Paul Ekman, a psychologist who linked thousands of facial expressions to the emotions they often subconsciously conveyed, and who used his research to advise FBI interrogators and screeners for the Transportation Security Administration as well as Hollywood animators, died Nov 17 at his home in San Francisco. He was 91.Ekman sought to add scientific exactitude to the human impulse to interpret how others feel through their facial expressions. He recorded 18 types of smiles, for example, distinguishing between a forced smile and a spontaneous one; a genuine smile, he discovered, crinkles the orbicularis oculi muscle – that is, it creates crow’s feet around the eyes.Sometimes described as the world’s most famous face reader, Ekman was influential in reshaping the way facial expressions were understood – as the product of evolution rather than environment – and his findings crossed over to popular culture.As a young researcher in the late 1960s, Ekman changed the scientific consensus on facial expressions. In the postwar era, the conventional wisdom of eminent anthropologists like Margaret Mead was that human facial expressions were learned and that they varied across cultures. Ekman believed otherwise. He showed photographs of people making faces expressing 30 different emotions – including anger, joy and fear – to subjects in the United States, Japan and South America. Across cultures, the study’s participants linked the expressions they were shown with the same emotions.He then travelled to Papua New Guinea with a colleague, Wallace V Friesen, and showed the same pictures to some 300 Indigenous people who had no exposure to modern media and could not have learned to interpret faces that way. These subjects also connected the expressions to the same emotions.“There is a pan-cultural element in facial expressions of emotion,” Ekman wrote in a paper in 1970 on returning to the United States.