Darwin examined the causes, physiological and psychological, of all the fundamental emotions in man and animals. He concluded that “the chief expressive actions exhibited by man and by the lower animals are now innate or inherited”, and that most of the movements of expression must have been gradually acquired. This is the only book by Darwin illustrated with photographs. It reproduces a number of photographs from Duchenne (No. 4973), and other photographs by Oscar Gustav Reijlander. Reprinted, New York, 1955. See P. Ekman (ed.): Darwin and facial expression: A century of research in review. New York, 1973.