When writing The Variation of Animals and Plants Under Domestication in 1866, Darwin intended to include a chapter including man in his theory, but the book became too big and he decided to write a separate "short essay" on ape ancestry, sexual selection and human expression which became two large volumes in The Descent of Man. After completing work on the proofs of The Descent of Man in January 1871, Darwin started on another book, using left over material on emotional expressions.
Darwin noted the universal nature of facial expressions in the book: "...the young and the old of widely different races, both with man and animals, express the same state of mind by the same movements."
He became diverted into making extensive revisions to the Origin of Species, then in the spring of 1872 Darwin pressed on with The Expression of Emotions in Man and Animals, pointing to shared evolution in contrast to Charles Bell's Anatomy and Physiology of Expression which claimed divinely created muscles to express man's exquisite feelings. Darwin drew on world wide responses to his questionnaires, hundreds of photographs of actors, babies and "imbeciles" in an asylum, as well as his own observations, with particular empathy for the grief following a family death.
The proofs, tackled by his daughter Henrietta and son Leo, needed major revision which made him "sick of the subject, and myself, and the world". It was to be one of the first books with photographs, with seven heliotype plates, and Murray warned that this "would poke a terrible hole in the profits". The Expression of Emotions in Man and Animals proved very popular, selling over 5,000 copies.
