so deeply ingrained that it could not be determined purely by cultural influences.

Centre for Chemical Senses

There is undeniably some cultural element in what people find disgusting. Pamela Dalton at the Centre for Chemical Senses in Philadelphia was asked by the United States government to find a smell which everyone finds repellent, so they could develop a universal stink bomb that could be used as an alternative to tear gas.

Dalton's team used smells based on sulphur, the chemical released by rotting eggs and vegetables. Most people find this smell highly repellent, but some Koreans were not disgusted by it as it reminded them of the fermented sauces they use in their cooking.

Paul Rozin

Paul Rozin is a psychologist who works with children and adults to show how our disgust responses vary and develop. He believes that nature and nurture both play a part in disgust.

Adults and children aged eight or over will not eat a chocolate shaped like dog poo, even if they know it is just ordinary chocolate. Babies, though, have no such qualms. As children grow older, they become suspicious of the dog poo, but with reassurance they will eat it. They are not yet disgusted by it.

On tasting something bitter or sharp, tiny babies make a 'distaste face', which is very similar to the adult 'disgust face'. Rozin believes that cultural influences mould this distaste into a more complex response — disgust.

Obsessive Compulsive Disorder

Disgust is a normal reaction to dirt. But how much disgust is normal? In people with Obsessive Compulsive Disorder (OCD), the part of the brain which deals with disgust is over-stimulated or damaged. Sufferers are disgusted by almost everything. They find any contact with dirt, real or perceived, disgusting and as a result their lives are hopelessly constrained. Everything they do, even simple tasks like making a cup of tea, turn into lengthy rituals designed to avoid contamination.

Social Induction

But if too much disgust is abnormal, so is too little. As we grow up we are taught that we should be disgusted by certain things. Society shapes our disgust response. Babies, for instance, have to be taught not to touch their faeces. Also, different cultural groups teach their children to find certain foods abhorrent.

Later in life, our disgust response is seen as a key element in what makes us civilised. People who eat with their mouths open, revealing saliva and half-chewed food, are disgusting. They must be taught to change their behaviour. Sensitivity to what others may find disgusting is fundamental to social interaction.

Val Curtis

Disgust is a complex subject, incorporating a number of different elements. Yet, more than a century after Darwin and Freud first analysed disgust, two distinct schools of thought endure.

Val Curtis takes the evolutionary view. She believes that disgust is a problem-solving tool which has evolved over many centuries.

What we find disgusting is what we believe may harm us, therefore we should avoid it. Certain universally disgusting things such as faeces and rotting flesh are 'inescapably dirty'.

Mary Douglas

On the other side of the debate is Mary Douglas, who argues that what is disgusting is what we find anomalous: things that appear where they should not be, or do not fit the generally accepted classifications.

Hair on the head is not disgusting, for instance, but nose hair is: it should not grow there. A dead rat in the kitchen is more disgusting than one lying on the street. If its innards are spilling out — not contained inside the animal's skin where they should be — it is even more disgusting.

Different cultures develop different categories of what is dirty and what is clean, and consequently what is disgusting and what is not. To a Jewish person, for example, pigs are unclean animals and therefore eating pork is disgusting.

Dirt, like beauty, is in the eye of the beholder.

Paul Rozin in classroom