Evolutionary psychologists believe that if behaviour exists in society today, then it must be a useful adaptation that has helped us survive and reproduce, a concept known in evolutionary theory as ‘the survival of the fittest’. They also point out that despite the wide diversity of human beings in different cultures scattered all over our planet, there are some reactions that seem to be almost universal. Examples of these are: the response of disgust to the smell of rotten eggs; ideas of what is attractive in a mate; fear or dislike of spiders and snakes. This is, they argue, because such responses are adaptive. The wide-ranging study by Curtis, Aungie and Rabie (2004) set out to test this possibility.
Curtis et al. (2004) added a survey to the BBC Science website after a documentary had been shown about human instinctive behaviour on one of the BBC channels. A sample of over 40,000 people completed the survey: the majority of participants came from Europe but a small proportion of the sample came from the Americas, Asia, Oceania and Africa. The participants viewed 20 photographs and rated them for level of disgust. The results indicated that photographs with objects representing a threat of disease were rated as more disgusting. Curtis et al. suggested these results were evidence of evolutionary mechanisms for detecting disease thus they play a role in survival.
More recent investigations of disgust have been undertaken as outlined in this article from The Guardian. Curtis argues that there are six categories of disgust: poor hygiene, animals that are vectors of disease (such as rats or cockroaches), sexual behaviours, atypical appearance, lesions and visible signs of infection, and food that shows signs of decay. What they all have in common is that disgust is all about avoiding infection.