A study by a scientist at the University of Portsmouth - who examined the facial muscles in cadavers - has revealed that the muscles which control our facial expressions are not common to everyone. The Risorius muscle, which experts believe controls our ability to create an expression of extreme fear, is found in only two thirds of the population.

Dr Bridget Waller, who conducted the first systematic study into the variations of muscles in the human face and how this relates to facial expression, said:  “Everyone communicates using a set of common signals and so we would expect to find that the muscles do not vary among individuals. The results are surprising - in some individuals we found only 60 per cent of the available muscles.”

Dr Waller collaborated with anatomists at the University of Pittsburgh and Duquesne University in the USA. They found that all humans have a core set of five facial muscles which they believe control our ability to produce a set of standard expressions which convey anger, happiness, surprise, fear, sadness and disgust. But there are up to nineteen muscles which may be present in the face and many people do not possess all of them.

Dr Anne Burrows from Duquesne University was one of the anatomists on the study. She said: “The problems with quantifying facial musculature is that they're not like other muscles. They're fairly flat, difficult to separate from surrounding connective tissue and they all attach to one another. They are very unlike muscles of the limbs, for example.”

The study appears in the American Psychological Association Journal.