The Expression of the Emotions in Man and Animals is Charles Darwin's third major work of evolutionary theory, following On the Origin of Species (1859) and The Descent of Man, and Selection in Relation to Sex (1871). Initially intended as a chapter in Descent of Man, Expression grew in length and was published separately in 1872. Darwin explores the biological aspects of emotional behaviour and the animal origins of human characteristics like smiling and frowning, shrugging shoulders, lifting eyebrows in surprise, and baring teeth in an angry sneer. A German translation of Expression appeared in 1872, and Dutch and French versions followed in 1873 and 1874. Though Expression has never been out of print since its first publication, it has also been described as Darwin's "forgotten masterpiece". Psychologist Paul Ekman has argued that Expression is the foundational text for modern scientific psychology. Before Darwin, human emotional life had posed problems to the traditional philosophical categories of mind and body. Darwin's interest in the subject can be traced to his time as an Edinburgh medical student and the 1824 edition of Anatomy and Philosophy of Expression by Charles Bell, which argued for a spiritual dimension to the subject. In contrast, Darwin's biological approach links emotions to their origins in animal behaviour, allowing cultural factors only an auxiliary role in shaping the expression of emotion. This biological emphasis highlights six different emotional states: happiness, sadness, fear, anger, surprise, and disgust. It also appreciates the universal nature of expression, implying a shared evolutionary heritage for the entire human species. Darwin points to the importance of emotional communication with children in their psychological development. Darwin sought out the opinions of some leading psychiatrists, notably James Crichton-Browne, in preparation for the book, which forms his main contribution to psychology. The book involves several innovations: Darwin circulated a questionnaire (probably inspired by his cousin, Francis Galton) during his preparatory research; simple psychology experiments on the recognition of emotions with his friends and family; and (like Duchenne de Boulogne, a physician at the Salpêtrière Hospital) the use of photography in his presentation of scientific information. Darwin's publisher warned him that including the photographs would "make a hole in the profits" of the book. Expression is considered an important landmark in the history of book illustration. Source: Wikipedia (en)