The Expression of the Emotions in Man and Animals
He explores the origins of such human characteristics as the lifting of the eyebrows in moments of surprise and the mental confusion which typically accompanies blushing. The book is very notable for being the first book to use photographs as the main way of showing scientific evidence. The field of study is now called behavioural genetics. One line of evidence he uses is the way many different peoples in different parts of the world have similar facial and emotional reactions.