Mankind's evolutionary secret has been revealed. And it's thoroughly disgusting. Scientists have found that our ability to sniff out all things loathsome, nauseous and repulsive may have propelled us to global domination. This idea stems from research which has shown that each of us possesses a 'disgust' centre in our brains. This controls our ability not just to spot repugnant things like foul food, snakes and dangerous insects, but to pinpoint revolting behaviour in others. As US researcher Professor Paul Rozin of Pennsylvania University puts it: 'Disgust developed from a system to protect the body from harm to a system to protect the soul from harm.'
Those who possess strong centres tend to be well-behaved, respectable members of society, the John Majors of our world. Individuals without them end up like Les Patterson.
'All animals have a sense of distaste,' says psychologist Andrew Calder. However, in humans it has been enhanced to give us a centre for highlighting both disgusting things, and disgusting acts. We need to be able to spot such behaviour because it could threaten society unless rooted out quickly, he says.
The discovery of the centre stems from observations by Calder and his team at the Cambridge Brain Unit. They had noticed that patients who suffer from the nerve ailment Huntington's Disease failed to recognise anti-social acts such as spitting or belching, and could not detect expressions of disgust on other people's faces.
As the disease affects a region of the brain called the insula, the observation suggested that our disgust centre is based in this region of the cortex. 'The trouble is that other areas of the brain are damaged in Huntington's patients, so we could not be sure these were not involved,' added Calder. 'We needed a more specific approach to the problem.'
The team was provided with one in the case of a 25-year-old man suffering from a unique type of stroke damage, a blood clot that had affected his insula. The result was startling: when shown photographs of other people, the patient could spot when they had angry, frightened or happy expressions. But when he was presented with photographs of people displaying disgust, he failed to recognise the emotion.
More importantly, when the patient was presented with a list of disgusting ideas - faeces-shaped chocolates, or people who didn't wash - he again showed no reaction.
The discovery of a disgust centre provides critical support for the ideas of biologists such as Rozin who argues that the sense that we once used to spot rotting food has evolved to become the guardian of our behaviour. Disgust has evolved from the rejection of bad-tasting food to being a source of morality.
Developments in human responses to offensive chemicals led the US government to commission scientists to find a smell which everyone would consider disgusting, so they could use it for a universal stink bomb to replace tear gas.
