Expression of the Emotions
After he had expanded on the idea of human evolution from the higher primates in "The Descent of Man", Charles Darwin published one final major work of scientific theory. "The Expression of the Emotions in Man and Animals" (1872) proposed the idea that the basic emotions we experience are common to all human races across all periods of history. The evidence for this, Darwin argues, lies in the fact that there are striking similarities in the facial expressions by which these emotions are registered.
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There is a face for fear that involves the opening wide of the eyes and drawing back of the corners of the mouth. Anger produces frowns and flashing eyes, while unhappiness is registered as a slackening of the mouth and a turning upwards of the inner ends of the eyebrows. Darwin identifies facial expressions for a whole range of other emotions too, although he notes that jealousy seems to be the only mental state that lacks one.
It was to take nearly 90 years before any other researcher in this field got around to putting these theories to a rigorous scientific testing procedure, whereupon it was established that they had been, in large measure, correct. We rightly think of Darwin as one of the pioneers of genetic evolution, but he also has a great claim to be at the forefront of evolutionary psychology too.