In addition to all his groundbreaking work within the field of biology and evolutionary theory, it turns out that Charles Darwin also conducted pioneering work within psychology; particularly in relation to the expression of emotion.
As a result of some wonderful academic archival research, Professor of Neurology, Peter Snyder uncovered details of an experiment conducted by Darwin that was one of the very first studies on how people recognize emotion in faces. This work arose from his correspondence with French physician Guillaume-Benjamin-Amand Duchenne who suggested that at least 60 discrete emotions - all with their own dedicated group of facial muscles - could be discerned from the human face.
Darwin was not convinced, believing instead that facial muscles worked in tandem to produce just a few universal emotional expressions. To test his hypothesis, Darwin conducted a single-blind study at his home in England. Darwin's house guests were randomly shown 11 of the picture slides Duchenne had employed in his research. Darwin asked each respondent to state what emotion the person in the picture slide appeared to be displaying.
During his archival research of Darwin's work on emotion professor Snyder found handwritten notes and data tables which showed that their was almost universal agreement among Darwin's respondents regarding emotions such as happiness, sadness, fear and surprise.
Professor Peter Snyder Discussing his fascinating Darwin archival research:
The Expression of The Emotions
Writing in1909 about his influence on psychology, James Rowland Angell had the following to say about Charles Darwin's work on emotion.
In his treatise on The Expression of the Emotions Darwin has brought together with characteristic patience and industry the most extended array of observations bearing on the subject, an array which has been of notable value to the defenders of the James-Lange theory of emotion. As finally put forth the work is a defense of three familiar theses concerning emotional expressions.
The first holds that serviceable bodily reactions become habitual and become associated with the state of mind in connection with which they arose. When the mental state recurs, the bodily reactions recur also, although they may long since have lost any immediate and obvious utility. The clenching of the fist and the showing of the teeth in anger illustrate this conception.
The second thesis, that of antithetic action, maintains that a state of mind opposed to one calling out a definite bodily attitude may evoke an opposite bodily attitude. As an illustration may be cited the fact that an angry cat naturally lashes its tail from side to side. On the other hand a cat which is pleased carries its tail erect and stiff.
The third thesis, that of nervous overflow, holds that apart from the two previous principles of explanation, conditions of emotional excitement are prone to release more cortical energy than can be effectively disposed of in the usual ways, and the superfluity pours out in muscular contractions of the most various kinds.
So far as concerns the adequacy of these explanatory hypotheses, it may be said that in the light of our present knowledge the first affords a highly probable account of certain emotional reactions, while it is quite inadequate satisfactorily to explain, others. The second hypothesis has always been viewed askance, as something of a scientific tour de force, while the third, which Darwin himself treats rather as a catch-all to take care of cases found bothersome to handle by his first two hypotheses, is probably of much more fundamental import than he imagined. In any event later writers have been unable to improve materially upon Darwin's catalogue of the causative influences provocative of our emotional attitudes.