Paul Ekman's Nesting Dolls

Origin
Paul Ekman (born February 15, 1934) is an American psychologist who was a pioneer in the study of emotions and their relation to facial expressions, has created an 'atlas of emotions' with more than ten thousand facial expressions, and has gained a reputation as "the best human lie detector in the world". He was ranked 59th out of the 100 most cited psychologists of the twentieth century. Ekman conducted seminal research on the specific biological correlates of specific emotions, demonstrating the universality and discreteness of emotions in a Darwinian approach.  Ekman's biggest discovery is the 'micro-expression', which shows up on our faces for fractions of a second as an indicator of emotion.

Emotions as Universal Categories
Charles Darwin theorized that emotions were biologically determined and universal to human culture in The Expression of the Emotions in Man and Animals published in 1872. However, the more popularized belief during the 1950s was that facial expressions and their meanings were culturally determined through behavioural learning processes. This was the belief of some anthropologists including Margaret Mead who had travelled to different countries examining how cultures communicated using nonverbal behaviour.

Through a series of studies, Ekman found a high agreement across members of diverse Western and Eastern literate cultures on selecting emotional labels that fit facial expressions. Expressions he found to be universal included those indicating anger, disgust, fear, happiness, sadness, and surprise. Findings on contempt are less clear, though there is at least some preliminary evidence that this emotion and its expression are universally recognized. Working with his long-time friend Wallace V. Friesen, Ekman demonstrated that the findings extended to preliterate Fore tribesmen in Papua New Guinea, whose members could not have learned the meaning of expressions from exposure to media depictions of emotion. Ekman and Friesen then demonstrated that certain emotions were exhibited with very specific display rules, culture-specific prescriptions about who can show which emotions to whom and when. These display rules could explain how cultural differences may conceal the universal effect of expression.

In the 1990s, Ekman expanded his list of basic emotions, including a range of positive and negative emotions that are not all encoded in facial muscles. The newly included emotions are: Amusement, Contempt, Contentment, Embarrassment, Excitement, Guilt, Pride in achievement, Relief, Satisfaction, Sensory pleasure, and Shame.