Psychologist Paul Ekman's cross-cultural research, including studies with isolated communities in Papua New Guinea with minimal outside media exposure, found that seven facial expressions — happiness, sadness, anger, fear, surprise, disgust, and contempt — are produced and recognized the same way across radically different cultures, suggesting they're biologically hardwired rather than learned. A microexpression is a fragment of one of these seven expressions that flashes across the face involuntarily, typically for less than half a second, often when someone is suppressing or masking their actual emotional reaction.
The practical value of knowing the seven is narrower than popular 'human lie detector' claims suggest: microexpressions reveal that a genuine emotional reaction occurred and is being masked, but they don't tell you why, and they're notoriously easy to over-interpret without training (Ekman's own training programs take substantial practice to apply reliably). The most defensible everyday use isn't diagnosing deception — it's noticing a flash of a suppressed reaction as a cue to ask a genuine follow-up question, rather than treating the person's stated reaction as the whole story.
To test whether facial expressions were universal or culturally learned, Ekman and Friesen traveled to Papua New Guinea to study the Fore people, an isolated community with almost no exposure to Western film, television, or outsiders at the time. They showed Fore villagers photographs of Western faces expressing different emotions and asked which of several simple stories matched each face; in the reverse direction, they filmed Fore villagers acting out emotional scenarios and showed the footage to American college students. In both directions, recognition rates for the seven core expressions were far above what chance guessing would produce, even though neither group had ever seen the other's faces or culture before.