LIKE many other aspects of biological investigation, the study of expression, as part of the general biology of man, was first given prominence by Darwin 1872 in his Expressions of the Emotions in Men and Animals [l]. However, the first major effect of the Darwinian revolution was to tie the biologist to his laboratory where the new insight gave rise to a tremendous amount of work on the readily available morphological material. It was not until the 1930’s that facial expressions was again investigated in any detail and a number of studies were conducted and published at this time, mainly by American psychologists. In general, these studies came to the rather surprising conclusion that human facial expressions carried no consistant meaning to observers and that no stable expression could be evoked by a given situation. There is little doubt now that the negative and contradictory results obtained at this period were due to inappropriate experimental techniques. The commonest of these techniques was to ask an actor to display a named emotion, to photograph him and then to ask the experimental subjects to name the emotion displayed in the photograph. This introduced artificial and static components into an essentially spontaneous and dynamic system. Even so, had they been willing to limit the investigation to the simplest emotions, e.g. pleasure, anger, they might have obtained positive results, and at the present time Eckman in America is using the “judgment of photograph” technique to good purpose [2]. One or two experiments published at that time used a situational method. Landis [3] photographed the expressions of people in a number of different experimental situations, e.g. receiving an electric shock, looking at nude photographs, picking up a live rat, and found little correspondance in facial expressions between individuals in the same situation. Although he took this as a negative result, there is no way of saying that the different subjects experienced the same emotion. All that could really be said was that different people reacted in different ways. At about the same period of the 1930’s, certain biologists again became interested in the living animal and its behaviour and, over the next couple of decades, the methods of ethology were developed to cope with the problems of the dynamic and variable interplay of ongoing behaviour. When, in recent years, the scientific interest in the non-verbal behaviour of man was reawakened, these methods could be brought to bear and we can now talk of a flourishing ethology of man. Facial expression is an important part of this non-verbal behaviour and I shall concentrate on the use of facial expressions and associated gestures during social contact. Behaviour, especially communicative social behaviour, is not a continuous process but is made up of a series of discrete patterns. For example, if we look at an individual, we can say that he is smiling or he is not smiling and, although the smile might vary in its morphological development, this difference can generally be easily determined;